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Preliminary studies on growth, nutrition and blood chemistry of beavers Stephenson, Arthur Bruce 1956

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PRELIMINARY STUDIES ON GROWTH, NUTRITION AND BLOOD CHEMISTRY OF BEAVERS by Arthur Bruce Stephenson B.A. University of Toronto, 1954 A Thesis Submitted i n the Requirements for the i n Department Part ia l Fulfilment of Degree of Master of Arts the of Zoology We accept this thesis as conforming to the standard required from candidates for the Degree of Master of Arts Members of the Department of Zoology The University of Br i t i sh Columbia A p r i l 1956 ix ABSTRACT This study was in i t ia ted to establish some basic factors concerning beavers which would aid i n understanding changes in population numbers. It was desired to obtain optimal and maxi-mal growth rates, to determine the caloric requirements neces-sary for maintenance, growth and reproduction, to establish "normal" values for various blood constituents and to correlate variations in these constituents with growth and nutr i t ion . In order to maintain beavers in captivity specially designed pens were constructed and a ration formulated and fed to the animals in a pelleted form. Growth rates were established from the weight increases of several yearling beavers and these were compared with data presented in the l i t erature . Only one rate was established for a k i t owing to the d i f f i cu l ty in obtain-ing young beavers, however, this was supplemented with published data. Body weights were regressed against several body measure-ments and organ weights were regressed against body weights i n order to establish the relat ive rates of gain for different body components. The caloric requirements necessary for maintenance were established for several beavers of different body weights and these were correlated with the quantity of natural beaver foods required for maintenance and growth. The d iges t ib i l i ty and time of food passage was also determined for the pelleted rat ion. "Normal" values for 25 different blood constituents and tests were determined on an age and seasonal basis. These values were d i s -cussed i n terms of growth, nutr i t ion , stress and disease and X compared w i t h p u b l i s h e d data obtained f o r other s p e c i e s . These s t u d i e s i n d i c a t e d that the beaver has a r e l a t i v e l y -f a s t growth r a t e and has the a b i l i t y to e f f i c i e n t l y u t i l i z e foods h i g h i n f i b e r content. I t showed a c l o s e s i m i l a r i t y to other h e r b i v o r e s , e s p e c i a l l y those w i t h l a r g e caecums, the s i t e of e x t e n s i v e c e l l u l o s e d e g r a d a t i o n . Minor p h y s i o l o g i c a l a d a p t a t i o n s to i t s semi-aquatic type o f l i f e were a l s o i n d i c a t e d . x i i ACKNOWLEDGEMENTS Grateful appreciation i s extended to Dr. I. MoT. Cowan, Department of Zoology, and to Dr. A. J . Wood and Dr. W. D. K i t t s , Department of Animal N u t r i t i o n , f o r t h e i r h e l p f u l advice, c r i t i -cism and encouragement throughout t h i s study. The author i s indebted to Miss M.C. Robertson f o r conduct-ing most of the hematology work and to Dr. R. J . Avery, Pathologist, Canadian Department of Agriculture, f o r performing post mortem examinations on the beavers. Many thanks are extended to Mr. D. R. Robinson and Mr. C. E. E s t l i n , B r i t i s h Columbia Game Department, f o r th e i r enduring e f f o r t s i n obtaining the animals f o r t h i s study. The monetary assistance of the National Research Council, which made t h i s study possible, has been greatly appreciated. i i TABLE OF CONTENTS PAGE I . INTRODUCTION 1 II . MATERIAL AND METHODS 2 1. Experimental Animals 2 2. Housing 2 3. Maintenance 6 4. Growth Studies 9 a. Body weights 9 b. Body measurements 11 c. Organ weights 11 5. Nutritional-Studies 12 a. Food intake 12 b. Diges t ib i l i ty 13 c. Time of food passage 18 6. Blood Chemistry and Hematology 18 a. Reducing sugars 20 b. Total protein i n whole blood, plasma and serum 20 c. Albumin 22 d. Globulin 22 e. Albumin-globulin ( A / G ) ratio 22 f. Fibrinogen 22 g. Non-protein nitrogen (N.P.N.) 22 h. Amino acid nitrogen 23 i . Creatinine 23 j . Creatine 23 i i i PAGE k. Cholesterol 23 1. Volat i le fatty acids 26 m. Hemoglobin 26 n. Packed red c e l l volume 26 0. Sedimentation rate 29 p. Red, white and di f ferent ia l c e l l counts 29 q. Red c e l l size 29 III . RESULTS IND DISCUSSION 30 1. Growth Studies 30 a. Body weights 30 b. Body measurements 43 c. Organ weights 52 2. Nutrit ional Studies 62 a. Pood intake 62 b. Diges t ib i l i ty 69 c. Time of food passage 70 3. Blood Chemistry and Hematology 72 a. Total reducing sugars 73 b. Total protein i n whole blood 75 c. Albumin 77 d. Globulin 80 e. Albumin-globulin ratio 82 f. Total protein i n serum 84 g. Fibrinogen ^ 86 h. Total protein in plasma 88 1. Non-protein nitrogen 89 j . Amino acid nitrogen 92 i v PAGE k. Creatine and creatinine 93 1. Cholesterol 96 m. V o l a t i l e f a t t y acids 98 n. Hemoglobin 100 o. Sedimentation rate 103 p. Packed red c e l l volume 104 q. Red c e l l counts 106 r. Red c e l l s i z e 108 s. White c e l l and d i f f e r e n t i a l c e l l counts 109 IV. SUMMARY AND CONCLUSIONS 115 V. LITERATURE CITED 123 VI. APPENDIX I 128 II 134 III 135 V LIST OP FIGURES Figure PAGE 1. Beaver shipping cage 4 2. Beaver pen 4 3. Beaver pen and weighing apparatus 10 4. Transmittance curves f o r acetone extracts of food and feces of beaver # 16 16 5. Standard curve f o r reducing sugars 21 6. Standard curve f o r amino acid nitrogen 24 7. Standard curve f o r creatinine and creatine 25 8. Standard curve f o r cholesterol 27 9. Standard curve f o r hemoglobin 28 10. Growth curves f o r beavers # 15 and # 16 31 11. Growth curves f o r beavers # 14 and # 17 32 12. Growth curves f o r beavers #19, #20, #23 and # 26 33 13. Growth curve f o r beaver # 8 37 14. T a i l and hind foot measurements of beavers # 15 and # 16 44 15. Regression of body weight against t o t a l length of beavers 4-5 16. Regression of body weight against hind foot length of beavers 46 17. Regressions of body weight against t a i l length, s c a l y - t a i l width, s c a l y - t a i l length and tail-base - circumference of beavers 47 18. Regression of body weight against product of scaly-t a i l width and s c a l y - t a i l length of beavers 48 19. Regression of heart weight against body weight of beavers 53 20. Regression of stomach weight against body weight of beavers 54 v i Figure 21. Regression of caecum weight against body weight of beavers 22. Regression of kidney weight against body weight of beavers 23. Regression of l i v e r weight against body weight of beavers 24. Regression of pancreas weight against body weight of beavers 25. Regression of adrenal weight against body weight of beavers 26. Relation of food intake of beaver # 16 and environmental temperature v i i LIST OF TABLES Table PAGE I. Per cent composition of rations fed to beavers 7 I I . Per cent proximate composition of rations fed to beavers 8 I I I . Instantaneous r e l a t i v e growth rates of beavers 35 IV. Instantaneous r e l a t i v e growth equations f o r Michigan k i t s 38 V. Comparison of instantaneous r e l a t i v e growth rates of beavers 41 VI. Relationship between body weight and l i n e a r measurements of beavers 49 VII. Comparison of adult and f e t a l measurements of beavers 51 VIII. Relationship between organ weight and body weight of beavers 60 IX. Quantity of r a t i o n # 204 consumed by beavers as compared with the calculated requirements 63 X. Quantity of r a t i o n # 8 consumed by beavers 66 XI. Reducing sugars i n beaver blood 73 XII. Total protein i n whole beaver blood 76 XIII. Albumin i n beaver blood 78 XIV. Globulin i n beaver blood 81 XV. Beaver albumin-globulin ( A / G ) r a t i o 83 XVI. Total protein i n beaver serum 85 XVII. Fibrinogen i n beaver blood 87 XVIII. Total protein i n beaver plasma 88 XIX. Non-protein nitrogen i n beaver blood 90 XX. Amino acid nitrogen i n beaver blood 92 XXI. Creatine i n beaver blood 94 XXII. Creatinine i n beaver blood 95 v i i i Table PAGE XXIII . Choles tero l i n beaver blood 97 XXIV. V o l a t i l e f a t t y acids i n beaver blood 99 XXV. Hemoglobin i n beaver blood 101 XXVI. Sedimentation rate of beaver blood 103 XXVII. l eaver packed red c e l l volume 105 XXVIII. Beaver red blood c e l l s 106 XXIX. Beaver erythrocyte diameter 109 XXX. Beaver white blood c e l l s 110 XXXI. Summary of d i f f e r e n t i a l c e l l counts for a l l beavers 110 XXXII. Summary of adult beaver blood const i tuents 121-122 INTRODUCTION Beavers have a re lat ive ly high rate of productivity with the result^ large increases i n population are not uncommon. As the population increases greater demands are placed on the a v a i l -able food supply which may be reflected in the animals themselves. Inadequacy of the quality and quantity of food w i l l result i n low growth rates and probably smaller beavers i n overpopulated areas. Accompanying these changes there tends to be an increase in social stress (Christ ian, 1950; Christian and Davis, 1955). These conditions could al ter the animals to such an extent that incipient diseases may reach epizootic proportions resulting i n serious mortality. As early as 1800 David Thompson recorded evidence of large scale mortality among beavers i n Western Canada ( T y r e l l , 1916). Seton (1924) and Warren (1927) also present similar accounts. Some of the more recent population reductions have been direct ly attributed to tularemia (Jel l i son et a l . , 1942; Banfield, 1954), while others have occurred without any apparent cause (Knuden, 1953; Lawrence and Pay, 1954). As an aid to interpreting changes brought about by an i n -creasing population, i t i s highly desirable to know the n u t r i -tional requirements of beavers for maintenance, growth and re -production as well as to establish optimal or maximal growth rates. This information w i l l be useful not only for theoretical consideration and comparison with other species but w i l l enable a management programme to be established to remove surplus animals in an increasing population before they are lost to the f u r i n d u s t r y as a r e s u l t o f other f a c t o r s . The p r e s e n t study attempts to e s t a b l i s h the growth r a t e s o f the d i f f e r e n t age c l a s s e s o f beavers on a se a s o n a l b a s i s , and to e s t a b l i s h the c a l o r i c requirements necessary f o r maintenance. C o r r e l a t e d w i t h these i n v e s t i g a t i o n s c o n s i d e r a b l e emphasis has been p l a c e d on the establishment o f normal v a l u e s f o r v a r i o u s b l o o d c o n s t i t u e n t s . T h i s w i l l enable an i n t e r p r e t a t i o n o f changes a s s o c i a t e d w i t h growth and w i l l a i d i n understanding the u t i l i z a t i o n o f i n g e s t e d n u t r i e n t s . I t w i l l a l s o enable a com-p a r i s o n to be made with the blood c o n s t i t u e n t s o f oth e r s p e c i e s . These d a t a w i l l p r o v i d e a b a s i s f o r d e t e c t i n g unfavourable c o n d i t i o n s i n beaver p o p u l a t i o n s , which c o u l d r e s u l t from e i t h e r a shortage o f food o r s t r e s s imposed by o v e r p o p u l a t i o n . - 3 -I I . MATERIALS AND METHODS 1. Experimental Animals Twenty-six beavers were obtained during the period from October 1954 to October 1955. Twenty-two were obtained from the Courtney area on Vancouver Island and were members of the sub-species Castor canadensis leucodontus. The others which came from Cranbrook region were probably of the subspecies C. c. sagittatus (Anderson, 1948). Fifteen of the animals were adults, ten were yearlings and one was a young of the year or k i t . The c lass i f icat ion into age groups was based on size according to Osborn (1953)« The animals were caught i n Bailey l ive traps (Couch, 1942) and expressed as soon as possible to the University. Special shipping cages were constructed for this purpose as i l lu s tra ted i n Figure 1. A container of water and some willow twigs were provided for the beaver during i t s 24 to 48 hour period of travel . Eight of the beavers were sacrif iced for digestive enzyme studies during the spring and winter of 1955. Several of the other beavers died during the course of the study for various reasons as discussed in Appendix I . 2. Housing In order to maintain beavers i n captivity special pens were constructed which ^ c ^ i m l i a j j £ ( l natural conditions as much - 4 -F i g u r e 1 Beaver s h i p p i n g cage F i g u r e 2 - - — - . ., Beaver pen - 5 -as possible. These pens, as shown i n Figure 2, consisted of a metal trough f i l l e d with water, a feeding platform at one end and an enclosed den at the opposite end. The trough was made of galvanized metal ten feet long, three feet wide and two and one half feet high and capable of containing 75 cubic feet of water. A three inch diameter drain was insta l led i n the bottom under the platform and a small overflow pipe was placed about three inches below the platform. The floor and walls of the den were constructed from metal-lined 3/4 inch plywood and the semicircular roof was covered with 24-gauge galvanized sheet metal. The inside d i -mensions of the den were;three feet long, two and one half feet wide and two feet high. There were three openings into the den which consisted of a 14 inch diameter hole in the floor leading into the tank, a 10 inch square door in the back and a 12 inch square door i n the roof. These lat ter two openings fac i l i t a t ed cleaning and capturing of the animals. The den was bolted to the tank and a wire covered ramp led from the den into the water. The three foot square feeding platform was constructed with a 3/4 inch plywood floor covered with one inch wire mesh to prevent the beavers from chewing the wood and to enable them to obtain traction on the slippery surface. The end of the platform was made from a metal-lined sheet of plywood screwed to the f loor . The platform was fastened to two dexion strips bolted along the edges of the tank and a wire covered ramp led from the platform into the water. The top of the cage was covered with one inch square wire mesh supported by three semicircular metal rods bolted to the - 6 -dexion. A three foot wide metal door supported with metal rods was located immediately in front of the platform. This door was used to gain access to the tank and platform for cleaning and feeding purposes. Ten pens were constructed during the winter and spring of 19155. They were mounted on six inch blocks on the cement f loor of an open shelter behind one of the Animal Nutrition barns. Adequate drainage was provided by the sloping f loor and a f u l l length drain which emptied into a septic tank. Water was supplied by a hose running over the pens which directed a continuous stream of water into each tank at a rate of 1/2 gallon per minute. This system kept the water f a i r l y clean but a weekly cleaning was essential . This was performed by removing the bottom drain cap and flushing the feces and food material from the tank. 3. Maintenance Unt i l September 1955 the basic food of the beavers con-sisted of an a r t i f i c i a l rat ion , U.B.C. # 15, compressed into pellets 3/8 inch in diameter and 1/4 inch long. The composition of this ration i s presented in Table I . The pel lets were supple-mented with bark from willow (Salix sp . ) , cottonwood (Populus  trichocarpa) and alder (Alnus rubra). During the f a l l kale^ (Brassica oleracea)?was also given to the animals. In September a special rat ion, # 204, was formulated and fed to the beavers instead of ration #15. Its composition i s presented in Table I . During December a third rat ion , # 8, con-TABLE I Percent Composition of Rations Fed to Beavers Constituent Ration Number 15 204 8 A l f a l f a meal 22.8 20.0 Grass, mixed 20.0 5.0 Corn, yellow 31.7 16.2 Wheat, No.5 16.2 Flaked Wheat 7.0 Wheat Bran 13.9 4.0 17.4 Flaked Barley 10.0 Rolled Oat Flour 22.3 Beet Pulp 9.9 4.0 Molasses 6.9 4.0 Soybean Meal 6.9 5.0 8.7 Linseed Meal 5.0 12.4 Cotton seed meal 3.0 Coconut meal 5.0 1.5 10.0 Stabi l iz ing fat 2.5 Fish O i l 0.5 Bone Meal 2.0 1.0 Mineral Premix 2.5 Iodized salt 1.0 1.0 1.0 - 8 -taining Aureomycin was temporarily used in an effort to rel ieve an apparent infectious condition. The composition of this ration i s also presented i n Table I . Proximate analysis was carried out on these rations by the standard methods outlined by the Association of O f f i c i a l Agricultural Chemists (1950). The results are presented i n Table I I . TABLE II Percent Proximate Composition of Rations Fed to Beavers Constituent Ration # 15 Ration #204 Moisture 10.9 12.8 Crude Protein 15.4 19.0 Crude Fiber 8.4 8.6 Ether Extract 4.0 5.6 i Ef-Free Extract 53.6 47.8 Ash 7.7 6.2 Preliminary investigations with different sized pellets indicated that larger pel lets were more easily handled by beavers. Therefore ration # 204 was pelleted into 3/4 inch diameter c y l i n -ders one inch long. These were fed in an enamel dish fastened to the side of the feeding platform. The dish was p a r t i a l l y covered with a removable aluminum l i d which provided a two inch border around the sides, thereby eliminating any wastage resul t -ing from the beavers' habit of pawing the pellets onto the platform. 4. Growth Studies The c r i t e r i a used to assess growth were the gain i n weight of the animal and the increase in external measurements. The relationship between organ weight and body weight was also established as an additional assessment of growth. a. Body weights Each beaver was i n i t i a l l y weighed upon a r r i v a l and at frequent intervals thereafter. Prom June to September weights were recorded at approx-imately two week intervals , and from October to January 1956 at weekly intervals . Techniques had to be devised for securing the animals for weighing purposes. Preliminary techniques employing a small cage with a s l id ing door placed against the door of the den proved ineff ic ient because the animals refused to enter the cage and invariably escaped into the water. Further investigations indicated that a metal cone could retain the animal i n a position which enabled both weight and measurements to be taken with con-siderable ease and with l i t t l e discomfort to the beaver. This cone was constructed from a sector of aluminum sheeting bolted into the shape of a cone 30 inches long having a 12 inch d ia -meter top and a 4 inch diameter bottom. This was mounted i n a tripod stand by means of two c ircular plywood discs cut so as to receive the cone and hold i t securely i n place. The weighing cone i s i l lus trated in Figure 3. To procure the beaver from the den a piece of metal was placed over the opening i n the f loor and the beaver's t a i l was 4 - 11 -grasped by hand and the animal l i f t e d through the rear door. It was then allowed to walk into the horizontal cone where i t became wedged. The cone was then placed i n a ver t i ca l posit ion on the platform scales and the weight determined to the nearest eighth of a pound. b. Body measurements Measurements were recorded at monthly intervals on a l l beavers while they were restrained in the weighing cone des-cribed above. A metal tape marked in mm. was used to determine the dorsal scaly t a i l length, scaly t a i l width, circumference of the t a i l immediately anterior to the scaly portion and the hind foot length from the calcaneus to the fleshy t ip of the third d ig i t . The claw was not included i n the lat ter measurement because of the var iab i l i t y result ing from di f ferent ia l wear. Total length, t a i l length and heart g ir th measurements were also taken on dead animals. These could not be used as routine measurements under the method employed to restrain the animals. An attempt was made to determine the volume and surface area of the scaly portion of the t a i l but proved impractical . Since i t was found that the product of scaly t a i l length and width when regressed against body weight yielded a slope similar to that when surface area was regressed against body weight, i t has been included as an additional growth assessment. This method was also used by Gsborn (1953). c. Organ weights A l l the dead or sacrif iced beavers were autopsied and the - 12 -following organs removed for weighing: kidneys, l i v e r , pancreas, adrenals, ovaries, testes, heart, lungs, stomach, gastric gland, caecum and small and large intestines. The weights were obtained to the nearest gram on a 600 gram spring balance except for the adrenals, ovaries and testes, the weights of which were obtained to the nearest 0.01 gram on a precision chain balance. In every case the organ was rinsed in cold water and dried with paper towels before weighing. 