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The effect of ’rc’ mutation on the performance of chickens under different densities and flock sizes 1983

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THE EFFECT OF ' r e ' MUTATION ON THE PERFORMANCE OF CHICKENS UNDER DIFFERENT DENSITIES AND FLOCK SIZES BY AHMED ALI M . S c , Bangladesh Agr i cu l tu ra l Un i ve r s i t y , 1970 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department o f Poultry Science) We accept th i s thes is as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1983 (C) Ahmed A l i , 1983 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or pub l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Ahmed A l i Department of , Poultry Science The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date October 12, 1983 7Q^ i i ABSTRACT The impact o f v i sua l contact or the lack o f i t on egg production was invest igated by u t i l i z i n g gene t i c a l l y b l ind chickens in a f a c t o r i a l expe r i - ment invo lv ing two genotypes (b l ind vs s igh ted ) , two dens i t i es (1000cm 2 per b i rd vs 2000cm2 per b i r d ) , two f lock s izes ( 1 $ 4 # vs 4SS 1 6 $ r ) , and two r e p l i c a t i o n s . Parameters measured were: number of eggs c o l l e c t e d , egg weight, amount o f feed taken from feed t rough, body weight ga in , f e r t i l i t y o f eggs, feather pecking and comb damage sco res , leukocyte count, plasma cor t i cos terone leve l and adrenal gland weight. During the two-month experimental pe r i od , b l ind hens produced 12.7% more eggs while requ i r ing 44 . lg less feed per b i rd per day compared to normal hens. There was no s i g n i f i c a n t d i f f e rence in body weight gained between the two genotypes. Thus b l ind hens had better feed e f f i c i e n c y compared to normal hens. S i g n i f i c a n t genotype x f lock s i ze and genotype x densi ty in te rac t ions a lso ind ica ted that the performance of the b l ind chickens was less sens i t i v e to dens i t i es and f lock s izes compared with normal ch ickens. Other parameters measured provided evidence that the b l ind chickens were less ac t i ve s o c i a l l y , and had better feather coverage during the experimental pe r iod . These parameters a lso provided c i rcumstant ia l evidence that the b l ind chickens were under less s t ress than normal ones. It is therefore concluded that the b l ind chickens had less energy requirement for a c t i v i t i e s other than egg product ion . Results from th i s experiment ind ica te that the gene t i c a l l y b l ind chicken not only has good potent ia l as an experimental animal but a lso may have some commercial va lue . i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS i x INTRODUCTION 1 REVIEW OF LITERATURE 5 I. P roduc t i v i t y 5 1. Egg production 5 2. Egg weight , 9 3. Feed consumption 12 4. Body weight •••••• 15 5. F e r t i l i t y 18 II. Parameters measuring s t ress 21 1. Feather pecking 21 2. Adrenal weight 23 3. Cort icosterone 25 4. Leukocytes 28 METHODS 31 I. Experimental animals 31 II. Rearing condi t ions o f birds before s t a r t o f experiment 31 II I . Management o f experimental birds 32 i v TABLE OF CONTENTS (Continued) Page IV. Experimental design 32 V. Parameters measured 33 1. Number o f eggs co l l e c t ed and egg weight 33 2. Amount o f feed taken from feed trough 34 3. Body weight gain 34 4. F e r t i l i t y o f eggs 34 5. Feather pecking and comb damage scores 35 6. Leukocyte count and plasma cor t i cos terone leve l 37 7. Adrenal gland weight 38 VI. Data analyses 38 RESULTS 41 I. Number o f eggs co l l e c t ed . 41 II. Egg weight 48 III. Amount o f feed taken from feed trough 50 IV. Body weight gain 53 V. F e r t i l i t y o f eggs 55 VI. Leukocyte count, plasma cor t i cos terone leve l and adrenal gland weight 57 VI I . Feather pecking and comb damage scores 59 DISCUSSIONS 68 I. Performance o f b l ind chickens 68 1. Statement number 1 68 V TABLE OF CONTENTS (Continued) Page 2. Statement number 2 71 3. Statement number 3 73 4. Statement number 4 77 5. Other cons iderat ions 78 II. Ad i t iona l observat ions from experiment 78 1. F e r t i l i t y 78 2. Flock s i ze and densi ty 80 SUMMARY 8 4 REFERENCES 8 6 APPENDIX 101 vi LIST OF TABLES Table Page 1 Scoring method to assess the degree o f pecking damage to back and rump 36 2 Scoring method to assess the degree o f pecking damage to the comb . 36 3 E f fec ts of genotype on parameters measured 42 4 E f fec ts o f dens i ty on parameters measured 43 5 E f fec ts o f f lock s i z e on parameters measured 44 6 E f f ec t o f time on egg production and egg weight o f the experimental birds 45 7 E f fec ts o f r e p l i c a t i o n (hatch) on parameters measured 47 8 S i g n i f i c a n t DXF in te rac t i on for egg weight of experimental birds . . 49 9 S i g n i f i c a n t GXF i n t e r a c t i on for feed taken from feed troughs by experimental b irds 51 10 S i g n i f i c a n t DXF i n t e rac t i on for feed taken from feed troughs by experimental b irds 52 11 S i g n i f i c a n t DXF i n t e r a c t i on for body weight gain o f experimental hens 54 12 Mean body weight ga in , adrenal weight and leukocyte count of experimental roosters 56 13 S i g n i f i c a n t GXF i n t e rac t i on fo r leukocyte count o f experimental hens 58 14 Mean feather loss and comb damage scores o f the experimental b irds 60 15 S i g n i f i c a n t GXD in t e rac t i on fo r comb damage scores o f experimental b irds 61 16 S i g n i f i c a n t GXF i n t e r a c t i on for comb damage scores o f experimental b i rds 62 17 Analys is o f Variance fo r percent hen-day egg production o f experimental b i rds 102 v i i LIST OF TABLES (Continued) Table Page 18 Analys is of Variance for percent hen-day egg production o f experimental b i rds with adjustment fo r age d i f fe rences between r ep l i c a t i ons 103 19 Mean percent hen-day egg product ion , egg weight (g) and feed requirements (g) o f birds with adjustment fo r age d i f f e rences o f b i rds between r ep l i c a t i ons 104 20 Analys is of Variance for egg weight o f experimental birds 105 21 Analys is of Variance for egg weight o f experimental b irds with adjustment for age d i f fe rence between r ep l i c a t i ons 106 22 Analys is o f Variance for amount o f feed taken from feed troughs by experimental birds 107 23 Analys is of Variance fo r amount of feed taken from feed troughs by experimental b i rds with adjustment fo r age d i f fe rences between r ep l i c a t i ons 108 24 Analys is o f Covariance for body weight gain o f experimental hens . . 109 25 Analys is o f Variance for i n i t i a l body weight o f experimental hens . 110 26 Analys is of Variance for percent f e r t i l i t y o f experimental birds . . I l l 27 Analys is o f Variance for leukocyte count o f experimental hens 112 28 Analys is o f Variance for adrenal weight o f experimental hens 113 29 Analys is of Variance for plasma concentrat ion o f cor t i cos terone of experimental b irds 114 v i i i LIST OF FIGURES Figure Page 1 A comparison of weekly egg production between sighted and b l ind chickens 46 2 A comparison o f i n i t i a l back and rump feather damages between sighted and b l ind chickens 64 3 A comparison o f f i n a l back and rump feather damages between s ighted and b l ind chickens 65 4 A comparison o f wing and t a i l feather damages between s ighted and b l ind chickens 66 5 A comparison o f comb damages between s ighted and b l i nd chickens . . 67 ix ACKNOWLEDGEMENTS I am indebted to Dr. K.M. Cheng fo r the opportuni ty to learn theore t i ca l and p rac t i c a l aspects o f ag r i cu l t u r a l research under his supe r v i s i on . Dr. Cheng's cons i s ten t adv i ce , guidance and encouragement during the course o f th i s study are g r a t e f u l l y acknowledged. Valuable suggestions from Professor B.E. March, Dr. D.B. Bragg, Dr. C R . Krishnamurti and Dr. J . F . Richards are g r a t e f u l l y acknowledged. Plasma cor t i cos terone samples were analysed at the Un ivers i ty of Guelph, through the courtesy o f Dr. R.J. Etches and his a ssoc i a t es . I wish to thank Mel Hudson and Bob Chan for t he i r ass is tance in the care of experimental b i r d s , Cathleen N i cho l s , Dean C r i ck , Yousi f Yousi f and Andy Hickman for t he i r technica l a ss i s t ance , Roland K.C. Low for his suggestions and ass is tance in the preparat ion o f t h i s thes is and Kamily Cheung fo r her patience in the typing o f th i s t h e s i s . Very spec ia l thanks must be given to my wife and ch i ld ren fo r t he i r patience and understanding during the course of th i s study. I am gratefu l to the Bangladesh Agr i cu l tu ra l Research Council for making my stay at The Un ivers i ty o f B r i t i s h Columbia poss ib le under IDA Credi t Fund #828BD. This research study was supported by Agr i cu l tu re Canada Operating Grant #1027 and a lso by Natural Sciences and Engineering Research Council o f Canada Grant #A-8062. Bangladesh Agr i cu l tu ra l Un ivers i ty granted me a study leave so that I can perform th i s research at UBC. Ahmed A l i 1 INTRODUCTION The gene ' r c 1 , an autosomal recess ive mutat ion, causes bl indness in chickens when in the homozygous s t a t e . The birds lack rods and cones in the re t ina and cannot perceive l i g h t (Cheng et al_.» 1980). A f te r ana lys ing the genet ic back- ground of th i s mutant , Cheng et a]_. (1978) have designated th i s gene as ' r c ' to ind ica te the absence o f rods and cones in the r e t i n a . Hutt (1935) a lso reported a case o f heredi tary bl indness which seems to be s im i l a r to ' r c ' mutation in behavior and external eye morphology. Several other forms of reported cases of heredi tary bl indness in chickens are evident in the l i t e r a t u r e (C lay ton, 1975; Smith et aj_., 1977). Very l i t t l e information i s a va i l ab l e on the behavior and reproduct ive performance of b irds having v i s i on anomalies. It i s apparent, how- ever, from the works of Hutt (1935) and Cheng et aj_., (1980) that b l ind chicks learn to eat and dr ink as well as normal ones when they are exposed to r ead i l y ava i l ab le feed and water in an enclosed battery or pen. Under normal rear ing condi t ions , surv iva l rate o f a f fec ted b i rds has not yet been determined but performances in terms of egg product ion , body weight ga in , f e r t i l i t y and ha t chab i l i t y are thought to be in the normal range (Cheng et a ! . , 1980). Many environmental factors in f luence lay ing hens' performance, of which densi ty ( f l o o r area per b i rd) and f lock s i ze (number o f b irds per f lock ) have received considerable a t ten t ion (Adams and Jackson, 1970; Adams et al_.» 1978; H i l l , 1977 and Cunningham and Ostrander, 1982). In modern poultry manage- ment, layers are kept , as a general r u l e , in a place as small as poss ib le wi th - out lowering p roduc t i v i t y . This has occurred to keep a balance with increas ing 2 costs of b u i l d i n g , equipment and labour which, as a consequence, has brought about a s i g n i f i c a n t change i n l a y ing hens' environment. In a r e s t r i c t e d environment such as in an in tens ive production system, animals become dependent on each other and on the surrounding environment (K i lgour , 1972). This a f f ec t s normal behavior of animals . Intensive housing i s a lso a part o f in tens ive animal husbandry and i t demands behavioral adap- ta t ions by the animals concerned ( A r b i , 1978). The question o f adap tab i l i t y and non-adaptabi l i ty emerges under those cond i t i ons . Non-adaptabi l i ty may impose s t ress which may appear to be greater with higher dens i t i es and large f lock s izes than with lower dens i t i es and small f lock s izes ( H i l l , 1980). Such s t ress w i l l r e su l t in poor p roduc t i v i t y per b i r d . Studies concerning b i rd dens i ty and f l ock s i ze on the performances o f layers are progress ive ly increas ing in number. There i s a lso an increas ing i n t e r es t to manipulate other environmental condi t ions to reduce the leve l o f soc i a l i n - te rac t ions among birds in a f l o c k . For example, i n t ens i t y o f l i g h t in poultry houses could be manipulated to reduce soc ia l i n te rac t ions among the f lock mates. Hughes and Black (1974) observed that br ight l i g h t (55 to 80 lux) compared to dim l i g h t (17 to 22 lux) increased a c t i v i t y h ighly s i g n i f i c a n t l y in birds (Shaver 288) reared e i the r in cages or pens. They a lso found a d i r e c t r e - l a t i onsh ip between a c t i v i t y and pecking damages. Therefore , under low i n t ens i t y of l i g h t (dim l i g h t ) , probably, the birds cannot see each other w e l l , thus, reducing agon i s t i c encounters ( soc ia l i n te rac t ions ) among them. Some Sc i en t i s t s are a lso attempting to r e s t r i c t the v i s i on of the birds by using spectac les to reduce soc ia l s t r e s s . In A u s t r a l i a , the use o f ' specs ' (specs are ant i-pecking devices made o f a coloured f l e x i b l e polyethylene 3 mate r i a l . When f i t t e d on the nares o f the hens, they al low them to look to the s ide or down but not d i r e c t l y ahead) in commercial l a y ing f locks has been increas ing (Cumming and Epps, 1976). Several reports are ava i l ab l e in the l i t e r a t u r e desc r ib ing the e f f ec t s o f specs on the performance o f l ay ing hens (Cooper and Barnet, 1966; Cumming and Epps, 1976; Karunjeewa, 1977; A r b i , 1978). These works suggest that f i t t i n g specs to hens contro ls feather pecking by reducing v isua l contact and agon i s t i c behavior, save energy from reduced soc ia l i n te rac t ions and increases p roduc t i v i t y . The use of specs a lso has advantage in reducing soc ia l s t ress by l i m i t i n g v isua l contact and breaking down the soc ia l h ie ra rchy . More r e cen t l y , coloured contact lenses fo r l ay ing hens have been introduced in the United States for reduct ion o f cannibal ism in ch ickens ; hens f i t t e d with red lenses (rosy glasses) appeared to be the l eas t s t ressed (Time magazine, December 29, 1980, page 14). Despite many advantages o f using mechanical device to control v i s i on in l ay ing hens, there are some disadvantages a l s o . The hens f i t t e d with such devices need to adapt to them. In a d d i t i o n , they increase costs in terms of labour and cap i ta l investments. Furthermore, they could be a health hazard- to the birds ( i f not f i t t e d properly) i n v i t i n g bacter ia and paras i tes to cause d i sease . The gene t i c a l l y b l ind birds are obviously f ree from a l l such d i s - advantages. However, the opportunity to conduct inves t iga t ions into the use- fu lness or disadvantages o f gene t i c a l l y b l ind birds in th i s context has not presented i t s e l f unt i l now. This study was therefore undertaken to determine i f the lack of s ight a f f e c t s the performances o f chickens ( u t i l i z i n g the gene t i c a l l y b l ind birds and the i r sighted counterparts) under d i f f e r e n t ' d e n s i t y and f lock s i ze 4 cond i t i ons . 5 REVIEW OF LITERATURE I. P roduct i v i t y 1. Egg production Egg production is by f a r the most important t r a i t in commercial egg- lay ing s t ra ins and accounts for about 90% o f the to ta l farm income from commercial egg production (Oluyemi and Roberts, 1979). In the modern system o f in tens ive husbandry p r a c t i c e s , l ay ing hens' genet ic back-ground and i t s environment have been changed in many ways (C r a i g , 1982). The numerous breeds o f yesterday have been replaced e n t i r e l y by the White Leghorn fo r white egg production and by the Rhode Island Red and New Hampshire breeds fo r brown egg product ion. Within the White Leghorn breed, many s t ra ins fo r commercial egg production have been developed. These various s t ra ins are not expected to be equal ly well adapted to in tens ive housing con- d i t i o n s . Gene t i ca l l y in f luenced behavioral d i f fe rences ex i s t i ng among stocks probably bear on t he i r r e l a t i v e adaptatedness to high dens i ty environment (C ra ig , 1982). The response of d i f f e r e n t l ay ing s t ra ins under in tens ive rear ing con- d i t i ons has been the subject o f many i n ves t i ga t i ons . Adams and Jackson (1970) conducted two experiments over two years invo lv ing 6 commercial l ay ing s t r a i n s . They observed h igh ly s i g n i f i c a n t s t r a i n e f f e c t on hen-housed egg production in one experiment but not in the other . However, when production was expressed as hen-day product ion , the d i f f e rence between s t ra ins became non-s ign i f i cant in e i ther experiment. This r e su l t ind icated that s t r a i n d i f f e rence in egg pro- duct ion was due to d i f fe rences in sexual maturity o f the pu l l e t s as well as 6 d i f fe rences in mor ta l i t y o f l ay ing b i r d s . Another experiment on egg production was conducted by Marks et a]_. (1970). They a lso used 6 commercial egg lay ing stocks and recorded the i r egg production over a f u l l year . The same experiment was repeated in the fo l lowing year . In both o f t he i r t r i a l s , they observed h ighly s i g n i f i c a n t d i f fe rences among stocks in percent hen-day egg product ion. The number of chickens housed in the same cage a lso a f f ec t s egg product ion . Emmans (1971) surveyed 11 d i f f e r en t s t ra ins of layers kept in cages. Birds in 6 s t ra ins showed a reduct ion in egg production when they were housed at 4 per cage rather than 3, but the egg number o f the remaining 7 s t ra ins did not show any s i g n i f i c a n t d e c l i n e . In another study (Anon, 1974), 4 birds at 523cm 2 per b i rd were compared with 5 birds at 418cm 2 . Nine d i f f e r e n t s t ra ins were used, 8 o f those showed a reduct ion in egg production under the most crowded con- d i t i ons while one d id not change. The reduct ion in egg production var ied from 0.7 to 10.4%. That egg production i s s i g n i f i c a n t l y a f fec ted by s t ra ins was a lso reported by Feldkamp and Adams (1973); Aitken et al_. (1973) and H i l l (1977). In a recent study using two s t ra ins of White Leghorn p u l l e t s , Cunningham and Ostrander (1982) reported s i g n i f i c a n t s t r a i n d i f fe rences fo r hen-day and hen- housed egg product ion . In t he i r s tudy, 1 s t r a i n averaged 4% more eggs per hen on a hen-day