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The relation of mortality to egg production in poultry at the University of British Columbia Kosin, Igor L. 1936

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THE RELATION OP MORTALITY TO . EGG PRODUCTION IN POULTRY AT THE UNIVERSITY OP BRITISH COLUMBIA A THESIS submitted f o r tne degree of Master of Science i n A g r i c u l t u r e by Igor L. Kosin, B.S.A. May I 9 3 6 Vancouver, B.C. AGKKFQ FtDE DGME1"! T h e w r i t e r wishes to acknowledge h i s indebtedness to Professor E . A . L l o y d and M r . Jacob B i e l y f o r t h e i r i n -va luab le a s s i s t a n c e i n the p r e p a r a t i o n of the m a n u s c r i p t . TABLE OF CONTENTS Bart 1 I n t r o d u c t i o n . . 1 The problem of m o r t a l i t y i n l a y i n g p u l l e t s . . . . . 3 The work of H a r r i s and Bought on on the subject of the r e l a t i o n between m o r t a l i t y and egg production . 3 Rogers' i n v e s t i g a t i o n of c o n s t i t u t i o n a l vigour from the standpoint of n u t r i t i o n . . . . . . . . 6 P e a r l ' s theory of l o n g e v i t y of l i f e as an expression of genetic f a c t o r s . . . . . . . . . . . . . . . . . . . 7 Longevity as a p h y s i o l o g i c a l character, as• considered by Brody, Henderson and Eempster....9 Host resistance i n plants and animals..........11 The t h e o r i e s of the single and composite type of disease r e s i s t a n c e i n animals. ....14 The present stuatus of the inheritance of disease r e s i s t a n c e i n poultry lj> R i g i d s e l e c t i o n by man as a su b s t i t u t e to J u l l ' s d e f i n i t i o n of vigour.................... . 1 9 Part 1 1 M o r t a l i t y i n the p u l l e t f l o c k s i n the U n i v e r s i t y of B r i t i s h Columbia......... ....20 The trend In the r e l a t i o n between annual production and m o r t a l i t y i n the p o u l t r y f l o c k of the U n i v e r s i t y of B r i t i s h Columbia..........22 Differences i n the m o r t a l i t y rates of the three breeds, Single Comb white Leghorns, Barred Plymouth Rocks and Rhode Isl a n d Reds, used i n t h i s study and t h e i r s i g n i f i c a n c e 2 5 The weekly production of b i r d s which died i n t h e i r p u l l e t year. Reduction i n the l i f e span of these p u l l e t s since 1930 . 2 3 Relationship between egg production and m o r t a l i t y of bred-to-lay p u l l e t s . . . . . . . . . . . . . . . 2 6 TABLE OF CONTENTS Bar t 11 ( cont inued) S"11J11H1 £tl*y «*©«***»» © e © * * » « > « » » 9 9 « « . j > o © 1 Part 1 Introduction The question of m o r t a l i t y among the p o u l t r y f l o c k s of commercial poultrymen, breeders, and at the egg l a y i n g con-t e s t s w i t h i n the l a s t few years has assumed proportions of such magnitude as to c o n s t i t u t e a serious economical l o s s to the in d u s t r y . Each year the m o r t a l i t y f i g u r e s reported by the lea d i n g egg l a y i n g contests of Canada, Great B r i t a i n and the United States show a steadily, i n c r e a s i n g death t o l l among p u l -l e t s . Less than ten years ago, the m o r t a l i t y a t the l a y i n g t r i a l s recognized by the National P o u l t r y Council of Great B r i t a i n was 6 . 5 8 %j the corresponding f i g u r e i n 1934-55 was 17.97., a n increase of p r a c t i c a l l y 300%• The Canadian contests, on the average, have even exceeded the high mark established i n Great B r i t a i n , the m o r t a l i t y being about 20°/., and i n some cases reaching as much as 3 7^° of the b i r d s entered. The mor-t a l i t y among the f l o c k s of commercial poultrymen and breeders, as reported by various i n v e s t i g a t o r s , i s also i n c r e a s i n g , although i t i s d i f f i c u l t to estimate the exact rate of the i n -crease. The increase i n m o r t a l i t y seems, however, to be con-f i n e d to the most popular breeds which have been selected over a period of years f o r egg production. This f a c t n a t u r a l l y suggests a question: I f the rate of m o r t a l i t y increases as 2 the average production i n these same f l o c k s increases through s e l e c t i o n and breeding i s i t not p o s s i b l e , that there i s some close connection between these two f a c t o r s ? In other words, the question a r i s e s as to whether or not high production r e -s u l t s i n such reduced v i t a l i t y of b i r d s as could be expressed i n the increased m o r t a l i t y rates i n the high producing s t r a i n s of p o u l t r y . The problem of the maintenance of v i t a l i t y , or vigour, i n high.producing s t r a i n s of b i r d s i s of great economic importance and, therefore, e i t h e r d i r e c t l y or i n d i r e c t l y i t has received a good deal of a t t e n t i o n on the part of i n v e s t i g -ators i n the f i e l d of the science of p o u l t r y husbandry. The problem o f V i t a l i t y i n the domestic hen has been studied By-Rogers ( 1 9 1 2 , 1914), P e a r l (1923), Broody (1924), Hays ( 1 9 2 8 ) , Bunn ( I 9 2 8 ) , Damon (1930), Dunkerly ( 1 9 3 0 ), Mateu (1930) and others. Each, approaching the subject from a some-what d i f f e r e n t point of view, however, has l e f t - t h e m o r t a l i t y -p r o d u c t i v i t y problem e i t h e r e n t i r e l y aside, or else has d e a l t with i t i n a passing manner. To the w r i t e r T s knowledge, the work done by H a r r i s ( 1 9 2 6 , 1.927-) and H a r r i s and Boughton ( I 9 2 8 ) was the only i n v e s t i g a t i o n t h a t dealt s p e c i f i c a l l y with the re-* l a t i o n s h i p between m o r t a l i t y and production. S u r p r i s i n g a s i t may seem, during a l l of the years when m o r t a l i t y among p u l l e t f l o c k s was i n c r e a s i n g a t a n alarming r a t e , the work done by H a r r i s and Boughton was the only one.which attempted t o resolve and formulate the mass o f c o n f l i c t i n g opinion. H a r r i s ( 1 9 2 6 , 1927},-'working with records obtained from the I n t e r n a t i o n a l Egg Laying Contest a t S t o r r s f o r the period between I 9 I I - I 9 2 2 , found that b i r d s which had died dur-ing the f i r s t ( p u l l e t ) year^ had lower average egg records i n the months immediately preceding death than the b i r d s which had survived. This was found t o apply t o the three breeds which were kept under observation, I.e., Single Comb White l e g -horns, White fifyandottes and Rhode I s l a n d Reds. 4 Continuing t h i s study of m o r t a l i t y , H a r r i s and Boughton (192 8) found that the death rate of White Wyandotte b i r d s was s i g n i f i c a n t l y higher than that of Single Comb White leghorns or Rhode Island Reds. At the same time, the l a t t e r breed;, showed, according to t h e i r f i n d i n g s , a s l i g h t l y higher m o r t a l i t y rate than the Leghorns. The f a c t that the di f f e r e n c e i n the m o r t a l i t y among these three breeds was found to be s i g -n i f i c a n t , l e d the authors to conclude that breed d i f f e r e n c e s may e x i s t i n the death rate of b i r d s kept under i d e n t i c a l con-d i t i o n s . Furthermore, these w r i t e r s s t a t e : "A c e r t a i n p a r a l l e -l i s m i s Shown between the monthly death rates and the average monthly egg production of each breed. Both increase from the beginning of the l a y i n g year to a maximum and decrease toward the end of the l a y i n g year. I t i s suggested that there may be some r e l a t i o n s h i p "between the s t r a i n placed'upon the organism by heavy egg production and the Incidence of death." They found, moreover, that the