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Nitrogen excretion in the deer in relation to age and metabolic rate. Campbell, Gordon Alexander 1963

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NITROGEN EXCRETION IN THE DEER IN RELATION TO AGE AND METABOLIC RATE toy GORDON ALEXANDER CAMPBELL B.A., The U n i v e r s i t y of B r i t i s h Columbia, I 9 5 6 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF • MASTER OF SCIENCE i n the Department of Zoology We accept t h i s t h e s i s as conforming to the required, standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , I963 In presenting this thesis i n p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference and study. I further agree that per-mission for extensive copying of this thesis for scholarly purposes may be granted by. the Head of my Department or by his representatives,, It i s understood that copying, or publi-cation of this thesis for f i n a n c i a l gain shall not be allowed without my written permission. Department of Zoology • The University of B r i t i s h Columbia, Vancouver 8 , , Canada. Date nm^, 13. (9 6 3 i i . A b s t r a c t T o t a l n i t r o g e n e x c r e t i o n l e v e l s ' r e measured on f i v e male, and thr e e female Vancouver I s l a n d B l a c k - t a i l e d deer (Odo- c o i l e u s hemionus columbjanus), which, were r a i s e d i n c a p t i v i t y i n the deer u n i t at the U n i v e r s i t y of B r i t i s h Columbia. They were r a i s e d from approximately t h r e e weeks of age u n t i l they had reached an a d u l t body weight. The measurements were made at v a r i o u s i n t e r v a l s throughout the p r e p u b e r t a l growth p e r i o d of the deer. M e t a b o l i c r a t e d e t e r m i n a t i o n s were made on one of the deer, namely the doe R-5> a f t e r i t had reached an a d u l t body weight. N i t r o g e n balance t e s t s were made at the same time. The method used i n the n i t r o g e n balance t r i a l s c o n s i s t e d of a l t e r n a t e p e r i o d s of f a s t i n g and f e e d i n g . The r a t i o n used i s d e s c r i b e d i n Appendix I. It was g i v e n at one and two pound l e v e l s a l t e r n a t e l y . The procedure of f a s t i n g and f e e d i n g at d i f f e r e n t l e v e l s p e r m i t t e d the d e t e r m i n a t i o n of the p o i n t of n i t r o g e n balance, as w e l l as that of t o t a l n i t r o g e n e x c r e t i o n w h i l e f e e d i n g . The r e s u l t s and d i s c u s s i o n of the n i t r o g e n balance t r i a l s , and the d i s t r i b u t i o n of n i t r o g e n obtained, appear f i r s t , f o l l o w e d by th a t of the n t r o -gen e x c r e t i o n r e s u l t s observed d u r i n g growth. The p o i n t of n i t r o g e n balance was found to occur at 16.5 to 17-3 grams of n i t r o g e n i n t a k e per day. The crude p r o -t e i n requirement, c a l c u l a t e d on t h i s b a s i s , was approximately 100 grams f o r a p r o t e i n of p e r f e c t b i o l o g i c a l v alue. The energy requirement of B-5 w a s found to be 1,300 to 1,400 C a l o r i e s per day f o r maintenance. T h i s energy r e q u i r e -ment was met by the U.B.C. r a t i o n number 3&-57 (Appendix I.) at the one pound l e v e l . T h i s l e v e l a l s o p r o v i d e d more than adequate amounts of n i t r o g e n to f u l f i l l the above p r o t e i n requirement. The d i e t a r y requirement f o r n i t r o g e n , based on the lowest l e v e l of n i t r o g e n e x c r e t i o n obtained, was much lower than that c a l c u l -a ted from the p o i n t of n i t r o g e n balance. The lowest l e v e l ob-t a i n e d approximated the estimated endogenous t o t a l u r i n a r y n i t r o -gen e x c r e t i o n l e v e l f o r an animal of the same body weight. I t was concluded that i n s u f f i c i e n t time was allowed f o r n i t r o g e n de-p l e t i o n , and that the t r u e endogenous l e v e l was not obtained. The u r e a n i t r o g e n expressed as a percentage of the t o t a l n i t r o g e n e x c r e t i o n r e f l e c t e d the s t a t u s of p r o t e i n n u t r i t -i o n . Upon f a s t i n g the percentage f e l l r a p i d l y from the non-f a s t i n g l e v e l of 90 per cent to l e v e l s of l e s s than 85 per cent. A l e v e l of l e s s than 75 per cent was o b t a i n e d i n one case. When the animal was g i v e n f e e d the percentage immediately r e -turned to l e v e l s of 90 per cent or more. The prompt response on the p a r t of u r e a to changes i n p r o t e i n i n t a k e i n d i c a t e d that the percentage of t o t a l n i t r o g e n made up of u r e a n i t r o g e n might be of v a l u e as an index of p r o t e i n n u t r i t i o n a l s t a t u s f o r f i e l d i v . s t u d i e s . The c r e a t i n i n e n i t r o g e n e x c r e t i o n l e v e l a lso r e f l e c t e d , to a s l i g h t degree, the changes i n n i t r o g e n intake. Despite the ease i n determining c r e a t i n i n e l e v e l s , the r e l a t i v e l y greater constancy of c r e a t i n i n e e x c r e t i o n reduces the value of such de-terminations as i n d i c e s of p r o t e i n intake. The ammonia n i t r o g e n as a per cent of the t o t a l n i t r o -gen reacted i n an inverse manner to urea, and could be regarded as a check on the conclusions d e r i v e d from the r e s u l t s w i t h urea. The p a t t e r n of n i t r o g e n e x c r e t i o n during growth showed changes which were s i m i l a r to those observed by previous i n v e s t i -gators on the character of increase i n body weight dur i n g growth. The r a t e of increase i n t o t a l n i t r o g e n e x c r e t i o n i s c h a r a c t e r i z e d by changes i n r a t e of increase which occur at s i m i l a r times, and i n a s i m i l a r manner, to those of body weight. The t o t a l c r e a t i n i n e n i t r o g e n e x c r e t i o n increased i n a regu l a r manner during growth, from values of l e s s than 1 0 0 m i l l i g r a m s per day, to values of between 4 0 0 0 a n d 6 0 0 m i l l i g r a m s . This i s i n agreement w i t h the r e s u l t s of previous i n v e s t i g a t o r s , who have s t a t e d that c r e a t i n i n e e x c r e t i o n r e f l e c t s the s i z e of the " a c t i v e body mass!' V . The t o t a l n i t r o g e n e x c r e t i o n showed a t r e n d toward reduced l e v e l s at approximately three months of age. T h i s r e d u c t i o n c o i n c i d e s w i t h a major change i n the growth r a t e , which i s a s s o c i a t e d w i t h the appearance of puberty. The r e -d u c t i o n may i n d i c a t e i n c r e a s e d r e t e n t i o n of n i t r o g e n at t h i s time, although the same r e s u l t c o u l d be caused by reduced n i t r o -gen i n t a k e . The t o t a l n i t r o g e n e x c r e t i o n d u r i n g growth g r e a t l y exceeded the estimated endogenous e x c r e t i o n l e v e l , f o r a l l body weights, as a r e s u l t of the h i g h p l a n e of n u t r i t i o n enjoyed.by the ^eer throughout the growing p e r i o d . Because the l e v e l of t o t a l n i t r o g e n e x c r e t i o n r e f l e c t s the l e v e l of n i t r o g e n i n t a k e once the maintenance and growth requirements have been surpassed, i t i s d i f f i c u l t to i n t e r p r e t the l e v e l of e x c r e t i o n o b t a i n e d i n terms of metabolic f u n c t i o n s . The p a t t e r n of n i t r o g e n e x c r e t i o n d u r i n g growth was t h e r e f o r e c o n s i d e r e d s o l e l y from the p o i n t of view of r e p r e s e n t i n g the i n c r e a s e i n p r o t e i n s t o r e s , and i n the t o t a l amount of p r o t e i n metabolism a s s o c i a t e d w i t h i n c r e a s i n g body size. 5 1 The importance of these r e s u l t s i n terms of f i e l d s t u d i e s i s d i s c u s s e d . The l a c k of adequate techniques, at the p r e s e n t time, to enable samples to be taken from the f i e l d f o r the type of a n a l y s e s used i n t h i s experiment, makes the a p p l i -cation of n u t r i t i o n a l p r i n c i p l e s , such as the type discussed in t h i s experiment, very d i f f i c u l t . However the results of experiments performed in the laboratory may be seen from the res u l t s of t h i s experiment to be of great value i n attempting to understand the relationship between the game animal and i t environment. Acknowledgement s The w r i t e r \vishes to express h i s s i n c e r e g r a t i t u d e to Dr. A. J. Wood and Dr. II. Nordan f o r t h e i r many suggestions, h e l p and encouragement and f o r p r o v i d i n g the space, the neces s a r y apparatus and m a t e r i a l s , and much of the o r i g i n a l d i r e c t i o n needed to complete t h i s experiment. The w r i t e r a l s o wishes to express g r a t i t u d e to Dr. I. McTaggart-Cowan f o r p r o v i d i n g a major stimulus f o r the experiment and f o r p r o v i d i n g the experimental animals i n con-j u n c t i o n w i t h the D i v i s i o n of Animal Science. The w r i t e r a l s o wishes to thank a l l of the graduate students of the D i v i s i o n of Animal S c i e n c e and many o t h e r s of the Departments of Zoology and B a c t e r i o l o g y f o r i n v a l u a b l e a s s i s t a n c e i n many forms. The w r i t e r i s a l s o g r a t e f u l to the N a t i o n a l Research C o u n c i l of Canada f o r t h e i r f i n a n c i a l support i n the form of a r e s e a r c h a s s i s t a n t s h i p throughout the summer of 19&1, and to the U n i v e r s i t y of B r i t i s h Columbia f o r the a d d i t i o n a l f i n a n c i a l support i n the form of a l a b o r a t o r y i n s t r u c t i o n a s s i s t a n t s h i p . v i i i . T a b l e of Contents Introduct i o n . 1 Methods and M a t e r i a l s 27 I. Animals . ' 27 I I . Sample C o l l e c t i o n . 3 2 I I I . Sample A n a l y s i s 3 4 R e s u l t s and D i s c u s s i o n 3 7 I. Choice of Methods 3 7 I I . N i t r o g e n E x c r e t i o n i n A d u l t Deer 4 0 A. General D i s c u s s i o n of N i t r o g e n E x c r e t i o n R e s u l t s i n the L i g h t of P r e s e n t l y H e l d T h e o r i e s of P r o t e i n Metabolism - 4 0 B. Changes i n the Animal Which I n f l u e n c e D i e t a r y Requirements . . . . 4 6 C. Changes i n Feed F o l l o w i n g I n g e s t i o n Which I n f l u e n c e D i e t a r y Requirements . . . . 57 D. C a l c u l a t i o n of N i t r o g e n Requirements from U r i n a r y N i t r o g e n E x c r e t i o n 6 6 1. N i t r o g e n Requirements Based on the P o i n t of N i t r o g e n Balance 6 6 2 . N i t r o g e n Requirements Based on the Endogenous T o t a l U r i n a r y N i t r o g e n L e v e l 73 E. N i t r o g e n D i s t r i b u t i o n 77 1. Urea 77 i x . 2. Ammonia 83 3 . C r e a t i n i n e and C r e a t i n e 84 I I I . N i t r o g e n E x c r e t i o n d u r i n g Growth 91 A. T o t a l U r i n a r y N i t r o g e n E x c r e t i o n 91 B. C r e a t i n i n e and C r e a t i n e N i t r o g e n E x c r e t i o n 98 T a b l e s . 100 F i gur e s I l l C o n c l u s i o n 122 Appendix I. Fo r m u l a t i o n f o r U n i v e r s i t y of B r i t i s h Columbia Deer Ra t i o n s . 124 Appendix I I . Ammonia Formation . 125 Appendix I I I . Schematic R e p r e s e n t a t i o n of Urea Formation 127 Appendix IV. Schematic R e p r e s e n t a t i o n of C r e a t i n i n e and C r e a t i n e Formation 129 Appendix V. I l l u s t r a t i o n s of Large A p p a r a t i I 3 0 Appendix VI. Curve of Per Cent Transmittance of A l k a l i n e P i c r a t e S o l u t i o n s of V a r y i n g C o n c e n t r a t i o n s 133 B i b l i o g r a p h y 134 > X. L i s t of T a b l e s T a b l e Page Data from M e t a b o l i c T r i a l s Performed on A d u l t Deer I. Dry Matter R e l a t i o n s 100 I I . N i t r o g e n D i g e s t i b i l i t y Data 101 I I I . N i t r o g e n Balance Data 102 IV. Water Balance Date 103 V . N i t r o g e n D i s t r i b u t i o n Data 104 VI. M e t a b o l i c l a t e D etermination Data 105 N i t r o g e n E x c r e t i o n Data Obtained During Growth VI I . R-4 and R-6 106 V I I I . R-7 and R-8 107 IX. R-9 108 X. R - l 109 XI. R-5 and R - l 2 110 L i s t of F i g u r e s F i g u r e 1. Course of N i t r o g e n Balance Obtained on R-5 i n T r i a l II I l l 2. Course of N i t r o g e n Balance Obtained on R-5 i n T r i a l I I I 112 3« I l l u s t r a t i o n of the P o i n t of N i t r o g e n Balance i n T r i a l II 113 x i . 4 . I l l u s t r a t i o n o f t h e P o i n t o f N i t r o g e n B a l a n c e i n T r i a l I I I 114 5- C h a n g e s I n N i t r o g e n D i s t r i b u t i o n d u r i n g ' t h e B a l a n c e T r i a l s 115 6. T h e C h a n g e i n C r e a t i n i n e E x c r e t i o n d u r i n g t h e B a l a n c e T r i a l s 116 7. T h e C u m u l a t i v e C h a n g e i n T o t a l N i t r o g e n E x c r e t i o n w i t h I n c r e a s i n g B o d y S i z e , i n G r o w i n g B l a c k - t a i l e d D e e r . . . 117 8. 'The C h a n g e i n H a t e o f I n c r e a s e i n M a g n i t u d e : o f T o t a l N i t r o g e n E x c r e t i o n w i t h I n c r e a s e . i n B o d y S i z e , i n G r o w i n g B l a c k - t a i l e d D e e r . . . . 118 9 . T h e C u m u l a t i v e C h a n g e i n T o t a l N i t r o g e n E x c r e t i o n w i t h I n c r e a s e i n A g e , i n G r o w i n g B l a c k - t a i l e d D e e r .119 10. T h ; C u m u l a t i v e C h a n g e i n T o t a l N i t r o g e n E x c r e t i o n w i t h I n c r e a s e i n A g e , i n G r o w i n g M a l e B l a c k - t a i l e d D e e r . 120 11. T h e C u m u l a t i v e C h a n g e i n T o t a l C r e a t i n i n e . E x c r e t i o n w i t h I n c r e a s e i n B o d y S i z e , i n ' G r o w i n g - B l a c k - t a i l e d D e e r . .. 121 Introduct i o n S u c c e s s f u l game management i s p r e d i c a t e d upon an adequate understanding of two c o m p l e x i t i e s . These are; the environmental complex, of which the game p o p u l a t i o n forms an important p a r t , and the growth complex of the i n d i v i d u a l game animal. From an adequate understanding of these two complex-i t i e s , f o r example, the r e l a t i o n between the c h a r a c t e r of the food p r o v i d e d by the range and the n u t r i t i o n a l s t a t u s of the game animals i n r e s i d e n c e on t h i s range may become b e t t e r understood. Then the n u t r i t i o n a l s t a t u s of the game animal may be advantageously m o d i f i e d , i f necessary, by i n s t i g a t i n g s u i t a b l e reforms i n the c h a r a c t e r of the a v a i l a b l e herbage f o r example, and thus the b e t t e r understanding of the f a c t o r s which c o n t r i b u t e to the n u t r i t i o n a l s t a t u s of the game animal has been a p p l i e d to c r e a t e an important and powerful game management technique. The environmental complex c o n s i s t s of a great number of d y n a m i c a l l y i n t e r r e l a t e d f a c t o r s which i n t e r a c t with, and i n f l u e n c e i n v a r y i n g degree the r e s i d i n g animal p o p u l a t i o n . For example, f a c t o r s such as the f o l l o w i n g are i n a constant s t a t e of f l u x : ( 1 ) c l i m a t e and topography ( D a r l i n g t o n 195 7) ; ( 2 ) changes i n p a r a s i t e p o p u l a t i o n s (Chandler 1955> a n ( 1 Spencer I938); and (3) changes i n herbage as a consequence of changes i n f e e d i n g h a b i t s of i n s e c t s and other animals i n c l u d i n g the game animals under c o n s i d e r a t i o n (CoAvan 1 9 4 5 ) , chemical changes i n p l a n t composition w i t h age and i n response to c l i m a t i c c y c l e s (Cowan, Hoar and Ha t t e r I95O), and s p e c i e s changes produced by c l i m a t i c v a r i a t i o n s and c o m p e t i t i o n w i t h i n the f l o r a l p o p u l a t i o n ( B l a i s d e l l and Muegger I 9 5 6 , E l t o n 1 9 3 5 , Holmgreen I956 and Hubbard 1 9 5 7 ) . The t h r e e f a c t o r s mentioned form important con-t r o l s on the s i z e of r e s i d i n g animal p o p u l a t i o n s . They present a k a l e i d o s c o p e of environmental i n f l u e n c e s which e f f e c t game animals, f o r example, i n v a r y i n g degree depending on the ever-changihgg p h y s i o l o g i c a l s t a t e of the i n d i v i d u a l s . The game animals r e a c t to the changes i n environmental i n f l u e n c e s by changes i n v i a b i l i t y i n accordance w i t h t h e i r p h y s i o l o g i c a l s t a t e and t h e i r g e n e t i c c h a r a c t e r . With changes i n t h e i r p h y s i o -l o g i c a l c o n d i t i o n t h e i r r e s i s t a n c e to adverse c o n d i t i o n s tends to vary. In t h i s manner the constant tendency of the p o p u l a t i o n to i n c r e a s e i n s i z e i s c o n t r o l l e d and o f t e n l i m i t e d . Also, f o r p h y s i o l o g i c a l reasons o r i g i n a t i n g w i t h i n the game p o p u l a t i o n , changes i n s e l e c t i v i t y towards browse s p e c i e s a r i s e (Cowan 1 9 4 5 and Swank I956) . Thus the changing c h a r a c t e r i s t i c s of the animal p o p u l a t i o n form new s e t s of s t i m u l i f o r the f l o r a l pop-u l a t i o n . The net r e s u l t i s a c o n t i n u a l and o f t e n u n p r e d i c t a b l e v a r i a t i o n i n the composition and a v a i l a b i l i t y of browse s p e c i e s of herbage f o r h e r b i v o r o u s game animals ( D i e t z 1 9 5 § a n d Lauck-h a r t 1957). Because of the complexity of the r e l a t i o n s h i p be-tween the animal and i t ' s environment sound f i e l d o b s e r v a t i o n s —7 - j> ~ are e s s e n t i a l f o r a c c u r a t e assessment of environmental or range c o n d i t i o n s . The c a r r y i n g c a p a c i t y of the range f o r a p a r t i c u l a r game s p e c i e s depends on the a b i l i t y of the environment to supply the needs of the i n d i v i d u a l animals. A s i d e from s u i t -a b l e temperatures, humidity, and topography which may determine whether an animal w i l l or can enter and remain i n a c e r t a i n area,, the most important c h a r a c t e r of an animal's environment i s i t s a b i l i t y to s a t i s f y the game animal's primary need, that of tak-i n g i n n u t r i e n t . More p r e c i s e l y , i t must supply the n u t r i t i o n a l requirements f o r maintenance and growth of the i n d i v i d u a l animals. In order to e s t a b l i s h these requirements and thus to a p p r e c i a t e f u l l y the s i g n i f i c a n c e of the range c o n d i t i o n s , i t i s n e c e s s a r y to study the growth complex of the game animal. Maintenance of a p o p u l a t i o n of animals and maintenance and growth of an i n d i v i d u a l animal are both problems of balance between the r a t e of s y n t h e s i s of new body m a t e r i a l and the r a t e of i t s d e s t r u c t i o n . The e f f e c t i v e r e d u c t i o n i n p o p u l a t i o n numbers by the death of o l d a d u l t animals i s a continuous and i n e v i t a b l e occurrence, r e g a r d l e s s of the extent of the f a v o u r -a b l e c o n d i t i o n s f o r s u r v i v a l . T h i s must be compensated f o r by the a d d i t i o n of new i n d i v i d u a l s i f a s t a b l e or i n c r e a s i n g l y l a r g e p o p u l a t i o n i s to be obtained. The s u c c e s s f u l conception, growth to b i r t h , growth through l a c t a t i o n to ma t u r i t y , and c o n t i n u e d maintenance f o r a s u i t a b l e r e p r o d u c t i v e p e r i o d , of a c e r t a i n constant f r a c t i o n of the p o p u l a t i o n ensures the com-p e n s a t i o n r e q u i r e d . Maintenance of the a d u l t body of an organism i s a l s o a matter of c o n t i n u e d compensation, by syn-t h e s i s or growth, f o r a continuous n a t u r a l l o s s . Protoplasm i s thermodynamically u n s t a b l e and i s c o n t i n u a l l y d i s i n t e g r a t i n g (Brody 1945)* T h i s p r o c e s s i s f a c i l i t a t e d by the presence of many r e v e r s i b l e enzyme systems which are capable of speeding n a t u r a l c a t a b o l i c p r o c e s s e s (Harper 1961). U n c o n t r o l l e d d e s t r u c t i o n of protoplasm w i l l continue i f unopposed u n t i l i r r e v e r s i b l e changes take p l a c e and death ensues. T h i s c a t a -b o l i s m must be compensated f o r or r e v e r s e d by a n a b o l i c p r o -cesses i f the body form and f u n c t i o n , a,nd indeed l i f e i t s e l f , i s to be p r e s e r v e d . The r e v e r s a l i n the n a t u r a l r e l e a s e of energy and a s s o c i a t e d p r o t o p l a s m i c breakdown of body m a t e r i a l i s accomplished by means of " f r e e energy" which i s l i b e r a t e d as the r e l e a s e of c o n f i g u r a t i o n a l energy from i n g e s t e d m a t e r i a l s , and which i s trapped and coupled or e n t r a i n e d i n t o the s y n t h e t i c p r o c e s s e s to make them thermodynamically p o s s i b l e . In e f f e c t , the lower energy s t a t e i s t r a n s f e r r e d from the auto-c a t a l y t i c p r o d u c t s to the c e l l m a t e r i a l s i n accordance with the second law of thermodynamics. A l s o u n i t s of structure^must be s u p p l i e d by the same means to r e p l a c e those that are completely d e s t r o y e d or l o s t to the body. If i n g e s t e d m a t e r i a l becomes u n a v a i l a b l e , m a t e r i a l from l e s s important p a r t s of the c e l l or _ 5 -body may be used f o r the same purpose. T h i s a l t e r n a t i v e w i l l e v e n t u a l l y l e a d to s e r i o u s c o m p l i c a t i o n s as more and more e s s e n t i a l c o n s t i t u e n t s are s a c r i f i c e d to p r e s e r v e the most e s s e n t i a l ones. During e a r l y growth the s y n t h e t i c p r o c e s s e s exceed the replacement requirements and the animal gains body mass. During the ad u l t phase of l i f e a balance i s u s u a l l y maintained r e s u l t i n g i n a constant weight. The animal g r a d u a l l y l o s e s i t s a b i l i t y to balance c a t a b o l i c f o r c e s and i n e v i t a b l y they predominate and cause death. The d u r a t i o n and extent of anabolism i s a p p a r e n t l y under endocrine c o n t r o l , which i s i n t u r n determined by the genetic complex. The p o t e n t i a l s i n -s t i l l e d i n t o the animal by these means, however, are seldom r e a l i z e d due to the confounding e f f e c t s of environmental f a c t o r s which prevent the f u l l e x p r e s s i o n of the genetic complex. The dependence on i n g e s t e d m a t e r i a l as a source of energy and b u i l d i n g u n i t s f o r b i o s y n t h e s i s e x p l a i n s the importance of n u t r i t i o n i n c o n t r o l l i n g the extent and r a t e of s y n t h e s i s . The major p o r t i o n of protoplasm, e x c l u d i n g water, has been w e l l e s t a b l i s h e d to be p r o t e i n . B i o s y n t h e s i s of protoplasm i s t h e r e -f o r e l a r g e l y a p r o c e s s of p r o t e i n s y n t h e s i s . The game range must t h e r e f o r e be capable of s u p p l y i n g s t r u c t u r a l u n i t s f o r p r o t e i n s y n t h e s i s that can be made a v a i l a b l e to the game animal, and a l s o m a t e r i a l s from which enough f r e e energy can be l i b e r a t -ed and s i m i l a r l y be made a v a i l a b l e , to permit p r o t e i n s y n t h e s i s . Of course other e s s e n t i a l d i e t a r y c o n s t i t u e n t s are needed to - 6 -make t h i s p r o t e i n s y n t h e s i s p o s s i b l e such as v i t a m i n s and. mi n e r a l s , and a l s o of course other m a t e r i a l s to p r o v i d e f o r the s y n t h e s i s of the n o n - p r o t e i n p a r t s of body t i s s u e p r o t o -plasm. E s t a b l i s h i n g these needs q u a n t i t a t i v e l y p r o v i d e s the necessary complimentary i n f o r m a t i o n to that of the c h a r a c t e r of the environment to enable s u c c e s s f u l assessment of the adequacy of range c o n d i t i o n s i n terms of c a r r y i n g c a p a c i t y . Once the r e l a t i o n s h i p between range c o n d i t i o n s and c a r r y i n g c a p a c i t y has been e s t a b l i s h e d , p u r p o s e f u l management of range c o n d i t i o n s i n terms of the game i t supports i s p o s s i b l e . There have been put forward s e v e r a l approaches to the problem of a s s e s s i n g the adequacy of the range i n p r o v i d -i n g the e s s e n t i a l n u t r i e n t f o r good n u t r i t i o n a l s t a t u s i n game animals. One of these approaches has been the study of range herbage i n terms of p o p u l a t i o n d e n s i t y , s p e c i e s present, and of chemical a n a l y s i s of v a r i o u s s p e c i e s as to q u a l i t y , q u a n t i t y , and a v a i l a b i l i t y determined by f e e d i n g t r i a l s , of n u t r i e n t s normally c o n s i d e r e d e s s e n t i a l to animal maintenance and growth. These s t u d i e s p r o v i d e much d a t a which must be i n t e r p r e t e d i n terms of c a l c u l a t e d t h e o r e t i c a l requirements of game animals ( B i s s e l l and Strong 1 9 5 5 , B i s s e l l et a l . 1 9 5 5 , Cook 1 9 5 4 , B i e t z I 9 5 8 , E i n a r s e n 1 9 4 6 , Gordon and Sampson 1 9 3 9 , Smith 1 9 5 0 , Smith 1 9 5 2 , Smith 1 9 5 9 , and Swank I956). Another approach has been what might be termed a study of the b i o l o g y of the game animals found i n p a r t i c u l a r ranges under c o n s i d e r a t i o n . The "performance" of the animals i s " r a t e d " i n terms of the degree to which they achieve or f a i l to a c h i e ve c e r t a i n l i m i t s i n v a r i o u s parameters such as those concerned w i t h body c o n f i r m a t i o n , s i z e and weight, d i g e s t i v e c a p a c i t y , and c e r t a i n c h a r a c t e r s of b l o o d c h e m i s t r y and bone marrow, f o r example (Bandy et a l . 1955> Cowan 1945> E i n a r s e n I946, Forbes et a l . 1 9 4 1 , 1 9 4 6 , French 1955, K i t t s et a l . I956, L e o p o l d et a l . 1951, N i c h o l I938, Rosen and B i s c h o f f 1952, and S v i h l a et a l . 1955K 'The performance or extent to which c e r -t a i n parameters are developed i s o f t e n d i f f i c u l t to measure a c c u r a t e l y , f o r example, the bulk of an animal as a parameter a s s o c i a t e d w i t h n u t r i t i o n a l s t a t u s . However, i n d i r e c t methods are b e i n g developed, such as the r a t i o of h e a r t or chest g i r t h to the t h i g h length, as a measure of b u l f changes w i t h re s p e c t to the r e l a t i v e l y short term s t a b l e t h i g h length. Once ob-t a i n e d , the measures of v a r i o u s parameters may be compared wit h those determined on animals; of " i d e a l " n u t r i t i o n a l status, of d i f f e r e n t l o c a l i t i e s , or of d i f f e r e n t s p e c i e s . A t h i r d approach has been the experimental d e t e r -m i n a t i o n of n u t r i t i o n a l requirements f o r c e r t a i n of the above parameters, or o t h e r s such as the time of a n t l e r appearance, or maximum growth r a t e , u s i n g empirical' f e e d i n g methods with " i d e a l - 8 -d i e t s , range herbage d i e t s , or d i e t s used w i t h v a r y i n g degrees of success i n domestic animals (Cowan et a l . 1955> N i c h o l I938) . The l i n e s of demarcation between these s t u d i e s are not p r e c i s e as they a l l r e p r e s e n t d i f f e r e n t ways of approaching the same c e n t r a l problems, a l s o o u t l i n e d p r e v i o u s l y . However, they do r e p r e s e n t c l e a r l y d i f f e r e n t l i n e s of approach though the methods and r e s u l t s sometimes i n t e r m i n g l e . A f o u r t h approach, e x e m p l i f i e d by the present e x p e r i -ment, e n t a i l s an attempt to determine the requirement f o r one s p e c i f i c n u t r i e n t , namely p r o t e i n , d u r i n g growth and f o l l o w i n g puberty, f o r good n u t r i t i o n a l s t a t u s , by d i r e c t measurements of metabolism on the i n d i v i d u a l game animal. T h i s approach has been used e x t e n s i v e l y on humans, many l a b o r a t o r y animals, and a l s o e x t e n s i v e l y on animals a s s o c i a t e d w i t h a g r i c u l t u r a l p r o -d u c t i o n (Albanese 1959, A l l i s o n 1951, B l a x t e r and M i t c h e l l 194-8, B l a x t e r and Wood, 1956, B l o c k I956, Butcher and H a r r i s 1957. B r i c k e r et a l . 1945, Greaves and S c o t t , i 9 6 0 , Majumdar i 9 6 0 , M i t c h e l l 1924, 1926, I 9 2 9 , 1948, and 1950, Munro 1951, M u r l i n et a l . I946, and Waterlow et a l . 