and hen-housed basis than the other s t r a i n . Studies on genotypes invo lv ing s ing le locus on the v a r i a b i l i t y o f egg production are not common. In one study, Bullerman (1981) observed a reduct ion o f 17% in egg production o f dwarf genotype (dw/dw) compared to non dwarfs (Dw-) under i den t i ca l cond i t i ons . Merat and Bordas (1979), on the other hand, d id not f i nd any va r i a t ions in pea comb genotype (Pp) compared to s ing le comb (pp) . The e f f e c t o f f l o o r space, sometimes.referred to as b i rd densi ty on egg 7 production o f l ay ing hens has been widely i n ves t i ga ted . Hoffman and Tomhave (1945) observed the e f f e c t of densi ty on the egg production o f New Hampshire pu l l e t s at dens i t i es of 2564, 3437 and 4320cm 2 per b i r d . The high densi ty group (2564cm2 per b i rd) l a i d about 18 eggs less ( in a year) than the other two groups. S iegel (1959) compared two extreme dens i t i e s (3716 vs 1239cm 2 per b i rd ) in f l o o r pens. The egg production rates were 48% fo r low-density and only 38% for high-density groups. On the other hand, Nordskog (1959)> and Fox and Clayton (1960) reported only small dec l ines in production from decreasing f l o o r space. From the ear l y s i x t i e s onward, most densi ty re la ted studies were made in cages and have demonstrated a reduct ion o f egg production as the cage dens i ty increased (Lowe and Haywang, 1964; Moore et a l . , 1965; Cook and Dembnicki, 1966; Be l l and L i t t l e , 1966; Owing et a l . , 1 9 6 7 ; Wilson et al_.1967; Champion and Z i n d e l , 1968; Adams and Jackson, 1970; Grover et a l . , 1972; Foss and Carew, 1974; H i l l , 1977 and Cunningham and Ostrander, 1982). Group s i ze or colony s i ze a lso seem to s i g n i f i c a n t l y contr ibute to egg production o f l a y ing s tocks . In most o f the e a r l i e r s t u d i e s , i t has been d i f f i c u l t to evaluate i t s e f f e c t because group-size has been confounded with densi ty (Hughes, 1975). Aitken et a]_. (1973) observed that compared to birds housed two per cage those housed one per cage l a i d 9% more eggs. Feldkamp ejt al_. (1973) using 3 or 5 birds in small cages (41cm x 41cm) and 9 or 18 birds in la rge cages (72cm x 82cm) found s i g n i f i c a n t e f f e c t o f colony s i z e . Highest rate o f lay (78%) was from the small cage-low densi ty and lowest rate (70%) from the large cage-high dens i t y . Adams and Jackon (1970) a lso observed s im i l a r responses. The e f f e c t of increased colony s i ze on the hen-day rate of lay was studied by Wilson e_t al_. (1977). Increased colony s i ze depressed egg product ion. 8 Mean rate o f lay was s i g n i f i c a n t l y higher fo r i n d i v i d u a l l y caged birds (75.59%) than fo r birds housed e i the r 3 (67.39%) or 5 (67.39%) or 5 (63.54%) per cage. A review of l i t e r a t u r e ind ica ted that a l l group s izes in constant area per b i rd d id not respond in a l i n e a r order . As fo r example, Champion and Zindel (1968) found that 3 birds per cage had better egg production compared to 2, 4 or 6 birds per cage. In another study, Tower et a]_. (1967) had shown that 10 birds per cage was more productive than 2, 5 or 20 birds per cage. The egg production o f l ay ing hens i s a lso inf luenced by the behavior and soc i a l rank (according to peck order) o f the i nd i v idua l s within a f lock (Tindel and C ra i g , 1959). In studies invo lv ing s t ra ins d i f f e r i n g in soc i a l dominance a b i l i t y , Biswas and Craig (1970), Cra ig (1970) and Lowry and Abplanlp (1972) observed tha t , compared to t he i r r e l a t i v e performance when kept separate- ly, : s o c i a l l y dominant s t r a ins had higher l eve l s o f egg production r e l a t i v e to subordinate stocks when kept together . Ind i rect evidence o f the with in f lock aggressiveness on egg production was provided by Craig (1970) and by Biswas and Cra ig (1970). These workers reported that a s t r a i n o f h ighly aggressive White Leghorn had higher egg production than a s t r a i n o f more peaceful White Leghorn when kept in ind iv idua l cages. On the other hand, t he i r ranks for egg production were reversed when those s t ra ins were kept separate ly in f l o o r pens. McBride (1971) reported that the impact of v isual contact among hens i s great in crowding s i t u a t i o n s . F i t t i n g ' specs ' to the hens may reduce, to some extend, the chance o f v isua l contact and thus reduce the soc ia l s t ress (A rb i , 1978) and improve p roduc t i v i t y . Cumming and Epps (1976) in studies with spec- hens found increased egg production and feed e f f i c i e n c y . The spec-hens produced 11% more eggs than the control hens over 11-month l ay ing pe r iod . Other reported 9 studies using spec on hens showed considerable improvement in egg production of spec-hens (Karunajeewa, 1977 and Arbi, 1978). Among many other factors which can affect egg production of laying hens, the most important are dietary composition (Lebbie et ajk 1981; Vargas and Edward, 1982), light (Odom and Harrison, 1979; Nys and Morgin, 1981) and temperature (Arad et a]_. 1981). 2. Egg weight Egg size is very important in the production and marketing of eggs (Christmas et al_. 1979). Romanoff and Romanoff (1949) stated that egg size could be expressed in terms of egg weight, because weight provides a basis of comparison which is more convenient than dimensions or volume. The egg weight of laying hens is influenced by numerous hereditory, environmental and physiological factors. Earlier reports (Romanoff and Romanoff, 1949) on the egg weight of different avian species Indicated large variations between species. Ostrich for example lays eggs which are on the average 1400g, Swan 285g, Canada Goose 135g, Pea Fowl 90g, Turkey 85g, Duck 80g, Leghorn Fowl 58g, Pigeon 17g and Humming Bird 0.5g. The effect of heredity on egg weight of chickens has been investigated. Warren (1953) reported that egg weight is a highly heritable character. Numerous fieritability estimates were reported for this trait . King and Handerson (1954) found that the heritability of egg weight on the basis of full-sib correlation and regression of daughter on dam were 0.48 and 0.60 respectively. Hogsett and Nordskog (1958) reported heritability estimates to be 0.36, 0.45 and 0.41 in light breeds and 1.15, 0.55 and 0.85 in heavy breeds on the basis of paternal 10 half-sib, maternal half-sib and full-sib correlations respectively. Kinney (1969) summarised the reported heritabilities of light and heavy breeds for early egg weight and mature egg weight. For early egg weight light breeds averaged 0.45, 0.53, 0.45 and 0.52; heavy breeds 0.57, 0.65, 0.67 and 0.63; for mature weight, light breeds 0.36, 0.45, 0.50 and 0.44; heavy breeds 0.58, 0.54, 0.58 and 0.46 respectively according to sire, dam, full-sib and regression methods. Recent reviews on the heritability estimates of egg weight are not evident in the literature. The effect of strains on the egg weight of laying hens has been the subject of several investigations. Cunningham and Ostrander (1982) reported significant strain effects for average egg weight in two White Leghorn egg laying strains. Egg weight for one strain averaged 4g more than the other one (62g vs 58g). They also found that the strain which had the heaviest egg weight had also produced the most eggs. Akber et a]_. (1983) had also demonstrated differences in egg size of 7 genetic stocks of White Leghorn type chickens. On the other hand, Hill (1977) did not find such variations in two other commercial strains of White Leghorns. Several authors reported that they found no significant influence of bird density on egg weight. Cuinningham and Ostrander (1982) observed that birds housed 4 per cage compared to those housed 5 birds per cage had the same egg weight. Hill (1977) conducted two experiments with Babcock 300 and Shaver, 288 stocks. This author demonstrated that birds housed 310, 387 or 464cm2 per bird, or 3, 6, or 12 birds per group did not have significantly different egg weights in either of the experiments. Similar results were also reported by other workers (eg. Aitken et al_., 1973; Adams and Jackson, 1970). 11 Egg weight i s reported to be s i g n i f i c a n t l y a f fec ted by cage s i z e , but the resu l t s are i n conc lus i ve . Cunningham (1982) reported that White Leghorn layers housed in shallow cages l a i d s i g n i f i c a n t l y heavier eggs than b i rds i n the deep cages (60 . lg vs 58.9g) . S i g n i f i c a n t l y heavier average annual egg weight fo r birds in shallow cages compared to birds in deep cages were a lso reported by H i l l and Hunt (1978). Contrary to the above f ind ings ,Lee and Bolton (1976) reported that White Leghorn layers housed in deep cages l a i d s i g n i f i c a n t - l y heavier eggs than those housed in shallow cages. Adams and Jackson (1970), and Cunningham and Ostrander (1982) d id not f ind such d i f fe rence between shallow and deep cages with varying populat ion s i z e s . The r e l a t i onsh ip o f l ay ing hen's body weight and egg weight was i n - vest igated by several authors . Harms et al_. (1982) d iv ided Dekalb XL pu l l e t s at 28 weeks o f age into l i g h t ( L ) , medium (M) and heavy (H) body weight groups. The birds were housed in 20.3 x 45.7cm wire cages fo r a period of 16 weeks. They found egg weight to be re la ted to hen's body weight. S i g n i f i c a n t d i f f e r - ences were found between a l l three body weight groups. There were approximately 1 and 2g d i f fe rences in egg weight between the L to M and M to H groups. In another study Be l l et al_. (1981) used 3 s t r a ins o f SCWL pu l l e t s segregated in to two weight c lasses (heavy and l i g h t ) at 1 day o f age versus 18 weeks o f age. Performance records were kept to 68 weeks o f age. L ight pu l l e t s segregated at 1 day and 18 weeks produced s i g n i f i c a n t l y smal ler eggs. This amounted to 2.4g f o r the 1 day groups and 2.8g for the 18 week groups. McClung and Jones (1973) a l so reported s im i l a r r e s u l t s . Age o f the hen i s a lso a cont r ibu t ing fac tor to egg weight. G i lbe r t et al_. (1978) stated that egg weight i s a funct ion o f age of the hens rather 12 than the per iod o f l a y . Reports by previous workers (eg. Cowen et a l_ . , 1964; Saeki et a]_., 1967; Weatherup and Foster , 1980) ind icated that egg weight i n - creases monotonical ly with age and approaches an asymptote. Many other fac tors a lso a f f e c t egg weight. Some important ones are nu t r i t i on (Lebbie et a l_ . , 1981; McDeniel et a l_ . , 1981), ambient temperature (Arad et a]_., 1981) and l i g h t schedule (Nys and Morgin, 1981). 3. Feed consumption Feed cost accounts for at l e as t two-third of the to ta l cost of pro - ducing eggs (Wing and Nordskog, 1982) or 70% of to ta l cost for producing b ro i l e r s (Pym and N i c h o l l s , 1979). Any improvement in the e f f i c i e n c y o f feed u t i l i z a t i o n would be of economic bene f i t . The amount of feed that a b i rd consumes i s re la ted to i t s energy requirements which in turn i s a f fec ted by genetics and environment. One way of comparing feed consumption is by means of analys ing the ' r es idua l feed component' (Bordas and Merat, 1981). The res idual component was def ined as the amount of feed consumption remaining a f te r s t a t i s t i c a l adjustments for body weight and egg mass. Expected feed consumption was estimated from a mul t ip le regress ion equation using independent var iab les such as mean body weight, body weight change during the tes t pe r iod , and egg mass produced. The res idual was then ca l cu la ted as observed feed consumption minus expected feed consumption. Using th i s measurement, Merat and Bordas (1979) demonstrated that pea comb (Pp) hens consumed about 2% less feed than s ing le comb (pp) hens. They suggested that with the smal ler s i ze o f comb and wattles fo r Pp hens, heat losses and hence energy requirements are l e s s . In another study (Merat et aJL, 1979) i t was a lso found that white hens (I/I, I/i) consumed s i g n i f i c a n t l y less (140.8g) feed than coloured hens in a 28-day pe r iod . They could not , however, ass ign 13 any p laus ib le exp lanat ion . S i g n i f i c a n t va r i a t ions in res idual feed consumption with in genet ic l i nes were found by Bordas and Merat (1974), Watenabee et al_. (1975) and Hagger (1977). Conversely Arboleda (1971) and Lee and Nordskog (1975) f a i l e d to f ind such va r i a t i on in the White Leghorn l i n e s that they were s tudy ing . On the other hand, between l i n e d i f fe rences in res idual feed consumption ex i s t in ch ickens . Bordas and Merat (1981), comparing 2 brown egg s t r a i n s , observed h igh ly s i g n i f i c a n t d i f f e rences between s i r e f ami l i es in both s t r a i n s . Wing and Nordskog (1982) estimated the h e r i t a b i l i t y of res idua l feed consumption in two populations o f White Leghorns cons is ted o f 4909 birds to be 0.29 ± 0.07 and 0.15 ± 0.06 r e spec t i v e l y . These moderately high h e r i t a b i l i t y estimates ind ica tes that ind iv idua l feed consumption records should be considered in r e - l a t i o n to se l e c t i on fo r e f f i c i e n c y o f egg product ion . Quite a number o f studies have so far measured feed consumption in chickens in r e l a t i on to such environmental factors as group s i ze and densi ty (eg. Feldkamp and Adams, 1973; Jensen et a l_ . , 1976). In these studies group s ize ranged from 1 to 5 birds and dens i t i es were between 350 and 1400cm2 per b i r d . Jensen et al_. (1976) reported that hens housed alone ate more than groups o f three kept in the same a rea . Ouart and Adams (1982) conducted two experiments to compare the e f f ec t s o f cage shape, feeder space, cage des ign , b i rd dens i t y , leve l o f f eed ing , and feeding period on feeding behavior and b i rd movements. They found that feed consumption was s i g n i f i c a n t l y a f fec ted by b i rd dens i t y . Hens housed 2 per cage consumed 10.5g more feed per b i rd d a i l y than those housed 3 per cage. Furthermore, they a lso concluded that increased feeder space i s important in reducing feeder competit ion during feeding t ime. 14 Socia l rank and feeding behavior may have considerable in f luence on the amount of feed consumed and feed s p i l t . The soc ia l rank and p r i o r i t y in feeding was invest igated by Candland et al_. (1968). Within a r e s t r i c t e d en- vironment there ex i s t s a strong co r r e l a t i on between the two v a r i ab l e s . In t he i r study they used paired comparison technique, a l im i t ed feeding per iod and food deprived ch ickens , and found that i nd i v idua l s having high soc i a l rank spent a longer time in feeding than low ranked b i r d s . Longer feeding requires more energy expenditure. On the other hand Syme and Syme (1974) observed whole group competit ion for feed in a pen environment having 7 to 8 birds per pen and obtained a poor co r r e l a t i on between the peck order and time spent in command of the feed box. When animals feed in groups, another kind of soc ia l in f luence i s a lso opera t i ve : soc i a l f a c i l i t a t i o n (C ra ig , 1981). Soc ia l f a c i l i t a t i o n i s the repe- t i t i o n o f an act performed by one ind iv idua l by other i nd i v idua l s ( A rb i , 1978). Thus, the two kinds of soc ia l in f luences act in opposite d i r e c t i o n s , soc ia l f a c i l i t a t i o n in f luence feeding a c t i v i t y , whereas agon is t i c behavior i s l i k e l y to reduce feeding by subordinates . Soc ia l i n te rac t ions can be d r a s t i c a l l y a f fec ted by putt ing opaque spectac les on l ay ing hens and blocking t h e i r f ronta l v i s i o n . Cumming and Epps (1976) reported the e f f e c t o f spectac les on the feed consumption o f 4000 Leghorn-Australorp cross l ay ing hens. They found that hens wearing ' specs ' consumed 6% less tota l feed than control hens and there was a lso an improvement in feed e f f i c i e n c y as measured by g o f egg per kg o f feed consumed. Arbi (1978) studied the feeding behavior o f hens wearing specs and reported that control hens spent much time in p lay ing with the feed, f l i c k i n g i t around, f i l i n g i t up or 15 pecking at the feed trough. Spec hens tended to eat rather than play with the feed . They ate q u i c k l y , reduced time spent in feeding a c t i v i t y , and wasted less feed than control hens. He concluded that because o f the r e - duct ion in feeding time spent by spec hens, energy expenditure due to feeding a c t i v i t i e s was a lso reduced. Another advantage o f specs i s to reduce feather pecking and feather l o s s . Emmans and Charles (1976) ind ica ted that maintenance ME (Metabol izable Energy) requirement by hens with extensive feather loss i s much h igher . Hens with a large amount of feather loss may lose up to 40% more heat from the i r exposed surface than f u l l y feathered hens. Karunjeewa (1977) reported that the use o f specs s i g n i f i c a n t l y reduced feather loss i n pu l l e t s and resu l ted in a 6.6% reduct ion in to ta l ME in take . A study of feed consumption by pu l l e t s under cage or f l o o r s i tua t i ons was conducted by Stappers (1969). Pu l le ts in cages consumed 5.6% less energy than pu l l e t s in f l o o r pens. The feed consumption of l ay ing hens i s a l so a f fec ted by a host o f other fac tors such as i n t ens i t y o f egg product ion , body weight, and l i g h t schedule (Bordas and Merat, 1981; McDonald, 1978 and Nys and Morgin, 1981) 4. Body weight Commercial poul t ry breeders s t r i v e to develop small bodied va r i e t i e s o f chickens (White Leghorn s t r a ins ) that lay at a high rate (Nordskog and B r iggs , 1968). The purpose o f doing th i s i s to reduce feed requirement fo r maintenance. Nordskog (1960) demonstrated that an increase o f body weight of layers by 454g ( l i b ) above the mean decreased income, but s i m i l a r increase in body weight in birds below the mean was bene f i c i a l economical ly . These resu l t s 16 lead to the conc lus ion that a s a t i s f a c t o r y body weight in l ay ing hens i s important for economic ga in . Nordskog and Briggs a lso emphasized the im- portance o f an optimum body weight in layer s t r a i n s . They showed that lowering body weight by lOOg per b i rd from over a l l mean of 1500g decreased hen-housed egg production by 18 eggs in