maximum increase i n m o r t a l i t y always occurred a f t e r the period of maximum increase i n egg production. Llateu (1930) thought that s e l e c t i o n f o r higher pro-duction had been c a r r i e d too f a r , to the detriment of the health of the modern hen. Warren ( 1 9 3 0 ) , however, e v i d e n t l y disagreed with t h i s view since vigour, according to him, i s the e s s e n t i a l f a c t o r which a high producing l i n e must possess i n order to withstand the s t r a i n of in t e n s i v e production. He suggests, that i t i s the system of inbreeding p r a c t i c e d to e s t a b l i s h cer-t a i n c h a r a c t e r i s t i c s i n the foundation stock, together with the wide dissemination of such h i g h l y inbred stock ithat: has l e d 5 to lowered v i t a l i t y and higher m o r t a l i t y . Cole and Halpin (1916, 1922) observed that Rhode Is l a n d Reds that had been Inbred f o r four years were l e s s vigorous "than the o r i g i n a l non-inbred stock, i . e . , when the measure of c o n s t i t u t i o n a l vigour was considered as being the hatch-a b i l i t y of eggs and the l i v a b i l i t y of c h i c k s . Dunn (192 3) working with h i g h l y inbred Single Gomb White leghorn stock . also found that the inbred birds lacked vigour, hatcha'bility being taken as the measure of vigour. These r e s u l t s have since been substantiated by J u l l (1928a, 1939a, 1939b, 1930), Dank-er l y (1930) and Aim on (1950) . Dumon (I930) suggested that a c e r t a i n percentage of the increased chick embryo m o r t a l i t y was due to homozygous l e t h a l f a c t o r s . I t i s possible , he s a i d , that some other f a c t o r s than the purely h e r e d i t a r y ones are responsible f o r what he terms to be the degeneration of c l o s e l y inbred stock* Hays and Sanborn (1928) made some i n t e r e s t i n g observations -about vigour i n p o u l t r y . They concluded t h a t , i n the pro-duction bred Rhode Is l a n d Reds, high h a t c h a b i l i t y hard a ten-dency to be associated with low m o r t a l i t y In the l a y i n g house. 'This d e f i n i t e l y supports the p r e v i o u s l y discussed views of J u l l , Mm on et a l . furthermore, they do not consider that the age at f i r s t egg, weight at f i r s t egg, winter pause or i n t e n s i t y of l a y i n g are the measure of vigour. On the other hand, t h e i r data i n d i c a t e that broodiness was associated with superior vigour because the b i r d s that we re broody, at l e a s t once before J u l y 1, showed lower m o r t a l i t y than the non-broody 6 b i r d s . • It' may, however, be possible to Int e r p r e t the d i f -ference i n m o r t a l i t y rates between the broody and non-broody l i n e s of Hays and Sanborn, i f i t be assumed that there i s a p o s i t i v e r e l a t i o n s h i p between the high rate of production and m o r t a l i t y . I t i s p o s s i b l e , f o r example, that the b i r d s that became broody at l e a s t once during t h e i r p u l l e t year have had the opportunity to r e s t before proceeding to l a y again. But apparently the authors do not consider that high persistency and i n t e n s i t y are at a l l detrimental to the vigour of the b i r d . Rogers (1912, 1914) studied c o n s t i t u t i o n a l vigour from the standpoint of n u t r i t i o n . He found that a large per-centage of the "weak p u l l e t s " became weak because of f a u l t y n u t r i t i o n and management. Unfortunately he does not state s p e c i f i c a l l y the c r i t e r i o n used by him i n d i s t i n g u i s h i n g between "weak"and '"-strong" l o t s of Barred Plymouth Rocks and Single Comb v'hite Leghorn p u l l e t s . Strangely enough, the m o r t a l i t y i n the two 11 strong" Single Oomb White Leghorn pens was higher than i n the "weak", although the reverse was the case i n the Barred Plymouth Rock pens. At the same time, production was higher i n a l l strong pens, again suggesting a p o s s i b i l i t y of close r e l a t i o n s h i p between m o r t a l i t y and production. In view of these r e s u l t s , the author's suggestion: "That In s e l e c t i n g f o r breeding stock to produce a large number of chickens and capable p u l l e t s , the f i r s t e s s e n t i a l i s to s e l e c t according to strength, with the expectation that hens so selected w i l l u s u a l l y be the most productive", does not seem to f i t the f a c t s , at any rate not i n the case of leghorns, which have d e f i n i t e l y shown higher m o r t a l i t y r a t e s i n the strong pens. On the other hand, the f a c t of higher m o r t a l i t y i n the strong pens could be explained on the basis of n u t r i t i o n of the f l o c k . The b i r d s that were l a y i n g at a heavy r a t e , as was the case with the "strong pens", n a t u r a l l y had a greater s t r e s s on t h e i r c o n s t i t u t i o n than the "weak" b i r d s , l a y i n g at a slower r a t e . Rogers does not mention whether, or not, there was any s i g n i f i c a n t difference i n the production of "strong", Leghorn and Barred Rock pens, although he points out that m o r t a l i t y with the former was decidedly higher than with the Plymouth Rocks. When the r e s u l t s of a l l these d i f f e r e n t i n v e s t i g a t i o n s on the subject of p o u l t r y vigour and m o r t a l i t y are considered i t becomes evident that there Is no general agreement as to what the word "vigour" a c t u a l l y means. Pearl'(1923) regards l o n g e v i t y of l i f e as the only possible measure of c o n s t i t u t i o n a l f i t n e s s . To quote him on the subject, " O r d i n a r i l y the poultry-nan uses as the p r i n c i p l e of h i s measure of c o n s t i t u t i o n a l f i t n e s s , the p h y s i c a l vigour of the individua,! as i n d i c a t e d by i t s behaviour*, Prom a b i o -l o g i c a l p o i n t , p h y s i c a l vigour, i s and can be, only a p a r t i a l i n t e g r a t i o n of the f a c t o r s involved i n the whole c o n s t i t u t i o n of the i n d i v i d u a l . I t , i n the main, concerns only the nervous and muscular systems. An i n d i v i d u a l may have a superior mus-cular system, but a quite poorly organized digestige or excret-ory system, f o r example. ' 8 I f I were i n a p o s i t i o n to do so, I should l i k e to t r y , f o r a period of years, the experiment of breeding each year the oldest hens, which could be had, and from which i t was possible to get any chicks at a l l . . . . I f e e l confident, from what l i t t l e I know of biology of p o u l t r y , on one hand, and of duration of l i f e , on the other hand, t h a t , a f t e r about f i v e years I should have a f l o c k of p o u l t r y of a s t o n i s h i n g l y strong constitution,, extremely low chick m o r t a l i t y and, I think high productiveness". Thus i t i s seen that P e a r l considered 1 ongevity as an e s s e n t i a l c r i t e r i o n f o r measuring c o n s t i t u t i o n a l vigour. While undoubtedly i t i s one of the necessary complementary f a c -tors i n v o l v e d , i n view of other considerations i t can not be promulgated as the only f a c t o r of importance that determines c o n s t i t u t i o n a l vigour. I n the same paper, P e a r l suggests that l o n g e v i t y i s i n h e r i t e d , so that i f h i s d e f i n i t i o n of vigour i s accepted, then the c o n s t i t u t i o n a l vigour i s also i n h e r i t e d . This i s , however, not n e c e s s a r i l y so. I f , as according to P e a r l , l o n g e v i t y , or c o n s t i t u t i o n a l vigour, i s a d e f i n i t e l y i n -h e r i t e d