1 9 5 9 ) . A review of the l i t e r a t u r e shows l e s s frequent a p p l i c a t i o n of t h i s method to game animals. The e v o l u t i o n of the p r e s e n t knowledge of metabolism and n u t r i t i o n i s based on the f i r m f o u n d a t i o n s of modern chemistry - 9 -w h i c h w e r e l a i d d o w n t o w a r d t h e c l o s e o f t h e l8th C e n t u r y . T h e g r a d u a l e s t a b l i s h m e n t o f a d e e p e r u n d e r s t a n d i n g o f m e t a -b o l i s m a n d o f t h e r e l a t i o n b e t w e e n n u t r i t i o n a n d m e t a b o l i s m n e c e s s i t a t e d t h e r e c e s s i o n a n d e v e n t u a l d i s s o l u t i o n o f t w o t r a d i t i o n a l a n d p o p u l a r s c h o o l s o f t h o u g h t , b o t h s t r e n g t h e n e d b y g e n e r a t i o n s o f a c c e p t a n c e a n d o n e o f t h e m a n h e i r l o o m f r o m a n c i e n t p h i l o s o p h i c g i a n t s . T h e f i r s t o f t h e s e w a s t h e p h l o g i s -t o n t h e o r y i n v e n t e d b y J. B e c h e r d u r i n g t h e 17th C e n t u r y ( M e n d e l I 9 2 3 ) . T h i s t h e o r y r e s t r i c t e d e a r l i e r a t t e m p t s t o u n d e r s t a n d t h e t r u e n a t u r e o f r e s p i r a t i o n , d u e t o i t s p e c u l i a r r e q u i r e -m e n t s . T h e s e c o n d w a s t h e h y p o t h e s i s o f a s i n g l e f u n d a m e n t a l a l i m e n t p r e s e n t i n a c r y p t i c f o r m i n a l l f o o d s . T h i s t h e o r y w a s p u t f o r w a r d b y H i p p o c r a t e s i n t h e C e n t u r y B . C . ( M e n d e l 1 9 2 3 ) , a n d s e e m i n g l y v e r i f i e d b y G a l e n i n t h e 2 n d C e n t u r y A.D. ( S a h y u n I948), a n d a s l a t e a s 1 8 3 3 b y W i l l i a m B e a u m o n t ( B e a u -m o n t 1 8 3 3 ) w i t h t h e o b s e r v a t i o n t h a t d i g e s t i v e p r o c e s s e s i n t h e s t o m a c h l e d t o t h e f o r m a t i o n o f a s i m i l a r l o o k i n g m a t e r i a l w h e t h e r t h e i n g e s t a w e r e p r e d o m i n a n t e l y s t a r c h y o r " a l b u m i n o u s " . T h e p h l o g i s t o n t h e o r y w a s d e s t r o y e d b y t h e w o r k s o f B l a c k , S c h e e l e , P r i e s t l y , C a v e n d i s h , B u t h e r f o r d a n d L a v o i s i e r ( B o u r n e 1953) w h o u n c o v e r e d t h e t r u e n a t u r e o f c o m b u s t i o n a n d l a i d t h e f o u n d a t i o n f o r m o d e r n c h e m i s t r y . T h e i r g r e a t c o n t r i -b u t i o n s h i n g e d o n t h e f a c t t h a t t h e y l e a r n e d t o r e c o g n i z e a t m o s p h e r i c C02> 02» a n ( i f i n a l l y E2> a n d t o o b s e r v e t h e c h a n g e s i n a m o u n t s o f t h e s e d u r i n g c o m b u s t i o n . T h e y a l s o o b s e r v e d - 10 -s i m i l a r changes a s s o c i a t e d w i t h animal r e s p i r a t i o n , and d u r i n g these experiments the presence of n i t r o g e n was i n d i c a t e d . D. Ru t h e r f o r d (Bourne) i s c r e d i t e d with the d i s c o v e r y and f i r s t i s o l a t i o n of atmospheric n i t r o g e n i n 1772. He c a l l e d i t azote because of abundant proof of i t s i n a b i l i t y to support r e s p i r a -t i o n or combustion. L a v o i s i e r made the most important and c u l m i n a t i n g c o n t r i b u t i o n w i t h r e g a r d to bioche m i c a l and n u t r i t i o n a l s t u d i e s , i n the o b s e r v a t i o n that the p r o c e s s of r e s p i r a t i o n i n animals i s e q u i v a l e n t to other combustion p r o -cesses i n terms of heat p r o d u c t i o n a s s o c i a t e d with a c e r t a i n amount of O2 consumption and CO2 p r o d u c t i o n . During the l8th Century and much of the 19th Century, p r o t e i n was be i n g d i s c o v e r e d to be w i d e l y d i s t r i b u t e d i n nature. G e l a t i n had been prepared from bones s i n c e the time of Boyle (I627-I69I) (Sahyun 1948). G l u t e n was i s o l a t e d by B e c a r r i (I682-I766) (Sahyun) from f l o u r . Z e i n was prepared by J. Gorham e a r l y i n the 19th Century (Gorham 1821). P. B e r t h o l e t i n 1786 r e p o r t e d that he found n i t r o g e n to be a constant c o n s t i t u e n t of a l l animal t i s s u e s (Bourne). Fourcroy i n I789 showed three k i n d s of animal p r o d u c t s (Bourne) on the b a s i s of t h e i r n i t r o g e n c o n c e n t r a t i o n and l a i d f o u n d a t i o n s f o r the study of p r o t e i n by n o t i n g the s i m i l a r i t y of g l u t e n and f l e s h . J . Gay-Lussac (1778-1850) h e l p e d to p e r f e c t n i t r o g e n a n a l y s i s and he found a l l seeds to c o n t a i n a p r i n c i p l e "abounding i n a z o t e " (McCollum 1939)' N i t r o g e n a n a l y s i s was slow and complicated u n t i l the time of the Danish chemist J. K j e l d a h l (I849-I900), who developed the r e l a t i v e l y r a p i d and v e r y a c c u r a t e ammonia method (Hawk 1954, and the d i s c o v e r i e s made bef o r e him co n c e r n i n g the amount and d i s t r i b u t i o n of n i t r o g e n r e p r e s e n t a great amount of p a i n s t a k i n g e f f o r t . In 1818 Braconnot s t u d i e d the p r o t e i n s of legumes and found a s i m i l a r i t y i n a l l (Bourne). Proust (I754-I876) improv-ed the i s o l a t i o n of g e l a t i n , and i s o l a t e d a white compound from cheese (Bourne) s i m i l a r to that which, a year l a t e r Braconnot, who a l s o s t a r t e d the a c i d h y d r o l y s i s of p r o t e i n , o b t a i n e d from a s u l p h u r i c a c i d d i g e s t of muscle f i b r e and wool (Sahyun). Braconnot termed t h i s product l e u c i n e . Besides n i t r o g e n , phos-phorus and sulphur were a l s o found to be common to a l l p r o t e i n by these and other i n v e s t i g a t o r s . G. Mulder i n 1838 and 1839 p r o b a b l y p r o v i d e d the g r e a t e s t i n i t i a l impetus f o r p r o t e i n r e s e a r c h w i t h h i s e f f o r t s to u n i f y thought on the a l b u m i n - l i k e or a z o t i z e d m a t e r i a l s being d i s c o v e r e d one by one up u n t i l t h i s time (Mulder 1838). He emphasized p r o t e i n i n n u t r i t i o n as being p r i m a r i l y important. He c a l l e d the albumen-like m a t e r i a l s p r o t e i n , and he showed the s i m i l a r i t y of p l a n t and animal p r o t e i n , h o l d i n g t h i s f a c t as the e x p l a n a t i o n f o r the as yet i n e x p l i c a b l e n u t r i t i v e v a l u e of p l a n t m a t e r i a l to animals. H i s views and i n f l u e n c e served how-ever to strengthen the age-old b e l i e f i n a s i n g l e fundamental aliment by p r o v i d i n g p r o t e i n as t h i s s i n g l e aliment. T h i s idea - 12 -had the u n f o r t u n a t e long term e f f e c t of c a u s i n g a s e p a r a t i o n , i n the minds of p h y s i o l o g i s t s , between r e s p i r a t i o n , and the r e l a t i o n s p e r t a i n i n g to i t s continuance, and body metabolism or n i t r o g e n metabolism and i t s a s s o c i a t e d phenomena. R e s p i r a -t i o n was to be thought of as being c o n t r o l l e d l a r g e l y by the amount of a v a i l a b l e oxygen, and to be a s p e c i a l mechanism f o r heat p r o d u c t i o n and maintenance of body temperature. While n i t r o g e n or p r o t e i n metabolism was to be thought of as l a r g e l y c a t a b o l i s m to p r o v i d e energy f o r muscular work. Magendie, at the b e g i n n i n g of the 19th Century, founded the study of n u t r i t i o n by demonstrating the u n l i k e n u t r i t i v e v a l u e of the then r e c o g n i z e d t h r e e types of f o o d s t u f f s , l a t e r d e s i g n a t e d : s a c c h a r i n a , o l e o s a and albttminosa, by Prout (Sahyun). He made a c l e a r d i s t i n c t i o n between nitrogenous and non-nitrogenous foods and he demonstrated that the o n l y source of n i t r o g e n f o r the animal body was n i t r o g e n c o n t a i n i n g foods (Bourne). However, t h i s r e s u l t was not e n t i r e l y accepted u n t i l almost 100 years l a t e r when Kroghin 1906 gave i n c o n t e s t i b l e p r o o f i n h i s exhaustive s e r i e s of r e s p i r a t o r y experiments (Krogh I906). Magendie's work supplemented the work of L a v o i s i e r and of Depretz and Dulong, who s t u d i e d r e s p i r a t i o n f o r the Academie de S c i e n c e i n 1839 and saw r e s p i r a t i o n as the s o l e source of body heat (Bourne), to g i v e the f o u n d a t i o n f o r the modern t h e o r i e s of metabolism. - 13 -In 1 8 4 4 B o u s s i n g a u l t invented the balance technique (Bourne). He s t u d i e d the r e l a t i o n between C,H,N, and 0 of the maintenance d i e t and of the u r i n e , f e c e s and milk. He r e -a f f i r m e d the a b s o l u t e e s s e n t i a l l l t y of n i t r o g e n i n the d i e t . Carbohydrate and f a t were s t i l l c o n s i d e r e d to be c a t a b o l i z e d by oxygen s o l e l y f o r the p r o d u c t i o n of body heat. B a r r a l ( 1 8 1 9 -1 8 8 4 ) was the f i r s t to use t h i s method on humans (Bourne). Along with t h i s work came f u r t h e r attempts to q u a n t i t a t e meta-bolism. In I 8 4 9 Kegnault and R e i s i t (Brody 1 9 4 5 and McCollum 1 9 3 9 ) d e v i s e d a c l o s e d c i r c u i t r e s p i r a t o r y apparatus and were the f i r s t to determine R.Q. 1 s. They a l s o f u r t h e r e d the e n u n c i a t i o n of Bergman i n 1 8 4 5 (Brody) of the i n c r e a s e i n basal metabolic r a t e w i t h the i n c r e a s e i n s u r f a c e a r e a r e l a t i v e to weight. The age of c a l o r i m e t e r s i s s a i d to have begun wi t h t h e i r heat p r o d u c t i o n s t u d i e s . J u s t u s von L i e b i g ( 1 8 0 3 - 1 8 7 3 ) i s o f t e n regarded as the c e n t r a l f i g u r e i n the e a r l y h i s t o r y of p r o t e i n theory. The importance of h i s work i s p r i m a r i l y t hat of o r g a n i z i n g and g r e a t l y s t i m u l a t i n g f u t u r e thought ( L i e b i g 1 8 4 3)• By b r i n g i n g the p r i n c i p l e s of o r g a n i c chemistry, which he was a l s o develop-ing, to b i o l o g y , he l a i d the f o u n d a t i o n s f o r the study of i n t e r -mediary metabolism. He s t r e s s e d the importance of n o t i n g the chemical change between f o o d and metabolic end p r o d u c t s as the key to u n d e r s t a n d i n g energy changes r e g a r d l e s s of the unknown d e t a i l s of the metabolic paths u t i l i z e d . H i s work l e d to the - 14 -;ver i f i c a t i o n of the p r i n c i p l e of the c o n s e r v a t i o n of energy i n the metabolism of l i v i n g organisms. He extended the n i t r o -gen balance technique to s t u d i e s of n i t r o g e n e q u i l i b r i u m . How-ever, h i s v e r y dominant pronouncements on p r o t e i n as the p l a s t i c p r i n c i p l e and as the o n l y source of energy f o r muscular a c t i v i t y served to p r e s e r v e the s e p a r a t i o n i n thought of r e s p i r a t i o n , and carbohydrate and f a t metabolism, from the " p r i m a r i l y important'* p r o t e i n metabolism. Though the methods and the knowledge nece s s a r y f o r the approach to modern day understanding of meta-b o l i s m were becoming more and more abundant the necessary steps c o u l d not be taken u n t i l the e s s e n t i a l u n i t y of carbohydrate, f a t , and p r o t e i n metabolism was accepted. In I852, F. Bidder and C. Schmidt (McCollum 1939) p u b l i s h e d r e s u l t s of n i t r o g e n balance work u s i n g r e f i n e d t e c h -niques, showing an a c c u r a t e a c c o u n t i n g of f o o d n i t r o g e n i n u r i n e and f e c e s of a d u l t c a t s . The n i t r o g e n balance technique became a powerful instrument i n the hands of C. V o i t ( I 8 3 I-I908), and von P e t t e n -k o f f e r , who i n 1866 showed that p r o t e i n was not metabolized p r i m a r i l y f o r energy (Brody and Sahyun). V o i t showed that " c i r c u l a t i n g p r o t e i n " d i d not have to enter i n t o the body s t r u c t u r e i n order to be c a t a b o l i z e d , c o n t r a r y to the i n s i s t e n c e of von L i e b i g . P e t t e n k o f f e r confirmed that p r o t e i n was not the primary energy source, V o i t i n t r o d u c e d many ideas and observa-t i o n s which h o l d today. He i n t r o d u c e d the i d e a that the f u n c t i o n of f o o d p r o t e i n was to r e p l a c e body p r o t e i n which was i n e v i t a b l y broken down to a small degree d u r i n g i t s o p e r a t i o n . He a l s o demonstrated a time l a g i n adjustment of the body from a h i g h p l a n e p r o t e i n d i e t to a low plane, suggesting two types of p r o t e i n metabolism and two types of body p r o t e i n , namely; "organ" or s t a b l e s t r u c t u r a l p r o t e i n with l i t t l e a v a i l a b i l i t y f o r m etabolic needs, and l o o s e l y bound r e s e r v e p r o t e i n i n c e l l s and " c i r c u l a t i n g " . Rubner i s c r e d i t e d with c o n f i r m i n g the f i r s t law of thermodynamics as a p p l i e d to animal metabolism (Brody). He, l i k e V o i t , d i s c o v e r e d many aspects of animal n u t r i t i o n which s t i l l h o l d . Examples of these are: o b s e r v a t i o n and q u a n t i t a -t i o n of S.D.A., f i r s t observed by S a n c t o r i u s ( C h i t t e n d e n I 9 0 7 ) and l a t e r by Bidder and Schmidt ( C h i t t e n d e n ) , o b s e r v a t i o n of d i f f e r e n c e s i n d i e t a r y p r o t e i n a v a i l a b i l i t y w i t h d i f f e r e n t p r o-t e i n sources, u s i n g r e f i n e d f e c a l n i t r o g e n a n a l y s i s , c o n f i r m a t i o n of " s u r f a c e law"; and o b s e r v a t i o n that e f f i c i e n c y of growth de-cre a s e s w i t h d e c r e a s i n g growth r a t e . O u t s i d e of c o n t i n e n t a l Europe, Lawes and G i l b e r t (Bourne) at the r e s e a r c h s t a t i o n i n Rothamsted, Great B r i t a i n , showed the a g r i c u l t u r a l world the importance of nit r o g e n o u s foods f o r p r o d u c i n g non-nitrogenous bodies such as s t a r c h and c e l l u l o s e . Before the t u r n of the century, E. Smith (Bourne) i n England f o r e c a s t a major development toward the deeper understanding of p r o t e i n metabolism by demonstrating two important f a c t s ; namely, he saw that not a l l u r e a came from food, taut that almost a l l d i d p r o v i d e d the p r o t o p l a s m i c mass was kept uniform. I f the bulk i n c r e a s e d the urea output r e -p r e s e n t e d the food n i t r o g e n minus the amount of t i s s u e n i t r o -gen gained. If i t decreased, the amount of u r e a n i t r o g e n l o s t was r e p r e s e n t e d by an e q u i v a l e n t i n c r e a s e over that produced by the food. A s s o c i a t e d w i t h the r e a l i z a t i o n t h a t the primary f u n c t i o n of p r o t e i n i n the d i e t was not f o r energy, came the gradual r e a l i z a t i o n t h a t accepted d i e t a r y recommendations of more than 100 grams of p r o t e i n f o r the average human male was u n n e c e s s a r i l y h i g h . Values such as l l S grams set by V o i t were based on e m p i r i c a l o b s e r v a t i o n s of c u r r e n t d i e t s r a t h e r than on experimentation. In I89O H i r s c h f e l d (Bourne) i n B e r l i n , s t a r t e d t h i s movement, showing that there was no i n c r e a s e i n n i t r o g e n e x c r e t i o n w i t h heavy e x e r c i s e , p r o v i d e d the c a l o r i c i n t a k e was l a r g e enough to supply the body's need. E a r l i e r workers had not grasped the importance of having an energy balance and n i t r o g e n balance s i m u l t a n e o u s l y i n d e t e r m i n i n g the o v e r a l l p i c t u r e of n i t r o g e n balance. A l s o , many d i e t recommendations were based on o b s e r v a t i o n s of d i e t of working man. In 1895 Atwater (Sahyun) s t a t e d the energy y i e l d i n g f u n c t i o n s of f o o d as an a l t e r n a t i v e to b u i l d i n g t i s s u e , or as - 1 7 -the sole function, or both, depending on the food and. on the body's needs. In I907, Chittenden saw high lev e l s of protein intake as p o t e n t i a l l y dangerous to body health (Chittenden 1 9 0 7 ) . He f e l t that even though i t was of prime n u t r i t i o n a l importance, protein was not needed in greater amounts than carbohydrates. During t h i s evolution of ideas concerning the true purpose and fat e of dietary proteins, a p a r a l l e l f i e l d of study was continuing which was to be of great importance i n understanding the mechanisms of protein n u t r i t i o n and metabolism. This study concerned the chemical structure of protein and the metabolic significance of t h i s structure. The observation that protein subjected to hydrolytic action by b o i l i n g acid was de-composed into r e l a t i v e l y simple c r y s t a l l i n e substances was made near the beginning of the 1 9 t h Century. Wollaston (Vickery 1 9 3 1 ) i s credited with the discovery of the f i r s t true amino acid, namely, cystine, i n 1 8 1 0 though Vanguelin and Bobiquet had i d e n t i f i e d asparagine i n 1 8 0 6 (Bourne). He c a l l e d i t c y s t i c oxide due to i t s occurrence in urinary c a l c u l i . Proust i s credited with leucine in I8I9, Braconnet with glycine in 1 8 2 0 and so on u n t i l by I903, 1 8 amino acids were known (Vick-ery). The 2 0 t h Century, therefore, began with an environ-ment of knowledge of protein n u t r i t i o n and metabolism which had - 13 -four important aspects. F i r s t , p r o t e i n though capable of y i e l d i n g energy was not u t i l i z e d p r i m a r i l y f o r energy f o r muscular a c t i v i t y . Second, a l a r g e i n t a k e of p r o t e i n r e l a t i v e to carbohydrate or f a t was not co n s i d e r e d necessary or d e s i r -a b l e . T h i r d , t h e r e were p o s i t i v e i n d i c a t i o n s that p r o t e i n served, two purposes i n the body, impl y i n g t h e r e f o r e two types of p r o t e i n metabolism, one an energy p r o d u c i n g f u n c t i o n , and the other a t i s s u e b u i l d i n g f u n c t i o n . A l s o , the l e v e l of p r o -t e i n c a t a b o l i s m c o u l d be estimated f a i r l y a c c u r a t e l y by the l e v e l of u r e a n i t r o g e n i n the u r i n e . Fourth, t h e r e was abun-dant evidence that though p r o t e i n from a l l sources was funda-m e n t a l l y s i m i l a r i t c o n t a i n e d a wide range of q u a l i t a t i v e d i v e r s i t y of chemical s t r u c t u r e or arrangement. A l s o there was a growing b e l i e f t h a t the key to understanding p r o t e i n n u t r i t i o n and metabolism l a y i n the a v a i l a b i l i t y and h a n d l i n g by the body of amino a c i d s . Otto F o l i n of Munich, i n 1905J demonstrated c l e a r l y the dichotomy i n p r o t e i n metabolism ( F o l i n 1905). By q u a n t i t a t i v e and q u a l i t a t i v e a n a l yses of human u r i n a r y n i t r o g e n e x c r e t i o n he demonstrated the e x i s t e n c e of an i r r e d u c i b l e l e v e l of n i t r o g e n e x c r e t i o n of c h a r a c t e r i s t i c composition and constancy on a low or n i t r o g e n f r e e d i e t . He f u r t h e r showed that e l e v a t i o n i n u r i n a r y n i t r o g e n e x c r e t i o n by e l e v a t i n g the d i e t a r y p r o t e i n l e v e l , was accompanied by an i n -cre a s e i n the r e l a t i v e importance of ure a n i t r o g e n . Urea was known at t h i s time to be s o l e l y a s s o c i a t e d with the deamination - 19 -of amino a c i d s . He suggested that the lower l e v e l of n i t r o g e n e x c r e t i o n which he termed endogenous e x c r e t i o n r e p r e s e n t e d the breakdown of body s t r u c t u r e and that d i e t a r y p r o t e i n i n excess of the amount needed to balance t h i s was used f o r energy, and u l t i m a t e l y gave r i s e to the exogenous n i t r o g e n of the u r i n e . P r e l i m i n a r y establishment of a q u a n t i t a t i v e r e l a t i o n -ship between energy p r o d u c t i o n at a b a s a l l e v e l , and t o t a l en-dogenous n i t r o g e n e x c r e t i o n was o b t a i n e d by T e r r o i n e and Sorg-Matter i n I 9 2 7 ( T e r r o i n e 1 9 2 7 ) . They found an approximately constant r a t i o . o f 2 . 3 to 2 . 9 m i l l i g r a m s of t o t a l n i t r o g e n ex-c r e t e d per C a l o r i e ' o f energy produced u s i n g mature animals of d i f f e r e n t s p e c i e s . They a l s o found that f l u c t u a t i o n s i n en-dogenous e x c r e t i o n p a r a l l e l e d those i n b a s a l energy metabolism. Smuts, i n 1935> w i t h a more d e f i n i t i v e approach, found an aver-age r a t i o of 1 .99 m i l l i g r a m s of endogenous u r i n o u s n i t r o g e n per C a l o r i e per day (Smuts 1 9 3 5 ) * Improvements i n h i s method were; u s i n g u r i n a r y n i t r o g e n only, which c o n s t i t u t e d a more r e f i n e d technique, and measuring the metabolic r a t e on the same i n d i v i d -u a l s used f o r n i t r o g e n e x c r e t i o n measurements. He a l s o used a wider range i n weight. H i s r e s u l t s confirmed those of T e r r o i n e and Sorg-Matter. The higher v a l u e ( 2 . 3 to 2 . 9 m i l l i g r a m s ) r e -p o r t e d by the l a t t e r authors i n c l u d e d the endogenous f e c a l n i t r o g e n and as s t a t e d above r e p r e s e n t e d the t o t a l n i t r o g e n e x c r e t i o n e x c l u s i v e of r e s p i r a t o r y and sweat- l o s s e s . - 20 -Much of the d i f f i c u l t y i n e s t a b l i s h i n g the t r u e n a t u r e of p r o t e i n metabolism and the energy r e q u i r e d f o r p r o t e i n s y n t h e s i s has been and i s due to the d i f f i c u l t y i n o b t a i n i n g b a s a l c o n d i t i o n s ^ A c t i v i t y , and many other f a c t o r s , both d i e t -a ry and p h y s i o l o g i c a l , i n c r e a s e p r o t e i n c a t a b o l i s m and energy p r o d u c t i o n beyond b a s a l l e v e l s . However, once e s t a b l i s h e d , the b a s a l l e v e l p r o v i d e s an e x c e l l e n t r e f e r e n c e p o i n t f o r s t u d y i n g the increments caused by these v a r i o u s f a c t o r s . S t u d i e s of t h i s n ature add g r e a t l y to the understanding of metabolic events that l e a d to the minimal or b a s a l metabolism. During the e a r l y p a r t of the 2 0 t h Century great impetus was p r o v i d e d f o r the chemical aspect of p r o t e i n meta-b o l i s m study by the b r i l l i a n t a n a l y t i c a l work of E. F i s c h e r ( F i s c h e r I 9 I 4 ) , A. K o s s e l (Kossel I 9 0 0 ) , Van S l y k e (Sahyun), and many other p h y s i o l o g i s t s and b i o c h e m i s t s who g r a d u a l l y demonstrated that p r o t e i n was broken down to the amino a c i d l e v e l d u r i n g d i g e s t i o n . A l s o amino a c i d s were demonstrated to be absorbed i n t o the p o r t a l c i r c u l a t i o n f o l l o w i n g d i g e s t i o n , and f i n a l l y i t was shown that animals c o u l d s y n t h e s i z e blood p r o t e i n from an i n g e s t a of amino a c i d s . In 1901, 0. Cohneim (Cohneim 1901) showed that amino a c i d s were formed i n e r e p t i c d i g e s t i o n i n the i n t e s t i n a l mucosa. At the same time, F. Kutscher and J. Seemann (Kutscher et a l . I 9 0 2 ) found them i n chyme, and 0. Loewi (Sahyun) showed that amino a c i d s of d i g e s t i o n c o u l d produce n i t r o g e n e q u i l i b r i u m . The n i t r o g e n requirement of - 21 -animals t h e r e f o r e was shown to be f o r n i t r o g e n i n the form of amino a c i d s . The f i r s t p r o of of the n u t r i t i v e importance of q u a l i -t a t i v e d i f f e r e n c e s i n p r o t e i n was shown by E. W i l l c o c k and Hop-k i n s (Sahyun) w i t h the demonstration i n 1 9 0 6 of the i n d i s p e n s i -b i l i t y of tryptophane f o r maintenance i n mice. There has s i n c e been a great amount of work done on the amino a c i d requirements of animals extending up u n t i l the p r e s e n t time. T. Osborne and L. Mendel i n I9I2 showed that l y s i n e was i n d i s p e n s a b l e f o r growth i n r a t s , though p r o t e i n s d e f i c i e n t i n t h i s amino a c i d would support l i f e . Thus, the q u a l i t a t i v e d i f f e r e n c e s i n amino a c i d requirements f o r growth and maintenance were demonstrated. In I9I5 they enunciated the "law of minimum" and i n I 9 I 9 Osborne developed the procedure of e s t i m a t i n g the b i o l o g i c a l v a l u e of foo d p r o t e i n u s i n g growth as the c r i t e r i o n (Osborne and Mendel, 1 9 1 2 , 1915> a n ( i Osborne et a l 1 9 1 9 ) . T h i s l a t t e r method was a m o d i f i c a t i o n of the method of K. Thomas, (Ch i t t e n d e n I907) a student of Eubner who f i r s t measured the amount of v a r i o u s p r o -t e i n sources r e q u i r e d to produce n i t r o g e n e q u i l i b r i u m on h i m s e l f , i n cognisance of the n e c e s s i t y of d e f i n i n g the s t a t e of the a n i -mal due to the d i f f e r e n t a s s o c i a t e d n i t r o g e n requirements. Hose i n the p e r i o d from I 9 3 5 to I 9 3 8 (Hose 1 9 5 5 , and West et a l 1 9 5 7 ) brought the many experiments on amino a c i d r e -quirements together w i t h t e s t s u s i n g p u r i f i e d amino a c i d s . T h i s - 22 -b r i l l i a n t s e r i e s of experiments showed that; of n i n e t e e n amino a c i d s r e q u i r e d f o r body s y n t h e s i s nine are e s s e n t i a l as p r e -formed d i e t a r y c o n s t i t u e n t s f o r maintenance and growth, f i v e of the r e s t are s e m i - e s s e n t i a l as preformed amino a c i d s i n the d i e t depending on the p h y s i o l o g i c a l s t a t e of the experimental animal and on i t s d i e t a r y c h a r a c t e r , and the remainder are non-e s s e n t i a l as preformed amino a c i d s i n d i e t . He a l s o o b t a i n e d v a l u e s f o r the amount of each needed under d i f f e r e n t c o n d i t i o n s . In the l i g h t of present day knowledge of carbohydrates and f a t metabolism, the requirement of the animal f o r amino a c i d s r a t h e r than preformed p o l y p e p t i d e n u c l e i f o r s y n t h e s i s of body p r o t e i n p r o v i d e s an e x p l a n a t i o n of the mechanism f o r the p r o t e i n spar-i n g e f f e c t of carbohydrate and f a t . However, the requirement f o r n i n e preformed amino a c i d s p l a c e s a l i m i t on the p r o t e i n s p a r i n g e f f e c t and on Runner's isodynamic law which suggested complete c a l o r i c i n t e r c h a n g e a b i l i t y . The s y n t h e s i s of non-e s s e n t i a l amino a c i d s from carbohydrate i l l u s t r a t e s a s i m i l a r dichotomy i n carbohydrate metabolism to that of p r o t e i n meta-b o l i s m and h e l p s to e x p l a i n the n o n s p e c i f i c i t y of the source of n o n - e s s e n t i a l n i t r o g e n . Schoenheimer i n 1939 (Schoenheimer 1942) and l a t e r , found a complete interchange of amino a c i d s and p a r t s of amino a c i d s , between body p r o t e i n , and d i e t a r y p r o t e i n v i a the amino a c i d metabolic p o o l of t e m p o r a r i l y f r e e amino a c i d s . T h i s showed that n i t r o g e n of exogenous and endogenous metabolism was i n d i s -- 23 -t i n g u i s h a b l e on a p h y s i c a l b a s i s . However, as M i t c h e l l showed i n 1 9 5 5 (Albanese 1 9 5 9 , Maynard 1 9 5 6 ) there was s t i l l a con-stant amount of p r o t e i n c a t a b o l i s m which was independent of p r o t e i n i n t a k e . Schoenheimer 1s r e s u l t s showed that m e t a b o l i t e s i n v o l v e d i n v a r i o u s r e a c t i o n s are i n a dynamic e q u i l i b r i u m of interchange and that metabolic r e a c t i o n s represent t r e n d s . Thus d i e t a r y m a t e r i a l may s t i l l serve two independent purposes. S i n c e 1949 the development and a p p l i c a t i o n of new procedures has p e r -m i t t e d the u n c o v e r i n g of a great deal of i n f o r m a t i o n on the com-p l e x i n t e r r e l a t e d f a c t o r s which a f f e c t amino a c i d requirements as w e l l as general n u t r i t i o n a l requirements. F a c t o r s such as s p e c i e s and i n d i v i d u a l d i f f e r e n c e s i n p r o t e i n s t r u c t u r e , which i s to a great extent due to v a r i a t i o n s i n amounts of enzymes, d i f f e r e n c e s i n the type of t i s s u e c u r r e n t l y under c o n s t r u c t i o n , the source of n o n - e s s e n t i a l n i t r o g e n , the balance among essen-t i a l amino a c i d s , the q u a n t i t y and q u a l i t y of the non-nitrogen-ous i n g e s t a , and the p h y s i o l o g i c a l s t a t e of the animal are a l l i n t e r r e l a t e d and exert some i n f l u e n c e on the n i t r o g e n r e q u i r e -ment of the animal. A l l of these minutiae do not i n v a l i d a t e the general laws of m e t a b o l i c r a t e and waste per u n i t s u r f a c e a r e a a r r i v e d at by Brody and o t h e r s b.efore 1949> which show that the endogenous n i t r o g e n e x c r e t i o n and b a s a l energy p r o -d u c t i o n are r e l a t e d to the b i o l o g i c a l l y a c t i v e s i z e of an a n i -mal and that as the s i z e of the animal i n c r e a s e s the endogenous e x c r e t i o n and energy p r o d u c t i o n are e l e v a t e d by d e c r e a s i n g - 2 4 -increments. The equation set f o r t h by Brody and K l i e b e r i s : C a l o r i e s of b a s a l energy p r o d u c t i o n = 7 0 . 5 x (Weight i n k i l o -grams to the power 0 . 7 5 ) f © r the r e l a t i o n between b i o l o g i c a l s i z e and c a l o r i c requirement (Brody 1945» K l i e b e r 1 9 3 2 ) . T h i s equation shows that f o r a one percent i n c r e a s e i n body weight i n k i l o g r a m s t h e r e i s a 0 . 6 6 percent i n c r e a s e i n energy r e -quirement. Because of the r e l a t i o n e s t a b l i s h e d by Smuts the above equation can be used to estimate the minimum requirement f o r a b i o l o g i c a l l y p e r f e c t p r o t e i n . Thus minimum p r o t e i n r e -quirement i n pounds = 2 x 7 ° x ^kg;. x 6 . 2 5 . 1 0 0 0 x ' 4 5 4 The f i g u r e 6 . 2 5 a r i s e s from the f a c t that the average n i t r o g e n content of body p r o t e i n i s s i x t e e n p e r c e n t . The p r o t e i n r e -quirement thus estimated i s i n a c c u r a t e due to the f a c t that p a r t of the n i t r o g e n of endogenous e x c r e t i o n i s a s s o c i a t e d w i t h c r e a t i n i n e , c r e a t i n e and u r i c a c i d . A p p l i c a t i o n of the minimum p r o t e i n requirement to a c t u a l d i e t a r y p r o t e i n i s complicated by the great d i f f i c u l t y i n e s t i m a t i n g the true b i o l o g i c a l v a l u e of the d i e t a r y p r o t e i n . Once o b t a i n e d i t i s r e l a t i v e l y easy to c o r r e c t the minimum p r o t e i n requirement f o r a p e r f e c t p r o -t e i n to that of the d i e t a r y p r o t e i n . The accepted p a t t e r n of n i t r o g e n metabolism i n mono-g a s t r i c animals presumably a p p l i e s to ruminants except f o r m o d i f i c a t i o n s brought about by the s y n t h e s i s of m i c r o b i a l p r o -t e i n i n the rumen and by the l o s s of nitrogenous m a t e r i a l s from the rumen by d i r e c t a b s o r p t i o n (Lewis 1957)* The rumen i s a s w e l l i n g i n the d i g e s t i v e t r a c t f o r d e l a y i n the passage of crude f i b r e . It i s f u n c t i o n a l l y a f e r m e n t a t i o n vat su p p o r t i n g a l a r g e p o p u l a t i o n of p r o t o z o a and b a c t e r i a which degrade d i e t -a r y p r o t e i n and carbohydrate to short c h a i n v o l a t i l e f a t t y a c i d s . These a c i d s and ammonia from the d e g r a d a t i o n of p r o t e i n are r a p i d l y absorbed from the rumen. Part of the ammonia, f o l l o w i n g normal d e t o x i f i c a t i o n by the l i v e r , i s r e c y c l e d v i a the s a l i v a i n t o the rumen. However, n i t r o g e n removed from the rumen t h i s way, even though i t i s r e c y c l e d , must be i n c o r p o r a t -ed i n t o b a c t e r i a l or p r o t o z o a l c e l l p r o t e i n or i t i s soon l o s t as exogenous n i t r o g e n e x c r e t i o n . The degree of l o s s depends on; the extent of d e g r a d a t i o n as u n a f f e c t e d p r o t e i n may be u t i l i z e d i n a s i m i l a r way to the mono-gastric animals a f t e r i t passes on from the rumen i n t o the abomasum and small i n t e s t i n e , and on the r a t e of degradation, as t h i s determines the amount of r e l e a s e d ammonia which can be u t i l i z e d by the o m i c r o f l o r a and the amount which can be r e c y c l e d as urea. A l s o p r o t e i n s y n t h e s i s by the m i c r o f l o r a depends on. an adequate supply of carbohydrate to the rumen to p r o v i d e adequate energy and carbon c h a i n u n i t s f o r u t i l i z a t i o n of ammonia. Once u t i l i z e d i n the s y n t h e s i s of m i c r o b i a l p r o t e i n n i t r o g e n i s a v a i l a b l e to the host by d i g e s t i o n of the continuous passage of excess micro-f l o r a a long the d i g e s t i v e t r a c t to the abomasum and small i n -t e s t i n e . The n u t r i t i v e v a l u e of m i c r o b i a l p r o t e i n has been - 26 -analysed by f e e d i n g experiments w i t h m i c r o b i a l p r e p a r a t i o n s w i t h r e s u l t a n t t r u e d i g e s t i b i l i t y v a l u e s of approximately 70 and b i o l o g i c a l v a l u e s of approximately 80 (Annison 1959)• These r e s u l t s show a good but not o u t s t a n d i n g f e e d i n g v a l u e . Though there i s a great deal of m a t e r i a l i n the l i t e r a t u r e r e g a r d i n g e m p i r i c a l f e e d i n g t r i a l s w i t h deer, t h e r e i s v e r y l i t t l e c o n c erning the d e t e r m i n a t i o n of p r o t e i n r e q u i r e -ment from metabolic s t u d i e s . The m a t e r i a l p r e s e n t e d here i s d e r i v e d from measurements made on n i t r o g e n metabolism d u r i n g metabolic s t u d i e s on i n d i v i d u a l animals. The animals s t u d i e d are Vancouver I s l a n d genotype of b l a c k - t a i l e d deer, Odocoileus, faemionus columbianus (Richardson). - 27 -Methods and M a t e r i a l s  Animals E i g h t c o a s t a l or Vancouver I s l a n d b l a c k - t a i l e d deer, Odo co ileus,,, hemionus, columbianus, (Vancouver I s l a n d genotype), of which t h r e e were female, were captured near Courtenay, B.C. i n e a r l y June, i 9 6 0 . They were approximately t h r e e weeks of age and i n a p p a r e n t l y good p h y s i c a l c o n d i t i o n . Nothing i s known of t h e i r n u t r i t i o n a l h i s t o r y p r i o r to capture nor of the n u t r i t i o n a l h i s t o r y of t h e i r r e s p e c t i v e dams. They were taken • d i r e c t l y to the U n i v e r s i t y of B. C. and housed i n a s p e c i a l w i l d ungulate u n i t . T h i s u n i t i s d e s c r i b e d i n the J o u r n a l of W i l d l i f e Management (Wood, Nordan, and Cowan 1 9 6 1 ) . They were housed i n i n d i v i d u a l pens and coded B - l to R - 8 . In accordance w i t h the methods d e s c r i b e d i n the above r e f e r e n c e , f o r the care and management used i n r a i s i n g deer i n c a p t i v i t y , the fawns were immediately p l a c e d on a regimen of evaporated m i l k mixed i n warm water. A f t e r s i x weeks, or when the animals had reach-ed a weight of twelve to f i f t e e n pounds, they were weaned to a dry r a t i o n . (see Appendix 1 ) A f t e r f i v e months they were switched from the weaning r a t i o n to an a d u l t r a t i o n . (see Appendix 1 ) At a pproximately one month i n t e r v a l s , e x c l u d i n g the month of November, and extending from J u l y to December i 9 6 0 , and i n some cases January I 9 6 I , t o t a l metabolism s t u d i e s of twenty-four hours' d u r a t i o n each were performed on the growing deer as p a r t of a separate experiment. The f i n a l t r i a l on each deer was of t h r e e days' d u r a t i o n . A l l of these s t u d i e s were done i n a s p e c i a l l y c o n s t r u c t e d r e s p i r a t i o n c a l o r i m e t e r which c o n t a i n e d a g a l v a n i z e d i r o n animal cage, (see Appendix V). The cage was c o n s t r u c t e d to f a c i l i t a t e the c o l l e c t i o n of f e c e s and u r i n e . The u r i n e and f e c e s samples thus o b t a i n e d were f r o -zen f o r storage. Advantage was taken of the u r i n e c o l l e c t i o n from t h i s separate experiment to study the n i t r o g e n metabolism of growing b l a c k - t a i l e d deer. The r e s u l t s of t h i s study r e -present the f i r s t p a r t of the present experiment. They are a l s o of v a l u e i n e s t a b l i s h i n g and p r o v i n g the methods used. The second p a r t of the experiment c o n s i s t e d of three combined n i t r o g e n balance and metabolism t r i a l s , performed on one w h i t e - t a i l e d deer (Odocoileus v i r g i n i a n u s o c r u r u s ) and on one b l a c k - t a i l e d deer d u r i n g the animal's r e s i d e n c e i n the r e s p i r a t i o n c a l o r i m e t e r . The f i r s t was on P - l , an a d u l t white-t a i l e d doe; and the second and t h i r d were on R-5> an a d u l t b l a c k - t a i l e d doe, both a l r e a d y on the a d u l t r a t i o n . The f i r s t of these t r i a l s was s t a r t e d on October l 6 t h , and was stopped a f t e r f o u r days f o r t e c h n i c a l reasons. It i s thus incomplete. The second and t h i r d t r i a l s were s t a r t e d on January 1 5 t h and March 1 2 t h , and l a s t e d 1 3 and 1 1 days r e s p e c t i v e l y . Feces and u r i n e were c o l l e c t e d d a i l y as i n the t h r e e day t r i a l s d u r i n g the growth p e r i o d . 