a production period o f 332 days. It has been reported that body weight or gain in body weight are normally d i s t r i bu t ed and are a f fec ted by many genes each with a small e f f e c t and a lso by many environmental factors (McCarthy, 1977). Adult body weight of chicken i s a h ighly her i t ab le t r a i t (Clayton . and Robertson, 1966). Kinney (1969) summarised most o f the publ ished her i- t a b i l i t i e s of mature body weight obtained by paternal ha l f - s ib co r r e l a t i on method. The values obtained averaged 0.52 fo r l i g h t breeds and 0.49 for heavy breeds. These h e r i t a b i l i t y estimates are i nd i c a t i v e o f the h igh ly he r i t ab l e nature of th i s t r a i t . For th is reason body weight responded well to se l ec t ion and has been one o f the important factors in se l e c t i ve breeding (McCarthy, 1977). Body weights of chickens vary according to breed. Standard weight of Rhode Island Red adults and that of White Leghorn adults are reported to be 3856g vs 2722g respec t i ve l y for males and 2948g vs 2041g respec t i ve l y for females (Nesheim et a l_ . , 1979). On the other hand, reports on d i f fe rences in body weight gain between s t ra ins of White Leghorns are c o n f l i c t i n g . S i g n i f i c a n t va r i a t ions in weight gain o f commercial l ayer s t ra ins were reported by Aitken et a}_. (1973), Lee and Bolton (1976) and a lso by H i l l (1977). Conversely, Cunningham and Ostrander (1982) found no such va r i a t i on in body weight gain o f 2 s t r a ins of White Leghorn l a y e r s . Genetic studies regarding the e f f e c t o f a s ing le gene on body weight of 17 chickens were conducted by several authors using d i f f e r e n t gene l o c i . Bullerman (1981) compared the body weight o f dwarf hens (caused by the e f f e c t o f a sex- l inked recess ive gene, dw, Hut t , 1953) with the i r normal non-dwarf (Dw+) counter- parts in two temperatures (normal 18°C-20°C and high 3 2 ° C ) . From 17 week of age, h a l f o f 74 dwarf and 80 normal s i zed hens were kept in ind i v idua l cages at 18-20 °C and the others a lso in cages but at 32 °C . For dwarf hens at the two temperatures r e s p e c t i v e l y , body weight at 91 week of age averaged 1356 and 1131g vs 1958 and 1523g fo r normals. The reduct ion in body weight o f the dwarf hens was 30% of that of the normal hens in the moderate temperature and the correspon- ding value in the high temperature cond i t ion was 24%. In another study of layers Koroleva et al_. (1980) demonstrated that dwarf birds from 20 week of age to the age o f f i r s t egg (176 days) gained on an average o f 13.33g per b i rd per day com- pared to 16.93g for normal hens. Touchburn et al_. (1980) a lso reported 27% r e - duct ion in body weight gain o f dwarf chicks at 5 week o f age compared with t he i r normal counterpar ts . Other gene l o c i do not seem to have as much in f luence in causing va r i a t i on in body weight gain o f ch ickens . For example, the pea comb (Pp) gene was studied by several authors (Kan et a l_ . , 1959; Smith, 1961; Siegel and Dudley, 1963; and Wil l iums et aj_., 1977) but no r e l a t i onsh ip was found be- tween th i s locus and body weight in ch ickens. Studies concerning b i rd dens i ty on body weight o f egg l ay ing s t ra ins are va r i ab le and the resu l t s are i nconc lus i ve . In most o f the studies group s i ze and area per b i rd were confounded. In those studies some have observed reduced body weight gain as b i rd dens i ty increased (Grover et a l_ . , 1972; Wilson et a l . , 1967; Foss and Carew, 1974; Dorminey and A r s c o t t , 1971; Jensen et a l_ . , 1976, H i l l , 1977 and Cunningham and Ostrander, 1982), others observed increased body 18 weight gain in mul t ip le caged birds compared to i n d i v i d u a l l y caged birds (Lowe and Haywang, 1964; Tower et a K » 1967; Aitken et a l_ . , 1973) and s t i l l others found no e f f e c t of b i rd densi ty on body weight gain (Cook and Domnicki, 1966; Champion and Zindel , 1968). Bes ides , in one study in which group s i ze and area per b i rd were var ied sys temat i ca l l y and independently (Wel ls , 1973), a reduct ion in space al lowance, at a given group s i z e , resu l ted in a lower weight ga in . The group s izes used in th i s pa r t i cu l a r experiment were 3, 4, 5 or 6 birds per cage. On the other hand, varying group s i z e , at a given space al lowance, had no e f f e c t on weight ga in . The space provided was 387, 465 and 581cm 2 per b i r d . 5. F e r t i l i t y F e r t i l i t y in the general meaning of the term is the a b i l i t y o f ind iv idua ls to become parents . Many f a c t o r s , both genetic and environmental in o r i g i n are reported to a f f e c t f e r t i l i t y in domestic fowls . The evidence that f e r t i l i t y in chickens i s a heredi tary t r a i t was not r ea l i z ed before the work o f Ju l l (1935), who reported a s i g n i f i c a n t co r r e l a t i on o f 0.19 ± 0.05 between f e r t i l i t y o f dams with the i r daughters. Blow et al . , (1951) reported that f e r t i l i t y in Standard Bronze turkey was inf luenced by hered i t y . These authors estimated h e r i t a b i l i t y of f e r t i l i t y to be as high as 0 .81. Another l a t e r report (Abplanalp and Kos in , 1953) a lso confirmed t he i r f i n d i n g s . In New Hampshire chickens Cri t tenden et_ a]_. (1957) reported h e r i - t a b i l i t y of f e r t i l i t y to be very low (0 .02) . Using the same breed (New Hampshire) as Cr i t tenden et a K used , G i lbreath et a]_. (1962) obtained h e r i - t a b i l i t y o f f e r t i l i t y to be 0.02, 0.21 and 0.14 according to s i r e , dam and f u l l - s i b co r re l a t i ons r e spec t i v e l y . Buckland (1971) estimated the genet ic variance o f th i s t r a i t and obtained h e r i t a b i l i t y of f e r t i l i t y to be 0 .21, 0.31 19 and 0.22 fo r three measures of f e r t i l i t y such as durat ion o f f e r t i l i t y , percent f e r t i l i t y and percent hens f e r t i l e . In one more study (Sa lonia and Shushu, 1972) reported h e r i t a b i l i t y values o f 0.25 and 0.44 fo r f e r t i l i t y in two l i nes of ch ickens . The above reports ind icated that in chickens h e r i t a b i l i t y estimates of f e r t i l i t y var ied from low (0.02) to high (0.81) with intermediate values (0.20- 0.40) being more f requent . These resu l t s suggest that f e r t i l i t y in avian species i s pa r t l y under heredi tary control and se l ec t ion for i t s improvement could be e f f e c t i v e . Breed d i f fe rences in male f e r t i l i t y have been reported in the l i t e r a t u r e (Parker, .1961; Sol 1 er et a l_ . , 1965). These authors obtained s i g n i f i c a n t l y lower f e r t i l i t y in Cornish males than in Delware, New Hampshire and White Rock males. They a t t r ibu ted th i s to the f a i l u r e o f Cornish males to mate n a t u r a l l y , s ince there was no s i g n i f i c a n t d i f f e rences i n f e r t i l i t y between breeds when a r t i f i c i a l insemination was used. F e r t i l i t y o f White Wyandotte, White Leghorn and Rhode Island Reds was compared by Hutt (1940). He found lower f e r t i l i t y in White Wyandotte than in the other two breeds. Furthermore, d i f f e rences between s t ra ins (Bhagwat and C ra i g , 1975), between ind i v idua l s ( So l l e r et a l_ . , 1965) and whether or not the males and the females were re la ted (Dunn, 1927) have been reported to have s i g n i f i c a n t e f f e c t s on f e r t i l i t y . The presence o f a c e r t a i n gene may a lso a f f e c t f e r t i l i t y . Buckland and Haws (1968) reported lowered f e r t i l i t y in pea comb (Pp) and rose comb (RR) chickens compared to birds with s ing le combs. Adams et al_ (1978) found that f e r t i l i t y was s i g n i f i c a n t l y a f fec ted by f lock s i z e . They tested two experimental s t r a ins o f White Leghorn chickens housed in cages at a constant densi ty o f 534cm 2 per b i rd e i the r in small f locks 20 (l«t:10??) or in large f lock (2J$:20??). From 20-44 week o f age the mean f e r t i l i t y o f the birds was 39.4% fo r small f lock vs 55.5% fo r la rge f l o c k . In th i s study they fur ther reported that f e r t i l i t y o f ind iv idua l f locks var ied from 0 to 100%. In another study invo l v ing birds in l a rger f locks (8$i :80$| ) , Hughes and Holleman (1976) reported f e r t i l i t y o f 94%. It i s ev ident , the re fo re , that the l a rge r the s i z e o f the f lock (with a constant male-female r a t i o ) , the higher the f e r t i l i t y r a t e . This may be due to male-male competit ion for mating with in the f l o c k . There 1s some evidence that f e r t i l i t y in chickens i s a f fec ted by soc ia l rank or peck order o f the b i r d s . Guhl and Warren (1946) suggested that the soc ia l rank or peck order o f the hens to which males are introduced a f f ec t s t he i r mating behavior. Males tend to mate more f requent ly with the hens which are intermediate in soc ia l rank but not with the highest or lowest ranking hens. The same authors a l so stated that when three or more males are put together in a pen, both the frequency of mating and f e r t i l i t y are highest fo r the top- ranking males. The lowest ranking males mate l ess f requent ly with few females, because o f in ter fe rence from the highest ranking males. It was reported in several studies that the age o f a pu l l e t has an e f f e c t on the f e r t i l i t y of eggs produced. Sunde and B i rd (1959) reported that eggs l a i d by pu l l e t s which had j u s t reached sexual matur i ty d id not hatch as well as l a t e r eggs presumably due to i n f e r t i l i t y . Tomhave (1958) a lso found greater v a r i a t i on in percentage o f f e r t i l e eggs from pu l l e t s o f ea r l y matur i ty and l a te maturity groups. Garwood and Lowe (1982) reported that in the ear l y matur i ty group (1st egg on 159 days) f i r s t f e r t i l e egg was found two days a f t e r the f i r s t egg but in. the la te maturity group (1st egg on 174 days) one day a f t e r . 21 This d i f f e rence was not s i g n i f i c a n t . Other fac tors a f f e c t i ng f e r t i l i t y are season, s tate o f n u t r i t i o n and health (Lake, 1974; Lorenz, 1959). II. Parameters measuring s t ress 1. Feather pecking Feather pecking in Gal l inaceous b i rds i s a behavioral phenomena ( O t t e l , 1873), more of ten th i s term i s confused with aggressive pecking and sometimes with canniba l i sm. Genera l l y , feather pecking and cannibal ism are quite d i f - fe rent from aggressive behavior (Wennrich, 1974). Feather pecking i s the loss o f feathers due to pecking by other birds sometimes associated with hemorrhaging o f sk in (Hughes and Duncan, 1972). Aggressive pecking i s the vigorous and quick pecking a c t i v i t y o f a b i rd at the head of another b i rd (Wennrich, 1974). On the other hand, feather and c a n n i b a l i s t i c pecks are performed much less v igorous ly and qu ick ly and genera l ly not d i rec ted towards the need o f the pen- mates. Feather pecking i n most o f the cases does not r e s u l t in bloody wounds, but the bloody wounds caused by cannibal ism are usua l l y due to feather pecking. A l l en and Perry (1975) a lso reported that cannibal ism in birds i s in f luenced by feather pecking and they are independent phenomena with add i t i ve e f f e c t s . Various causat ive fac tors that can in f luence feather pecking in birds have been c l a s s i f i e d by Hughes and Duncan (1972). The main fac tors involved are d ie ta ry composi t ion, environment, hormones and psychic f a c t o r s . Whether feather pecking i s under genetic control i s s t i l l c o n t r o v e r s i a l . The in f luence of inher i tance or heredity on the occurance o f feather pecking has been inves t iga ted by several authors . R i tcher (1954) found 22 cons iderable s t r a i n d i f fe rences in the incidence o f feather peck ing. He con- cluded tha t , f ea the r eat ing i s a heredi tary c h a r a c t e r i s t i c . Hughes and Duncan (1972) and Charles (1976) a lso observed d i f fe rences between s t ra ins for feather loss due to peck ing, wear, or both, in l ay ing hens. They d id not analyse the causal fac tors and genet ic basis o f th i s ' t r a i t ' . However, they suggested tha t , i r r e spec t i v e o f the cause, ce r ta in genet ic factors may be involved in modifying the ind iv idua l s u s c e p t i b i l i t y to these causes. S im i l a r l y Cuthbertson (1980) stated that feather pecking behavior when i d e n t i f i e d in a su i t ab le way, has an inher i ted component and that se l e c t i on to reduce i t s occurance should be f e a s i b l e . A l l en and Perry (1975) reported that in chicken feather pecking occurs in birds by the end o f the rear ing pe r i od , but cont inuat ion o f i t s occurance dur ing lay ing per iod i s in f luenced by group s i ze and dens i ty per b i r d . Adams et aj_. (1978) demonstrated that birds housed 22 and 20$$) per group had s i g n i f i c a n t l y poorer feather ing than those housed 11 (1 & and 10$%) per group. Hughes and Duncan (1972) a lso found a s i g n i f i c a n t group s i z e e f f e c t on feather damage with more severe damages i n groups o f 8 growing pu l l e t s housed in cages than in groups o f 4. According to Kivimae (1976) high dens i ty o f layers in battery cages had a negative e f f e c t on the plumage. S i m i l a r l y , Hoffmeyer (1969) observed that high densi ty and f lock s i ze in combination increased feather pecking in pheasants. Type o f housing or design o f cages may a lso in f luence feather pecking in b i r d s . Simenson et al_. (1980) reported that birds housed in wire f l o o r had s i g n i f i c a n t l y higher feather damage than those housed in l i t t e r f l o o r . S imi la r r e su l t s were a lso observed by Duncan and Hughes (1973) and Touson (1977). 23 Both found that housing system inf luenced the infegument of the b i r d s . The use of specs in l ay ing hens was e f f e c t i v e in c o n t r o l l i n g feather pecking and cannibal ism ( A r b i , 1978). Pecking damage scores were 3.3 for control hens vs 1.2 for spec-hens. This d i f f e rence was h igh ly s i g n i f i c a n t . Cumming and Epps (1976) a lso reported that spec-hens were better feathered a f t e r 11 months o f lay than control hens, but no quant i ta t i ve data were presented. 2. Adrenal weight The adrenal glands play a centra l ro le in the fowl 's response to s t ress ( S i ege l , 1971). In mature b i r d s , increases and decreases in adrenal weight f requent ly occur in response to seasonal and environmental changes, and these va r i a t ions usua l ly r e f l e c t for the most part growth and atrophy o f the adreno- c o r t i c a l t i s sue (Holmes and Cronshaw, 1980). On the other hand, a number of studies have reported the s i gn i f i c ance o f genet ic in f luence and soc i a l dens i ty on the response of adrenal gland in domestic fowl . S iegel and Siegel (1969) compared adrenal weights i n s i x d i f f e r e n t genetic stocks o f chickens in two t r i a l s . Adrenal glands were excised at 57 days of age of the ch i ck s . In both o f t he i r t r i a l s they observed s i g n i f i c a n t d i f f e rences among stocks fo r adrenal weight expressed as mg per lOOg body weight. In one t r i a l adrenal weight fo r males and females ranged from 7.63- 10.30mg and 6.87-8.81mg r e spec t i v e l y . In the other t r i a l , the same var ied from 6.74-8.95 in males and 6.82-8.20 in females. In a more recent experiment, A l i and March (unpublished data) studied two commercial egg l ay ing s t ra ins and one b r o i l e r s t r a i n fo r adrenal weights o f chicks at ages from one day to t h i r t y f i ve days. The glands were monitored at day 1, 14, 21 and 35. A cons is tent and h ighly s i g n i f i c a n t s t r a i n d i f fe rence was evident in a l l days o f measurements 24 (expressed as mg per g o f body weight) with an exception fo r day 1 where i t was found not to be s i g n i f i c a n t l y d i f f e r e n t . Lowest adrenal weight was from b r o i l e r s t r a i n . Bareham (1972) on the other hand, found no s i g n i f i c a n t d i f - ference in adrenal response o f 2 layer s t ra ins reared e i the r in battery cages or in deep l i t t e r pens. Adrenal gland s i z e may a lso be inf luenced by soc ia l dens i t y . Siegel (1960) demonstrated the e f f e c t s of crowding on the adrenal weight o f White Leghorn cockere ls aging from 7-17 weeks. The dens i t i e s provided were 929.0, 743.0 557.0 and 371.6cm 2 per b i r d . No cons is tent e f f ec t s o f housing dens i ty were observed up to 11 weeks. Whereas heavier adrenals were found beyond th i s age. Birds housed 371.6cm 2 per b i rd compared with 929cm 2 per b i rd had s i g n i f i c a n t l y heavier adrena ls . From these r e s u l t s , the author stated that in higher populat ion dens i t i e s such as 371.6cm 2 per b i r d , symptoms of adaptat ion , associated with phys io log ica l s t ress were produced. Another study (Siegel and S i e g e l , 1969) invo l v ing 6 genetic s tocks , housed at two b i rd dens i t i es of 464.5 and 929cm 2 per b i rd resu l ted in no s i g n i f i c a n t e f f e c t s o f densi ty on adrenal weights. Three other studies a lso reported no e f f e c t o f dens i ty on th i s gland (Bareham, 1972; Bolton et a l_ . , 1972; and Pesti and Howarth, 1983). These non-s ign i f i can t r e su l t s were obtained presumably because, the dens i t i es used were not c r i t i c a l l y below the phys io log ica l l i m i t imposed by the birds general we l l-be ing . Soc ia l i n t e r a c t i on between ind i v idua l s within a f lock not necessar i l y assoc ia ted with crowding may a lso in f luence adrenal gland weight. F l i c k inge r (1961) reported that cockerels in uncrowded colonies es tab l i sh dominance h ie rarch ies as sexual maturity approaches. The adrenal gland weight then 25 becomes cor re la ted r e c i p r o c a l l y with the soc ia l rank of each ind iv idua l . It i s well known that adrenal gland weight response to s t ress (Freeman, 1971). Arbi (1978) demonstrated that wearing specs (see pages 2 & 3 for desc r ip t ion ) in l ay ing hens reduced s t ress assoc iated with agon is t i c acts and feather ea t i ng . This was a lso r e f l e c t ed by a reduct ion in adrenal gland weights. When specs had been on for th i r teen and a ha l f months, the adrenal gland weight of the spec-hens were s i g n i f i c a n t l y l i g h t e r in comparison with contro l hens (hens without specs ) . This r e su l t ind ica tes that c o n t r o l l i n g v i s i o n in layers may be assoc iated with a reduct ion in s t ress due to l ess agon i s t i c and feather pecking a c t i v i t i e s . 