character, then, the question a r i s e s as to why i t should be so modified by environmental c o n d i t i o n s , such as weather, n u t r i t i o n , disease e t c . I f l o n g e v i t y were purely a genetic f a c t o r , then an I n d i v i d u a l would be expected to l i v e the number of days, months, or years, as determined by i t s genetic complex, provided that i t i s given reasonably good care. Apparently, the s i t u a t i o n i s a more complicated one than P e a r l ' s conclusions would i n d i c a t e . A more promising 9 avenue of approach to the subject of l o n g e v i t y i s from the standpoint of combination of complex p h y s i o l o g i c a l and hered-i t a r y f a c t o r s , a l l of them a c t i n g complementary to one another. Brody, Henderson and Dempster (1923) have p r a c t i c a l -l y adopted t h i s theory s t a t i n g that the n a t u r a l duration of l i f e i s determined by a rate of chemical r e a c t i o n and the rate of production of toxins w i t h i n the body. Studying the k i n e t -i c s of senescence, Brody (1924) suggested that the cause of decline of v i t a l i t y with age i s due to the process of senes-cence which i s present throughout the l i f e of the i n d i v i d u a l . The e f f e c t s of t h i s process of senescence are, however, masked f o r a time by the process of growth. The degree of v i t a l i t y of senescence , Brody s t a t e s , i s always a constant percentage of the degree of v i t a l i t y or senescence of the moment preced-ing to that i n question. I t would appear therefore , Brody concludes, that t h i s exponential law i s s i m i l a r to the law of monomolecular change i n chemistry. From t h i s i t i s evident that what appeared to P e a r l to be purely a question of i n h e r i t a n c e , to Brody i s a phys-i o l o g i c a l process, dependant to a large extent on the environ-mental c o n d i t i o n s . I f Brody's i n t e r p r e t a t i o n of vigour, or l o n g e v i t y i s accepted, then the influence of environment . should be very g r e a t . One only has to consider the question of growth to see that such i s the case. In t h i s connection, J u l l ( l 9 3 2 ) , states: " P r a c t i c a l l y no information i s a v a i l a b l e concerning the inheritance of the rate of growth i n the chicks of the d i f f e r e n t breeds and var-10 i e t i e s . This i s r e a d i l y understood when the f a c t i s r e a l i z e d that the inherent a b i l i t y to grow i s affected by such e n v i r -onmental f a c t o r s as the kind of r a t i o n f e d , seasonal influences throughout the growing season, the number of chicks per brood-er and per house, general conditions of f l o c k management, and the presence of p a r a s i t e s and disease, a l l of which may vary from year to year Berner and Asmundson (1,952, 1934) have found that the rate of growth i s due to breed and s t r a i n d i f f e r e n c e s . These d i f f e r e n c e s i n the rate of growth, i t i s suggested, are gov-erned by m u l t i p l e f a c t o r s . The authors are i n agreement wi th the above quotation of J u l l to the e f f e c t that environment plays a very important part i n the study of the rate of growth, which i s a p h y s i o l o g i c a l character. I t has been suggested p r e v i o u s l y that l o n g e v i t y i s only one component part of the vigour complex and t h i s appears to be true whether one accepts P e a r l T s or Brody Ts view on the subject. I t has also been mentioned that the i n v e s t i g a t o r s have used f e r t i l i t y , h a t c h a b i l i t y , l i v a b i l i t y of chicks and egg production of females as measures of vigour. The most im-portant i n v e s t i g a t i o n s on the above mentioned subjects have already been mentioned i n the e a r l i e r part of the d i s c u s s i o n . I t w i l l become c l e a r , however, on a c l o s e r examin-a t i o n of these f a c t o r s , that not one of them could be consid-ered alone to be a c r i t e r i o n of vigour. A b i r d might l a y very few eggs and yet show e i t h e r high h a t c h a b i l i t y or l i v a b i l i t y of her c h i c k s . She may also possess the a b i l i t y to l i v e far-11 longer than i s considered to he a normal span of l i f e f o r a domestic fowl tand5 r Q' t succumb to a disease. On the other hand, a b i r d may l a y a large number of eggs which w i l l show poor h a t e h a b i l i t y , l i v e long and produce a large progeny, although the l a t t e r would be produced over a period of years. F i n a l l y , the l i v a b i l i t y of chicks or adult b i r d s may not n e c e s s a r i l y be due to the inherent l o n g e v i t y but rather to immunity against diseases and attacks of p a r a s i t e s . The a b i l i t y of c e r t a i n i n d i v i d u a l s , both i n the plant and animal kingdoms to with-stand adverse environmental conditions has been observed by p r a c t i c a l breeders: of plants and animals. Leoanrdo da "Vinci was the f i r s t to ca r r y out d e f i n -i t e l y recorded experiments on the subject of host r e s i s t a n c e . In animals, zebu and bison r e s i s t a n c e to t i c k s i s a c l a s s i c example of host r e s i s t a n c e . Mohler (1914) found that i n the c a t t l e areas of southern United States, the comparatively high r e s i s t a n c e of range c a t t l e to t i c k s was always n o t i c e a b l y lowered when i t w a s bred to such breeds a s Herefords or Short-horns. Apparently these two breeds lacked some f a c t o r , or f a c t o r s , possessed by the common run range c a t t l e , which en-abled the l a t t e r ' t o withstand the attacks of t i c k s . In plant breeding i t has been known f o r a long time that c e r t a i n species, and i n may e a s e l s , even v a r i e t i e s of plants are r e s i s t a n t to attacks of c e r t a i n i n s e c t s while the r e l a t e d v a r i e t i e s are h e a v i l y attacked by these i n s e c t s . Re-sistance to attacks of i n s e c t s i n general i s exemplified i n the case of r e s i s t a n t indigenous plants (Wardie , 1929). 12 Without going i n t o a d e t a i l e d d i s c u s s i o n of a l l the known f a c t o r s involved i n t h i s subject of host r e s i s t a n c e i t should s u f f i c e to say that the r e a l basis of host r e s i s t a n c e , as i t i s understood today, i s the f a c t o r of host avoidance. This h a b i t may take the form of polyphagy, where the inse c t while avoiding a few host species y e t , on the whole, attacks a wide range of hosts; or else become oligophagy, where the ins e c t attacks only a narrow range of hosts; and f i n a l l y mono-phagy, where the in s e c t l i m i t s i t s attack to one p a r t i c u l a r host specie or even one v a r i e t y of such specie. At the present time y there are c e r t a i n f a c t o r s i n the plant host resistance theory which are d e f i n i t e l y known to influence the degree of resistance.. War die and Buckle (1925) subdivide these f a c t o r s i n t o two groups; physico-chemical, such as presence of a l k a l o i d s , thickness of c u t i c l e , h a i r i n e s s e t c . r and p h y s i o l o g i c a l which in c l u d e s p r e c o c i t y , e a r l y maturity, quick recovery from i n j u r y , absence of response to s p e c i f i c s t i m u l i , and so on. I t i s the second group which seems to o f f e r more hope i n connection wi th the host resistance problem i n an-imal s. Apparently i n preparing t h i s l i s t , the authors con-sidered vigour as a separate e n t i t y i n i t s e l f . In the opinion of the w r i t e r , i t i s d i f f i c u l t to r e c o n c i l