29 -The f e e d i n g schedule used d u r i n g these t r i a l s con-s i s t e d of an i n i t i a l s t a r v a t i o n p e r i o d , a c o n t r o l l e d f e e d i n -take t e s t p e r i o d , and a f i n a l s t a r v a t i o n p e r i o d . Free access to d r i n k i n g water was p r o v i d e d throughout. The i n i t i a l s t a r -v a t i o n p e r i o d i n the second and t h i r d t r i a l l a s t e d four days. T h i s l e n g t h of time was n e c e s s a r y to ensure complete passage of d i e t a r y m a t e r i a l through the d i g e s t i v e t r a c t of the rumin-ant. A l s o , due to the l a c k of incoming carbohydrate or rough-age to the rumen, the metabolic a c t i v i t y of the rumen micro-organisms i s markedly decreased c a u s i n g a decreased absorp-t i o n of m e t a b o l i c by-products of m i c r o b i a l o r i g i n . During t h i s f o o d - f r e e p e r i o d the l e v e l of u r i n a r y n i t r o g e n was ex-p e c t e d to drop i n c u r v i l i n e a r f a s h i o n to a new lowered l e v e l a s s o c i a t e d w i t h the maintenance c a t a b o l i s m of p r o t e i n . The o b j e c t of the c o n t r o l l e d f e e d i n t a k e t e s t p e r i o d was to meas-ure increments or decrements i n n i t r o g e n e x c r e t i o n at v a r i o u s l e v e l s of f e e d i n t a k e . B e - a l i m e n t a t i o n was begun wi t h one pound of a d u l t r a t i o n . If t h i s amount was a l l consumed w i t h i n twenty-four hours two pounds were given on the second day. If this'amount was a l s o w e l l consumed, f o r example, up to 75%> one pound was a g a i n given and the f e e d l e v e l was a l t e r n a t e d be-tween these two v a l u e s d u r i n g each day of a f i v e day t e s t p e r i o d . The f e e d was w e l l consumed at the one pound l e v e l and f a i r l y w e l l consumed at the two pound l e v e l . However, i n the t h i r d t r i a l , R -5 consumed one pound of f e e d o n l y a f t e r i t had been r e p e a t e d l y p r e s e n t e d f o r t h r e e days, and consumed s l i g h t -l y more than one pound on the f o u r t h day when o f f e r e d two pounds. The f e e d i n g p e r i o d was t h e r e f o r e terminated at t h i s p o i n t . F o l l o w i n g the r e a l i m e n t a t i o n p e r i o d , a second s t a r v a -t i o n p e r i o d , comparable to the f i r s t , was i n s t i t u t e d to a l l o w v e r i f i c a t i o n of the r e s t i n g u r i n a r y n i t r o g e n l e v e l f o l l o w i n g a measured f e e d i n t a k e . The two l e v e l s of feed i n t a k e used i n these t r i a l s were s e l e c t e d a c c o r d i n g to the weight of the does. The weight of the w h i t e - t a i l e d doe was 2 0 3 pounds, and that of the b l a c k - t a i l e d doe was approximately 1 0 0 pounds or 4 5 4 kilograms, d u r i n g these experimental p e r i o d s . The general r e l a t i o n s h i p between b a s a l energy requirement, and a d u l t , non-pregnant, non - l a c t a t i n g body weight, f o r homeotherms, has been s t a t e d p r e v i o u s l y to be: Basal m e t a b o l i c C a l o r i e s = 7 ° « 5 x Weight i n k i l o g r a m s ®'75 The more a c c u r a t e power of 0 . 7 3 w a s used (Brody 1 9 4 5 ) J a n t * the t o t a l d i g e s t i b l e energy requirement f o r b a s a l metabolism was c a l c u l a t e d to be 1 , 3 3 6 and 1 , 1 4 2 C a l o r i e s per day f o r the deers E - 5 and P - l . I f the c a l o r i c requirement f o r maintenance meta-b o l i s m i s assumed to be twice the b a s a l requirement, as Brody and o t h e r s have suggested, the maintenance requirement of the two does would be 2 , 6 7 2^and 2 , 2 4 8 C a l o r i e s per day. The a d u l t deer r a t i o n c o n t a i n e d approximately 1 , 3 0 0 C a l o r i e s of d i g e s t -i b l e energy per pound. T h e r e f o r e , the f e e d i n t a k e was set to a l t e r n a t e between the ba s a l energy requirement and the main-tenance energy requirement. A c c o r d i n g to the r e l a t i o n s h i p between ba s a l energy expenditure and endogenous u r i n a r y n i t r o g e n e x c r e t i o n , a l s o s t a t e d p r e v i o u s l y , the requirement f o r endogenous n i t r o g e n meta-b o l i s m f o r S-5 was approximately 2.3 grams of n i t r o g e n per day, and f o r P - l i t was 3-8 grams per day. The a d u l t deer r a t i o n c o n t a i n e d approximately 2.49% n i t r o g e n or 11.3 grams of n i t r o -gen per pound. The n i t r o g e n i n t a k e was t h e r e f o r e w e l l above the endogenous requirement. During the second and t h i r d n i t r o g e n b alance t r i a l s the water i n t a k e was measured four times d a i l y to the nearest gram. I n s e n s i b l e water l o s s , which i n c l u d e d a f r a c t i o n eva-p o r a t e d from the f e c e s , on s t a n d i n g f o l l o w i n g d e f e c a t i o n and u n t i l c o l l e c t i o n , was measured th r e e times d a i l y to the near-est m i l l i l i t e r . In accordance with the normal f u n c t i o n i n g of the r e s p i r a t i o n c a l o r i m e t e r , measurements of methane, carbon d i o x i d e , and heat p r o d u c t i o n (by c a l c u l a t i o n ) , and oxygen consumption were c o n t i n u o u s l y recorded throughout a l l the t r i a l s. _ 32 -Sample C o l l e c t i o n The i l l u s t r a t i o n , i n c l u d e d i n AppendixY, shows the animal cage which was used to c o n f i n e the experimental animals w i t h i n the c a l o r i m e t e r d u r i n g the metabolic t r i a l s . The p r o -v i s i o n s b u i l t i n t o the cage to f a c i l i t a t e sample c o l l e c t i o n are shown. . F i n e wire mesh scr e e n i n g , a t t a c h e d to a frame f o r support, and p l a c e d immediately below the t h i c k g a l v a n i z e d i r o n mesh f l o o r of the animal cage, f u r n i s h e d the means f o r both f e c a l c o l l e c t i o n and s e p a r a t i o n of f e c e s from u r i n e . The s c r e e n was s l i g h t l y l a r g e r i n o v e r a l l dimensions than the cage f l o o r to prevent l o s s e s . The frame of the screen was arranged to s l i d e on s i d e t r a c k s secured to the cage support members. The scree n c o u l d thus be withdrawn e n t i r e l y from the c a l o r i m e t e r to f a c i l i t a t e f e c a l c o l l e c t i o n . On removal of the screen, f e c a l m a t e r i a l was brushed c a r e f u l l y i n t o a c o l l e c t i n g pan, weighed, and then f r o z e n f o r storage. A g a l v a n i z e d i r o n t r a y shaped i n t o a shallow f o u r -s i d e d f u n n e l , which d r a i n e d a c e n t r a l l y through a short p i e c e of p i p e , was used f o r c o l l e c t i n g u r i n e . The d r a i n was near the f r o n t of the c a l o r i m e t e r to f a c i l i t a t e h a n d l i n g of c o l l e c t i n g f l a s k s . U r i n e was c o l l e c t e d under a t h i n f i l m of mi n e r a l o i l i n narrow-necked f l a s k s of approximately f i v e l i t e r s c a p a c i t y . - 3 3 -Upon removal of a u r i n e sample, a new f l a s k c o u l d be quickly-put i n the o l d one's p l a c e to prevent l o s s of u r i n e . A l a r g e pyrex l a b o r a t o r y f u n n e l was p l a c e d i n the neck of each f l a s k to prevent s p i l l a g e of u r i n e . A pa,d of f i b r e g l a s s wool set i n the f u n n e l prevented contamination of the u r i n e w i t h d e t r i -t u s of f e c a l or epidermal o r i g i n . F o l l o w i n g c o l l e c t i o n the volume of the u r i n e sample was measured to the nearest m i l l i -l i t e r , and the s p e c i f i c g r a v i t y was measured by weighing a f i v e m i l l i l i t e r a l i q u o t on an a n a l y t i c a l balance. The u r i n e was then f r o z e n f o r storage. The u r i n e t r a y was arranged to s l i d e i n the same manner as the f e c a l screen, being the same s i z e as the s c r e e n and f i t t i n g immediately below i t , to f a c i l i t a t e c l e a n i n g . Chaff brushed from the t r a y was c o l l e c t -ed s e p a r a t e l y from the f e c e s . T h i s was p r i m a r i l y of epidermal o r i g i n . The t r a y was washed down wit h d i s t i l l e d water and d r i e d w i t h paper towels d u r i n g the l a s t two balance t r i a l s . Both the t r a y and the w i r e screen were steam cleaned a f t e r each c o l l e c t i o n p e r i o d d u r i n g the growth s t u d i e s . T h i s c o u l d not be done wit h the c o n t i n u i n g regime of the n i t r o g e n balance t e s t s . The f o o d and d r i n k i n g water pans i n the animal cage were o f f s e t toward the f r o n t of the c a l o r i m e t e r to prevent un-due s p i l l a g e onto the c o l l e c t i o n media. - 34 -Sample A n a l y s i s As mentioned p r e v i o u s l y , the u r i n e samples were measured as to volume and s p e c i f i c g r a v i t y immediately upon removal at the end of each twenty-four hour p e r i o d . In the second and t h i r d balance t r i a l s the pH was a l s o recorded. The pH was never g r e a t e r than 7*21 and t h e r e f o r e no a c i d was added. In most cases a l i q u o t s were taken immediately f o r a n a l y s i s and the remainder of the samples were f r o z e n f o r s t o r -age. T h i s procedure was p r e f e r r e d s i n c e i t was f e l t t h a t p r e -c i p i t a t e s formed d u r i n g the freeze-thaw p r o c e s s might c o n t r i -bute to a n a l y t i c a l e r r o r . The u r i n e was an a l y s e d f o r t o t a l n i t r o g e n by the K j e l d a h l micro method u s i n g steam d i s t i l l a t i o n ( C o n s o l a z i o 1951)' Two grams of copper sulphate and d i b a s i c potassium phosphate mixture i n 3;1 r a t i o were used as the d i g e s t i o n c a t a l y s t . A two p e r c e n t b o r a t e s o l u t i o n , w i t h brom c r e s o l green and methyl r e d added as mixed i n d i c a t o r , was used to tra p the ambient or d i s s o l v e d ammonia d u r i n g d i s t i l l a t i o n . The trapped ammonia was t i t r a t e d d i r e c t l y w i t h N/14 hydro-c h l o r i c a c i d , made from a s t o c k s o l u t i o n of constant b o i l i n g a c i d . The constant b o i l i n g a c i d was d i s t i l l e d at 109°C. and at a barometric p r e s s u r e of 758*8 mm. Hg. The n o r m a l i t y of the s o l u t i o n used f o r t i t r a t i o n was s e l e c t e d to f a c i l i t a t e subsequent c a l c u l a t i o n s . - 3 5 -The d i s t r i b u t i o n of the t o t a l n i t r o g e n among i t s components: urea, ammonia, c r e a t i n e and c r e a t i n i n e , was d e t e r -mined. Urea and ammonia content i n the u r i n e s gmples was determined u s i n g the Conway m i c r o d i f f u s i o n method (Conway 1 9 5 7 ) - A urease p r e p a r a t i o n was o b t a i n e d from f i n e l y ground Jack bean meal, i n accordance with the method of Conway. For the u r e a d e t e r m i n a t i o n u r i n e and b u f f e r e d urease were p l a c e d i n the outer w e l l , and a f t e r the u n i t s were sealed, the two m a t e r i a l s were mixed by t i l t i n g the u n i t . A f t e r mixing they were l e f t s t a n d i n g at room temperature f o r one-half hour. F o l l o w i n g t h i s the l i d was s l i d to one s i d e and s a t u r a t e d potassium carbonate was added, to the outer w e l l . The l i d was q u i c k l y r e p l a c e d and the u n i t s were again l e f t s t a n d i n g at room temperature f o r t h r e e to four hours. L i b e r a t e d ammonia from the above p r o c e s s e s was trapped i n the b o r i c a c i d s o l u t i o n d e s c r i b e d above, p l a c e d i n the center w e l l i n i t i a l l y . The trapped ammonia was t i t r a t e d as above, u s i n g N/28 h y d r o c h l o r i c a c i d made by d i l u t i o n from N/14- Pre-formed ammonia was d e t e r -mined by r e p e a t i n g the p r o c e s s without the a d d i t i o n of enzyme. The r e l i a b i l i t y of the Conway method was e s t a b l i s h e d u s i n g r e -agents of known n i t r o g e n c o n c e n t r a t i o n . V a r i a t i o n s i n the times used f o r the v a r i o u s steps had no e f f e c t on the r e l i a b i l -i t y of the method. The a l k a l i n e p i c r a t e method of F o l i n ( C o n s o l a z i o 1 9 5 1 ) was used to determine the c r e a t i n e and c r e a t i n i n e content - 36 -of the u r i n e . The c r e a t i n i n e p i c r a t e c o n c e n t r a t i o n f o l l o w i n g one-half hour f o r c o l o r development, was determined photo-m e t r i c a l l y u s i n g a Coleman spectrophotometer, model 11A. A standard curve was prepared r e l a t i n g t r a n s m i t t a n c e to known amounts of c r e a t i n i n e . The r e s u l t s are p r e s e n t e d i n Appendix VI. Those samples intended f o r d e t e r m i n a t i o n of pre-formed c r e a t i n i n e were made a l k a l i n e w i t h t e n pe r c e n t sodium hydrox-ide, w i t h no p r e v i o u s treatment. Those samples intended f o r d e t e r m i n a t i o n of c r e a t i n e i n d i r e c t l y hy c o n v e r s i o n of c r e a t i n e to c r e a t i n i n e were a u t o c l a v e d with p i c r a t e f o r more than one-h a l f hour, at 121°C. and 15 pounds p r e s s u r e , b e f o r e b e i n g made a l k a l i n e . The same treatment as f o r pre-formed c r e a t i n i n e f o l l o w e d t h i s a f t e r the f l a s k was allowed to c o o l to room temp-e r a t u r e . Pre-formed c r e a t i n i n e was then s u b t r a c t e d from the t o t a l c r e a t i n i n e p r e s e n t to determine the newly converted c r e a t i n i n e . S i n c e t h i s p r o c e s s i s c o n s i d e r e d to be o n l y e i g h t y percent complete i n a l l cases, ( C o n s o l a z i o I 9 5 I ) , the amount of newly formed c r e a t i n i n e was m u l t i p l i e d by a c o r r e c t i o n f a c t o r of 1 . 1 6 . - 37 -R e s u l t s and D i s c u s s i o n  Choice of Methods In order to understand f u l l y the r e l a t i o n s h i p between the animal body and i t s i n g e s t e d f o o d s t u f f s , i t i s necessary, at the o u t s e t , to measure and a n a l y s e the f o l l o w i n g ! the changes which occur i n the f e e d and i n the animal a f t e r the f e e d has been taken i n t o the d i g e s t i v e t r a c t , f a c t o r s a s s o c i a t e d w i t h the a b s o r p t i o n of a f r a c t i o n of the i n g e s t e d feed, and the changes which occur i n the absorbed n u t r i e n t and i n the animal body f o l l o w i n g a b s o r p t i o n . The f i r s t two are accomplished by q u a n t i t a t i o n and chemical a n a l y s i s of f e e d and f e c e s , accompanied by methods of d e t e r m i n i n g f e c e s of metabolic o r i g i n . The t h i r d aspect i s p a r t of the greater study of a l l of the a c t i v i t i e s and c h a r a c t e r i s t i c s of l i v i n g c e l l s and t i s s u e s and the n u t r i t i o n -i s t draws upon e n t i r e f i e l d s of study, such as the f i e l d of b i o -chemistry or p h y s i o l o g y , a l l of which are converging on t h i s same c e n t r a l area, f o r innumerable methods and procedures of study. The study of n u t r i t i o n i t s e l f , t h e r e f o r e , becomes one of u n l i m i t e d scope w i t h i n d e f i n i t e boundaries. However, f o r p r a c -t i c a l purposes, the study of n u t r i t i o n uses more l i m i t e d p a r t s of a l l t h r e e a s p e c t s to assess the n u t r i t i v e s t a t e of the a n i -mal body i n r e l a t i o n to i t s f e e d i n t a k e r e l y i n g p r i m a r i l y on s t u d i e s of growth, metabolic r a t e , r e s p i r a t o r y q u o t i e n t , u r i n -a l y s i s and body composition cha,nges to assess the i n t e r n a l - 3 8 -changes. Body composition s t u d i e s , though extremely u s e f u l , are o f t e n u n a v a i l a b l e , as was the case i n t h i s experiment, because they i n v o l v e s l a u g h t e r and post morten a n a l y s i s of the animal under i n v e s t i g a t i o n . However, i f they cannot be performed, they may at l e a s t be estimated i n p a r t from the r e s u l t s of the other s t u d i e s combined. F e c a l and f e e d a n a l y s i s were used i n t h i s experiment to e s t a b l i s h the be-h a v i o r of the animal towards the f e e d used. U r i n a l y s e s and metabolic s t u d i e s were a l s o used to study the metabolic r e -a c t i o n s to the absorbed n u t r i e n t . S i n c e p r o t e i n metabolism was of primary concern the u r i n a l y s e s c o n s i s t e d of n i t r o g e n analyses. The n i t r o g e n balance method was used to e s t a b l i s h the n u t r i t i v e requirement f o r p r o t e i n and the f a s t i n g c a t a -b o l i s m of p r o t e i n i n the animal. Though the n i t r o g e n balance method has b u i l t - i n e r r o r s ( A l l i s o n 1951, Albanese 195'9> Darke i 9 6 0 , Wallace 1959 and Waterlow i 9 6 0 } , i t i s , i n p r i n c i p l e , one of the best methods a v a i l a b l e to study the extent of i n v i v o p r o t e i n s y n t h e s i s and c a t a b o l i s m . A l s o , i f the p o i n t of n i t r o g e n e q u i l i b r i u m can be estimated f o r c e r t a i n w e l l d e f i n e d c o n d i t i o n s , i t p r o v i d e s an e x c e l l e n t b a s e l i n e f o r e s t i m a t i n g the d i e t a r y p r o t e i n requirement and the c h a r a c t e r of p r o t e i n metabolism under other w e l l d e f i n e d c o n d i t i o n s such as range c o n d i t i o n s f o r deer. It i s c h a r a c t e r i s t i c of the study of n u t r i t i o n that - 39 -s i n g l e measurements of changes i n the body d u r i n g f e e d i n g or f a s t i n g do not o f t e n r e p r e s e n t s i n g l e p r o c e s s e s , not do they i n f a c t o f t e n p i n down the cause of a change to a s i n g l e agency. T h i s i s so f o r two important reasons. F i r s t , the measurement i t s e l f o f t e n does not p r o v i d e the means of d i f f e r e n t i a t i n g the cause r e g a r d l e s s of i n t e r p r e t a t i o n . For example, weight l o s s may be due to a l o s s of water or i t may be e q u a l l y due to a c a t a b o l i s m of body f a t . Secondly, i n most of the b o d i l y changes t h e r e are u s u a l l y two or more causes f o r a change i n a s i n g l e parameter. For example, weight l o s s i s o f t e n both water l o s s and c a t a b o l i s m of body m a t e r i a l p a r t i c i p a t i n g together i n an unknown r a t i o n . In order to overcome such a m b i g u i t i e s i t i s n e c e s s a r y to employ s e v e r a l methods simultaneously. S e v e r a l measurements of concurrent a c t i v i t i e s a s s o c i a t e d with a body change p r o v i d e p i e c e s of i n f o r m a t i o n which tend to p o i n t to a s i n g l e h i g h l y p r o b a b l e cause or to a d e f i n i t e set of such causes f o r a s i n g l e event. By a p r o c e s s l a r g e l y of e l i m i n a t i o n of many p o s s i b i l i t i e s a u n i f i e d r e s u l t may be obtained. However, even the most e x a c t i n g experimental procedures g i v e r e s u l t s which bear l i m i t e d i n t e r p r e t a t i o n . A l s o , i t i s most c h a r a c t e r -i s t i c of n u t r i t i o n a l experiments that experimental r e s u l t s apply to the c o n d i t i o n s of the experiment, both known and un-known, and can o n l y apply to other more general c o n d i t i o n s w i t h proper m o d i f i c a t i o n s of i n t e r p r e t a t i o n . N u t r i t i o n a l experiments are t h e r e f o r e f r a u g h t with d i f f i c u l t i e s , and they t e s t the - 40 -i n g e n u i t y of the experimenter as to the c h o i c e of methods and techniques best s u i t e d to r e v e a l the i l l u s i v e causes of the measured change. The s e v e r a l methods used i n t h i s experiment were chosen wi t h these views and aims i n mind and are accompani-ed by s e v e r a l methods of i n t e r p r e t a t i o n of the data. N i t r o g e n E x c r e t i o n i n A d u l t Deer General D i s c u s s i o n of N i t r o g e n E x c r e t i o n R e s u l t s i n the  L i ^ h t of P r e s e n t l y H e l d T h e o r i e s of P r o t e i n Metabolism The r e s u l t s of the t h r e e n i t r o g e n balance t r i a l s are p r e s e n t e d i n T a b l e s I to VI. The f i r s t t r i a l , u s i n g the white-t a i l e d doe, P - l , was h a l t e d due to t e c h n i c a l d i f f i c u l t i e s w i t h the c a l o r i m e t e r , and t h e r e f o r e does not c o n s t i t u t e a completed n i t r o g e n balance experiment. Included w i t h the d a t a f o r the n i t r o g e n r e l a t i o n s are the d a t a f o r the changes i n dry matter, i n T a b l e I, the water balance, i n T a b l e IV, and oxygen uptake, i n T a b l e VII. The r e s u l t s of the two complete n i t r o g e n balance t r i a l s on the b l a c k - t a i l e d doe H-5 are shown g r a p h i c a l l y i n F i g u r e s 1 and 2 . These f i g u r e s i n c l u d e the t o t a l u r i n a r y n i t r o -gen e x c r e t i o n throughout the experimental p e r i o d s . They a l s o i n c l u d e the t o t a l n i t r o g e n i n t a k e and t r u e d i g e s t i b l e i n t a k e d u r i n g each day of the t e s t f e e d i n g p e r i o d . S e v e r a l other parameters of the n i t r o g e n e x c r e t i o n o b t a i n e d d u r i n g these t r i a l s are shown i n F i g u r e s 3 "to 6. The u r i n a r y n i t r o g e n e x c r e t i o n of both the white-- 41 -t a i l e d , and b l a c k - t a i l e d does appeared to be c h a r a c t e r i z e d by-o c c a s i o n a l sudden l a r g e i n c r e a s e s which o c c u r r e d w i t h i n a 24 hour c o l l e c t i n g p e r i o d . F o l l o w i n g the e l e v a t e d l e v e l , the ex-c r e t i o n decreased to th a t o b t a i n e d on p r e v i o u s days. These increments were unexpected, and remain, f o r the most p a r t un-exp l a i n e d . They seemed to occur at j u s t the wrong times, from a t h e o r e t i c a l p o i n t of view, as i n the case of the c o l l e c t i o n f o l l o w i n g the f o u r t h f e e d i n g day i n the l a s t t r i a l . For ex-ample, i n T r i a l I I I , on the n i n t h day, a l a r g e amount of n i t -rogen was ex c r e t e d (21 grams). T h i s was not accompanied by a l a r g e excess i n c a l o r i c output (1,260 C a l o r i e s ) and o c c u r r e d at a time of t h e o r e t i c a l maximum n i t r o g e n d e p l e t i o n i n the balance t r i a l and i n the o v e r a l l seasonal v a r i a t i o n which no r m a l l y o c c u r s i n these animals. These l a r g e i n c r e a s e s could be due to v a r i a t i o n s i n u r e a r e t e n t i o n at the r e n a l l e v e l as has been shown wit h other ruminants ( S c h m i d t — N i e l s e n 1957, I958). However, i f r e n a l r e g u l a t i o n had p l a y e d a s i g n i f i c a n t r o l e i n the e x c r e t i o n p a t t e r n of these experiments, much lower l e v e l s of e x c r e t i o n would have been d i s p l a y e d d u r i n g the p e r i o d s of r e s t r i c t e d i n t a k e . In order to a c c u r a t e l y assess the s t a t u s of r e n a l r e g u l a t i o n of urea, plasma urea c o n c e n t r a t i o n s would have to be c a r r i e d out throughout the t e s t s . Blood u r e a d e t e r -m inations were made at v a r i o u s times, on a l l of the b l a c k - t a i l e d deer, d u r i n g t h e i r r e s i d e n c e i n the deer enclosure. In order to secure f r e s h whole b l o o d f o r t h i s purpose advantage had to - 42 -be taken of i m m o b i l i z a t i o n procedures on a d u l t deer due to t h e i r extreme r e f r a c t i l e nature. These o p p o r t u n i t i e s were n e c e s s a r i l y r a r e due to the u n d e s i r a b l e s i d e e f f e c t s r e s u l t -i n g from t h i s treatment. In; March 1962, R-5 had a u r e a n i t -rogen v a l u e of 3 3 - 2 m i l l i g r a m s per 100 m i l l i l i t e r s of whole blood. In A p r i l I962, R -5 had a v a l u e of 2 5 . 0 m i l l i g r a m s per 100 m i l l i l i t e r s . These v a l u e s compare f a v o u r a b l y w i t h those o b t a i n e d w i t h c a t t l e , sheep and goats (Spector 1 9 5 6 ) . The v a l u e s f o r these animals are 6 - 2 7 , 1 3 - 2 8 , and 8 - 2 0 m i l l i g r a m s of u r e a n i t r o g e n per 100 m i l l i l i t e r s of b l o o d r e s p e c t i v e l y . The v a l u e s f o r R-5 are r e p r e s e n t a t i v e of the h i g h e s t l e v e l s i n these ranges. T h i s i s understandable c o n s i d e r i n g the h i g h l e v e l of n u t r i t i o n a l s t a t u s maintained i n t h i s deer. The second balance experiment began with one of these h i g h l e v e l s of e x c r e t i o n . A l e v e l of 2 5 . 4 grams of n i t r o g e n , or more than twice the l e v e l o b t a i n e d d u r i n g the next two c o l l e c t i o n p e r i o d s , was o b t a i n e d on the second day of r e s i d e n c e . However, t h i s may be e x p l a i n e d p a r t l y by the f a c t that u r i n e was r e t a i n e d d u r i n g the f i r s t day of r e s i d e n c e i n the c a l o r i m e t e r . Though th e r e i s no r e c o r d of the amount of u r i n e r e l e a s e d d u r i n g the l a s t day of r e s i d e n c e i n the deer pen, t h i s apparent u r i n e r e t e n t i o n must to some extent r e -p r e s e n t a c t u a l storage of u r i n e i n the bladder and the e l e v a t i o n i n n i t r o g e n l e v e l i n the f i r s t u r i n e c o l l e c t i o n , on the second - 4 3 -day of r e s i d e n c e , must represent n i t r o g e n e l i m i n a t e d i n p a r t to the bladder d u r i n g the f i r s t day i n the c a l o r i m e t e r . The r e t e n t i o n was presumed to be a s s o c i a t e d w i t h s t i m u l a t i o n caused by the t r a n s f e r e n c e of the animal from the deer enc l o s u r e to the l a b o r a t o r y and c a l o r i m e t e r ( F u l t o n I946}. The t o t a l n i t r o g e n e x c r e t i o n decreased markedly i n the w h i t e - t a i l e d deer, upon f e e d r e s t r i c t i o n , from a l e v e l of 2 3.I grams immediately f o l l o w i n g withdrawal of feed, to a l e v e l of about 9 grams per day. Upon resumption of f e e d i n g an un-expectedly e a r l y and l a r g e i n c r e a s e of 4 3 - 2 grams r e s u l t e d . Even i f the l a r g e 24-hour excesses are discounted;, however, i t can be seen that the f a s t i n g decrease i n n i t r o g e n e x c r e t i o n was not great i n any of the t r i a l s and that the n i t r o g e n ex-c r e t i o n l e v e l l e d o f f at a r a t h e r h i g h l e v e l i n a l l cases. T h i s r e s u l t i n general d i f f e r s i n p a r t from the r e s u l t s ob-t a i n e d by p r e v i o u s authors with both monogastric animals and ruminants. Lower v a l u e s of between 0 . 0 4 and 0 . 0 5 grams of n i t r o g e n per k i l o g r a m ef^body weight were o b t a i n e d w i t h v a r i o u s ruminants ( B r i c k e r , Kinsman and M i t c h e l l , 19415, Hutchinson and M o r r i s I936, Majumdar i 9 6 0 , M i t c h e l l I929) and s i m i l a r v a l u e s f o r v a r i o u s monogastric animals ( B r i c k e r , Kinsman and M i t c h e l l ) i n accordance w i t h the general r e l a t i o n s h i p between endogenous n i t r o g e n e x c r e t i o n and body weight (Brody 1 9 4 5 ) * T n e decrease i n t o t a l n i t r o g e n e x c r e t i o n , expected and o b t a i n e d to a degree, - 44 -i s caused by changes i n the l a b i l e p r o t e i n s t o r e s which have a c h a r a c t e r i s t i c turnover ( A l l i s o n 1 9 5 1 , 1 9 5 3 , Block I 9 5 6 , Tut t i e 1 9 5 9 , and Wallace I 9 5 9 ) . These s t o r e s are f u l l y main-t a i n e d o n l y d u r i n g p e r i o d s of h i g h p l a n e p r o t e i n i n t a k e w i t h otherwise a d e q u g t e d i e t , and at t h i s time they have a c h a r a c t e r -i s t i c h igh r a t e of turnover and consequently are a s s o c i a t e d w i t h a h i g h l e v e l of n i t r o g e n c a t a b o l i s m and n i t r o g e n e x c r e t i o n . On f a s t i n g these s t o r e s r a p i d l y decrease i n s i z e because of t h e i r h i g h r a t e of a c t i v i t y . As t h i s happens the areas of h i g h e s t turnover are exhausted f i r s t , and at a r a p i d r a t e , and conse-quently, w i t h the r e d u c t i o n of the s i z e of p r o t e i n s t o r e s the n i t r o g e n e x c r e t i o n decreases p r o p o r t i o n a t e l y . When the body p r o t e i n s t o r e s are n e a r l y exhausted, more s l o w l y moving and important areas of body p r o t e i n begin to give up amino a c i d s . Because of t h e i r slower turnover these areas give up amino a c i d s much more s l o w l y and consequently i n smaller volume than i n the case of the h i g h p l a n e p r o t e i n s t o r e s . As t h i s p r o c e s s continues, p r o t e i n c a t a b o l i s m , and consequently n i t r o g e n ex-c r e t i o n approaches a minimum l e v e l a s s o c i a t e d w i t h v i t a l p r o -cesses e s s e n t i a l f o r continued e x i s t e n c e . T h i s l e v e l i s the endogenous l e v e l of p r o t e i n metabolism. In the ruminants, d e s p i t e c o n t i n u e d f a s t i n g , t h e r e i s u s u a l l y p r e s e n t a continued l e v e l of r e s t r i c t e d n i t r o g e n metabolism i n the rumen and con-t i n u e d small s u p p l i e s of m i c r o b i a l p r o t e i n are given up to the host (Annison and Lewis 1 9 5 7 ) . These a d d i t i o n s of p r o t e i n to - 45 -the i n t e s t i n a l t r a c t of the host p r o v i d e small s u p p l i e s of n i t r o g e n to the animal's metabolic p o o l by a b s o r p t i o n of amino a c i d s . T h i s p r o c e s s p r e v e n t s the constant r a p i d c a t a b o l i s m of l a b i l e p r o t e i n s t o r e s from causing p r o t e i n d e p l e t i o n as q u i c k l y as i s the case w i t h monogastric animals. The l e v e l l i n g of the t o t a l n i t r o g e n e x c r e t i o n to the average l e v e l of approximately 11 grams d u r i n g the second t r i a l and 6 . 