5. Nutrit ional Studies a. Pood Intake In order to establish the quantity of food required to maintain beavers of different body weights, nine beavers were fed a caloric intake calculated to be s l ight ly above their maintenance requirements. These calculations were based on the statement that maintenance calories expressed as total digest-ib le nutrients (T.D .N.), i s equal to twice the calories produced under basal conditions (Brody p. 478, 1945). This implies that maintenance per unit weight declines with increasing body weight according to the 0.7 power of body weight. Basal metabolism also varies as the 0.73 power of body weight for nearly a l l mature animals of different species. The equation presented by Brody (1945) for this relationship i s BM = 70.5W 0* 7 5 which was the expression used to calculate the basal metabolism of the beavers. The number of calories expressed as T.D.N, was calculated from the fact that one pound of T.D.N) contains 1814 Calories. - 13 -This i s a f a i r l y well established and accepted value used i n animal nutri t ion studies (Brody p. 32, 1945). Making the additional assumption that ration # 204 was 60 per cent digest-ib le resulted i n a value of 1080 Calories of T.D.N, per pound of rat ion. This figure was used i n calculating the amount of food to be fed each beaver. However, i t was found that the beavers could not consume a l l of the ration due to mechanical and physical d i f f i cu l t i e s resulting from some of the food adher-ing to the corners and edges of the dish. To compensate for this an additional 10 per cent was added to each dai ly feeding. This investigation commenced i n November when v i r t u a l l y no growth was taking place. The animals were starved one day preceding the determinations. Daily intake was obtained by weighing out the calculated amount each day on a pan balance to the nearest half ounce and reweighing any food remaining on the following day. The food dishes were cleaned dai ly . After four weeks of controlled feeding with ration # 204, four beavers appeared i l l and i t was recommended that the diet be changed to U.B.C. ration # 8 containing Aureomycin to a l l e -viate the s ituation. This ration was temporarily used during December. A maximum and minimum thermometer was placed in the beaver shelter and readings were taken dai ly at 5 p.m. i n order to determine the effects of environmental temperature on food consumption. b. D iges t ib i l i ty Tests were performed to determine the percentage of ration - 14 -# 204 absorbed by the digestive tract . This percentage i s an expression of the d iges t ib i l i t y of this ration under the con-ditions which i t was determined. In order to conduct this determination a suitable arrangement was required for housing the beaver so that feces could be collected. A cage eight feet square and 2^ feet high was set up in the nutri t ion laboratory. The cage was constructed from a dexion frame with a wooden floor and wire sides. Two enamel dishes with aluminum l ids were fastened into two of the corners to serve as water and feeding dishes respectively. Beaver # 16 was placed i n the cage on December 24, 1955. During the f i r s t week i t ate very l i t t l e and defecated only once. After this i n i t i a l period i t ate and defecated regularly. Following the investigation on the time of food passage the beaver was maintained on ration # 204 for 10 days. The food consumed was determined daily to the nearest half ounce on a pan balance. Feces were collected from the floor of the pen as carefully as possible by means of a scraper and retained through-out the period in.an enamel dish. Portions of feces from the last three days of col lect ing were mixed and a sample of this taken to determine percentage d iges t ib i l i ty by a chromogen method. The method used was essentially the same as that des-cribed by Reid et a l . (1950) i n that the chromogens were ex-tracted from the feces and feed with 85 per cent acetone and the transmittance of the extracted solution determined in a Beckman model DU spectrophotometer. Several of the details of the procedure had to be modified to be applied i n this investigation. - 15 -The ration and fecal samples were dried and the percent moisture determined by the standard 1 .0 .A.C. method ( A . O . A . C , 1950). The dried material was f inely ground i n a Wiley M i l l using a number 12 screen. One gram of the ration and one-half gram of the feces were placed i n separate 250 ml. round-bottomed flasks. To this was added 50 ml. of 85 per cent acetone, stoppered with a metal f o i l covered rubber stopper and shaken on a mechanical shaker for one hour. The flasks were then placed in the dark for 24 hours to complete extraction. The extract was then f i l t ered through # 40 Whatman paper into a 100 ml. volumetric f lask. The extracted material was further shaken with two 25 ml. aliquots of the acetone solution to en-sure complete chromogen extraction. This was f i l t e r e d into the flasks which were then made up to volume. The extracts were diluted 1 in 4 and the transmittances determined for both the feces and rat ion. These curves are presented i n Figure 4. The point of maximum absorption was at 412 millimicrons. Irwin et a l . (1953) obtained peak absorption at 415 millimicrons and Reid et a l . (1950) obtained the peak at 406 millimicrons. Diges t ib i l i ty was calculated direct ly from the Beer-Lambert law (Daniels, p. 79, 1948). This law i s formulated as follows: log - ° - Eel I Io i s the l ight intensity passing through the control solution or 85 per cent acetone in this case. Io i s adjusted to 100 per cent transraittance. I i s the l ight intensity emitted from the - 17 -t e s t s o l u t i o n , E i s the eq u a t i o n c o n s t a n t , c the c o n c e n t r a t i o n of ehromogen m a t e r i a l and 1 the width o f the s o l u t i o n i n the c u v e t t e . The ehromogen c o n c e n t r a t i o n i n 0.25 grams o f r a t i o n was a r b i t r a r i l y s e t a t one u n i t and the v a l u e o f E determined. T h i s E v a l u e was then used to c a l c u l a t e the u n i t s o f ehromogen i n the f e c e s . The d i g e s t i b i l i t y was then determined from the r a t i o o f ehromogen u n i t s i n the r a t i o n and f e c e s . T h i s method g i v e s f a i r l y a c c u r a t e r e s u l t s when the tr a n s m i t t a n c e o f both the r a t i o n and f e c e s s o l u t i o n s are o f the same order o f magnitude. The f e c e s c o l l e c t e d over the ten day p e r i o d were d r i e d to a constant weight i n the cyclone d r i e r and the dry weight determined. R e l a t i n g t h i s v a l u e to the dry weight o f f o o d i n -take a d i r e c t measure o f d i g e s t i b i l i t y was o b t a i n e d . A t h i r d method was a l s o c a r r i e d out u s i n g chromium oxide as an i n d i c a t o r . The r a t i o n was ground to a medium t e x t u r e w i t h a mortar and p e s t l e and thoroughly mixed w i t h chromium oxide a t a one per cent l e v e l . T h i s r a t i o n was o f f e r e d to beaver # 16 f o r 10 days and a sample s e l e c t e d from the l a s t three days' f e c e s . T h i s f e c a l sample and a r a t i o n sample were d r i e d i n the u s u a l manner (A.O.A.C., 1950). F i v e hundred mg. and t h r e e hundred mg. o f r a t i o n and f e c e s r e s p e c t i v e l y were ana l y s e d f o r t h e i r chromium oxide content u s i n g the method d e s c r i b e d by B o l i n et a l . (1952). A sample o f the d i l u t e d o x i d i z e d s o l u t i o n s were p l a c e d i n the spectrophotometer a t a wavelength of 440 m i l l i -microns and the tr a n s m i t t a n c e determined f o r both the r a t i o n and f e c a l s o l u t i o n s . Percent d i g e s t i b i l i t y was determined by the - 18 -method used i n the chromogen procedure. c. Time of Pood Passage After the beaver had become established i n the pen des-cribed i n the previous section, investigations were conducted to determine the time required for food material to pass through the alimentary system. Three chemical indicators contained i n the food were fed to the beaver on three successive days. The indicators used were chromium oxide which i s green i n colour, f e r r i c oxide, a red powder, and charcoal. Each was added to the f inely ground ration at a level of two per cent. Each coloured ration was offered for one day and then the dish cleaned and the next mixture offered. Feces were collected every day and the colour compared with various mixtures of the coloured food material. In this way a rough estimate of the time required for food passage was obtained. 4. Blood Chemistry and Hematology Blood was obtained from 22 different beavers over the period from January to October 1955. During the winter samples were taken from eight anaesthetized animals, by means of cardiac punctures. Nembutal was used as the anaesthetic. This was i n -jected intraperitoneally at a level of one grain per five pounds of body weight. The remainder of the samples were taken from unanaesthetized animals. In order to restrain them suff ic ient ly to enable a heart puncture to be performed a wire cone was con-structed from half inch wire mesh. The dimensions were similar - 19 -to those o f the weighing cone. Once a beaver was p l a c e d i n the cone the wi r e was bent around the p o s t e r i o r r e g i o n h o l d i n g the animal s e c u r e l y . L i t t l e r e s i s t a n c e was o f f e r e d , even when the beaver was p l a c e d on i t s back. To perform the c a r d i a c puncture the wire and f u r above the h e a r t r e g i o n was p a r t e d and l i b e r a l q u a n t i t i e s o f 70 per cent a l c o h o l a p p l i e d . A 2^ i n c h 18-gauge needle was then i n s e r t e d i n t o the h e a r t . Blood was withdrawn by means of a 10 ml. s y r i n g e or a commercial vacuum tube a t t a c h e d to the n e e d l e . I n i t i a l l y the s y r i n g e was used e x c l u s i v e l y but the vacuum c o n t a i n e r s were l a t e r found to be more expedient. Approximately 40 ml. o f bloo d was taken from each beaver. Twenty ml. were o x a l a t e d u s i n g one to two mg. of potassium o x a l a t e per ml. o f blood as an a n t i c o a g u l a n t . Ten ml. were o x a l a t e d w i t h a mixture o f ammonium and potassium o x a l a t e f o r the h e m a t o l o g i c a l work and ten ml. were allowed to coagulate to obtain, the serum. The coagulated b l o o d was c e n t r i f u g e d and the supernatant poured o f f i n t o a t e s t tube. A l l tubes c o n t a i n i n g blood samples were w e l l stoppered and s t o r e d i n the r e f r i g e r a t o r a t 6°C u n t i l the t e s t s were performed. In o r d e r to determine changes o f the b l o o d c o n s t i t u e n t s a s s o c i a t e d with growth blood was taken from 11 beavers on f o u r d i f f e r e n t o c c a s i o n s . During the summer bloo d was ob t a i n e d from s i x y e a r l i n g s on J u l y 7 and J u l y 21 and from f i v e a d u l t s on J u l y 28 and August 8. I n the f a l l b l o o d was obtained from s i x y e a r -l i n g s and f o u r a d u l t s on September 27 and October 8. Blood was a l s o o b t a i n e d from one k i t on October 8. The t e s t s performed on the bloo d are o u t l i n e d below. Duri n g the winter o n l y n i n e d i f f e r e n t t e s t s were performed but by July techniques had been evolved to enable values to be ob-tained for over 20 different constituents. For some of these constituents over 40 determinations were made. A l l tests were performed i n duplicate. a. Reducing Sugars were determined by the t i t ra t ion method of Shaffer and Hartmann and Somogyi (Koch and Hanke, 1953). The test involved the precipitation of the proteins with a zinc sulphate solution and oxidizing the reducing sugars i n an alkaline copper solution. The result ing cuprous oxide was oxidized in an acid solution i n the presence of excess iodine. The amount of iodine left after oxidation was deter-mined by t i t ra t ion with a standard sodium thiosulphate solution and compared with a blank to give a measure of the reducing sugars. The actual quantity of sugars present was determined from a standard curve as i l lus tra ted in Figure 5. A curve was prepared with glucose whenever a fresh copper solution was prepared. . When possible the tests were performed within two hours from the time the blood was taken. During this interval the blood was kept i n the refrigerator to minimize g lycolyt ic action which breaks glucose down to l ac t i c ac id . b. Total protein in the whole blood, plasma and serum was determined by a micro-Kjeldahl method as outlined by Styermark (1951) and Hawk, Oser and Summerson (1954). Plasma was obtain-ed by centrifuging a portion of the oxalated blood and removing the plasma supernatant. One ml. of each portion of the blood 1 5 0 - 22 -was d i l u t e d to 50 ml. i n 0.9 per cent s a l i n e . One or two ml. o f t h i s was d i g e s t e d w i t h s u l p h u r i c a c i d , potassium s u l p h a t e and m e r c u r i c o x i d e . The r e s u l t i n g ammonium su l p h a t e was converted to ammonia i n the m i e r o - K j e l d a h l apparatus and c o l l e c t e d i n b o r i c a c i d . T h i s was t i t r a t e d w i t h a s t a n d a r d a c i d s o l u t i o n to determine the amount of n i t r o g e n p r e s e n t . P r o t e i n v a l u e s were o b t a i n e d by m u l t i p l y i n g the n i t r o g e n v a l u e s by 6.25. c. Albumin v a l u e s were o b t a i n e d by p r e c i p i t a t i n g the g l o b u l i n from the serum as d e s c r i b e d i n Hawk, Oser and Summerson (1954) and determining the albumin n i t r o g e n by the micro-K j e l d a h l method o u t l i n e d above. d. G l o b u l i n was determined i n d i r e c t l y by s u b t r a c t i n g the albumin from the t o t a l p r o t e i n i n the serum. e. The A l b u m i n - g l o b u l i n (A/G) r a t i o was o b t a i n e d by d i v i d i n g the albumin v a l u e s by the g l o b u l i n v a l u e s . f . F i b r i n o g e n was d e r i v e d i n d i r e c t l y by s u b t r a c t i n g the t o t a l p r o t e i n i n the serum from that i n the plasma. g. Non-protein n i t r o g e n (N.P.N.) was determined p a r t l y by the m o d i f i e d Folin-Wu method o u t l i n e d i n Koch and Hanke (1953) and p a r t l y by the m i c r o - K j e l d a h l method p r e v i o u s l y d e s c r i b e d . E s s e n t i a l l y t h i s t e s t c o n s i s t e d of p r e c i p i t a t i n g the p r o t e i n w i t h t u n g s t i c a c i d and d i g e s t i n g the f i l t r a t e with s u l p h u r i c a c i d and hydrogen p e r o x i d e to o x i d i z e any o r g a n i c matter. The n i t r o g e n r e t a i n e d as ammonium sul p h a t e was then determined - 23 -by the m i c r o - K j e l d a h l method. h. Amino a c i d n i t r o g e n was determined c o l o u r i m e t r i c a l l y by the m o d i f i e d D a n i e l s o n method d e s c r i b e d i n Hawk, Oser and Summerson (1954). A p o r t i o n o f the p r o t e i n - f r e e b l o o d f i l t r a t e was t r e a t e d w i t h 1,2-napthoquinone-4-sulphonic a c i d i n an a l k a l i n e medium and the t r a n s m i t t a n c e o f the r e s u l t a n t c o l o u r determined i n the Beckman spectrophotometer. A standard curve shown i n F i g u r e 6 was prepared u s i n g g l y c i n e and g l u t a m i c a c i d . i . C r e a t i n i n e was determined by the Polin-Wu method as o u t l i n e d i n Hawk, Oser and Summerson (1954). The t e s t c o n s i s t e d o f t r e a t i n g a p o r t i o n o f the p r o t e i n - f r e e b l o o d f i l t r a t e w i t h an a l k a l i n e p i c r a t e s o l u t i o n and deter m i n i n g the tr a n s m i t t a n c e i n the Coleman spectrophotometer. A standard curve as shown i n F i g u r e 7 was prepared u s i n g pure c r e a t i n i n e . j . C r e a t i n e was determined by the Folin-Wu method which c o n s i s t e d o f d e h y d r a t i n g the c r e a t i n e i n the p r o t e i n - f r e e b l o o d f i l t e r e d w i t h a s t r o n g a c i d to convert i t to c r e a t i n i n e . The t o t a l c r e a t i n i n e was determined as above and the c r e a t i n i n e p o r t i o n s u b t r a c t e d to g i v e the c r e a t i n e v a l u e . k. C h o l e s t e r o l was determined by the m o d i f i e d B l o o r - S a c r e t t method as o u t l i n e d i n Koch and Hanke (1953). The t e s t con-s i s t e d o f d i s s o l v i n g the l i p i d s i n an a l c o h o l - e t h e r s o l u t i o n and p r e c i p i t a t i n g the p r o t e i n s . The s o l v e n t was evaporated and the dry r e s i d u e d i s s o l v e d i n chloroform. A c e t i c anhydride too C • 3 0 CKeat i <\.e.-t o VVcy ^cv \oo n\V ^ \ o o i - 26 -and s u l p h u r i c a c i d were added and the t r a n s m i t t a n c e of the r e s u l t a n t c o l o u r determined i n the Beckman spectrophotometer. A standard curve shown i n F i g u r e 8 was prepared from r e -c r y s t a l i z e d c h o l e s t e r o l . 1. V o l a t i l e f a t t y a c i d s were determined by the method o u t l i n e d by N e i s h (1950). T h i s c o n s i s t e d of t r e a t i n g a p o r t i o n o f the p r o t e i n - f r e e b l o o d f i l t r a t e w i t h s u l p h u r i c a c i d and magnesium su l p h a t e to l i b e r a t e the v o l a t i l e o r g a n i c a c i d s . The a c i d s were then removed by steam d i s t i l l a t i o n and t i t r a t e d w i t h a sodium hydroxide s o l u t i o n . The d i s t i l l i n g apparatus was d i f f e r e n t from that used by N e i s h . I t c o n s i s t e d o f a flame heated 250 ml. round-bottom f l a s k removably j o i n e d to a g l a s s column c o n t a i n i n g a K j e l d a h l t r a p . T h i s column was connected to a s m a l l s t r a i g h t - t u b e condenser. Steam generated by a h e a t i n g f i l a m e n t i n a 1000 ml. f l a s k passed i n t o the d i s -t i l l i n g f l a s k by means o f a tube l e a d i n g to the bottom o f the s o l u t i o n . m. Hemoglobin was determined by the Wong method (Hawk et a l . , 1954). The i r o n was removed from the hemoglobin molecule by treatment w i t h s u l p h u r i c a c i d and potassium p e r s u l p h a t e . The p r o t e i n s were then p r e c i p i t a t e d and the t r a n s m i t t a n c e of the f i l t r a t e determined i n the Coleman spectrophotometer. The mg. of i r o n as hemoglobin per 100 ml. o f blood was o b t a i n e d from the standard i r o n curve shown i n F i g u r e 9. n. Hematocrit or packed r e d c e l l volume was determined by the Wintrobe method (Pe r r y et a l . , 1954). T h i s c o n s i s t e d o f 0 v 04 a Siandard C u r v e f o r C h o l e s t e r o l tA<y Q A c A e s ^ e v o A p c v \ o o mV. ^ \ o o ^ 52-416b Ltthu'd by Best Mimeograph C o . L t d . , Vancouver, B C ......... ...... - 29 -c e n t r i f u g i n g an hematocrit tube f i l l e d w i t h whole blood a t 3000 r.p.m. f o r 30 minutes. The percent o f r e d blood c e l l s was then determined from the g r a d a t i o n s on the tube. o. Sedimentation r a t e was determined by the m o d i f i e d Westergen method ( P e r r y et a l . , 1954). Samples were s e t up w i t h i n one hour a f t e r t a k i n g the bloo d whenever i t was p o s s i b l e . The l e v e l o f r e d b l o o d c e l l s was determined a f t e r s t a n d i n g one hour. The d i f f e r e n c e from the o r i g i n a l l e v e l gave a measure of the sed i m e n t a t i o n r a t e . p. C e l l counts were performed on b l o o d smears s t a i n e d w i t h Wright's s t a i n . F or r e d c e l l s the bloo d was d i l u t e d 1:200 with Hayem's s o l u t i o n , and f o r white c e l l s the bloo d was d i l u t e d 1:20 with two per cent a c e t i c a c i d ( P e r r y ejb a l . , 1954). The counts were made i n d u p l i c a t e i n each case. D i f f e r e n t i a l c e l l counts were performed by a v e r a g i n g t h r e e separate counts o f a hundred c e l l s i n each sample. q. Red c e l l diameters were ob t a i n e d from 543 measurements made on the b l o o d from 18 beavers. The c e l l s were s t a i n e d w i t h Wright's s t a i n and examined under o i l immersion u s i n g a s t a n d a r d i z e d o c u l a r micrometer t o measure diameters. S t a t i s t i c a l a n a l y s e s o f the b l o o d v a l u e s were performed by the methods o f Snedecor (1946). Comparisons between age c l a s s e s were performed by the St u d e n t - t method at the 95 to 99 per cent l e v e l . The d i f f e r e n c e s which had a p r o b a b i l i t y o f l e s s than 0.05 were c o n s i d e r e d s i g n i f i c a n t . These are the o n l y d i f f e r -ences f o r which a p r o b a b i l i t y i s i n d i c a t e d i n the r e s u l t s . - 30 -I I I . RESULTS AND DISCUSSION !