e the view, when one considers a l l those f a c t o r s that are believed to have a def-i n i t e bearing on the degree of vigour possessed by an i n d i v -i d u a l . I t seems that the f a c t o r s of p r e c o c i t y , e a r l y matuur-i t y , quick recovery from I n j u r y e t c . should a l l be considered 13 under one main heading of vigour. On the other hand, there i s another possible i n t e r p r e t a t i o n that may be applied to these p h y s i o l o g i c a l f a c t o r s i n . t h e i r r e l a t i o n to vigour. While from one point of view, vigour may be regarded as a sum t o t a l of a l l f a c t o r s c o n t r i b u t i n g to make up a strong and healthy i n -d i v i d u a l , yet i t i s j u s t as f e a s i b l e to say that the afore-mentioned f a c t o r s are, so to speak, the by-products of vigour. In other words, a specie i s host r e s i s t a n t because i t i s v i g -ourous• The other view would be to put the above offered hyp-othesis i n a t o t a l l y d i f f e r e n t form; i t would be that the i n -d i v i d u a l i s vigorous because i t i s host r e s i s t a n t , the l a t t e r c o n d i t i o n depending on a large number of f a c t o r s . As f a r as host resi s t a n c e i n animals Is concerned, i n the l i g h t of r e -cent i n v e s t i g a t i o n s of disease r e s i s t a n c e , n e i t h e r of these two postulates appear to be wholly c o r r e c t . While, as was mentioned p r e v i o u s l y , there are several gradations of resistance which, undoubtedly, were acquired by w i l d species through n a t u r a l s e l e c t i o n over countless gener-a t i o n s , there i s no reason at a l l to be l i e v e that man could not i m i t a t e , to some extent at l e a s t , Mature i n s e l e c t i n g d i s -ease r e s i s t a n t s t r a i n s e i t h e r of plants or of animals. In f a c t i t may become abs o l u t e l y e s s e n t i a l to adopt some sort of a r t i f i c i a l s e l e c t i o n i n order to preserve the domestic species of plants and animals from ultimate e x t i n c t i o n through the attacks of parasites and diseases. -Roberts (1933) had sounded such warning when he point-14 ed out that "when man displaces n a t u r a l processes which are " b i o l o g i c a l l y b e n e f i c i a l (having i n mind at l e a s t a p a r t i a l e l i m i n a t i o n of the n a t u r a l s e l e c t i o n f a c t o r ) , i t i s incum-bent upon him to replace them by others of h i s own c r e a t i o n , which are also b i o l o g i c a l l y b e n e f i c i a l , unless he i s to s u f f e r from t he changes which he has instituted"« And indeed man i s already t r y i n g to f i n d t h i s s u b s t i t u t e f o r n a t u r a l s e l e c t i o n i n a form of breeding f o r disease r e s i s t a n c e . (Lambert 193jj) Dealing with the animal side-of the question oniy^at the present time there are two theories oh disease resistance.. The f i r s t theory c l o s e l y corresponding to the theory of plant host r e s i s t a n c e , wiich has already been presented e a r l i e r i n the d i s c u s s i o n , i s that the -resistance i s of the s i n g l e u n i t type, which enables the animal to r e s i s t a number of diseases or poisons. I f t h i s were true, then the problem of breeding for disease resistance would he g r e a t l y s i m p l i f i e d . I t would be necessary under t h i s theory merely to breed t h i s s i n g l e resistance f a c t o r i n t o a s t r a i n of animals i n order to obtain a high.degree of r e s i s t a n c e or even complete immunity against a large number of diseases or parasites.',. The second theory holds that a r e s i s t a n t c o n s t i t u t i o n i s of a composite type, made up of numerous genetic f a c t o r s , the f o r t u i t i o u s combin-a t i o n of which leads to a high degree of r e s i s t a n c e * 'This second theory of the complex nature of r e s i s t -ance i s , at the present time, considered more l i k e l y to o f f e r a key to the s o l u t i o n of the problem of the a r t i f i c i a l breed-i n g - i n of the disease and p a r a s i t e r e s i s t a n c e . Gowen (1933), 15. working with mice, favoured t h i s theory as he had found that r e s i s t a n c e , or even immunity, to one disease does not neces-s a r i l y render the s t r a i n or the i n d i v i d u a l r e s i s t a n t to an-other disease. Indeed, even the type of resistance to one disease may not he of the same type as the resistance to an-other disease. M i l l e r (1953) suggested that from a gene M e a l standpoint, there are three main categories of disease i n animals; (a) the chronic n o n - s p e c i f i c c o n d i t i o n associated with profound t i s s u e changes, (b) chronic s p e c i f i c i n f e c t i o n terminating f a t a l l y i n a m a j o r i t y of cases i f permitted to do so, and f i n a l l y , (c) the acute s p e c i f i c i n f e c t i o n with death or r e s o l u t i o n r a p i d l y f o l l o w i n g . He regards such diseases as t u b e r c u l o s i s as belonging to c l a s s (b) as i t i s an example of l o w - i n h e r i t e d r e s i s t a n c e to i n f e c t i o n , but of high i n h e r i t -ed r e s i s t a n c e to the progress of the disease a f t e r i n f e c t i o n . In the l i g h t of t h i s hypothesis.,, i t may' then be safe to say that Pullorum disease belongs to type ( c ) , where i n h e r i t e d r e s i s t e n c e to i n f e c t i o n may be high but resistance to the progress a f t e r i n f e c t i o n i s 1ow, u s u a l l y r e s u l t i n g i n death. The seme may be s a i d of the eaecal type of coceidiosis„ On the other hand the chronic form of the disease would belong to c l a s s ( b ) . leukemia would, i n t h i s c l a s s i f i c a t i o n , come under ( a ) , together with the various types of tumorous growths. Comparatively few studies have been made wi th regard to the inheritance of disease resistance i n p o u l t r y , i'rateur (1924) found that the resist a n c e to avian d i p t h e r i a can be bred i n t o the stock by breeding only from b i r d s that have 16 'shown themselves non-receptive to the a r t i f i c i a l i n o c u l a t i o n with " b a c i l l i of d i p t h e r i a . He suggested that the resistance to t h i s disease i s due to the presence of a sole Mendelian dominant f a c t o r R, the absence of which produces r e c e p t i v i t y towards the disease. Roberts and Card ( I 9 2 6 , 1927) have found that i n c h i c k s , a n a t u r a l resistance to pullorum disease i s h e r e d i t a r y or, at l e a s t p a r t l y , due to genetic factors.. Lam-bert and Knox (I927, 1932) and Lambert (1952) came to a con-c l u s i o n t h a t resistance to fowl typhoid i s i n h e r i t e d , being governed by m u l t i p l e f a c t o r s . Asmundson and B i e l y (1932) stated that the evidence which they obtained pointed to the p o s s i b i l i t y of existence of genetic f a c t o r s which influence r e s i s t a n c e to fieurolymphomatosis Gallinarum. According to them, the mode of inheritance i s simple. Thus there seems to be general agreement among the i n v e s t i g a t o r s of the subject that such disease resistance may be b u i l t up by a r t i f i c i a l s e l e c t i o n f o r each p a r t i c u l a r disease, thus agreeing with Gowen's conclusions. In other words, a r e s i s t a n t c o n s t i t u t i o n i s of composite character, made up of numerous Mendelian f a c t o r s , each one of which (or a group of f a c t o r s ) determines the degree of resistance to one s p e c i f i c disease. This conclusion would preclude any reasonable p o s s i b i l i t y of developing a s t r a i n of b i r d s that would be immune to diseases and parasites In the absolute sense of the word. Lambert (1955) recognized these d i f f i c u l t i e s , although he is*-of the opinion that an attempt should be made In that d i r e c t i o n . 