9 grams d u r i n g the t h i r d t r i a l r e p r e s e n t s the c l o s e s t r e l a t i v e l y constant approach to the endogenous l e v e l d u r i n g the r e s p e c t i v e f a s t i n g p e r i o d s . There was one c o l l e c t i o n on the f o u r t h f a s t i n g day of the second t r i a l when the l e v e l was 3 . 2 grams of t o t a l n i t r o g e n . The expected endogenous l e v e l of n i t r o g e n e x c r e t i o n may be c a l c u l a t e d from the experimental r e l a t i o n to body weight of Brody, v i z . E.U.N. = 1 4 6 W 0 * 7 2 (Brody 1945) where E.U.N, corresponds to the amount of endogenous u r i n a r y n i t r o g e n e x c r e t i o n , and W corresponds to body weight i n k i l o -grams. T h i s r e l a t i o n a p p l i e s , however, to a non-pregnant, non-l a c t a t i n g , a d u l t monogastric mammal under b a s a l c o n d i t i o n s . From t h i s r e l a t i o n the endogenous l e v e l f o r the w h i t e - t a i l e d doe at 203 pounds should be 3 . 8 0 grams per day, and f o r the b l a c k - t a i l e d doe at 1 0 0 pounds i t should be 2 . 2 8 grams and at 9 0 pounds 2 . 1 1 grams of n i t r o g e n per day. From the r e l a t i o n of - 46 -Smuts of 2 m i l l i g r a m s of e x c r e t e d t o t a l u r i n a r y n i t r o g e n per k i l o c a l o r i e of b a s a l energy p r o d u c t i o n , these l e v e l s of ex-c r e t i o n would be a s s o c i a t e d w i t h b a s a l c a l o r i e outputs of a p p r o x i -mately 1 , 9 0 0 , 1 ,138 and 1 , 0 5 5 k i l o c a l o r i e s per day. These v a l u e s are s l i g h t l y lower than those o b t a i n e d u s i n g K l i e b e r ' s formula f o r the r e l a t i o n between b a s a l heat p r o d u c t i o n and body weight, but are approximately 1 k i l o c a l o r i e per k i l o g r a m body weight per hour (IQieber 1 9 3 2 ) . The l e v e l of 3 . 2 grams i s t h e r e f o r e v e r y c l o s e to the expected endogenous u r i n a r y t o t a l n i t r o g e n e x c r e t i o n . It i s important i n order to d i s c u s s the d i e t a r y p r o t e i n r e q u i r e -ment of these deer to t r y and f u r t h e r i n t e r p r e t the e l e v a t i o n o b t a i n e d i n t h i s experiment i n the l e v e l of u r i n a r y n i t r o g e n e x c r e t i o n of about 4 . 8 to 8 . 7 grams of n i t r o g e n per day over the expected endogenous l e v e l . Changes i n the Animal which I n f l u e n c e D i e t a r y Requirements Assuming, f o r t h e o r e t i c a l c o n s i d e r a t i o n s , that the average b a s a l energy p r o d u c t i o n per day f o r the b l a c k - t a i l e d deer was 1 ,138 C a l o r i e s , and a l l o w i n g an a d d i t i o n a l 50 percent i n c r e a s e f o r a c t i v i t y , the t o t a l energy requirement per day would be approximately 1 ,700 C a l o r i e s . T h i s would i n c l u d e an a d d i t i o n -a l increment, d u r i n g the f e e d i n g p e r i o d , due to the s p e c i f i c dynamic a c t i o n caused by i n g e s t e d and abosrbed food. If the 1 ,700 C a l o r i e s of energy had to be s u p p l i e d - 47 -e n t i r e l y by p r o t e i n catabolism, 4 2 5 grams of metabolizable pro-tein, either from feed or body sources, would have to be u t i l i z -ed per day. The same amount of absorbed protein as body protein would be needed because both suffer the same losses to urine (Brody 1945» ancL Maynard I956), thus providing the same amount of c u t i l i z a b l e energy per gram to the body. This amount of pro-t e i n catabolism would resu l t i n a t o t a l urinary nitrogen ex-c r e t i o n of 68 grams per day. However, some of the energy would be supplied by the limited amount of carbohydrate stored i n muscle and i n the l i v e r , e s p e c i a l l y during the i n i t i a l stages of f a s t i n g catabolism. Also, during the u t i l i z a t i o n of stored carbohydrate, some of the energy would be supplied by catabolism of body f a t , and follow-ing the exhaustion of the carbohydrate supply, a large proportion would then be derived from storage f a t . If a l l the energy was obtained by f a t catabolism, I 9 0 grams of fat would be required, and there would be a resultant weight loss of t h i s amount per day as compared with a loss of up to 4 pounds i f a l l was obtain-ed by protein catabolism. The f i g u r e of 4 pounds i s suggested because of the fact that body protein i s associated with body water i n a r a t i o of I part to 3 (Brody, and Kinney 1 9 5 9 ) . When body proteins are catabolized t h i s water i s freed, and may be completely eliminated depending on the conditions of water b a l -ance. This balance i s determined on the one hand by the physio-- 48 -l o g i c a l s t a t e of the animal, and on the other by the water int a k e . The weight l o s s o b t a i n e d i n the second t r i a l was c a l c u l a t e d as an a r b i t r a r y average to be approximately 2 . 3 pounds per day from the t o t a l weight l o s s of 30 pounds i n 13 days. T h i s l o s s was not due to observed water l o s s , as the water balance d a t a shows a g a i n of 2 .1 kilograms f o r the same p e r i o d . I f the n i t r o g e n e x c r e t i o n increment above the p r e d i c t -ed l e v e l , c o n s i s t i n g of 8 . 7 2 grams per day i n the second t r i a l and 4 . 6 9 grams i n the t h i r d , r e p r e s e n t e d the c o n t r i b u t i o n of body p r o t e i n to energy p r o d u c t i o n , then 54*5 grams and 2 8 . 8 grams of p r o t e i n r e s p e c t i v e l y would be a v a i l a b l e , thus r e p r e s e n t i n g 218 and 115 C a l o r i e s . T h i s would leav e between 1 ,500 and 1 ,600 C a l o r i e s per day to be s u p p l i e d by f a t c a t a b o l i s m . T h i s would r e q u i r e about 170 grams of f a t . T h i s would set the weight l o s s per day at 310 to 3 9 ° grams. The gaseous exchange a s s o c i a t e d w i t h t h i s amount of p r o t e i n and f a t c a t a b o l i s m would r e s u l t i n a r e s p i r a t o r y q u o t i e n t of about O . 7 2 , a v a l u e which i s c h a r a c t e r -i s t i c of energy p r o d u c t i o n d e r i v e d from f a t metabolism. I n c l u d -in g the water a s s o c i a t e d w i t h body p r o t e i n , the weight l o s s which would occur i n the f i r s t of the above two i n s t a n c e s would be up to 388 grams per day or 0 . 8 pounds w i t h a t o t a l l o s s of 6 pounds f o r seven f a s t i n g days. During the t h i r d t r i a l the d a i l y weight l o s s would be 310 grams or n e a r l y i pound and the t o t a l l o s s f o r eight f a s t i n g days would be 4 pounds. The - 49 -smaller d a i l y l o s s of l e s s than a pound compared to about 4 pounds w i t h p r o t e i n as the s o l e energy source r e f l e c t s the c a l o r i c d e n s i t y of f a t r e l a t i v e to p r o t e i n . The above f i g -u r e s show that the observed e l e v a t i o n i n n i t r o g e n e x c r e t i o n i s not a c t u a l l y v e r y l a r g e from the p o i n t of view of p r o t e i n c a t a b o l i s m f o r energy, due to the r e l a t i v e i n f e r i o r i t y of p r o -t e i n as an energy f u e l compared to f a t . As w i l l be shown, the i n c r e a s e of 50 per cent i n energy p r o d u c t i o n over the c a l c u l a t e d b a s a l l e v e l , i s too gen-erous. The animals were p l a c e d i n q u i e t surroundings w i t h a r e l a t i v e l y constant a i r temperature of 15°C., which i s w i t h -i n the zone of t h e r m o - n e u t r a l i t y , and w i t h l i m i t e d space i n order to enforce l i m i t e d p h y s i c a l a c t i v i t y . V a r i o u s workers i n c l u d i n g Brody have estimated the maintenance requirement f o r energy to be approximately 20 to 2 5 per cent h i g h e r than the b a s a l energy requirement. The maintenance requirement may be de-f i n e d as the b a s a l energy requirement p l u s those increments asso-c i a t e d w i t h a c t i v i t y and the s p e c i f i c dynamic e f f e c t of f e e d i n g . Of t h i s f i g u r e s l i g h t l y l e s s than h a l f i s s a i d to be due to SDA. The r e s t i s due to the i n c r e a s e d t o n a l a c t i v i t y of the p o s t u r a l muscles and to other p h y s i o l o g i c a l e f f o r t s a s s o c i a t e d w i t h standing. A f i g u r e of 1 2 per cent of the t o t a l energy p r o -d u c t i o n has been s t a t e d by Kinney as the f r a c t i o n used i n t h i s k i n d of a c t i v i t y , (Kinney 1 9 5 9 ) . T h e r e f o r e , a f i g u r e of 15 per - 5 0 -cent would not seem unreasonable i n the case of these deer under the c o n d i t i o n s i n d i c a t e d . T h i s would r e v i s e the f i g u r e s f o r the t o t a l energy p r o d u c t i o n of the b l a c k - t a i l e d deer to about 1 , 3 4 0 C a l o r i e s per day. The r e v i s e d f i g u r e f o r the body f a t c a t a b o l i s m requirement would be about 1 3 0 grams per day and the t o t a l weight l o s s would be lowered o n l y s l i g h t l y to about 1 0 pounds i n 3 ° days. The JR.Q. would remain n e a r l y the same. The water l i b e r a t i o n a s s o c i a t e d w i t h the above a c t i v i t i e s would be up to 3 6 0 grams per day, i n c l u s i v e of the water p r o d u c t i o n a s s o c i a t e d w i t h f a t o x i d a t i o n . The b a s a l metabolic r a t e s o b t a i n e d d u r i n g the three metabolic t r i a l s are r e c o r d e d i n T a b l e VI. They were computed from the amount of oxygen consumed d u r i n g the t h r e e t e s t p e r i o d s per day of 6 , 1 0 , and 5 hours r e s p e c t i v e l y , s t a r t i n g at about 4 P.M. each day, w i t h about an hour r e q u i r e d between each p e r i o d f o r f l u s h i n g out the chamber. The oxygen consumption was c a l -c u l a t e d from d a t a made on the percentage oxygen decrement which o c c u r r e d d u r i n g each t e s t p e r i o d . The oxygen content of the chamber was measured and recorded on a continuous r e c o r d i n g apparatus which c o n s t a n t l y sampled a i r from the chamber v i a a b l e e d tube that p r o v i d e d a c i r c u i t of a i r through the r e c o r d e r and back to the chamber again. Even d u r i n g the longest t e s t p e r i o d which was the ten hour p e r i o d from 1 1 P.M. u n t i l 9 A.M., and with the h i g h e s t r a t e s of a c t i v i t y o b t a i n e d w i t h the r e s i d e n t - 51 -animals, the oxygen c o n c e n t r a t i o n d i d not decrease at any time to l e v e l s that c o u l d he c o n s i d e r e d to have had an i n f l u e n c e on the metabolic r a t e , i n accordance w i t h standard p h y s i o l o g i c a l c o n s i d e r a t i o n s (Guyton 1 9 5 6 ). The t o t a l oxygen consumptions f o r each 2 4 hour p e r i o d are shown i n Table VI. The carbon d i o x i d e p r o d u c t i o n was recorded i n s i m i l a r f a s h i o n to the oxygen consumption, u s i n g a continuous recorder to measure the increment i n percentage carbon d i o x i d e d u r i n g each t e s t p e r i o d . Values f o r the r e s p i r a t o r y q u o t i e n t were c a l c u l a t e d f o r some of the 2 4 hour p e r i o d s , and the v a l u e s f o r those o b t a i n e d i n the t h i r d t r i a l are i n c l u d e d i n Table VI. The average heat p r o d u c t i o n d u r i n g the second t r i a l was 1 , 4 0 0 C a l o r i e s per day. During the t h i r d t r i a l i t was 1 , 3 0 0 C a l o r i e s per day. These v a l u e s were c a l c u l a t e d on the b a s i s of the average R.Q. , which was 0 . 8 2 . The average was o b t a i n e d l a r g e l y from the v a l u e s o b t a i n e d i n the t h i r d t r i a l , and i t agrees w i t h the v a l u e s used by p r e v i o u s i n v e s t i g a t o r s . At t h i s R.Q. one l i t e r of oxygen consumed r e p r e s e n t s the ex-p e n d i t u r e of 4 * 8 3 C a l o r i e s . The c a l o r i e expenditure would be o n l y s l i g h t l y l e s s w i t h an R.Q. of Q. 7« The a,verage e x p e r i -mental r e s u l t s quoted above f o r the heat p r o d u c t i o n o b t a i n e d are o n l y s l i g h t l y higher than the v a l u e s computed from the formula of Brody and K l i e b e r f o r the body weight metabolic r a t e r e l a t i o n s h i p s . - 5 2 -The i n d i v i d u a l v a l u e s f o r d a i l y heat p r o d u c t i o n are however more i l l u s t r a t i v e of the changes which o c c u r r e d i n metabolic a c t i v i t y d u r i n g the t e s t p e r i o d s . They a l s o supply more i n f o r m a t i o n as to the c h a r a c t e r of r e s t i n g metabolism i n t h i s animal by the degree of change i n response to the v a r i o u s changes i n the p a t t e r n of f e e d i n g , and by the extent of de-c r e a s e d u r i n g p e r i o d s of i n a c t i v i t y and i n a n i t i o n . Taken s i n g l y they enable a more a n a l y t i c a l study of the c h a r a c t e r of p r o t e i n metabolism i n t h i s animal as w e l l . During the f i r s t p e r i o d of i n a n i t i o n , i n the second t r i a l , the metabolic r a t e of R - 5 dropped from a l e v e l of 1 , 6 4 0 on an i n t a k e of approximately 1 . 7 pounds standard f e e d as given i n the pen, to a l e v e l of 1 , 3 0 0 C a l o r i e s a f t e r 9 6 hours of s t a r -v a t i o n w i t h f r e e access to water. F o l l o w i n g t h i s i t went lower, to 1 , 1 7 0 C a l o r i e s on the second day of f e e d i n g , d u r i n g the p r e s -umed a b s o r p t i o n and u t i l i z a t i o n of about 3 / 4 of a pound, of feed. The l e v e l of 1 , 1 7 0 i s v e r y c l o s e to the p r e d i c t e d v a l u e f o r R - 5 at about 1 0 0 pounds. F o l l o w i n g the p o s t a b s o r p t i v e s t a t e , the average c a l o r i c output of R - 5 b e f o r e the t e s t f e e d i n g p e r i o d i s 1 , 3 3 0 . T h i s corresponds to a 12% increment over the p r e d i c t e d b a s a l l e v e l and r e p r e s e n t s the maintenance requirement of R - 5 f o r the above d e s c r i b e d c o n d i t i o n s . During the second t r i a l w i t h R - 5 the c a l o r i c output d u r i n g the same p e r i o d i s w i t h i n 1% of the b a s a l requirement showing a v e r y s l i g h t degree of p h y s i o -- 53 -l o g i c a l a c t i v i t y on the p a r t of R - 5 at t h i s time. T h i s f a c t p r o b a b l y e x p l a i n s the r e l a t i v e i n d i f f e r e n c e of the deer to the r a t i o n p r e s e n t e d to i t f o r s e v e r a l c o n s e c u t i v e days, compared to i t s r e a c t i o n to the r a t i o n i n the f i r s t t r i a l w i t h R - 5 -F o l l o w i n g the f e e d i n g p e r i o d i n the f i r s t t r i a l the c a l o r i c output of R - 5 was reduced to o n l y a 4 per cent i n c r e a s e over the b a s a l l e v e l . In the l a s t t r i a l however i t was 10 per cent higher. The r e l a t i v e l y moderate metabolic r a t e s encountered i n these experiments would not be expected to n e c e s s i t a t e l a r g e expenditures of body r e s o u r c e s i n order to r e p l a c e d i e t a r y i n -take of c a l o r i e s . However, i n the second t r i a l , f o r example, d u r i n g the f e e d i n g p e r i o d , the d i e t a r y i n t a k e of c a l o r i e s f e l l s h o r t of adequacy by s i g n i f i c a n t amounts. On the f i r s t f e e d i n g day i t was short by 269 C a l o r i e s , on the t h i r d day by 9 2 0 C a l -o r i e s , and on the f i f t h day i t was short by 5 2 3 C a l o r i e s . T h e r e f o r e i t i s not e n t i r e l y s u r p r i s i n g t h a t an exact n i t r o g e n balance was not achieved on each f e e d i n g day, even though the t o t a l c a l o r i c d i s c r e p a n c y f o r the e n t i r e f e e d i n g p e r i o d was o n l y 1 , 8 3 7 C a l o r i e s and c o u l d thus be s a t i s f i e d by the c a t a -b o l i s m of 2 0 4 grams of body f a t , or 3 6 7 grams of body carbo-hydrate, and l e s s than 3 6 7 grams of a mixture of the two. T h i s a p p l i e s e s p e c i a l l y to the f i r s t two days of the l a s t t r i a l where the number of c a l o r i e s needed from endogenous sources was more - 5 4 -than.1,000- C a l o r i e s per day. The r e s u l t s of the n i t r o g e n analy-s i s d u r i n g t h i s f e e d i n g p e r i o d are v e r y i n t e r e s t i n g however, i n that they show the i n c r e a s i n g importance of body p r o t e i n s t o r e s as a source of endogenous energy. During the f i r s t two f e e d i n g days mentioned above, body p r o t e i n s u p p l i e d v e r y l i t t l e energy toward r e c t i f y i n g the r a t h e r l a r g e d e f i c i t of c a l o r i c output. However, on the t h i r d and f o u r t h day i t suddenly.rose i n im-portance. On the t h i r d day i t s u p p l i e d almost one h a l f the c a l o r i c output, and on the f o u r t h day i t s u p p l i e d 99 per cent of the c a l o r i c output. T h i s o b s e r v a t i o n , together w i t h know-ledge c o n c e r n i n g the n a t u r a l h i s t o r y of b l a c k - t a i l e d deer which shows that i n l a t e s p r i n g they tend to be i n a s t a t e of d e p l e t e d energy r e s e r v e s f o r s e v e r a l reasons other than d i e t a r y , seems to i n d i c a t e that R -5 had f i n a l l y reached a s t a t e wherein i t ' s body carbohydrate and f a t s t o r e s were d e p l e t e d s u f f i c i e n t l y to n e c e s s i t a t e the use of body p r o t e i n as the n e a r l y s o l e source of endogenous energy. The h i g h weight l o s s i n the second t r i a l i s d i f f i c u l t to e x p l a i n . It i s i n d i c a t i v e of a predominantly l e a n body mass type body wastage i n response to a high t o t a l metabolic r a t e . The general e l e v a t i o n i n the u r i n a r y n i t r o g e n e x c r e t i o n l e v e l i s not great enough to i n d i c a t e a l a r g e p a r t i c i p a t i o n of lean body mass, or d i e t a r y p r o t e i n i n the p r o d u c t i o n of energy. At the same time the water balance d a t a shows a g a i n of a few k i l o -- 5 5 -grams i n 13 days. T h i s leaves f a t as the o n l y source of energy, but t h i s should g i v e a f a i r l y slow r a t e of weight l o s s . A c c o r d i n g to Kinney d u r i n g e a r l y s t a r v a t i o n which i n the case of monogastric animals means from l | to 3 clays f o l l o w i n g a good n u t r i t i o n a l h i s t o r y , the mammalian body tends to l o s e a h i g h p r o p o r t i o n of l e a n body mass. (Kinney 1 9 5 9 ) T h i s l e a n body mass c o n s i s t s of l a b i l e body p r o t e i n s t o r e s p l u s a s s o c i a t e d water. The composition of the t o t a l l o s s i s about 8 0 per cent LBM and 20 per cent body f a t . T h i s l o s s produces approximately 2 , 6 0 0 c a l o r i e s per k i l o g r a m of weight l o s s . For a d a i l y energy p r o d u c t i o n of 1 , 7 ° 0 C a l o r i e s a O . 6 5 k i l o g r a m l o s s i s needed. For a p r o d u c t i o n of 1 , 4 0 0 C a l o r i e s , a l o s s of 0 . 5 4 kilograms i s needed. For 1 , 3 0 0 C a l o r i e s , a l o s s of 0 . 5 0 k i l o g r a a i s or about 1 pound i s needed. T h i s e a r l y s t a r -v a t i o n type of composition of l o s s i n weight h o l d s u n t i l the storage carbohydrate has been used up. The extent of the c a r -bohydrate s t o r e s and thus of t h i s type of l o s s i s dependent on the p r e v i o u s n u t r i t i o n a l h i s t o r y of the animal, and on i t s p h y s i o l o g i c a l age and c o n d i t i o n which i n f l u e n c e the use to which n u t r i e n t s are put. The carbohydrates s t o r e i n a 7 0 k i l o -gram mammal of good p r e v i o u s n u t r i t i o n a l h i s t o r y average, about 2 0 0 grams, which i s capable of s u p p l y i n g o n l y 8 0 0 C a l o r i e s by i t s e l f . F o l l o w i n g the use of t h i s "emergency" energy s t o r e the composition of the l o s s changes to approximately 50 per cent l e a n - 56 -t i s s u e and 50 per cent depot f a t . T h i s type of t i s s u e combina-t i o n c o n t r i b u t e s about ^,000 C a l o r i e s per k i l o g r a m on c a t a b o l i s m . It would thus produce a d a i l y weight l o s s of 0.34 kilograms to s a t i s f y an energy requirement of 1,700 C a l o r i e s per day. For 1,400 C a l o r i e s , a 0.28 k i l o g r a m l o s s would be r e q u i r e d , and f o r 1,300 C a l o r i e s , a 0.26 k i l o g r a m l o s s or n e a r l y h a l f a pound would be r e q u i r e d . The r a t e of weight l o s s per day i s thus i n -d i c a t i v e of the type of t i s s u e being c a t a b o l i z e d . T h i s i s so, p r o v i d e d t h e r e are no o v e r r i d i n g e n d o c r i n a l or other p h y s i o -l o g i c a l f u n c t i o n s , f o r example, body temperature r e g u l a t i o n i n an adverse temperature gra d i e n t between animal and environment, which demand a d i f f e r e n t i a l l o s s of body water. U n f o r t u n a t e l y no method was a v a i l a b l e f o r d e t e r m i n i n g d a i l y weight f l u c t u a t i o n d u r i n g the metabolism t r i a l s . As the body mass i s used up, both the l e a n t i s s u e and the f a t depots decrease i n s i z e , d e s p i t e the f a c t that the c a t a -bolism of f a t i s l a r g e l y designed to spare l e a n t i s s u e . As the l e a n t i s s u e decreases i n s i z e the b a s a l energy p r o d u c t i o n , which i s c l o s e l y a s s o c i a t e d w i t h or dependent on the s i z e of the l e a n body mass, i n e v i t a b l y decreases. There i s a l s o an i n e v i t a b l e r e d u c t i o n i n endogenous n i t r o g e n e x c r e t i o n because of the decreas-ed dynamic turnover and maintenance requirement of the smaller l e a n mass. The reasons f o r the r e d u c t i o n of energy p r o d u c t i o n and f o r the l o w e r i n g of endogenous n i t r o g e n e x c r e t i o n are - 57 -e s s e n t i a l l y the same. These f a c t o r s , however, s t e a d i l y lower the p r o t e i n and energy requirements f o r energy and n i t r o g e n e q u i l i b r i u m throughout the f a s t i n g p e r i o d . T h i s i n d i r e c t l y p r o v i d e s g r e a t e r chance of s u r v i v a l f o r the animal d u r i n g p e r i o d s of n u t r i e n t r e s t r i c t i o n , e s p e c i a l l y s i n c e the p r o c e s s can be c a r r i e d to subnormal l i m i t s w i t h extreme body wastage. Below average maintenance requirements may be e s t a b l i s h e d at any l e v e l which p r o v i d e s continued l i f e i n an i n d i v i d u a l , even though s e v e r a l normal and f a i r l y important f u n c t i o n s are tem-p o r a r i l y or permanently h e l d i n abeyance through wastage of t i s s u e . Changes i n Feed F o l l o w i n g I n g e s t i o n which I n f l u e n c e  D i e t a r y Requirements The establishment of r e s t i n g m e tabolic requirements from the measurements of f a s t i n g c a t a b o l i s m , permit the es-t i m a t i o n of n u t r i e n t requirements i n terms of t o t a l d i g e s t i v e n u t r i e n t , or T.D.F. (M o r r i s o n I956), p r o v i d e d the changes which take p l a c e , f o l l o w i n g i n g e s t i o n , i n the p a r t i c u l a r f e e d under study, are determined d i r e c t l y from f e e d i n g experiments. In t h i s experiment the f e e d i n g t e s t was combined with the e s t a b l i s h -ment of f a s t i n g requirements i n s i n g l e experimental runs. These requirements can a l s o be expressed as m e t a b o l i z a b l e energy, or m e t a b o l i z a b l e n i t r o g e n , and as net energy, f o l l o w i n g metabolic t e s t s . Once these f a c t o r s are e s t a b l i s h e d , and expressed i n terms of one or more of the above c a t a g o r i e s , the i n v e s t i g a t o r can express the t e s t animals' requirements f o r n a t u r a l f e e d such as, f o r example, browse s p e c i e s f o r deer. These p r e -d i c t i o n s , of course, depend on chemical a n a l y s e s of the browse i n order to compare the content w i t h that of the f e e d t e s t e d on a d r y weight b a s i s . Feeding t r i a l s are s t i l l needed, how-ever, to show the exact requirements. T h i s i s so because f a c -t o r s such as d i g e s t i b i l i t y cannot always be a c c u r a t e l y p r e -d i c t e d . A l s o , the e f f e c t of amino a c i d imbalance and chemicals which act a n t a g o n i s t i c a l l y w i t h i n the metabolic machinery, must at p r e s e n t be e s t a b l i s h e d or d i s c o v e r e d through d i r e c t e x p e r i -ment. As s t a t e d p r e v i o u s l y , the use of the n i t r o g e n balance method f o r d e t e r m i n i n g p r o t e i n requirement can be m i s l e a d i n g . Annison c o n s i d e r s i t of l i t t l e use i n ruminants due to the n i t r o g e n metabolism of the rumen organisms (Annison and Lewis 1959). However, t h e r e are, even i n h i s t r e a t i s e on ruminant metabolism, s e v e r a l arguments which show that u s e f u l i n f o r m a t i o n may be o b t a i n e d from c a r e f u l use and i n t e r p r e t a t i o n of t h i s method. The most important of these i s , that d u r i n g complete s t a r v a t i o n of ruminants, the rumen m i c r o b i a l a c t i v i t y i s severe-l y r e s t r i c t e d w i t h i n a few days. T h i s occurs because the symfei-orits• i n the rumen need a ready source of carbohydrate f o r b i o -s y n t h e s i s . The carbohydrate requirement i s twofold. There i s a need f o r carbon and f o r o x i d a t i v e energy i n order to e f f e c t m i c r o b i a l p r o t e i n s y n t h e s i s . T h e r e f o r e i t i s necessary, as was - 59 -done i n t h i s experiment, to s t a r v e the ruminant f o r 4 or more days w h i l e n o t i n g the decrease i n n i t r o g e n output. Part of the care i n i n t e r p r e t a t i o n as mentioned p r e v i o u s l y enters i n t o the e x t r a p o l a t i o n of r e s u l t s to f i e l d or other c o n d i t i o n s . In a d d i t i o n , although the above r e a s o n i n g has shown that the n i t r o -gen balance method i s not i n f a l l i b l e i n d e t e r m i n i n g the s t a t e of p r o t e i n s t o r e s i n an undernourished animal, on a low l e v e l d i e t , i t i s u s e f u l i n d e t e c t i n g d e f i c i e n c i e s i n a d i e t . Hence the many experiments of M i t c h e l l and o t h e r s on the b i o l o g i c a l v a l u e of f e e d p r o t e i n were con c e i v e d u s i n g the appearance of n e g a t i v e balance as an i n d i c a t i o n of inadequacy. The e r r o r s of the balance method i n ruminants i s added to those a l r e a d y p r e s e n t w i t h monogastric animals. The ones most o f t e n mentioned are dermal l o s s and a d u l t growth. Dermal l o s s , as the term i s used here, r e f e r s to n i t r o g e n c o n t a i n e d i n sweat and sebum. A d u l t growth r e f e r s to l o s s , and consequently c o n t i n u a l replacement by growth, of c o r n i f i e d e p i t h e l i a l c e l l s and h a i r from the i n -tegument. N i t r o g e n i s a l s o l o s t by s i m i l a r means from o r a l s u r f a c e s and from the d i g e s t i v e e p i t h e l i u m , but t h i s f r a c t i o n i s accounted f o r by i t s i n c l u s i o n i n the e s t i m a t i o n of meta-b o l i c f e c a l n i t r o g e n . There was an attempt made i n t h i s exper-iment to account f o r both these sources of n i t r o g e n l o s s . The metabolic f e c a l n i t r o g e n was c a l c u l a t e d , as mentioned p r e v i o u s l y , on the b a s i s of the r e s u l t s of MitchelI, 1 9 4 3(Maynard 1 9 5 6 ) , who s t a t e d that the amount of MFN depended on the amount of d r y - 60 -matter excreted.., M i t c h e l l s t a t e d that approximately 0 . 2 grams of MFN are excreted per 1 0 0 grams of d r y matter on a low roughage d i e t , w h i l e approximately 0 . 5 grams are e x c r e t e d with 1 0 0 grams of h i g h roughage d i e t . The v a l u e f o r the low rough-age d i e t s was used i n the c a l c u l a t i o n s i n t h i s experiment, i n accordance with the c h a r a c t e r of the U.B.C. r a t i o n s used. The a d u l t growth o b t a i n e d w i t h R-5 i n terms of h a i r and f l a k e s of s k i n amounted to approximately one gram of d r y matter per day. T h i s m a t e r i a l was not analysed f o r n i t r o g e n content. However i t would, of course i n d i c a t e a l e v e l of n i t r o g e n l o s s of l e s s than one gram per day from t h i s source. M i t c h e l l , 1949 J gave a v a l u e of 0 . 5 6 grams / meter^ / day, which would i n d i c a t e a v a l u e of somewhat l e s s than a gram per day f o r R -5- Maynard s t a t e d a v a l u e of 0 . 