• Growth S t u d i e s a. Body Weights The weights f o r each beaver were p l o t t e d on semi-l o g a r i t h m i c paper and the l i n e o f best f i t c a l c u l a t e d by the method o f l e a s t squares (Brody p. 399, 1945). These graphs are presented i n F i g u r e s 10 to 12. T h i s type of p l o t r e p r e s e n t s the k t l o g a r i t h m i c e x p r e s s i o n o f the growth formula W = Ae , where W i s the weight o f the animal at time t , A i s a constant of the equation, e the base of the n a t u r a l l o g a r i t h m s and k the instantaneous r e l a t i v e growth r a t e . D i f f e r e n t i a t i n g t h i s dW equation y i e l d s the e x p r e s s i o n ^ = kW which i m p l i e s that the r a t e of i n c r e a s e i n weight i s p r o p o r t i o n a l to the weight which has a l r e a d y been gained. The i n s t a n t a n e o u s growth r a t e , k, i s o b t a i n e d from the graph by m u l t i p l y i n g the s l o p e o f the l i n e by 2.303 to convert i t to n a t u r a l l o g a r i t h m s . Other methods o f i n d i c a t i n g the r a t e o f growth do not g i v e a true nor comparable e x p r e s s i o n o f growth. Absolute r a t e s g i v e o n l y the average change i n weight over a c e r t a i n time i n t e r v a l . I f these time i n t e r v a l s are extremely s h o r t then the t r u e r e l a t i v e growth r a t e i s approached. S i m i l a r l y the average W — w r e l a t i v e growth r a t e which i s g i v e n by the e x p r e s s i o n 2 1 or M 2 * W l tCW^ + Wg) g i v e a t r u e r e p r e s e n t a t i o n o f growth o n l y when the g5j jHS ||a ^ ^ -•*" taa ca;:jg;: i i : s» ss: iffll as: iiiii ssn |^ suu UK: sss sys: ^ :uii :a[ gffl ns* i^ - 34 -change i n weight i s q u i t e s m a l l i n comparison w i t h the weight of the animal. F i g u r e s 10 to 12 r e v e a l that growth d i d not take p l a c e at a constant percentage r a t e over the e n t i r e p e r i o d . In the f a l l t h ere was a marked decrease i n growth r a t e as compared with t h a t i n the summer. T h i s i s f u r t h e r i l l u s t r a t e d by comparing the "k" v a l u e s i n T a b l e I I I . The average d a i l y summer growth r a t e was 0.27 per cent which was 11 times g r e a t e r than the d a i l y average w i n t e r r a t e of 0.025 per c e n t . Beaver # 15 had a summer growth r a t e o f 0.50 per cent per day which was s l i g h t l y lower than the d a i l y r a t e o f 0.52 per cent obtained f o r beaver # 16. However, t h i s animal continued to i n c r e a s e i n weight f o r t h r e e weeks l o n g e r i n the f a l l than beaver # 16 w i t h the r e s u l t that they both entered the w i n t e r growth phase at the same weight. Beaver # 17 had a summer growth r a t e o f 0.29 per cent per day which was s i m i l a r to that o b t a i n e d f o r the o t h e r beavers. T h i s animal was o r i g i n a l l y c l a s s i f i e d as an a d u l t a c c o r d i n g to body s i z e but s i n c e i t s growth r a t e was s i m i l a r to that o f the y e a r l i n g s t h i s may not be the case. Whether i t should be c l a s s i f i e d as a sub-adult or y e a r l i n g w i l l have to await f u r t h e r study on maximum growth r a t e s on l a r g e r numbers of animals. The r a t e o f growth o f t h i s animal was d i s r u p t e d i n e a r l y August and f u r t h e r i n c r e a s e i n body weight d i d not take p l a c e throughout the remainder o f the summer. In November the animal's d i e t was changed and i t went o f f f o o d f o r s e v e r a l days. T h i s r e s u l t e d i n a c o n s i d e r a b l e weight l o s s . When i t recommenced to eat i t s TABLE I I I Instantaneous R e l a t i v e Growth Rates o f Beavers Beaver Summer "k" Value Winter "k" Value 15 0.00300 0.000451 16 0.00317 0.000135 17 0.00291 0.000167 19 0.00205 20 0.00253 14 0.00231 21 0.00154* 23 0.000249 26 ( K i t ) 0.00141* Average 0.00266 0.00025 omitted from c a l c u l a t i o n o f mean - 36 -growth r a t e was r a p i d , q u i t e s i m i l a r to the summer r a t e as i l l u s t r a t e d i n F i g u r e 11. Upon r e g a i n i n g i t s weight l o s s i t continued to i n c r e a s e a t a steady r a t e o f growth comparable w i t h that o f the other beavers. Beavers # 14, # 19, # 20 and # 21 i n c r e a s e d i n weight at a s l i g h t l y lower r a t e than the other animals p r i o r to August. A f t e r t h i s p e r i o d t h e i r weights decreased, which e v e n t u a l l y culminated i n the animals' death (see Appendix I ) . T h i s decrease i n weight was observed to some extent i n a l l of the beavers f o l l o w i n g the f i r s t o f August. P r i o r to t h i s date the animals were on r a t i o n # 15 supplemented w i t h w i l l o w and cottonwood bark. During August t h i s r a t i o n was not supplemented and a l l o f the beavers e x h i b i t e d r e d u c t i o n i n t h e i r growth r a t e s . I n e a r l y September the r a t i o n was changed to # 204 and a g a i n supplemented wi t h w i l l o w bark and kale.' Only f o u r beavers, # 8 , # 1 5 , # 1 6 and # 17 responded to the changed d i e t by g a i n i n g weight d u r i n g t h i s p e r i o d , the ot h e r s e v e n t u a l l y d i e d . O b v i o u s l y r a t i o n # 15 by i t s e l f was not adequate f o r beavers but s a t i s f a c t o r y r e s u l t s were o b t a i n e d when supplementation was c a r r i e d out. The e f f e c t of the q u a l i t y o f the r a t i o n on weight changes i s f u r t h e r i l l u s t r a t e d by P i g u r e 13 which p r e s e n t s the weights o f an a d u l t beaver obtained f o r an e n t i r e year. Prom May to August, when l i t t l e to no supplementation was c a r r i e d out, the animal l o s t weight. T h i s l o s s was not re g a i n e d u n t i l September when the p e l l e t e d r a t i o n was supplemented w i t h w i l l o w and k a l e . Changing the r a t i o n i n November r e s u l t e d i n another decrease i n weight which was not r e g a i n e d u n t i l the r a t i o n was a g a i n s u p p l e -0 . 54 - 38 -merited w i t h willow bark i n January. During the f a l l y e a r l i n g # 23 and k i t # 26 were ob t a i n e d and p l a c e d on r a t i o n # 204. The y e a r l i n g e x h i b i t e d a d a i l y w inter growth r a t e o f 0.025 per cent which was comparable w i t h that o f the oth e r y e a r l i n g s . The k i t had a much h i g h e r r e l a t i v e growth r a t e o f 0.14 per cent per day. I f i t had continued to grow a t t h i s r a t e i t would have a t t a i n e d a weight o f 18 pounds by the f o l l o w i n g May. T h i s was approximately the weight o f the y e a r l i n g s i n e a r l y June. T h e r e f o r e t h i s w i n t e r growth r a t e o f the k i t appears s i m i l a r to that which must take p l a c e under n a t u r a l c o n d i t i o n s i n t h i s a r e a . Owing to the d i f f i c u l t y i n o b t a i n i n g k i t s the above growth r a t e was the o n l y one obt a i n e d d u r i n g t h i s study. How-ever, Bradt (1939) g i v e s the monthly weights f o r a one year p e r i o d o f f o u r beaver k i t s born on May 18, 1932 at the U n i v e r s i t y o f Michigan. These weights were used to o b t a i n the ins t a n t a n e o u s r e l a t i v e growth r a t e s f o r young beavers. The equations r e p r e -s e n t i n g these growth r a t e s a re presented i n Table IV. TABLE IV Instantaneous R e l a t i v e Growth Equations f o r Michigan K i t s * K i t Summer E q u a t i o n Winter E q u a t i o n i I n ¥ = In 0.50 + 0.0204t In ¥ = I n 1.42 + 0.0049t In ¥ = In 2.05 + 0.0028t 2 In ¥ = I n 0.62 + 0.0117t In ¥ = In 2.21 + 0.0029t 3 I n ¥ = I n 1.22 + 0.0088t In ¥ = In 2.08 + 0.0030t 4 In W - In 1.22 + 0.0087t In ¥ = In 1.95 + 0.0035t * Computed from data p r e s e n t e d by Bradt, 1959. - 39 -Three of the k i t s exhibited constant percentage growth rates from the time of their f i r s t weighing on June 22 to October, at which time growth declined to the lower winter rate which continued u n t i l the following May. Their average daily increase i n weight during the summer was 0.97 per cent which was three times greater than the winter rate of 0.31 per cent per day. Ki t # 2 had a faster growth rate than # 3 and # 4 but the break i n i t s growth curve occurred two weeks ear l i er , implying that this k i t was probably physiologically older. A similar situation was observed in the yearling beavers previously discussed. Un-l ike the other three k i t s , # 1 did not have as fast a summer growth rate and did not have a f a l l break in i t s growth curve. The summer rate of increase was 0.49 per cent per day which con-tinued u n t i l mid February when i t assumed a rate of 0.28 per cent per day. This value i s quite similar to the winter rate of the other three k i t s . At one year of age i t was only three pounds l ighter than # 3 and # 4 but six pounds l ighter than # 2, the animal which had the fastest summer growth rate. The birth weight of these k i t s was probably close to one pound. Bradt found that the average weight of 10 newly born young from three different l i t t e r s was 17.5 ounces. Shadle (1930) records the average b i r th weight of six k i t s at 14.8 ounces and Grinnell et a l . (1937) states that beavers weigh about one pound at b i r t h . Since these k i t s weighed 4_r pounds at 5 weeks of age then they must have gained about 3_: pounds in 35 days. Assuming that the percentage rate of growth was constant over this period then the i n i t i a l i n s t a n t a n e o u s r e l a t i v e growth r a t e would have been 3.6 per cent per day. However, d u r i n g t h i s e a r l y growth p e r i o d the r a t e may not have been constant as i s the case i n many animals (Brody p. 484, 1945). T h i s was i n d i c a t e d by k i t # 1 which was ap p a r e n t l y p h y s i o l o g i c a l l y younger and e x h i b i t e d a r a t e o f i n c r e a s e o f 2.0 per cent per day from the f i f t h to the n i n t h week. P r i o r to the f i f t h week i t must have had a much hi g h e r d a i l y percentage i n c r e a s e . T h i s suggests that r a t h e r than one growth r a t e i m p l i e d f o r the three f a s t e r growing animals there were p r o b a b l y at l e a s t two, the f i r s t h a v i ng a r a t e c l o s e to 5 per cent per day and the second near 2 per cent per day as was e x h i b i t e d by k i t # 1. Buckley and Libby (1955) i n A l a s k a computed l i n e a r r e -g r e s s i o n s of weight on age o f 105 d i f f e r e n t animals over a one year p e r i o d . Instantaneous r e l a t i v e growth r a t e s have been com-puted from these r e g r e s s i o n l i n e s f o r comparison w i t h Bradt's d a t a and that o b t a i n e d d u r i n g the present study. These f i g u r e s are p r e s e n t e d i n Table V. The t a b l e a l s o i n c l u d e s "k" v a l u e s computed from data c o l l e c t e d on Maine beaver (Hodgden and Hunt, 1953). These v a l u e s are not s t r i c t l y comparable s i n c e they were computed from a r e g r e s s i o n l i n e f i t t e d to average weights over 14 day i n t e r v a l s . N e v e r t h e l e s s they do i n d i c a t e a f a i r approx-i m a t i o n o f the growth r a t e s o f Maine beaver f o r comparative purposes. The summer d a i l y percentage i n c r e a s e i n weight o f the Al a s k a n beaver k i t s was 1.3 per cent which was s i m i l a r to that o b t a i n e d f o r the k i t s i n Maine but h i g h e r than the 1.0 per cent d a i l y i n c r e a s e computed from the Michigan data. A l l o f the workers i l l u s t r a t e a much lower r a t e d u r i n g w i n t e r . The A l a s k a n d a t a had a r a t e of 0.07 per cent per day w h i l e the average g a i n f o r the Maine k i t s was almost n e g l i g i b l e . Bradt's beavers were r a i s e d i n c a p t i v i t y and presumably adequately s u p p l i e d w i t h f o o d m a t e r i a l w i t h the r e s u l t t h a t a r e l a t i v e l y h i g h w i n t e r growth r a t e was o b t a i n e d . T h i s r a t e was over twice as gr e a t as the 0.14 per cent d a i l y i n c r e a s e o b t a i n e d from the one k i t i n the p r e s e n t study. TABLE V Comparison of Instantaneous R e l a t i v e Growth Rates o f Beavers «k" Values Summer Winter Reference K i t s 0.010 0.013 0.014 0.0031 0.00069* 0.0014 Bradt, (1939) Buckley & L i b b y , 1955 Hodgdon & Hunt, 1953 Present Study Y e a r l i n g s 0.0043* 0.00314* 0.00303 0.00069* 0.00025 Buckley & L i b b y , 1955 Hodgdon & Hunt , 1953 Present Study * c a l c u l a t e d from r e g r e s s i o n l i n e - 42 -The average summer growth r a t e o f 0.30 per cent per day f o r the y e a r l i n g beavers i n the present study i s s i m i l a r to t h a t o b t a i n e d from the Maine data but c o n s i d e r a b l y below the r a t e o f 0.43 per cent per day f o r the Alaskan beavers. L i k e the k i t s a marked decrease was observed d u r i n g the w i n t e r . Buckley and Li b b y (1955) a l s o present r e g r e s s i o n c o-e f f i c i e n t s o b t a i n e d from New York beavers which i n d i c a t e t h a t the summer growth r a t e s of the k i t s and y e a r l i n g s i n t h i s S t a t e are much lower than those o b t a i n e d i n A l a s k a . A l s o the w i n t e r r a t e s a re h i g h e r . They c r e d i t t h i s d i f f e r e n c e to the l e n g t h o f the growing season which i s much s h o r t e r i n A l a s k a than i n New York and to the f a c t t h a t the Ala s k a n beavers are f o r c e d to l i v e on s t o r e d w i n t e r f o o d f o r l o n g e r p e r i o d s o f time. To sub-s t a n t i a t e t h i s they c i t e a case o f two beavers i n h a b i t i n g a warm water slough which was not s u b j e c t e d to the normal w i n t e r con-d i t i o n s . These beavers had a r e l a t i v e l y r a p i d growth r a t e . T h i s s i t u a t i o n , d u p l i c a t e d i n c a p t i v i t y , c o u l d account f o r the r a p i d growth r a t e s e x h i b i t e d by the Michigan beaver k i t s p r e v i o u s l y d i s c u s s e d . The low v a l u e s obtained f o r our beavers may have r e -s u l t e d from inadequate composition o f the r a t i o n . T h i s remains to be t e s t e d by f u t u r e i n v e s t i g a t i o n s . Other f a c t o r s such as l i g h t , maintenance energy r e q u i r e -ments and q u a l i t a t i v e changes i n s t o r e d f o o d may a l s o be o f importance i n deter m i n i n g the d i f f e r e n c e between summer and win t e r growth r a t e s . That these s e a s o n a l changes do take p l a c e i n mammals has been w e l l i l l u s t r a t e d i n deer and o t h e r s p e c i e s i n c l u d i n g man (Cowan and Wood, 1955; Brody p. 222, 1945). - 43 -b. Body Measurements Thd body measurements taken on the i n d i v i d u a l beavers d u r i n g the summer are of l i t t l e v a l u e because of t h e i r i n f r e -quency and extreme v a r i a b i l i t y . The f i r s t s et was taken i n e a r l y J u l y and a t monthly i n t e r v a l s t h e r e a f t e r . S i n c e growth ceased a f t e r J u l y i n a l l y e a r l i n g s except # 15 and # 16 the g e n e r a l p a t t e r n o f the data shows an i n i t i a l i n c r e a s e from June to August or September f o l l o w e d by a decrease i n a l l the t a i l measurements u n t i l the death of the animals. The d a t a f o r beavers # 15 and # 16 are shown i n F i g u r e 14. The graphs i n d i c a t e an i n c r e a s e i n the f o u r measurements p r e s e n t e d up to the end of September. The decrease a t t h i s time corresponds to the decrease i n growth as determined by weight. The v a r i a -b i l i t y o f the f i g u r e s i s p r o b a b l y due l a r g e l y to mechanical e r r o r s i n measurement. The measurements f o r 26 beavers are p r e s e n t e d i n Appendix I I i n o r d e r of i n c r e a s i n g body weight. R e g r e s s i o n l i n e s f i t t e d to these d a t a are shown i n F i g u r e s 15 to 18. The equations w i t h t h e i r standard e r r o r s of estimate are presented i n Table V I . The exponents o f the l i n e a r measurements range from 1.3 f o r s c a l y t a i l width to 3.0 f o r h i n d f o o t l e n g t h . T h i s i n d i c a t e s the d i f f e r e n c e i n growth r a t e s of the v a r i o u s p a r t s of the body i n r e l a t i o n to body weight. The h i g h e r the exponent the lower the r e l a t i v e growth r a t e . For h i n d f o o t l e n g t h an i n c r e a s e of one per cent r e p r e s e n t e d an i n c r e a s e o f 3.0 per cent i n body weight. In g e n e r a l the t a i l measurements have a g r e a t e r r e l a t i v e r a t e of i n c r e a s e than e i t h e r h i n d f o o t l e n g t h or body l e n g t h . - 49 -TABLE VI R e l a t i o n s h i p Between Body Weight and L i n e a r Measurements o f Beavers Measurement Eq u a t i o n W ( k g . ) " a L ( c m . ) b Standard E r r o r of E s t i m a t e T o t a l l e n g t h W 0 . 0 0 0 0 3 3 6 L 2 , 7 9 8 + S r = 10.2* " s r 9.2% T a i l Length w 0 . 0 0 5 9 2 L 2 - 0 6 1 6 + S r = 19.5% " S r — 16.3% S c a l y - t a i l w 0 . 0 0 7 8 6 L 2 , 2 7 2 + S r = 19.1% Length " s r ES 16.0% S c a l y - t a i l w 0 . 4 9 9 L 1 , 3 1 5 + s r = 14.4% Width 12.6% T a i l - b a s e w 0 . 1 3 4 L 1 * 6 0 1 2 + s r = 6.8% Circumference " S r 6.3% Hind f o o t w 0 . 0 0 2 0 8 L 3 * 0 4 1 + S r = 8.1% Length " S r 7.6% S c a l y - t a i l width w 0 . 1 4 0 L 0 ' 7 9 5 + S r = 21.6% X Length " S r = 17.8% - 50 -T h i s i m p l i e s that these l a t t e r body components have a t t a i n e d a g r e a t e r percentage o f t h e i r maximum growth a t b i r t h . To sub-s t a n t i a t e t h i s f a c t f i g u r e s f o r the average measurements of 10 a d u l t s and t h r e e almost f u l l term f o e t u s e s a re pres e n t e d i n Table V I I . These d a t a i n d i c a t e t h a t h i n d f o o t l e n g t h and body l e n g t h had a t t a i n e d 27 per cent o f t h e i r mature v a l u e s w h i l e t a i l l e n g t h had completed o n l y 16 per cent. T h e r e f o r e i t would be expected that the t a i l measurements should i l l u s t r a t e a h i g h e r r e l a t i v e r a t e o f growth as compared wi t h h i n d f o o t l e n g t h . From t h e o r e t i c a l dimensional a n a l y s i s weight v a r i e s w i t h the cube o f l i n e a r s i z e but a l l body measurements do not f o l l o w a s t r i c t geometric p a t t e r n o f growth. The r e g r e s s i o n o f weight on h i n d f o o t l e n g t h d i d , however, i n d i c a t e that weight growth does v a r y w i t h the cube o f l i n e a r growth f o r t h i s measurement. S i m i l a r l y t o t a l l e n g t h showed a c l o s e r e l a t i o n to the t h e o r e t i c a l l i n e a r growth such that a one per cent i n c r e a s e i n t o t a l l e n g t h r e p r e s e n t s a 2.8 per cent i n c r e a s e i n weight. These two measure-ments are the most c l o s e l y c o r r e l a t e d w i t h body weight and a r e most n e a r l y r e p r e s e n t a t i v e o f the l i n e a r s i z e o f the animal. The product o f s c a l y t a i l l e n g t h and width r e p r e s e n t s the g r e a t e s t dimensional change with i n c r e a s i n g weight but the v a r i a b i l i t y o f the data i s q u i t e g r e a t as i n d i c a t e d by the l a r g e standard e r r o r o f es t i m a t e . The l e a s t v a r i a b l e measurement as i n d i c a t e d i n these data was the circumference o f the base o f the t a i l . T h i s may be the r e s u l t o f i n s u f f i c i e n t measurements because the monthly measurements i n d i c a t e d t h a t t h i s body com-ponent was q u i t e v a r i a b l e w i t h both h e a l t h and season, due to TABLE V I I Comparison o f A d u l t and P e t a l Measurements of Beavers* T o t a l Length T a i l Length Body Length S c a l y t a i l Length S c a l y t a i l Width Hind f o o t Length T a i l - b a s e Circumference A d u l t s 106.3 44.6 61.7 26.9 13.1 17.9 19.2 Fetuses 23o6 6.9 16.7 5.0 2.6 4.8 4.7 . Per cent o f Mature S i z e 22.2 15.5 27.1 18.6 19.8 26.8 24.5 * Average v a l u e s f o r 10 a d u l t s and 3 n e a r l y f u l l term f e t u s e s - 52 -the l a r g e d e p o s i t o f f a t t y t i s s u e i n t h i s r e g i o n . The r e g r e s s i o n o f body weight on h i n d f o o t l e n g t h appears to be the best c r i t e r i o n f o r e s t i m a t i n g the weight of a growing animal. I t i s o f l i t t l e v a l u e a f t e r two years of age as i n d i c a t e d by the divergence o f the measurements f o r the r e g r e s s i o n l i n e a t the h e a v i e r body weights. To some extent t h i s divergence o f the l a r g e r animals from the r e g r e s s i o n l i n e i s i n d i c a t e d by a l l o f the l i n e a r measurements. T h i s i m p l i e s that f o l l o w i n g the r a p i d growth d u r i n g the f i r s t two years any f u r t h e r i n c r e a s e i n s i z e i s extremely slow. A d d i t i o n a l d a t a would be r e q u i r e d to i l l u s t r a t e any r e l a t i o n s h i p i n a d u l t beavers. c. Organ Weights The organ weights arranged i n the order o f i n c r e a s i n g body weight are presented i n Appendix I I I . R e g r e s s i o n l i n e s f o r some of these weights p l o t t e d a g a i n s t body weight on l o g - l o g graph paper are pres e n t e d i n F i g u r e s 19 to 25. Tab l e V I I I summarizes the r e g r e s s i o n equations w i t h t h e i r standard e r r o r s o f estimate as obtained by the method o u t l i n e d i n Brody (p. 399, 1945). S i n c e a change i n body weight i s r e p r e s e n t e d by a p r o -p o r t i o n a t e change i n organ weight i t . can best be r e p r e s e n t e d by the p a r a b o l i c e q u a t i o n y = ax . Thus f o r a one per cent i n c r e a s e i n x there i s a b per cent i n c r e a s e i n y. When b equals one, then a l i n e a r r e l a t i o n s h i p e x i s t s between the two measurements. Of the beaver organs o n l y the stomach and caecum i l l u s t r a t e d a u n i t percentage i n c r e a s e f o r both body weight and organ weight. G e n e r a l l y the v i s c e r a l organs do not have the same r e l a t i v e growth - 60 -TABLE V I I I R e l a t i o n s h i p Between Organ Weight and Body Weight o f Beavers Organ 0 E q u a t i o n (gram) = a ¥ ( k g . ) b Standard E r r o r o f E s t i m a t e Heart H = 7.26W 0- 7 0 1 + S r = 30.8% " S r = 23.6% Stomach S = 6.271W 1* 1 3 7 + S r = 21.9% " S r 18.0% Caecum c = 7.84W 1 , 1 1 + S r = 16.0% " S r 13.8% Kidneys K = 17.0W 0' 6 3 + s r 13.0% " S r = 12.5% L i v e r L = 5 3.25W 0 , 7 7 2 + S r 16.2% " s r 13.9% Pancreas P = 5.00W 0* 6 8 5 + S r = 15*9% " S r 13.1% A d r e n a l s A(mg.) " 34.5W 1-5 2 2 + S r " s r = 19.1% 16.5% - 61 -rate as that of the body and are usually much less. Without exception this i s true for mature animals of different species (Brody p. 619, 1945). The regression l ine for heart weight indicates that for a one per cent increase i n body weight there i s a 0.7 per cent increase in heart weight. The weight of this organ i s correlated with the exercise level of the species and i n most mammals has a unity relationship with body size (Brody p. 628, 1945). Since aquatic animals have their weight counterpoised by the displaced water their hearts are re lat ive ly smaller than t erres tr ia l forms. Whether this explanation can be applied to a semi-aquatic mammal l ike the beaver i s questionable. The high degree of v a r i a b i l i t y of the data and the few numbers involved precludes much speculation. The qualitative and quantitative nature of the beavers' diet probably accounts for the unity relationship between stomach and caecum weight and body weight. The caecum i s r e l -atively large i n the beaver and i s presumably the s ite of c e l l u -lose breakdown by bacterial action. With increasing age more food material of a higher f iber content i s eaten and i t i s less well masticated (Grinnell et a l . , 1937). This increase i n bulkiness of food material and dependence on bacterial decompo-s i t ion probably accounts for the high relat ive growth rate of these organs. The kidneys had a fract ional increase of 0.63 per cent per unit percentage increase i n body weight. This was the least variable of the organ weights. The value agrees quite closely - 62 -with several other species of growing animals (Brody p. 625, 1945). Similarly the relationship between body weight and l i v e r and pancreas weights were quite comparable with that of other species. The adrenals showed a greater growth rate relat ive to body weight than any of the other organs. In mature and growing species this relationship i s less than unity (Brody p. 585, 1945). Kibler et a l . , (1943) has shown that there i s an i n -crease i n the slope of the curve at the onset of puberty i n both rabbits and guinea pigs. Christian (1955) shows that a similar . situation occurs when the animals are under stress. Since the range of data covers a l l ages of beavers the increase i n relative growth rate cannot be ascribed to pubertal changes. The increase i s probably a result of the stress imposed on the captive animals as well as the general stress syndrome asso-ciated with the factors which led to the death of some of the animals. 