3. Cort icosterone The major sec re t ion o f the adrenal gland o f most avian species i s cor t i cos terone (Assenmacher, 1973). It had been used as one o f several ob jec - t i ve measures o f s t ress (Eskeland, 1978). S t ressors are t y p i c a l l y mediated v ia ACTH sec re t ion by the hypothalamus (Chester , 1957) and resu l t s in an elevated cor t i cos te rone l e v e l . As stated by Selye (1976) a r i s e in cor t i cos terone i s a very constant c h a r a c t e r i s t i c o f s t r e s s . The consequences o f increased leve l of cor t i cos terone are mani fo lds . B irds which are more stressed are suscept ib le to various types o f diseases (Gross and Colmano, 1971; Gross, 1972; and Brown and Nestor, 1973). Increased cor t i cos te rone induces osteoporosis in adult b irds (Siegel and Lat imer, 1970). Although increased cor t i cos terone leve l increases the potent ia l for short term surv iva l under acute s t r e s s , growth and development o f young bi rds are depressed, i f such high leve l i s maintained over extended period of t ime. There are a lso losses in body weight and reduced reproduct ive capac i ty (Bartov et a l_ . , 1980). 26 Brown and Nestor (1973) found that turkeys se lected for low adrenal co r t i c a l secretory a c t i v i t y improved egg product ion , growth rate and reduced mor t a l i t y . I t has been reported that the plasma concentrat ion of cor t i cos terone in unstressed b i rds i r r e spec t i v e o f l i nes or s t ra ins se lected fo r high or low l eve l s o f cor t i cos terone are not very d i f f e r e n t and that the d i f fe rences become apparent only i f the birds were stressed (Brown and Nestor, 1973 and Edens and S i e g e l , 1975). Freeman and Manning (1975) reported Rhode Island Reds to be more sens i t i v e to s t ress than Light Sussex. On the other hand, Siegel and Siegel (1966) found non-s ign i f i can t d i f fe rences in the responsiveness o f 4 s t ra ins of chickens they studied to ACTH. The reported estimates o f normal concentrat ion o f plasma cor t i cos terone in avian species vary according to the method of quant i ta t ion (Etches, 1976). Three methods - F luorometr ic , Competitive Prote in B ind ing , and Radioimmunoassay were commonly used (Beuving, 1980). A de ta i l ed d iscuss ion of the use o f these methods and the i r r e l a t i v e e f fec t i veness have been provided by Etches (1976) and by Beuving (1980). Normal plasma cor t i cos terone in l ay ing hens was assayed by Culbert and Wells (1975) who found values in the range of 7 to 20ng per ml o f plasma. An aston ish ing high value (about lOOng per ml) in 21-day-old chicks was reported by Nir et a]_. (1975), but Buckland and Blagrave (1973) obtained a value o f only 5ng per ml in 39 day-old ch i cks . The evidence that plasma concentrat ion o f cor t i cos te rone in lay ing hens fo l lows a d a i l y rhythm was provided by Beuving and Vonder (1977). They housed White Leghorn layers (25-30 weeks old) in ind iv idua l cages and examined the plasma cor t i cos te rone every 3 hours fo r 24 hours and found considerable i n - d iv idua l va r i a t ions and a lso a c l e a r d a i l y rhythm. A maximum (2.3ng per ml) 27 was found at the end of the night (5:30) and a minimum (0.5ng per ml) at the beginning of the night (20:30) . Their f ind ings a lso confirmed that a r i s e in cor t i cos terone occurs j u s t p r i o r to o v i p o s i t i o n . It has been observed that cor t i cos terone l e ve l s o f l ay ing hens are increased by in tens ive husbandry pract i ces (Gross and S i e g e l , 1973). But un t i l the work o f Mashaly et a]_. (1982) i t was not f u l l y r e a l i z e d . These workers studied the response o f adrenal glands of l ay ing hens under d i f f e r e n t cage dens i t i e s by radioimmunoassay fo r cost i costerone from serum of samples. The birds were housed 3, 4 or 5 birds per cage at 19 weeks o f age in 12' x 20' cages. A f te r 48 hours subsequent to housing average cor t i cos terone concen- t ra t ions fo r 3, 4 or 5 birds per cage were 1.038, 1.599 and 2.058ng per ml r e spec t i v e l y . This r e su l t i s an i nd i ca to r o f a pos i t i ve co r r e l a t i on between number o f birds per cage and the i n i t i a l response o f the adrenal g lands. In another more recent study with b r o i l e r chicks to determine the e f f ec t s o f populat ion densi ty on the growth, feed e f f i c i e n c y and plasma cor t i cos te rone , Pesti and Hawarth (1983) brooded chicks in bat ter ies at 116, 232, 348 and 697cm per b i r d . They observed s i g n i f i c a n t l y higher plasma cor t i cos terone for chicks kept at 697 (14.5ng per ml) and 348 (12.2ng per ml) c m 2 per chick than at 232 (4.9ng per ml) or 116 (5.4ng per ml) cm 2 per chick at 3 weeks. The resu l t s obtained by Pesti and Hawarth were opposite to that of Mashaly et al_. It could be a t t r i bu ted to d i f f e rences in age o f the b i rds and/or to d i f fe rences in b i rd dens i t i e s used by these authors . Furthermore, in one experiment, Barnett and Ba r t l e t t (1981) studied the e f f e c t s of spectac les (polypeepers) on the concentrat ion o f plasma cor t i cos terone in White Leghorn (WL) and crossbred (XB) hens. WL was housed 28 e i t he r i n cages or on l i t t e r , but XB only in cages. From day 1 of the experiment up to 14-day a l l birds were without spec tac l es . On day 15 o f the experiment specs were f i t t e d to ha l f o f the b i r d s . Blood samples were c o l l e c t - ed from a l l b i rds on days 1, 3, 7, 11 and 14 fo r the f i r s t h a l f and on days 15, 17, 21, 25 and 28 for the second ha l f o f the experiment. The overa l l mean c o r t i c o s t e r o i d concentrat ion in XB was s i g n i f i c a n t l y (P<0.01) higher than WL in cages. The mean c o r t i c o s t e r o i d concentrat ion on day 1-14 fo r WL in cages and on l i t t e r were 0.88 ± 0.08 and 1.32 ± O.lOng per ml r e spec t i v e l y . They did not f i nd any s i g n i f i c a n t e f f e c t of specs on plasma leve l o f co r t i cos te rone . 4. Leukocytes Leukocytes are agents in the defence o f the body against i n f e c t i o n and are able to remove p a r t i c l e s and micro-organisms fore ign to the body (Hodges, 1974). It i s known that , leukocyte count in birds var ies according to breed, age of the birds and sex. Barger et al_. (1958) reported that fowl 's blood contains from 15000 to 30000 white blood c e l l s per ml o f b lood. Schermer (1967) has summarised values obtained by d i f f e r e n t authors and showed that the range i s from 9300 to 32000 with an average of 20000. These f igures demonstrate a great deal o f va r i a t ions in the est imat ion o f leukocyte numbers in ch ickens . In pa r t , these d iscrepenc ies may be a t t r i bu ted to the method of making the count, and in many cases', to the small number o f b irds used ( S tu rk ie , 1976). A de ta i l ed desc r i p t i on o f d i f f e r e n t counting methods for leukocyte can be found in Lucas and Jamroz (1961), and Schermer (1967). Studies with e f f e c t s o f breed, sex and age o f the b i rds on tota l leukocyte counts are not numerous. Most estimates o f leukocyte counts in chickens are from White Leghorn breed (Fenstermacher, 1932; B i e l y and Palmer, 1935; Twisselmann, 29 1939 and Lucas and Jamroz, 1961). Lucas and Jamroz (1961) reported tota l white blood c e l l s (per ml) to be 35787 in Rhode Island Red females; comparative f igures fo r males were not g iven. They a lso reported that White Leghorn male contains 16615 leukocytes compared to 29397 in females. B le in (1928) reported leukocytes to be 18630 in dominique ch ickens . Total leukocyte counts in turkeys ' appeared to be higher than what i s reported for ch ickens . McGuire and Cavett (1952) found tota l leukocyte counts (per ml) to be 38700 in turkey b lood. Sex d i f f e rence in leukocyte counts in adult chickens was observed by Olson (1937) but not in c h i c k s . Cook (1937) reported no s i g n i f i c a n t v a r i a t i on i n the count a t t r i bu t ab l e to sex in chickens aging from 26 to 183 days. Young chicks and qua i l s usua l l y have s l i g h t l y lower counts than adults ( S tu rk ie , 1976). Barton and Harr ison (1969) demonstrated that the blood of the neonate chicks i s low in leukocytes and changes r ap id l y dur ing the growing pe r iod . By 3 weeks o f age, the c e l l numbers increase and reach e s s e n t i a l l y the adul t l e v e l . Freeman (1971) stated that changes in leukocyte count could poss ib l y be used as s t ress ind i ca to rs in ch ickens . Wolford and Ringer (1962) concluded that leukocyte response were p a r t i c u l a r l y s ens i t i v e to s t ress and perhaps was the best i nd i ca to r o f s t ress fo r the fowl . Leukocyte count may a lso be a r e l i a b l e index o f adrenocort ica l hyperac t i v i t y (Newcomer, 1958). Leukocytes are found to be very sens i t i ve to s t ressors such a co r t i co t roph in ( S i ege l , 1968). It i s genera l ly agreed that there i s a leukocytos is fo l lowing i n j e c t i on o f ACTH (Huble, 1955; Newcomer, 1958). An increase in leukocyte number due to s t ress may probably be assoc iated with increased demand for immune response of the stressed animal 's body system so that i t could cope with the stress (Selye, 1963). 30 The response of leukocytes a f t e r an i n j e c t i o n o f ACTH was studied by Davison and Flack (1981) using 3-week o ld Rhode Is land Red ch ickens . Number o f leukocytes were counted at various i n te r va l s over an extended per iod o f 32 hours a f t e r the i n j e c t i o n . They observed a b iphasic response of leukocytes . There was an 18% decrease in the number o f leukocytes one hour a f t e r the i n - j e c t i on and 40 to 50% increase between 4 and 8 hours a f t e r the i n j e c t i o n . A s i g n i f i c a n t leukocytos is was s t i l l in evidence a f t e r 12 hours but the counts returned to normal 24 hours a f t e r the i n j e c t i o n . Environmental fac tors such as r e s t r a i n t , hand l ing , cold and s ta rva t ion cause a change in leukocyte numbers s im i l a r to treatment with ACTH (Huble, 1955; Newcomer, 1958; Wolford and Ringer, 1962 and S tu rk i e , 1976). Olson (1937) showed that adult b i rds ra ised in bat te r ies within a bu i ld ing had 17000 leukocytes compared to 23600 fo r those ra ised ou ts ide . However, very l i t t l e i s known con- cerning the e f f e c t o f b i rd dens i ty on the change o f leukocyte count. One recent study (Pest i and Howarth, 1983) with 3-week o ld female b r o i l e r chicks demonstrat- ed no s i g n i f i c a n t d i f fe rences in leukocyte counts as dens i ty increased from 697cm 2 per b i rd to 116cm 2 per b i r d . Other fac tors such as d i e t (Goff et a l_ . , 1953), drugs (Hunt and Hunt, 1959) and exposure to X-rays (Lucas and Demington, 1957) a l so play a s i g n i f i c a n t ro le in changing leukocytes . 31 METHODS I. Experimental animals Data were obtained from two genotypic c lasses o f chickens maintained at the Avian Genetics Laboratory, The Un ivers i ty o f B r i t i s h Columbia. One type was heterozygous for the autosomal recess ive gene ' r c ' and has s ight v i s i o n . The other genotype i s homozygous for ' r c ' and is b l i n d . Detai led descr ip t ion of the genotypes was out l ined by Cheng et al_. (1980). II. Rearing condi t ions o f b irds before s t a r t of experiment The chicks for th is experiment were of two age groups. The f i r s t group was hatched on August 24, 1982 and the second hatched two weeks l a t e r on September 7, 1982. Immediately a f t e r each hatch a l l the chicks were wing- banded for i d e n t i f i c a t i o n and brooded in Jamesway battery chick brooders at dens i t i e s of 335cm 2 per b i rd and group s izes o f 50 chicks per group. The two genotypes from each hatch were kept separated but ra ised under s im i l a r condi t ions by ass igning chicks to randomized sect ions o f the brooders. Brooding heat was provided up to 4.weeks a f t e r hatching. Chick s t a r t e r conta in ing 21% prote in was suppl ied ad l i b i t um during the en t i re brooding period with f ree access to water. At the end o f the 4th-week, brooder space for each group o f 50 chicks was doubled to al low for the increase in body s i z e . When the birds atta ined 7 weeks, they were moved to l i t t e r e d f l o o r pens. Eighty birds ( 2 0 ^ and 60-??) from each genotype and age group were kept (4 groups). Each group was kept in a 3.2m x 5.9m pen (approximate densi ty o f 2350cm 2 per b i r d ) . The birds r e - mained in these pens un t i l f i n a l l y being moved into the experimental pens on 32 January 25, 1983. During the en t i r e growing per iod a grower ra t ion (18% pro- te in ) and water were provided ad l i b i t u m . A l l the birds were under 14L/10D l i g h t schedule dur ing en t i re brooding and growing per iods . III. Management o f experimental birds At the time birds were put into the experimental pens the f i r s t hatch was 22-weeks o ld and the second hatch was 20-weeks o l d . A l l the birds were fed a commercial layer ra t ion conta in ing 16% p ro t e i n . Feed and water were provided ad l i b i t u m . However, feeder space and water space were standardised at e ight centimeters each per b i r d . Wood shaving 10-12cm deep were used as l i t t e r . They were replaced from time to time as and when necessary. A l l the birds received a standard photoperiod o f 14 hours of a r t i f i c i a l l i g h t in a 24-hour day. IV. Experimental design The design o f th i s experiment was a 2 x 2 x 2 x 2 f a c t o r i a l with two hatches ( r e p l i c a t i o n s ) , two genotypes, two dens i t i es and two f lock s i z e s . The two hatches were two weeks apart in terms of age but were put into the expe r i - mental pens at the same t ime. The two dens i t i es used in th i s experiment were of 1000cm 2 per bird (high densi ty ) and 2000cm 2 per b i rd (low dens i t y ) . These dens i t i es were used in the l i g h t of what other workers used under experimental s i tua t i ons o f high and low dens i ty l e v e l s . For example, Simmenson et a]_. (1980) used 714cm 2 and 1428cm 2 per b i rd for high and low densi ty condi t ions r e spec t i v e l y . The birds used were White Leghorn type l a y e r s . Normal body weight o f White Leghorn type pu l l e t s during housing at 20 weeks i s about 1406g (McClung and Jones, 1973). On the other hand, the birds used in th i s experiment were Rhode 33 Island Red type having much higher body weight (average body weight o f pu l l e t s at housing 1865g) compared to White Leghorn types . Therefore more space was allowed per b i rd to compensate fo r the bigger body s i z e . The two f lock s izes used were one o f 5 birds (IS and 4$$) per f lock (small f l ock ) and 20 b i rds (4J i and 16££) per f lock ( large f l o c k ) . Although i t i s des i rab le to have l a rger number o f b irds in the large f locks to approximate commercial product ion s i t u a t i o n s , the s i ze o f f l o o r pens ava i l ab le l im i t ed the s i ze of the experimental f l o c k s . The durat ion o f the experiment was 8 weeks. V. Parameters measured The parameters considered in th i s experiment were: i ) Number of eggs co l l e c ted i i ) Egg wei ght i i i ) Amount o f feed taken from feed trough iv ) Body weight gain v) F e r t i l i t y of eggs v i ) Feather pecking and comb damage scores v i i ) Leukocyte count v i i i ) Plasma cor t i cos te rone leve l ix) Adrenal gland weight 1. Number o f eggs co l l e c t ed and egg weight Egg number and egg weight were recorded d a i l y . Eggs from each t r e a t - ment pen were co l l e c t ed twice a day (at 10:00 and 16:00 hr) to minimize the number o f broken eggs due to pecking and t rampl ing. The co l l e c t ed eggs were 34 each marked according to date and pen number. The co l l e c ted data were then converted to egg production on a hen-day basis a f t e r ad just ing fo r mor ta l i t y whenever necessary. A f te r each days c o l l e c t i o n , eggs from each treatment pen were weighed together to the nearest gram using a 'To ledo ' balance. Broken eggs were included in egg production data , however, they were not weighed. Egg weights were converted to mean weight per egg for s t a t i s t i c a l a n a l y s i s . 2. Amount of feed taken from feed trough The amount of feed taken from the feed troughs in d i f f e r e n t t r e a t - ment pens was recorded separa te ly . The feed troughs were f i l l e d twice a day a f te r egg c o l l e c t i o n . Each sack o f feed used for a p a r t i c u l a r pen was weighed (kg) and marked according to pen number for i d e n t i f i c a t i o n . The l e f t over feed at the end o f the experiment was weighed and subtracted from the tota l feed g iven. The feed data were then converted to kg feed per hen per day. These data were a lso adjusted for mor ta l i t y whenever necessary. 3. Body weight gain Indiv idual body weight (g) of a l l the experimental b irds were measured twice during the whole experimental pe r iod . The f i r s t weight was taken immediately before p lac ing the birds into the experimental p l o t s . This weight cons t i tu ted the ' i n i t i a l body we ight ' . The birds were weighed again at the end o f the experiment (March 21, 1983) and ' f i n a l body weight' was recorded. The gain in body weight was then ca l cu la ted by subtract ing ' i n i t i a l body weight' from ' f i n a l body we ight ' . 4. F e r t i l i t y o f eggs Eggs from three sample periods during the experiment were incubated 35 in a Jamesway 252 e l e c t r i c forced a i r incubator to tes t for f e r t i l i t y . The three sample periods were: (1) days 8-17, (2) 28-37 and (3) 48-57. Eggs saved fo r f e r t i l i t y tes t were stored i n a cool room at a temperature o f 55 °F and a r e l a t i v e humidity o f 65%. For each period a tota l o f 10 days cumulating stored eggs were set fo r incubat ion at the same t ime. Eggs were incubated fo r 8-10 days. A f te r that incubat ion period a l l the eggs were candled and f e r t i l i t y determined. A l l the ' i n f e r t i l e ' eggs were broken out to determine whether they were t r u l y i n f e r t i l e or ea r l y embryonic death (Kos in , 1944). F e r t i l i t y was measured as a percentage o f tota l eggs set fo r incubat ion . 