7 grams of n i t r o g e n per day f o r 100 pound sheep (Maynard 1 9 5 6 ) . The amount of n i t r o g e n l o s t from dermal sources depends on environmental c o n d i t i o n s and p h y s i o l o g i c a l s t a t e of the animal. Values of 2 3 - 1 4 1 m i l l i g r a m s of n i t r o g e n per 1 0 0 m i l l i l i t e r s of sweat have been g i v e n i n the l i t e r a t u r e (Darke i 9 6 0 ) f o r humans. Under the i d e a l c o n d i t i o n s p r o v i d e d f o r E - 5 the amount of sweat should have been v e r y small. Un-f o r t u n a t e l y , although the amount of i n s e n s i b l e water l o s s was determined f o r each day of r e s i d e n c e i n the c a l o r i m e t e r , there was no method of s e p a r a t i n g t h i s c o l l e c t i o n i n t o the component r e l e a s e d from the lungs and the component excreted from the integumental s u r f a c e . Using the maximum f i g u r e f o r the n i t r o -- 61 -gen content of sweat, and assuming 50 per cent of the i n s e n s i b l e water l o s s to be sweat, the maximum dermal n i t r o g e n l o s s would be 0.5 grams per day u s i n g the l a r g e s t volumes of water o b t a i n e d i n e i t h e r t r i a l . These l e v e l s are e x e m p l i f i e d by the r e s u l t s shown i n the second f a s t i n g p e r i o d of T r i a l 2 where they range from 6 1 3 - 6 9 8 m i l l i l i t e r s per day. In the l i g h t of the above con-s i d e r a t i o n s a v a l u e of one gram of n i t r o g e n per day was con-s i d e r e d a s a f e estimate of the combined dermal n i t r o g e n l o s s and a d u l t growth. The e r r o r caused by t h i s v a l u e i s i n d i c a t e d by the d o t t e d l i n e shown below the l e v e l of t o t a l u r i n a r y n i t r o -gen e x c r e t i o n i i i F i g u r e s 1 and 2. In u s i n g the n i t r o g e n balance method with ruminants, one of the major problems w i t h the c o n v e n t i o n a l approach i s the d e t e r m i n a t i o n of the a c t u a l amounts of metabolic f e c a l n i t r o g e n and endogenous u r i n a r y n i t r o g e n . M i t c h e l l found the M.F . N , to be p r o p o r t i o n a l to the roughage content and dry matter content of the d i e t , as s t a t e d p r e v i o u s l y . Though the endogenous u r i n a r y n i t r o g e n i s presumably r e l a t e d to body s i z e , as i n monogastric animals, i t i s d o u b t f u l that the t r u e l e v e l can be e a s i l y a c hieved f o r reasons s t a t e d p r e v i o u s l y . An un-known endogenous l e v e l of p r o t e i n c a t a b o l i s m would a l s o o b t a i n among the members of the rumen m i c r o f l o r a and microfauna. T h i s would r e s u l t i n the l i b e r a t i o n of ammonia to the rumen contents, and much of t h i s would be absorbed d i r e c t l y through - 62 -the rumen w a l l , converted i n p a r t to urea, and r e c y c l e d i n p a r t to the rumen v i a r e s i d u a l s a l i v a r y flow. T h i s ammonia or u r e a would remain u n a v a i l a b l e to the b a c t e r i a u n t i l r e -sumption of carbohydrate i n t a k e . The p a r t not r e c y c l e d would r e s u l t i n i n e v i t a b l e a d d i t i o n s to u r i n a r y e x c r e t i o n . Using M i t c h e l l ' s v a l u e s f o r the amount of metabolic f e c a l n i t r o g e n on a low roughage d i e t the t r u e d i g e s t i b i l i t y was c a l c u l a t e d f o r each f e e d i n g day. The M.F.N, v a r i e s from about 0.3 grams d u r i n g the v e r y low i n t a k e of. 17»3 grams dry matter to 0.8 grams f o r a one pound i n t a k e and 1.3 grams on a 650 to 690 gram dry matter i n t a k e . The low i n t a k e v a l u e of 0.3 grams compares with the f e c a l n i t r o g e n obtained a f t e r 3 to 4 days s t a r v a t i o n i n the second t r i a l . However, the l e v e l remained nearer the v a l u e f o r the one pound i n t a k e l e v e l on s t a r v a t i o n i n the l a s t t r i a l , thus showing a p o s s i b l e slower time of passage. The h i g h i n t a k e v a l u e of 1.3 grams compares wit h the v a l u e s o b t a i n e d immediately upon the s t a r t of a l l s t a r v a t i o n p e r i o d s . However, i t must be r e c o g n i z e d that much of t h i s was c o n t r i b u t e d by the p r e v i o u s d i e t of the animals w h i l e i n the deer enclosure. The p r e v i o u s n u t r i t i o n a l h i s -t o r y of H-5 i s f a i r l y uniform i n terms of monthly int a k e . The d a i l y average i s between 0.8 pounds and one pound c a l c u l a t e d on a 30-day b a s i s . During December i t was 0.8 pounds, and d u r i n g January i t was 1 pound. The d a i l y i n t a k e i t s e l f , however, - 6 3 -shows a d e f i n i t e c y c l i n g or f l u c t u a t i o n r a n g i n g from 0 . 2 to 2 . 8 pounds as a maximum h i g h v a l u e and with 1 . 7 pounds as a common h i g h v a l u e . The h i g h and low l e v e l s are u s u a l l y a l t e r -nated and l a s t f o r 3 to 5 days. There was no r e l a t i o n between the amount of f e e d p r e s e n t e d to the animals, i n terms of t o t a l apparent mass v i s i b l e to them, as the consumption does not c o r r e l a t e w e l l w i t h the amount i n i t i a l l y p r e s e n t i n the f e e d pan. The d i e t a r y l e v e l g i v e n i n the f e e d i n g t e s t p e r i o d i s v e r y s i m i l a r to the i n t a k e on the above mentioned ad l i b i t u m regimen. The v a l u e s f o r the second f a s t i n g p e r i o d s of the t r i a l s , i n both the second and t h i r d runs, were lower than those of the i n i t i a l one r e f l e c t i n g the smaller o v e r a l l i n -take of the r e l a t i v e l y short f e e d i n g p e r i o d s . The v a l u e s chosen to repr e s e n t M.F.N, were t h e r e f o r e c o n s i d e r e d reasonable estimates of the t r u e M.F.N. The c o e f f i c i e n t of d r y matter d i g e s t i b i l i t y ob-t a i n e d , v a r i e d from about 60 to 9 0 per cent. A c c o r d i n g to Schneider and Maynard the normal v a l u e f o r most ruminant feeds i s 6 5 per cent. The higher v a l u e s o b t a i n e d here of 7 5 percent and 8 7 per cent, averages of the second and t h i r d t r i a l s are not unreasonable f o r two reasons. The low amount of roughage i n the d i e t seems to reduce the passage time g r e a t l y , as the e f f e c t s of p r e v i o u s ad l i b i t u m f e e d i n g appear f o r 3 to 4 days, i n d i c a t i n g the normal passage time of up to 2 days f o r the - 64 -major p o r t i o n of the feed. Meanwhile, the low amount of roughage reduces the amount of p r o t e c t i o n a g a i n s t b a c t e r i a l and d i g e s t i v e enzyme a t t a c k . I t should be borne i n mind, however, t h a t e x t e n s i v e b a c t e r i a l a t t a c k reduces the ener-g e t i c e f f i c i e n c y of the f e e d i n g p r o c e s s by r a i s i n g the l e v e l of p r o d u c t i o n of m e t a b o l i c a l l y u n a v a i l a b l e methane, thus mak-i n g a l a r g e r amount of f e e d energy u n a v a i l a b l e to the deer than would be so w i t h l e s s e x t e n s i v e a t t a c k . The l e v e l s of methane p r o d u c t i o n were v e r y small d u r i n g t h i s experiment, however, A l s o , M i t c h e l l showed that the p l a n e of n u t r i t i o n a f f e c t s the d i g e s t i b i l i t y o b t a i n e d w i t h a given r a t i o n . While experimental animals were f u l l y f e d a v a l u e of 65 per cent c o u l d be obtained, while, at or near the maintenance l e v e l a v a l u e of 80 per cent was p o s s i b l e . The l e v e l s used i n t h i s experiment were near the maintenance l e v e l f o r energy and f o r p r o t e i n at the one pound l e v e l . However, c o n f u s i n g v a r i a t i o n o c c u r r e d . In the second t r i a l , v a l u e s of about 60 per cent and 70 per cent were o b t a i n e d at the 1 pound l e v e l on two o c c a s i o n s . In the t h i r d t r i a l 85 per cent to 90 per cent were o b t a i n e d w i t h the l e v e l j u s t below the 1 pound l e v e l . At n e a r l y twice t h i s l e v e l the v a l u e v a r i e s between 77 per cent and 91 per cent. High d i g e s t i b i l i t i e s a r e a s s o c i a t e d w i t h feeds w i t h narrow n u t r i t i v e r a t i o s such as t h i s one. A c t u a l l y , the d i g e s t -i b i l i t y i s , i n many cases, o n l y a p p a r e n t l y lowered f o r the most p a r t , as the n u t r i t i v e r a t i o i s widened. T h i s i s due to the f a c t - 65 -that a constant amount of M.F.N, tends to he a s s o c i a t e d w i t h a constant amount of f e e d dry matter, r e g a r d l e s s of the percentage of f e e d n i t r o g e n . T h i s i s not r i g i d due to the f a c t t hat, f o r example, c e r t a i n sources of p r o t e i n tend to have a d i f f e r e n t i a l e v o c a t i n g e f f e c t on d i g e s t i v e enzyme outflo w v i a the endocrine system. With feeds of narrow n u t r i t i v e r a t i o , the l a r g e r amounts of n i t r o g e n , whether i t i s p r o t e i n which can be u t i l i z e d by the rumen organisms, or i t i s N . P . N . , does c o n t r i b u t e to i n -c r e a s e d d i g e s t i b i l i t y by s t i m u l a t i n g b a c t e r i a l a t t a c k on the h i g h e r carbohydrates of the feed. T h i s greater u t i l i z a t i o n of the h i g h e r carbohydrates i n t u r n makes other n u t r i e n t s more a v a i l a b l e . The percent d i g e s t i b i l i t y of n i t r o g e n gave d i f f e r e n t v a l u e s , and a d i f f e r e n t p a t t e r n with variation i n i n t a k e l e v e l from the dry matter d i g e s t i b i l i t y . The d i g e s t i b i l i t y d u r i n g the second t r i a l seems to be i n v e r s e l y p r o p o r t i o n a l to that of d r y matter wi t h h i g h d i g e s t i b i l i t y c o e f f i c i e n t s when that f o r d r y matter i s low. C o n t r a r y to the d r y matter r e s u l t s , the n i t r o g e n d i g e s t i b i l i t y tends to agree more c l o s e l y w i t h the r u l e of M i t c h e l l ' s i n both the second and t h i r d t r i a l s , by h a v i n g h i g h e r v a l u e s d u r i n g lower i n t a k e l e v e l s . At the one pound l e v e l of i n t a k e w i t h the observed d i g e s t i b i l i t y of 90 per cent, the t o t a l d i g e s t i b l e p r o t e i n a v a i l a b l e to the deer i s approximately 58 grams or 9-5 grams of n i t r o g e n . A c c o r d i n g to the r e l a t i o n of Brody f o r endogen-ous n i t r o g e n wastage per u n i t body weight, t h i s amount i s more - 66 -than enough to e s t a b l i s h n i t r o g e n e q u i l i b r iumi even wi t h a b i o -l o g i c a l v a l u e somewhat lower than 100. However, w i t h a c o n t i n -u i n g f a s t i n g c a t a b o l i s m of about 11 grams of n i t r o g e n , i t would, of course, be inadequate even w i t h a p e r f e c t b i o l o g i c a l value. The n e a r l y s i m i l a r i n t a k e i n the t h i r d t r i a l w ith the f a s t i n g l e v e l of about 7 grams should have been s u f f i c i e n t to e f f e c t n i t r o g e n r e t e n t i o n . A l s o , the two pound l e v e l of f e e d ad-m i n i s t r a t i o n i n the second t r i a l which made between 12 and 15 grams of n i t r o g e n a v a i l a b l e r e s p e c t i v e l y , should have p r o v i d e d s u f f i c i e n t e x t r a n i t r o g e n f o r r e t e n t i o n . The m e t a b o l i z a b l e energy at the one pound l e v e l , as w i l l be shown l a t e r , was p r o b a b l y below the c u r r e n t maintenance requirement. C a l c u l a t i o n of N i t r o g e n Requirements from U r i n a r y N i t r o g e n E x c r e t i o n N i t r o g e n Requirements Based on the P o i n t of  N i t r o g e n Balance The behavior of the n i t r o g e n e x c r e t i o n a f t e r repeated a b s o r p t i o n of 6 and then 9 grams of m e t a b o l i z a b l e n i t r o g e n , both as stated.being i n s u f f i c i e n t to e f f e c t immediate n i t r o g e n e q u i l i -brium, was v e r y i n t e r e s t i n g . At f i r s t , as expected, the absorp-t i o n of 6 grams n i t r o g e n showed a 6 gram d e f i c i t or -. 6 grams n i t r o g e n balance. L a t e r , f o l l o w i n g a b s o r p t i o n and probable u t i l i z a t i o n of an a d d i t i o n a l 15 grams of n i t r o g e n , 9 grams of n i t r o g e n caused near e q u i l i b r i u m of n i t r o g e n balance. S t i l l l a t e r , f o l l o w i n g a 12.16 gram a b s o r p t i o n , 9 grams caused - 6 7 -r e t e n t i o n . Though the two high e r l e v e l s i n t r o d u c e c o m p l i c a t i o n s i n i n t e r p r e t i n g the r e s u l t s , the greater a b i l i t y of the one pound l e v e l of f e e d to s a t i s f y the n i t r o g e n requirement, and thus s i m u l t a n e o u s l y the energy requirement of the b l a c k - t a i l e d deer, showed the p r o g r e s s i v e r e d u c t i o n i n n i t r o g e n turnover and bas a l m e t a b o l i c r a t e a s s o c i a t e d with the r e d u c t i o n i n l a b i l e n i t r o g e n s t o r e s caused by the steady l o s s of n i t r o g e n d u r i n g the appearance of n e g a t i v e n i t r o g e n balance. The f i n a l r e t e n t i o n of 3 ' 2 grams of n i t r o g e n r e p r e s e n t s 2 0 . 0 grams of body p r o t e i n , 8 0 C a l o r i e s of s t o r e d a v a i l a b l e energy, and 8 0 grams of le a n body mass. The r e s i s t a n c e to establishment of n i t r o g e n balance on the s e v e r a l o c c a s i o n s of 2 pound f e e d i n g when, a c c o r d i n g to e s t i m a t i o n and to the f a s t i n g l e v e l of n i t r o g e n e x c r e t i o n , more than adequate n i t r o g e n was a p p a r e n t l y absorbed, i s d i f f i c u l t to e x p l a i n . There were two marked examples of t h i s r e s i s t a n c e . In the second t r i a l f o l l o w i n g near e q u i l i b r i u m from a b s o r p t i o n of 9 grams of n i t r o g e n 1 2 grams f a i l e d even to equal the reduc-t i o n i n e x c r e t i o n of 9 grams. F o l l o w i n g a n e g a t i v e n i t r o g e n balance of 3 grams wit h an a b s o r p t i o n of "J.8 grams of n i t r o g e n , a f u r t h e r a b s o r p t i o n of 7 - 8 9 grams of n i t r o g e n was a s s o c i a t e d w i t h a d e f i c i t of 13 grams of t o t a l n i t r o g e n . The d i f f i c u l t y i n a c h i e v i n g n i t r o g e n e q u i l i b r i u m may be e x p l a i n e d , as suggested above, by the use of i n g e s t e d p r o t e i n - 6 8 -f o r energy. The p e l l e t e d r a t i o n used c o n t a i n e d 2 , 0 0 0 C a l o r i e s of t o t a l energy per pound, and 1 , 3 0 0 C a l o r i e s of m e t a b o l i z a b l e energy per pound c a l c u l a t e d on an average d i g e s t i b i l i t y of 6 5 per cent. T h i s i s e q u i v a l e n t to 2 . 9 C a l o r i e s per gram. The one pound l e v e l of f e e d gave 1 , 2 1 3 C a l o r i e s t o t a l energy on t h i s b a s i s throughout the l a t t e r p a r t of the second t r i a l and 1 , 0 3 7 to 1 , 0 9 9 C a l o r i e s i n the t h i r d . With the a c t u a l amount of d r y matter absorbed, however, i t gave 7 9 5 , 6 8 2 , 9 1 0 and 8 9 6 on the 4 o c c a s i o n s 1= pound was consumed. F o l l o w i n g l o s s e s i n d i g e s t i o n , the one pound l e v e l was between 5°Q and 6 0 0 C a l o r i e s short of the c a l c u l a t e d 1 , 3 0 0 C a l o r i e s per day maintenance r e -quirement i n the second t r i a l , and 5 4 6 C a l o r i e s short i n the t h i r d t r i a l . The t o t a l n i t r o g e n l o s s d u r i n g the 3 one pound f e e d i n g days i n the second t r i a l should have been 7 . 8 grams assuming a steady 11 grams of n i t r o g e n f o r e s s e n t i a l catabolism. With the lower endogenous u r i n a r y n i t r o g e n of 7 grams per day i n the t h i r d t r i a l a t o t a l n i t r o g e n r e t e n t i o n of I . 7 2 grams should have been r e a l i z e d . The lower than expected l o s s i n the second t r i a l , of 2 . 6 grams r e f l e c t s a lowered endogenous l e v e l d u r i n g f e e d i n g , perhaps r e p r e s e n t i n g l e s s n i t r o g e n wastage f o r endogenous c a t a b o l i s m . It a l s o r e f l e c t s a smaller energy de-f i c i t . During the t h i r d t r i a l , the l a c k of r e t e n t i o n i n d i c a t e s an e l e v a t i o n i n p r o t e i n c a t a b o l i s m above the endogenous l e v e l . T h i s i n d i c a t e s that the energy absorbed i s inadequate. The amount was, i n f a c t , up to 4 0 0 C a l o r i e s per day short of the - 69 -c a l c u l a t e d requirement d u r i n g the l a s t two f e e d i n g days, when the deer began to consume s i g n i f i c a n t amounts of feed. Even though most of t h i s energy c o u l d be s u p p l i e d by body f a t , some body or d i e t a r y p r o t e i n would be expected to be used. The d i s c r e p a n c y of 14.28 grams between a r e t e n t i o n of l."J2 grams, as a t h e o r e t i c a l f i g u r e , and the a c t u a l n e g a t i v e balance of 16 grams n i t r o g e n , i s equal to 89.3 grams of p r o t e i n . T h i s amount of p r o t e i n , from e i t h e r endogenous or exogenous source would supply about l8o C a l o r i e s per day. A f t e r c a l o r i c l o s s to u r i n e , p r o t e i n would be expected to be u t i l i z e d f o r energy, even w i t h adequate f a t supply, f o r the f o l l o w i n g reasons. Though f a t i s a l r e a d y b e i ng m o b i l i z e d and u t i l i z e d f o r energy, i t cannot completely r e p l a c e carbohydrate or p r o t e i n i n t h i s f u n c t i o n , because i t cannot supply e s s e n t i a l two-carbon com-pounds needed f o r the o p e r a t i o n of the c i t r i c a c i d c y c l e . These can o n l y be s u p p l i e d by metabolism of glucose, or c e r t a i n of the e s s e n t i a l amino a c i d s which are k e t o g e n i c . P r o t e i n i s t h e r e f o r e a n u t r i e n t of c h o i c e , to a c e r t a i n extent, f o r energy p r o d u c t i o n . Another e x p l a n a t i o n f o r the i n a b i l i t y on s e v e r a l o c c a s i o n s to e s t a b l i s h expected n i t r o g e n e q u i l i b r i u m i s th a t , a d d i t i o n of f o o d s t u f f s i n the ruminant may s t i m u l a t e n i t r o g e n metabolism i n the rumen to the extent of i n c r e a s i n g blood a.nd u r i n e n i t r o g e n l e v e l s . Non-protein n i t r o g e n i n the fe e d p a r t i - , c i p a t e s a c t i v e l y i n t h i s s t i m u l a t i o n . The i n t e r f e r i n g f a c t o r s - ?o -are: i n c r e a s e d a b s o r p t i o n of ammonia and u r e a from the rumen to the b l o o d stream, and i n c r e a s e d m i c r o b i a l p r o t e i n i n the d i e t of the host. The amount, r a t e and time of appearance and d u r a t i o n <of these e f f e c t s can be a n t i c i p a t e d o n l y w i t h d i f f i -c u l t y . Despite r e c y c l i n g of urea v i a s a l i v a , some urea and ammonia i s l o s t to the u r i n e simply because of mass a c t i o n . The u t i l i z a t i o n of n o n - p r o t e i n n i t r o g e n i n the rumen has the e f f e c t of i n c r e a s i n g the b i o l o g i c a l v a l u e of the d i e t a r y p r o -t e i n . T h i s i n t u r n reduces the n i t r o g e n wastage. At the same time, f e r m e n t a t i o n i n c r e a s e s the n i t r o g e n wastage by r e d u c i n g d i e t a r y p r o t e i n to s h o r t - c h a i n f a t t y a c i d s w i t h the consequent r e l e a s e of amino acid, n i t r o g e n . Much of t h i s r e l e a s e d n i t r o -gen i s e x c r e t e d along w i t h the f e c e s thus becoming u n a v a i l a b l e to both the m i c r o f l o r a and the host. The balance between these a n t a g o n i s t i c f u n c t i o n s depends on the amount of n o n - p r o t e i n n i t r o g e n i n the d i e t r e l a t i v e to p r o t e i n of good b i o l o g i c a l v a l u e . The n o n - p r o t e i n n i t r o g e n l e v e l i n the r a t i o n used i n t h i s experiment was low. The graphs i n F i g u r e s 3> and 4, show the r e s u l t of c a l c u l a t i o n s of the p o i n t of n i t r o g e n balance. These were ob t a i n e d by p l o t t i n g the e f f e c t of the n i t r o g e n i n t a k e i n grams, shown on the a b s c i s s a , on the n i t r o g e n balance i n grams, shown on the o r d i n a t e , and on the grams of n i t r o g e n balance per k i l o -gram of body weight, shown on a second o r d i n a t e , t o the l e f t of t h e f i r s t . T h e p o i n t o f i n t e r s e c t i o n o f t h e t w o l i n e s w i t h t h e m s e l v e s a n d . w i t h t h e a b s c i s s a i n d i c a t e s t h e p o i n t o f n i t r o -g e n b a l a n c e . T h i s m e t h o d o f o b t a i n i n g t h e point o f n i t r o g e n b a l a n c e i s a m o d i f i e d v e r s i o n o f t h e g r a p h i c a l m e t h o d o f L e i t c h a n d D u c k w o r t h ( L e i t c h a n d D u c k w o r t h 1 9 3 7 ) - A c c o r d i n g t o t h e w o r k o f M a j u n d a r ( M a j u n d a r i 9 6 0 ) , t h e r e s u l t s of t h i s t e c h -n i q u e c o m p a r e f a v o u r a b l y w i t h o t h e r m e t h o d s o f a n a l y s i n g n i t r o -g e n b a l a n c e d a t a . A s v e r i f i c a t i o n o f t h i s h e u s e d t h i s m e t h o d a n d s e v e r a l o t h e r s t o a n a l y s e h i s o w n n i t r o g e n b a l a n c e r e s u l t s o b t a i n e d w i t h Jumna. P a r i g o a t s o f 7 ° - 9 4 p o u n d s . H o w e v e r , o t h e r a u t h o r s h a v e s t a t e d t h a t t h e n i t r o g e n r e q u i r e m e n t s c a l c u l a t e d b y t h e a b o v e m e t h o d a r e h i g h e r t h a n t h o s e o b t a i n e d f r o m v a l u e s f o r t h e e n d o g e n o u s u r i n a r y t o t a l n i t r o g e n e x c r e t i o n a l o n e . T h e p o i n t o f i n t e r s e c t i o n i n t h e f i r s t t r i a l w i t h B - 5 i s a t a b o u t 1 7 . 3 g r a m s , a n d i n t h e s e c o n d t r i a l i t i s a t 1 6 . 5 grams. As the f o l l o w i n g r e s u l t s show t h i s value i s a great d e a l higher than the most p r o b a b l e f i g u r e f o r the e n d o g e n o u s level o f n i t r o -g e n e x c r e t i o n . T h e n i t r o g e n b a l a n c e i n d e x w a s c a l c u l a t e d f o r e a c h o n e pound f e e d i n g d a y , w h e r e B j - B Q e q u a l s t h e b a l a n c e i n d e x , a n d i n w h i c h ; B j r e p r e s e n t s t h e n i t r o g e n b a l a n c e d u r i n g i n t a k e , a n d B Q r e p r e s e n t s t h e n i t r o g e n e x c r e t i o n o r n i t r o g e n b a l a n c e w i t h n o i n t a k e , a n d I r e p r e s e n t s t h e n i t r o g e n i n t a k e . T h e n u m e r i c a l v a l u e o f t h i s i n d e x a p p e a r s a b o v e t h e o n e p o u n d f e e d l e v e l c o l u m n s o n t h e h i s t o g r a m s o f n i t r o g e n b a l a n c e . - 72 -The index r e f l e c t s the e f f e c t of absorbed n i t r o g e n per day on the n i t r o g e n balance and should i n c r e a s e n u m e r i c a l l y w i t h con-stant i n t a k e . When the p r o t e i n s t o r e s of an animal are f u l l , a s they are d u r i n g c o n d i t i o n s of good n u t r i t i o n a l s t a t u s , i t i s d i f f i c u l t to o b t a i n n i t r o g e n r e t e n t i o n . When the p r o t e i n s t o r e s are d e p l e t e d , on the other hand, i t i s r e l a t i v e l y easy to o b t a i n r e t e n t i o n even w i t h small amounts of d i e t a r y p r o t e i n . As the p r o t e i n s t o r e s g r a d u a l l y become dep l e t e d , as i s the case when the animal i s under a regimen of a l t e r n a t e f a s t i n g and f e e d i n g , u s i n g a f e e d i n t a k e at about the maintenance l e v e l f o r the a l -t e r n a t e p e r i o d s when f e e d i s given, the degree of r e t e n t i o n w i l l g r a d u a l l y i n c r e a s e even though the f e e d l e v e l remains constant. If the n i t r o g e n balance per day i s p l o t t e d a g a i n s t the absorbed n i t r o g e n per day, a curve i s o b t a i n e d which r e f l e c t s the change i n the animal's p r o t e i n s t o r e s . It a l s o r e f l e c t s the b i o l o g i c a l v a l u e of the p r o t e i n used as the fee d source. The n i t r o g e n b a l -ance index of the int a k e on any p a r t i c u l a r day may be repr e s e n t e d by the tangent of the curve at the p o i n t i n q u e s t i o n (Albanese 1959). The n i t r o g e n balance index i s the f r a c t i o n of n i t r o g e n r e t a i n e d of that absorbed; i f the endogenous n i t r o g e n e x c r e t i o n , r e p r e s e n t e d by the e x c r e t i o n at zero, i n t a k e i s constant and i n -dependent of n i t r o g e n i n t a k e . The f r a c t i o n r e p r e s e n t s the b i o -l o g i c a l v a l u e of the f e e d p r o t e i n . In the f i r s t t r i a l w ith B-5 the n i t r o g e n balance index i n c r e a s e d from 0 . 6 to 1.1 and on the day of t h e t h i r d one pound l e v e l f e e d i n g a r e t e n t i o n was obtained. - 73 -N i t r o g e n Requirements Based on the Endogenous T o t a l  U r i n a r y N i t r o g e n L e v e l On the f i f t h day of the second n i t r o g e n balance t r i a l , the lowest l e v e l of n i t r o g e n e x c r e t i o n d u r i n g s t a r v a t i o n was achieved. T h i s l e v e l was o b t a i n e d on the f i f t h day of f a s t i n g . The t o t a l n i t r o g e n e x c r e t i o n at t h i s time was 3 - 2 2 5 grams. T h i s v a l u e was o b t a i n e d i n a s s o c i a t i o n w i t h a c a l o r i c output of 1 , 4 5 7 C a l o r i e s c a l c u l a t e d on the b a s i s of an estimated B. Q. of 0 . 8 2 , o b t a i n e d as an average v a l u e i n the t h i r d t r i a l and recommended by p r e v i o u s authors (Brody). The a c t u a l B.Q. was p r o b a b l y nearer 0 . 7 at t h i s time but as mentioned p r e v i o u s l y the d i f f e r -ence caused by u s i n g the average v a l u e i n s t e a d of an a c t u a l value, which was not a v a i l a b l e i n the second t r i a l , i s not great. The r e l a t i o n s h i p between n i t r o g e n e x c r e t i o n and c a l o r i e s of r e s t -i n g heat p r o d u c t i o n i s 2 . 2 1 m i l l i g r a m s n i t r o g e n per c a l o r i e , which i s v e r y c l o s e indeed to the r e l a t i o n s h i p between the endogenous u r i n a r y t o t a l n i t r o g e n e x c r e t i o n and b a s a l C a l o r i e s of heat p r o d u c t i o n known to e x i s t between a d u l t mammals of d i f f e r e n t s p e c i e s , s i z e and age. It seems j u s t i f i a b l e , t h e r e -f o r e , to suggest that t h i s v a l u e of t o t a l u r i n a r y n i t r o g e n ex-c r e t i o n i s a f a i r r e p r e s e n t a t i o n of the endogenous u r i n a r y n i t r o -gen e x c r e t i o n and thus the minimum n i t r o g e n r e q u i r e d of R - 5 , and t h e r e f o r e r e p r e s e n t s the minimum amount of n i t r o g e n r e q u i r e d by an a d u l t non-pregnant female Columbian b l a c k - t a i l e d deer. In c a l c u l a t i n g the minimum p r o t e i n requirements of - 74 -animals the v a l u e f o r endogenous u r i n a r y n i t r o g e n i s m u l t i -p l i e d by a f a c t o r of 6 . 2 5 . The r e s u l t i s then c o r r e c t e d f o r the b i o l o g i c a l v a l u e of the d i e t a r y p r o t e i n under c o n s i d e r a t i o n , f o r example, i f the b i o l o g i c a l v a l u e of the p r o t e i n i s 5°> a f a c t o r of x 2 i s used. The value f o r endogenous u r i n a r y n i t r o -gen x 6 . 2 5 r e p r e s e n t s the minimum requirement f o r m e t a b o l i z a b l e p r o t e i n . A f t e r t h i s v a l u e has been c o r r e c t e d f o r the b i o l o g i c a l v a l u e of the p r o t e i n b e i ng used, the new value r e p r e s e n t s . t h e minimum requirement f o r d i g e s t i b l e crude p r o t e i n . Losses i n -c u r r e d d u r i n g d i g e s t i o n must a l s o be accounted f o r , u s i n g f a c -t o r s o b t a i n e d from d i g e s t i b i l i t y t r i a l s on the p r o t e i n source being used, e i t h e r on n i t r o g e n i t s e l f or on d r y matter. Once these l o s s e s have been accounted f o r the p r o t e i n requirement i n terms of the f e e d may be obtained. It must then be r e a l i z e d that the v a l u e thus o b t a i n e d r e p r e s e n t s the minimum p r o t e i n requirement based on the lowest l e v e l of p r o t e i n c a t a b o l i s m , i n a s s o c i a t i o n w i t h the lowest l e v e l of body amino a c i d t u r n -over and i r r e v e r s i b l e amino a c i d n i t r o g e n l o s s , p o s s i b l y asso-c i a t e d w i t h the s m a l l e s t s i z e of l a b i l e p r o t e i n s t o r e s , i n keeping w i t h the maintenance of normal body form and f u n c t i o n . T h e r e f o r e , a d d i t i o n a l c o r r e c t i o n s must be made i n a r r i v i n g at the most d e s i r a b l e p r o t e i n requirement, based on n i t r o g e n balance t r i a l s , f o r the achievement of a h i g h p l a n e of n u t r i -t i o n a l s t a t u s . The s t a r t i n g p o i n t f o r t h i s process,, however, remains the establishment of the l e v e l s of n i t r o g e n e x c r e t i o n - 7 5 -o b t a i n e d tinder b a s a l c o n d i t i o n s . The d i g e s t i b l e crude p r o t e i n requirement of R - 5 i s c a l c u l a t e d , on the b a s i s of the above formula i s 2 0 . 8 8 7 grams per day f o r R-5» a 4 5 k i l o g r a m a d u l t female, non-pregnant, b l a c k - t a i l e d deer. With an average n i t r o g e n and dry matter d i g e s t i b i l i t y of 8 4 - 8 5 per cent f o r the U.B.C. r a t i o n used (Appendix I) t h i s would i n d i c a t e a minimum requirement f o r t h i s f e e d of 2 4 . 8 5 6 grams of d i e t a r y t o t a l crude p r o t e i n per day and c o n s i d e r i n g the e x p e r i m e n t a l l y determined v a l u e f o r the percentage of crude p r o t e i n i n t h i s r a t i o n , namely, 1 5 - 5 5 per cent, a minimum f e e d requirement of 1 5 9 - 8 grams per day i s i n d i c a t e d . T h i s would not, of course, s a t i s f y the c a l o r i c needs of the animal, but l e v e l s of f e e d which would, that i s , approximately 7 0 0 grams per day, would supply more than four times the minimum t o t a l crude p r o t e i n requirement as c a l c u l a t e d by the above method. To supply s u f f i c i e n t d i g e s t i b l e crude p r o t e i n to s a t i s f y the n i t r o g e n c a t a b o l i s m a s s o c i a t e d w i t h the h i g h p l a n e of n u t r i t i o n experienced by animals such as R -5- or more s p e c i f i c a l l y , to m a i n t a i n a n i t r o g e n balance i s a s s o c i a t i o n w i t h a n i t r o g e n e x c r e t i o n of about 12 grams per day, as was found i n R - 5 immediately a f t e r s t a r v a t i o n was begun, 9 2 grams of d i e t a r y crude p r o t e i n would be needed n e c e s s i t a t i n g the con-sumption of 6 0 0 grams of U.B.C. p e l l e t t e d f e e d d r y matter per day. T h i s l e v e l of n i t r o g e n requirement i s r e f l e c t e d to a - 76 -g r e a t e r degree by the p r e v i o u s method which used the c a l c u l a t i o n of the p o i n t of n i t r o g e n balance to i n d i c a t e the d i e t a r y r e q u i r e -ments. The balance p o i n t of 17 grams of d i e t a r y n i t r o g e n i n -take i n d i c a t e s a need f o r approximately 1 0 0 grams of p r o t e i n d a i l y f o r maintenance of minimal n i t r o g e n s t o r e s alone. T h i s r e s u l t i s , of course, too h i g h f o r the purposes of m a i n t a i n i n g minimal n i t r o g e n s t o r e s and t h e r e f o r e the agreement between the v a l u e s of the two methods i s of l e s s s i g n i f i c a n c e than i f i t had been f o r the maintenance of a h i g h p l a n e of p r o t e i n n u t r i t i o n . The v a l u e of 92 grams of d i e t a r y p r o t e i n and 600 grams of p e l l e t -t e d f e e d o b t a i n e d above by c a l c u l a t i o n from e x p e r i m e n t a l l y d e t e r -mined n i t r o g e n e x c r e t i o n does, i n f a c t , r e p r e s e n t w e l l the nor-mal v o l u n t a r y f e e d i n t a k e of R-5 and o t h e r s of the b l a c k - t a i l e d deer maintained at U.B.C, although the males commonly eat poor-l y d u r i n g the season of r u t . There have been many n i t r o g e n balances c a r r i e d out w i t h domestic ruminants. R e c e n t l y Majundar found a v a l u e of O .65 pounds per 1 , 0 0 0 pounds l i v e weight to be the minimum p r o -t e i n requirement f o r maintenance. T h i s r e s u l t was o b t a i n e d from the endogenous u r i n a r y n i t r o g e n e x c r e t i o n which was O .052 grams per k i l o g r a m l i v e weight. The r e s u l t of t h i s experiment ex-p r e s s e d i n these terms i s 0 . 0 7 I grams per k i l o g r a m l i v e weight. A c c o r d i n g to Maynard (Maynard 1936), the r e s u l t s of many meta-b o l i c t r i a l s w i t h ruminants i n d i c a t e a requirement f o r t r u e - 77 -d i g e s t i b l e d i e t a r y p r o t e i n of 0 . 5 pounds, or 0 . 