2. Nutrit ional Studies a. Pood Intake The average food intake for each beaver with a measure of the variation while on ration # 204 i s presented in Table IX. The calculated intake values are also presented for comparison. These figures indicate a f a i r l y close agreement which implies that the general considerations used i n the calculation of the food requirements were quite applicable to beavers as they are to most other mammals. Beaver #19 was i l l during this period there-TABLE IX Quan t i t y o f R a t i o n # 204 consumed by beavers as compared wit h the c a l c u l a t e d requirements Beaver Body Weight Pounds C a l c u l a t e d C a l o r i e s o f T.D.N. C a l c u l a t e d Pood Intake Pounds A c t u a l Pood Intake i n Pounds Mean Standard D e v i a t i o n C o e f f i c i e n t of v a r i a t i o n (per cent) 26 13* 530 0.50 0.50 0.01 20.6 19* 22 760 0.70 0.84 0.21 25.6 23 22 760 0.70 0.76 0.14 18.2 15 254 840 0.78 0.75 0.10 13.5 16 26 850 0.79 0.73 0.16 21.6 25 26 850 0.79 0.74 0.09 12.0 8** 29* \ 940 0.88 0.70 0.10 14.6 24 31 970 0.90 0.83 0.11 12.9 17** 31 970 0.90 0.69 0.10 14.4 * A c t u a l i n t a k e v a l u e i s not comparable s i n c e the animal was i l l . **Beaver i n i t i a l l y l o s t weight t h e r e f o r e observed v a l u e s were low. - 64 -f o r e i t s v a l u e i s not comparable w i t h the o t h e r s . Beaver # 8 and # 17 went o f f food when the experiment commenced which r e -s u l t e d i n an i n i t i a l l o s s i n weight. T h i s weight l o s s probably-r e s u l t e d i n the lower v a l u e s observed f o r these beavers. The other beavers had v a l u e s v e r y s i m i l a r t o , o r s l i g h t l y lower than, the c a l c u l a t e d ones. The lower v a l u e s may have r e s u l t e d from the use o f the 6G per cent d i g e s t i b i l i t y f a c t o r employed i n the c a l c u l a t i o n s . L a t e r work i n d i c a t e d t h at the d i g e s t i b i l i t y was a c t u a l l y between 65 and 70 per cent on t h i s r a t i o n which would make the c a l c u l a t e d f i g u r e s s l i g h t l y h i g h e r , n e a r e r to the e m p i r i c a l v a l u e s . The r e l a t i v e l y l a r g e standard d e v i a t i o n and c o e f f i c i e n t o f v a r i a t i o n i n d i c a t e t h at the f o o d i n t a k e was q u i t e v a r i a b l e . Most o f the v a r i a t i o n s were a s s o c i a t e d with temperature f l u c t u -a t i o n s . F i g u r e 26 p r e s e n t s the f o o d i n t a k e v a l u e s f o r beaver # 16 which e x h i b i t e d t y p i c a l f l u c t u a t i o n s o f f o o d i n t a k e w i t h temperature. With the b e g i n n i n g of the f i r s t c o l d s p e l l on November 11 the i n t a k e dropped p r e c i p i t o u s l y and remained low f o r the f i r s t two or t h r e e days before i n c r e a s i n g . C o n s i d e r a b l e f l u c t u a t i o n took p l a c e u n t i l warmer weather a r r i v e d and then f a i r l y s t a b l e v a l u e s were o b t a i n e d . Whenever the temperature dropped below f r e e z i n g the food i n t a k e a l s o decreased. During December the beavers were f e d ad l i b i t u m on r a t i o n # 8 . No growth took p l a c e d u r i n g t h i s p e r i o d . Food i n t a k e v a l u e s a r e p r e s e n t e d i n Table X. Beavers # 19 and # 24 should be omitted f o r comparative purposes s i n c e they were a p p a r e n t l y i l l (see Appendix I ) . T h i s was p a r t l y r e f l e c t e d by the l a r g e - 66 -c o e f f i c i e n t o f v a r i a t i o n which i n d i c a t e d a h i g h degree o f v a r i a b i l i t y f o r these beavers. The oth e r animals e x h i b i t e d a p r o g r e s s i v e i n c r e a s e i n food i n t a k e w i t h body weight. TABLE X Qu a n t i t y o f R a t i o n # 8 consumed by beavers Beaver Number Body weight Pounds Pood Intake i n Pounds mean standard d e v i a t i o n c o e f f i c i e n t o f v a r i a t i o n 19* 19 5/8 0.54 0.20 37.6 23 21 1/2 0.43 0.07 15.8 25 25 0.57 0.08 14.2 15 26 1/8 0.53 0.09 17.1 16 26 5/8 0.59 0.10 17.1 8 27 1/2 0.63 0.06 9.1 24* 27 3/4 0.78 0.20 25.1 17 31 7/8 0.69 0.11 16.2 * animal appeared i l l A comparison o f the f i g u r e s f o r r a t i o n # 204 w i t h those f o r r a t i o n # 8 r e v e a l a s m a l l e r i n t a k e on the l a t t e r r a t i o n which r e f l e c t s i t s h i g h e r net c a l o r i c v a l u e . Prom Table IX i t appears that a 26 pound beaver would r e -qu i r e about 850 C a l o r i e s o f T.D.N, f o r maintenance. Por maximum growth K l e i b e r s t a t e s that f i v e times the c a l c u l a t e d energy - 67 -f o r b a s a l metabolism i s r e q u i r e d . T h i s would amount to about 2100 C a l o r i e s of T.D.N. S i n c e one pound o f r a t i o n # 204 con-t a i n s about 1180 C a l o r i e s T.D.N., and assuming a 65 per cent d i g e s t i b i l i t y f a c t o r , then the beaver would have to consume about 1.8 pounds o f the r a t i o n per day f o r maximal growth. Determining the g r o s s energy o f the r a t i o n by m u l t i p l y i n g the q u a n t i t y o f p r o t e i n , f a t and carbohydrate by the r e s p e c t i v e f a c t o r s o f 5.65, 9.45 and 4.10 g i v e s a t o t a l c a l o r i c v a l u e o f the r a t i o n o f 1780 C a l o r i e s . I f the d i g e s t i b i l i t y i s 65 per cent then the d i g e s t i b l e C a l o r i e s are 1160 which i s q u i t e s i m i l a r to the f i g u r e used i n the above c a l c u l a t i o n . The n a t u r a l w i n t e r d i e t o f beavers c o n s i s t s p r i n c i p a l l y o f the bark and twigs o f p o p l a r and w i l l o w . I f the 26 pound beaver under c o n s i d e r a t i o n were to s u b s i s t on these s p e c i e s the d a i l y i n t a k e can be approximated from t h e i r percentage composition. Cowan et a l . (1950) g i v e the proximate a n a l y s i s o f these s p e c i e s from which i t can be r e a d i l y c a l c u l a t e d that the g r o s s energy i s 2020 C a l o r i e s per pound dry matter f o r aspen and 1990 C a l o r i e s per pound f o r w i l l o w . The moisture content o f aspen was 46.3 per cent and f o r the willow 49.8 per cent, t h e r e f o r e the c a l o r i c v a l u e o f f r e s h aspen twigs i s 1165 C a l o r i e s per pound and f o r the w i l l o w about 1000 C a l o r i e s per pound. S i n c e crude f i b e r averages 26 per c e n t , and d i g e s t i b i l i t y decreases as the percent of f i b e r i n the d i e t i n c r e a s e s , a v a l u e o f approximately 50 per cent d i g e s t i b i l i t y may not be too much i n e r r o r ( S w i f t et a l . , 1954). T h e r e f o r e , one pound of aspen and w i l l o w r e s p e c t i v e l y y i e l d s 580 and 500 C a l o r i e s o f d i g e s t i b l e energy. S i n c e the beaver r e q u i r e 850 C a l o r i e s o f - 68 -T.D.N, f o r maintenance, i t would r e q u i r e 1.5 and 1.7 pounds o f aspen and w i l l o w twigs r e s p e c t i v e l y per day. F o r maximum growth i t would r e q u i r e 3.6 and 4.2 pounds r e s p e c t i v e l y . Aldous (1938) s t a t e s that an a d u l t beaver consumed 1.4 to 2.1 pounds o f aspen bark and twigs per day. An a d u l t beaver would weigh between 35 and 40 pounds. The c a l c u l a t e d amount o f aspen twigs r e q u i r e d f o r maintenance i s 1.8 to 2.0 pounds a c c o r d i n g to the above con-s i d e r a t i o n s . T h i s shows a f a i r l y c l o s e agreement wi t h the observed data. Beaver k i t s are weaned when n e a r l y two months o l d a t which time they weigh about 5 to 6 pounds ( B a i l e y , 1922). Growth i s r a p i d as p r e v i o u s l y i n d i c a t e d by the instantaneous r e l a t i v e growth r a t e u n t i l e a r l y f a l l when a weight o f 15 or 16 pounds i s a t t a i n e d . Taking the average weight o f 11 pounds and assuming th a t b a s a l metabolism i n c r e a s e s by the 0.73 power of body weight then the b a s a l metabolism o f t h i s beaver would be 225 C a l o r i e s per day. U s i n g K l e i b e r ' s r e l a t i o n s h i p o f f i v e times b a s a l metab-o l i s m f o r maximum growth then a t o t a l o f 1125 C a l o r i e s of T.D.N, would be r e q u i r e d per day. During the summer the food o f the beaver c o n s i s t s p r i n c i p a l l y o f he r b a c i o u s m a t e r i a l w i t h the woody components o f the d i e t i n c r e a s i n g as w i n t e r approaches (Bradt, 1947). For t h e o r e t i c a l c o n s i d e r a t i o n the t o t a l d i e t a r y i n t a k e can be c a l c u l a t e d from the proximate a n a l y s i s o f immature green mixed g r a s s e s (Schneider, 1947). Proximate a n a l y s i s g i v e s the f o l l o w i n g percentage composition: crude p r o t e i n 22.1, crude f i b e r 20.4, N-free e x t r a c t 42.9, ether e x t r a c t 4.2, ash 10.4 and moisture 75.1. - 69 -Calculation of gross energy reveals 1930 Calories per pound of dry matter or 480 Calories per pound of fresh grass. The total digestible nutrients of this ration when fed to cattle i s 68.9 per cent but because of the high f iber content this value i s probably closer to 60 per cent for young beavers. Therefore fresh grass provides 290 Calories of T.D.N, per pound. Since the beaver requires 1125 such Calories for maximum growth, then on a diet of grasses i t would have to consume 3.9 pounds of fresh grass per day for maximum growth. b. Diges t ib i l i ty The three methods employed to determine the d iges t ib i l i ty of ration # 204 gave the following results: (i) Chromogen method - 70.7 per cent ( i i ) Chromium oxide method - 66.2 per cent ( i i i ) Direct method - 76.3 per cent In the f i r s t two methods d iges t ib i l i ty was calculated direct ly from the Beer-Lambert law employing the transmittances of the ration and fecal extracts at the point of maximum absorp-t ion. In the chromogen method the transmittance of the ration and fecal extracts were 49.0 and 29.8 per cent respectively and i n the chromium oxide method they were 69.1 and 51.9 per cent respectively. Which method i s better for determining digest i -b i l i t y of beaver foods cannot be concluded from one determination. The 4.5 per cent difference could be accounted for by the individual's v a r i a b i l i t y . Both methods have proved highly sat is -factory on domestic species (Clawson et a l . , 1955; Kane et a l . , - 70 -1950; R e i d et a l . , 1950; Schurch e_t a l . , 1950). S i n c e the chromogen method g i v e s f a i r l y a c c u r a t e r e s u l t s and can be a p p l i e d to v a r i o u s beaver foods under n a t u r a l and a r t i f i c i a l c o n d i t i o n s i t appears to be the b e t t e r method f o r beaver s t u d i e s . In the d i r e c t d e t e r m i n a t i o n the t o t a l d r y weight o f the f e c e s was r e l a t e d to the t o t a l f o o d i n t a k e over the ten day p e r i o d . These weights were r e s p e c t i v e l y 285 grams and 1260 grams. The h i g h v a l u e o b t a i n e d by t h i s method may be the r e s u l t o f mechanical e r r o r s i n h e r e n t i n the method. T h i s i n c l u d e d the i m p o s s i b i l i t y o f c o l l e c t i n g a l l o f the f e c e s under the c o n d i t i o n employed and the e r r o r i n weighing the food o n l y to the n e a r e s t h a l f ounce. S i n c e the average food i n t a k e was o n l y f i v e ounces per day t h i s l a t t e r f a c t o r c o u l d amount to a 10 per cent e r r o r . A l s o t h i s l e v e l o f f o o d i n t a k e was c o n s i d e r a b l y below t h a t r e q u i r e d f o r maintenance which r e s u l t e d i n a s m a l l weight l o s s . T h i s r e -d u c t i o n i n i n g e s t e d f o o d c o u l d be r e f l e c t e d i n the h i g h e r d i g e s t i b i l i t y f i g u r e s i n c e d i g e s t i b i l i t y obeys the law o f d i m i n i s h i n g increments (Brody p. 76, 1945). N e v e r t h e l e s s from the three methods employed i t appears that the d i g e s t i b i l i t y of r a t i o n # 204 was approximately 70 per cent. c. Time of Food Passage Observations on the f e e d i n g behaviour o f the beaver used i n t h i s i n v e s t i g a t i o n i n d i c a t e d that f e e d i n g commenced about 6 or 7 p.m. and that the m a j o r i t y of the f o o d was consumed d u r i n g the evening. D e f e c a t i o n was u s u a l l y performed l a t e i n the even-i n g or e a r l y morning u n l i k e the beavers kept i n the tanks which defecated i n the evening as soon as they entered the water. - 71 -Prom the c o l o u r o f the f e c e s on the three s u c c e s s i v e days f o l l o w i n g the f e e d i n g o f the three d i f f e r e n t c o l o u r e d r a t i o n s i t was evident that the m a j o r i t y o f the f o o d passed through the a l i m e n t a r y system i n 24 to 36 hours. On the second day f o l l o w i n g the i n t a k e o f the r a t i o n c o n t a i n i n g c h a r c o a l the f e c e s were s l i g h t l y darker than normal hut by the t h i r d day the f e c e s were q u i t e normal i n c o l o u r . T h i s i n d i c a t e s that some o f the f o o d r e q u i r e d about 48 to 60 hours f o r complete passage through the a l i m e n t a r y system. On October 15 f r e s h k a l e was g i v e n to the beavers which had p r e v i o u s l y been on r a t i o n # 204 f o r s e v e r a l days. On October 16 beaver # 13 d i e d , a p p a r e n t l y from an o b s t r u c t i o n o f the p o s t e r i o r vena cava. I t had p r e v i o u s l y been i n good h e a l t h and was i n e x c e l l e n t p h y s i c a l c o n d i t i o n when i t d i e d . On autopsy remains o f k a l e were found i n the stomach, s m a l l i n t e s t i n e and the upper p o r t i o n o f the l a r g e i n t e s t i n e . About one per cent o f the c a e c a l contents was a l s o k a l e . I t i s es t i m a t e d that the animal d i e d 8 to 10 hours a f t e r f i r s t commencing to eat the k a l e . S i n c e the l a s t f o u r f e e t o f the l a r g e i n t e s t i n e c o n t a i n e d the r a t i o n remains i t was evident that t h i s would not have been def e c a t e d f o r an a d d i t i o n a l 24 hours. T h i s i m p l i e s t h a t the food r e q u i r e s up to 48 hours f o r .complete passage through the i n t e s t i n e . How l o n g the f o o d remains i n the caecum i s d i f f i c u l t to a s c e r t a i n , but from the amount o f k a l e found i n the caecum i t i s apparent that l i t t l e e n t e r s the caecum from any one f e e d i n g which would imply a c o n s i d e r a b l e l e n g t h o f time f o r the f o o d m a t e r i a l i n t h i s organ. - 72 -I n man over 70 per cent o f the food r e s i d u e s are ex-c r e t e d w i t h i n 72 hours although some may be d i s c h a r g e d w i t h i n 24 hours. Cows, goats and r a b b i t s a l s o d i s c h a r g e p a r t of the f o o d r e s i d u e w i t h i n 24 hours but r e q u i r e over 82 hours f o r com-p l e t e e v a c u a t i o n . The average time f o r complete e x c r e t i o n i n p i g s i s 48 hours (Dukes, 1955). 3. Blood Chemistry and Hematology The r e s u l t s p resented a re those from "normal" animals. "Normal" being used i n the sense that the animals showed no v i s i b l e s i g n s o f be i n g i l l and were i n an apparent h e a l t h y con-d i t i o n . Although s e v e r a l of the beavers d i e d d u r i n g l a t e f a l l and e a r l y winter there were no grounds f o r e x c l u d i n g t h e i r blood v a l u e s i n the c o m p i l a t i o n of the data, a p a r t from two e x c e p t i o n s , s i n c e they were a p p a r e n t l y "normal" a t the time when bloo d samples were taken. These two exce p t i o n s were beavers # 14 and # 22. Both o f these animals became i l l a f t e r the f i r s t s e t o f deter m i n a t i o n s were performed, thus subsequent d e t e r m i n a t i o n s were not i n c l u d e d . Both o f these beavers l a t e r r e v e a l e d the presence o f a heavy st a p h y l o c o c c u s i n f e c t i o n (see Appendix I ) . The v a l u e s obtained f o r the beavers a re c o n s i d e r e d to be r e p r e s e n t a t i v e o f the p o p u l a t i o n from which the animals were ob t a i n e d . T h i s was s u b s t a n t i a t e d by the f a c t t h a t v a l u e s o b t a i n e d from beavers w i t h i n a day or two from the time o f t h e i r capture were s i m i l a r to those from animals which had been i n c a p t i v i t y f o r s e v e r a l months. There were, however, c e r t a i n v a l u e s which d i d d e v i a t e c o n s i d e r a b l y from the mean but these were c o n s i d e r e d - 73 -to r e p r e s e n t o n l y an i n d i v i d u a l v a r i a t i o n w i t h i n the "normal" range. Where p e r t i n e n t such v a l u e s are d i s c u s s e d i n the t e x t . a. T o t a l Reducing Sugars The v a l u e s o b t a i n e d f o r the d i f f e r e n t age c l a s s e s are summarized i n Table XI. I s i n d i c a t e d by the wide range and the l a r g e standard d e v i a t i o n there was c o n s i d e r a b l e v a r i a t i o n i n the t o t a l r e d u c i n g sugars. There was no s i g n i f i c a n t d i f f e r e n c e between the y e a r l i n g s and a d u l t s but the k i t e x h i b i t e d a r a t h e r low v a l u e . S i n c e t h i s was a s i n g l e d e t e r m i n a t i o n and i t f a l l s w i t h i n the range f o r the oth e r beavers i t probably has no s i g n i f i c a n c e . P e t e r s et a l . (1946) s t a t e that there i s no s i g n i f i c a n t age d i f f e r e n c e i n blood sugar l e v e l s a l t h o u g h there i s some evidence t h a t i n humans the l e v e l i n c r e a s e s s l i g h t l y d u r i n g o l d age. TABLE XI Reducing Sugars i n Beaver Blood - mg. per 100 ml. o f Blood K i t Y e a r l i n g s A d u l t s A l l beavers Mean and Standard E r r o r 58.5 95.8^5.2 98.8±5.7 96.4-3.8 Standard D e v i a t i o n 27.0 26.6 26.9 Range 67-160 49-141 49-160 P l u c t u a t i o n s i n the blood sugar l e v e l a re brought about - 74 -by differences i n the rate of interconversion of l i v e r glycogen and glucose under the influence of hormones. When the glucose level increases as a result of an intake of food or some other factor, the pancreas secretes insu l in which increases carbo-hydrate oxidation and the formation of glycogen and fat . This process i s counteracted by the action of adrenalin, secreted by the adrenal medulla, which increases the rate of breakdown from l i ver glycogen to glucose. During the post-absorptive state these processes tend to