5. Feather pecking and comb damage scores Feather and comb damages o f the experimental birds due to pecking were rated by v isua l es t imat ion . Back, rump, comb, wing and t a i l were con- s idered fo r eva luat ion o f such damages. Back and rump feather losses were evaluated by the procedure descr ibed by Hughes and Duncan (1972) and i s shown in Table 1. The method used to measure the comb damage scores was as present - ed in Table 2. Wing and t a i l feather losses o f the birds were evaluated by: a . B irds with no broken, no missing feather scored 0 b. Sub jec t i ve ly scored 1-3 according to degree of feather loss c . B irds with skin damage and/or bleeding scored 4 Feather and sk in damages o f the experimental b irds were measured two times during the experimental pe r iod . The f i r s t measurement was made jus t p r io r to p lac ing the b i rds into the experimental p lots and f i n a l l y at the end of the experiment. No comb damage was recorded during the f i r s t measurement 36 Table 1. Scoring method to assess the degree o f pecking damage to back and rump Score Descr ipt ion 0 No denuded area of sk in 1 Denuded area less than 1 c m 2 2 Denuded area less than 25 c m 2 3 Denuded area more than 25 cm 2 4 Skin damage (haemorrhage, scab) regardless o f s i ze of denuded area Table 2. Scor ing method to assess the degree o f pecking damage to the comb Score Descr ipt ion 0 No s ign of pecking damage 1 A s ing le mark o f pecking damage 2 Two to three marks o f pecking i n j u r i e s on both s ides of the blade 3 More than three marks o f pecking on the comb 4 Severe i n j u r i e s , b leed ing , extensive damage to the comb 37 nor wing and t a i l feather l o s s e s . 6. Leukocyte count and plasma cor t i cos terone leve l Immediately a f t e r the end o f the two months experimental period blood samples for leukocyte counts and cor t i cos terone ana lys is were co l l e c t ed from a tota l o f 80 b i r d s , taking 5 {li and 4 # ) from each treatment pen. The birds from large f locks were picked at random. From each b i rd two samples o f 2ml each were co l l e c t ed into two hepar in ized tes t tubes by the method of vene- puncture o f the wing ve i n . Blood samples were co l l e c t ed fo r a period o f 8- days from 1:00pm to 1:30pm each day. This was done to minimize the e f f e c t o f time d i f f e r e n c e , s ince cor t i cos terone leve l in l ay ing hens i s known to change during the day (Beuving and Vonder, 1977). The time required between ca tch - ing the b i rd and bleeding var ied from 40 seconds to one minute in most cases . The f i r s t co l l e c t ed sample from each b i rd was used for cor t i cos terone ana lys is and the second one for leukocyte count. Immediately a f t e r blood c o l l e c t i o n , a l l the co l l e c t ed samples were brought into the l abora tory . Blood samples fo r cor t i cos te rone were centr i fuged in a Sorval GLC-I General Laboratory Centr i fuge for 15 minutes at 2000rpm. The separated plasma was then stored at a temperature o f - 2 0 ° C pending shipment to the Un ivers i ty o f Guelph, Canada, where i t was analysed by radio-immunoassay technique out l ined by Etches (1976). Leukocyte number was counted using haematocytometer under the l i g h t microscope at magni- f i c a t i o n o f 40x. The White Blood Cel l (WBC) d i l uen t used for leukocyte count was prepared according to the fo l lowing rec ipe recommended by Schermer (1967): Crysta l v i o l e t lO.Omg Sodium c i t r a t e 3.8g Formal in 0.4ml D i s t i l l e d water 100.0ml 38 The d i l u t i o n rate o f blood and WBC d i luen t was in the r a t i o o f 1:100. Leukocyte number was expressed as the number o f leukocytes per ml o f b lood. The method used for counting was descr ibed in M in i s t ry o f A g r i c u l t u r e , F i sher ies and Food, Reference Book 365 (1978). The formula used for tota l leukocyte number was = (number counted in 4 squares o f the haematocytometer v 4) x depth of the haematocytometer x d i l u t i o n r a t e . 7. Adrenal gland weight The number o f b i rds from which adrenal glands were excised and weighed was the same as leukocyte counts. From each large f lock 5 birds (IS and 4$$) were randomly drawn independently of b irds used for leukocyte counts. A l l the b i rds in the small f lock were used. One week a f t e r the blood samples were drawn, birds were s a c r i f i e d , d issected arid both the r i gh t and l e f t adrenal glands were exc i sed . Connective and fa t t i ssues were c a r e f u l l y trimmed from a l l the glands by the same person. The glands were then weighed using a sens i t i ve balance (Mett ler H-10 Ana l y t i ca l Ba lance) . Glands were kept moist unt i l and during weighing. VI. Data analyses Data were analysed by Ana lys is o f Variance using e i the r f lock means or ind iv idua l measurements. Analys is o f Variance with Repeated Measures (Steel and T o r r i e , 1980) was appl ied to t r a i t s measured repeatedly at d i f f e r e n t periods or ages. In these s i tua t ions hatches, genotypes, b i rd dens i t i es and f lock s izes were the main p lo t f a c t o r s , whi le periods or weeks was the sub- p lo t f a c t o r . A l l data in percentages were a rcs in transformed before s t a t i s t i c a l t e s t s . Duncan's Mu l t ip le Range Tests were performed to tes t 39 for d i f fe rences among ind iv idua l means when treatment invo lv ing more than one degree of freedom were found to be s i g n i f i c a n t l y d i f f e r e n t . Analys is of Covariance (Steel and T o r r i e , 1980) was used to tes t body weight gain with ' i n i t i a l body weight' as the cova r i a t e . The general s t a t i s t i c a l model is as fo l l ows : Y i j k l m = * + R i + G j + D k + F l + < G D>jk + ( G p ) j l + ( D p ) k l + ( G D F > j k l + E 1 i j k l + Tm + ^ j m + ^ k m + < F T>lm + ( G D T ) j k m + ( G F T > j l m + ( D F T >k lm + E 2 i j k l m and i = 1 , 2; j = 1 , 2; k = 1, 2; 1 = 1 , 2; and m = l , . . . , x ; where Y ^ . ^ = one of the dependent v a r i a b l e s . Y...-, i s the mean for the parameter in the i t h r e p l i c a t i o n invo l v ing birds o f the j th genotype housed under kth b i rd dens i ty and 1th f lock s i z e , measured during the mth pe r i od , p = the t h e o r e t i - cal populat ion mean, R. = e f f e c t o f the i t h r e p l i c a t i o n , G. = e f f e c t o f whether the b i rd involved was b l ind or s i gh ted , = e f f e c t o f high or low dens i t y , F-| = e f f e c t o f large or small f l ock s i z e , T m = e f f e c t o f measurements made during the mth time pe r iod , ( G D ) ^ , (GF )^ , (DF )^ , ( G T ) j m , ( D T ) k m , ( F T ) l m = two-factor i n t e r a c t i o n s , ( G D F ) j k l , (GDT ) j | < m , (GFT)J-Jm> ( D F T ) k l m = t n r e e " f a c to r i n t e r a c t i o n s , E l - j ^ = e r ror term for main p lo t comparisons, and £ 2 ^ ^ = sub-plot e r ror term. This general model was s l i g h t l y modif ied fo r ana lys is o f each parameter. The analyses were conducted with the a id o f a computer program, 'UBC - MFAV (Lee, 1980), at the Un ivers i ty o f B r i t i s h Columbia Computer Center. Since the scor ing fo r feather and comb damage; are considered as rank data , a parametric ana lys i s cannot be appl ied (Steel and T o r r i e , 1980). Instead, such 40 data were analysed by the Kruskal-VJallis one-way ana lys is of variance ( S i ege l , 1956) appropriate for ranked data . The formula fo r th i s ana lys is i s : k 2 . - E ILL' - 3 (N + 1) H = N ^ N * ^ — ^ 3 , d i s t r i bu t ed as chi-square with d f k-1 1 - 3 N - N where H = the s t a t i s t i c used i n the Kruskal-Wal l is t es t def ined by the formula, n- = number of observat ions in j th sample, N = En., R. = sum of ranks in j th J k 3 sample, E = sum over the k samples, T = t 3 - t , where t = number of t i ed obser- j va t ions . Because of s i m i l a r i t y in nature , back and rump feather scores from each ind i v idua l were added together and the mean c a l c u l a t e d . The ca lcu la ted mean scores were then ranked fo r the Kruskal-Wal l is t e s t . S im i l a r treatment for wing and t a i l feather losses was a lso done. The only known independent va r i a t i on between the two r ep l i c a t i ons i s that there was a two week d i f f e rence in the age o f the b i r d s . In order to determine whether th i s v a r i a t i on caused s i g n i f i c a n t d i f fe rences between the two r e p l i c a - t i o n s , data fo r number o f eggs c o l l e c t e d , egg weight and amount o f feed taken from feed trough (where weekly data were obtainable) were re-analysed a f te r cor rec t ing for the age d i f fe rences between the two r e p l i c a t i o n s . This was done by matching data taken during weeks 3 to 8 from r e p l i c a t i o n 2 (younger b i rds ) with data taken during weeks 1 to 6 from r e p l i c a t i o n 1 (older b i r d s ) . In other words, data co l l e c t ed dur ing week 3 from birds in r e p l i c a t i o n 2 and week 1 from r e p l i c a t i o n 1 would be from birds o f the same age. In these ana lyses , data co l l e c t ed during weeks 7 and 8 from r e p l i c a t i o n 1 and weeks 1 and 2 from r e p l i c a t i o n 2 were not u t i l i z e d . 41 RESULTS I. Number o f eggs co l l e c t ed Analys is o f var iance (ANOVA) table fo r percent hen-day egg production i s presented in Table 17 (Appendix). S i g n i f i c a n t (P<0.05) d i f f e rences were found between genotypes with b l ind chickens producing higher number o f eggs compared to s ighted ch ickens . The mean rate o f production was 54.0% fo r b l ind b i rds compared to 41.3% fo r s ighted birds (Table 3 ) . Density e f f e c t on egg production was not s i g n i f i c a n t (Table 4 ) , ne i ther was the e f f e c t o f f lock s i z e (Table 5 ) . However, when corrected for the d i f f e rences in ages o f the two hatches, f lock s i ze became a s i g n i f i c a n t (P<0.05) f a c to r . Percent hen-day production for small f l ocks was 58.5% com- pared to 48.9% fo r large f l o c k s . The d i f f e rence between small and large f locks was 9.6% (Table 19 in Appendix). There was no s i g n i f i c a n t two-way or three-way in te rac t ions invo lv ing genotype, dens i ty or f lock s i z e . The resu l t s on percent hen-day egg production over d i f f e r e n t weekly periods demonstrated h igh ly s i g n i f i c a n t (P<0.001) period e f f e c t (Table 6 ) . Egg product ion increased from 15.4% in the f i r s t week to 58.0% in the fourth week, but remained s tab le a f t e r the fourth week. The TX6 i n t e r a c t i on was not s i g n i f i c a n t . B l ind chickens had higher production rate in a l l weeks o f pro- duct ion in the experimental pens (Figure 1 ) . From Figure 1, i t could be seen that egg production in b l ind chickens was uniformly better over a l l weeks compared to s ighted ones. The e f f ec t s o f the two hatches ( r ep l i c a t i ons ) on egg production are shown in Table 7. The mean for the f i r s t hatch was 52.3% against 43.2% for the 42 Table 3. E f fec ts of genotype on parameters measured Genotype means Di f ference Parameters Sighted B l ind between genotypes Apparent mean egg production (hen-day %) 41.30± 6.90 54.00± 4.30 12.70* Mean egg weight (g) 46.82± 4.88 46.07± 4.07 0.75 Apparent feed requirement (g , per b i rd per day) 179.40± 29.00 135.30± 14.00 44.10*** Body weight gain (g , females only) 263.30+158.90 267.10±234.80 3.80 F e r t i l i t y {%) 84.20± 5.00 48.20± 17.10 36.00* Leukocyte count (1,000 per ml) 19.27± 4.96 20.19± 4.56 0.92 Adrenal weight (mg per lOOg body weight) 7.30± 1.66 6.69+ 1.19 0.61 Cort icosterone leve l (ng per ml o f plasma) 1.22± 0.59 1.04± 0.74 0.18 *P<0.05 ***P<0.001 43 Table 4 . E f fec ts of dens i ty on parameters measured Density means Di f ference Parameters • High Low between d e n s i t i e s 1 Apparent mean egg production (hen-day %) 42.20± 7.40 49.80± 4.50 7.60 Mean egg weight (g) 46.04± 4.50 46.85± 4.48 0.81 Apparent feed.requirement (g , per b i rd per day) 154.40± 26.00 160.40± 38.00 6.00 Body weight gain (g , females only) 263.40±121.90 267.10±256.30 3.90 F e r t i l i t y (%) 58.80± 18.50 75.70± 9.50 16.90 Leukocyte count (1,000 per ml) 19.52± 4.63 19.94± 4.93 0.42 Adrenal weight (mg per lOOg body weight) 7.08± 1.30 6.90± 1.63 0.18 Cort icosterone leve l (ng per ml of plasma) 1.23+ 0.73 1.03± 0.60 0.20 1 None of the d i f f e rences were s i g n i f i c a n t at 0.05 l e v e l . 44 Table 5. E f fec ts of f lock s i ze on parameters measured Flock s i ze means Dif ference Parameters Small Large between f locks Apparent mean egg production (hen-day %) 52.30± 6.60 43.00± 5.00 9.30 Mean egg weight (g) 46.55± 4.77 46.34± 4.24 0.21 Apparent feed requirement (g, per b i rd per day) 173.60± 35.00 141.10+ 18.00 32 .50*** Body weight gain (g , females only) 330.90±209.00 199.60±165.20 131.30** F e r t i l i t y (%) 62.80± 21.10 72.10± 7.80 9.30 Leukocyte count (1,000 per ml) 19.15± 4.80 20.31± 4.70 1.16 Adrenal weight (mg per lOOg body weight) 6.75± 1.09 7.23± 1.75 0.48 Cort icosterone leve l (ng per ml of plasma) 1.09± 0.67 1.16± 0.68 0.07 **P<0.01 ***P< 0.001 Table 6 . E f fec t o f time on egg production and egg weight o f the experimental b irds Week1 Means Parameters 2 _ _ _ 1st 2nd 3rd 4th 5th 6th 7th 8th Apparent mean (L9n-d rayU%) i 0 n 15.4&5.40 31.20b±3.20 42.70C±2.50 58.00d±2.00 58.8c4l.20 60.7 0 d±2.80 63.60±4.20 54.70±5.20 Mean egg wei (g) 39.50±2.50 42.20+3.10 44.70±2.00 46.30±2.60 48.10+2.50 48.90+2.10 50.10±1.80 51.7(8=1.90 1 Time measured s ince the i n i t i a t i o n o f the experiment. Figure 1. A comparison o f weekly egg production between s ighted and b l ind chickens 100 9 0 I" Sighted l l l im 80 K B l i n d = 70 o •5 60 o J - CL. ^ 50 •D I C <v Z 4 ° c <u o ai 30 20 10 H J i i ! i i i i n i i II II =! 1st 2nd 3rd 4th , 5th 6th 7th 8th Weeks 47 Table 7. E f fec ts o f r e p l i c a t i o n (hatch) on parameters measured Parameters Hatch means F i r s t Second Di f ference between hatches Apparent mean egg production (hen-day %) 52.30± 5.00 43.20± 6.60 9.10 Mean egg weight (g) 47.46± 3.66 45.43± 5.02 2.03 Apparent feed requirement (g , per b i rd per day) 154.40± 28.00 162.30± 36.00 10.00 Body weight gain (g , females only) 192.20±164.60 338.30±205.10 146.10*** F e r t i l i t y (g) 75.10+ 8.80 58.60± 19.10 16.50 Leukocyte count (1,000 per ml) 18.72± 4.81 20.74± 4.54 2.02 Adrenal weight (mg per lOOg body weight) 6.84± 1.72 7.15± 1.17 0.31 Cort icosterone leve l (.ng per ml of plasma) 1.07+ 0.66 1.19± 0.68 0.12 **P<0.01 ***P< 0.001 48 second hatch. The d i f f e rence (9.1%) however was not s i g n i f i c a n t . ANOVA of same parameter a f t e r ad just ing for the d i f fe rences in age of the birds i n the two hatches d id not reveal any c o n f l i c t i n g trends (see Tables 18 and 19 in Appendix) compared to the previous a n a l y s i s . II. Egg weight AtlOVA for data on egg weight i s presented i n Table 20 (Appendix). No s i g n i f i c a n t d i f f e rences were observed fo r genotype, density or f lock s i z e . However, there was a s i g n i f i c a n t (P<0.001) dens i ty by f lock s i ze i n t e r a c t i o n . This i n t e r a c t i on i s reported in Table 8 . From Table 8, i t could be seen that the heaviest egg weight was from chickens in small f locks at low densi ty (48.00g) and the lowest from small f locks at high dens i ty (45.11g). On the other hand, there was no s i g n i f i c a n t d i f f e rence between low densi ty (45.76g) and high densi ty (46.97g) for chickens kept in large f l o c k s . The two hatches d i f f e r e d h igh ly s i g n i f i c a n t l y (P=0.01) in mean egg weight (Table 7 ) . The f i r s t hatch averaged 2.03g more (weight per egg) than the second hatch. Egg weight was apparently a f fec ted by age o f the b i r d s . During the f i r s t week of product ion in the pens, egg weight averaged 39.51g. There- a f t e r i t increased at a rapid r a t e . In the fo l lowing weeks of 2, 3, 4, 5, 6, 7 and 8, mean egg weight was 42.18, 44 .69 , 46 .33, 48 .11 , 48.94, 50.09 and 51.71 g r e spec t i v e l y . Duncan's Mu l t ip l e Range Tests ind ica ted that any two means (except between 5 and 6 weeks) in the above weeks were s i g n i f i c a n t l y (P<0.05) d i f f e r e n t from each other (Table 6 ) . The e f f e c t o f r e p l i c a t i o n (hatch) became non-s ign i f i can t a f t e r adjustment for the age d i f f e rences (see Table 21 and 19 in Appendix) . From the above r e s u l t s , i t could be concluded 49 Table 8. S i g n i f i c a n t DXF i n t e rac t i on for egg weight o f experimental birds Flock S ize Density >— Small Large High 4 5 . 1 1 a b 4 6 . 9 7 b c Low 48 .00 C 45 .70 b Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Duncan's Mu l t ip le Range Test . 50 tha t ,dur ing the experimental per iod,egg weight increased with age o f the b i r d s . III. Amount o f feed taken from feed trough ANOVA table fo r th i s t r a i t i s presented in Table 22 (Appendix). Highly s i g n i f i c a n t (P< 0.001) d i f f e rence was found between the two genotypes. Mean amount o f feed taken by the b l ind birds was 135.3g per b i rd per day compared with 179.4g by the s ighted birds (Table 3 ) . The d i f f e rence between the two genotypes in the mean feed requirements was 44 .lg per b i rd per day. There was a lso a s i g n i f i c a n t GXF i n t e r a c t i o n . The feed requirements fo r various combinations o f genotypes and f lock s i zes are shown in Table 9. From Table 9, i t could be seen that s ighted birds took more feed per b i rd d a i l y when kept in small f locks (202.Og) than when kept in the large f locks (156.8g). The same pattern was a lso apparent for b l ind birds kept in small and large f locks (145.2g vs 125.4g r e s p e c t i v e l y ) . The d i f f e rence between s ighted and b l i nd ch ickens, however, was much bigger in small f locks (56.8g) than in large f locks (31.4g) . Flock s i ze was h igh ly s i g n i f i c a n t (P<0.001) in a f f e c t i ng feed requirements of the b i r d s . Chickens in small f locks took more feed per b i rd d a i l y (173.6 g) than birds in la rge f locks (141.lg). On the average, .b i rds in small f locks took 32.5g more feed per b i rd per day compared to birds i n la rge f locks (Table 5 ) . Density as a main e f f e c t was not s i g n i f i c a n t in feed requirements o f the b i r d s . However, the i n t e rac t i on term DXF was s i g n i f i c a n t (P<0.05). This has been tabulated in Table 10. From Table 10 i t could be seen that birds kept in small f locks at low dens i ty took the highest amount o f feed (183.5g) and birds in large f locks at the same densi ty the lowest (140.lg). Feed taken by birds in small f l ocks a t high dens i ty was 163.7g compared to 145.Og by b i rds kept in 51 Table 9. S i g n i f i c a n t GXF in te rac t ion for feed taken from feed troughs by experimental birds Flock S ize Genotype Small Large Sighted 202.00 C 156.80 b Bl ind 145.20 b 125.40 a Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Duncan's Mu l t ip l e Range Test' ; Table 10. S i g n i f i c a n t DXF in te rac t i on for feed taken from feed troughs by experimental birds Flock S ize Density Small Large High 163.70 b 145.00 a Low 183.50 C 140.10 a Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Duncan's Mu l t ip le Range Test ' , . 