17 The only other way i n which disease resistance of frocks could he appreciably increased i s by adopting' such r i g i d methods of c u l l i n g as would take the place"of Natural S e l e c t i o n . As suggested by Soberts (.1932} some system such as t h i s should .be adopted i f man i s not to s u f f e r from the unbal-ancing of the n a t u r a l system of e l i m i n a t i n g of weaklings. I t i s d o u b t f u l , however, I n view of the past and present experience w i t h c u l t i v a t e d plants and domesticated animals i f man can ad-opt a system of a r t i f i c i a l s e l e c t i o n that would be as e f f e c t -ive as Natural S e l e c t i o n . For an average I n d i v i d u a l p o u l t r y -man i t would be extremely d i f f i c u l t , i f not impossible, to c u l l out of h i s f l o c k a l l b i r d s which should be c u l l e d out to make the s e l e c t i o n one hundred percent e f f e c t i v e . 6 The widespread use of vaccines., f o r example, undoubt-edly a s s i s t s a poultryman sfor a time ? to reduce the danger to h i s f l o c k from i n f e c t i o u s diseases. In the long run, however, i t means that the b i r d s which are s u s c e p t i b l e , and would pro-bably die,from c e r t a i n diseases under domesticated conditions are helped i n b u i l d i n g up a r t i f i c i a l l y ; acquired immunity. So f a r ;as I t i s knovm at the present time immunity i s not hered-i t a r i l y , t r a n s m i s s i b l e . . In t h i s way nature i s prevented from v/eeding out the undesirable characters* furthermore, b i r d s which are considered to be good breeders under the protected Surroundings of a modern breeding p l a n t , would p o s s i b l y be found to be c o n s t i t u t i o n a l l y weak i f made to face the rigours of the struggle f o r existence'without - such p r o t e c t i o n . I t seems,, the r e f o r e , the best, that man can hope to do, i s to " . - . 18 . c a r r y out the most r i g i d c u l l i n g programme p o s s i b l e . At the same time he should pay a t t e n t i o n not only to egg production but a l s o to s e l e c t f o r f a c t o r s which are known, or b e l i e v e d , to enter i n t o the vigour complex. I t i s apparent from the foregoing discussion of the subject of vigour i n p o u l t r y t h a t , m i l e vigour as such may be governed by genetic f a c t o r s at the same time i t i s profound-l y influenced by many environmental c o n d i t i o n s . Thus, disease r e s i s t a n c e , and high production alone would not f i t the i n d i v i d u a l as a breeder of healthy progeny. Furthermore, while such c h a r a c t e r i s t i c s as high h a t c h a b i l i t y , l i v a b i l i t y e t c . , which have been used as c r i t e r i a of vigour by P e a r l and Surface (1909), Dunn (192.1, 1923c, 1928) , Hays and Sanborn (1924), Hyre and H a l l (1931) and others, are i n -h e r i t e d , yet they are also g r e a t l y a f f e c t e d by external con-d i t i o n s i n , the incubator and, l a t e r on, during the period of r e a r i n g and the c o n d i t i o n of the breeding stock ( J u l l , 1930) The two types of f a c t o r s concerned with v i t a l i t y , the genetic and p h y s i o l o g i c a l , are so c l o s e l y bound together that i n studying the problem of v i t a l i t y or c o n s t i t u t i o n a l vigour, they must of n e c e s s i t y be considered side by side. Each i s c o n t r i b u t i n g i t s share towards g i v i n g the outward expression of the sum t o t a l of a l l those f a c t o r s i n the shape of what i s v a r i a b l y termed as c o n s t i t u t i o n a l vigour, c o n s t i t u t i o n a l f i t -ness, v i t a l i t y , vigour e t c . And i t i s because of t h i s extreme complexity, that no d e f i n i t i o n of vigour has yet been found which would do j u s t i c e to a l l c o n t r i b u t i n g f a c t o r s . 1? J u l l (1952) f u l l y r e a l i z e d the above -when he sugges-ted a t e n t a t i v e d e f i n i t i o n of vigour: "A b i r d with an abund-ance of c o n s t i t u t i o n a l vigour i s one so w e l l endowed with h e a l t h and p h y s i c a l f i t n e s s as to be able to withstand unfav-ourable environmental c o n d i t i o n s * to r e s i s t disease, to pro-duce o f f s p r i n g most e f f i c i e n t l y and to be capable of l i v i n g a r e l a t i v e l y long l i f e " , or, i n other words, vigour, though pos-s i b l y i n h e r i t e d i n a Mendelian way i s profoundly a f f e c t e d by environmental c o n d i t i o n s , even to such an extent as to over-shadow the expression of the genetic complex. 20 • • Part 11 In view.of the p r e v a i l i n g opinion among many p r a c t i c a l poultrymen that the increased m o r t a l i t y i n p o u l t r y f l o c k s i s l a r g e l y due to breeding f o r high egg production the present i n v e s t i g a t i o n was undertaken with two main objects i n mind: (a) to determine the average percentage of m o r t a l i t y i n the high producing f l o c k of the U n i v e r s i t y of B r i t i s h Columbia from I929 to 1934 S (b) whether or not high egg production i s associated with high m o r t a l i t y . To obtain the necessary data, the records of breeding of the U n i v e r s i t y f l o c k from 1922 to 1934 were studied. In one case the records of the l a s t four years, 1931-1934, were omit-ted on.account of the incompleteness of the data. The records of three breeds, S i n g l e Gomb White Leghorns, Barred Plymouth Rocks and Rhode I s l a n d Reds, were chosen because they were more complete and a l s o because these breeds have been and are, at the present time, undoubtedly, the most popular breeds that have been bred f o r high egg production over a large num-ber of years. In dealing with high producing s t r a i n s of b i r d s , such as are kept at the U n i v e r s i t y of B r i t i s h Columbia, one consider-a t i o n that must be taken i n t o account i s that most of the poor l a y e r s were u s u a l l y removed from the pens as soon as t h e i r trap nest records ind i c a t e d t h e i r comparative i n f e r i o r i t y as p o t e n t i a l breeders.. There i s a p o s s i b i l i t y that a number of these b i r d s would have eventually died, not as a r e s u l t of high rate of egg. production, hat rather because they lacked i n c o n s t i t u t i o n a l vigour. The percentage of m o r t a l i t y , there-f o r e , as i n d i c a t e d i n the pen records i s obviously below the probable percentage of m o r t a l i t y had no hens been removed from the pens. On the other hand these records r e f l e c t to a grea-t e r degree the rate of m o r t a l i t y among the more in t e n s i v e l a y e r s , thus considerably s i m p l i f y i n g the task by e l i m i n a t i o n , to some extent, of one complicating f a c t o r of m o r t a l i t y , i . e . , i n h e r i t e d low v i t a l i t y . Three pens of f i f t y b i r d s each were selected each year as basic u n i t s . Thus approximately lj?0 b i r d s came under ob-s e r v a t i o n i n any one year. In some years, however, p a r t i c -u l a r l y i n the l a s t three years of the period s l i g h t l y smaller u n i t s had to be accepted, because of the greater percentage of withdrawals during the l a y i n g year. The accuracy of the f i n a l records of i n d i v i d u a l b i r d s was a f f e c t e d somewhat by the f a c