balance each other with only small fluctuations produced. Any interruption i n this homeostatic mechanism can result i n wide fluctuations. Increased blood sugar levels or hyperglycemia commonly result from insufficient insul in secretion or from an increase i n adrenalin. Under any condition of imposed stress there tends to be an increase i n adrenalin output which results i n hyper-glycemia (Selye, 1946). Hypoglycemia i s usually associated v/ith malnutrition. Under such conditions the l i v e r glycogen i s insuff ic ient to maintain the blood glucose level and gluconeogenesis takes place from the amino acids of the tissue protein. This results in a general lowering of the blood sugar level as has been indicated in humans and cattle (West and Todd, 1951; Dukes, 1955). Undoubtedly most of the high fluctuations observed i n the beaver blood were due to increased adrenalin output. This would be brought about by the beavers' reaction to stress produced as a result of their being captured and handled, although struggling was minimized as much as possible. Blood taken from the anaes-t h e t i z e d animals a f t e r 50 minutes of quiescence i n d i c a t e d a l e v e l o f 77.4 mg. per cent which i s c o n s i d e r a b l y lower than t h a t obtained from the unan a e s t h e t i z e d animals. A l s o 11 o f the 12 y e a r l i n g s t e s t e d i n the f a l l had a mean value o f 80.0 mg. per cent and three a d u l t s had a mean o f 83.8 mg. per c e n t . There was a minimum o f s t r u g g l i n g by the beavers at t h i s time p r o b a b l y as a r e s u l t o f t h e i r c o n d i t i o n i n g . These v a l u e s tend to i n d i c a t e t h a t perhaps the t r u e sugar l e v e l i s i n the or d e r o f 80 mg. per cent r a t h e r than 96 mg. per cent as i n d i c a t e d by the o v e r - a l l average. The normal range f o r humans by t h i s method i s between 70 and 100 mg. per cent (Hawk et a l . , 1954). M c B i r n i e et a l . (1953) obtained a range o f 69 to 122 mg. per cent f o r the ground hog du r i n g s p r i n g and Dunn et a l . (1951) g i v e a v a l u e o f 80 mg. per cent f o r the l a b o r a t o r y r a t . The horse and dog have a range be-tween 55 and 95 mg. per cent w h i l e the ruminants tend to have a lower range between 50 and 70 rag. per cent (Dukes, 1955; Bandy, 1955). b. T o t a l P r o t e i n i n Whole Blood Values f o r the d i f f e r e n t age c l a s s e s a re summarized i n Table X I I . The summer de t e r m i n a t i o n s were lower than those obtained i n the f a l l f o r bot h the y e a r l i n g s and a d u l t s . The y e a r l i n g summer v a l u e was s i g n i f i c a n t l y lower than that o b t a i n e d i n the f a l l and s i g n i f i c a n t l y lower than the a d u l t summer v a l u e . T o t a l p r o t e i n i n the whole b l o o d i n c l u d e s albumin, g l o b u l i n , f i b r i n o g e n , hemoglobin and to a l e s s e r extent the pr o t e i n a c e o u s m a t e r i a l o f the blood c e l l w a l l s . Hemoglobin i s TABLE XII T o t a l P r o t e i n i n Whole Beaver Blood Grams per 100 ml. o f Blood K i t Y e a r l i n g s A d u l t s P a l l Summer P a l l T o t a l Summer P a l l T o t a l Mean and Standard E r r o r 21.77 17.72*0.33 * 20.03*0.41 18.85*0.36 19.43*0.23 20.40*0.58 19.40*0.29 Standard D e v i a t i o n 1.00 1.37 1.67 0.72 1.54 1.38 Range 16.49-19.10 19.18-23.35 16.49-23.35 18.14-20.18 17.99-22.31 16.89-22.31 *,** i n d i c a t e s P < 0.01 by f a r the l a r g e s t c o n s t i t u e n t t h e r e f o r e any v a r i a t i o n i n t h i s component w i l l g r e a t l y a l t e r the t o t a l p r o t e i n l e v e l . I t has been shown that the l e v e l o f hemoglobin g r a d u a l l y i n c r e a s e s as m a t u r i t y i s reached i n such s p e c i e s as man and cow (West and Todd, 1951; Dukes, 1955). The v a l u e s obtained f o r the beavers i l l u s t r a t e the same s i t u a t i o n , the summer d e t e r m i n a t i o n b e i n g s i g n i f i c a n t l y lower than those o b t a i n e d i n the f a l l . P a r t o f t h i s apparent d i f f e r e n c e i s due to the lower c e l l volume i n the y e a r l i n g beavers as i n d i c a t e d by the hematocrit v a l u e s . The plasma p r o t e i n s were a l s o s i g n i f i c a n t l y lower i n the y e a r l i n g s d u r i n g summer. T h i s d i f f e r e n c e may be due to the g r e a t e r p r o t e i n requirements o f the growing beaver and/or to the d i f f e r e n c e i n the water content o f the b l o o d . A h i g h e r water l e v e l i n the y e a r l i n g s would be i n d i c a t e d by the lower l e v e l s of the con-s t i t u e n t s . The range f o r the a d u l t s d u r i n g the summer and f a l l were 18.0 to 22.3 grams per cent which i s s i m i l a r to the normal range i n man o f 18.5 to 23.0 grams per cent (West and Todd, 1951). c. Albumin The summer and f a l l albumin v a l u e s are summarized by age c l a s s i n Table X I I I . Both y e a r l i n g s and a d u l t s had a lower v a l u e d u r i n g summer than i n the f a l l . The y e a r l i n g s i n summer had a lower v a l u e than the a d u l t s . None o f the d i f f e r e n c e s was s i g n i f i c a n t . The s i n g l e v a l u e obtained f o r the k i t was h i g h e r than any of the o t h e r d e t e r m i n a t i o n s . The albumin f r a c t i o n i s r e l a t i v e l y homogeneous as compared w i t h the g l o b u l i n f r a c t i o n and has a g r e a t e r s o l u b i l i t y , lower TABLE X I I I Albumin i n Beaver Blood Grams per 100 ml. o f serum K i t Y e a r l i n g s A d u l t s Summer F a l l T o t a l Summer F a l l T o t a l Mean and Standard E r r o r 5.29 4.18*0.05 4.36*0.08 4.24*0.51 4.28*0.12 4.51*0.21 4.37*0.10 Standard D e v i a t i o n 0.17 0.25 0.25 0.36 0.55 0.44 Range 3.94-4.49 3.96-4.74 3.73-4.74 3.78-4.84 3.86-5.26 3.78-5.26 - 79 -molecular weight and a more a c i d i s o e l e c t r i c p o i n t . S i n c e i t s i s o e l e c t r i c p o i n t i s lower and the i o n s do not pass through c a p i l l a r y w a l l s the albumin binds c o n s i d e r a b l e numbers of c a t i o n s to i t s s t r u c t u r e . T h i s , along with the o t h e r p r o p e r t i e s o f a l -bumin are r e s p o n s i b l e f o r i t s m a i n t a i n i n g over 80 per cent o f the e f f e c t i v e osmotic p r e s s u r e o f the bl o o d , which i s important i n the r e g u l a t i o n o f water between the bloo d and t i s s u e s . When the albumin l e v e l i s low water w i l l pass i n t o the t i s s u e s r e -s u l t i n g i n edema and a decreased b l o o d volume. Normally these c o n d i t i o n s are prevented by an i n c r e a s e i n g l o b u l i n which u s u a l l y accompanies a decrease i n albumin. B e s i d e s the maintenance of osmotic p r e s s u r e and a i d i n g i n the r e g u l a t i o n of the a c i d - b a s e balance o f the b l o o d , albumin a l s o s e r v e s as a ready source o f p r o t e i n . Whipple, Schoenheimer and o t h e r s have shown t h a t the p r o t e i n s a re i n a continuous dynamic s t a t e and d u r i n g growth when the body p r o t e i n s a r e being enlarged the albumin l e v e l w i l l be lowered as a r e s u l t o f t h e i r i n c o r p o r a t i o n i n the new t i s s u e ( P e t e r s e_t a l . , 1946). S i m i l a r -l y under s t a r v a t i o n c o n d i t i o n s the albumin l e v e l w i l l be lowered as heavy demands are p l a c e d upon the body p r o t e i n s to su p p l y the necessary energy f o r maintenance. Albumin has a l s o been shown to decrease i n d i s e a s e s which a f f e c t the l i v e r such as c i r r h o s i s and c h r o n i c h e p a t i t i s , s i n c e the l i v e r i s the centre of albumin f o r m a t i o n . General i n f e c t i o n s and v i t a m i n d e f i c i e n c i e s can a l s o cause a r e d u c t i o n i n albumin. The apparent lower v a l u e s observed i n the y e a r l i n g s i s pr o b a b l y due to the l a r g e p r o t e i n requirements o f these growing - 80 -animals as compared with the a d u l t s . During the f a l l the beavers were on a h i g h e r p r o t e i n d i e t which may account i n p a r t f o r the l a r g e r v a l u e s o b t a i n e d a t that time. The albumin range o f the beaver was from 3.7 to 5.3 grams per cent which i s g r e a t e r than the normal human range o f 3.5 to 4.5 grams per cent (West and Todd, 1951). The mean o f 4.4 grams per cent i s a l s o h i g h e r than that o f the horse, cow, sheep, goat, dog and cat which have mean v a l u e s between 5 and 4 grams per cent (Dukes, 1955). d. G l o b u l i n The summer and f a l l v a l u e s a re summarized by age c l a s s i n Table XIV. In g e n e r a l the y e a r l i n g s have a lower l e v e l than the a d u l t s . T h i s d i f f e r e n c e i s s i g n i f i c a n t f o r the summer d e t e r -m i n a t i o n s . The k i t a l s o had a low v a l u e . G l o b u l i n c o n s i s t s o f a v a r i e t y o f p r o t e i n s having a hi g h e r molecular weight than albumin and a more a l k a l i n e i s o -e l e c t r i c p o i n t . Thus they a re not as important as albumin i n water r e g u l a t i o n but they do p l a y a s i g n i f i c a n t p a r t . They a l s o a i d i n the b u f f e r i n g a c t i o n of the b l o o d and i n n u t r i e n t sources. The gamma f r a c t i o n produces a n t i b o d i e s f o r defence a g a i n s t i n -f e c t i o n . T h i s accounts i n p a r t f o r the i n c r e a s e i n g l o b u l i n d u r i n g c h r o n i c i n f e c t i o n s , malignancy and n e p h r o s i s . An i n c r e a s e i s o f t e n encountered i n c o n d i t i o n s which cause a decrease i n water content o f the b l o o d , such as m a l n u t r i t i o n , but t h i s i s only an apparent i n c r e a s e and not an a b s o l u t e one. Decreases are u s u a l l y a s s o c i a t e d w i t h l i v e r d i s o r d e r s and i n p a r t i c u l a r l i v e r c i r r h o s i s . TABLE XIV G l o b u l i n i n Beaver Blood Grams per 100 ml. o f serum K i t Y e a r l i n g s A d u l t s Summer P a l l T o t a l Summer P a l l T o t a l Mean and Standard E r r o r 1 . 95 * 2.64*0.13 2.93*0.08 #* 2.76*0.08 * 3.32*0.22 3.12*0.31 3.19*0.17 Standard D e v i a t i o n 0.46 0.26 0.39 0.68 0.83 0.73 Range 1.87-3.60 2.56-3.52 1.87-3.60 2.55-4.79 2.37-4.41 2.38-4.79 *, ** i n d i c a t e s P < 0.05 - 82 -The low v a l u e s o b t a i n e d f o r the y e a r l i n g s d u r i n g summer may be p a r t l y a r e s u l t o f the g r e a t e r p r o t e i n demands by the growing t i s s u e s o f these animals. The range of 1.8 to 4.8 grams per cent i s q u i t e com-p a r a b l e to the normal range i n humans which i s 2.0 to 4.5 grams per cent (West and Todd, 1951). The mean f o r the a d u l t s was 3.2 grams per cent which i s s i m i l a r to that o f the horse which has a v a l u e o f 3.25 grams per cent (Dukes, 1955). The cow and cat have h i g h e r v a l u e s while dog, sheep and goat have lower average v a l u e s . e. Albumin - G l o b u l i n R a t i o The summer and f a l l r a t i o s are summarized by age groups i n Table XV. There was c o n s i d e r a b l e v a r i a t i o n as i n d i c a t e d by the l a r g e standard d e v i a t i o n and no s i g n i f i c a n t d i f f e r e n c e s were i n d i c a t e d between the groups. Many d i s e a s e s a r e c h a r a c t e r i z e d by a l t e r a t i o n s i n t h i s r a t i o . The c o n d i t i o n s which b r i n g about a decrease i n albumin are u s u a l l y accompanied by an i n c r e a s e i n g l o b u l i n so that the t o t a l serum p r o t e i n may not be a l t e r e d , a lthough the r a t i o may be g r e a t l y changed. I n i n f e c t i o u s d i s e a s e s p a r t o f the i n c r e a s e i n g l o b u l i n i s due to the gamma g l o b u l i n f r a c t i o n which i n c r e a s e s the antibody f o r m a t i o n . I n m a l n u t r i t i o n albumin decreases and the b l o o d volume i s lowered because o f l o s s o f water which r e -s u l t s i n an apparent i n c r e a s e i n g l o b u l i n . Each s p e c i e s has i t s own c h a r a c t e r i s t i c r a t i o . The horse has a normal r a t i o o f u n i t y w h i l e that of the cow i s l e s s than u n i t y . The sheep, goat, dog and cat have an average r a t i o w i t h i n TABLE XV Beaver A l b u m i n - G l o b u l i n (A/G) Ra t i o K i t Y e a r l i n g s A d u l t s Summer P a l l T o t a l Summer P a l l T o t a l Mean and Standard E r r o r 2.71 1.65*0.09* 1.50*0.06 1.58*0.05 1.33^0.10* 1.54*0.17 1.46*0.08 Standard D e v i a t i o n 0.31 0.19 0.26 0.31 0.45 0.36 Range 1.15-2.26 1.13-1.85 1.13-1.85 0.82-1.79 0.91-2.07 0.82-2.07 * i n d i c a t e s P < 0.05 - 84 -the range of 1.1 to 1.5 (Dukes, 1955). The normal range f o r man i s 1.2 to 1.8 (West and Todd, 1951). The beaver has a s l i g h t l y -h i g h e r albumin l e v e l than the above s p e c i e s which r e s u l t s i n a hi g h e r r a t i o . The mean a d u l t r a t i o i s 1.5 and t h a t o f the y e a r -l i n g s 1.6. Beaver # 8 e x h i b i t e d i n f o u r d i f f e r e n t d e t e r m i n a t i o n s , a r a t i o r a n g i n g between 0.82 and 0.95. I n a l l cases the albumin was lower than that o f the oth e r beavers and the g l o b u l i n was hi g h e r . T h i s animal showed no v i s i b l e s i g n s o f i l l n e s s and the other d e t e r m i n a t i o n s f e l l w i t h i n t h e i r c h a r a c t e r i s t i c ranges. Whether t h i s s i t u a t i o n was produced by a p a t h o l o g i c a l c o n d i t i o n or whether i t i s merely an i n d i v i d u a l v a r i a t i o n w i l l have to await f u r t h e r study. Two oth e r beavers, # 14 and # 22 had r a t i o s c l o s e to u n i t y . Both of these animals d i e d s h o r t l y a f t e r these d e t e r -minations were made and c u l t u r e s from the l e s i o n s on t h e i r organs i n d i c a t e d a heavy st a p h y l o c o c c u s i n f e c t i o n . From these observa-t i o n s i t appears t h a t n o r m a l l y a r a t i o c l o s e to u n i t y i s pr o g -n o s t i c o f an i n f e c t i o u s s t a t e . f . T o t a l P r o t e i n i n Serum Summer and f a l l d e t erminations are summarized by age c l a s s i n Table XVI. There was a s i g n i f i c a n t d i f f e r e n c e between the summer and f a l l y e a r l i n g v a l u e s and between the summer v a l u e s f o r the y e a r l i n g s and a d u l t s . Serum c o n t a i n s the albumin and g l o b u l i n f r a c t i o n s p r e -v i o u s l y d i s c u s s e d , and as i n d i c a t e d by the A/G r a t i o t h e i r p r o p o r t i o n s remain r e l a t i v e l y constant among the i n d i v i d u a l s o f TABLE XVI T o t a l P r o t e i n i n Beaver Serum Grams per 100 ml. of Serum K i t Y e a r l i n g s A d u l t s P a l l Summer P a l l T o t a l Summer F a l l T o t a l Mean and Standard E r r o r 7.25 6.70*0.' 10 7.28*0.07 *** 6.96*0.04 7.61*0.17 7.63*0.25 7.49*0.14 Standard D e v i a t i o n 0.32 0.23 0.19 0.54 0.67 6.20 Range 6.08-7.04 7.06-7.71 6.08-7.71 6.81-8.69 6.46-8.44 6.46-8.69 * t » * t * * * i n d i c a t e s P < 0.01 - 86 -the same s p e c i e s but they can var y g r e a t l y between s p e c i e s . F o r i n s t a n c e the cow has a mean v a l u e o f 7.6 grams per cent as com-pared w i t h 7.5 grams per cent f o r the a d u l t beaver but the A/G r a t i o i s l e s s than u n i t y i n d i c a t i n g a r e l a t i v e l y h i g h g l o b u l i n f r a c t i o n . Most of the other domestic s p e c i e s except the cat have a lower serum p r o t e i n l e v e l (Dukes, 1955). Man has a l e v e l o f 7.1 grams per cent w i t h a f r a c t i o n a l d i s t r i b u t i o n s i m i l a r to that i n the beaver ( R e i n e r , 1953). The lower v a l u e s obtained f o r the y e a r l i n g s , e s p e c i a l l y d u r i n g the summer i s r e f l e c t e d i n both the albumin and g l o b u l i n l e v e l s p r e v i o u s l y d i s c u s s e d . T h i s was p a r t i a l l y c r e d i t e d to the g r e a t e r p r o t e i n u t i l i z a t i o n o f the growing animals coupled w i t h the lower p r o t e i n d i e t d u r i n g the summer. S i n c e the serum pro-t e i n a l s o r e g u l a t e s the water content o f the blood any d i f f e r -ences i n t h e i r l e v e l s w i l l cause v a r i a t i o n s i n the b l o o d volume which may r e s u l t i n apparent v a r i a t i o n s i n plasma c o n s t i t u e n t s . This c o u l d a l s o account f o r the lower apparent l e v e l i n the y e a r l i n g s d u r i n g summer. g. F i b r i n o g e n The v a l u e s obtained d u r i n g the summer f o r the y e a r l i n g s and a d u l t s are summarized i n Table XVII. The d i f f e r e n c e between the two groups i s s i g n i f i c a n t a l t h o u g h the v a r i a b i l i t y i s q u i t e g r e a t . The main f u n c t i o n o f f i b r i n o g e n i s i n the c o n t r o l o f bl o o d c l o t t i n g although i t does a i d i n the r e g u l a t i o n o f the water con-t e n t o f the plasma. I t i n c r e a s e s i n t i s s u e i n j u r y , acute i n f e c -t i o n s , n e p h r o s i s and pneumonia. Decreases a re brought about by - 87 -c o n d i t i o n s which damage the l i v e r , s i n c e t h i s organ i s the s i t e of f i b r i n o g e n f o r m a t i o n . TABLE XVII F i b r i n o g e n i n Beaver Blood Grams per 100 ml. of Plasma Y e a r l i n g s ( T o t a l ) A d u l t s ( T o t a l ) Mean and Standard E r r o r 0.47*0.07* 0.58*0.07* Standard D e v i a t i o n ; 0.17 0.24 Range 0.26-0.79 0.16-1.03 * i n d i c a t e s P < 0.01 The v a l u e o f 0.58 grams per cent i s h i g h e r than the normal range o f 0.2 to 0.4 grams per cent f o r humans (West and Todd, 1951). The horse and sheep a l s o have lower average v a l u e s of 0.34 and 0.36 grams per cent r e s p e c t i v e l y w h i l e the goat and cow l e v e l s are hig h e r w i t h r e s p e c t i v e v a l u e s of 0.6 and 0.72 grams per cent (Dukes, 1955). The lower v a l u e s obtained f o r the y e a r l i n g s p a r a l l e l the c o n d i t i o n s found f o r the albumin and g l o b u l i n v a l u e s . T h i s may be due to the g r e a t e r p r o t e i n demands of the growing animals or to a d i l u t i o n e f f e c t o f the plasma g i v i n g an apparent lower v a l u e - 88 -as p r e v i o u s l y d i s c u s s e d . h. T o t a l P r o t e i n i n the Plasma The summer and t o t a l v a l u e s f o r the y e a r l i n g s and a d u l t s are summarized i n Table X V I I I . The t o t a l v a l u e s i n c l u d e the determinations o b t a i n e d d u r i n g the p r e c e d i n g w i n t e r . The y e a r -l i n g s had a s i g n i f i c a n t l y lower average v a l u e than the a d u l t s i n both cases. TABLE XVIII T o t a l P r o t e i n i n Beaver Plasma Grams per 100 ml. o f Plasma Y e a r l i n g s A d u l t s Summer T o t a l Summer T o t a l Mean and Standard E r r o r * 6.87*0.12 ** 6.93*0.13 * 8.24*0.22 ** 8.01*0.20 Standard D e v i a t i o n 0.27 0.35 0.57 0.63 Range 6.39-7.04 6.39-7.50 7.61-9.08 7.16-9.08 *,** i n d i c a t e s P < 0.01 Plasma p r o t e i n s i n c l u d e albumin, g l o b u l i n and f i b r i n o g e n although s m a l l amounts of n e u c l e o p r o t e i n and seromucoids are pr e s e n t . The l e v e l w i l l f l u c t u a t e as a r e s u l t o f a l l o f the f a c t o r s p r e v i o u s l y d i s c u s s e d i n the above c o n s t i t u e n t s . Apparent - 89 -changes w i l l be observed when the water balance mechanisms a r e upset producing changes i n the osmotic p r e s s u r e o f the b l o o d . A c t u a l decreases may r e s u l t from d i e t a r y d e f i c i e n c e s as i n m a l n u t r i t i o n , n e p h r o s i s , hemorrhage and l i v e r d i s e a s e s . The average v a l u e o f 8.0 grams per cent f o r the a d u l t s i s lower than the va l u e of 8.3 grams per cent g i v e n f o r the cow but h i g h e r than that found i n the goat, sheep, horse, dog and man (Dukes, 1955). The lower v a l u e o b t a i n e d f o r the y e a r l i n g s r e f l e c t s the sum t o t a l of the i n d i v i d u a l c o n s t i t u e n t d i f f e r e n c e s p r e v i o u s l y d i s c u s s e d . Beaver # 8 i n d i c a t e d a r a t h e r h i g h l e v e l o f plasma p r o t e i n (9.1 grams per cent) which was p r i n c i p a l l y due to the h i g h g l o b u l i n c ontent. i . Non-protein N i t r o g e n Values f o r the d i f f e r e n t age c l a s s e s are summarized i n Table XIX. The summer dete r m i n a t i o n s f o r both y e a r l i n g s and a d u l t s were s i g n i f i c a n t l y lower than the f a l l d e t e r m i n a t i o n s . There was no a p p r e c i a b l e d i f f e r e n c e between members of the d i f f e r e n t age groups. Non-protein n i t r o g e n i n c l u d e s a l l the n i t r o g e n o u s substances i n the p r o t e i n - f r e e f i l t r a t e such as urea, u r i c a c i d , amino a c i d s , g l u t a t h i o n e , c r e a t i n e , c r e a t i n i n e and a few oth e r compounds c o n t a i n i n g minute amounts of n i t r o g e n . Urea r e p r e -sents about 45 per cent o f the N.P.N, and i s u s u a l l y the cause of l a r g e v a r i a t i o n s i n the n i t r o g e n l e v e l (Hawk e_t a l . , 1954). Although c o n d i t i o n s which g e n e r a l l y cause an i n c r e a s e i