53 large f locks at the same dens i t y . The d i f f e rence in feed requirements between birds in small f locks and large f locks was greater at low b i rd dens i ty (43.4g) than in high b i rd dens i ty (18.7g) . The e f f e c t o f hatch on th i s t r a i t was not s i g n i f i c a n t (Table 7 ) . ANOVA a f t e r removing age e f f e c t o f the two r ep l i c a t i ons d id not show any d i f f e rence in trends (see Tables 23 and 19 in Appendix). IV. Body weight gain Body weight gain o f the experimental hens during the experimental period was subjected to ana lys i s o f covariance with i n i t i a l body weight being the covar ia te (see Table 24 in Appendix) . No d i f fe rences were observed between the two genotypes (Table 3). The e f f e c t of f lock s i z e , however, was h igh ly s i g n i f i c a n t (P<0.01). Hens in small* f locks gained more weight than those in large f l o c k s . On the average, each hen in small f locks gained 131.3g more than t h e i r counterparts in large f locks over the 2-month period (Table 5 ) . The e f f e c t o f dens i ty was not s i g n i f i c a n t for th i s t r a i t , but the i n - t e rac t ion term DXF was s i g n i f i c a n t (P<0.01). This could have rendered the main e f f e c t non-s ign i f i c an t . The various combinations of dens i t i es and f lock s izes a f f e c t i n g body weight gain o f hens are reported in Table 11. As can be seen from Table 11 that hens in small f lock-low densi ty condi t ions gained the most weight (392.7g) and those in large f lock-low densi ty condi t ions the l eas t (141.5g). On the other hand, under high densi ty cond i t i ons , f lock s i ze was not s i g n i f i c a n t in a f f e c t i ng weight ga in . Furthermore, the two hatches used in th i s experiment d i f f e r ed h ighly s i g n i f i c a n t l y (P<0.001) in body weight ga in . The f i r s t hatch (o lder b i rds ) 54 Table 11. S i g n i f i c a n t DXF in te rac t i on for body weight gain of experimental hens Flock S ize Density Small Large High 269.00 b 257.70 b Low 392.70 C 141.50 a Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Duncan's Mul t ip le Range Test-. 55 gained 146. lg per b i rd less than the second hatch (younger b i r d s ) . Regression o f body weight gain on i n i t i a l body weight was not s i g n i f i c a n t . Although covariance ana lys is removed the e f f e c t o f i n i t i a l body weight (body weight taken before s t a r t of experiment) d i f f e rence on the body weight gain o f the hens, i t d id not reveal whether there was any d i f f e rence in i n i t i a l body weight. This was tested by an ANOVA on i n i t i a l body weight. No s i g n i f i c a n t d i f f e rence was found in any o f the main fac tors involved or t he i r in te rac t ions thereof (see Table 25 in Appendix) except the GXDXF i n t e r a c t i o n . Because o f very small sample s izes (8 per group) body weight gains of roosters were not analysed s t a t i s t i c a l l y . However, means were ca lcu la ted and are presented in T a b l e l 2 . The mean weight per b i rd o f b l ind and s igh ted , low and high d e n s i t i e s , large and small f locks and o lder and younger hatches were 339 and 142g, 277 and 204g, 253 and 228g, and 83 and 398g r e spec t i v e l y . V. F e r t i l i t y o f eggs F e r t i l i t y o f eggs from the experimental birds was determined over three d i f f e r e n t periods during the experiment. Except for genotype, none o f the main e f f e c t s nor t he i r in te rac t ions was s i g n i f i c a n t (Table 26 , Appendix). The mean f e r t i l i t y fo r the sighted birds was 84.2% compared to 48.2% for the b l ind birds (Table 3 ) . This d i f f e rence was s i g n i f i c a n t (P<0.05). Period had a h igh ly s i g n i f i c a n t (P<0.01) e f f e c t on f e r t i l i t y . F e r t i l i t y was lowest (50.9%) during the i n i t i a l period (days 8 to 17). It increased by 20.2% (to 71.1%) and 28.2% (to 79.1%) r espec t i ve l y dur ing the second (days 28 to 37) and the t h i r d (days 48 to 57) per iods . A l l i n t e r a c t i on terms invo lv ing period as a fac tor were not s i g n i f i c a n t . 56 Table 12. Mean body weight g a i n , adrenal weight and leukocyte count of experimental roos te r s 1 Factors Parameters Weight gain Adrenal weight Leukocyte count N (g) (mg per lOOg body weight) (1,000 per ml) Hatch F i r s t : 8 Second : 8 83 398 7.36 7.32 16.64 22.42 Genotype : S ighted : 8 B l ind : 8 142 339 7.74 6.99 20.63 18.43 Density High Low : 8 : 8 204 277 6.89 7.74 20.29 18.77 Smal 1 Flock s i z e : 8 Large : 8 228 253 7.11 7.54 19.68 19.38 1 Not tested s t a t i s t i c a l l y . 57 V I . Leukocyte count, plasma cor t i cos terone leve l and adrenal gland weight Ana lys is of leukocyte count per ml o f blood from experimental hens i n - d icated no s i g n i f i c a n t e f f e c t s of genotype, b i rd dens i t y , f l ock s i ze or hatch (Table 2 7 , Appendix). The only s i g n i f i c a n t e f f e c t observed fo r th i s t r a i t was the i n t e rac t i on term GXF. This i n t e r a c t i on i s presented in Table 13. Analys is by Duncan's Mu l t ip le Range Tes t shows that b l ind birds in small f locks had the lowest counts and i s s i g n i f i c a n t l y lower than counts for b l ind b i rds kept i n la rge f l o c k s . Between these two extremes were the counts for s ighted birds kept in small f locks and large f l o c k s . However, ne i ther counts fo r the b l ind birds were s i g n i f i c a n t l y d i f f e r e n t from counts for the s ighted birds (Table 13) . The e f f ec t s o f d i f f e r e n t fac tors on leukocyte counts of roosters are pre- sented i n Table 12. Although not tested fo r l eve l o f s i g n i f i c a n c e (due to small sample s i zes ) the means presented in Table 12 showed large d i f f e rences in leukocyte counts in most o f the cases . The adrenal gland weight was measured as mg per lOOg of body weight. For th i s t r a i t , the data from roosters and hens were a lso separate ly presented. The ANOVA Table fo r experimental hens i s presented i n Table 28 (Appendix). This Table showed that none of the main e f f ec t s nor t he i r in te rac t ions was s i g n i f i c a n t . The means and standard deviat ions o f th i s t r a i t for two hatches, two genotypes, two b i rd dens i t i e s and two f lock s i zes can be found i n Table 7, 3, 4 and 5 r e spec t i v e l y . The mean adrenal weights of roosters are presented in Table 12. There appears to be l i t t l e va r i a t i on in mean adrenal weights o f roosters from d i f - ferent treatment groups. 58 Table 13. S i g n i f i c a n t GXF i n te rac t i on for leukocyte count o f experimental hens Flock S ize Genotype Small Large Sighted 1 9 . 9 6 a b 1 8 . 5 9 a b Bl ind 18 .35 3 22 .02 b Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Duncan's Mul t ip le Range Tes t " . 59 The plasma cor t i cos terone leve l (ng per ml o f plasma) o f roosters and hens was analysed j o i n t l y . The ANOVA Table (Table 29 , Appendix) ind icated no s i g - n i f i c a n t e f f ec t s o f hatch, genotype, densi ty and f lock s i z e . The means c a l - culated fo r each leve l of hatch, genotype, densi ty and f lock s i ze for c o r t i - costerone data are reported in Tables 7, 3, 4 and 5 r e spec t i v e l y . A l l two-way and three-way in te rac t ions invo lv ing genotype, densi ty and f l ock s i ze were not s ign i f i c a n t . VII. Feather pecking and comb damage scores Means and leve l o f s i gn i f i c ance for feather loss and comb damage scores are presented in Table 14. Observations from i n i t i a l back and rump scores ind icated h ighly s i g n i f i c a n t (P<0.001) genotype e f f e c t . B l ind birds scored 0.0063 per b i rd against 0.2000 fo r s ighted b i r d s . Back and rump feather losses scored at the end o f the experiment a lso had h ighly s i g n i f i c a n t (P<0.001) genotype e f f e c t . The mean scores per b i rd were 0.0316 fo r b l ind and 1.1948 fo r s ighted b i r d s . Wing and t a i l feather losses scored at the end o f the experiment a lso had a h igh ly s i g n i f i c a n t (P<0.001) genotype e f f e c t . B l i nd chickens had score o f 0.1646 per b i rd compared to 0.5649 for s ighted ones. Density or, f l ock s i ze e f f e c t on feather scores o f the two combined areas were not s i g n i f i c a n t nor was the i n t e rac t i on term invo lv ing the two f a c t o r s . Comb damages were s i g n i f i c a n t l y (P<0.001) higher in s ighted birds compared to b l ind b i r d s . Mean score for s ighted birds was 0.8961 per b i rd as against 0.3544 for b l ind ones. In add i t ion to a s i g n i f i c a n t genotype e f f e c t , there was a l so s i g n i f i c a n t GXD and GXF in te rac t ions fo r comb damage s co res . The GXD in te rac t i on is presented in Table 15; s i m i l a r l y the GXF i n t e rac t i on in Table 16. Table 14. Mean feather loss and comb damage scores of the experimental birds Factors Period- I n i t i a l Final Body area Genotype Density Flock s i ze Bl ind Sighted Dif ference Di f ference Dif ference High Low Smal 1 Large Back and rump 0.0063 0.2000 0.1937*** Back and rump 0.0316 Wing and t a i l 0.1646 Comb 0.3544 1.1948 1.1632*** 0.6538 0.5577 0.5649 0.4003*** 0.3462 0.2500 0.8961 0.5417*** 0.7051 0.5385 0.0961 0.5781 0.6129 0.0348 0.0962 0.1875 0.3266 0.1391 0.1666 0.2188 0.7258 0.5070*** 1 I n i t i a l period re fe rs to score taken p r io r to s t a r t of the experiment. F inal period re fe rs to score taken at the end of the experiment. * * * P<0.001 cn o Table 15. S i g n i f i c a n t GXD in te rac t i on for comb damage scores of experimental birds Density Genotype — High Low Sighted 1.13 c 0 .67 b Bl ind 0 .30 a 0 .41 a Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Kruskal-Wal l is k-sample Test . Table 16. S i g n i f i c a n t GXF i n te rac t i on for comb damage scores of experimental birds Flock S ize Genotype Small Large b C Sighted 0.31 1.05 B l ind 0 .13 3 0 . 41 b Means with d i f f e r e n t superscr ip ts are s i g n i f i c a n t l y d i f f e r e n t (P<0.05) by Kruskal-Wal l is k-sample Test . 63 Regarding GXD s i g n i f i c a n t i n t e r a c t i o n , s ighted birds kept in high dens i ty had more comb damage scores than when they were kept in low dens i t y . On the other hand, b l ind birds kept in high or low densi ty had no d i f f e rence in comb damage scores . Even when b l i nd birds were kept in high densi ty cond i t i ons , t h e i r comb damage- scores were s i g n i f i c a n t l y lower than s ighted birds kept in low dens i ty cond i t i ons . S i g n i f i c a n t GXF i n te rac t i on ind ica ted tha t , both genotypes kept in la rge f locks had higher comb damage scores than when they were kept in small f l o c k s . The d i f f e r ence between s ighted and b l ind chickens was bigger i n large f locks than in small f l o c k s . The important point i s tha t , when b l ind birds were kept in la rge f locks t he i r comb damage scores were only s im i l a r to s ighted birds kept in small f l o c k s . Density as a main fac to r d id not a f f e c t comb damage sco res , but f lock s i ze s i g n i f i c a n t l y (P<0.001) a f fec ted th i s parameter. Large f locks suf fered more damage (0.7258) per b i rd than small f locks (0.2188). The above resu l t s on feather loss and comb damage scores considered t o - gether ind ica te that s ighted birds suf fe red more feather and comb damages than b l ind b i r d s . Histograms dep ic t ing the d i s t r i b u t i o n of birds in the two genotypes with r e l a t i onsh ip to seve r i t y of feather and comb damages are presented in Figure 2 and 3 fo r i n i t i a l and f i n a l 'back and rump' feather scores , in Figure 4 for f i na l 'wing and t a i l ' feather scores and f i n a l l y in Figure 5 fo r f i n a l comb damage scores . 64 Figure 2. A comparison o f i n i t i a l back and rump feather damage between s ighted and b l ind chickens 0 0.5 Scores 1.0 65 Figure 3. A comparison o f f i n a l back and rump feather damager between sighted and b l i nd chickens -o <+- o S-tt> X3 80 70 60 50 40 3 30 20 10 1 I I I I I J II II IL Sighted l l l l l l l l B l ind Wm^mn 0.5 1.0 1.5 2.0 2.5 Scores 3.0 3.5 66 Figure 4 . A comparison o f wing and t a i l feather damage between s ighted and b l ind chickens 67 Figure 5. A comparison o f comb damage between s ighted and b l ind chickens 68 DISCUSSION I. Performance of b l ind chickens This study was undertaken to determine the e f f e c t s o f s ight or the lack o f i t on the performance of chickens under two d i f f e r en t dens i t i es and two d i f f e r e n t f lock s i z e s . It has been reported that a reduct ion of f ronta l v i s ion reduced st ress when hens were wearing specs (A rb i , 1978). It might be that tota l e l im ina t ion of s ight would lead to fur ther reduct ion of soc ia l stress by breaking down soc ia l h ierarchy which might cont r ibute to the increased pro- d u c t i v i t y per b i r d . It was a lso suspected that the lack of s ight might i n - t e r f e re with feeding and other maintenance a c t i v i t i e s of the b i rd which in turn may abo l i sh any potent ia l advantage gained by reduced soc ia l s t ress ex- perienced by these ch ickens . Keeping in mind these c o n f l i c t i n g tendencies , a nu l l hypothesis was developed which stated 'The lack o f v i s i o n did not r e - su l t in better performance for the b l ind birds compared to the s ighted ones through decreased soc ia l in te rac t ions because bl indness in te r fe red with feeding and other maintenance p r a c t i c e s ' . The object ive o f th i s study was therefore to gather evidence e i the r to support or to re jec t the nul l hypothesis through a study o f nine parameters re l a ted to p roduc t i v i t y and st ress of the b i r d s . Sighted and b l ind chickens were compared as per t he i r r e l a t i v e performance i n the parameters measured. Based on the resu l t s of th i s experiment, a number o f statements can be made and arguments for or against each statement can be d i scussed . 1. Statement number 1 69 'Under the condi t ions of the experiment b l ind chickens out-performed sighted ones in egg p roduc t ion . ' . a) Number of eggs co l l e c t ed from pens with b l ind chickens were s i g n i f i c a n t l y higher than the number o f eggs co l l e c t ed from pens with s ighted ch ickens . For a 56-day tes t period b l i nd hens had a production rate o f 54.0% compared to 41.3% for s ighted hens. The ca l cu la ted egg numbers per hen for th i s period were 30.24 (56 days x 0.540) and 23.13 (56 x 0.413) for b l ind and s ighted hens r e spec t i v e l y . Therefore , there was a d i f f e rence o f 7.11 eggs per hen for the 2-month study pe r iod . There was no s i g n i f i c a n t i n t e rac t i on between genotype and dens i ty nor between genotype and f lock s i z e in egg product ion , i nd i c a t i ng that the b l ind chickens out-performed the s ighted ones in both types of dens i t i es and f lock s i z e s . b) The mean egg weight of the two groups was not d i f f e r e n t s t a t i s t i c a l l y . Although egg production can be evaluated by using number o f eggs co l l e c ted as a c r i t e r i o n , th i s may not accura te ly r e f l e c t to ta l egg mass output. Total egg mass may be changed e i ther by changing the number o f eggs or by changing the mean egg weight (W i l l s , 1974). It i s therefore important that the d i f f e rences exh ib i ted by the two groups of birds in egg number and egg weight need to be proper ly balanced against each other to demonstrate the r e l a t i v e egg mass output. Because o f the s i g n i f i c a n t d i f f e rence in the number o f eggs co l l e c t ed from each genotype, the to ta l egg mass co l l e c t ed from each b l ind hen was ca l cu la ted to be 1485.30g (30.24 x 46.07) compared to 1082.95g (23.13 x 46.82) from each s ighted hen. From the above est ima- t ions i t i s apparent that to ta l egg mass co l l e c t ed from b l i nd chickens was 70 heavier (402.35g per hen) than from s ighted ones. The above facta and f igures suggest egg production to be higher in b l ind ch ickens . On the other hand, because s ighted birds were observed to be break- ing and eat ing eggs more f reqent l y than b l ind b i r d s , i t couTd.be argued that the number of eggs co l l e c t ed did not r e f l e c t egg production in these b i r d s . However, eggs were co l l e c t ed at l e as t twice a day from a l l pens to minimize egg breaking and eat ing and i t seems un l i ke l y that the d i f f e rence in the number of eggs co l l e c t ed can t o t a l l y be accounted for by the number o f eggs broken and eaten by the s ighted b i r d s . Moreover, i t was observed that birds in only one pen (pen A5; s ighted high dens i ty- large f lock rep. 1) developed th i s hab i t . Egg breaking by s ighted birds in other pens was very s l i g h t i f at a l l . A f t e r excluding data from th i s p a r t i c u l a r pen there was s t i l l a d i f f e rence (not s t a t i s t i c a l l y tested) in the means; egg production percentage fo r the s ighted b i r d s , however, increased from 41.13 to 45.36%. The mean d i f f e rence between the two genotypes was s t i l l large (8.64%). Since egg eat ing i s a learned behavior in ch ickens , i t takes time to develop th i s habit in a group. I f egg eat ing was the only reason for d i f f e rence in egg production between these two genotypes, s ighted birds could have at l e as t equal or higher production rate during the ear l y weeks before th i s habit was developed. It could be seen from Figure 1 that the weekly p roduc t i v i t y o f b l ind chickens was uniformly better over a l l weeks. There was not a s ing le week in which p roduc t i v i t y was better in s ighted ch ickens . This ind ica tes that egg production in s ighted hens may indeed be i n f e r i o r to b l ind hens. From the above observat ions , i t could be argued that under the condit ions o f the experiment egg production in b l i nd chickens was at l eas t equal but may 71 indeed be better than s ighted ones. It i s the re fo re , worthwhile to i n v e s t i - gate how b l ind chickens would perform in cages under more intense cond i t i ons . Egg qua l i t y i s an important aspect o f egg product ion . Although no measurement was made, the eggs from b l ind hens seem to be comparable to those produced by s ighted ones. Further studies are required to compare the interna l and external q u a l i t i e s o f eggs from both groups o f chickens under s im i l a r environmental cond i t i ons . Another aspect o f future research i s how well b l ind hens w i l l perform over a f u l l year product ion. This requires the computation o f genetic co r r e - l a t i on between ear l y rates of production with annual r a t es . Such computations were made in the recent past . Lowe and Garwood (1980) estimated the genetic co r re l a t i ons o f rate o f egg production between ear l y records and annual records and obtained a c o r r e l a t i o n c o e f f i c i e n t o f 0 .77. Another study (Kinney et a l . , 1968) a lso reported such co r r e l a t i on to be high (0 .80) . These co r re l a t ions reported by the above authors among many others suggest that the ind i v idua l s which had hiqher egg production in the ear ly period of lay w i l l tend to have higher egg production in the annua l ' ra te of l a y . In th i s connect ion, i t would be i n t e r es t i ng to compare annual egg production o f b l ind chickens with s ighted ones to see i f the durat ion o f egg production i s a f fec ted by the bl indness which may a l t e r the amount o f photost imulat ion received by these b i r d s . 