t that c e r t a i n p u l l e t s of high inte n s i t y ' were sold before they had completed t h e i r l a y i n g period. In t h i s connection i t might be pointed out that during that period the farm was managed by a p r i v a t e company. The b i r d s which were included i n these pens had been selected at random, the two p r e r e q u i s i t e s being that e i t h e r a b i r d l i v e d t i l l November 1 of the f o l l o w i n g year, or else had died i n the l a y i n g house during the p u l l e t year. As was men-tioned before, a l l birds that were c u l l e d out or sold before completing t h e i r f i r s t year i n the l a y i n g house were not i n -cluded i n t h i s study. Tables 1, 11 and 111. show the annual production and mort-a l i t y rates over a twelve year period among the representative pens of the three breeds. Of the three breeds, Barred Plymouth r Rock, with only one exception i n I929-I93Q, i s thp only breed that has shown any c o n s i s t e n t increase i n average annual egg production during t h i s period. At the same time t h i s was not followed by any large corresponding increase i n the m o r t a l i t y r a t e . In f a c t , i n 1929-1930, when the production had gone down considerably, the m o r t a l i t y f i g u r e had reached i t s highest point of l8fo. I t i s d i f f i c u l t to account f o r such a sudden drop i n production and the r i s e i n m o r t a l i t y since the b i r d s that l i v e d through that year showed a production f i g u r e lowest i n the e n t i r e twelve year period under observation. Thus t h i s breed, with a s t e a d i l y improving rate of production, which on the whole was the highest among the b i r d s of the three breeds, yet showed the lowest m o r t a l i t y r a t e . The rate of m o r t a l i t y f o r the Barred Plymouth Rocks was only 8.8% as compared with 14.2°/. and 13.7% i n the Single Comb White Leghorn and Rhode I s l a n d breeds res-p e c t i v e l y . I t i s i n t e r e s t i n g to note i n t h i s connection, that the Rhode I s l a n d Red p u l l e t s , the chicks of which breed show considerable v i t a l i t y at hatching time and during the rearing period, had a m o r t a l i t y rate that was p r a c t i c a l l y on a par with the Leghorns and considerably above that of the Barred Rocks. At the same time the production of the RhoSe Island Red p u l l e t s which l i v e d f o r at l e a s t twelve months was consid-erably below that of both the Rocks and Leghorns. In view of the large difference i n the m o r t a l i t y rates of Barred Plymouth Rocks and the other two "breeds, i t was considered advisable to determine whether or not t h i s difference "was s t a t i s t i c a l l y s i g n i f i c a n t . Using the assumed mean method, which accounts f o r s l i g h t discrepancies i n the values of the corresponding a r i t h m e t i c a l and corrected assumed means, i t was found that the difference was s i g n i f i c a n t (Table 1V). On the other hand there was no s i g n i f i c a n t difference between the av-erage twelve year m o r t a l i t y f i g u r e s of leghorns and Rhode Is l a n d Reds. This l a t t e r f i n d i n g does not agree with that of H a r r i s and Bought on (1928) , who found that the death rate of Rhode Isl a n d Reds was s i g n i f i c a n t l y higher than that of White Leghorns. Such a difference might be due to difference i n the s t r a i n s used i n the respective studies rather than to d i f -ferences i n breeds. In any case, there i s l i t t l e doubt that the;: U n i v e r s i t y of B r i t i s h Columbia Barred Plymouth Rocks d i f -f e r s i g n i f i c a n t l y i n t h e i r death rate from the other two breeds, the d i f f e r e n c e apparently being due to the f a c t o r s which are c l o s e l y associated with the c h a r a c t e r i s t i c s of the breeds. I f t h i s supposition be correct i t would be i n t e r e s t i n g to de-termine not only the r e l a t i v e importance of breed and s t r a i n c h a r a c t e r i s t i c s but, i f p o s s i b l e , the extent to which e n v i r -onmental conditions and breeding may modify these f a c t o r s . Besides showing a lower m o r t a l i t y r a t e , the U n i v e r s i t y Barred Plymouth Rocks also showed a lower production f i g u r e i n the case of b i r d s that died i n t h e i r .pullet year, On the b a s i s of the. supposition that was ..offered i n the above para 24 graph i n connection with m o r t a l i t y r a t e s , i t i s quite f e a s i b l e that genetic f a c t o r s also have great influence over the l i f e span of d i f f e r e n t breeds. In other words, he r e d i t y may play a very important part i n determining the l o n g e v i t y of i n d i v i d -u a l s of d i f f e r e n t breeds, which i s i n accordance with P e a r l (1923). I t must be admitted, however, that before d e f i n i t e conclusions on the sub j e c t could be a r r i v e d a t 7 l a r g e numbers of b i r d s of various breeds would have to be kept u n t i l n a t u r a l death under i d e n t i c a l environmental conditions to secure the necessary data. In an attempt to determine the r e l a t i o n s h i p , i f any, be-tween m o r t a l i t y and production, a c o r r e l a t i o n table was worked out between the average annual death rate and the production of b i r d s that survived t h e i r p u l l e t year. The c o r r e l a t i o n f i g u r e was found to be +.112 -fe .111. I t i s apparent, therefore, that no such simple c o r r e l a t i o n e x i s t s . • The second p o r t i o n of t h i s i n v e s t i g a t i o n has been devoted to the study of records of b i r d s which started to l a y but died before completing the p u l l e t year. Harris.and. Boughton (1928) have found that i n the case of f l o c k s under t h e i r observation, by f a r the l a r g e s t proportion of deaths occurred i n the month f o l l o w i n g the period of high production. The authors suggested that perhaps the s t r a i n of production a f f e c t s weak b i r d s , and i f t h i s s t r a i n continues f o r a considerable period of time, 2j5 such b i r d s w i l l eventually d i e . This I n t e r p r e t a t i o n of the e f f e c t of production on the h e a l t h of l a y i n g b i r d s , though l o g i c a l i n i t s e l f , would appear to be open to c r i t i c i s m by p r a c t i c a l p o u l t r y breeders. Thus, instead of considering mor-t a l i t y i n t h e i r p u l l e t f l o c k s as an e v i l i n c i d e n t a l to modern in t e n s i v e methods of p o u l t r y keeping, i t may be regarded as a n a t u r a l method of breeding, out b i r d s l a c k i n g i n vigour. The suggestion of H a r r i s and Boughton that c o n s t i t u t i o n a l l y weak int e n s i v e l a y e r s are automatically eliminated i s quite plaus-i b l e under one c o n d i t i o n , that i s that the birds which die under normal environmental c o n d i t i o n s , are a c t u a l l y i n t e n s i v e l a y e r s . I f t h i s i s not the case, then i t i s possible that they die not because they are at the same time c o n s t i t u t i o n a l -l y weak and i n t e n s i v e l a y e r s , but rather because they lack i n vigour regardless of production. In Tables Y and V l are brought out several, i n t e r e s t i n g f a c t s i n connection with the points mentioned i n the preceding paragraph. I t i s apparent from these tables that, on the whole, there i s a d e f i n i t e trend each year i n the U n i v e r s i t y f l o c k to a shorter l i f e span among bi r d s which die i n t h e i r p u l l e t year, ^'or sane reason, unknown at the present time, the b i r d s , which f a i l e d to l i v e through t h e i r f i r s t year, dur-ing the l a s t three years of .the study have been dying r e l a t i v e -l y e a r l y i n the season, the date of m o r t a l i t y occurring, on the average., not more than f i v e months a f t e r commencing to l a y i n the f a l l and winter. At the same time, the average weekly production of these b i r d s during the weeks a c t u a l l y i n l a y , 26 as would be expected, had also been considerably reduced. Thus i n 1924-2_5 the weekly production of b i r d s while a c t u a l l y i n l a y was 3.50 t . 