n the l e v e l o f b l o o d u r e a a l s o cause an i n c r e a s e i n the oth e r major TABLE XIX N.P.N, i n Beaver Blood Mg. per 100 ml. of Blood Kit Yearlings Adults Summer P a l l Total Summer P a l l Total Mean and Standard Error 38.4 35.6*1.3* 45.3*2.2 40.5*1.5 36.9*1.6** 43.6*2.3** 39.0*1.5 Standard Deviation 4.6 7.3 7.5 5.2 6.0 6.6 Range 29.6-44.8 30.2-54.9 29.6-54.9 28.0-44.0 36.1-53.2 28.0-53.2 * , * * indicates P < 0.01 - 91 -N.P.N* c o n s t i t u e n t s (Reiner, 1953). Thus r e n a l d i s o r d e r s which impare u r e a s y n t h e s i s r e s u l t i n an i n c r e a s e i n N.P.N. The l e v e l i s a l s o i n c r e a s e d d u r i n g e x c e s s i v e t i s s u e c a t a b o l i s m such as i n i n f e c t i o n s , f e v e r , s t a r v a t i o n and severe m a l n u t r i t i o n . Low valu e s are a s s o c i a t e d with n e p h r o s i s which i s pro b a b l y o f metab-o l i c o r i g i n r a t h e r than o f r e n a l o r i g i n (West and Todd, 1951). The normal range of N.P.N, i n human blood i s 28 to 39 mg. per cent (West and Todd, 1951). The ranges g i v e n by Dukes (1955) f o r s e v e r a l domestic s p e c i e s f a l l between 20 to 45 mg. per cent. Por beaver the range i s s l i g h t l y h i g h e r , extending from 28 to 55 mg. per cent, although the summer range was lower. S i n c e the three N.P.N, components t e s t e d d i d not show an a p p r e c i a b l e s e a s o n a l d i f f e r e n c e the s i g n i f i c a n t d i f f e r e n c e observed i n the t o t a l N.P.N, was pr o b a b l y due to an i n c r e a s e i n blood u r e a . The d i f f e r e n c e cannot be c r e d i t e d to a m a n i f e s t a t i o n o f growth s i n c e i t was present i n the non-growing a d u l t s as w e l l as the y e a r l i n g s . P a r t o f the d i f f e r e n c e may be due to the h i g h e r p r o t e i n l e v e l o f the f a l l d i e t as compared wi t h that i n the summer. Por i f the animal i s to m a i n t a i n a balance between n i t r o g e n a b s o r p t i o n and u r i n a r y output, an i n c r e a s e d a b s o r p t i o n n e c e s s i t a t e s a g r e a t e r f o r m a t i o n o f urea. T h i s may have r e s u l t e d i n the i n c r e a s e , i n the l e v e l o f N.P.N, i n the beaver blood d u r i n g the f a l l . The amino a c i d n i t r o g e n a l s o e x h i b i t e d h i g h e r v a l u e s i n beaver bl o o d than i n the ot h e r domestic s p e c i e s (Dukes, 1955). T h i s may a l s o be a r e s u l t of the h i g h e r p r o t e i n l e v e l o f the f a l l d i e t . Blood from two beavers which l a t e r d i e d as a r e s u l t o f - 92 -emaciation and a staphylococcus i n f e c t i o n gave h i g h v a l u e s o f N.P.N. Beaver # 14 had a l e v e l o f 59 mg. per cent and # 22 a l e v e l o f 143 mg. per cent. In both cases t h i s was accompanied by a l a r g e i n c r e a s e i n the c r e a t i n e and c r e a t i n i n e l e v e l s . j . Amino A c i d N i t r o g e n Values f o r the d i f f e r e n t age c l a s s e s are summarized i n Table XX. The a d u l t s had a s l i g h t l y h i g h e r l e v e l than the younger age group but the d i f f e r e n c e was not s i g n i f i c a n t . TABLE XX Amino A c i d N i t r o g e n i n Beaver Blood Mg. per 100 ml. of Blood K i t Y e a r l i n g s A d u l t s Mean and Standard E r r o r 8.2 8.93*0.34 9.28*0.38 Standard D e v i a t i o n 1.17 1.27 Range 7.1-11.2 7.4-12.0 S i n c e p r o t e i n metabolism i s i n a continuous dynamic s t a t e the o v e r - a l l l e v e l o f the amino a c i d s i n the blood i s changed v e r y l i t t l e , although i t w i l l i n c r e a s e s l i g h t l y a f t e r i n g e s t i o n o f f o o d . V i r t u a l l y no change i s observed d u r i n g s t a r v a t i o n s i n c e the body p r o t e i n s are c o n s t a n t l y b e i n g c a t a b o l i z e d which m a i n t a i n s - 93 -the blood amino aeid leve l . Similarly most pathological con-ditions do not cause a change i n the amino acid content on a total quantitative basis. Although diseases l ike nephritis and acute yellow atrophy of the l i ver w i l l cause a small change since they interfere with the deaminating process of the l i ver (West and Todd, 1951). Age and sex appear to have l i t t l e effect, although values for young animals tend to be lower than i n adults. This i s probably related to the greater u t i l i z a t i o n of amino acids for tissue formation i n young animals (Peters et a l . , 1946). This could account for the lower values obtained for the beaver yearlings as compared with the adults. The level of amino acid nitrogen in the beaver ranged between 7 and 12 mg. per cent which i s higher than the normal ranges for man and several domestic species which have values between 4 and 8 mg. per cent (Hawk e_t a l . , 1954; Dukes, 1955). k. Creatine and Creatinine The creatine and creatinine values for the different age classes are summarized i n Table XXI and XXII respectively. Both constituents showed a s ignif icantly lower yearling value as com-pared with the adults and the summer creatine value for the yearlings was s ignif icantly lower than the f a l l value. Creatine exists primarily within the red blood ce l l s i n the phosphate form, where i t serves as a source of high energy phosphate bonds for the adenosine phosphate complex so important in energy transformation. Creatine i s constantly being converted into the dehydrated form, creatinine, which i s excreted i n the urine. Creatinine appears to serve no useful function in the body TABLE XXI C r e a t i n e i n Beaver Blood Mg. per 100 ml. o f blood K i t Y e a r l i n g s A d u l t s Summer F a l l T o t a l Summer F a l l T o t a l Mean and Standard E r r o r 3.00 # ** 2.36±0;09 * 2.72*0.13 2.53*0.09 ** 2.97*0.14 2.58*0.13 2.81*0.11 Standard D e v i a t i o n 0.31 0.45 0.41 0.43 0.34 0.43 Range 1.96-3.20 1.95-3.29 1.95-3.29 2.02-3.45 2.00-3.00 2.00-3.45 * i n d i c a t e s P < 0.05 ** i n d i c a t e s P < 0.01 TABLE XXII C r e a t i n i n e i n Beaver Blood Mg. per 100 ml. o f Blood K i t Y e a r l i n g s A d u l t s Summer P a l l T o t a l Summer P a l l T o t a l Mean and Standard E r r o r 1.30 1.23*0.05 1.25*0.15 * 1.25*0.07 1.56*0.06 1.47*0.10 * 1.53*0.05 Standard D e v i a t i o n 0.16 0.48 0.36 0.18 0.27 0.21 Range 1.07-1.67 0.90-1.81 0.90-1.81 1.28-1.92 0.95-1.75 0.95-1.92 * i n d i c a t e s P < 0.01 - 96 -but simply r e p r e s e n t s the waste product of c r e a t i n e metabolism. C r e a t i n e l e v e l s i n human blood range between 3 and 5 mg. per cent which i s h i g h e r than the range of 2 to 3.5 mg. per cent found i n beavers. I t i n c r e a s e s i n c h r o n i c n e p h r i t i s as was i l l u s t r a t e d by the h i g h v a l u e of 11.4 mg. per cent obtained f o r beaver # 22. T h i s animal which d i e d s h o r t l y a f t e r the determina-t i o n was made i n d i c a t e d e x t e n s i v e c h r o n i c n e p h r i t i s . S t a r v a t i o n , m a l n u t r i t i o n and, i n g e n e r a l , d i s i n t e g r a t i o n o f body p r o t e i n s w i l l a l s o r e s u l t i n an i n c r e a s e i n the c r e a t i n e l e v e l . C r e a t i n i n e i s the l e a s t v a r i a b l e n i t r o g e n o u s c o n s t i t u e n t i n b l o o d . I t s range i s between 1 and 2 mg. per cent i n man and most domestic s p e c i e s (West and Todd, 1951; Dukes, 1955). A s i m i l a r range was o b t a i n e d f o r beaver. The l e v e l w i l l i n c r e a s e i n n e p h r i t i s as was i l l u s t r a t e d by the 2.63 mg. per cent v a l u e o b t a i n e d f o r beaver # 22. 1. C h o l e s t e r o l . The r e s u l t s f o r the y e a r l i n g s and a d u l t s are summarized i n Table X X I I I . The d i f f e r e n c e between the two groups i s s i g n i -f i c a n t but the v a l i d i t y of t h i s d i f f e r e n c e i s q u e s t i o n a b l e , i n view o f the v a r i a b i l i t y o f the few d e t e r m i n a t i o n s made. C h o l e s t e r o l i s an important c o n s t i t u e n t i n the body. I t i s found i n a l l c e l l s as p a r t of the p r o t o p l a s m i c s t r u c t u r e and c e l l membranes. There i s some evidence that c h o l e s t e r o l may be a p r e c u r s o r o f the s t e r o i d hormones and r e l a t e d v i t a m i n compounds (Re i n e r , 1953). I t a l s o takes p a r t i n the f o r m a t i o n o f b i l e s a l t s and i n the t r a n s p o r t a t i o n o f f a t t y a c i d s . I n the b l o o d the m a j o r i t y i s found i n the plasma, two t h i r d s o f which i s e s t e r f i e d - 97 -and the remainder i n the f r e e s t a t e . That w i t h i n the r e d c e l l s i s a l s o i n the f r e e s t a t e . TABLE XXIII C h o l e s t e r o l i n Beaver Blood Mg. per 100 ml. o f Blood Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 113.9*3.9* 96.9*5.4* 105.8*3.7 Standard D e v i a t i o n 13.0 17.1 17.1 Range 100-148 75-127 75-148 * i n d i c a t e s P < 0.05 C h o l e s t e r o l can be s y n t h e s i z e d w i t h i n the body from an a c e t i c a c i d p r e c u r s o r which p r i m a r i l y a r i s e s from f a t t y a c i d c a t a b o l i s m . The l i v e r and s k i n are the main c e n t r e s of s y n t h e s i s although other p a r t s o f the body can s y n t h e s i z e c h o l e s t e r o l . The p r o d u c t i o n i s i n v e r s e l y p r o p o r t i o n a l to the c h o l e s t e r o l i n t a k e thus the l e v e l i s maintained f a i r l y constant f o r any i n d i v i d u a l . There have been no sex d i f f e r e n c e s i l l u s t r a t e d and age d i f f e r e n c e s have been r e p o r t e d by some workers and denied by others ( R e i n e r , 1953). Marked v a r i a t i o n s are observed i n v a r i o u s d i s e a s e s and c o n d i t i o n s which i n t e r f e r e w i t h normal m e t a b o l i c - 98 -processes. In diabetes and starvation the body l ip ids are mobilized as a result of a decreased carbohydrate metabolism. This results i n an increase i n the cholesterol l eve l . It i s increased i n hyperthyroidism, lipemia, b i l i a r y obstruction and acute infections. It i s decreased i n hypothyroidism, pernicious anemia and i n infectious diseases l ike tuberculosis and diseases of the l i v e r which decrease synthesis and esterfication by the l i ver (Reiner, 1953). The concentration of cholesterol in the blood i s maintained at a level partly dependent on the level of phospholipids to which i t bears a f a i r l y constant rat io (Peters e_t a l . , 1946). This correlation between blood l i p i d s is also i l lus trated by the other l i p i d components. Their relationship to one another i s more im-portant than the absolute level of any one l i p i d (West and Todd, 1951). Thus each species has a different cholesterol level just as they have different total l i p i d levels , although the variat ion may be quite great within any one species. The beaver had an average level of 106 mg. per cent which i s lower than the average value of 152 and 110 mg. per cent ex-hibited by man and cow respectively. Lower values have been obtained for the cat, rat , rabbit and guinea pig which have res-pective mean values of 93, 52, 45 and 32 mg. per cent (Boyd, 1942). These values indicate that the beaver had a cholesterol level similar to that of the cow and that in general herbivores have a re lat ive ly low cholesterol l eve l . m. Volat i le Patty Acids The values for the yearlings and adults are summarized i n Table XXIV. There was no a p p r e c i a b l e d i f f e r e n c e between the two age groups. TABLE XXIV V o l a t i l e F a t t y A c i d s i n Beaver Blood M i l l i - e q u i v a l e n t s times 10 per 100 ml. o f Blood Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 19.04*1.51 18.55*2.03 18.78*1.23 Standard D e v i a t i o n 4.52 6.42 5.38 Range 10.6-25.5 9.9-32.3 9.9-32.3 V o l a t i l e f a t t y a c i d s i n c l u d e the s h o r t c h a i n f a t t y a c i d s such as a c e t i c , b u t y r i c , p r o p r i o n i c and f o r m i c a c i d s . These are produced d u r i n g f a t metabolism and by b a c t e r i a l a c t i o n i n the rumen or caecum o f h e r b i v o r o u s s p e c i e s . Humans and dogs have a normal v a l u e o f approximately 0.0003 m.e. (McLendon, 1944). T h i s v a l u e i s c o n s i d e r a b l y below that o f the cow as i n d i c a t e d by the 0.0021 m.e. v a l u e o b t a i n e d i n c o n j u n c t i o n w i t h the present study. The beaver a l s o had a h i g h l e v e l , a v e r a g i n g 0.0019 m.e. T h i s i n d i c a t e s the c l o s e s i m i l a r i t y between beavers and ruminants and a l s o i n d i c a t e d the h i g h b a c t e r i a l a c t i v i t y which must take p l a c e i n the caecum o f the beaver i n order to y i e l d a v a l u e so much g r e a t e r than that i n - 100 -c a r n i v o r e s . I n g e n e r a l these r e s u l t s imply that h e r b i v o r e s have a hig h e r v o l a t i l e f a t t y a c i d l e v e l than non-herbivorous s p e c i e s because o f the h i g h l e v e l o f b a c t e r i a i n t h e i r d i g e s t i v e t r a c t s , s i t e o f c e l l u l o s e d e g r a d a t i o n . n. Hemoglobin Values f o r the d i f f e r e n t age c l a s s e s a re summarized i n Table XXV. The summer v a l u e s were s i g n i f i c a n t l y lower than the f a l l d e t e r m i n a t i o n s and the summer y e a r l i n g average was s i g n i -f i c a n t l y lower than that o f the a d u l t s . V a r i a t i o n s i n the hemoglobin l e v e l can be brought about by a b s o l u t e changes or by c o n d i t i o n s which a f f e c t i t s r e l a t i v e abundance. Thus changes i n the bloo d c e l l d e n s i t y or the plasma volume as a r e s u l t o f changes i n c l i m a t e , a l t i t u d e , e x e r c i s e o r ex c e s s i v e f l u i d i n t a k e can a l t e r i t s apparent l e v e l . Hemo-c o n e e n t r a t i o n as a r e s u l t o f shock or d e h y d r a t i o n can a l s o i n -crease the apparent c o n c e n t r a t i o n . There i s a d e f i n i t e age d i f f e r e n c e which has been w e l l i l l u s t r a t e d i n man and domestic s p e c i e s (Sunderman and Boernerj 1949; Dukes, 1955). F o l l o w i n g the i n i t i a l h i g h l e v e l s h o r t l y a f t e r b i r t h the hemoglobin l e v e l remains r e l a t i v e l y low d u r i n g the e a r l y p o r t i o n o f the a n i m a l ^ l i f e , g r a d u a l l y i n c r e a s i n g to a p o i n t s h o r t l y a f t e r puberty. At t h i s time a sex d i f f e r e n c e a l s o becomes apparent, w i t h a h i g h e r l e v e l i n males. P a r t o f t h i s d i f f e r e n c e i s a t t r i b u t e d to the lower r e d c e l l numbers i n females. N a t u r a l v a r i a t i o n s are brought about to compensate f o r TABLE XXV Hemoglobin i n Beaver Blood Grams per 100 ml. o f Blood K i t Y e a r l i n g s A d u l t s P a l l Summer P a l l T o t a l Summer P a l l T o t a l Mean and Standard E r r o r 14.9 12.8*0.2* 13.6*0.4 13.2*0.3 13.5*0.2* 14.0*0.4 13.7*0.3 Standard D e v i a t i o n 0.6 1.4 1.1 0.7 1.1 1.2 Range 12.3-14.2 12.0-16.0 12.0-16.0 12.6-14.7 11.1-15.8 11.1-15.8 * i n d i c a t e s P < 0.05 - 102 -changes i n oxygen t e n s i o n . A l s o i n response to s t r e s s the s p l e e n w i l l d i s c harge more r e d c e l l s i n t o the g e n e r a l c i r c u l a t i o n which i n c r e a s e s the hemoglobin l e v e l . P a t h o l o g i c a l c o n d i t i o n s which i n t e r f e r e with the oxygenation of blood w i l l cause an i n -c r e a s e . Decreases r e s u l t i n anemias which are u s u a l l y brought about.by f a c t o r s which i n t e r f e r e w i t h b l o o d f o r m a t i o n or by i n -creased b l o o d d e s t r u c t i o n . In g e n e r a l any f a c t o r which causes a change i n the number o f r e d b l o o d c e l l s g r e a t l y a l t e r s the hemo-g l o b i n l e v e l . The hemoglobin l e v e l v a r i e s f o r d i f f e r e n t s p e c i e s . Most o f the domestic s p e c i e s have mean v a l u e s between 10 and 13 grams per cent (Dukes, 1955)• Thoroughbred horses s e l e c t e d f o r t h e i r speed have h i g h e r mean v a l u e s which p a r t i a l l y accounts f o r t h e i r g r e a t e r oxygen supply d u r i n g p e r i o d s of heavy demand (Hansen et a l . , 1950). Humans have a range of 11 to 16 grams per cent (Hawk et a l , 1954) which i s s i m i l a r to t h a t o b t a i n e d f o r the beaver. The low v a l u e s f o r y e a r l i n g s d u r i n g the summer were com-pa r a b l e to the s i t u a t i o n found i n o t h e r young growing s p e c i e s . By f a l l when growth had p r a c t i c a l l y ceased the l e v e l was s i m i l a r to t h a t of the a d u l t s . P a r t o f t h i s low v a l u e may be a t t r i b u t e d to a more d i l u t e d b l o o d as was i n d i c a t e d by the low plasma p r o t e i n l e v e l obtained d u r i n g the summer. No sex d i f f e r e n c e s were apparent from the r e s u l t s o b t a i n e d . Beaver # 14 and # 22 were anemic s h o r t l y b e f o r e t h e i r deaths as i n d i c a t e d by the low hemoglobin v a l u e s o f 10.3 and 10.7 grams per cent r e s p e c t i v e l y . T h i s anemic s t a t e was a l s o i l l u s t r a t e d by the c e l l counts which d e v i a t e c o n s i d e r a b l y from the average o f the - 103 -o t h e r beavers. o. Sedimentation Rate A summary of the v a l u e s f o r the d i f f e r e n t age groups i s presented i n Table XXVI. As i s i n d i c a t e d by the standard d e v i a -t i o n and range the v a r i a b i l i t y was q u i t e g r e a t . TABLE XXVI Beaver Sedimentation Rate - mm. per hour Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 34.7*6.5 40.1*7.3 36.6*4.8 Standard D e v i a t i o n 22.5 23.2 22.4 Range 9-72 10-78 9-78 Sedimentation r a t e i s a measure o f the s e t t l i n g o f r e d blood c e l l s under standard c o n d i t i o n s . T h i s r e f l e c t s the sus-pension s t a b i l i t y of the plasma. I t might be expected t h a t c e r -t a i n p h y s i c a l changes such as s p e c i f i c g r a v i t y and v i s c o s i t y of the plasma as w e l l as changes i n c e l l s i z e would a f f e c t t h i s s t a b i l i t y . However, none o f these f a c t o r s have been known to p r o -duce s i g n i f i c a n t changes. The major f a c t o r i s the degree o f a g g l u t i n a t i o n of the r e d c e l l s . The more a g g l u t i n a t i o n the f a s t e r the r a t e o f s e t t l e m e n t . The l e v e l of f i b r i n o g e n and p o s s i b l y - 104 -globulin axe considered to be the factors causing the difference i n rate, although, how they influence the rate is unknown (Best and Taylor, 1955). It has been indicated that when fibrinogen increases the sedimentation rate i s accelerated. Alpha globulin also appears to increase the rate but gamma globulin i s less effective. To some extent the rate depends on the relat ion of the various plasma fractions to one another (Perry ejb a l . , 1954). The changes are non-specific and are not indicative of any particular pathological condition, although the rate is i n -creased i n septicemia, pulmonary tuberculosis, anemia and inflammatory conditions (Dukes, 1955). There i s considerable interspecif ic variat ion. Coffin (1945) states that ruminants have l i t t l e to no settlement i n one hour while the pig has a rate of 1 to 14 mm. per hour and the dog 5 to 25 mm. per hour. The horse i s unique with i t s extremely fast rate of 15 to 58 mm. in 20 minutes. Man has a very slow rate of 1 to 7 mm. per hour with the females having a faster rate (Sunderman and Boerner, 1949). Bandy (1955) found a re la t ive ly fast rate in deer with a high degree of v a r i a b i l i t y . The average value obtained for the adult beaver was 40 mm. per hour with a range from 10 to 78 mm. per hour. This implies that the beaver is much l ike the horse with respect to the rapid sedimentation rate. p. Packed Red Ce l l Volume The packed red c e l l volume or hematocrit values are sum-marized i n Table XXVII. The yearlings exhibited a lower value but the difference was not s ignif icant. - 105 -TABLE XXVII Beaver Packed Red C e l l Volume - per cent Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 40.3*0.6 42.1*0.5 41.2*0.4 Standard D e v i a t i o n 2.6 2.0 2.5 Range 36-45 40-46 36-46 The hematocrit v a l u e i s an e x p r e s s i o n of the r e l a t i v e percentage o f e r y t h r o c y t e s i n the whole b l o o d . Thus any f a c t o r which causes a change i n the number of r e d blood c e l l s w i l l p r o -duce v a r i a t i o n s i n the hematocrit l e v e l . Red b l o o d c e l l s i n c r e a s e i n response to decreased oxygen t e n s i o n which may be brought about by changes i n a l t i t u d e , muscular e x e r t i o n , c l i m a t e , age, sex and d i s e a s e . Decreases are s i m i l a r l y a s s o c i a t e d w i t h c o n d i t i o n s which i n c r e a s e oxygen t e n s i o n and w i t h i n f e c t i o n s and d i s e a s e s , p a r t i c -u l a r l y those which produce anemia. Change i n b l o o d volume and hemoconcentration as a r e s u l t o f s t r e s s a l s o i n f l u e n c e s the hematocrit v a l u e s . Blood volumes i n r e l a t i o n to body weight tend to be h i g h e r i n younger animals but as the p r o p o r t i o n of f u n c t i o n a l hemato-p o i e t i c t i s s u e i n c r e a s e s the r e d b l o o d c e l l s tend to i n c r e a s e . T h i s r e s u l t s i n an apparent decrease i n b l o o d volume w i t h i n -- 106 -c r e a s i n g age (Dukes, 1955). T h i s c o u l d p a r t l y account f o r the lower v a l u e s observed i n the y e a r l i n g beavers. A l b r i t t o n (1952) g i v e s some hematocrit v a l u e s f o r domes-t i c s p e c i e s . H i s v a l u e of 42 per cent f o r the r a b b i t and p i g i s s i m i l a r to t h a t o b t a i n e d f o r the beaver. Man and dog have a hi g h e r l e v e l near 45 per cent w h i l e the horse, sheep and goat have a mean v a l u e c l o s e to 34 per cent. q. Red C e l l Counts The summer v a l u e s o b t a i n e d f o r the y e a r l i n g s and a d u l t s are presented i n Table XXVIII. As was i n d i c a t e d by the hemato-c r i t l e v e l the y e a r l i n g s e x h i b i t e d a s l i g h t l y lower e r y t h r o c y t e count. TABLE XXVIII Beaver Red Blood C e l l s - m i l l i o n per c u b i c mm. Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 4.22*0.21 4.35*0.10 4.28*0.11 Standard D e v i a t i o n 0.72 0.35 0.55 Range 3.7 - 5.0 3.8 - 4.9 3.7 - 5.0 V a r i a t i o n s i n the number o f r e d blood c e l l s were d i s c u s s e d under the hemoglobin s e c t i o n . I n b r i e f changes are brought about by age» sex and p h y s i c a l and p a t h o l o g i c a l c o n d i t i o n s which a l t e r - 107 -the oxygen tension. Conditions which decrease the c e l l numbers produce anemia. This may result from an increased blood des-truction as a result of the hemolytic action due to specific infections or an interference with hematopoesis as a result of i r o n , protein or vitamin deficiencies (Best and Taylor, 1955). The lower values observed i n the yearlings may be due to an increased blood volume as was indicated by the other blood components. I l l the values presented by Dukes (1955) indicate that the majority of domestic mammals have average values between 6 and 8 mi l l ion per cubic mm. Man has a lower value of 4.8 mi l l ion in the female and 5.4 mil l ion in the male. The average value for the adult beaver was 4.5 mi l l ion per cubic mm. In the formation of red blood ce l l s several stages are passed through i n their development. The ret icular ce l l s i n the bone marrow give r ise to a nucleated hemocytoblast which contains no hemoglobin. As development advances the hemoglobin concentra-tion increases and the basophilic proportion of the ce l l also increases. During this early stage they are called megaloblasts but as the hemoglobin increases and the basophilic material de-creases the ce l l s are termed erythroblasts. The older erythro-blasts give r ise to normoblasts which are similar to mature erythrocytes i n size and hemoglobin content but they s t i l l re -tain their nuclei . This i s the last stage of the erythrocyte development in the bone marrow and normally no normoblasts are found i n the general c irculat ion. When the normoblasts mature the nucleus disappears and the c e l l i s extruded into the blood stream as a reticulocyte, so called because of i t s basophilic - 108 -r e t i c u l a t i o n o f the cytoplasm. Normal human blood has about two per cent o f the r e d c e l l s as r e t i c u l o c y t e s which mature to e r y -t h r o c y t e s i n 10 to 24 hours (Best and T a y l o r , 1955). Under some c o n d i t i o n s normoblasts do escape i n t o the blood stream and t h e i r presence i s i n d i c a t i v e of an i n t e r f e r e n c e w i t h e r y t h r o p o i e s i s r e s u l t i n g i n anemia. I t was found i n the beaver examined t h a t over h a l f o f the animals had normoblasts p r e s e n t . The l e v e l amounted to about one per cent of the d i f f e r e n t i a l count except i n beaver # 17 which had normoblasts amounting to two to f o u r per cent o f the l e u k o c y t e s . T h i s animal showed no other s i g n s of anemia. The e r y t h r o c y t e s and hemoglobin l e v e l s of t h i s beaver were average but i t s l e u k o c y t e s were low. The s i g n i f i c a n c e of the normoblasts i n beaver b l o o d i s not c l e a r s i n c e anemic c o n d i t i o n s were not i n d i c a t e d by the o t h e r components. r . Red C e l l S i z e Diameter measurements are summarized i n Table XXIX. The y e a r l i n g s and a d u l t s had i d e n t i c a l mean v a l u e s of 7.56 microns. The beaver r e d bloo d c e l l s are bi-concave non-nucleated d i s c s s i m i l a r i n shape to those of most other mammalian s p e c i e s . They a r e , however, s l i g h t l y l a r g e r than most s p e c i e s . The mean diameter f o r the e r y t h r o c y t e s o f man i s 7.2 microns (Best and T a y l o r , 1955). Por the guinea p i g and r a b b i t the r e s p e c t i v e v a l u e s are 7.5 and 7.0 microns and f o r the sheep and horse a common v a l u e o f 5.5 microns ( P r o s s e r et a l . , 1950). In g e n e r a l a low c e l l diameter i s compensated f o r by l a r g e r numbers o f r e d c e l l s and v i c e v e r s a i n order to m a i n t a i n a f a i r l y c onstant - 109 -hemoglobin l e v e l . T h i s appears to be the case f o r beaver which have a r e l a t i v e l y low c e l l count and a s l i g h t l y l a r g e r c e l l s i z e . The packed c e l l volume and hemoglobin l e v e l s a re s l i g h t l y lower than those o b t a i n e d f o r man as might be expected from the s l i g h t -l y lower c e l l count. TABLE XXIX Beaver E r y t h r o c y t e Diameter - microns Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 7.56*0.07 7.56*0.07 7.56*0.05 Standard D e v i a t i o n 1.18 1.15 1.18 Range 6.0 - 9.7 6.0 - 9.0 6.0 - 9.7 The t r u e diameter may be g r e a t e r than t h a t observed as a r e s u l t o f me t h o d o l o g i c a l procedures. Best and T a y l o r (1955) s t a t e that human e r y t h r o c y t e s decrease about 0.8 microns d u r i n g p r e p a r a t i o n o f the m a t e r i a l . T h i s i s not a s e r i o u s e r r o r f o r comparative purposes s i n c e standard methods were employed f o r the d e t e r m i n a t i o n . s. White C e l l and D i f f e r e n t i a l C e l l Counts Table XXX summarizes the white c e l l counts f o r the y e a r -l i n g and a d u l t beavers. The y e a r l i n g v a l u e s were s i g n i f i c a n t l y h i g h e r than those o f the a d u l t s . - 110 -TABLE XXX Beaver White Blood C e l l s - thousand per c u b i c mm. Y e a r l i n g s A d u l t s A l l Beavers Mean and Standard E r r o r 14.65*1.01 11.62*0.92 13.20*0.74 Standard D e v i a t i o n 3.48 3.06 3.56 Range 7.6 -18.2 7.0 -16.7 7.0 -18.2 The d i f f e r e n t i a l c e l l counts a r e summarized i n Table XXXI. TABLE XXXI Summary of D i f f e r e n t i a l C e l l Counts f o r A l l Beavers Expressed as Percent o f Leukocytes N e u t r o p h i l s E o s i n o p h i l s B a s o p h i l s Lymphocytes Monocytes Mean 63.4 2.4 0.6 29.8 3.5 Median 66 2 1 30 3 Range 52 - 71 1 - 5 0 - 2 23 - 41 1 - 7 The-leukocytes or white b l o o d c e l l s i n c l u d e s e v e r a l d i f -f e r e n t types o f c e l l s which are grouped a c c o r d i n g to t h e i r a b i l i t y to take d i f f e r e n t s t a i n s and a c c o r d i n g to t h e i r n u c l e a r - I l l -s t r u c t u r e . The lymphocytes and monocytes have a s i n g l e n u c l e u s and a c l e a r non-granular cytoplasm. The g r a n u l o c y t e s , which are d i v i d e d i n t o t hree groups, the n e u t r o p h i l s , e o s i n o p h i l s and "basophils, have l o b e d o r p a r t i t i o n e d n u c l e i and f i n e chromophil g r a n u l e s i n the cytoplasm. Each type of c e l l v a r i e s i n number under d i f f e r e n t c o n d i t i o n s and each has i t s own f u n c t i o n as f a r as i t i s known. The t o t a l l e u k o c y t e count i s q u i t e v a r i a b l e , which i s due p r i m a r i l y to changes i n the n e u t r o p h i l s and lymphocytes which comprise the g r e a t e r percentage o f the white blood c e l l s . D u r i n g t i s s u e damage and i n f e c t i o n s l e u k o c y t e s i n c r e a s e markedly. I n c e r t a i n d i s e a s e s l i k e t y p h o i d f e v e r t h e r e i s a g e n e r a l r e d u c t i o n i n t h e i r numbers. I n g e n e r a l l e u k o c y t e s e x e r t t h e i r main f u n c t i o n i n the t i s s u e s where they a c t as a defence a g a i n s t i n v a d i n g organ-isms. Sunderman and Boerner (1949) i n d i c a t e h i g h l e u k o c y t e counts i n young c h i l d r e n which g r a d u a l l y decrease to the a d u l t l e v e l as m a t u r i t y i s reached. The same c o n d i t i o n s may apply to beaver as was i n d i c a t e d by the h i g h e r v a l u e s o b t a i n e d f o r the y e a r l i n g beavers as compared w i t h the a d u l t s . The normal range o f l e u k o c y t e s i n man i s between 5 and 10 thousand per c u b i c mm. (Sunderman and Boerner, 1949). Horse, c a t t l e , sheep and goat have ranges w i t h i n 5 to 14 thousand w h i l e the p i g , dog and cat have normal ranges above 20 thousand per c u b i c ram (Dukes, 1955). The range f o r beaver was found to be between 7 and 18 thousand per c u b i c mm. alth o u g h beaver # 22 which had a known sta p h y l o c o c c u s i n f e c t i o n had a value o f 20.2 thousand per c u b i c mm. - 112 -Lymphocytes are the second most numerous white blood c e l l s . They a r e formed i n the lymphoid t i s s u e , have amoeboid p r o p e r t i e s and are b e l i e v e d to produce a n t i b o d i e s and to f i x t o x i n s . They i n c r e a s e i n c e r t a i n inflammatory c o n d i t i o n s , i n c o l o n i n f e c t i o n s , t u b e r c u l o s i s and m a l a r i a but t h e i r a c t u a l f u n c t i o n i s unknown (Best and T a y l o r , 1955). The range i n the beaver was from 23 to 41 per cent o f the t o t a l l e u k o c y t e s , although the two i n f e c t e d beavers, # 14 and # 22, had minimum v a l u e s o f 19 per cent and 17 per cent r e s p e c t i v e l y . T h i s was p r o b a b l y due to the s t a p h y l o -coccus i n f e c t i o n p r e s e n t i n these beavers f o r i t i s known t h a t such an i n f e c t i o n w i l l cause a decrease i n l e u k o c y t e s ( C a r t e r , 1944). Cats and dogs have r e s p e c t i v e ranges o f 15 to 44 per cent and 10 to 28 per cent ( A l b r i t t o n , 1945). Man has a 20 to 30 per cent range (Sunderman and Boerner, 1949). The monocytes are l a r g e c e l l s w i t h g r a n u l a r cytoplasm and a s i n g l e n u c l e u s . They have p h a g o c y t i c p r o p e r t i e s which enable them to c o u n t e r a c t i n f e c t i o u s micro-organisms. T h e i r numbers i n -crease i n g l a n d u l a r f e v e r , pulmonary t u b e r c u l o s i s and m a l a r i a (Best and T a y l o r , 1955). Normally the percentage o f monocytes i s not l a r g e . I n humans they range from 2 to 6 per cent (Sunder-man and Boerner, 1949). Cats and dogs have a range o f 0.5 to 7 per cent and 3 to 9 per cent r e s p e c t i v e l y ( A l b r i t t o n , 1945). The v a l u e s f o r beaver ranged from 1 to 7 per cent w i t h a mean of 3.5 per cent. Of the g r a n u l o c y t e s the n e u t r o p h i l s are by f a r the most numerous and from a time s h o r t l y a f t e r b i r t h they are the common-est l e u k o c y t e . These c e l l s have a f i n e l y g r a n u l a r cytoplasm i n - 113 -which i s l o c a t e d a nucleus d i v i d e d i n t o lobes and connected by-f i l a m e n t s . N e u t r o p h i l s are formed i n the bone marrow, are amoe-b o i d i n nature and possess p h a g o c y t i c p r o p e r t i e s . T h e i r main f u n c t i o n i s the defence a g a i n s t i n v a d i n g organisms. Thus they i n c r e a s e i n i n f e c t i o n s to co u n t e r a c t pus-forming organisms l i k e s t a p h y l o c o c c u s . Man has a normal range o f 60 to 70 per cent, and dog and cat have r e s p e c t i v e ranges of 62 to 80 per cent and 44 to 82 per cent (Sunderman and Boerner, 1949; A l b r i t t o n , 1945). Ex-c l u d i n g the two beavers which had a known staphylococcus i n f e c t i o n and a maximum n e u t r o p h i l v a l u e o f 86 per cent the range f o r beavers was from 52 to 71 per cen t . E o s i n o p h i l s are r e l a t i v e l y l a r g e c e l l s w i t h l a r g e c y t o -p l a s m i c g r a n u l e s t h a t take an a c i d s t a i n . The n u c l e u s i s l e s s l o b u l a t e d than t h a t o f the n e u t r o p h i l s . -They possess s l i g h t amoeboid and p h a g o c y t i c c h a r a c t e r i s t i c s but t h e i r a c t u a l f u n c t i o n i s unknown (Best and T a y l o r , 1955). They i n c r e a s e i n c e r t a i n s k i n d i s e a s e s and i n p a r a s i t i c i n f e c t i o n s and are known to be more numerous i n h y p e r s e n s i t i v e animals ( A l b r i t t o n , 1945). The normal range i n humans i s from 1 to 4 per cent (Sunderman and Boerner, 1949). Dogs and c a t s have a h i g h e r range extending from 2 to 14 per cent ( A l b r i t t o n , 1945). The range obtained f o r the beaver was from 1 to 5 per c e n t . Number 22 which had c h r o n i c n e p h r i t i s and a staphylococcus i n f e c t i o n , had a range from 8 to 16 per cent three weeks bef o r e i t d i e d . B a s o p h i l s have l a r g e c y t o p l a s m i c g r a n u l e s which are s t a i n e d i n an a l k a l i n e dye. T h e i r f u n c t i o n i s the l e a s t understood o f a l l the l e u k o c y t e s and they occur i n a ve r y s m a l l p r o p o r t i o n , u s u a l l y - 114 -l e s s than 1 or 2 per cent i n man and domestic animals (Best and T a y l o r , 1955; Dukes, 1955). In beaver the range was from 0 to 2 per cent. - 115 -IV. SUMMARY AND CONCLUSIONS Twenty-six animals were obtained f o r t h i s study which was conducted from October 1954 to February 1956. The animals^ were housed i n s p e c i a l l y designed pens c o n s t r u c t e d from a l a r g e g a l v a n i z e d tank, wire s c r e e n i n g and metal-covered plywood. The pens p r o v i d e d a den, f e e d i n g p l a t f o r m and ample space f o r swim-ming purposes. The beavers were maintained on s p e c i a l p e l l e t e d r a t i o n s which were o c c a s i o n a l l y supplemented w i t h willow and p o p l a r bark. Weights and measurements were taken a t r e g u l a r i n t e r v a l s and an assessment o f growth o b t a i n e d by computing the inst a n t a n e o u s r e l a t i v e growth r a t e s f o r each beaver. The average d a i l y percentage i n c r e a s e i n the weight o f the y e a r l i n g s was 0.27 per cent d u r i n g summer and 0.025 per cent d u r i n g w i n t e r . These v a l u e s were not optimal s i n c e they were s m a l l e r than those c a l -c u l a t e d from beavers l i v i n g under n a t u r a l c o n d i t i o n s . T h i s lower growth r a t e may have r e s u l t e d from a q u a l i t a t i v e l y inadequate d i e t d u r i n g the g r e a t e r p a r t o f the summer. The average growth r a t e f o r k i t s , as r e c a l c u l a t e d from p u b l i s h e d data, appears to be between 1.0 and 1.4 per cent per day d u r i n g summer. The winter r a t e can be as h i g h as 0.5 per cent per day under i d e a l c o n d i t i o n s , but t h i s i s seldom achieved under n a t u r a l c o n d i t i o n s . One k i t i n the present study had a wi n t e r r a t e o f 0.14 per cent per day which appears to be the approximate normal r a t e f o r young beavers i n t h i s a r e a . R e g r e s s i o n l i n e s were c a l c u l a t e d from the measurement data - 116 -by p l o t t i n g body weights a g a i n s t l i n e a r measurements on l o g - l o g graph paper. The measurements i n c l u d e d t o t a l l e n g t h , t a i l l e n g t h , s c a l y t a i l l e n g t h , s c a l y t a i l width, h i n d f o o t l e n g t h , c i r c u m f e r -ence o f the t a i l base and h e a r t g i r t h . I t was found that h i n d f o o t l e n g t h and body l e n g t h bore the c l o s e s t t h e o r e t i c a l l i n e a r r e l a t i o n s h i p to body weight. The t a i l measurements i n d i c a t e d r e l a t i v e l y f a s t e r growth r a t e s because they had not a t t a i n e d as g r e a t a percentage of t h e i r mature s i z e a t b i r t h as had the h i n d f o o t or body l e n g t h . Thus body weight i n c r e a s e d as the 1.3 to 2.3 power o f the l i n e a r t a i l measurements. Organ weights were o b t a i n e d from a l l s a c r i f i c e d animals and r e g r e s s i o n l i n e s computed by p l o t t i n g the organ weight a g a i n s t body weight on l o g - l o g graph paper. The stomach and caecum weights i l l u s t r a t e d a f a i r l y c l o s e l i n e a r r e l a t i o n s h i p to body weight which i n c r e a s e d a t a r e l a t i v e r a t e o f u n i t y . The r a t e o f i n c r e a s e i n the h e a r t weight o f most mammals a l s o has a u n i t y r e l a t i o n s h i p w i t h body weight s i n c e i t s s i z e i s p a r t i a l l y c o r r e l a t e d w i t h the e x e r c i s e l e v e l o f the s p e c i e s . However, i n the beaver i t i n c r e a s e d as the 0.7 power o f body weight. T h i s lower r a t e o f h e a r t growth r e l a t i v e to body weight may be a s s o -c i a t e d w i t h the f a c t that a q u a t i c animals, which have t h e i r weight c o u n t e r p o i s e d by the d i s p l a c e d water, g e n e r a l l y have a r e l a t i v e l y s m a l l e r h e a r t . A l s o , I r v i n g (1937) has shown t h a t the h e a r t r a t e o f the beaver i s g r e a t l y reduced when the animal d i v e s and i s not g r e a t l y i n c r e a s e d when the animal s u r f a c e s . Thus these two f a c t o r s c o u l d reduce the f u n c t i o n a l s t r e s s imposed on the h e a r t r e s u l t i n g i n a lower r a t e o f h e a r t growth r e l a t i v e - 117 -to body weight. T y p i c a l l y the organ weights of the beaver i n c r e a s e d a t a lower r e l a t i v e r a t e than body weight. The a d r e n a l s were, however, an e x c e p t i o n . These had a r e l a t i v e r a t e g r e a t e r than u n i t y which probably i n d i c a t e d the g r e a t e r s t r e s s imposed on the animals while i n c a p t i v i t y . The q u a n t i t y of f o o d r e q u i r e d f o r maintenance was d e t e r -mined f o r beavers of v a r i o u s weights on two d i f f e r e n t p e l l e t e d r a t i o n s . The c l o s e agreement between c a l c u l a t e d and observed food consumption i m p l i e s that the beaver has a b a s a l m e t a b o l i c r a t e which i n c r e a s e s as the 0.73 power of body weight as do most mammalian s p e c i e s and that the maintenance energy requirement i s twice the c a l o r i e s produced under b a s a l c o n d i t i o n s . The c a l o r i c requirements were expressed as c a l o r i e s o f t o t a l d i g e s t i b l e n u t r i e n t s and were r e l a t e d to q u a n t i t i e s of n a t u r a l beaver f o o d s . F o r i n s t a n c e , a 26 pound beaver r e q u i r e s 850 C a l o r i e s o f T.D.N, which i s e q u i v a l e n t to 1.5 pounds of aspen twigs or 1.7 pounds o f w i l l o w twigs. These f i g u r e s were i n v e r y c l o s e agreement w i t h those p u b l i s h e d f o r beavers l i v i n g under n a t u r a l c o n d i t i o n s . F l u c t u a t i o n s i n f o o d i n t a k e d u r i n g the i n v e s t i g a t i o n were l a r g e l y caused by below f r e e z i n g temperatures which t e m p o r a r i l y decreased a c t i v i t y and f o o d consumption. D i g e s t i b i l i t y s t u d i e s were c a r r i e d out by t h r e e d i f f e r e n t methods on one beaver to determine the percentage u t i l i z a t i o n o f the p e l l e t e d r a t i o n and to determine the b e s t method f o r a s s e s s i n g d i g e s t i b i l i t y o f beaver f o o d s . These s t u d i e s i n d i c a t e d a d i g e s t i -b i l i t y f a c t o r of approximately 70 per cent f o r the p e l l e t e d r a t i o n . - 118 -T h i s f i g u r e i s probably h i g h e r than that o b t a i n a b l e w i t h n a t u r a l foods s i n c e the f i b e r content o f t h i s r a t i o n was lower than most beaver f o o d s . The chromogen method f o r determining d i g e s t i b i l i t y appeared to be a s a t i s f a c t o r y method, e s p e c i a l l y with n a t u r a l f o o d m a t e r i a l which c o n t a i n s f a i r l y l a r g e q u a n t i t i e s of chromo-g e n i c substances. I n v e s t i g a t i o n s to determine the time o f food passage by means of col o u r e d compounds r e v e a l e d that the m a j o r i t y o f the un-d i g e s t e d food i s d e f e c a t e d w i t h i n 24 to 48 hours a f t e r i n g e s t i o n . T h i s r a t e i s s i m i l a r to that of most h e r b i v o r e s which have a l a r g e caecum, but f a s t e r than most ruminants. In view of the nature of the beaver's f o o d , which i s h i g h i n c e l l u l o s e , the c a e c a l contents p r o b a b l y have a much slower r a t e o f turnover as was i n d i c a t e d i n the present study. Twenty-five d i f f e r e n t b l o o d c o n s t i t u e n t s were determined to e s t a b l i s h "normal" b l o o d v a l u e s and to determine changes asso -c i a t e d w i t h growth. These "normal" v a l u e s were c o n s i d e r e d to be those o