6 pounds of t o t a l d i g e s t i b l e d i e t a r y p r o t e i n , per 1 , 0 0 0 pounds of l i v e body weight. These v a l u e s are equal to 2 2 5 grams of t r u e d i g e s t i b l e p r o t e i n and 2 8 0 grams of t o t a l d i g e s t i b l e p r o t e i n per 1 , 0 0 0 pounds of l i v e body weight. The r e s u l t s of t h i s experiment i n d i c a t e a requirement of 249 grams of d i e t a r y t o t a l crude p r o t e i n with a d i g e s t i b i l i t y c o e f f i c i e n t of about 8 5 and a b i o l o g i c a l v a l u e of 1 0 0 . U s i n g feeds of a lower b i o l o g i c a l v a l u e , as i s commonly the case with domestic ruminants, the requirement of 249 grams would be c o r r e s p o n d i n g l y i n c r e a s e d . No r e f e r e n c e s were made i n the l i t e r a t u r e p e r t a i n i n g to n i t r o g e n balance experiments with w i l d ruminants, and t h e r e f o r e these r e s u l t s cannot be compared w i t h v a l u e s f o r other members of the f a m i l y Cervidae. However, the s i m i l a r i l y between the r e s u l t s o b t a i n e d i n t h i s experiment and those o b t a i n e d w i t h domestic ruminants i s reasonable. N i t r o g e n D i s t r i b u t i o n  Urea F o l i n i n v e s t i g a t e d the changing l e v e l s of t o t a l urea and ammonia e x c r e t i o n w i t h changes i n n i t r o g e n i n t a k e i n humans ( F o l i n 1 9 0 5 ) . He found the l e v e l of u r e a e x c r e t i o n dropped s i g -n i f i c a n t l y when n i t r o g e n i n t a k e was r e s t r i c t e d and rose again w i t h the r e t u r n of normal n i t r o g e n i n t a k e . S i n c e F o l i n many authors have s t u d i e d u r e a e x c r e t i o n i n both monogastric animals and domestic ruminants and have i n general c o r r o b o r a t e d F o l i n 1 s - 7 8 -r e s u l t s . However, p r i o r to the work of Schmidt-Nielsen ( S c h m i d t - N i e l s e n 1 9 5 7 and 1 9 5 § ) was thought that the ex-c r e t i o n of urea, formed from ambient ammonia of the b l o o d as a d e t o x i f i c a t i o n measure as shown i n Appendix I I I was e f f e c t -ed by means of simple glomerular f i l t r a t i o n , and the occurrence of u r e a r e t e n t i o n was due to simple back d i f f u s i o n at the c o l l e c t i n g t u b u l e s . No r e g u l a t i o n of ur e a e x c r e t i o n was p o s t -u l a t e d . The amount of u r e a e x c r e t e d was t h e r e f o r e a s s o c i a t e d d i r e c t l y w i t h the amount formed and the amount formed was due i n t u r n to the amount of excess n i t r o g e n i n g e s t e d and absorbed. The requirements f o r the proof of t u b u l a r r e g u l a t i o n only, are: independent r a t e s of glomerular f i l t r a t i o n and subsequent c l e a r a n c e , w i t h the glomerular f i l t r a t i o n r a t e remaining un-changed at d i f f e r e n t l e v e l s of b l o o d urea. Schmidt-Nielsen ( 1 9 5 7 ) found that these requirements were met by the camel to a great degree d u r i n g p e r i o d s of n i t r o g e n r e s t r i c t i o n . Work-in g w i t h other ruminants as w e l l he found that the urea c l e a r -ance may be h i g h l y r e s t r i c t e d w h i l e t h e r e was l i t t l e change i n glomerular f i l t r a t i o n r a t e with d i f f e r e n t l e v e l s of n i t r o g e n i n t a k e . T h i s was so as long as there was no i n t e r f e r e n c e caus-ed by changes i n s a l t i n t a k e . The c l e a r a n c e r a t e was found to be independent of the plasma c o n c e n t r a t i o n of urea, but v e r y s e n s i t i v e to the l e v e l of n i t r o g e n i n t a k e . T h i s was e s p e c i a l l y t r u e d u r i n g growth. Schmidt-Nielsen (I958) found a q u a l i t a t i v e -l y s i m i l a r s i t u a t i o n i n non-ruminants such as rodents, dogs and - 79 -man, but r e s u l t s were q u a n t i t a t i v e l y v e r y much smal l e r . He p r o -posed a c o u n t e r - c u r r e n t m u l t i p l i e r system f o r re c o v e r y and con-c e n t r a t i o n of ure a d u r i n g c l e a r a n c e , s i m i l a r i n f u n c t i o n i n g p r i n c i p l e to the arrangement of blo o d v e s s e l s he found i n ex-t r e m i t i e s of s i n g u l a r a q u a t i c and wading t e r r e s t r i a l mammals f o r c o n s e r v i n g body heat at the expense of r e g u l a t i n g the temp-e r a t u r e of the e x t r e m i t i e s (Scholander 1955)* I*1 these systems body heat b e i n g c a r r i e d to the e x t r e m i t i e s v i a the blood stream i n the major a r t e r i e s r a p i d l y conducts to s e v e r a l c l o s e l y a p p l i e d r e t u r n i n g v e s s e l s before i t i s c a r r i e d f a r i n t o the e x t r e m i t i e s and l o s t by cond u c t i o n to the environment. The same f u n c t i o n a l p r i n c i p l e , i n v o l v i n g u r e a d i f f u s i o n was p o s t -u l a t e d f o r the r e t e of venules surrounding the r e n a l c o l l e c t i n g t u b u l e s to prevent back d i f f u s i o n of c l e a r e d urea. The e x t e n s i v e s t u d i e s of Somers (Somers 1961) show that ruminants can and do r e c y c l e urea, which has been absorbed from the rumen p r i m a r i l y i n the form of ammonia, back i n t o the rumen v i a s a l i v a r y s e c r e t i o n . He showed that the u r e a content of the s a l i v a of Merino sheep was r e l a t e d to the amount of c i r -c u l a t i n g b l o o d urea. He showed that the content of ure a i n s a l i v a was g r e a t e s t when the animal was r e c e i v i n g inadequate amounts of d i e t a r y p r o t e i n . He a l s o showed that a much l a r g e r amount of u r e a i n j e c t e d i n t o the b l o o d appeared i n the u r i n e w i t h the animal on an adequate p r o t e i n d i e t than on an inade-quate d i e t . T h i s l a t t e r r e s u l t p r o b a b l y r e f l e c t s the r e n a l - 8o -r e g u l a t i o n of u r e a found by Schmidt-Nielsen, however, as w e l l as the s a l i v a r y r e c y c l i n g e f f e c t . Houpt (Houpt 1 9 5 9 ) found that together w i t h the above two mechanisms f o r u r e a c o n s e r v a t i o n ruminants c o u l d a l s o r e -c y c l e u r e a by d i r e c t a b s o r p t i o n from the b l o o d back i n t o the rumen. The work of D. Lewis (Lewis 1957)> which demonstrated that b l o o d u r e a c o n c e n t r a t i o n s i n c r e a s e as a d i r e c t r e s u l t of i n c r e a s e d ammonia p r o d u c t i o n by the rumen m i c r o f l o r a , t i e s a l l the above r e s u l t s together and shows that ruminants have evolved a s e r i e s of mechanisms which enable them to conserve n i t r o g e n which would be wasted d u r i n g p e r i o d s of n i t r o g e n r e s t r i c t i o n i n t h e i r environment. The rumen m i c r o f l o r a continue to deaminate amino a c i d s d e s p i t e impending shortages such as appear d u r i n g the hot d r y season when the n i t r o g e n content of herbage drops to e x c e e d i n g l y low l e v e l s , and t h i s deamination r e p r e s e n t s l o s s of n i t r o g e n to the f l o r a and consequently i n e v i t a b l y to the host. By means of these c o n s e r v i n g mechanisms the host can r e s t o r e "wasted" n i t r o g e n to the m i c r o f l o r a which w i l l use i t once giv e n a "second chance" f o r the s y n t h e s i s of m i c r o b i a l p r o t e i n and thus e s s e n t i a l l y p r o v i d e the host w i t h amino a c i d n i t r o g e n from what would have otherwise been waste n i t r o g e n . Presumably some r e c y c l e d u r e a may a r i s e from endogenous host body p r o t e i n c a t a b o l i s m p r o v i d i n g an a d d i t i o n a l o p p o r t u n i t y to r e c a p t u r e - 81 -what f o r monogastric animals i s unquestionably wasted, or l o s t n i t r o g e n . P h i l l i p s o n ( P h i l l i p s o n i 9 6 0 ) has shown that there must be a c e r t a i n amount of carbohydrate a v a i l a b l e to the rumen m i c r o f l o r a i n order f o r r e c y c l e d u r e a to be u t i l i z e d . The p r o -v i s i o n of exogenous carbon chains as w e l l as n i t r o g e n f o r the m i c r o b i a l synthesis' of amino a c i d s i s not an unreasonable p r o -p o s i t i o n . The l i m i t a t i o n thus set on the c o n s e r v a t i o n of n i t r o -gen i s , of course, that i t cannot be undertaken to a s i g n i f i c a n t degree under c o n d i t i o n s of complete s t a r v a t i o n . The l e v e l of u r e a n i t r o g e n as a percentage of the t o t a l n i t r o g e n responds to the presence and l e v e l of p r o t e i n i n t a k e q u i t e markedly i n a l l of the t r i a l s i n t h i s experiment. The r e s u l t s a re shown g r a p h i c a l l y i n F i g u r e 5» During p e r i o d s of i n a n i t i o n , the percentage u r e a n i t r o g e n drops 1 0 - 1 5 per cent from v a l u e s of 9 0 per cent and over to v a l u e s of 7 7 - 8 5 per cent of the t o t a l n i t r o g e n . The v a l u e s of the second t r i a l p resent the most un i f o r m response to p r o t e i n n u t r i t i o n . The p r e v i o u s n u t r i t i o n a l h i s t o r y of R - 5 p r i o r to the second t r i a l was s i m i -l a r to the one pound l e v e l of f e e d i n g . The s i m i l a r i t y of the urea percentage n i t r o g e n a f t e r a b sorbing one pound, to the i n i t i a l f a s t i n g l e v e l i s not s u r p r i s i n g . Upon r e a l i m e n t a t i o n the l e v e l r i s e s s t e e p l y to that found p r e c e d i n g the f a s t i n g l e v e l , p r o v i d e d that the f e e d i s accepted and consumed to the - 8 2 -extent of more than a f r a c t i o n of a pound. T h i s was not the case d u r i n g the f e e d i n g t e s t p e r i o d of the t h i r d t r i a l . The gradual consumption of more f e e d each day caused a v a r i a b l e i n c r e a s e i n percentage with a d i p i n the curve d u r i n g the f i r s t consumption of n e a r l y one pound. During the second consumption of almost one pound, the percentage rose s h a r p l y to 95 per cent of the t o t a l n i t r o g e n . A f t e r the b r i e f p e r i o d of consumption d u r i n g the t h i r d t r i a l , the l e v e l f e l l r a p i d l y again, w i t h i n twenty-four hours, to a new low of about 72 per cent. Follow-in g the longer l a s t i n g and t h r e e times l a r g e r a b s o r p t i o n of the second, t r i a l , the l e v e l f e l l to l e s s than 8 4 per cent, a f t e r f o r t y — e i g h t hours. These time r e l a t i o n s l e n d support to the p o s s i b i l i t y of a f a i r l y short passage time i n the doe B.-5 w i t h the p a r t i c u l a r p e l l e t e d r a t i o n used. These d a t a i n d i c a t e that i t might be p o s s i b l e to estimate the p r o t e i n or n i t r o g e n n u t r i -t i v e c o n d i t i o n of b l a c k and w h i t e - t a i l e d deer by the r e l a t i v e l e v e l of u r e a n i t r o g e n e x c r e t i o n compared wi t h t o t a l n i t r o g e n e x c r e t i o n . L e v e l s above 9 ° per cent, except f o r one a b s o r p t i o n day of 7 - 0 8 grams of n i t r o g e n , i n d i c a t e recent a b s o r p t i o n of s i g n i f i c a n t amounts of n i t r o g e n . A l s o , l e v e l s below 85 per cent are i n d i c a t i v e , i n t h i s experiment, of a f a s t i n g s t a t e w i t h r e s p e c t to d i e t a r y p r o t e i n . The s i m p l i c i t y of the Conway m i c r o - d i f f u s i o n method f o r the d e t e r m i n a t i o n of u r i n a r y and b l o o d urea n i t r o g e n makes - 83 -i t an a t t r a c t i v e method f o r r e s e a r c h . From a t h e o r e t i c a l p o i n t of view i t would be p a r t i c u l a r l y advantageous f o r conducting a survey of the p r o t e i n n u t r i t i o n a l s t a t u s of a p o p u l a t i o n of game animals. The technique i t s e l f i s s u i t a b l e f o r f i e l d con-d i t i o n s . However, the d i f f i c u l t i e s of o b t a i n i n g u r i n e samples from game animals under f i e l d c o n d i t i o n s are, at the present time, p r a c t i c a l l y insurmountable. A l s o , even i f animals c o u l d be captured and c o n f i n e d w i t h i n the necessary s t r u c t u r e f o r ob-t a i n i n g the sample c o l l e c t i o n , i t i s extremely u n l i k e l y that normal samples c o u l d be taken without a lengthy p e r i o d of ad-justment to the new surroundings. Ammonia The l e v e l of u r i n a r y ammonia n i t r o g e n behaves i n an i n v e r s e manner to that of urea i n t h i s experiment. In t h i s way, i t agrees w i t h other p r e v i o u s f i n d i n g s which have shown i t to be an o p p o s i t e index,to u r e a n i t r o g e n , of p r o t e i n n u t r i t i o n . Dur-i n g p r o t e i n s t a r v a t i o n the l e v e l r i s e s from a normal range of 1 to 4 per cent of t o t a l n i t r o g e n , to v a l u e s greater than 5 per cent, f o r example, 7 - 5 to 10 per cent. Urea and ammonia f l u c t u a t e i n o p p o s i t e d i r e c t i o n s i n p a r t because t h e i r p r o d u c t i o n i s i n e x t r i c a b l y i n v o l v e d i n a c i d -base r e g u l a t i n g mechanisms. The p r o d u c t i o n of ure a from f r e e ammonia i s brought about by the l i v e r as a d e t o x i f i c a t i o n measure. T h i s p r o c e s s i s shown s c h e m a t i c a l l y i n Appendix I I I . - 84 -Ammonia i s produced by deamination of amino a c i d s and i t c i r -c u l a t e s through the body f l u i d s as ammonium c h l o r i d e . The r e -le a s e of h y d r o c h l o r i c a c i d ana c o n v e r s i o n of ammonia together r e v e r s e e x c e s s i v e e l e v a t i o n of body f l u i d pH. The f o r m a t i o n of u r i n a r y ammonia i s brought about by the kidneys as shown i n Appendix I I , i n order to p r e s e r v e b o d i l y f i x e d bases such as sodium which have combined w i t h m e t a b o l i c a l l y produced a c i d s i n order to prevent abnormal lowering of pH. The extent of the f o r m a t i o n of ammonia i s then a r e f l e c t i o n of the metabolic a c i d p r o d u c t i o n and of the f u n c t i o n of the acid-base r e g u l a t i n g mechanism i n e l e v a t i n g body pH. During f a s t i n g the i n c r e a s e i n r e l a t i v e importance of f a t metabolism tends to produce metabolic a c i d o s i s . A l s o , the deamination of amino a c i d s decreases w i t h the d r i f t of pro-t e i n metabolism to lower l e v e l s a s s o c i a t e d w i t h p r o t e i n d e p l e -t i o n . C r e a t i n i n e and C r e a t i n e In the s e r i e s of experiments mentioned p r e v i o u s l y F o l i n found t o t a l c r e a t i n i n e e x c r e t i o n to be r e l a t i v e l y con-s t a n t from day to day and to be r e l a t i v e l y independent of n i t r o -gen intake, u n l i k e urea e x c r e t i o n . There have been, s i n c e t h i s time, many experiments the r e s u l t s of which support F o l i n ' s o b s e r v a t i o n s . Burroughs et a l have s a i d that the endogenous metabolism of F o l i n , which r e p r e s e n t s the summation of the - 85 - - • i r r e v e r s i b l e r e a c t i o n s of n i t r o g e n , (see Appendix V) are e x e m p l i f i e d by the b o d i l y c o n v e r s i o n of c r e a t i n e to c r e a t i n i n e which r e p r e s e n t s an i n e v i t a b l e l o s s of n i t r o g e n from the body (Burroughs, Burroughs and M i t c h e l l 1 9 4 0 ). The n i t r o g e n d i s -t r i b u t i o n d a t a of B l a x t e r and Wood ( B l a x t e r and Wood 1 9 5 1 ) i n d i c a t e that about 1 2 per cent of the endogenous n i t r o g e n metabolism of the growing c a l f on n i t r o g e n f r e e d i e t , i n -v o l v e s the above i r r e v e r s i b l e r e a c t i o n . For comparison 25 per cent i n v o l v e s p u r i n e metabolism and 50 per cent i n v o l v e s r e a c t i o n s t e r m i n a t i n g i n u r e a and ammonia. S e v e r a l i n v e s t i -g a t o r s have shown that c r e a t i n e i s the b o d i l y p r e c u r s o r of c r e a t i n i n e and that c r e a t i n i n e i s the o n l y normal u r i n a r y c o n s t i t u e n t w i t h a s i g n i f i c a n t amount of body c r e a t i n e n i t r o -gen, (Myers and F i n e I 9 I 3 . Scho enheimer and Block I94I)• Schoenheimer showed that t h r e e amino a c i d s were i n v o l v e d i n the b i o s y n t h e s i s of c r e a t i n e (Schoenheimer 1 9 4 2 ) . G l y c i n e formed the f a t t y a c i d chain, a r g i n i n e formed the guanidine nucleus, and the compound glycocyamine thus formed i s methy-l a t e d by t r a n s m e t h y l a t i o n u s i n g l a b i l e methyl groups from methionine;, (see Appendix IV). S c h a f f e r ( I 9 0 8 ) showed that c r e a t i n i n e e x c r e t i o n r e -pr e s e n t e d o n l y p a r t of endogenous n i t r o g e n metabolism and took p l a c e p r i m a r i l y i n muscle. Palmer, Means and Gamble ( 1 9 1 4 ) showed that c r e a t i n i n e e x c r e t i o n was p r o p o r t i o n a l to metabolic - 86. -r a t e i n man. Catherwood and Stearns (1937) found c r e a t i n i n e e x c r e t i o n to be a f u n c t i o n of body weight to the power of 0.9 where muscle mass u s u a l l y dominates the endogenous n i t r o g e n metabolism. A l s o the usual leanness of young animals and p e o p l e removes the d i s t u r b i n g e f f e c t of n p n - m e t a b o l i c a l l y f u n c t i o n a l f a t weight. Macy found a s i m i l a r c o e f f i c i e n t w i t h normal a d u l t s (Macy 1942). T a l b o t (1936) and Macy (I942) con-f i r m e d that c r e a t i n i n e was i n d i r e c t l y r e l a t e d to body weight and that i t was an e x c e l l e n t i n d i c a t o r of s k e l e t a l muscle s i z e . T a l b o t showed that the e x c r e t i o n of c r e a t i n i n e was s i m i -l a r f o r a d u l t men and women upon c o r r e c t i n g f o r f a t d i f f e r e n c e s . McCluggage (I93I) found the same r e l a t i o n of c r e a t i n i n e to muscle mass i n a d u l t s as c h i l d r e n , and that w i t h no f a t i n t e r -f e r e n c e the e x c r e t i o n remains constant, and f a l l s o f f a f t e r the age of 65 along with decrease i n BMR and muscle mass. Wuthier et a l showed that serum c r e a t i n i n e c o n c e n t r a t i o n i s r e l a t e d to c a r c a s s composition and per cent of l e a n body mass (Wuthier et a l 1957). De Groot et a l s t u d i e d the above mentioned constancy of c r e a t i n i n e e x c r e t i o n (De Groot i 9 6 0 ) . In t h e i r o p i n i o n none of the p r e v i o u s i n v e s t i g a t o r s had p a i d s u f f i c i e n t a t t e n t i o n to the constancy of c r e a t i n i n e e x c r e t i o n per hour or to the e x i s -tence of p o s s i b l e v a r i a t i o n i n e x c r e t i o n d u r i n g the day. A l s o Butcher and H a r r i s had s t a t e d that s i n c e ruminants had a h i g h l e v e l of c r e a t i n e e x c r e t i o n , they would not e x h i b i t a constant c r e a t i n i n e e x c r e t i o n . De Groot showed that c r e a t i n i n e e x c r e t i o n i s constant d u r i n g the day and t h a t h i g h l e v e l s of c r e a t i n i n e e x c r e t i o n d u r i n g a short i n t e r v a l are immediately balanced by low l e v e l s g i v i n g a constant average l e v e l per minute a l l day long even d u r i n g p e r i o d s of l a r g e c r e a t i n e e x c r e t i o n . He show-ed t h e r e f o r e t h a t the l a r g e l e v e l s of c r e a t i n e e x c r e t i o n found i n ruminants does not a l t e r the constancy of c r e a t i n i n e excre-t i o n and a l s o that the sum of c r e a t i n e and c r e a t i n i n e d u r i n g 24 hours i s not constant as was p o s t u l a t e d by Harding and Gaebler (1922) from t h e o r e t i c a l c o n s i d e r a t i o n s . The r e l a t i v e constancy of c r e a t i n i n e n i t r o g e n e x c r e t i o n i s shown i n F i g u r e 5-Butcher and H a r r i s demonstrated t h a t c r e a t i n i n e may serve as an index of the t o t a l volume of e x p e l l e d u r i n e because of i t s r e l a t i v e constancy d e s p i t e f a i r l y wide v a r i a t i o n s i n u r i n e volume, and i t s constant e x c r e t i o n w i t h time from hour to hour and day or n i g h t as shown by de Groot. There has been some work done over the years to show that the constancy of c r e a t i n i n e can be e f f e c t e d by the p r o t e i n i n t a k e . In p a r t i c u l a r Hehyami (I958) showed that the l e v e l of a r g i n i n e had. a p o s i t i v e i n f l u e n c e on the l e v e l of c r e a t i n i n e and c r e a t i n e e x c r e t i o n . D i n i n g et a l (1949) found a s i g n i f i c a n t v a r i a t i o n between d i f f e r e n t s p e c i e s of beef s t e e r s and between i n d i v i d u a l s of the same s p e c i e s (Herefords) of s i m i l a r weight, (300 k i l o g rams) and age (2 y e a r s ) w h i l e he found r e l a t i v e l y constant l e v e l s w i t h i n i n d i v i d u a l s i n a l l these c a t e g o r i e s . These r e s u l t s are - 88 -confirmed i n t h i s experiment as f a r as r e l a t i v e constancy of c r e a t i n i n e e x c r e t i o n w i t h i n i n d i v i d u a l animals i s concerned, and i n the l i g h t of the above c o n s i d e r a t i o n s p r o b a b l y to some extent r e f l e c t d i f f e r e n c e s i n body composition. A c c o r d i n g to B r i n k e r k i n k , p a r t or perhaps a l l of the v a r i a t i o n i n c r e a t i n e e x c r e t i o n i s due to e r r o r s of un-known extent inherent i n the a l k a l i n e p i c r a t e method. He says that the degree of c o n v e r s i o n of c r e a t i n e to newly formed c r e a t i n i n e i n the presence of pre-formed c r e a t i n i n e i s subject to 1 0 - 5 0 per cent e r r o r ( B r i n k e r k i n k I 9 6 1 ) . T h i s i s because the r e a c t i o n i s that of an e q u i l i b r i u m s i t u a t i o n i n which the degree of c o n v e r s i o n i s r e l a t e d to the amounts of c r e a t i n e and pre-formed and newly formed c r e a t i n i n e as w e l l as the other standard v a r i a b l e s such as pH and temperature and the presence of other chromogenic m a t e r i a l s . The r e s u l t s t h e r e f o r e depend p a r t l y on the v a r i a t i o n i n c r e a t i n i n e and c r e a t i n e e x c r e t i o n , thus compounding the apparent v a r i a b i l i t y of c r e a t i n e e x c r e t i o n . C r e a t i n i n e d e t e r m i n a t i o n s on separate samples are, on the other hand, u n a f f e c t e d by t h i s e q u i l i b r i u m s i t u a t i o n and are a c c o r d i n g to the author f a i r l y a c c u r a t e . These r e s u l t s are c o r r o b o r a t e d by the pr e s e n t author's experience i n o b t a i n i n g v a r i a b l e r e s u l t s w i t h c r e a t i n e standards when these are i n c l u d e d i n u r i n e samples of known c r e a t i n e content. A c c o r d i n g to B r i n k e r k i n k , the r e a c -t i o n can even pass i n r e v e r s e under s u i t a b l e c o n d i t i o n s such - 89 -that the pre-fbrmed c r e a t i n i n e i s converted to c r e a t i n e and the r e s u l t i s an a p p a r e n t l y smaller sum of pre-formed and new c r e a t i n i n e than the o r i g i n a l pre-formed value. T h i s r e s u l t was a l s o o b t a i n e d i n the p r e s e n t experiment upon o c c a s i o n . In the l i g h t of the above c o n s i d e r a t i o n s the s i g n i f i c a n c e of the c r e a t i n e r e s u l t s d u r i n g growth and f o l l o w i n g puberty are not d i s c u s s e d i n d e t a i l . The r e s u l t s of the c r e a t i n i n e n i t r o g e n d e t e r m i n a t i o n s o b t a i n e d d u r i n g the balance t r i a l s of t h i s experiment appeared, i n general, to support the p r e v i o u s statements r e g a r d i n g the r e l a t i v e independence of c r e a t i n i n e e x c r e t i o n l e v e l s and changes i n n i t r o g e n i n t a k e . The c r e a t i n i n e n i t r o g e n , as a percentage of t o t a l n i t r o g e n e x c r e t i o n , tended to be f a i r l y constant d u r i n g wide f l u c t u a t i o n s i n t o t a l n i t r o g e n e x c r e t i o n . However, the t o t a l c r e a t i n i n e n i t r o g e n e x c r e t i o n per day showed a s l i g h t tendency to r e f l e c t changes i n n i t r o g e n i n t a k e and e x c r e t i o n , ( F i g u r e 6 ) as de Groot ha,d found to be the case. The s l i g h t r e d u c t i o n i n c r e a t i n i n e e x c r e t i o n d u r i n g f a s t i n g i s not unrea-sonable because the r e d u c t i o n i n p r o t e i n s t o r e s which occurs at t h i s time i n v o l v e s p r o t e i n from the s k e l e t a l muscles. The r e -d u c t i o n i n c r e a t i n i n e e x c r e t i o n thus r e f l e c t s a r e d u c t i o n i n a c t i v e body mass. Although the c r e a t i n i n e e x c r e t i o n showed t h i s tendency to respond to changes i n n i t r o g e n i n t a k e w i t h i n the two b alance t r i a l s , they d i d not show a corresponding t e n -- 9 0 -dency between t r i a l s . As shown i n F i g u r e 6 , the general l e v e l of c r e a t i n i n e n i t r o g e n e x c r e t i o n was s i m i l a r at l e v e l s of t o t a l n i t r o g e n e x c r e t i o n of about 14 grams i n T r i a l I I , and about 7 . 5 grams i n T r i a l I I I . These r e s u l t s suggest t h a t the c o n d i t i o n s surrounding the d e t e r m i n a t i o n of c r e a t i n i n e e x c r e t i o n must be c a r e f u l l y standardized.when attempting to i n t e r p r e t them i n terms of the c h a r a c t e r i s t i c c r e a t i n i n e e x c r e t i o n l e v e l of an i n d i v i d u a l animal. There were no measurements a v a i l a b l e on the constancy of c r e a t i n i n e e x c r e t i o n per hour as the samples of u r i n e were c o l l e c t e d o n l y once i n each 2 4 hour p e r i o d . C r e a t i n i n e n i t r o g e n c o n c e n t r a t i o n per m i l l i l i t e r of u r i n e showed a tendency to decrease i n r e g u l a r f a s h i o n as the t o t a l volume of u r i n e f l o w i n c r e a s e d . Although the r e s u l t s of these d e t e r m i n a t i o n s d i f f e r e d q u a n t i t a t i v e l y between the two t r i a l s w i t h R - 5 , they showed evidence of being of p o s s i b l e v a l u e as an index of u r i n e volume, as Butcher and H a r r i s have suggested. For example, i n the second t r i a l , the c o n c e n t r a t i o n of c r e a t i n i n e n i t r o g e n was 2 . 3 m i l l i g r a m s per m i l l i l i t e r when the u r i n e output was 4 1 2 m i l l i l i t e r s , 2 m i l l i g r a m s w i t h 6 5 8 m i l l i l i t e r s and 1 . 7 m i l l i g r a m s w i t h 1 , 2 7 2 m i l l i l i t e r s . There were i n t e r m e d i a t e v a l u e s between these. In the t h i r d t r i a l , however, the v a l u e s were 1 . 2 m i l l i g r a m s w i t h 3 7 ° m i l l i l i t e r s of u r i n e output, 1 m i l l i g r a m w i t h 3 8 5 m i l l i l i t e r s , 0 . 8 m i l l i -grams with 5 7 7 m i l l i l i t e r s and 0 . 3 w i t h 1 , 6 4 6 m i l l i l i t e r s . Values f o r t h i s r e l a t i o n s h i p would have to be o b t a i n e d from a l a r g e r amount of data, and under normal d i e t a r y c o n d i t i o n s to e l i m i n a t e the i n t e r f e r i n g e f f e c t s caused by f l u c t u a t i o n s i n n i t r o g e n s t o r e s , i n order to determine the a c t u a l value of c r e a t i n i n e n i t r o g e n as an index bf t o t a l u r i n a r y output f o r an i n d i v i d u a l animal. I f the l e v e l of c r e a t i n i n e n i t r o g e n was found to be r e l i a b l e as an index of u r i n e volume i t would p r o v i d e a v a l u a b l e t o o l f o r d e t e r m i n i n g the t o t a l n i t r o g e n output u s i n g a small sample of deer u r i n e . As i s the case with the urea a n a l y s i s d e s c r i b e d above, the ease of conducting the c r e a t i n i n e d e t e r m i n a t i o n makes i t a good method f o r f i e l d work, but the problem of o b t a i n i n g even small samples of u r i n e under f i e l d c o n d i t i o n s remains. N i t r o g e n E x c r e t i o n d u r i n g Growth  T o t a l U r i n a r y N i t r o g e n E x c r e t i o n The r e s u l t s of t o t a l u r i n a r y n i t r o g e n e x c r e t i o n ob-t a i n e d d u r i n g the growing p e r i o d on the t h r e e female and f i v e male b l a c k - t a i l e d deer are shown i n Tables VII to XI, along w i t h the n i t r o g e n d i s t r i b u t i o n data. The r e s u l t s are shown i n graphic form i n F i g u r e s 7 to 11. The i n c r e a s e i n t o t a l n i t r o g e n e x c r e t i o n with the i n c r e a s e i n body weight i s shown on a r i t h m e t i c g r i d i n F i g u r e 7 and on a r i t h l o g g r i d i n F i g u r e 8. The t o t a l n i t r o g e n e x c r e t i o n , as i l l u s t r a t e d , i n F i g u r e 7, can be seen to take the form of a curve which i n c r e a s e s w i t h ever d e c r e a s i n g increments, or w i t h n e g a t i v e a c c e l e r a t i o n , as growth p r o g r e s s e s . T h i s curve i s s i m i l a r i s gross form to that o f t e n used to express the aver-age i n c r e a s e i n body s i z e with age d u r i n g the l a t e r , or n e g a t i v e a c c e l e r a t i o n phase, of animal growth. The same d a t a expressed i n a r i t h l o g form i s more i l l u s t r a t i v e of the c h a r a c t e r of the changes which occured i n t o t a l n i t r o g e n e x c r e t i o n d u r i n g the growing p e r i o d of the deer ( F i g u r e 8 ) . The d a t a expressed i n t h i s manner shows that the p a t t e r n of change i n t o t a l n i t r o g e n e x c r e t i o n c o n s i s t s of s e v e r a l phases of d i f f e r e n t constant percentage r a t e s of i n c r e a s e . These phases are separated by "breaks" or i n f l e c t i o n s i n the curve which i n d i c a t e the areas of r a t h e r abrupt change i n the r a t e of i n c r e a s e . The r e l a t i v e l y small amount of d a t a a v a i l a b l e shows at l e a s t two, and p o s s i b l y three, of these phases. In accor-dance w i t h the method of e x p r e s s i o n used i n F i g u r e 8 , that i s , the l o g of the grams of t o t a l n i t r o g e n e x c r e t i o n per day as a f u n c t i o n of the change i n body weight i n kilograms, the r a t e of i n c r e a s e i n t o t a l n i t r o g e n e x c r e t i o n may be s t a t e d i n terms of a power v a l u e of body weight. For example, i n the f i r s t phase, which extends from a body weight of about 4 kilograms to about 8 kilograms the r a t e of i n c r e a s e i n t o t a l n i t r o g e n e x c r e t i o n with i n c r e a s i n g body weight i s p r o p o r t i o n a l to the power 4 - 0 - 93 -of body weight. T h i s means that f o r a 1 per cent i n c r e a s e i n body weight, t h e r e w i l l be an i n c r e a s e i n t o t a l n i t r o g e n ex-c r e t i o n on the order of about 4 per cent. I f the r a t e of i n -crease i n t o t a l n i t r o g e n e x c r e t i o n f o l l o w i n g the body weight of 8 kilograms i s expressed i n terms of a s i n g l e constant v a l u e , the r a t e of i n c r e a s e i s p r o p o r t i o n a l to the 1 . 0 8 power of body weight. However, the d a t a appear to suggest the presence of two separate phases f o l l o w i n g the body weight of 8 kilograms. The f i r s t of these extends over a p e r i o d of growth from 8 k i l o -grams of body weight to about 22 kilograms. The r a t e of i n -c r e a s e i n magnitude of t o t a l n i t r o g e n e x c r e t i o n d u r i n g t h i s p e r i o d i s p r o p o r t i o n a l to the 1 . 0 6 pwer of body weight. The second phase extends from 22 kilograms to over 35 kilograms of body weight and the r a t e of i n c r e a s e d u r i n g t h i s p e r i o d i s p r o p o r t i o n a l to 0 . 