7 4 7 eggs and i n 1951 was 5 . 1 7 ± . 2 6 0 . I t the same time the corresponding l i f e span was reduced from 41 . 0 0 0 1.310 to 1 6 * 0 5 2 - .631 weeks. During the f o l l o w i n g two years, however, with the reduction of the rate of l a y per week to 4 . 7 9 and 4.83 r e s p e c t i v e l y , the number of weeks of l i f e increased to 20.8. . . In view of these f a c t s , i t would appear that e x c e s s i v e l y high production may have a detrimental e f f e c t on the c o n s t i t -u t i o n of b i r d s , p a r t i c u l a r l y when weekly production i s near-ing the f i v e egg mark. But at the same time, the f i g u r e s seem to i n d i c a t e that whatever e f f e c t s heavy production may have on the l o n g e v i t y of p u l l e t s , these e f f e c t s accumulate gradually and are probably a f f e c t i n g the weaker b i r d s f i r s t , as was suggested by H a r r i s and Boughton. I t i s , evident, furthermore that i f heavy weekly production i s at a l l detrimental to the h e a l t h of b i r d s , i t . i s i n d i r e c t . In other words, the health of the b i r d s may be undermined by such other f a c t o r s as reduced resi s t a n c e to disease, elements of weather and improper n u t r i -t i o n and death be brought about by a cumulative e f f e c t of a combination of these f a c t o r s , rather than by high production alone. The c o r r e l a t i o n between the number of weeks -that the b i r d s l i v e and the rate of l a y per week was found to be def-i n i t e l y i n s i g n i f i c a n t i n White leghorns and Rhode J-sland Reds. In the case of Barred Plymouth Rocks, however, the c o r r e l a t i o n may be s i g n i f i c a n t . (Table 711) 27 Summary 1. This i n v e s t i g a t i o n was based on the study of egg pro-duction and m o r t a l i t y records of Single Comb White leghorns, Rhode Island Reds and 'Barred Plymouth Rocks at the U n i v e r s i t y of B r i t i s h Columbia from 1922 to 1954 I n c l u s i v e . 2. No c o r r e l a t i o n was found between average egg prod-u c t i o n and m o r t a l i t y . 5. Breed and s t r a i n c h a r a c t e r i s t i c s were found to have a d e f i n i t e bearing on the production and m o r t a l i t y of p u l l e t f l o c k s . 4. The l i f e span of p u l l e t s which f a i l e d to l i v e through t h e i r f i r s t year has been gr a d u a l l y diminishing among the Un-i v e r s i t y p u l l e t f l o c k s , The average weekly production of these p u l l e t s on the other hand has been r i s i n g s l i g h t l y . 5 . There was no c o r r e l a t i o n between the number of weeks of l i f e and. the r a t e of l a y i n g per week i n Single Comb White leghorns and Rhode I s l a n d Reds and only a s l i g h t p o s i t i v e co-r r e l a t i o n In Barred Plymouth Rocks. The l a t t e r r e s u l t , how-ever, can not be considered to be s i g n i f i c a n t . 6* There was no c o r r e l a t i o n between the number of weeks of l i f e and the age at f i r s t egg. Nor was any c o r r e l a t i o n found to e x i s t between the number of weeks i n production and the rate of production during these weeks. 7. Although high production may have an adverse e f f e c t upon the health of p u l l e t s as expressed by m o r t a l i t y , the e f f e c t would appear to be i n d i r e c t . 28 8. The i n c r e a s i n g rate of m o r t a l i t y i n p u l l e t f l o c k s i s probably due to no si n g l e f a c t o r . In the absence of a specif ic outbreak of an i n f e c t i o u s disease, the m o r t a l i t y among p u l l e t s , on the whole, probably r e s u l t s from a combination of f a c t o r s which'are cumulative i n e f f e c t . , REFERENCES 'Asmundson & B i e l y J . 1932 Inheritance of resistance to Fowl P a r a l y s i s (Neurol-piphMa 10 s i s-gal 1 i n a r urn). 1 - Difference i n s u s c e p t i b i l i t y . Can . J . of Research. 6 : 1 7 1 - 1 7 6 Berner I . & Asmundson V.S. 1932 Inheritance of Rate of Growth i n Domestic Fowl. 1 - Methods and P r e l i m i n a r y Report on r e s u l t s obtained In the two breeds. S c i . A g r i c . 12:6 .52-664 Asmundson Y.S. & Lerner I.M. I 9 5 4 Inheritance of Rate of Growth i n Domestic Fowl. I l l - Comparative rates of Growth of Leghorns and Rocks. Poul. S c i . X l l l 6:348 T352' Bate son W. & Pinmett R.C. 1905 Experimental Studies i n the Physiology of Heredity. Reports to the E v o l u t i o n Committee of the Royal Society 2:99-131 Bateson W. , Punjiett R.C, 190,5" Experimental Studies i n the Physiology of Heredity. Reports to the E v o l u t i o n Committee of the Royal Society 3:11-30 BrOdy S,. Henderson E.W. & Kemps ton H.L. 1 9 2 3 The Rate of Senescence of the Domestic Fowl as measured by The Decline of Egg Production with Age. I . Gen. P h y s i o l . 6:41-4,5 Broody S. \ The K i n e t i c s of Senescence. I . Gen. P h y s i o l . IV -34.5 Cole L . J . & Ha l p i n J.G. I 9 1 6 P r e l i m i n a r y Report of an Experiment on Close Inbreeding i n Fowls• Jour. Am. Ass. Instr.& Invest, of P. Husb. 3. 157-8 Cole. L . J . & Haloin J.G. 1 9 2 2 Results of Eight Years of Inbreeding of R.I.R. Fowl. Anaf. Rec. 2 3 : 9 7 •Grew F.A.F & Roberts J.A.F. 1 9 3 3 Heredity as a Factor i n Animal Disease. Proc. Roy. S 0 C ( Med. 2 6 , S e c t . Gonf. Med. 1 1 -18 ,Dumon A.G. 1930 The E f f e c t s of Inbreeding on H a t c h a b i l i t y 4th World 1 s P o u l t r y Congress, London, ppl-_5 Dunkerly J. S. 1950 The E f f e c t s of Inbreeding. 4th World's P o u l t r y Congress, London, pp 48-71 Dunn L.C, 1921-22 H a t c h a b i l i t y and Chicle M o r t a l i t y . P'i Sc. 1. p 5 3 Dunn L.C. Experiments on Close Inbreeding i n .Fowls. A Prel i m i n a r y Report. Sto.rrs Agr. Exp. St. B u i . I l l bp 138-172 Dunn l . U . 192 3c The Problem of K a t c h a b i l i t y from the Standpoint of Genetics. Set. Agr. 4 Dunn L.C. The e f f e c t of Inbreeding and Cross Breeding on Fowls.. Transactions of 5 t h I n t e r n . Congress f o r Genetics, B e r l i n , 1927 v . l . p p 6 0 9 - 6 l 7 Frateur J.L C 1924 The Hereditary Resistance of the Fowl to the B a c i l l u s of D i p t h e r i a , Proc. World's 2nd Poul. C o n g r . Sec. 1 pp 68-71 Gowen T.W. 1 9 3 3 On the Genetic Structure, of Inherited C o n s t i t u t i o n f o r Disease Resistance. • Quar. Rev* B i o l . 8 ( 3 ) pp358-547 H a r r i s 3:. Arthur 1926 The Monthly Egg- Record of Birds Which Die during the F i r s t Laying Year. Pi Sc.. 6 pp 1-8 H a r r i s F:. Arthur I927 tether Studies on the Monthly Egg Record of Birds Which Die During the F i r s t Laying Year. P. S c i . 6 pp 21^-224 H a r r i s J . Arthur & Bought on B.C. 1928 The .Death Rates of Three Standard Breeds of Fowl. P. Sci.. 7 PP 120-131 ,r Harvey G.W. & Decker M. I 9 2 6 Rate of M a t u r i t y and F i r s t Year Production i n leghorns, P. S c i . 5 ( 3 ) :149 Hays F.A. 1928 R e l a t i o n of Age of Parents to H a t c h a b i l i t y , L i v a b i l and fe c u n d i t y i n the Domestic Fowl. P. S c i . v o l . 