2. Statement number 2 'Under the condi t ions of th is experiment b l ind chickens consumed less feed than the s ighted ch ickens . ' The amount o f feed taken from the feed troughs by the b l ind chickens (135.3g per b i rd per day) was s i g n i f i c a n t l y less than the s ighted birds (179.4g). 72 Such a large d i f f e rence in feed requirements suggests d i f f e rences in the u t i l i z a t i o n o f feed by the two genotypes. Of the d i f f e rences exh ib i ted by the two genotypes in the amount of feed taken, a substant ia l amount of which could be a t t r ibu ted to feed sp i l l age with more sp i l l age by the s ighted b i rds than by the b l i nd ones. Arbi (1978) reported reduced feed s p i l l a g e by hens wearing specs p a r t i c u l a r l y when the feed troughs were f i l l e d . He a lso not iced that sp i l l age by the control hens i n - creased with an increase in the amount o f feed placed in the feed troughs. Observations from th i s experiment supported A r b i ' s f i n d i n g s . Sighted birds were observed f requent ly to scratch and s p i l l feed out o f troughs lead ing to feed wastage. Such behavior was r a r e l y observed in the b l i nd ch ickens . There- f o r e , feed s p i l l a g e could account fo r part o f the va r i a t i on in the amount o f required feed between the two genotypes. Flock s i z e was a s i g n i f i c a n t f ac to r i n a f f e c t i n g the amount o f feed taken from the feed troughs. Dai ly feed requirement per b i rd in the small f lock was higher compared to large f lock (see Table 5 and a lso l a t e r d i scuss ion on e f f e c t s o f f lock s i z e on performance). The i n t e r a c t i on term GXF for required feed was a lso found to be s i g n i f i c a n t (P<0.05). Although b l ind chickens took s i g n i f i c a n t l y l ess feed than s ighted ones i n both the small and large f lock s i t u a t i o n s , the d i f f e rence in feed taken between the two genotypes was much bigger in small f locks s i t u a t i o n than in the large f locks s i t u a t i o n . Al-Rawi et al_. (1976) stated that genotype X housing environment in te rac t ions are l i k e l y to be detected when s t ra ins amd environments great ly a f f e c t p roduc t i v i t y . The l a rges t amount o f feed taken per b i rd by the s ighted chickens associated with small f l ocks may be a t t r ibu ted to greater feed sp i l l age and a lso higher 73 consumption per b i r d . Previous research ind ica ted that when bi rds were housed s ing l y they ate s i g n i f i c a n t l y more feeid than those housed 3 to a group (Jensen et a]_., 1976) , and 2 b i rds per group consumed s i g n i f i c a n t l y higher feed compared to 3 birds per group (Ouart and Adams, 1982). Therefore increased feed sp i l l age and increased feed consumption by the s ighted chickens in small f locks may be responsib le fo r the s i g n i f i c a n t increase in amount o f feed taken from the t rough. At th i s po in t , i t should be pointed out that body weight gains of the b l ind and s ighted chickens during the experimental period were not s i g n i f i c a n t l y d i f f e r e n t . Nor did the body weight measured j u s t p r i o r to the s t a r t o f the experiment s i g n i f i c a n t l y d i f f e r between the two genotypes. The Analys is of Covariance a lso demonstrated that there was no s i g n i f i c a n t regress ion o f body weight gain on i n i t i a l body weight. Although i t i s v a l i d to an t i c ipa te that s ighted chickens w i l l put on more weight than the b l ind ones due to a higher feed consumption and less egg mass output , th is was not r e f l e c t ed in the r e s u l t s . Emmans (1974) demonstrated that the energy required for growth and egg production not only depends on the energy contents of the weight gain and egg produced but a lso on the e f f i c i e n c y with which d i e ta r y energy is converted to carcass and egg mass. 3. Statement number 3 ' Higher a c t i v i t y leve l and feather damages in f locks o f s ighted chickens lead to higher energy cost not re la ted to p roduc t i v i t y . ' Although feed s p i l l a g e could be a f ac to r cont r ibut ing to the d i f f e rence in feed requirements between the two genotypes, the impact o f soc ia l i n te rac t ion and s t ress i s a lso important. This i s r e f l e c t ed in the amount of increased 74 soc i a l a c t i v i t y shown by sighted birds as evidenced from higher pecking damages (Table 14) to the combs of b irds in th i s group. Wennrich (1974) stated that pecking in chickens is usua l l y d i rec ted at the head o f the i n d i v i d u a l s . When roosters grasp hens in a mating attempt, they a lso grasp hens by the comb or by the back o f the head. Thus the combs of the birds are a f fec ted the most. Aga in , when a b i rd pecks another b i r d , the l a t t e r t r i e s to escape or f i g h t . This leads to increased b i rd movement (Hughes and B lack, 1974). Behavioral observations on the same experimental b i rds in th i s study by Cheng (unpublished data) a l so demonstrated that there were s i g n i f i c a n t l y more soc i a l i n te rac t ions by s ighted b i rds compared to b l i nd ones. Wilson et al_. (1959) demonstrated that any kind o f physical a c t i v i t y increases energy expenditure. Although such energy expenditure may vary cons iderab ly , i t represents a substant ia l proport ion o f maintenance requirements (Morrison and Leeson, 1978) and i s usua l l y 50% of the basal metabolism (Card and Nesheim, 1967). It i s therefore l og i c a l to assume that more a c t i v i t y in the s ighted birds was accompanied by higher energy expenditure which, in t u r n , . l e d to higher feed consumption to compensate for the extra energy expenditure. In add i t ion to a s i g n i f i c a n t genotype e f f e c t fo r comb damage scores , there were a lso s i g n i f i c a n t GXD and GXF in te rac t ions observed for th i s t r a i t . Sighted birds in high dens i ty condi t ions had higher comb damages than in low dens i ty cond i t i ons . B l ind ch ickens , however, were not a f fec ted by a change in dens i t y . This GXD s i g n i f i c a n t i n t e rac t i on might have rendered the main densi ty e f f e c t non-s ign i f i c an t . Al-Rawi and Craig (1975) and Pol ley et al_. (1974) observed increased soc ia l in te rac t ions as area per b i rd decreased. A l a t e r study (Simmonsen et a l_ . , 1980) a lso confirmed the same tendencies . The r i s e 75 in soc ia l a c t i v i t i e s (as evidenced from higher comb damage scores due to i n - creased densi ty observed in the present experiment) o f . s i gh ted birds may pre - sumably be assoc iated with increased physical contact because o f reduced i n - d iv idua l d i s t ances . A s i g n i f i c a n t GXF i n te rac t i on observed fo r th i s t r a i t (Table 16) ind ica ted tha t , although sighted birds had more soc i a l i n te rac t ions than b l ind b i r d s , both s ighted and b l ind chickens had higher a c t i v i t y l e ve l s in large f locks compared to small f l o c k s . However the d i f f e rence between s ighted and b l ind birds was much bigger in la rge f locks than in small f l o c k s . Al-Rawi et a]_. (1976) observed higher agon i s t i c behavior in groups of 8 and 14 birds compared to 4 b i r d s . Hughes and Black (1974) a lso reported more pecking damages in groups o f 4 b i rds than in groups of 2 b i r d s . Perry (1977) reported that large f locks provide more oppor tun i t ies fo r agon i s t i c behavior than small f l o c k s . S ighted b i r d s , the re fo re , were more a f fec ted by the d i f f e rence in f lock s i z e , because, lack of s ight in b l ind birds hindered intense soc ia l i n t e r a c t i o n s . The d i f f e rence in the amount o f feather loss as evidenced in th i s ex- periment (see Table 14 and a lso Figures 2, 3 and 4) could be another reason fo r the va r i a t i on in feed requirements o f the two genotypes. Feather loss was f a r more severe in s ighted b i rds compared to b l i nd b i r d s . P r a c t i c a l l y , by the end of the experiment, a l l b l ind birds were s t i l l f u l l y feathered. Emmans and Charles (1976) reported that heat loss from exposed surface under extensive feather loss may be up to 40% more than f u l l y feathered hens. Lee et al_. (1983) found that when hens were defeathered they had s i g n i f i c a n t l y higher heat loss compared to f u l l y feathered hens. Another study using naked 76 neck (na/na) fowls (Touchburn et aj_., 1980) observed i n f e r i o r thermochemical e f f i c i e n c y in these b i rds compared to normal feathered ones. S t i l l another report (Ernst and Boas, 1933) ind ica ted that ' f r i z z l e (F/f or F/F) fowl ' with scanty plumage had a high basal metabolism and increased feed consumption. It i s the re fo re , obvious that more heat was l o s t from exposed surface of the s ighted birds compared to b l ind ones. The extra heat loss by the s ighted birds must therefore be compensated by increase in feed consumption. Leeson and Morrison (1978) a lso stated that poor feather cover is associated with i n - creased feed consumption to compensate for extra heat l o s s . It has been demonstrated that hens wearing specs had higher egg pro- duct ion and lower feed consumption than cont ro l s (Cumming and Epps, 1976 and A r b i , 1978). These authors concluded that the phenomenon was pa r t l y because o f reduced incidence o f s t r e s s fu l s i tua t i ons encountered by hens wearing specs Wells and Wright (1971) suggested that regardless o f feather cover , s t r e s s fu l s i tua t ions could a lso a l t e r thermoregulatory responses in chickens and render them less e f f i c i e n t . It i s not conc lus ive whether in th i s study, the sighted birds experienced more s t ress than the b l ind ones. Circumstant ia l ev idence, however, ind ica tes that th i s may be true because sighted birds suf fered more skin and feather damages than b l ind b i r d s . The d i f f e rence could be even more d ras t i c had pine ta r not been appl ied to a l l wounds caused by pecking in order to avoid unnecessary su f f e r i ng by the experimental b i r d s . Pine tar tends to deter fur ther pecking on the wounds because of i t s b i t t e r t a s t e . Despite th i s remedy, three b i rds from the s ighted groups died because o f pecking i n j u r i e s dur ing the experiment but none from the b l ind groups d i e d . There was no s i g n i f i c a n t d i f f e rence between the two genotypes in leukocyte count, adrenal 77 weight and plasma cor t i cos te rone leve l . However, the means fo r adrenal weight and plasma cor t i cos terone leve l were both lower for the b l ind genotype. Each o f the four fac tors taken separate ly may not be meaningful , but taken ' together , they ind ica te that the sighted birds were under more s t ress than the b l ind ch ickens . Although u n l i k e l y , the gene ' r c ' could a lso be causing d i f ferences in feed requirements o f the two genotypes through gene act ions other than those causing bl indness in the homozygotes. Di f ferences in feed u t i l i z a t i o n because o f s ing le gene d i f fe rences has been observed by Merat et al_. (1979). Their white hens ( I / i , I/I) consumed s i g n i f i c a n t l y l ess feed compared to coloured hens ( i / i ) . Although i t i s not f a i r to compare the resu l t s o f th i s study with that of Merat et a]_. (because o f a lack o f s i m i l a r i t y in the experimental condi t ions and type o f b i rds used) i t never the less , does ind ica te that genotypic d i f f e rence at one locus could cause a s i g n i f i c a n t va r i a t i on in feed u t i l i z a t i o n through unknown mechanisms. 4. Statement number 4 ' B l i nd chickens may have bet ter feed e f f i c i e n c y than normal chickens. ' Based on arguments presented under the f i r s t three statements, one can conclude that when compared in terms of feed e f f i c i e n c y , b l ind birds were more e f f i c i e n t in using feed . Because, while they consumed less feed they produced higher egg mass. Moreover, there was no d i f f e rence in body weight gain between b l ind and s ighted hens. Further i nd i ca t i on that b l ind birds were u t i l i z i n g feed more e f f i c i e n t l y can be found by examining the body weight gain o f roosters (Table 12). Although the means were not s t a t i s t i c a l l y t e s t ed , b l ind roosters on the average gained more than double in body weight compared to s ighted ones. 78 This ind ica tes that b l ind chickens were e f f i c i e n t converters o f feed into products. However, i t i s worthwhile to fur ther explore the potent ia l of b l ind chickens under modern system of management p r a c t i c e s . 5. Other cons iderat ions Whatever may be the reason fo r higher number o f eggs co l l e c t ed and less amount o f feed taken by the b l ind birds compared to s ighted ones, the former would s t i l l be bene f i c i a l in farm yard s i t u a t i o n s . In a recent review o f 'Global Poul try I ndus t r y 1 , Jasper (1979) reported that changes in the cost of l i v i n g and other fac tors have rev i ved , to a small degree, the backyard f l o c k . As a matter o f f a c t , many developing countr ies o f A s i a , South America and A f r i c a have not developed an in tens ive and modernized poul t ry indus t ry . In those countr ies pou l t ry i s predominantly a backyard en te rp r i s e . Under those condi t ions b l ind birds would be more economical , because other things being equa l , the farmers would s t i l l c o l l e c t more eggs for l ess feed compared to sighted ones. II. Addi t ional observat ions from experiment 1. F e r t i l i t y A p a r t i c u l a r behavior or component of a behavior exhib i ted by an animal i s considered i t s phenotype. As such, i t i s a f fec ted by both genetic and en- vironmental f a c t o r s . Learning usua l l y involve the in te rac t ions o f both the aud i tory and v i sua l moda l i t i e s . B l ind animals can be useful fo r studying l e a r n - ing in animals., because they al low the experimenter to hold constant the sensory input from one modality while studying the other . A thorough search in the l i t e r a t u r e has f a i l e d to turn up with any 79 instances of previous research dea l ing with mating behavior of gene t i c a l l y b l ind animals. This could be due to lack of a v a i l a b i l i t y of experimental animals which are gene t i ca l l y b l i n d . The b l ind chickens used in th i s ex- periment would provide a good opportunity to study such behavioral pa t te rns . Previous casual observat ions (Cheng, personal communication) o f b l ind chickens d id not ind ica te that b l ind birds could mate success fu l l y under natural mating s i t u a t i o n s . For propagation o f th i s l i n e a r t i f i c i a l insemination was used. From Cheng's observat ions , i t i s an t i c ipa ted that very low or no f e r t i l i t y could be expected through natural mating from b l ind b i r d s . Contrary to th i s expec ta t ion , the resu l t s obtained in the present study were s u r p r i s i n g . Percent f e r t i l i t y of eggs from the b l ind chickens was 48.2% compared to 84.2% for the s ighted birds (Table 3) . Adams et a]_. (1978) reported the f e r t i l i t y o f two s t ra ins of White Leghorns (normal v i s ion ) kept with a male to female r a t i o of 1:10 to be 48.7% and 36.2% r e spec t i v e l y . Under th i s p a r t i c u l a r s i t u a t i o n , the performance o f b l ind chickens in the present study was not too much out o f l i n e in comparison. Moreover, f e r t i l i t y of eggs from d i f f e r e n t pens o f the b l ind birds var ied cons iderab ly . The f e r t i l i t y o f eggs from one pa r t i cu l a r pen (Pen A3 low density-smal l f l ock ) was 85% during the f i r s t period (8-17 days) , 92% during the second period (28-37 days) and 100% during the t h i r d period (48-57 days ) . F e r t i l i t y from a pen of s ighted birds under the same condit ions was only 64.4%, 78.3% and 77.3% respec t i ve l y for the f i r s t , second and th i rd per iods . However, f e r t i l i t y o f eggs from b l ind birds was usua l ly lower than from sighted b i r d s . In one pa r t i cu l a r pen (pen B2, high density-small f lock ) f e r t i l i t y was 0% throughout the experiment. 