7 3 power of body weight. Because of the r e l a t i v e l y small amount of d a t a a v a i l a b l e , and of the hazards i n v o l v e d i n a t t a c h i n g s i g n i f i c a n c e to v a l u e s of t o t a l n i t r o g e n e x c r e t i o n without c o n s i d e r i n g changing body composition, meta-b o l i c r a t e , and n i t r o g e n and c a l o r i c i n t a k e simultaneously, s t a t i s t i c a l a n a l y s i s was not employed i n a r r i v i n g at these values. They t h e r e f o r e r e p r e s e n t approximations of changes i n magnitude of n i t r o g e n e x c r e t i o n d u r i n g growth. However, the i l l u m i n a t i o n of the p a t t e r n of the change i n magnitude of t o t a l n i t r o g e n e x c r e t i o n , even i f l a r g e l y of a q u a l i t a t i v e nature, can serve i n an attempt to understand the u n d e r l y i n g mechanisms i n v o l v e d - 94 -i n b r i n g i n g these changes about. The type of change i n r a t e of i n c r e a s e i n s i z e of n i t r o g e n output, i l l u s t r a t e d by the above r e s u l t s with growing deer, i s v e r y i n t e r e s t i n g because i t resembles the changes i n growth r a t e o b t a i n e d with advancing age, or i n c r e a s e i n body s i z e , when growth d a t a are handled i n the above manner. Brody (1945) and many other i n v e s t i g a t o r s s i n c e , have shown that the r a t e of i n c r e a s e i n body s i z e i s dependant on the growth a l -ready achieved d u r i n g the p r e - p u b e r t a l p e r i o d of growth. F o l l o w i n g puberty the growth r a t e appears to be a f u n c t i o n of the s i z e yet to be achieved i n terms of the a d u l t body weight. The f i r s t phase i s c h a r a c t e r i z e d by p o s i t i v e a c c e l e r a t i o n , w h i l e the second i s c h a r a c t e r i z e d by n e g a t i v e a c c e l e r a t i o n . The p e r -centage r a t e of i n c r e a s e i n body s i z e i s markedly d i f f e r e n t i n the two phases of growth, and when the d a t a f o r the body weight, expressed l o g a r i t h m i c a l l y , are c o n s i d e r e d as a f u n c t i o n of i n -c r e a s i n g age, a major i n f l e c t i o n occurs i n the curve at the p o i n t of puberty i n s i m i l a r f a s h i o n to the i n f l e c t i o n s demon-s t r a t e d by the n i t r o g e n e x c r e t i o n d a t a above. When other p a r a -meters a s s o c i a t e d w i t h metabolic f u n c t i o n are t r e a t e d i n t h i s f a s h i o n as a f u n c t i o n of i n c r e a s i n g age or body s i z e they a l s o tend to f o l l o w a s i m i l a r p a t t e r n , f o r example, the change i n endogenous n i t r o g e n e x c r e t i o n , or i n basal metabolic r a t e with advancing age, (Brody I945). _ 95 -The p o i n t s at which the two i n f l e c t i o n s i n the n i t r o -gen e x c r e t i o n curve occur, i n terms of age and body weight, correspond to the ages and weights wherein the v a l u e f o r the r a t e of growth of b l a c k - t a i l e d deer i s found to change (Cowan : and Wood 1955)* The f i r s t i n f l e c t i o n c o i n c i d e s w i t h the change i n growth r a t e which occurs at IA days i n the d a t a of Cowan and Wood, however, and t h e r e f o r e o n l y agrees w i t h the body weight d a t a and not w i t h the age. The l a c k of agreement i n age p r o -b a b l y r e f l e c t s a l e s s r a p i d growth r a t e d u r i n g the f i r s t weeks f o l l o w i n g c a p t u r e on the p a r t of the deer i n the present e x p e r i -ment, whereas the deer i n the 1955 experiment were r a i s e d i n c a p t i v i t y from b i r t h and presumably had access to a higher p l a n e of n u t r i t i o n d u r i n g the p e r i o d of extremely r a p i d and important weight gain. A l s o , as s t a t e d p r e v i o u s l y , the exact date of b i r t h i s not known f o r the deer used i n the present experiment. The second i n f l e c t i o n occurs at approximately 100 days of age i n t h i s experiment. T h i s agrees in;terms of both age and body weight w i t h the growth curve date of Cowan and Wood. It was f u r t h e r e s t a b l i s h e d by Cowan and Wood that the i n f l e c t i o n i n the growth curve at t h i s age and weight i s a s s o c i a t e d w i t h the appearance of puberty, as s i g n a l l e d by the appearance of naked a n t l e r buds and the demonstration of f e r -t i l i t y i n two i n d i v i d u a l s . The agreement between the n i t r o g e n curve and the growth curve i n terms of body weight i s of g r e a t -er s i g n i f i c a n c e than that of age, as suggested e a r l i e r due to - 9 6 -the f a c t that " p h y s i o l o g i c a l a g i n g " i s p r i m a r i l y dependent upon environmental i n f l u e n c e s , e s p e c i a l l y those a f f e c t i n g n u t r i t i o n a l s t a t u s , and not upon the passage of time i t s e l f . The exact v a l u e s of n i t r o g e n e x c r e t i o n o b t a i n e d dur-i n g normal f e e d i n g p e r i o d s depends to a v e r y l a r g e extent upon the degree of n i t r o g e n i n t a k e once the maintenance and growth requirements have been met and surpassed. Th e r e f o r e , i t i s reasonable to assume that f l u c t u a t i o n s i n the e x c r e t i o n l e v e l o b t a i n e d i n t h i s experiment would, be i n p a r t due to f l u c t u a t i o n s i n i n t a k e d u r i n g growth. However, the p a t t e r n of e x c r e t i o n ob-t a i n e d i s more s u g g e s t i v e of changes i n p h y s i o l o g i c a l c o n d i t i o n a s s o c i a t e d w i t h growth, i n the same way that the changing p a t t e r n of growth r a t e i s so a f f e c t e d , due to the r e g u l a r man-ner i n which i t appears to change i n magnitude as growth pro-gresses. For example, i t would be expected that the l e v e l of n i t r o g e n e x c r e t i o n should i n c r e a s e as the animal grows l a r g e r . It i s a l s o reasonable to expect that the l e v e l of n i t r o g e n e x c r e t i o n would i n c r e a s e at a l e s s e r r a t e when the general metabolic a c t i v i t y and growth r a t e of the animal assumes a reduced r a t e of i n c r e a s e f o l l o w i n g an i n f l e c t i o n i n the growth curve. The i n c r e a s e i n n i t r o g e n e x c r e t i o n w i t h age i l l u s -t r a t e d i n F i g u r e s 9 and 10 p r o v i d e u s e f u l i n f o r m a t i o n f o r the i l l u m i n a t i o n of the u n d e r l y i n g metabolic mechanisms which - 97 -i n f l u e n c e the l e v e l of n i t r o g e n e x c r e t i o n d u r i n g growth. The d a t a i n these f i g u r e s show ^ marked tendency f o r a r e d u c t i o n i n output at the age of three months. T h i s i s e s p e c i a l l y evident i n the d a t a from the male deer. The e x c r e t i o n r i s e s again w i t h i n a short p e r i o d of time. T h i s r e s u l t i s i n d i c a t i v e of a short p e r i o d of i n c r e a s e d n i t r o g e n r e t e n t i o n . It would be reasonable to expect c e r t a i n p e r i o d s of i n c r e a s e d r e t e n t i o n d u r i n g growth when greater needs of p r o t e i n f o r t i s s u e f o r m a t i o n a r i s e . The p o i n t of puberty i s an example of a c r i t i c a l p e r i o d of p h y s i o l o g i c a l and s t r u c t u r a l r e - o r g a n i z a t i o n wherein such an i n c r e a s e d need f o r d i e t a r y p r o t e i n would a r i s e . At t h i s time the growth i n muscle i s emphasized, and the p r o t e i n ana-b o l i c e f f e c t of androgens and estrogens i s w e l l e s t a b l i s h e d . The t o t a l n i t r o g e n e x c r e t i o n per k i l o g r a m of body weight i s f a i r l y uniform throughout the e n t i r e growing p e r i o d . T h i s i s a reasonable r e s u l t because of the f a c t that d u r i n g the growing p e r i o d the muscular mass dominates the n i t r o g e n e x c r e t i o n p i c t u r e to a c e r t a i n extent. During the growing p e r i o d the b u i l d - u p of f a t storage depots i s v e r y s l i g h t un-t i l the r a t e of growth begins to decrease markedly. However, the l a r g e e l e v a t i o n of the n i t r o g e n e x c r e t i o n over the estimat-ed endogenous l e v e l based on body weight shows that the l e v e l of e x c r e t i o n i s c o n t r o l l e d l a r g e l y by the n i t r o g e n intake. The p r e d i c t e d endogenous l e v e l of e x c r e t i o n i s shown i n - 98 -F i g u r e 8. T h i s h i g h e l e v a t i o n , which r e p r e s e n t s an i n c r e a s e over the endogenous l e v e l of about 1,000 per cent, would seem to suggest that the p a t t e r n of n i t r o g e n e x c r e t i o n d u r i n g growth, as i t was o b t a i n e d i n t h i s experiment, more t r u l y r e f l e c t s the behavior of the animals tested, i n terms of n i t r o g e n intake, than the a c t u a l growth requirements. However, i t should be r e i t e r a t e d t h at the r e s u l t s a l s o represent the degree of p r o -t e i n c a t a b o l i s m a s s o c i a t e d with growth under i d e a l c o n d i t i o n s of n u t r i t i o n a l s t a t u s , and thus with the development and p r e -s e r v a t i o n of an i d e a l l e v e l of p r o t e i n r e s e r v e s . C r e a t i n i n e and C r e a t i n e N i t r o g e n E x c r e t i o n The i n c r e a s e i n c r e a t i n i n e n i t r o g e n e x c r e t i o n with the i n c r e a s e i n body weight i s shown i n F i g u r e 11. The l e v e l of e x c r e t i o n i n c r e a s e s i n a l i n e a r manner wit h the i n c r e a s e i n body weight. T h i s r e s u l t agrees wi t h t h e o r e t i c a l c o n s i d e r a t i o n s (Albanese 1959)- As mentioned p r e v i o u s l y , the i n c r e a s e i n body weight i s l a r g e l y r e p r e s e n t e d by a c t i v e body mass d u r i n g the p e r i o d of growth. The c r e a t i n i n e n i t r o g e n e x c r e t i o n r e p r e s e n t s unavoidable n i t r o g e n l o s s from t h i s f r a c t i o n of body m a t e r i a l , and should, t h e r e f o r e , be a r e p r e s e n t a t i v e index of the i n -crease i n body weight d u r i n g t h i s p e r i o d . A l s o , i t i s not i n f l u e n c e d by the degree of n i t r o g e n i n t a k e to the extent that the t o t a l n i t r o g e n e x c r e t i o n i s a f f e c t e d . The c r e a t i n i n e n i t r o -gen e x c r e t i o n per k i l o g r a m of body weight was uniform throughout - 99 -the growing period of a l l the individuals and was similar in value from one individual to another. The creatine nitrogen excretion was very variable and ranged from values of 10 to 150 milligrams. These values are similar to those quoted for humans. The creatine nitrogen excretion tended to reach peak values with each individual, and in both sexes, at about 120 to 135 days and with body weights of between 16 and 2 2 kilograms. This peak excretion coincides with the establishment of puberty. T a b l e s and f i g u r e s - 100 -TABLE I. Dry Matter R e l a t i o n s Date D.M. Intake i n Gr. F e c a l D.M. i n Gr. * T o t a l Dig. Nut-r i e n t (appar. *) i n Gr. % Dig. D.M. True Dig. Nut-r i e n t * i n Gr. True % Dig. D.M. Dig. C a l s . T o t a l C a l s . 17 18 19 20 421.4 no d a t a T r i a l 1 Oci tober (I 3 - l ) 15/16 16/17 17/18 18/19 19/20 20/21 21/22 22/23 23/24 24/25 25/26 26/27 27/28 322. 690.4 421.4 657.O 421.4 72.9 X 10. 1 J_5.5 ,186.6 45.9 6.9 11.9 T r i a l 2 Jai l u a r y (.1 *-5) 759-8 1,513.8 794-6 1,713.9 68I.5 1, 222 1,222 262. 2 1 522. 1 V . 274.1 590.6 .234.8 81.8 75,5 65.1 89.9 55.7 272. 2 532.1 284.1 600.6 244.8 84 77 67 9 i 58 12/13 13/1A 14/15 15/16 16/17 18/19 19/20 20/21 21/22 22/23 17.3N 142.2 378.8 357-7 "68.-5 56.2 64.3 25.0 none ~T3. 2 31.2 64.7 22.5 18.0 T r i a l 3 Mew rch (R-[ 5) -I I 8.9 319.0 910.6 896.I 1,098 1,037 4.1 110. 0 308.6 42. 2 77.4 IVs $6.3 14.1 120.0 ,324.1 3^18.6 • \ 82 § 5 §5 89 ; . • i - 101 -TABLE I I . N i t r o g e n D i g e s t i b i l i t y Data Dat e Feed N.. Meta-b o l i c F e c a l N. F e c a l N. • Appar. Dig. N. True Dig. N. D i g e s t -i b i l i t y ' or C o e f f i -c i e n t ( t r u e ) True Dig. N./kg. Body Wt. T r i a l I October ( P - l ) 1 6 / 1 7 17/18-1 8 / 1 9 1 9 / 2 0 10 .48 1 5 / 1 6 1 6 / 1 7 1 7 / 1 8 1 8 / 1 9 1 9 / 2 0 2 0 / 2 1 2 1 / 2 2 2 2 / 2 3 2 3 / 2 4 2.4/25 2 5 / 2 6 2 6 / 2 7 2 7 / 2 8 T r i a l 2 January (R-5) ' 8 " . 61' 1 7 . 1 8 1 0 . 4 8 1 6 . 3 5 1 0 . 4 8 0 . 6 2 T 1 . 3 8 0 . 8 4 1 . 3 1 \O . 8 4 2 . 3 0 0 . 3 2 0 . 5 1 2 . 0 5 "2TJ4-3,43 1.91 5.50 1 . 8 2 ^ 0 7 2 3 0 . 4 6 ~ 5 , 6 7 1 3 . 7 5 8 . 5 7 1 0 . 8 5 8 . 6 6 6 . 3 1 1 5 . 1 3 9 . 4 1 1 2 . 16 9 . 5 0 l l 90 74 91 0 . 1 3 9 0 . 3 3 4 0 . 2 0 7 0 . 2 6 8 0 . 2 0 9 1 2 / 1 3 1 3 / 1 4 1 4 / 1 5 1 5 / 1 6 1 6 / 1 7 17 / 1 8 1 8 / 1 9 1 9 / 2 0 2 0 / 2 1 2 1 / 2 2 2 2 / 2 3 T r i a l 3 March (R-5) 0 . 4 3 3 - 5 4 9. 4 2 8.90 O . 3 4 6 0 . 2 8 4 0 . 7 5 8 , 0 . 7 1 5 0 . 3 8 3 1 . 0 9 5 2 . 3 4 9 1 . 7 2 3 0 . 7 3 4 0 . 6 2 8 0 . 0 4 7 2 . 4 4 5 7 .08I 7 . 1 7 7 0 . 0 8 2 . 7 3 7.83 7 . 8 9 19 83 89 0 . 0 0 2 0 . 0 6 0 O . I 7 3 0 . 1 7 4 - 102 -TABLE I I I . N i t r o g e n Balance Data Date True Dig. N. i n G. U r i n a r y N. i n G. N. . Balance IN Q. •' N. Bal y4Cg. b. wt. Gr. b. Prot. Used f o r Energy C a l . Equiv. of t h i s amt. Body Pr o t . C a l s . Req'd. from Body CHO &/or Fat T r i a l 1 October ( P - l ) 16 /17 18/19 19/20 0.28 2 3 . 1 2 4 8 . 8 0 6 9 . 2 0 0 4 3 . 2 2 1 •23 .124 . 8 . 8 0 6 • 9 . 2 0 0 •43.221 0.509> 0 . 1 9 4 0 . 2 0 2 ; 0 . 9 5 3 : 1 4 4 . 5 5 5 . 0 5 7 . 5 2 7 1 . 2 6 1 2 . 7 2 3 3 . 3 2 4 3 . 8 1 , 1 4 5 . 0 T r i a l 2 January (R - 5 ) 15/16 16 /17 17/18 18/19 19/20 20/21 21/22 22/23 23/24 24/25 2^/26 2 6 / 27 27/28 15.31 9 . 4 1 12.16 9 . 5 0 2 5 . 3 8 4 1 2 . 0 9 6 1 2 . 9 2 9 _3..„225.. 11.719 15 .531 1 0 . 2 5 2 -.14.537 6 . 3 4 3 8 . 9 0 0 11 .501 1 0 . 4 1 3 - 2 5 . 3 8 4 - 1 2 . 0 9 6 - 1 2 . 9 2 9 ^ 3 ^ 2 2 5 - 5 . 4 0 9 - 0 . 2 2 1 - O . 8 4 2 - 2 . 3 7 7 1-157 - 8 . 9 0 0 - 1 1 . 5 0 1 - 1 0 . 4 1 3 0 . 5 6 0 0 . 2 6 7 0 . 2 8 5 0^071 0.119" 0 . 0 0 5 0 . 0 1 9 0 . 0 5 2 0 . 0 7 0 0.196" 0 . 2 5 4 0 . 2 3 0 1 5 8 . 6 8 0 . 8 2 0 . 2 77.7 14.9 i £ i 7 _ 5 5 . 7 7 1 . 9 6 5 . 1 .672. 6 3 2 0 . 4 3 4 2 . 6 143.1 5 3 . 0 21 . 2 6 3 . 6 _ 84._8 23578 3 0 4 . 7 2 7 5 . 9 1 , 6 3 6 . 5 2 1 9 . 6 1 , 0 1 0 . 0 1 , 1 0 4 . 6 1 , 2 2 9 . 1 2 6 9 . 0 8 0 . 7 9 1 9 . 8 4 4 . 4 97079 8 9 9 . 0 9 5 9 . 5 T r i a l 3 March (R-5) 12/13 13/14 14/15 15/16 1 6 / 1 7 17/18 18/19 19/20 20/21 21/22 22/23 6. 6. 17. 6. 0 . 0 8 K 8 . 2 .73 7 . 8 3 67 8 . 10. N 2 i 002 674 702 720 488 '834" 068 836 000 032 437 • 6 . 0 0 2 • 6 . 6 7 4 • 1 7 . 7 0 2 • 6 . 7 2 0 ^ 8 . 4 8 8 • 6 . 7 5 4 • 5 . 3 3 8 • 3 . 0 0 6 .13.110 7.032 6.437 0./132 3 7 . 5 0 . 1 4 7 4 2 . 7 0 . 3 9 0 111 .0 0 . 1 4 8 4 3 . 0 0 . 1 8 7 __53..._i_ 6 . 1 4 9 4 2 . 2 0 . 1 1 8 3 3 . 4 0 . 0 6 6 1 8 . 8 : 0 .289. 8 2 . 1 0 . 1 5 5 4 3 . 9 0 . 1 4 2 4 0 . 2 1 5 9 . 0 176.9 4 6 9 . 0 178.1 1 , 3 8 8 . 3 1 , 0 9 6 . 4 5 3 8 . 3 9 4 6 . 2 2 1 4 0 . 5 8 0 . 0 3A-LA 18673 1 7 0 . 6 .775-950 9 5 5 - 5 1 1 0 . 0 1 6 . 8 1 , 0 0 0 . 7 9 7 2 . 9 - 103 -TABLE IV, Water Balance Data Date Water from Feed Dr ink-ing Water Meta-bol ic Water from Feed Insens-ible Water Loss Fecal Water Loss Urine Water Loss Water. Balance 16/17 17/18 18/19 19/20 32.2 ' Tri« i l 1 0 ctober (1 3 - l ) 887 428 406 1,882 +1,713 + 872 + 166 - 29 2,600 1,300 1,828 no data no dat< 15/16 16/17 17/18 I8/19 19/20 20/21 21/22 22/23 23/24 24/25 25/26 26/27 27/28 1 . / x24.6 52.8 32. 2 50.7 32. 2 Tri< i l 2 J anuary ( l *-5) 962 •828 1,443 258 1,686 1,099 2,126 450 394 634 590 + 206 - 768 - 249 - 918 + 120 - 205 855 - 19 " i 7 9 - 57I - 423 696 700 514 . 1,664 \l,172 1,424 1,606 2,053 2. 471 ^ 495 410 705 632 ~ 163 319 171 360 *47 490 343 435 434 14 168 • 282 224 . 698 613 619 627 437 89 19 , 36 -. 7 117 194 92 58 58 4 22 28 12/13 13/14 14/15 15/16 16/17 17/18 18/19 19/20 20/21 21/22 22/23 1.3 10.9 29.0 27.3 Tr: tal 3 Viarch (R-• 5) 377 837 382 346 372 551 1,598 1,120 361 296 - 520 • 374 - 638 - 676 - 535 +1,281 - 615 -1,076 - 167 63 1,209 ." 832 446 \ 179 1,990 754 1,493 \ 310 • 320 400 " " 9 72 194 191 142 493 597 \ 680 A 367 357 318 628: 420 216 242 64 I6 none 62 103 37. 29 - 104 -T A B L E V. N i t r o g e n D i s t r i b u t i o n Data Date T o t a l Nitro--gen Urea f» N. T.N. Ni t r o g e n D i s t r i b u t i o n A:nm. ~f0 N. T.N. Cr ' N. T T.N. C r ^ N. % T.N. T o t a l % T r i a l 1 ; October ( P - l ) 1 6 / 1 7 23.360 1 7 / 1 8 8 . 8 0 6 I8/19 9 . 2 0 0 I9/2O 43. 221 20.990 90 8.211 93 7.618 82 41.507 96 0. 086 0 . 0 4 4 0.194 0.199 GO. 4 0 . 5 2. 1 0.5 0.530 2.3 0.283 3 * 2 O.315 3 - 4 1.446 3-3 0.162 0 . 7 0.023 0.3 0.023 0.3 0.069 0 . 2 9 2 . 9 9 7 - 2 8 5 . 6 100.0 T r i a l 2 January (R-5) 16/17 1 7 / 1 $ 18/19 19/20 20/21 21/22 22/23: 23/24 25/26 26/27 27/2$ 2 5 . 3 8 5 : 12. 096 12.929 3. 225 11.719 15.531 10.252 14.537 6.343." ,8.-899 11.501 10.413 24.001 95 10.292 85 10.884 84 2.713 84 10.147 87 14.640 94 9\746 95 13.788 95 - 5 . 7 2 5 90 8.281 93 9.950 87 8 . 6 8 2 83 0.734 2.9 0.913 7.5 1.299 10. 1 0.^274 8 . 5 0:889 7.6 0.254 1.7 0.124 1.2 0.217 1.5 0.115 1.8 0.196 2. 2 0.431 3 . 8 0.621 6. 0 0.601 2 . 4 0.438 3 . 6 0.570 4 . 4 0.145 4 . 5 0.595 5.1 0.566 3 . 7 0.358 3 . 5 0.524 3 . 6 0.246 3 . 9 0.257 2.9 0.371 3 . 2 0.361 3 . 5 0.049 0.153 0.176 0. 002 0.0S9. 0.071 0.025 0. 000 0.016 0.015 0 . 0 6 4 0.050 0. 2 1-3 1-4 0. 1 0 . 8 0 . 5 0. 2 0. 0 0.3 0 . 2 0 . 5 0.48 100. o! 9 7-4 100.0: 9 7 . 2 100. o; 100.0: 100.0 9 9 . 9 9 6 . 3 9 8 . 4 9 4 . 0 9 3 . 3 T r i a l 3; March (R - 5 ) 12/13 13/14 14/15 15/16 1 6 / 1 7 1 7 / 1 8 18/19 19/20 20/21 21/22 22/23 6. 002 6.674 I7 .702 6.720 8." 488 6 . 8 3 4 8 . 0 6 8 10.836 21". 000 7.032 6/437 5.421 90 5.985 90 14.785 84 5.193 77 6.703 79 5.754 $4 • 6.847 85 9-033 83 19.926 95 5.047 72 5.687 88 0.421 0 . 7 0.068 1.1 0.518 2.9 0.516 . ' '7.7 0.641 7.6 0.609 8 . 9 0.740 9 . 2 1.007 9 ' 1 0.372 1.8 0.246 3 . 5 0.361 5 . 6 0.213 3 . 5 0.076 1.1 0.144 0 . 8 0.366 5 . 4 0.467 5-5 0.448 6.6 0.473 5-9 0.612 5 . 7 0.687 3 . 3 O.390 5 . 4 0.334 5 . 2 0 . 0 0 4 0.019 0 . 0 6 4 0.137 0.061 0.023 0 . 0 0 8 0.183 0 . 0 0 0 0 . 0 0 2 0.055 0.1 0.3 0 . 4 2 . 0 0 . 7 0.3 0.1 1-7 0 . 0 0 . 0 0 . 9 9 4 . 6 9 2 . 2 8 7 . 6 9 2 . 4 9 2 . 8 100.0 100.0 100.0 9 9 - 9 8 0 . 9 9 9 . 9 1 1 - 1 0 5 -TABLE VI. Metab o l i c Rate Determination Data, and Required Changes i n Body Composition at the R.Q. of 0 . 8 2 Date O2 Cons-umpt i o n i n L i t e r s Value of 0 2 i n C a l s at R.Q. of 0 . 8 2 Grams of Body Fat f o r NPN C a l s Grams of Body CHO f o r NPN C a l s Pounds of T o t a l Wt. Loss Prot. -Ass. Water Prot. Alone T r i a l 1 October ( P - l ) no d a t a 1 6 / 1 7 1 7 / 1 8 1 0 / 1 9 1 9 / 2 0 2 0 / 2 1 2 1 / 2 2 2 2 / 2 3 2 3 / 2 4 2 4 / 2 5 2 5 / 2 6 2 6 / 2 7 2 6 / 2 7 2 7 / 2 8 T r i a l 2 January (R - 5 ) 3 3 9 - l S . 2 5 2 . 76 2 7 5 . 7 3 3 0 2 . 0 0 2 7 2 . 4 5 2 4 2 . 9 1 3 3 1 - 5 3 3 5 9 - 7 3 3 7 7 - 4 9 2 6 9 . 1 7 2 5 1 . 7 6 2 4 9 . 4 8 2 5 6 . 0 4 , 6 3 6 : 5 , 2 1 9 . 6 , 3 3 0 . 4 , 4 5 7 . 2 , 3 1 4 . 6 , 1 7 2 . 0 , 5 9 9 . 6 , 7 3 6 . 0 , 8 2 1 . 4 , 2 9 8 . 7 , 2 1 4 . 7 , 2 0 3 . 7 , 2 3 5 . 4 1 0 0 . 7 75-1 8 1 . 9 * 8 9 . 7 ' 8 0 . 9 7 2 . 1 \ 9 8 . 5 I O 6 . 9 1 1 2 . 1 8 0 . 0 7 4 . 8 7 4 . 1 . 7 6 . 0 1 3 . 2-1 5 . 0 I 6 . 4 1 7 . 9 1 6 . 2 1 4 . 4 1 9 . 7 2 1 . 4 2 2 . 4 1 6 . 0 1 7 . 0 16.8 1 7 . 2 7 2 4 . 5 4 0 0 . 7 4 3 0 . 8 1 7 7 . 9 2 2 1 . 7 1 4 5 . 4 1 5 9 . 1 1 9 4 - 1 1 7 4 . 8 3 1 4 . 6 3 7 8 . 5 3 5 3 . 6 2 4 8 . 7 1 7 3 . 9 1 8 8 . 4 1 1 7 . 3 1 2 0 . 3 1 2 5 . 0 1 3 6 . 0 1 4 9 . 4 1 1 5 . 7 1 4 7 . 5 1 6 2 . 8 1 5 8 . 3 1 2 / 1 3 1 3 / 1 4 1 4 / 1 5 1 5 / 1 6 1 6 / 1 7 1 7 / 1 8 1S/19 1 9 / 2 0 1 0 / 2 1 2 1 / 2 2 2 2 / 2 3 T r i a l 3 March (R - 5 ) 3 2 0 . 6 8 2 6 3 . 8 9 1 8 8 . 0 4 2 3 3 . 0 2 2 0 7 . 3 3 2 3 7 . 7 8 2 9 3 . 3 5 2 2 8 . 20 2 6 l . l 6 2 4 6 . 0 1 2 4 6 . 0 1 1 , 5 4 7 . 3 1 , 2 7 3 . 3 9 0 7 . 3 1 , 1 2 4 . 3 1 , 0 0 0 . 4 1 , 1 4 7 . 3 1 , 4 1 5 . 4 1 , 1 0 1 . 1 2 6 0 . 1 1 , 1 8 7 . 0 1 , 1 4 3 . 5 9 5 . 2 7 8 . 4 5 5 . 9 6 9 . 2 6 1 . 6 7 0 . 6 8 7 . 1 6 7 . 8 7 7 : 6 7 3 . 1 7 0 . 4 1 9 . 0 1 5 . 7 1 1 . 2 13.8 1 2 . 3 1 6 . 1 ' 1 7 . 4 [13. 5 1 5 . 5 1 4 . 6 1 4 . 1 2 6 4 . 2 2 6 4 . 9 5 1 1 . 1 2 5 5 . 0 2 8 6 . 3 2 5 5 . 5 2 3 8 . 1 1 5 6 . 5 4 2 1 . 5 2 6 3 . 3 2 4 5 . 3 1 5 1 . 7 1 3 6 . S 1 7 8 . 1 1 2 6 . 0 1 2 7 . 0 1 2 8 . 8 1 3 7 . 9 1 0 0 . 0 1 7 5 . 2 1 3 1 . 6 1 2 4 . 7 TABLE V I I . N i t r o g e n E x c r e t i o n During Growth Dat e I960 J u l y 2 4 / 2 5 Aug. 4 / 5 1 7 / 1 8 Aug. 3 1 -3 ep t. 1 Sept 1 5 / 1 6 Oct. 2 0 / 2 1 Dec. 2/3 3 / 4 4 / 4 4 / 5 i 9 6 0 2 6 / 2 7 J u l y 3 5 Aug. 2 5 / 2 6 & Sept. 6 / 7 8 0 2 0 / 2 1 9 2 Dec. 6 / 6 1 7 0 7 / 7 7 / 8 11 S/8 8 / 9 it Age i n Days (appr.) 3 5 ' 4 5 5 5 1° . 8 5 1 2 2 I65 11 11 11 Veight i n Kg. 6 . 8 8 . 2 9 . 3 1 3 . 8 1 9 . 3 2 7 . 2 ti it 11 8 . 6 1 1 . 6 1 4 . 7 1 7 . 9 3 0 . 8 it 11 11 Volume of Ur ine i n cc. Time Int er-v a l Taken f o r T r i a l (hours) T o t a l N i t r o g e n Excreted i n U r i n e Gr./dy Ammonia N i t r o g e n %T.N. Male B l a c k - t a i l e d Deer 4 3 0 4 0 0 6 5 7 5 6 2 5 1 8 8 6 2 1 , 3 6 9 1 , 1 0 0 4 2 0 5 6 O 2 1 . 18 1 8 5, 18 -1 7 . 3 1 2 . 2 2 4 2 4 1 2 1 2 4 . 7 2 8 9 . 5 5 2 8 . 0 6 4 6 . 7 9 2 9 . 4 0 8 1 6 . 3 3 9 1 3 . 8 7 7 1 0 . 1 0 4 . 1 4 . 2 3 2 3 . 0 4 1 . 2 0 7 . 2 2 9 . 7 0 5 . 9 4 2 . 1 3 3 . 0 6 J 2 . 4 7 -2 . 5 2 B - 6 : M a l e B l a c k - t a i l e d Deer 4 6 0 _ 3 . 9 3 6 1 1 . 3 0 7 4 2 18 ' 7 . 2 0 0 1 . 9 6 4 4 2 2 2 8 . 2 6 5 3 . 3 1 7 7 3 1 9 . 3 9 . 6 0 0 3 . 1 4 8 5 0 1 2 . 5 2 0 . 7 6 O O . 5 8 9 1 0 1 2 2 2 . 4 9 5 0 . 8 4 7 8 0 1 2 1 5 . 9 1 2 2 . 66 6 2 0 12 1 2 . 0 9 6 1. 64 7 8 0 12 I 4 . 4 2 4 2 . 9 6 T o t a l i n Gr, 1 . 4 4 0 0 . 1 1 5 O v 5 8 2 0 . 6 5 9 , 0 . 5 5 9 0 . 9 4 4 0 . 3 4 8 0 . 4 2 5 0 . 3 2 4 0 . 3 5 9 0 . 4 4 5 0 . 1 4 1 0 . 2 7 3 0 . 3 0 1 0 . 1 2 0 0 . 1 8 9 0 . 4 2 3 0 . 1 9 8 0 . 4 2 7 Urea N i t r o g e n %T. N. -28. 5 9 6 . A 9 4 . 6 9 0 . 3 6 8 . 7 9 0 . 7 8 8 . 3 5 2 . 7 9 4 - 3 9 4 - 5 9 5 - 6 9 4 . 7 9 7 . 2 T o t a l In Gr 1.-350 9 . 2 0 8 7 . 6 2 9 6 . 1 3 3 6 . 4 6 3 1 4 . 8 1 9 1 2 , 4 7 5 8 . 9 2 2 7 . 5 0 0 6 . 7 9 0 7 . 8 0 2 9 . 1 7 8 2 1 . 3 0 3 1 4 . 0 2 0 Creat i n e N i t r o g e n ^ T T N . 0 . 6 4 1 . 1 5 1 . 3 3 0 . 9 3 0 . 8 7 0 . 8 9 1 . 4 2 0 . 6 1 0 . 9 6 0 . 1 1 0 . 8 1 0 . 6 3 0 . 7 7 0 . 1 7 T o t a l i n Gr, 0 . 0 3 1 -0 . 110 0 . 1 0 7 0 . 0 8 7 < 0 . 1 4 2 0 . o ;90 0 . 1 0 2 0 . 0 5 0 0 . 0 9 2 0 . 0 2 3 0 . 1 8 2 0 . 1 0 0 0 . 0 9 3 0 . 0 2 5 Great i n i n e N i t r o g e n $T. N. -I.-44 1. 26 1 . 8 2 1 . 5 4 5 . 3 6 9 . 2 5 2 . 27 I . 3 6 2 . 4 9 2 . 0 4 I . 8 4 2 . 14 2 . 3 9 2 . 6 3 T o t a l i n Gr. 0 . 0 6 8 0 . 1 2 0 0 . 1 4 7 0 . 1 4 5 0 . 3 0 1 0 . 8 7 6 0 . 9 3 5 0 . 1 6 3 0 . 1 1 2 0 . 239 0 . 4 2 4 0 . 4 1 4 0 . 3 4 1 0 . 2 8 9 0 . 3 7 9 T o t a l N i t r o g e n Expressed as N./Kg./dy 0 . 6 9 5 1. I 6 5 O . 8 6 7 0 . 6 8 2 0 . 6 0 1 0 . 5 1 0 0 . 3 7 1 0 . 5 2 3 0 . 4 5 7 0 . 621 0 . 5 6 2 0 . 5 3 6 0 . 6 7 4 0 . 7 3 0 0 . 5 1 7 0 . 3 9 3 0 . 4 6 8 C r e a t i n i n e N i t r o g e n Expressed as N./Kg./dy 0 . 0 0 1 0 . 0 1 5 0 . 0 1 6 0 . 0 1 6 < 0 . 0 1 6 0 . 0 3 2 O.O34 0 . 014 0 . 008 0 . 0 1 3 0 . 0 1 4 0 . 0 1 3 0 . 011 0 . 0 0 9 0 . 0 1 2 TABLE V I I I . N i t r o g e n E x c r e t i o n During Growth Date Age i n Days (appr.) Weight i n Kg. Volume of Dr ine i n cc. Time I n t e r -v a l Taken f o r T r i a l (hours) T o t a l N i t r o g e n E x c r e t e d i n U r i n e Gr./dy Ammonia N i t r o g e n %T. N. T o t a l i n Gr, Urea N i t r o g e n T o t a l i n Gr. Great i n e N i t r o g e n J6T.N. T o t a l i n Gr C r e a t i n i n e N i t r o g e n %T.N. T o t a l i n Gr, T o t a l N i t r o g e n E x p r e s s e d as N./Kg./dy Creat i n i n e N i t r o g e n Expressed as N./Kg./dy I960 J u l y 29/30 Aug. 10/11 23/24 i 9 6 0 Aug. 1/2 11/12 24/25 Sept. 12/13 23/24 Nov. 1/2 Dec. 19/19 19/20 20/20 20/21 21/22 42 52 65 40 50 65 •85 95 18.5 8 . 6 1 0 . 7 1 2 . 2 R -7: Male B l a c k - t a i l e d Deer 330 428 312 21 16. 5 18.1 4. 944 7.224. 7.512 2. 83 2.39 6 . 6 7 P.-8: Male B l a c k - t a i l e d De'er 11.6 554 6. 264 3 . 5 9 •' — 592 18 - -15.5 617 18.5 1.920 3.13 20. 0 537 1 7 . 7 9 . 6 4 8 3 . 1 2 19.1 556 16 9 . 4 0 8 8 . 5 9 1 8 . 8 790 10.8 - -3 6 . 3 1,220 13 - 0.10 11 1,040 11 23.112 1.25 11 1,620 12 16.200 1. 00 11 1,860 12 2 0 . 0 4 6 1.28 n 1,180 12 21.672 1.49 0.140 0.173 0.501 0 . 2 2 8 0.543 0 . 0 6 0 0.310 0 . 8 0 8 0.203 0.2S9 0 . 1 6 2 .0.257 0.323 9 3 . 7 3 3 . 3 55.1 5 2 . 0 68.1 8 7 . 3 9 0 . 9 9 5 - 5 100. 0 96.1 6.769 2.501 3 . 4 5 0 0.154 0 . 9 6 0 6 570 8. 213 2 0 . 2 6 0 21.009 15.471 2 0 . 0 4 6 2 0 . 8 7 2 1.86 1 .50 7-77 1.24 1 .00 0 . 9 8 1 0 . 4 8 0 . 1 0 0 . 8 6 0 . 1 3 4 0. 094 0 . 1 5 4 0.149 0.120 0 . 0 9 4 0.931 0. 226 0 . 3 4 0 0.016 0.186 2. 01 2 . 0 4 0.145 0.153 0 . 4 6 4 0 . 4 6 4 2. 26 0.142 0 . 5 4 0 0.207 10. 99 0. 211 0 . 1 2 4 2. 35 0.190 0.356 3- 19 0.300 e-. 493 0.405 -— 0. 634 2. 03 O . 4 6 9 0 . 6 3 7 2. 81 0.577 0 . 4 6 6 2. 54 0.509 0 . 5 5 2 2. 12 0.459 0 . 5 9 7 0.014 0.013 0 . 0 1 2 0. 014 0. 011 0.016 0. 022 0.013 0.016 0.014 0.013 TABLE IX. N i t r o g e n E x c r e t i o n During Growth Date Age i n Days (appr.) Weight i n Kg. Volume of TJr ine i n cc. Time I n t e r -v a l Taken f o r T r i a l (hours) T o t a l N i t r o g e n E x c r e t e d i n U r i n e Gr./dy \ Ammonia N i t r o g e n foT. N. T o t a l i n Gr. Urea N i t r o g e n %T.N. T o t a l i n Gr. Creat ine N i t r o g e n ^T.N. T o t a l i n Gr. C r e a t i n i n e N i t r o g e n #T.N. T o t a l .^ i n Gr. • x • T o t a l N i t r o g e n Expr essed as N./Kg./dy C r e a t i n i n e N i t r o g e n Expressed as N./Kg./dy I960 J u l y Aug. 2/3 29/30 Sept.13/14 Oct. 18/19 Nov. 29/30 1961 Jan. 16/17 18/19 sa. 30 40 70 85 120 I65 214 it •1 3.6 7.8 10.4 15.9 23.1 2 V 11 100. 0 77.2 2.477 75.3 7.952-1 77.1 9-790 91.0 6.923 94.4 7.98S 88.2 11.029 • . • •- -- •' \ O.97 0.032 2.73 0.157 0.052 1.32 0.139 O.75 0.095 1.27 0.097 0. 56 0.047 O.34 0.043 / . ' •I I.48 0.035 1.43 0.046 1-57 0.090 0.130 1.67 0.176 1.61 0.204 5.68 0.432 2. 92 0.247 4.94 0.618 0.653 0.782 0.735 0.664 0.550 0.275 0.306 0.451 0. 010 0.011 0.012 0.013 0.011 0.009 0.016 0.009 0.223 E-9: Male B l a c k - t a i l e d Deer 1 300 325 365 ;365 592 373 . 860 450 160 21 17.7 19.5 18.3 17 ' 12 24 24 24 2.352 3.209 ' 5.736 10.560 12. 698 7.608 8.472 12.504 9.77 O.23O O.55 0.018 ^7.51 0.431 6.00 0.634 2.12 0.269 2.01 0.153 2.08 0.176 TABLE X. N i t r o g e n E x c r e t i o n During Growth Date Age i n Days (appr.)" Weight i n Kg. Volume of U r i n e i n c c. T ime Int e r -;va l Taken f o r T r i a l (hours) T o t a l N i t r o g e n E x c r e t e d i n U r i n e Gr./dy Ammonia N i t r o g e n %T. N. T o t a l i n Gr, Urea N i t r o g e n T o t a l i n Gr, Cr eat ine N i t r o g e n T o t a l i n Gr. C r e a t i n i n e N i t r o g e n J6T.N. T o t a l i n Gr, T o t a l N i t r o g e n Expressed as N./Kg./dy C r e a t i n i n e ., N i t r o g e n Expressed as '• N./Kg./dy i 9 6 0 J u l y 2 1 / 2 2 Aug. 3 / 4 1 6 / 1 7 3 0 / 3 1 Sept 1/2 1 4 / 1 5 2 2 / 2 3 Oct. 1 9 / 2 0 Nov. 3 0 -Dec. 1 1961 Jan. 11/11 1 1 / 1 2 1 2 / 1 2 1 2 / 1 3 1 3 / 1 3 1 3 / 1 4 R - l : Female B l a c k - t a i l e d Deer 3 0 4 5 5 5 7 0 70 $ 5 9 0 1 2 0 1 6 5 204 •» it 11 11 1:1 9 . 8 1 2 . 5 I 5 o 0 2 0 . 0 89 .5 II II , II • II 3 7 0 3 7 9 6 2 0 , 7 1 8 5 7 6 3 7 2 2 8 5 5 8 8 4 2 0 0 2 0 8 2 0 84O 21 18 18 1 8 . 5 1 8 1 8 . 6 18 1 6 . 5 - r i T 6 1 2 12 12 24 1 2 1 2 2 . 1 1 2 5 . 2 3 2 7 . 1 2 8 3 . 6 0 0 5 ^ 8 0 8 3 . 3 8 4 1 2 . 9 3 6 6 . ,768 i o . i 4 . 8 8 1 6 . 6 0 8 1 7 . 5 4 4 1 7 . 4 2 4 1 5 . 9 3 6 2 0 . 3 2 8 1 . 5 5 3 . 3 6 9 . 7 0 1 8 . 4 5 . 6 9 9 . 8 3 1 9 . 0 3 5 - 5 9 1.20"^ 0 . 8 7 1 . 2 1 0 . 3 8 0 . 9 9 - 0 . 9 2 0 . 3 2 0 . 0 3 3 0 . 1 7 6 0 . 6 9 1 0 . 6 6 2 0 . 5 7 1 0 . 6 4 4 0 . 7 2 3 0 . 0 8 1 0 . 0 9 1 0 . 201 0 . 0 6 7 0 . 1 7 2 0 . 1 4 7 0 . 0 7 7 6 5 . 8 7 5 . 2 8 8 . 4 6 8 . 3 9 0 . 5 9 1 . 7 8 l ? 6 1 ^ 8 9 3 - 9 3 4 6 . 5 0 8 3 . 1 8 2 3 . 9 6 7 6 . 1 2 5 9 . 6 1 7 1 6 . 5 8 8 0 . 5 0 1 . 3 4 0 . 9 6 0 . 5 0 1 . 3 4 3 . 2 5 0 . 61 0 . 4 5 O.O57 o~68 6. o i l 0 . 0 7 0 0 . 0 6 8 0 . 0 1 8 0 . 1 0 0 0 . 4 2 0 0 . 0 6 4 0 . 0 7 5 0 . 1 0 0 0 . 1 3 8 4 . 3 7 2 . 0 1 1 . 6 2 1 . 7 9 2 . 3 9 1 . 7 2 6 . 8 8 1 . 7 6 2 . 2 6 3 . 3 6 2 . 3 5 2 . 4 0 2 . 21 0 . 0 9 2 0 . 1 0 5 0 . 1 1 5 0 . 0 6 4 0 . 1 0 0 0 . 2 3 3 0 . 2 2 8 0 . 2 3 0 . 5 5 8 0 . 4 1 2 0 . 3 8 2 0 . 4 4 9 0 . 2 8 9 0 . 6 0 8 0 . 7 2 7 0 . 2 8 8 0 . 3 S 7 6 . 4 7 0 . 3 5 6 0 . 5 6 3 0 . 5 9 5 0 . 5 9 1 0 . 5 4 0 0 . 6 8 9 0 . 1 2 6 0 : 0 1 2 0 . 0 1 2 0 . 0 0 5 0 . 0 0 7 0 . 1 1 4 0 . 0 0 S 0 . 0 1 9 0 . 0 1 4 0 . 0 1 3 0 . 0 1 5 TABLE X I . N i t r o g e n E x c r e t i o n During Growth Date I960 J u l y 28/29 Aug. 9/10 19/20 Sept. 7/8 Oct. 13/14" 24/25 26/27 . 27/28 Dec. 12/12 12/13 13/14 14/14 14/15 i 9 6 0 J u l y 25/26 Aug. 8/9 ; 18/19 21/22 Sept. 1/2 19/20 Age i n Days (appr. ) 42 l l 80 115 125 11 130 175 11 ti 11 »• . 35 60 65 70 90 Weight i n Kg. 8.9 10. 2 12.7 22. 7 22:7 29.0 11 11 11 »i 7.5 10. 1 1 0 . 8 13.0 Volume of Ur ine i n cc. Time Int e r-v a l Taken f o r T r i a l (hour s) T o t a l N i t r o g e n E x c r e t e d i n U r i n e Gr./dy Ammonia N i t r o g e n %T. N. T o t a l i n Gr. R-5: Female B l a c k - t a i l e d Deer 440 4 12 428 647 1, 260 884 676 706 680 1,280 1, 260 420 680 2 0 . 5 19.8 19 .8. 19.6 24 12 12 12 12 12 24 12 12 5.6AO 7 . 4 6 4 7.776 6.312 13.142 18. 120 12.816 16.680 16. 704. 16. 242 10.496 20. 692 4. 6 l 1. 56 O.59 1.68 1.95 1.71 0.61 0.344 0.121 0,. 078 0 . 3 0 4 0. 250 0. 285 0.101 R-12: Female B l a c k - t a i l e d Deer 650 820 491 778 791 847 20 16 18 18 19 19 7 . 0 3 2 6. 072 4-152 6. 600 1.13 5.91 3 . 8 3 9 . 8 6 Urea Ni t r o g e n /oT.N. 8 4 . 7 91, 2 9 7 . 4 9.6.5, 9 5 - 9 9 8 . 3 9 5 . 7 9 7 - 8 9 7 . 5 44--3 78.4 4 6 . 3 T o t a l i n Gr, 4- 777 6 . 8 0 7 7 .574 12. 603 17.812 12. 265 16.313 16.286 2. 590 1 . 0 4 5 2. 080 C r e a t i n e N i t r o g e n 1.19 1. 03 0. 01 0 . 2 8 I o i 11 0 * 8 4 0 . 3 6 0 . 4 9 0 . 6 4 0. 25 1.46 T o t a l i n Gr, 0 . 0 6 7 0 . 0 7 7 0. 008 o»oi8 0 . 0 1 4 0 . 1 0 8 0 . 0 6 0 0 . 0 7 9 0 . 0 6 7 0 . 0 5 2 0 . 0 8 7 0. 112 Creat i n i n e Nitrosen J6T.N. 2. 29 2 . 2 8 O .98 2. 17 3 . 4 2 2~2S I.83 2. 73 2.75 2.-92 2. 19 T o t a l i n Gr, 0.013 0.170 0.076 0.137 0.449 0.292 O .305 0.444 0. 260 O.-289 0.-604 0.013 0. 203 T o t a l Ni t r o g e n Expressed as N./Kg./dy 0 . 6 3 7 0. 732 0.612 O.565 O.565 0.735 0.576 O .560 0 . 3 7 2 O.714 O .938 0.411 0 . 5 0 8 . Great i n i n e N i t r o g e n Expr essed as N./Kg./dy 0.015 0.017 0. 006 0.013 0 . 0 1 3 0.015 0 . 0 0 9 0. 010 0. 021 Fig. 1 . Course%f nitrogen balance obtained.-.on R-5 in Trial II. + 20 -30 I 1 ' ' • 1 1 • « ' ' ' < -0 1 2 3 4 5 6 7 8 9 1 1 ) 1 1 24 HOUR PERIODS IN CALORIMETER Fig. 2. Course of nitrogen.; balance obtained on R-5 i n T r i a l I I I . F A S T I N G D A Y S D A Y S O N F E E D F A S T I N G D A Y S F A S T I N G D A Y S . .. D A Y S O N F E E D F A S T I N G D A Y S F i g . 5. C h a n g e s " i ~ n n i t r o g e n d i s t r i b u t i o n d u r i n g t h e b a l a n c e t r i a l s , s h o w i n g t h e c h a n g e s i n p e r . . c e n t " t o t a l riit"rogerrcyf u r e a , a m m o n i a , a n d c r e a t i n i n e n i t r o g e n , d u r i n g - p e r i o d s — - - - - - — o f f a s t i n g a n d o f f e e d i n g v - - ' - T h e - a m o u t i - t - e f ^ g ^ i s i ^ r b l e n i t r o g e n i n t a k e , i n g r a m s , i s . - .shown i n t h e l o w e r r i g h t h a n d c o r n e r . / 22 • i i _ L _ 1 — ; 1 : L_ 5 10 15 " "~ 20 25 30 35 BODY WEIGHT IN KILOGRAMS . — _.Fig..'