7 , 3 pp I O 6 - I I 5 Hays #.A. & Sanborn Ruby I 9 2 6 The Inheritance of F e r t i l i t y and H a t c h a b i l i t y i n P o u l t r y ; Mass*, Agr. Exp. St. 6 pp 20-42 Hays .F.A. & Sanborn R. 1928 Vigour i n Production Bred I l o c k s . Mass. Agr. S Xp. Sta. B u l l . 242 Hutt F.B. I 9 3 5 On the P h y s i o l o g i c a l Basis of Genetic Resistance to S. P u l l 0 r u m i n the Powl. Am. Nat. LXlX 70 p 66 Hyre H.M. & H a l l G.G. 1951 The Constancy of Hatching Power i n Hens. P . S c i . .10 p 4 0 6 J u l l 'M.A. 1 9 2 9 a Studies i n H a t c h a b i l i t y * I I H a t c h a b i l i t y i n R e l a t i o n to the Consanguinity of the Breeding Stock-P. S c i . V l l l 4 pp 219-224 J u l l M.A. I 9 2 9 o Studies i n H a t c h a b i l i t y r I I I H a t c h a b i l i t y i n R e l a t i o n to 0Oeffi§ients of Inbreeding* P. S c i . V l l l 6 pp 361-368 J u l l M.A. 1 9 5 0 Studies i n H a t c h a b i l i t y . IV The E f f e c t of I n t e r c r o s s i n g Inbred St r a i n s of chickens on F e r t i l i t y and H a t c h a b i l i t y . P. S c i . IX, 5 , 149-156 J u l l M.A. 1 9 3 0 V Studies i n H a t c h a b i l i t y . The Inheritance of H a t c h a b i l i t y . 4th World's P o u l t r y Congress pp I 6 7 - I 7 2 ' J u l l M.A. 1952 P o u l t r y Breeding. 576 pp John Wiley & Sons, Hew York Lambert W . V . & En ox C . W . 192 7 On the Inheritance of .Resistance to Fowl Typhoid i n Ghiekens• Anat. Rec. 57 pp 174-175 Lambert W . V . & Knox C.W. 1952 S e l e c t i o n f o r Resistance to Fowl Typhoid i n the Chicken with reference to i t s Inheritance. Iowa Agr. Exp. Sta. Res. B u i . I 5 5 pp 2 61-295 Lambert W.V. 1952 Genetic S e l e c t i o n f o r Resistance to Fowl Typhoid i n the Chicken* Proc. V. I n t . G 0ng. Gen. 2 pp 113-114 Lambert W . V . Inheritance as a f a c t o r i n P o u l t r y Disease. P. S c l * X I V , 3, pp 131-13> Mateu F.F. 1930 Should there be a L i m i t to S e l e c t i o n i n Laying Hens? Proc* 4th World's P o u l t r y Cong, pp 126-127 Sec. A M i l l e r W . C . . 1953 . Heredity as a Factor In Animal Disease. Prcc. Roy. S Q C * Med> 26. Sect. Conf. Med. 18-23 Mohler T . R . 1914 Tex&s or Tick Fever. U.S. Farmers' B u i . No. 569 P e a r l R. & Surface F.M. 1909 Data on Ce r t a i n Factors Influencing the F e r t i l i t y and Hatching Power of Eggs . Maine Agr. Exp. Sta. B u i . 168 pp. 10J5-164 . P e a r l R. 1925 ' Duration of L i f e as an Index of C o n s t i t u t i o n a l Fitness. P. S c i . 5 pp 1-10 Roberts F. & Card L» F. The Inheritance of Resistance to B a c i l l a r y White Diarrhea* -P. S c i . 6 p. 18 Roberts E . & Card. B„ E . 1927 Genetic Studies on Resistance to Disease. Anat. Record 37 pp 1 7 5 - 1 7 6 Roberts E. Inheritance of Resistance to Disease In Animals. Proc. VI I n t e r . cong. Gen. 2 pp 1 6 9 - I 7 0 Rogers C.A. . 1912 C o n s t i t u t i o n a l v i g o u r i n P o u l t r y • C o r n e l l Univ. Agr. Exp. Sta. B u i . 318 Rogers 0 . A. 1914 A continued Study of C o n s t i t u t i o n a l Vigour i n P o u l t r y C o r n e l l Univ. Agr. Exp. Sta. B u i . 545 War die R. & Buckle P. 192 3 The P r i n c i p l e s of Insect C o n t r o l . 295 PP Manchester U n i v e r s i t y Press Wardie R.A. 1 9 2 9 The Problems of Applied Entomology. 5 6 0 pp Manchester U n i v e r s i t y Press Warren B.C. 1 9 3 0 Inheritance of Vigour i n the Domestic Powl. 4th World's P o u l t r y Congress, Sec. A* pp 148-153 Table 1 Year Breed Ho. of Hens Aver. Prod. Ho. of dead Average Prod.of B i r d s that died Ho. of Bead as % of t o t a l Average Prod, of h i v i n g Birds 1922-25 S . 0 o W e l i . 47 207*8 119.2 10.6 218 .1 1923-24 tt 50 203 . 1 3 . 26*0 6 .0 214 .4 1924-25 tt 50 224 .1 2 6 8 . 5 4 . 0 2 34.7 1925-26 t t 50 2 34.8 5 115 • 6 10 .0 248 .0 1926-27 SI 50 243*9 5 169-6 10..0 274.3 1927-2 8 tt 50 224.3 8 1 9 3 7 . 0 1 6 . 0 250 .7 1928-2-9 tt 30 203*4 118.8 10 .0 212 .8 -1929--SD I I 50 199.3 4 100 .8 8 .0 2Q7«5 19SB-51 tt 48 187 »5 20 95*1 .41.7 256 . 1 1951-52 w 33 231.5 4 82 .0 1 2 . 1 252 .2 1952-33 tt 50 191 .9 13 12 9.8 2 6 . 0 213 .7 1933-34 t j 45 207*2 7 94.6 I 5 . 6 £27*9 1922-34 tt . 4.7-4.8.. 2 X 2 * 3 6.9 .1.Q3-.4 Table 11 Year Breed No. Of Hens Aver. Prod* No. of dead Average Prod.of b i r d s that died No. of dead as fo of t o t a l Average Prod. 0 l i v i n g Birds 1 9 2 2 - 2 3 50 I87 .2 3 68*0 6.0 194 .8 1923-24 t! 50 197-2 1 84.0 2.0 . 199.5 1924-25 11 50 216.6 1 109.0 2.0 218,8 1925-26 it 50 211.3 3 110.5 6.0 218.0 1926-27 It 50 210.5 2 155*6 4*0 212.8 1927-28 tl 50 221.1 2 15-5 4.0 251.8 1928-29 II 50 200.2 8 105.0 16.0 221.0 1929-30 » 45 171.7 9 84.4 18.0 195 .6 1930-31 It 50 219.8 7 85.7 14.0 241.8 1951-52 31 2 32.2 5 128.5 9-7 243.3 1932-35 tl 50 235.7 6 47-8 12 ,0 259.O 1933-54 I! 50 220.8 6 ' 87*8 12.0 2 39 • 0 1922-34 tt 48 210.9 4 .5 88*0 8.8 242.7 Table 111 Average -Mo., of Average No.of Aver. No.of Prod, of dead as Prod.of Year Breed Hens Prod. dead Birds. % of L i v i n g that Died t o t a l Birds 1922-23 H. 1 *R » 5 0 I74..4 9 I07.O 18 . 0 186.7 1923-24 ;i '50 191.6 3 6*0 200.3 1924-25 tl 50 2 2 5 . 1 1 185 .0 2 . 0 228.1 1 9 2 5 - 2 6 tt 5 0 211.8 2 147*5 1 . 0 2 35 .5 1 9 2 6 - 2 7 tt 5°: 204 ,0 4- 122 .8 8 . 0 211 . 1 1 9 2 7 - 2 8 tt 50 2 06:. 7 8 103 .0 1 6 * 0 226.4 1 9 2 8 - 2 9 it 50 230.2 2 I 8 5 . 5 4 . 0 2 52 .0 192 9-30 tt 50 208 .2 3 7 9 - 3 6 . 0 217.7 1930-31 tt . 50 164.4 ' 20 43*1 40 . 0 245.2 1931-32 27 211 .0 5 90*8 . . I 8 . 5 2 58.4 1932-33 it 50 164 . 9 15 59 . 2 26.O 202 .0 1953-54 tt 47 1 9 5 « 4 9 •76.O 18.4 225.7 1922-34 tt 4 7 . 8 1 9 8 . 8 5 . 8 104.6 13.7 220.6 Table IT Differences i n M o r t a l i t y Rates of the Three Breeds under Observation Breed % of M o r t a l i t y Difference R.I.R. I 3 . 5 O O O - 1*08 B.P.R. 8.666 ± .521 S.O.W.L. 13.850 % .931 B.P.R. ' 8.666 £ .521 S.O.W.L. 15.850 4- .951 R.I.R. 15 .500 - 1.08 4.85 t 1.202 5.184 t I .O67 ,550 ± 1.421 Table Y Year Average A l l 3 Ho.of eggs Breeds per week while a l i v e M 1922 -2 5 • 3.16*.382 2 .49 192 5-24 5 . 0 8 t.605 2 .34 -1924--25 2 . 8 0 ^ . 6 7 5 2 ,25 192-5 - 2 6 ' 5.70"-.480 2 .25 1926--27 3 . 7 8 t . 5 i o 2 »27 1927' -28 5.32L.476 3 .08 1928- -29 3 . 9 5 t . 2 5 5 1 .45 1929. -30 4 . 5 5 ! .?42 1 .19 1950- -31 5.52t .259 2 .35 1951- -32 5.001.512 • 1 .15 1952- -35 5.64±.243 2 .15 1953- -34 3 .70" h .407 2 .06 Average Ho.of weeks alive a f t e r commencing to l a y M • S 27.06ot.528 3,25 41.000+1.310 4 . 5 5 2 8 . 0 0 0 t - ,549 2 .57 %5°555- »498 2 .25 28 . 9 4 5 t .581 2 .46 50 . 5 3 5 t .494 2 . 8 4 52.2751 .78O 3.87 1 7 . 9 7 5 t .243 2 .19 l 6 . 0 5 2 t .631 2.29 20.855+- .289 2 .55 2 0 . 8 5 5 t . 4 8 5 2.48 TABLE VI Year A l l Three -•Breeds Average No* of eggs per week While Laying -M f Ave rage Ho. of Weeks i n Lay M f 1 9 2 2 - 2 3 3.62^*40? 2.66 24 . 7 0 5 1 . 4 9 2 5.009 1 9 2 3 - 2 4 1 9 2 4 - 2 5 3.501»747 2.57 51.000+..900 2 . 9 9 0 1 9 2 5 - 2 6 3 . 9 0 1 . 4 9 0 2.32 2 6 . 5 0 0 1 . 5 7 4 2 . 6 9 0 1 9 2 6 - 2 7 4 . 0 6 + . 5 3 5 . 2.38 51.6651 .675 2 . 6 7 0 1927-28 3.811 .438 2.85 25.OOOt.674 2.540 1 9 2 8 - 2 9 4.40+.302 1 . 7 3 28.6651*507 2 . 9 9 0 1 9 2 9 - 3 0 4 . 6 8 + . 2 5 4 1.25 50 . 9 1 0 + . 6 5 8 5.240 1 9 3 0 - 3 1 4 o78t=205 I.85 15.135+.240 2 . 1 6 0 1 9 3 1 - 5 2 5 . 1 7 1 . 2 6 0 .94 1 5 . 0 0 0 1 . 6 5 1 2 . 2 9 0 1 9 5 2 - 3 3 4.791-241 2.14 I 7 . 7 i 5 i . 2 7 7 2.430 1 9 5 3 - 3 4 4.831.288 1 . 4 8 l 6 . 6 6 5 i . 5 3 O 2 . 7 2 0 Table ¥ 1 1 S . C • W.L . 1922-50 1922-50 R. © X»R © 1922-3,0 C o r r e l a t i o n Tables + .142"-. 002 + . l 8 2 t . Q Q l -.055-.009 + .11^ . 0 8 9 + .141"-. 013 +.O86-.OOI - . 0 7 3 - . 0 9 5 -.040-.095 -.004t . 0 9 5 Weeks i n l a y and rate of la;/ per week while l a y i n g , Weeks a l i v e and rate of l a y per week while l a y i n g , Days to mature: weeks a l i v e . 

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