80 As evidenced from the resu l t s (see page 55). f e r t i l i t y in d i f f e r e n t periods increased over t ime. In the f i r s t pe r i od , the mean f e r t i l i t y of s ighted and b l i nd birds was 50.9%, in the second, 71.1% and in the th i rd 79.1%. These increases in f e r t i l i t y may be a t t r ibu ted to l ea rn ing experience o f the roos te r s . Adams et aj_. (1978) a lso reported higher f e r t i l i t y from experienced males com- pared to inexperienced males. The v a r i a b i l i t y observed fo r f e r t i l i t y parameter among b l ind birds in d i f f e r e n t pens, r e f l e c t that b l ind roosters may vary cons iderably i n l ea rn ing a b i l i t y to suc ces s fu l l y mount females. As ev idenced, some could learn more qu ick ly than o thers . Therefore , i t would be o f i n t e res t to (a) examine s i tua t ions where successfu l mating can be enhanced and (b) determine whether frequency of successful mating can be increased through se l e c t i v e breeding. Observations in th i s experiment ind ica te that the b l ind chicken would be a good model fo r behavioral s tud i e s . 2. Flock s i ze and densi ty Most o f the e a r l i e r studies invo lv ing b i rd densi ty and f lock s i ze were not well designed to separate the e f fec ts of these two f a c t o r s . Hughes (1975) reviewed a wide range o f l i t e r a t u r e dea l ing with ' s tock ing dens i t y ' and stated that much o f the e a r l i e r work was poor ly designed in that i t mostly confounded colony s i z e (number o f b irds per cage) and area per b i r d . More recent s tudies have attempted to separate the e f f ec t s o f these two fac tors but l i t t l e emphasis have been given on the importance o f in te rac t ions invo l v ing these two fac tors (Adams and Jackson, 1970; Al-Rawi et a l_ . , 1976; Perry, 1977). In view of the above f a c t s , th i s study was planned in an attempt to separate the e f f ec t s of f lock s i ze and b i rd densi ty upon the parameters measured and a lso to examine 81 the in te rac t ion between these two f a c t o r s . Flock s i ze s i g n i f i c a n t l y a f fec ted some of the parameters s tud ied . Percent hen-day egg production was s i g n i f i c a n t l y higher (P<0.05) in small f locks compared to large f l o c k s . Higher egg production obtained from the small f locks confirmed the work o f Al-Rawi et al_. (1976) who, working with group s izes o f 4, 8 and 14 birds per group, found lowest production rate in group s i ze o f 14. Production dec l ined as group s i ze increased . S imi la r r esu l t s on group s i ze e f f e c t can be found in H i l l and Binns (1973) and Aitken et al_. (1973). No explanat ion however, was provided by these authors for such r e s u l t s . The e f f e c t o f f lock s i z e on feed consumption, body weight gain and comb damage (pecking a c t i v i t y ) o f the experimental birds were h igh ly s i g n i f i c a n t (P<0.001). B irds i n small f locks had higher feed in take , gained more weight, and less comb damages. A higher feed requirement by birds in small f locks could be accounted fo r increases in the number o f to ta l co l l e c t ab l e eggs and higher body weight ga in . How much of th i s excess feed consumption in small f l bck was accounted fo r by increases i n egg number and body weight gain was not quant i tated in th i s study. However, previous research ind ica ted that feed consumption de- creases as b i rd number per group increases (eg. Jensen ejt a]_., 1976; Ouart and Adams, 1982). Higher body weight gain by birds in the small f locks as observed in t h i s study is in agreement with that o f Cunningham and Ostrander (1982). These authors found s i g n i f i c a n t l y higher body weight gain in groups o f 4 birds compared to 5 b i r d s . From the i r r esu l t s i t appeared that body weight gain could be re la ted to group s i z e . The present study with a bigger d i f f e rence in group s izes (5 vs 20) confirmed Cunningham and Ostrander 's f i nd i ngs . S i g n i f i c a n t l y higher comb 82 damage in the large f locks ind ica ted higher agon i s t i c and sexual a c t i v i t i e s in those f l o c k s . Al-Rawi and Craig (1975) observed a pos i t i v e r e l a t i onsh ip between group s i ze and ind i v idua l frequencies o f aggression with f locks o f 4, 8, 14 and 28 b i r d s . The leve l of aggression var ied d i r e c t l y with group s i ze and was most ev ident dur ing feeding t ime. Therefore , i t i s poss ib le that feeding in te r rupt ions occur under those condi t ions more f requent ly i n la rge f locks than in small f l o c k s . Due to a reduced in te r rup t ion in f eed ing , b irds in small group s izes have the opportunity to eat more and perform be t te r . Flock s i ze was not only the fac to r which a f fec ted these t r a i t s , dens i ty a lso played a s i g n i f i c a n t r o l e . Although densi ty as a main fac to r was not s i g n i f i c a n t in any case , 4 out of 9 parameters studied showed s i g n i f i c a n t in te rac t ions invo l v ing densi ty as a f a c to r . A s i g n i f i c a n t GXD i n t e r a c t i on fo r comb damage scores has a l ready been discussed .:. e a r l i e r (see page 74 ) . Aside from th i s i n t e r a c t i o n , a l l others were invo lv ing dens i ty and f lock s i z e . S i g n i f i c a n t DXF in te rac t ions were observed for egg weight, feed consumption and body weight ga in . In a l l o f these in te rac t ions a general and convincing trend was not iced in that small f locks in low densi ty took the highest f eed , had the heaviest egg weight and had the most gain i n body weight. On the other hand, for large f locks in low dens i t y , the resu l t s were the opposite (Table 8, 10 and 11). The d i f f e rences exh ib i ted by these two f lock s izes in low and high densi ty s i t ua t i ons were greater in low dens i ty than in high dens i t y . From these resu l t s i t could be concluded that f lock s i ze as a f ac to r i s not as important in high dens i ty as in low dens i t y . Therefore , i t could be suggested that when birds are to be housed in low densi ty they should be housed in small group s i z e s . The above d iscuss ions emphasised the need o f examining in te rac t ions in 83 a f a c t o r i a l experiment l i k e the present one for a v a l i d i n t e rp re ta t i on o f the e f f e c t o f each fac to r invo lved . For example, in th is study, i f the in te rac t ions between genotype and dens i ty or densi ty and f lock s i ze were not examined and separated from the main e f f e c t s , the resu l t s could be mis in terpreted because these in te rac t ions masked the s i gn i f i c ance o f dens i ty as a main e f f e c t . How- ever , there could be other reasons fo r densi ty e f f e c t being not s i g n i f i c a n t . It may be that the two dens i t i e s used in th i s experiment were not d i f f e r e n t enough to cause a c l ea r separat ion o f densi ty e f f e c t s . The sample s izes used were often quite small leading to greater sampling va r i a t ions r e f l e c t ed in the higher standard dev iat ions for most t r a i t s (Table 4).~ 84 SUMMARY The impact o f v isua l contact or lack o f i t was accessed i n two genetic groups o f chickens maintained at the Avain Genetics Laboratory o f the Un ivers i ty of B r i t i s h Columbia. Each of the two genotypic groups (s ighted and b l ind) were reared in two f l o o r dens i t i e s and two f lock s i z e s . A tota l of nine parameters was measured to compare the r e l a t i v e performance of each genetic group under these experimental cond i t i ons . Although i t was o r i g i n a l l y suspected that bl indness w i l l i n t e r f e r e with feeding and other maintenance p r a c t i c e s , there was no such i nd i ca t i on from data co l l e c t ed in th is experiment. Moreover, b l ind birds performed better than sighted ones in the number of to ta l c o l l e c t a b l e eggs and had lower feed requirements while body weight gain was s i m i l a r . Total egg mass output was a lso higher in b l ind b i r d s . A l l these fac tors in combinations ind ica ted that b l i nd b i rds were more e f f i c i e n t in u t i l i z i n g feed fo r body weight gains and egg product ion . From other parameters measured in th i s experiment, poss ib le reasons fo r the better performance in b l ind chickens can be o f f e r ed . Although s ighted birds were apparent ly breaking and eat ing eggs more f requent ly than b l ind ones, the d i f f e rence in number of eggs co l l e c t ed cannot be t o t a l l y a t t r ibu ted to th i s f a c t o r . Rather, s ighted birds may be u t i l i z i n g more energy fo r other purposes than egg product ion , because, they were seemingly more act ive and may a lso be under more s t ress compared to b l ind b i r d s . Though no conc lus ive evidence to support th i s c la im can be der ived from th i s experiment, the s ighted birds were observed to su f f e r more feather and sk in damages than b l ind b i r d s . In a d d i t i o n , although not s t a t i s c a l l y s i g n i f i c a n t , mean adrenal weight and cor t i cos te rone 85 l eve l for s ighted birds were higher than b l ind ones. Higher amount o f feed taken from the feed troughs by the s ighted birds was pa r t l y due to feed s p i l l a g e and pa r t l y due to increased a c t i v i t y leve l in that group. Another poss ib le reason for higher feed requirements by the sighted chickens could be a t t r ibu ted to increased skin and feather damages. Under those s i t u a t i o n s , heat losses from exposed surface o f the bared sk in would i n - crease energy requirement. Although f e r t i l i t y from natural mating was much lower in b l ind birds com- pared with s ighted ones, and may be considered as an adverse e f f e c t due to the lack of s i g h t , i t was su rp r i s i ng that they did show successful mating behavior and learned how to mount females. These b l ind birds could be useful animal models fo r studying l ea rn ing behavior in those aspects such as feed ing , d r i nk - i n g , r es t ing and reproduct ive behaviors . Under the condi t ions o f the experiment, the resu l t s obtained suggest that b l ind birds were at l eas t as good as or better than s ighted b i rds in terms o f e f f i c i e n c y in feed convers ion. It could therefore be concluded that lack of s ight did not i n t e r f e r e with feeding and other maintenance processes (except mating behav ior ) . Therefore , the nul l hypothesis that ' l a ck o f s i gh t w i l l i n - t e r fe re with feeding and other maintenance processes which may i n t e r f e re with the normal performance o f the b i rd s ' can be r e j e c t ed . 86 REFERENCES Abplanalp, H . , and I.L. Kos in , 1953. Genetic va r i a t i on o f f e r t i l i t y and ha t chab i l i t y in the Broad Breasted Bronze turkey. Poultry S c i . 32: 321-322. Adams, A.W., J . V . C r a i g , and L. Bhagwat, 1978. E f fec ts o f f lock s i z e , age at housing and mating experience on two s t ra ins of egg-type chickens in colony cages. Poultry S c i . 57:48-53. 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Analys is of Variance for percent hen-day egg p roduc t ion 1 of experimental birds Source df SS MS Rep l i ca t ion 1 889.58 889.58 4.54 Genotype (G) 1 1715.40 1715.40 8.75* Density (D) 1 7.83 7.83 0.04 Flock s i z e (F) 1 919.35 919.35 4.69 GXD 1 202.26 202.26 1.03 GXF 2 1 0.00 0.00 0.00 DXF 1 8.61 8.61 0.04 GXDXF 1 284.65 284.65 1.45 Error 1 7 1372.20 196.03 Week (W) 7 12182.00 1740.30 20.35* WXG 7 358.12 51.16 0.60 WXD 7 597.06 85.30 1.00 WXF 7 390.18 55.74 0.65 WXGXD 7 144.65 20.66 0.24 WXGXF 7 643.15 91.88 1.07 WXDXF 7 209.24 ' 29.89 0.35 Error 2 63 5386.70 85.50 Total 127 25311.00 1 A rcs in transformation appl ied to the data before a n a l y s i s . 2 SS i s equal to 0.0032. *P<0.05 ***P< 0.001 103 Table 18. Analys is of Variance for percent hen-day egg p roduc t ion 1 o f experimental b irds with adjustment for age d i f f e rences between r ep l i c a t i ons Source df SS MS F Rep l i ca t ion 1 67.55 67.55 0.65 Genotype (G) 1 875.74 875.74 8.39* Density (D) 1 159.62 159.62 1.53 Flock s i ze (F) 1 734.22 734.22 7.04* GXD 1 14.92 14.92 0.14 GXF 1 0.03 0.03 0.00 DXF 1 7.35 7.35 0.07 GXDXF 1 180.48 180.48 1.73 Error 1 7 730.29 104.33 Week (W) 5 4762.80 952.55 22.44*** WXG 5 314.94 62.99 1.48 WXD 5 226.13 45.23 1.07 WXF 5 214.34 42.87 1.01 WXGXD 5 242.15 48.43 1.14 WXGXF 5 219.01 43.80 1.03 WXDXF 5 40.06 8.01 0.19 Error 2 45 1910.40 42.45 Total 95 10700.00 1 Arcs in transformation appl ied to the data before ana l y s i s . *P<0.05 ***P< 0.001 104 Table 19. Apparent mean percent hen-day egg product ion , egg weight.(g,<> and apparent feed-requirements ( g ) o f birds with adjustment for age d i f fe rences o f birds between r ep l i c a t i ons Factor Egg production Egg weight Feed requirements F i r s t 52 .3±4.4 46.07±2.98 155.6+30 Rep l i ca t ion Second 55.2±2.3 27.68+3.38 163.U38 Di f ference 2.9 1.66* 8.0 • Sighted 48 .4±4 .3 47.2U3.67 182.8±31 Genotype B l ind 58 .9±2.1 46.54±2.80 136.0±16 Di f ference 9.5* 0.67 48 . 8 * * * High 57.7±4.0 46.42±2.81 156.1+27 Density Low 51.4±2.7 47.33±3.64 162.6140 Dif ference 6.3 0.91 3.9 Small 58 .5±3.8 46 .95±3.76 174.5137 Flock s i ze Large 48.9±2.6 46".80±2.72 144.2123 Di f ference 9.6* 0.15 30 . 0 * * * *P<0.05 ***P< 0.001 105 Table 20. Ana lys is o f Variance for egg weight o f experimental b irds Source df SS MS F Rep l i ca t ion 1- 132.57 132.57 14.41** Genotype (G) 1 18.41 18.41 2.00 Density (D) 1 21.12 21.12 2.30 Flock s i ze (F) 1 1.50 1.50 0.16 GXD 1 18.73 18.73 2.04 GXF 1 1.39 1.39 0.15 DXF 1 138.73 138.73 15.08*** GXDXF 1 6.99 6.99 0.76 Error 1 7 64.42 9.20 Week (W) 7 1908.70 272.68 108.69*** WXG 7 24.44 3.49 1.39 WXD 7 21.42 3.06 1.22 WXF 7 11.67 1.67 0.66 WXGXD 7 7.67 1.10 0.44 WXGXF 7 8.68 1.24 0.49 WXDXF 7 23.40 3.34 1.33 Error 2 63 158.06 2.51 Total 127 2567.90 **P< 0.01 ***P< 0.001 106 Table 21. Ana lys is o f Variance fo r egg weight o f experimental b irds with adjustment for age d i f f e rence between r ep l i c a t i ons Source df SS MS F Rep l i ca t ion ! 61.99 61.99 7.00* Genotype (G) 1 10.83 10.83 1.22 Density (D) 1 19.64 19.64 2.22 Flock s i ze (F) 1 0.50 0.50 0.06 GXD 1 10.02 10.02 1.13 GXF 1 2.98 2.98 0.34 DXF 1 125.17 125.17 14.13** GXDXF 1 4.38 4.38 0.49 Error 1 7 62.00 8.86 Week (W) 5 594.90 118.98 73.12*** WXG 5 5.15 1.03 0.63 WXD 5 16.35 3.27 2.01 WXF 5 13.90 2.78 1.71 WXGXD 5 3.22 0.64 0.40 WXGXF 5 2.87 0.57 0.35 WXDXF 5 7.60 1.52 0.93 Error 2 45 73.23 1.63 Total 95 1014.70 *P<0.05 **P=0.01 ***Pc 0.001 107 Table 22. Analys is of Variance for amount of feed taken from feed troughs by experimental birds Source df SS MS F Repl i ca t ion ! 0.00040 0.00040 3.65 Genotype (G) 1 0.00778 0.00778 71.42*** Density (D) 1 0.00014 0.00014 1.33 Flock s i ze (F) 1 0.00423 0.00423 38.84*** GXD 1 0.00004 0.00004 0.34 GXF 1 0.00064 0.00064 5.89* DXF 1 0.00075 0.00075 6.93* GXDXF 1 0.00017 0.00017 1.55 Er ror 7 0.00076 0.00011 Total 15 0.01491 *P<0.05 ***P<0.001 108 Table 23. Analys is of Variance for amount of feed taken from feed troughs by experimental b irds with adjustment fo r age d i f f e rences be- tween r ep l i c a t i ons Source df SS MS F Rep l ica t ion ! 0.0013 0.0013 1.69 Genotype (G) 1 0.0525 0.0525 66.67*** Density (D) 1 0.0010 0.0010 1.27 Flock s i z e (F) 1 0.0220 0.0220 27.94*** GXD 1 0.0003 0.0003 0.36 GXF 1 0.0033 0.0033 4.16 DXF 1 0.0051 0.0051 6.51* GXDXF 1 0.0014 0.0014 1.76 Error 1 7 0.0055 0.0008 Week (W) 5 0.0013 0.0003 1.10 WXG 5 0.0012 0.0002 0.98 WXD 5 0.0006 0.0001 0.51 WXF 5 0.0009 0.0002 0.74 WXGXD 5 0.0007 0.0001 0.56 WXGXF 5 0.0004 0.0001 0.33 WXDXF 5 0.0012 0.0002 1.00 Error 2 45 0.0108 0.0002 Total 95 0.1095 *P<0.05 ***P< 0.001 109 Table 24. Analys is of Covariance for body weight gain of experimental hens Source df SS MS F Rep l i ca t ion ! 346320 346320 13.43*** Genotype (G) 1 1586 1586 0.06 Density (D) 1 769 769 0.03 Flock s i ze (F) 1 282400 282400 10.95** GXD 1 11900 11900 0.46 GXF 1 478 478 0.02 DXF 1 220510 220510 8.55** GXDXF 1 63623 63623 2.47 Er ror 54 1392700 25792 Total 62 2320286 **P<0.01 ***P< 0.001 110 Table 25 . Ana lys is o f Variance for i n i t i a l 1 body weight of experimental hens Source df SS MS F Rep l i ca t ion 1 2197.3 2197.3 0.06 Genotype (G) 1 84463.0 84463.0 2.36 Density (D) 1 21572.0 21572.0 0.60 Flock s i z e (F) 1 7119.1 7119.1 0.20 GXD 1 5166.0 5166.0 0.14 GXF 1 11963.0 11963.0 0.33 DXF 1 10635.0 10635.0 0.30 GXDXF 1 530170,0 530170.0 14.83*** Error 55 1966500.0 35754.0 Total 63 2639800.0 1 Body weight taken before s t a r t of experiment. ***P<0.001 I l l Table 26- Analys is of Var ance for percent f e r t i l i t y 1 o f experimental birds Source df SS MS F Rep l i ca t ion ! 1364.60 1364.60 1.54 Genotype (G) 1 6151.50 6151.50 6.93* Density (G) 1 1294.30 1294.30 1.46 Flock s i ze (F) 1 383.92 383.92 0.53 GXD 1 1203.10 1203.10 0.28 GXF 1 2.75 2.75 0.00 DXF 1 303.36 303.36 0.34 GXDXF 1 367.47 367.47 0.41 Error 1 7 6216.40 888.06 Period (P) 2 2524.90 1262.50 9.36** PXG 2 312.32 156.16 1.16 PXD 2 344.44 172.22 1.28 PXF 2 100.77 50.39 0.37 PXGXD 2 107.10 53.55 0.40 PXGXF 2 101.24 50.62 0.38 PXDXF 2 449.57 224.79 1.67 Error 2 18 2428.60 134.92 Total 47 23656.00 1 A rcs in transformation appl ied to the data before a n a l y s i s . *P<0.05 **P<0.01 112 Table 2 7 . Analys is o f Variance fo r leukocyte count o f experimental hens Source df SS MS F • Repl i c a t i on 1 65675000 65675000 3.07 Genotype (G) 1 13443000 13443000 0.63 Density (D) 1 2847700 2847700 0.13 Flock s i ze (F) 1 21199000 21199000 0.99 GXD 1 5299200 5299200 0.25 GXF 1 101460000 101460000 4.74* DXF 1 22069000 22069000 1.03 GXDXF 1 12105000 12105000 0.57 Error 55 1177100000 21403000 Total 63 1421200000 *P< 0.05 113 Table 2 8 . Analys is of Variance for adrenal weight of experimental hens Source df SS MS F Rep l i ca t ion 1 1.5252 1.5252 0.68 Genotype (G) 1 5.9231 5.9231 2.65 Density (D) 1 0.5123 0.5123 0.23 Flock s i ze (F) 1 3.6864 3.6864 1.65 GXD 1 0.0030 0.0030 0.00 GXF 1 0.2207 0.2207 0.10 DXF 1 0.1189 0.1189 0.05 GXDXF 1 0.0007 0.0007 0.00 Error 55 123.1300 2.2388 Total 63 135.1200 114 Table 2 9 . Analys is o f Var iance fo r plasma concentrat ion o f cor t i cos terone of experimental b irds Source df SS MS Rep l i ca t ion 1 0.2771 0.2771 0.62 Genotype (G) 1 0.6344 0.6344 1.42 Density (D) 1 0.7940 0.7940 1.77 Flock s i ze (F) 1 0.0854 0.0854 0.19 GXD 1 0.8137 0.8137 1.82 GXF 1 1.0848 1.0848 2.42 DXF 1 0.0001 0.0001 0.00 GXDXF 1 0.0100 0.0100 0.02 Error 71 31.8070 0.4480 Total 79 35.5060

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