.J8.._.The^c_h.gng.e i n r a t e o f i n c r e a s e i n m a g n i t u d e o f t o t a l n i t r o g e n e x c r e t i o n w i t h i n c r e a s e i n body s i z e , i n -grossing b l a c k - t a i l e d d e e r . Fig. ;• 10. The cumulative change in total nitrogen excretion with increase in age, in growing male black-tailed deer. * . % 1.00 Q Fig. H i the curtailative change in total creatinine excretion with increase in body size, la-growing blackmailed deer. - 122 -C o n c l u s i o n The crude p r o t e i n requirement of R-5 has been c a l c u l a t e d , o n the b a s i s of the experimental v a l u e o b t a i n e d f o r the endogenous l e v e l of t o t a l u r i n a r y n i t r o g e n e x c r e t i o n to be approximately 25 grams. T h i s v a l u e i s taken as the most a c c u r a t e estimate of the minimum p r o t e i n requirement, f o r a p r o t e i n of p e r f e c t b i o l o g i c a l v a l u e and 85 per cent d i g e s t i b i l i t y , f o r a r e p r e s e n t a t i v e of the s p e c i e s . The v a l u e s were o b t a i n e d on a 100 pound doe and, t h e r e f o r e , comparative v a l u e s from a male of the s p e c i e s would be of i n t e r e s t . The crude p r o t e i n requirement based on the p o i n t of n i t r o g e n balance i n d i c a t e s a much l a r g e r requirement. T h i s l a t t e r estimate i s taken as a r e p r e s e n t a t i v e v a l u e f o r the maintenance of i d e a l n u t r i t i o n a l s t a t u s w i t h r e g a r d to p r o t e i n n u t r i t i o n . Although t h e r e are l i m i t a t i o n s to the n i t r o g e n balance method as a method of d e t e r m i n i n g n i t r o g e n r e q u i r e -ments, the r e s u l t s are of c o n s i d e r a b l e v a l u e because they are based on d i r e c t measurements of the c h a r a c t e r and extent of n i t r o g e n metabolism i n an experimental animal. Measure-ments on the c h a r a c t e r of n i t r o g e n metabolism on an animal such as the one used i n t h i s experiment are of p a r t i c u l a r s i g n i f i c a n c e because they are r e l a t e d to the extent of n i t r o -gen turnover a s s o c i a t e d w i t h an animal which has a l a r g e amount - 123 -of p r o t e i n r e s e r v e s . They are i n d i c a t i v e of the extent, and ch a r a c t e r of n i t r o g e n i n t a k e r e q u i r e d to produce a hig h p l a n e of p r o t e i n n u t r i t i o n a l s t a t u s i n a s i m i l a r animal. T h i s requirement may be s t a t e d i n q u a n t i t a t i v e terms once the degree of s i m i l a r i t y between the experimental animal, and the second animal under c o n s i d e r a t i o n , has been thoroughly e s t a b l i s h e d . T h e r e f o r e , i t i s p o s s i b l e i n p r i n c i p l e to extend the r e s u l t s o b t a i n e d from experiments such as the present one to animals under range c o n d i t i o n s , , p r o v i d e d the r e l a t i o n s h i p between the experimental animal and the game animals i s p r o p e r l y understood. Measurements of n i t r o g e n e x c r e t i o n made d u r i n g the growing p e r i o d have been found, i n t h i s experiment, to be i n d i c a t i v e of the nature of n i t r o g e n requirements a s s o c i a t e d w i t h the r a t e and c h a r a c t e r of growth. The same a p p l i c a t i o n of these r e s u l t s to range animals, as d i s c u s s e d above f o r t r i a l s on a d u l t animals, i s t h e o r e t i c a l l y p o s s i b l e . The measurement of n i t r o g e n e x c r e t i o n under v a r y i n g c o n d i t i o n s of growth, and of metabolic r a t e , can thus be seen to be of v a l u e i n p r o v i d i n g complementary i n f o r m a t i o n to that o b t a i n e d i n f i e l d s t u d i e s , f o r the grea t e r understanding of the s i g n i f i c a n c e of f i e l d c o n d i t i o n s i n terms of the s u c c e s s f u l management of game animals. i - 124 -Appendix I F o r m u l a t i o n f o r U n i v e r s i t y of B r i t i s h Columbia  Beer Weaning Ration. No. 36-S-6Q. Pounds Pounds Const i t u e n t per ton per 100 Ground No. 5 f e e d wheat 660 33-00 Ground oat g r o a t s 260 13.00 Ground wheat bran 200 10. 00 Ground y e l l o w corn 200 10. 00 F i s h meal (70%) h e r r i n g 200 10. 00 Soybean meal (50%) 100 5.00 Skim m i l k powder (spray) 200 1.0.00 • Dehydrated grass 100 5.00 D i c a l c i u m phosphate 10 0.50 I o d i z e d s a l t 15 0.75 S t a b i l i z e d animal f a t 50 2. 50" V i t a m i n pre-mix : 5 0.25 2, 000 100.00 F o r m u l a t i o n f o r U n i v e r s i t y of B r i t i s h Columbia Adult R a t i o n f o r Deer. No. 36-57-Pounds Pounds C o n s t i t u e n t per ton per 100 Ground y e l l o w corn 600 30.00 Ground No. 5 f e e d wheat 250 12. 50 Ground wheat bran 275 13.75 Molasses (cane) 150 7.50 Ground beet p u l p 200 10.00 Dehydrated grass meal 200 10. 00 Soybean meal (50%) 175 8.75 F i s h meal (70%) h e r r i n g 110 5.50 Steamed bone meal 20 1. 00 I o d i z e d s a l t 20 1.00 2,000 100.00 - 125 -Appendix I I Ammo n i a f o rmat i o n i The amino/ a c i d s serve as the source of blo o d and u r i n -a r y ammonia. The p r o d u c t i o n of ammonia w i t h i n the g a s t r o i n t e s t i n -a l t r a c t by.the a c t i o n of i n t e s t i n a l b a c t e r i a on n i t r o g e n o u s s u b -stances a c c o u n t s \ f o r the h i g h ammonia content of the p o r t a l blood. The kidney a l s o produces ammonia and adds i t to the bloo d of the r e n a l v e i n . O x i d a t i v e deamination of amino a c i d s i n the l i v e r ad.ds a f u r t h e r f r a c t i o n depending upon the s u r p l u s of amino a c i d s not taken up i n p r o t e i n s y n t h e s i s . Most of t h i s ammonia i s converted to ur e a w i t h i n the l i v e r as shown i n Appen-d i x LTX However, a small remainder and an important p o r t i o n p r o -duced by the kidney t u b u l e c e l l s i s e x c r e t e d i n t o the u r i n e . T h i s p r o c e s s i s an important mechanism f o r the c o n s e r v a t i o n of f i x e d base, see below. Glutamine i s the most important amino a c i d source of ammonia from deamination, as f o l l o w s : . c H i . _ J s » c H ^ C O O H coow A diagram i s shown below of the mechanism f o r the e l i m i n a t i o n of hydrogen ions by combination w i t h ammonia w i t h i n the t u b u l e c e l l or i n the t u b u l a r f i l t r a t e . - 126 -BLOOD COa. or- ftnuiJo PS - IBS —> N B j - - _ . ' \ TUI3V1-E' CEi-L. H No?" -v- C L * +• • • - 127 -Appendix I I I . A schematic r e p r e s e n t a t i o n of the b o d i l y f o r m a t i o n of u r e a i s shown on the f o l l o w i n g page. Blood ammonia enters i n t o the s e r i e s of r e a c t i o n s which l e a d u l t i m a t e l y to the form-a t i o n of u r e a by combining w i t h and phosphate to form c a r -bamyl phosphate. T h i s p r o c e s s r e p r e s e n t s an a c t i v a t i o n of ammonia which i s necessary i n order to enable i t to enter the a r g i n i n e - o r n i t h i n e c y c l e . The a r g i n i n e - o r n i t h i n e c y c l e con-s i s t s of a s e r i e s of r e a c t i o n s connected w i t h u r e a f o r m a t i o n the most important of which i s the i n t e g r a t i o n w i t h a segment of c i t r i c a c i d c y c l e . T h i s i n t e g r a t i o n p r o v i d e s a c a t a l y t i c r e t u r n of a s p a r t i c a c i d , formed d u r i n g the f o r m a t i o n of a r g i n i n e , to the beginning of the c y c l e , where i t r e a c t s w i t h carbamyl phosphate to f a c i l i t a t e the entrance of the carbamyl group to the a r g i n i n e - o r n i t h i n e c y c l e . The a s p a r t i c a c i d molecule thus a c t s as a t r a n s f e r agent f o r the carbamyl group. There are three other amino a c i d s d i r e c t l y connected w i t h u r e a formation. These are a r g i n i n e , o r n i t h i n e and c i t r u l l i n e . A s p a r t i c a c i d i s formed i n two ways i n a s s o c i a t i o n with u r e a formation. I t i s r e a d i l y a v a i l a b l e by the t r a n s a m i n a t i o n of o x a l o a c e t i c a c i d from the c i t r i c a c i d c y c l e , and i s a l s o formed from o r n i t h i n e . O r n i t h i n e and c i t r u l l i n e a r i s e from a r g i n i n e d u r i n g the a c t u a l f o r m a t i o n of urea. The f o r m a t i o n of a r g i n i n e from a r g i n i n o -s u c c i n i c a c i d r e s u l t s i n the s p l i t t i n g o f f of fumaric a c i d which then enters the c i t r i c a c i d c y c l e , thus l i n k i n g the c i t -r i c a c i d c y c l e w i t h the a r g i n i n e - o r n i t h i n e c y c l e . - 128 -7. i o i CC or 2 it o F c x s- <c~ rl 3r Oil- X • Z i l l X ul of CL 2-0 J - 129 -Appendix I V . C r e a t i n i n e and C r e a t i n e Formation i C H - i H C - N H v C O O H O f t S Y r T I N t i N J e — <CH 3 Livers s ^ 1 riw - c C = COOH C,iif:,.rJiOoP>tcT>c HM - C SJ - e - c = o The f o r m a t i o n of c r e a t i n i n e and c r e a t i n e i s o u t l i n e d s c h e m a t i c a l l y above.' C r e a t i n i n e i s formed from g u a n i d o a c e t i c a c i d by the removal of a. s i n g l e methyl group. T h i s a c t i o n takes place' i n the l i v e r and the c r e a t i n i n e thus formed i s transported to the t i s s u e s . C r e a t i n e i s produced i n the t i s s u e s f o r the purpose of high energy bond storage, and t h e r e f o r e to f a c i l i t a t e energy metabolism. Because c r e a t i n e remains where i t i s formed, and i s of v a l u e to the t i s s u e s r a t h e r than being a waste product, i t i s not as e a s i l y l o s t to the u r i n e as c r e a t i n i n e . - 1 3 0 -A b o v e i s s h o w n a s k e t c h o f t h e c a g e u s e d t o r e s t r a i n . [ I j . t h e e x p e r i m e n t a l a n i m a l s d u r i n g t h e m e t a b o l i c t r i a l s . T h e ' [ f e c a l s c r e e n a n d u r i n e t r a y w e r e p l a c e d on t r a c k s b e l o w t h e f f l o o r of t h e c a g e , a t A . T h e d o o r s c o u l d . b e s h u t t o r e s t r a i n ! t h e a n i m a l w h i l e t h e f r o n t o f t h e c a g e , , s h o w n o n p a g e 1 3 2 w a s b e i n g p r e p a r e d . T h e e n t i r e c a g e w a s p l a c e d w i t h i n a l a r g e . ' r e s p i r a t i o n c a l o r i m e t e r , o u t l i n e d o n p a g e 1 3 2 a . A p p e n d i x V . L a r g e A p p a r a t i - 131 -i R E S T R A I N I N G ftiSES lis/ "THIS uJEUU W H E W T V i C CAC,e II IN THe- c f t u o d iAI sr-nrR. Fee-j> T R A Y ( P f t S S C S OUT T W A O « H t T H E - u r t U . O F T H E C A U 0 f i i m e ' " T 4 i " R t - \ N D C O N N E C T S " T S T H E w P T e a T U < j R O N T CASTORS \^QuNT-f?t> ON SV'tK ' GACK L(=<Ssr T h e f r o n t e n d o f t h e a . n i m a l - c a / g e i s s h o w n a b o v e , f a s t e n e d t o t h e c a g e , p a g e 1 3 0 , d u r i n g m e t a b o l i c t r i a l s t s u p p l i e s w a t e r a n d f e e d t o t h e a n i m a l a d . l i b i t u m . T h e a b o v e s k e t c h i s t h a t o f a n . o u t l i n e o f t h e r e s p i r a t i o n c a l o r i m e t e r . T h e c a g e i s m o v e d i n t o t h e c a l o r i m e t e r o n c a s t o r s w h i c h r u n o n t h e w o o d e n p l a n k s s o . i n d i c a t e d . T h e w a t e r h o s e f r o m t h e c a g e i s t h e n a t t a c h e d t o t h e w a t e r s u p p l y a s i n d i c a t e d a t A . T h e l e v e l s o f w a t e r a r e a d j u s t e d s u c h t h a t a s t h e a n i m a l d r i n k s , t h e s u p p l y i s r e n e w e d . - 133 AppendiX-_YJ,. 90 . 8 0 70 : .60 . 5,0 40 30 20 10 7. TRANSMITTANCE AT- 520 - 134 -Bitaliography Albanese, A.A. A l l i s o n , J.B. Annison, E.F. , and. D. Lewis. Bandy, P.J., I.McT. Cowan, W.D. K i t t s , and A.J. Wood. Beaumont, W. B i s s e l l , H.D. B i s s e l l , H.D., and H. Strong. B i s s e l l , JI.D., B. H a r r i s , H . Strong, and. F. James. B l a i s d e l l , J.P. and W.-F.;;Muegger. 1959 1951 1959 1 9 5 6 1833 1 9 5 2 1 9 5 5 1 9 5 5 1 9 5 6 B l a x t e r , K.L. and H.H. M i t c h e l l . 1 9 4 8 P r o t e i n and Amino A c i d N u t r i t i o n . Academic Press, New York. I n t e r p r e t a t i o n of Ni t r o g e n Balance Data. Fed. P r o c , 1 0 : 6 7 6 - 6 8 2 . Metabolism i n the Rumen. Methuen & Co. L t d . , London. A Method f o r the Assessment of the N u t r i t i o n a l S tatus of W i l d Ungu-l a t e s . 4 8 - 5 2 . Can. Jour, of Z o o l . , 3 4 ' Experiments and Observations on the G a s t r i c J u i c e and the P h y s i -ology of D i g e s t i o n . F.P. A l l e n , P l a t t s b u r g . N u t r i t i o n a l S t u d i e s on C a l i f o r n i a B i g Game. 32nd Proc. An. Conf. Western Assoc. Commissioners, S t a t e F i s h and Game pp. I 7 8 - I 8 4 . The Crude P r o t e i n V a r i a t i o n s i n the Browse Diet of C a l i f o r n i a Deer. C a l i f . F i s h and Game, 4 1 : 1 4 5 - 1 5 5 -The D i g e s t i b i l i t y of C e r t a i n Nat-u r a l and A r t i f i c i a l Foods Eaten by Deer i n C a l i f o r n i a . C a l i f . F i s h and Game, 4 1 : 5 7 - 5 8 . S p r o u t i n g of B i t t e r b r u s h (Pur sh i a  t r i d e n t a t a ) F o l l o w i n g Burning or Top Removal: I n f l u e n c e d by both Genetic and Environmental F a c t o r s . E c o l . , 3 7 : 3 6 7 - 3 7 0 . The F a c t o r i z a t i o n of the P r o t e i n Requirements of Ruminants and of the P r o t e i n Values of Feeds, with P a r t i c u l a r Reference to the S i g -n i f i c a n c e of the M e t a b o l i c F e c a l N i t r o g e n . Jour. Animal S c i . , Ji 351-369. - 135 -Blaxter, K.L., and 1951 W.A. Wood. Block, R.J. I 9 5 6 Block, R.J., and I 9 4 I R. Schoenheimer. Borsook, H., and 1935 G. Keighley. Bourne, G. 1953 Bricker, M. , II.H. 1945 M i tch.e 11,; and G.M. Kinsman. Brinkerkink, P.C. I96I Brody, S. 1945 Burroughs, E.W., H.S.. I94O Burroughs, and H.H. Mi t c h e l l . Butcher, J.E., and 1957 L.E. Harris. Catherwood, S., and 1937 G. Stearns. Chandler, A.C. I 9 5 5 The N u t r i t i o n of the Ayrshire Calf. Br. Jour, of Nut., 5 : 11-25. Protein Requirements of Animals Including Man. Borden's Review of N u t r i t i o n a l Res., 1 ? : 7 5 - 9 6 . The B i o l o g i c a l Precursor of Crea-t i n i n e . Jour. B i o l . Chem., 138: 1 6 7 - I 9 4 . The Continuing Metabolism of Ni-trogen in Animals. Proc. of the Royal Soc. of London, B l l 8 : 4 8 8 -5 2 1 . Biochemistry and Physiology of Nutrition. Academic Press, New York. The Protein Requirements of Adult Human Subjects i n Terms of the Protein Contained in Individual Foods and Food Combinations. Jour, of Nut., 3 0 : 269-28.3. Determination of Creatine in Urine. C l i n . Chem. Acta., 6 : 531-537-Bioenergetics and Growth. Rein-hold Publ. Corp., New York. The Independence of the Endogenous and Exogenous Metabolism of Nitro-gen. Jour, of Nut., 19: 2 7 1 - 2 8 3 . Creatinine as an Index Material for Evaluation of Ruminant Nutri-tion. Jour. Animal S c i . , 16: 1020. Creatine and Creatinine Excretion in Infancy. Jour. B i o l . Chem., 119: 2 0 1 - 2 1 4 . Introduction to Parasitology. 9 t n ed., John Wiley & Sons, Inc., New York. - 136 -Chittenden, R.H.. 1907 Cohneim, 0. 1901 C o n s o l a z i o , F. I 9 5 I Conway, M. 1950 Cook, CW. , L.A. 1954 Stoddard, and L.E. H a r r i s . Cowan, I.McT. I 9 4 5 Cowan, I.McT., and 1955 A.J. Wood Cowan, I.McT., W.S. 1950 Hoar, and J. H a t t e r Darke, S.J. i960 D a r l i n g t o n , P.S. I957 D i e t z , D. 1958 The N u t r i t i o n of Man. F.A. Stokes & Co., New York. Die Unwandlung des E i w e i s s Durch Darmwand. Z. P h y s i o l . Chem., 33: 451-456. M e t a b o l i c Methods. C.V. Mosby Co., St. L o u i s . M i c r o d i f f u s i o n A n a l y s i s and V o l u -m e t r i c E r r o r . C. Lockwood, London. The N u t r i t i v e Value of Winter Range P l a n t s i n the Great B a s i n as Deter-mined with D i g e s t i b i l i t y T r i a l s w ith Sheep. B u l l . 372. Utah Sta. A g r i c . C o l . A g r i c . Exp. Sta. The E c o l o g i c a l R e l a t i o n s h i p s of the Food of the Columbian B l a c k - t a i l e d Deer 0. Hemionus columbianus, (Richardson), i n the Coast F o r e s t Region of Southern Vancouver I s -land, B.C. E c o l . Monographs, 15 1 III-I39. The Growth Rate of the B l a c k -t a i l e d Deer (0. Hemionus columbja-nus). Jour. W i l d l . Mgt., 19: 331-33S. The E f f e c t of F o r e s t S u c c e s s i o n upon the Q u a n t i t y and upon the N u t r i t i v e Value of Woody P l a n t s used as Food by Moose. Can. Jour. Res., 28: 249-271. The Cutaneous Loss of N i t r o g e n i n A f r i c a n A d u l t s . B r i t . Jour, of Nut., 14: I I 5 - I I 9 . Zoogeography. John Wiley & Sons, Inc., New York. Seasonal P r o g r e s s i o n i n the Chemi-c a l Content of F i v e Key Browse Species i n Colorado. Proc. Soc. of Amer. F o r e s t e r s , Utah. - 1 3 7 -Dining, J.S. , W. D. I949 Gallu p , and. H . M . -Briggs. E i n a r s e n , A.S. I946 E l t o n , C. 1 9 3 5 F i s c h e r , E. 1914 F o l i n , 0 . 1 9 0 5 Forbes, E. B., and I 9 4 I L.F. Marcy. Forbes, E.B. , B.F. I 9 4 6 E l l i o t , H.W. Sw i f t , W.H. James, and V.F. Smith. French, C.E., and 1 9 5 5 L.C. McEwen. F u l t o n , J.F. I946 Gordon, A., and 1 9 3 9 A.W. Sampson. Gorham, J. 1821 Greaves, J.P., and i 9 6 0 P.P. S c o t t . E x c r e t i o n of C r e a t i n i n e and Crea-t i n e by Beef S t e e r s . Jour. B i o l . Chem., 1 7 7 : I 5 7 - I 6 I . Crude P r o t e i n Determinations of Deer Food as an A p p l i e d Manage-ment Technique. Trans. N. Amer. W i l d l . Conf., 1 1 : 3 0 9 - 3 1 2 . Animal Ecology. Rev. ed., S i d g -wick •& Jackson, L t d . , London. Chemistry of the P r o t e i n s . Man, London. G. A Theory of P r o t e i n Metabolism. Amer. Jour, of P h y s i o l . , 1 3 ' H 7 -1 3 8 . The D i g e s t i v e C a p a c i t i e s of the W h i t e - t a i l e d Deer. Jour, of W i l d l . Mgt., 5 : 1 0 8 - 1 1 4 . V a r i a t i o n s i n Determinations of the D i g e s t i v e C a p a c i t y of Sheep. Jour. Animal S c i . , 5 : 2 9 8 - 3 0 5 . N u t r i t i v e Requirements of Whitey t a i l e d Deer f o r Growth and A n t l e r Development. B u l l . 6 0 0 . Penn. S t a t e U n i v e r s i t y ( C o l . of A g r i c . ), Howell's Textbook of Physiology. W.B. Saunders Co., P h i l a d e l p h i a and London. Composition of Common C a l i f o r n i a F o o t h i l l P l a n t s as a Factor i n Range Management. C a l . A g r i c . Exp. Sta. B u l l . 6 7 6 . A n a l y s i s of In d i a n Corn. The Annals of Philosophy, 1 7 : 4 7 0 . N u t r i t i o n of the Cat. B r i t . Jour, of Nut., 1 4 : 3 6 1 - 3 6 9 . - 138 -de Groot, T. , and i 9 6 0 J. H. A a f j e s . Guyton, A.C. I 9 5 6 Harding, V.J., and 1 9 2 2 O.H. Gaebler. Harper, H.A. 1961 Hawk, P.B., B.L. Oser, 1954 and W.H. Slimmer son. E l Hehyami, M . 1 9 5 8 Holmgreen, B.C. 1 9 5 6 Ho up t, T.B. I 9 5 9 Hubbard, K.L. 1 9 5 7 Hutchinson, J.C.D. and 1936 S.M. M o r r i s On the Constancy of C r e a t i n i n e E x c r e t i o n i n the Ur i n e of the Dai r y Cow. B r i t . Vet. Jour., 116: 4 0 9 - 4 1 8 . Textbook of Med i c a l P h y s i o l o g y . W.B. Saunders Co., P h i l a d e l p h i a and London. On the Constancy of the C r e a t i n e and C r e a t i n i n e E x c r e t i o n i n C h i l d -ren on a High P r o t e i n D i e t . Jour, of B i o l . Chem., 54* 579-587-Review of P h y s i o l o g i c a l Chemistry. 8th ed., Lange Medical P u b l i s h e r s , Los A l t o s , C a l i f o r n i a . P r a c t i c a l P h y s i o l o g i c a l Chemistry. The B l a c k i s t o n Co., New York. S t u d i e s on the Metabolism of Crea-t i n e and C r e a t i n i n e i n the Dog. I. U r i n a r y E x c r e t i o n i n Animals under D i f f e r e n t Experimental C o n d i t i o n s . B r i t . Vet. Jour., 114: 4 8 O - 4 8 3 . Compit i t i o n between Annuals and Young B i t t e r b r u s h ( P u r s h i a t r i -dent at a) i n Idaho. E c o l . , 37* 3 7 0 - 3 7 7 . . U t i l i z a t i o n of Blood Urea i n Rumin-ants. Amer. Jour, of P h y s i o l . , 197: 115-120. The E f f e c t of P l a n t Competition on the Growth and S u r v i v a l of B i t t e r b r u s h S e e d l i n g s . Jour, of W i l d l . Mgt., 10: 135-137-The D i g e s t i b i l i t y of D i e t a r y Pro-t e i n i n the Ruminant. I. Endo-genous N i t r o g e n E x c r e t i o n on a Low N i t r o g e n D i e t and i n S t a r v a -t i o n . Biochem. Jour., 3 ° : 1682-1693. - 139 -Hutchinson, J.D.C., and S.M. M o r r i s . Kinney, J.M. K i t t s , W.D. , P.J. Bandy, A.J. Wood, and I.McT. Cowan. 1 9 3 6 The D i g e s t i b i l i t y of D i e t a r y Pro-t e i n i n the Ruminant. I I . The D i -g e s t i b i l i t y of P r o t e i n F o l l o w i n g a Prolonged F a s t , w i t h a D e t a i l e d Study of the N i t r o g e n Metabolism. Bioch. Jour., 3 0 : 1 6 9 5 - 1 7 0 4 . 1 9 5 9 I n f l u e n c e of Intermediary Metab-o l i s m on N i t r o g e n Balance and ¥/eight Loss: Some C o n s i d e r a t i o n s B a s i c to an Understanding of Injury. Metabolism, 8 : 8 0 9 - 8 2 6 . 1 9 5 6 E f f e c t of Age and Plane of N u t r i -t i o n on the Blood Chemistry of the Columbian B l a c k - t a i l e d Deer ( 0 . he-mionus columbianus).., / Can. Jour, of 2 o o l . , 3 4 : 4 7 7 - 4 8 4 . K l i e b e r , M. Ko s s e l , A., and F Kutscher. Krogh, A. 1 9 3 2 1 9 0 0 1 9 0 6 Body S i z e and Metabolism. 6 : 3 1 5 - 3 5 3 . H i l g a r d i a , B e i t r a g e zur Kenntniss der E i w e i s s -korper. 2 . f u r P h y s i o l . Chem., 3 1 " 1 6 5 - 2 1 4 . Experimental Researches on the E x p i r a t i o n of Free N i t r o g e n from the Body. 3 6 4 - 4 2 0 . Skand. Arch. Phys. , 1 1 8 : Kutscher, F., and J. 1 9 0 2 Seeman. Lauckhart, J.B. 1 9 5 7 L e i t c h , I., and J. 1 9 3 7 Duckworth. 'Zur Kenntniss der Verdauungsvor-gange i n Dunndarn. I. Z. f u r P h y s i o l . Chem., 3 4 : 5 2 8 - 5 4 3 . Annual C y c l e s and Food. Jour. W i l d l . Mgt., 2 1 : . 2 3 0 - 2 3 3 . The Determination of the P r o t e i n Requirements of Man. Nut. Abstr. & Revs., 7 : 2 5 7 - 2 6 7 . Leopold, A.S., T. 1951 R i l e y , R. McCain, and L. T e v i s The Jawbone Deer Herd. Game B u l l . , 5 : 1 - 1 3 9 -C a l i f . Lewis, D. 1 9 5 7 Blood. Urea C o n c e n t r a t i o n i n R e l a -t i o n to P r o t e i n U t i l i z a t i o n i n the Ruminant. 4 3 8 - 4 4 6 . Jour. A g r i c . S c i . , 4 8 : - 140 -L i e b i g , L. Lusk, G. McCluggage, H. B. , G. Booth, and F.A. Evans. McCollum, E.V. Macy, I.G. Majumdar, B.N. Majumdar, R.N. Maynard, L. Mendel, L.B. M i t c h e l l , H.H. M i t c h e l l , H . H . M i t c h e l l , H . H . , and G. G. Carman. M i t c h e l l , H . H . 1 8 4 3 Animal Chemistry. W i l l i a m Grey, London. I928 The Elements of the Sc i e n c e of N u t r i t i o n . W.B. Saunders Co., P h i l a d e l p h i a . 1931 C r e a t i n i n e E x c r e t i o n i n Abnormal S t a t e s of N u t r i t i o n . Amer. Jour. Med. S c i . , 1 8 1 : 3 4 9 - 3 5 5 -1939 The Newer Knowledge of N u t r i t i o n . The M c M i l l a n Co., New York. 1 9 4 2 N u t r i t i o n and Chemical Growth i n Childhood. V o l . I. C.C. Thomas, S p r i n g f i e l d , I l l i n o i s . i 9 6 0 S t u d i e s on Goat N u t r i t i o n . I. Jour, of A g r i c . S c i . , 5 4 : 3 2 9 - 3 3 4 . i 9 6 0 S t u d i e s on Goat N u t r i t i o n . I I . Jour, of A g r i c . S c i . , 5 4 : 3 3 5 - 3 4 0 . I 9 5 6 Animal N u t r i t i o n . McGraw-Hill Bk. Co. Inc., New York. 1 9 2 3 N u t r i t i o n , The Chemistry of L i f e . Y a l e U n i v e r s i t y Press, New Haven. 1 9 2 4 A Method of Determining the B i o l o g i -c a l Value of P r o t e i n . Jour. B i o l . Chem., 5 8 : 8 7 3 - 9 2 9 . I 9 2 6 The B i o l o g i c a l U t i l i z a t i o n of Pro-t e i n s and P r o t e i n Requirements. B u l l . N a t l . Res. C o u n c i l No. 5 5 . I924 The B i o l o g i c a l Value f o r Maintenance and Growth of the P r o t e i n s of Whole Wheat, Eggs and Pork. Jour. B i o l . Chem.; 6 0 : 6 1 3 - 6 2 0 . I948 The B i o l o g i c a l U t i l i z a t i o n of Pro-t e i n s and P r o t e i n Requirements, i n M. Sahyun, P r o t e i n s and Amino A c i d s i n N u t r i t i o n . R e i n h o l d Publ. Corp., New York. - 141 -Morrison, F.B. Mulder, G. Munro, H.N. 1956 I 8 3 8 1951 Feeds and Feeding. M o r r i s o n Publ. Co., 2 2 n d ed.., Ithaca, New York. M u r l i n , J.R. ,~ L.E. I 9 4 6 Edwards, E.E. Hawley, and L.C. C l a r k . M u r l i n , J.R., L.E. I 9 4 6 Edwards, E.E. Hawley, and L.C. C l a r k . Myers, V.C., and M.S. F i n e . N i c h o l , A.A. Osborne, T.B., and L.B. Mendel. Osborne, T.B., and L.B. Mendel. Osborne, T.B., L.B. Mendel, and E.L. F e r r y . 1913 1 9 3 8 1 9 1 2 1 9 1 5 1919 Zusanimensel zung von F i b r i n , Albumin, L e u c i n v.s.w.; L i e b i g 1 s Chemie, 2 8 : 7 3 - 8 2 . Leimzucker, Annalen der Carbohydrate and Fat as F a c t o r s i n P r o t e i n U t i l i z a t i o n ' and Metabolism. P h y s i o l . Rev., 3 1 : 4 4 9 - 4 8 8 . The B i o l o g i c a l Value of P r o t e i n s i n R e l a t i o n to the Amino A c i d s which They Contain. I. The Endogenous N i t r o g e n of Man. Jour. Nut., 3 1 : 5 3 3 - 5 5 4 -The B i o l o g i c a l Value of P r o t e i n s i n R e l a t i o n to the Amino A c i d s which They Contain. I I . I n t e r c o n v e r t i -b i l i t y of B i o l o g i c a l Value I l l u s -t r a t e d by Sup p l y i n g Egg and Soy Pro-t e i n w i t h E s s e n t i a l Amino A c i d s . Jour. Nut., 3 1 : 5 5 5 - 5 6 4 . The C r e a t i n e Content of Muscle under Normal C o n d i t i o n s ; I t s Re-l a t i o n to the U r i n a r y C r e a t i n i n e . Jour. B i o l . Chem., 1 4 : 9 - 2 8 . Experimental Feeding of Deer. U n i v e r s i t y of A r i z . Exp. Sta. Tech. B u l l . , 7 5 ; - I - 3 9 . The Role of Jour. B i o l . G l i a d i n i n N u t r i t i o n . Chem., 1 2 : 4 7 3 - 5 1 0 . The Comparative N u t r i t i v e Value of C e r t a i n P r o t e i n s i n Growth, and the Problem of the P r o t e i n Minimum. Jour. B i o l . Chem., 2 0 : 3 5 1 - 3 9 0 . A Method of E x p r e s s i n g N u m e r i c a l l y the Growth Promoting Value of Pro-t e i n s . Jour. B i o l . Chem., 3 7 : 2 2 3 -2 2 9 . - 1 4 2 -Palmer, W.W. , J.H. 1 9 1 4 Means, and J.L. Gambia Phi 11 ipson, A.T. i 9 6 0 Rose, W.G., B.L. Wixom, 1 9 5 5 H.B". Lockhart, and G.F. Lambert. Rosen, M.N., and 1 9 5 2 A. B i s c h o f f . Sahyun, M. 1 9 4 8 Schmidt-Nielsen, B. 1 9 5 7 Schmidt-Nielsen, B., 1 9 5 8 and H. Osaki. Schmidt-Nielsen, B. , I 9 5 8 H. Osaki, H.V. Murdaugh, and R. O ' D e l l . Schoenheimer, R. Scholander, P.F. Smith, A.D. Smith, A.D. 1 9 4 2 1 9 5 5 1 9 5 0 1 9 5 2 B a s a l Metabolism and C r e a t i n i n e E l i m i n a t i o n . Jour. B i o l . Chem., 1 9 : 2 3 9 - 2 4 4 . The N u t r i t i o n of the Ruminant. The Vet. Rec. , 7 2 : 6 l 3 - 6 l 6 . The Amino A c i d Requirements of Man. 1 5 . V a l i n e Requirements: Summary and F i n a l Observations. Jour. B i o l . Chem., 2 1 7 : 9 8 9 - 9 9 5 . The R e l a t i o n of Hematology to C o n d i t i o n s i n C a l i f o r n i a Deer. Trans. N. Amer. W i l d l . Conf., 1 7 : 4 8 2 - 4 9 6 . P r o t e i n s and Amino A c i d s i n N u t r i t i o n . R e i n h o l d Publ. Corp., New York. Urea E x c r e t i o n i n the Camel. Amer. Jour, of P h y s i o l . , 1 8 8 : 4 7 7 - 4 8 4 . Renal Response to Changes i n N i t r o -gen Metabolism i n Sheep. Amer. Jour, of P h y s i o l . , I 9 3 : 6 5 7 - 6 6 1 . Renal R e g u l a t i o n of Urea E x c r e t i o n i n Sheep. Amer. Jour, of P h y s i o l . , 1 9 4 : 2 2 1 - 2 2 8 . The Dynamic S t a t e of Body C o n s t i t u -ents. Harvard U n i v e r s i t y Press, Cambridge, Mass. Counter-current V a s c u l a r Heat Ex-change i n the F i n s of Whales. Jour. Appl. P h y s i o l . , 3 : 2 7 9 - 2 8 2 . Sagebrush as a Winter Feed, f o r Deer. Jour, of W i l d l . Mgt., 1 4 : 2 8 5 - 2 8 9 . D i g e s t i b i l i t y of Some Native For-ages f o r Mule Deer. Jour, of W i l d l . Mgt., 1 6 : 3 0 9 - 3 1 2 . - 143 -Smith, A.D. 1 9 5 9 Smuts, D. 1 9 3 5 Somers, M. 1961 Somers, M. I96I Somers, M. 1961 Somers, M. 1961 Adequacy of Some Important Browse Spe c i e s i n Ove r w i n t e r i n g of Mule Deer. Jour, of Range Mgt., 1 2 : 8 -1 3 . The R e l a t i o n between the Basal Meta-b o l i s m and the Endogenous N i t r o g e n Metabolism, w i t h Reference to the E s t i m a t i o n of the Maintenance Re-quirement of P r o t e i n . Jour, of Nut., 9 : 4 0 3 -F a c t o r s I n f l u e n c i n g the S e c r e t i o n of N i t r o g e n i n Sheep S a l i v a . I. The D i s t r i b u t i o n of N i t r o g e n i n the Mixed and P a r o t i d S a l i v a of Sheep. A u s t r a l i a n Jour, of Exp. B i o l , and Med. S c i . , 3 9 : 1 1 1 - 1 2 2 . F a c t o r s I n f l u e n c i n g the S e c r e t i o n of N i t r o g e n i n Sheep S a l i v a . I I . The I n f l u e n c e of N i t r o g e n Intake upon Blood Urea N i t r o g e n and upon the T o t a l N i t r o g e n and Urea N i t r o -gen i n the P a r o t i d S a l i v a of Sheep. A u s t r a l i a n Jour, of Exp. B i o l , and Med. S c i . , 3 9 : 1 2 3-I3I. F a c t o r s I n f l u e n c i n g the S e c r e t i o n of N i t r o g e n i n Sheep S a l i v a . I I I . F a c t o r s A f f e c t i n g the N i t r o g e n F r a c t i o n s i n the P a r o t i d S a l i v a of Sheep wi t h S p e c i a l Reference to the In f l u e n c e of Ammonia P r o d u c t i o n i n the Rumen and F l u c t u a t i o n s i n L e v e l of B l o o d Urea. A u s t r a l i a n Jour, of Exp. B i o l , and Med. S c i . , 3 9 : 1 3 3 -1 4 3 . F a c t o r s I n f l u e n c i n g the S e c r e t i o n of N i t r o g e n i n Sheep S a l i v a . IV. The I n f l u e n c e of I n j e c t e d Urea on the Q u a n t i t a t i v e Recovery of Urea i n the P a r o t i d S a l i v a and the U r i -nary S e c r e t i o n s of Sheep. A u s t r a -l i a n Jour, of Exp. B i o l , and Med. S c i . , 3 9 : I45-I56. - 144 -Spector, W.S. Spencer, G.J. S u l l i v a n , M.X., and F. I r r e v e r r e . S v i h l a , A., H. Bowman, and R. Pearson. Swank, W. G. T a l b o t , N.B. T e r r o i n e , E. T u t t l e , S.G. V i c k e r y , H.B. Wallace, W.M. 1956 Handbook of B i o l o g i c a l Data, N a t l . Res. C o u n c i l . W.B. Saunders Co., P h i l a d e l p h i a . I 9 3 8 E c t o p a r a s i t e s of Deer i n B.C. Proc. Entomol. Soc. B.C., 3 5 : 39-' ,'45. 1958 A H i g h l y S p e c i f i c Test f o r Crea-t i n i n e . Jour. B i o l . Chem., 233s 5 3 0 - 5 3 4 . 1955 Blood P i c t u r e of the American B l a c k Bear (Ursus americanus), Jour. Mammo 1~ 3 b : 134-I35* 1956 P r o t e i n and Phosphorus Content of Browse P l a n t s as an I n f l u e n c e on Southwestern Deer Herd L e v e l s . Trans. N. Amer. W i l d l . Con-f., 2 1 : I 4 I - I 5 8 . 1936 Basal Energy Metabolism and Crea-t i n i n e i n the Urine. I. Observa-t i o n s on C h i l d r e n . Amer. Jour. Di s . C h i l d r e n , 5 2 : 1 6 - 2 4 . I 9 2 7 L o i Q u a n t i t a t i v e de l a Depense Azotee Minima des Homeotherms V a l i d i t e I n t e r s p e c i f i c . Arch, de I n t e r n a t . , P h y s i o l . 2 9 : 121. 1959 E s s e n t i a l Amino A c i d Requirements of Older Men i n R e l a t i o n to T o t a l N i t r o g e n Intake. Metabolism, 8 : 6 1 - 7 2 . 1931 The H i s t o r y of the D i s c o v e r y of Amino A c i d s . Chem. Revs., 9 : 169-318. 1959 N i t r o g e n Content of the Body and I t s R e l a t i o n to R e t e n t i o n and Loss of Nitrogen. F e d e r a t i o n Proceed-ings, 18: II25-II30. - M-5 -Waterlow, J.C., and i960 V.G. W i l l s . Waterlow, J . C. , V.G. i960 W i l l s , and P. Gyorgy. Waterlow, J.C., V.G. 1959 W i l l s , and K. Standard. West, E.S. , and R.T. 1957 Todd. Wood, A.J., I.McT. I 9 6 I Cowan, and H. Nordan. Wuthier, P.R., and I 9 5 7 P.O. S t r a t t o n . Balance S t u d i e s i n Malnourished Jamaican I n f a n t s . I. A b s o r p t i o n and R e t e n t i o n of N i t r o g e n and Phosphorus. B r i t . Jour, of Nut., 14: I 8 3 - I 9 8 . Balance S t u d i e s i n Malnourished Jamaican I n f a n t s . I I . Comparison of A b s o r p t i o n and R e t e n t i o n of Ni t r o g e n and Phosphorus from Human M i l k and a Cow's-milk Mixture. B r i t . Jour, of-Nut., 14: 199-206. I n d i r e c t I n d i c a t o r s of Muscle Mass i n Malnourished I n f a n t s . Amer. Jour, of C l i n . Nut., 7: 2 7 I - 2 7 9 . Textbook of Biochemistry. M c M i l l a n Co., New York. The The Care and Management of W i l d Ungulates f o r Experimental Purposes. Jour, of W i l d l . Mgt., 25: 295-302. The C r e a t i n i n e L e v e l of Blood Se-rum as an Index of Carcass Composi-t i o n . Jour. An. S c i . , 16: 9 6 I - 9 6 6 . 

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