b t a i n e d from a p p a r e n t l y h e a l t h y animals and to be r e p r e -s e n t a t i v e o f the p o p u l a t i o n from which the animals were o b t a i n e d . Twenty animals r e p r e s e n t i n g three d i f f e r e n t age c l a s s e s were i n -v o l v e d and over 40 separate d e t e r m i n a t i o n s were made f o r some o f the c o n s t i t u e n t s . Por most o f the beavers f o u r d i f f e r e n t s e t s of d e t e r m i n a t i o n s were c a r r i e d out d u r i n g the summer and f a l l . k summary o f the a d u l t v a l u e s i s pre s e n t e d i n Table XXXII. The r e s u l t s i n d i c a t e that the y e a r l i n g plasma p r o t e i n s were lower d u r i n g the summer than i n the f a l l and t h a t the summer y e a r l i n g v a l u e s were lower than the a d u l t v a l u e s which e x h i b i t e d - 119 -l i t t l e s e a s o n a l v a r i a t i o n . T h i s lower p r o t e i n l e v e l o f the y e a r -l i n g s was probably a s s o c i a t e d with the g r e a t e r p r o t e i n r e q u i r e -ments necessary f o r growth of the younger beavers. Although the p r o t e i n s were lower i n the summer than i n the f a l l the albumin l e v e l was the l e a s t v a r i a b l e w i t h the r e s u l t t h a t albumin was r e l a t i v e l y g r e a t e r d u r i n g the summer. S i n c e albumin i s the main water r e g u l a t i n g component of the bloo d i t i m p l i e s that the y e a r -l i n g s had a r e l a t i v e l y l a r g e r b l o o d volume d u r i n g the summer. T h i s c o u l d probably account f o r the apparent lower l e v e l o f hemo-g l o b i n , packed r e d c e l l volume and r e d c e l l numbers o b t a i n e d f o r the y e a r l i n g s d u r i n g the summer. None o f the other c o n s t i t u e n t s showed any s i g n i f i c a n t d i f f e r e n c e w i t h growth. The b l o o d sugar l e v e l o f d i f f e r e n t mammals r e f l e c t s , to some extent, a d i f f e r e n c e i n the animal's d i g e s t i v e mechanisms. As a r u l e c a r n i v o r e s have a r e l a t i v e l y h i g h b l o o d sugar l e v e l w h i l e ruminants have a low l e v e l . The beaver, l i k e most non-ruminant h e r b i v o r e s , had an i n t e r m e d i a t e l e v e l , a lthough i t s v a r i a b i l i t y was f a i r l y l a r g e . Conversely the v o l a t i l e f a t t y a c i d s o f the beaver were much h i g h e r than t h a t found i n the b l o o d of c a r n i v o r e s but s i m i l a r to t h a t found i n ruminants. T h i s i n d i -cates the h i g h l e v e l o f b a c t e r i a l a c t i v i t y which must take p l a c e i n the beaver's caecum. The c h o l e s t e r o l l e v e l o f the beaver was a l s o s i m i l a r to that o f the cow but much h i g h e r than i n most non-ruminant h e r b i v o r e s . The beaver a l s o e x h i b i t e d a h i g h e r albumin l e v e l and sedimen t a t i o n r a t e than most domestic s p e c i e s , but the s i g n i f i c a n c e o f these d i f f e r e n c e s cannot be r e a d i l y a s c e r t a i n e d . - 120 -The number o f r e d b l o o d c e l l s were a l s o lower i n the beaver than i n most s p e c i e s but t h i s was compensated f o r by a s l i g h t l y l a r g e r c e l l s i z e . T h i s l a r g e r s i z e o f the r e d c e l l s e x p l a i n s the f a i r l y h i g h packed c e l l volume and hemoglobin l e v e l . A lthough the hemoglobin l e v e l was not as h i g h as i n man i t was h i g h e r than i n most domestic s p e c i e s . T h i s hemoglobin l e v e l and l a r g e r e d c e l l s i z e are pro b a b l y a d a p t a t i o n s to the beaver's semi-aquatic type o f l i f e . The i n d i v i d u a l v a r i a t i o n o f b l o o d c o n s t i t u e n t s were q u i t e l a r g e , n e v e r t h e l e s s they do have some p r o g n o s t i c s i g n i f i c a n c e . Among beavers there a re th r e e main f a c t o r s which c o u l d cause v a r i a t i o n s . These are m a l n u t r i t i o n , s t r e s s and g e n e r a l patho-l o g i c a l c o n d i t i o n s . In m a l n u t r i t i o n , b l o o d sugars, serum p r o t e i n s and hemoglobin are reduced w h i l e an i n c r e a s e i s observed i n the N.P.N., c r e a t i n e and c h o l e s t e r o l l e v e l s . Under c o n d i t i o n s of s t r e s s t h e r e i s an i n c r e a s e i n blood sugars, r e d blood c e l l s , packed c e l l volume, hemoglobin and i n g e n e r a l most b l o o d con-s t i t u e n t s . P a t h o l o g i c a l c o n d i t i o n s can r e s u l t i n v a r i a t i o n s i n one or s e v e r a l o f the bloo d components depending on the s p e c i f i -c i t y o f the c a u s a t i v e f a c t o r . Under g e n e r a l i n f e c t i o u s con-d i t i o n s t h e r e i s a decrease i n albumin and an i n c r e a s e i n g l o b u l i n which r e s u l t s i n a lower A/G r a t i o even though the t o t a l serum p r o t e i n s may be unchanged. There i s a l s o an i n c r e a s e i n the number of l e u k o c y t e s which i s c h i e f l y due to the i n c r e a s e i n n e u t r o p h i l s and, to a l e s s e r degree, the e o s i n o p h i l s and mono-c y t e s . The lymphocytes decrease d u r i n g i n f e c t i o n . TABLE XXXII Summary of Adu l t Beaver Blood C o n s t i t u e n t s C o n s t i t u e n t Mean and Standard E r r o r Range Human Range 1.Reducing sugars - mg. per cent 96.4*3.8 49-160 70-100 2. T o t a l P r o t e i n i n whole blo o d - gm. per cent 19.4*0.3 16.9-22.3 18.5-23.0 3.Albumin - gm. per cent o f serum 4.4*0.1 3.8-5.3 3.5-4.5 4 . G l o b u l i n - gm. per cent o f serum 3.2*0.2 2.4-4.8 2.0-4.5 5.A/G r a t i o 1.5*0.1 0.8-2.1 1.2-1.8 6.Total P r o t e i n i n Serum - gm. per cent 7.5*0.1 6.5-8.7 6.0-6.9 7 . F i b r i n o g e n - gm. per cent plasma 0.6*0.1 0.2-1.0 0.2-0.4 8 . T o t a l P r o t e i n i n plasma - gm. per cent 8.0*0.2 7.2-9.1 6.5-7.5 9.N.P.N. - mg. per cent 39.0*1.5 28.0-53.2 28-39 10.Amino A c i d n i t r o g e n - mg. per cent 9.3*0.4 7.4-12.0 4-8 11.Creatine - mg. per cent 2.8*0.1 2.0-3.6 3-5 1 2 . C r e a t i n i n e - mg. per cent 1.5*0.05 1.0-1.9 1-2 TABLE XXXII (continued) C o n s t i t u e n t Mean and Standard E r r o r Range Human Range 13«Cholesterol - mg. per cent 106*4 75-148 150-290 1 4 . V o l a t i l e f a t t y a c i d s - m.e. X 10 per cent 18.8*1.2 9.9-32.3 (30.0) 15.Hemoglobin - gm. per cent 13.7*0.3 11.1-15.8 11-16 16.Sedimentation Rate - mm. per hour 37*5 9-78 1-7 17.Packed Red C e l l Volume - per cent 41.2*0.4 36-46 (45) 18.Red C e l l Count - m i l l i o n s per cu. mm. 4.3*0.1 3.7-5.0 4.0-6.5 19.Red C e l l Diameter - microns 7.56*0.05 6.0-9.7 5.4-9.0 20.White C e l l Count - thousands per cu. mm. 13.2*0.7 7.0-18.2 5-9 21.Neutrophils - per cent 63.4 52-71 33-75 2 2 . E o s i n o p h i l s - per cent 2.4 1-5 0-6 23.Basophils - per cent 0.6 0-2 0-2 24.Lymphocytes - per cent 29.8 23-41 15-60 25.Monocytes - per cent 3.5 ___ 1-7 0-9 - 123 LITERATURE CITED A l b r i t t o n , E.C. (ed.) 1952. Standard Values i n Blood. P h i l a d e l p h i a , W.B. Saunders Co. 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R e l a t i o n o f c e r t a i n endocrine glands to body weight i n growing and mature New Zealand white r a b b i t s . E n d o c r i n o l o g y 33:250-256. Knudsen, G.J. 1953. Beaver d i e - o f f . Wisconsin C o n s e r v a t i o n B u l l . 18:20-23. Koch, F.C. and M.E. Hanke. 1953« P r a c t i c a l methods i n b i o c h e m i s t r y . The W i l l i a m s and W i l l i a m s Co., B a l t i m o r e . - 126 -Lawrence, W.H. and L.D. Pay. 1954. Recent e p i z o o t i c among Michigan beaver. Paper presented a t 16th Midwest W i l d l i f e Conf. S t . L o u i s , Dec. 1-3 1954. (Unpub. ms.) McClendon, J . F . 1944. M i c r o d e t e r m i n a t i o n of v o l a t i l e f a t t y a c i d s i n b l o o d . J o u r . B i o l . Chem. 154:357-360. N e i s h , A . C 1950. A n a l y t i c a l methods f o r b a c t e r i a l f e r m e n t a t i o n . N a t i o n a l Research C o u n c i l of Canada, P r a i r i e R egional L a b o r a t o r y , Saskatoon. Report No. 46-8-3. Osborn, D.J. 1953. Age c l a s s e s , r e p r o d u c t i o n and sex r a t i o s o f Wyoming beaver. J o u r . Mamm. 34:27-44. P e r r y , W.H. and L. Morgan-Dean. 1954. Manual o f haematology. P u b l . Van. General H o s p i t a l , p. 119. P e t e r s , J.P. and B.D. Van S l y k e . 1946. Q u a n t i t a t i v e C l i n i c a l Chemistry. V o l . I I n t e r p r e t a t i o n s . W i l l i a m s and W i l l i a m s , B a l t i m o r e . P r o s s e r , C L . , D.W. Bishop, P.A. Brown, J r . , T.L. John, 1950. and V . J . W o l f f . Comparative Animal 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 . R e i d , J . I . , P.G. Woolfolk, C R . R i c h a r d s , R.W. Kaufmann, 1950. J.K. L o o s l i , K.L. Turk, J . I . M i l l e r &. R.E. B l a s e r . A new i n d i c a t o r method f o r the d e t e r m i n a t i o n o f d i g e s t i b i l i t y and consumption of f o r a g e s by ruminants. J . D a i r y Sc. ^3:60-71. Rein e r , Miriam, ed. 1953. Standard methods o f C l i n i c a l Chemistry. V o l . I . Amer. Assoc. o f C l i n i c a l Chemistry. Academic P r e s s Inc., N.Y. Schneider, B.H. 1947. Feeds o f the world. ( T h e i r d i g e s t i b i l i t y and composition)* J a r r e t t P r i n t i n g Co., C h a r l e s t o n , W. Va. Schttrch, A.F., L.E. L l o y d and E.W. Crampton. 1950. The use of chromium oxide as an index f o r determining the d i g e s t i b i l i t y o f a d i e t . J . Nut. 41: 629. - 127 -S e l y e , H. 1946. The g e n e r a l a d a p t a t i o n syndrome and the di s e a s e s o f a d a p t a t i o n . Jour. C l i n . E n d o c r i n o l . 6:117-230. Seton, E.T. 1929. L i v e s o f game animals. Doubleday, Page & Co., N.Y. Shadle, A.R. 1950. An unusual case o f p a r t u r i t i o n i n beavers. J o u r . Mamm. 11:483-485. Shedecor, G.W. 1946. S t a t i s t i c a l methods. 4th E d i t i o n . The Iowa S t a t e C o l l e g e P r e s s , Ames. Styermark, A l . • 1951. Q u a n t i t a t i v e o r g a n i c m i c r o a n a l y s i s . The B l a k i s t o n Co., P h i l a d e l p h i a . Sunderman, P.M. and P. Boerner. 1949. Normal v a l u e s i n c l i n i c a l medicine. W.-B. Saunders Co., P h i l a d e l p h i a & London. S w i f t , R.W. and C E . French. 1954. Energy metabolism and n u t r i t i o n . The Scarecrow P r e s s , Washington, D.C. T y r r e l l , J.B. ed. 1916. David Thompson's n a r r a t i v e of h i s e x p l o r a t i o n s i n Western America, 1784-1812. The Champlain S o c i e t y , Toronto. Warren, E.R. 1927. The beaver, i t s works and i t s ways. W i l l i a m s and W i l l i a m s , B a l t i m o r e , Md. West, E.S. and W.R. Todd. 1951. Textbook o f b i o c h e m i s t r y . The MacMillan Co., New York. - 128 -APPENDIX I H i s t o r y and Post Mortem R e s u l t s of C a p t i v e Beavers Beaver # 9 Received on March 26, 1955, and d i e d June 22, 1955. Ex-t e r n a l f e a t u r e s appeared normal but weight had decreased from 30 to 22 pounds p r i o r to death. I n t e r n a l anatomy appeared normal except f o r the kidneys which were g r e a t l y enlarged and pulpy i n nature i n d i c a t i v e o f e x t e n s i v e c h r o n i c n e p h r i t i s . The a x i l l a r y and i n g u i n a l lymph nodes were a l s o g r e a t l y s w o l l e n . Beaver # 13 Received on May 17, 1955, and d i e d October 16, 1955. I t appeared i n good c o n d i t i o n up to the time o f i t s sudden death. E x t e r n a l anatomy appeared normal. A l o s s o f three pounds i n body weight o c c u r r e d d u r i n g the two weeks p r i o r to death, although l a r g e d e p o s i t s o f subcutaneous f a t were s t i l l p r e s e n t . T h o r a c i c and abdominal organs were normal i n appearance except f o r a s m a l l l e s i o n on the h e a r t . A l a r g e b l o o d c l o t was present i n the p o s t e r i o r vena cava immediately p o s t e r i o r to the r e n a l v e i n s . Beaver # 1 4 Received on May 17 and d i e d October 8, 1955. The animal ceased to g a i n weight i n e a r l y August and r a p i d l y l o s t weight - 129 -a f t e r September 13. The f i r s t evidence o f i l l n e s s was n o t i c e d on September 19 when i t commenced to defecate on the f e e d i n g p l a t f o r m , a h a b i t not n o r m a l l y p r a c t i s e d . The f e c e s were v e r y s o f t and emitted a pungent odour. The autopsy r e v e a l e d numerous s m a l l white p u r u l e n t nodules on the l u n g s . C u l t u r a l examination o f these l e s i o n s by Dr. R. J . Avery r e v e a l e d the presence of c o a g u l a s e - p o s i t i v e s t a p h y l o c o c c u s . The o t h e r organs were normal i n appearance. Beaver # 18 Received on June 10 and d i e d October 6, 1955. A decrease . i n body weight, which was f i r s t n o t i c e d on September 9, continued u n t i l death. On September 19 s o f t f e c e s w i t h a pungent odour were d e f e c a t e d both i n the den and on the p l a t f o r m . The v e n t r a l s u r f a c e s o f the h i n d f e e t were worn to such an extent that the tendons were exposed. Pus was present i n these s o r e s . The a x i l l a r y and i n g u i n a l lymph nodes were g r e a t l y s w o l l e n but the organs appeared normal. C u l t u r a l examinations o f p o r t i o n s o f the lymph nodes, lung and kidney r e v e a l e d the presence o f P a s t u r e l l a m u l t o c i d a , Corynebacterium sp. and numerous c o l i f o r m s p e c i e s . Beaver # 19 Received on June 10, 1955 and d i e d January 1, 1956. Gain i n weight ceased i n e a r l y August but f l u c t u a t e d con-s i d e r a b l y t h e r e a f t e r . I t was a c t u a l l y g a i n i n g weight - 130 -s l i g h t l y , at the time o f death. On November 9 s o f t f e c e s were observed on the p l a t f o r m . The c h a r a c t e r i s t i c pungent odour was a l s o p r e s e n t . T r e a t -ment wit h S u l f a g u a n i d i n e d u r i n g the next f o u r days r e l i e v e d the s i t u a t i o n . On September 27 i t was f i r s t noted that the i n c i s o r s were d i f f e r e n t i a l l y worn. The upper i n c i s o r s a c t i n g as a wedge f o r c e d the lower ones to spread apart to such an extent t h a t by the end o f December they were r e l a t i v e l y l o n g and unevenly worn. On December 31 the beaver was a n a e s t h e t i z e d w i t h f i v e g r a i n s of Nembutal and the i n c i s o r s evened w i t h a m i n i a t u r e power saw. Before the animal had gained complete r e c o v e r y from the a n a e s t h e t i c i t was p l a c e d back i n t o i t s pen where i t a p p a r e n t l y drowned while i n a weakened c o n d i t i o n . Beaver # 20 Received June 10 and d i e d October 5, 1955. The weight decreased d u r i n g August, r o s e s l i g h t l y i n September and then decreased u n t i l death. The autopsy r e v e a l e d an e n l a r g e d n e p h r i t i c l e f t kidney and s w ollen lymph g l a n d s . C u l t u r a l examinations i n d i c a t e d a heavy Proteus sp. i n f e s t a t i o n . No a d d i t i o n a l c u l t u r e s were made. The remainder o f the organs appeared normal. Beaver # 21 Received on June 11 and d i e d November 2, 1955. The weight f l u c t u a t e d c o n s i d e r a b l y a l l summer w i t h l i t t l e a p p r e c i a b l e g a i n . I t s h a r p l y dropped a f t e r October 18. On - 131 -September 25 the animal appeared l e t h a r g i c and i n poor c o n d i t i o n . The c l o a c a l chamber and p e n i s were extruded over one i n c h where they remained i n a swollen s t a t e f o r over a week. On October 17 water from the pen o f t h i s beaver i n d i c a t e d the presence o f c o a g u l a s e - p o s i t i v e s t a p h y l o c o c c u s . On October 25 smal l s o r e s were present on the t a i l and the s k i n on the hind f e e t appeared r e d d i s h . Autopsy r e v e a l e d a f i b r i n o u s p e r i c a r d i t i s , p o s s i b l y r e -s u l t i n g from the c a r d i a c punctures. The organs a l l appeared normal. Beaver # 2 2 Received on J u l y 16 and d i e d August 18, 1955. The animal r e f u s e d to eat d u r i n g the f i r s t week and a t e v e r y l i t t l e t h e r e a f t e r . Seven pounds were l o s t d u r i n g the f i r s t t h r e e weeks. F i r s t s i g n s of i l l n e s s were noted on August 8 when i t appeared extremely l e t h a r g i c and d e f e c a t e d on the p l a t f o r m . The autopsy performed by Dr. R. J . Avery r e v e a l e d a s m a l l abscess on the h e a r t , e n l a r g e d f i b r o t i c kidneys and s m a l l white patches on the upper p o r t i o n o f the duodenum. A c r i t i c a l examination of the kidney r e v e a l e d a v e r y e x t e n s i v e c h r o n i c n e p h r i t i s . The white patches on the duodenum were a p p a r e n t l y g i a n t lymph f o l l i c l e s . C u l t u r a l examination o f the s p l e e n r e v e a l e d the presence o f Aerobact e r aerogenes. C u l t u r e of the pus from the heart l e s i o n r e v e a l e d the presence o f c o a g u l a s e - p o s i t i v e s t a p h y l o -- 132 -coccus. The kidney c u l t u r e s showed no pathogenic organisms. Beaver # 2 3 Received September 29 and d i e d December 23, 1955. There was a s m a l l weight g a i n d u r i n g the f a l l but a r a p i d l o s s d u r i n g the two weeks p r i o r to death. On November 15 the s k i n on the v e n t r a l s u r f a c e o f the h i n d f e e t was worn through. By December 6 these sores were w e l l f e s t e r e d . On December 15 s o f t f e c e s were d e f e c a t e d on the p l a t f o r m and the c h a r a c t e r i s t i c pungent odour was p r e s e n t . A l l organs appeared normal but the lymph nodes were e n l a r g e d . Beaver # 2 4 Received on October 5 and d i e d December 10, 1955. I t r e -f u s e d most o f the food d u r i n g the f i r s t t h r e e weeks which r e s u l t e d i n a l o s s of over f i v e pounds of body weight. On November 24 s o f t f e c e s were observed on the p l a t f o r m . On December 6 the s k i n o f the hind f e e t appeared r e d d i s h and s m a l l s o r e s were present on the t a i l . The animal was q u i t e weak and l e t h a r g i c . Blood was taken on December 10, the day that the animal d i e d . B a c t e r i o l o g i c a l examination o f the blood r e v e a l e d no s i g n i f i -cant pathogenic organism. A l a r g e blood c l o t was present i n the t h o r a c i c c a v i t y and myo c a r d i a l hemorrhage was e v i d e n t . None o f the organs appeared abnormal. Beaver # 25 Received October 5 and d i e d December 18, 1955. The weight was maintained f a i r l y constant u n t i l a week preeeeding death - 133 -when i t dropped precipitously. On November 15 soft feces were observed on the platform and a pungent odour was present. This situation continued u n t i l the death of the animal. Examination revealed that the skin on the right hind foot was worn through but a l l organs were normal. L i t t l e to no fat was present. Beaver # 26 Received October 5 and died November 25, 1955. The weight decreased after November 8. Soft feces with a pungent odour were observed on the platform from November 9 u n t i l time of death. Both pads on the hind feet were worn through on November 15. Both the external and internal anatomy appeared normal, although l i t t l e fat was present. APPENDIX I I Beaver Body Weights i n Kg. and Body Measurements i n cm. Beaver Weight T o t a l T a i l S c a l y - S c a l y - Hind T a i l - b a s e Heart Number Kg. Length Length T a i l T a i l Foot circum- G i r t h Length Width Length fe r e n c e 26 6.12 77.0 20.9 7.4 14.1 11.2 26 4 9.0 90.3 40.5 22.6 9.0 16.1 10 9.3 86.0 34.5 21.2 8.9 15.3 1 9.65 91.1 40.3 9.0 16.4 23 9.75 89.0 23.1 9.9 15.8 14.2 44 20 10.0 89.0 36.0 25.7 12.2 16.8 14.6 38.5 19 10.0 90.5 26.0 12.1 16.7 14.5 44 21 10.2 26.5 11.8 16.5 14.5 14 10.7 24.6 9.3 17.3 25 11.8 99.5 27.8 10.7 17.9 16.8 46 15 11.8 25.9 11.2 16.7 16.8 16 11.8 25.7 11.1 17.3 17.2 11 12.6 98.0 41.3 24.8 11.3 17.7 6 12.7 99.2 40.8 24.0 11.0 16.1 56.5 8 13.2 24.5 12.1 17.7 18.8 9 13.4 95.0 40.5 23.5 11.2 17.0 3 14.1 108.0 47.0 27.0 11.8 18.0 24 14.5 27.1 13.0 18.1 18.0 53 17 14.5 29.9 13.4 18.6 18.4 13 16.7 104.0 26.8 13.3 17.7* 20.9 5 16.8 103.0 42.0 27.2 11.8 17.0* 22 18.2 48.5 27.3 14.3 18.0* 20.0 18 19.0 110.0 45.5 28.2 16.5 18.0* 16.3 41.5 12 21.8 108.0* 44.0* 27.5* 13.8* 18.5* * omitted i n c a l c u l a t i o n o f r e g r e s s i o n l i n e APPENDIX I I I Body and Organ Weights of Beavers Beaver Body Kidney L i v e r Pancreas A d r e n a l Heart Lung Stomach Caecum Number Weight Weight Weight Weight Weight Weight Weight Weight Weight kg. gm. gm. gm. gm. gm. gm. gm. gm. 26 6.1 53 210 0.395 22 36 92 4 9.0 79 331 24 29 34 80 92 10 9.3 62 290 28 0.786 27 32 64 104 1 70 149 23 9.8 62 338 21 0.523 55 97 97* 78 20 10.0 83 370 0.920 52- 97 19 10.0 107* 446* 25 0.616 39 124 87 14 10.7 86 328 49 106 25. 11.8 72 300* 24 0.792 58 126 111 118 1A 12.3 89 326 30 34 50 142 11 12.6 66 408 25 1.064 33 41 102 134 6 12.7 81 485 23 0.975 31 44 87 162 9 13.4 129* 334* 55 86 130 5 14.1 97 434 32 39 49 151 123 2 14.1 85 497 17* 41 57 160 13 16.7 98 502 100* 207* 112 166 5 16.8 115 396* 41 44 45 194 18 19.0 107 368* 1.780 71 151 101* * omitted i n c a l c u l a t i o n o f r e g r e s s i o n l i n e 

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