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Genetic evaluation of egg mass and egg component traits in 3 lines of domestic fowl Jain, Genda Lal 1971

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A GENETIC EVALUATION OF EGG MASS AND EGG COMPONENT TRAITS IN 3 LINES OF DOMESTIC FOWL . by GENDA LAL JAIN B,Sc.(Agr,), Rajasthan U n i v e r s i t y , 1962 M.Sc.(Poultry Science), Punjab A g r i c u l t u r a l U n i v e r s i t y , I966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF'PHILOSOPHY i n the Department of Poultry Science We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July, .1971 In present ing t h i s thes is in p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L ib ra ry s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I fu r ther agree that permission for extensive copying o f th is thes is fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representa t ives . It i s understood that copying or p u b l i c a t i o n o f t h i s thes is fo r f i n a n c i a l gain sha l l not be allowed without my wr i t ten permiss ion . Department of ; POULTRY SCIENCE The Un ive rs i t y of B r i t i s h Columbia Vancouver 8, Canada Date July 19, 1971 A B S T R A C T A study was conducted to make a genetic evaluation of egg mass (weight of the total eggs laid in a given period) in order to deter/nine its genetic potential as a new criterion for selection as compared to the conventional selection program based on egg number (early and f u l l production records). In addition, biometrical evaluations of some egg component traits: yolk weight, albumen weight, shell weight, percent yolk, percent albumen, percent shell, albumen percent solid, yolk percent solid, yolk percent protein, albumen percent protein, yolk solid and albumen solid were made. The aforementioned traits were measured on 3 random bred lines of chickens in quarterly periods through the laying year. :, Within each line, the heritability estimates of egg number and egg mass for any given period (275, 325, 4-50 and 5^0 days of age) were found to be in close agreement. In general, for egg number and egg mass, selection from early production records showed higher gains per unit of time than f u l l year production records, A negative genetic correlation between egg number traits and egg weight traits and a positive genetic correlation between egg mass and egg weight traits was found, therefore, selection for egg mass was recommended. Relative merit of early and f u l l year egg records as selection criterion was discussed in the light of the results obtained for the three lines. It was concluded that the decision as to which criterion should be used would have to depend upon the genetic properties of the population in question. Line effects were found to be significant for a l l the egg component traits studied, except percent shell, A season-age effect was also found to be significant i n a l l the t r a i t s studied. Season-age by sire interactions were found to be non-significant for a l l the t r a t i s in a l l the three lin e s . The importance of yolk size from a human nutrition standpoint was discussed. A selection program based on total yolk weight produced by a hen i n a given period (yolk mass) was suggested.. Because of the water in the egg being an essential nutrient for the developing chick embryo, i t was suggested that selection be made on the egg solid or egg solid mass (total amount of solid l a i d by a hen in a given period). The he r i t a b i l i t y estimates of albumen percent solid and albumen percent protein were high and of the same magnitude. It was, therefore, suggested that an increase in percent protein in albumen should be achieved by selection of albumen percent solid. T A B L E O F C O N T E N T S Page LIST OF TABLES v i ACKNOWLEDGEMENTS v l i i INTRODUCTION 1 REVIEW OF LITERATURE ^ Egg Production T r a i t s 3 H e r i t a b i l i t y 3 S e l e c t i o n on the Basis of Part Records 5 Egg Component T r a i t s 8 Season-Age E f f e c t 9 Phenotypic C o r r e l a t i o n 10 H e r i t a b i l i t y and Genetic Correlations 11 MATERIAL'S AND METHODS 13 Egg Production T r a i t s 13 Egg Component T r a i t s 14 Percent S o l i d Determination 15 Procedure Used f o r Proitein Determination 16 Protein Determination 17 . Albumen 17 Yolk 17 STATISTICAL METHODS 19 Fixed E f f e c t s 19 Egg Production T r a i t s 19 Egg Component T r a i t s 19 H e r i t a b i l i t y and Genetic C o r r e l a t i o n 21 R e l a t i v e Se l e c t i o n E f f i c i e n c y Th RESULTS AND DISCUSSION 25 Egg Production T r a i t s 25 Means and Standard Deviations . 25 H e r i t a b i l i t y 25 Genotypic and Phenotypic Correlations 33 Relative E f f i c i e n c y of Different C r i t e r i a of Selection- 40 Egg Component T r a i t s ' 48 Means and Standard Deviations ' 48 Fixed Effects 48 Phenotypic Correlations . 6 0 H e r i t a b i l i t i e s and Genetic Correlations 65 SUMMARY AND CONCLUSION ' 80 Egg Production T r a i t s 80 Egg Component T r a i t s 82 BIBLIOGRAPHY 85 L I S T O F T A B L E S Table ;' page 1 Analyses of Variance f o r the Estimation of S i r e Variance 23 Component. 2 Analyses of Variance f o r the Estimation of Sire'Covariance. 23 Component, 3 Means and Standard Deviations of the Egg Component T r a i t s . 26 k- Summary of Analyses of Variance: 27 Line Differences f o r the Egg Production T r a i t s . 5 . H e r i t a b i l i t y Estimates (h 2) and Standard Er r o r (S.E.) of 28 the Egg Production T r a i t s . 6 S i r e Component of Variance (s) and Progeny Within S i r e 29 (P/s) Variance f o r the Egg Production T r a i t s , 7 The Genotypic (XQ) and the Phenotypic (rp) Correlations of 34-36 the UBC Line f o r the Egg Production T r a i t s . 8 The Genotypic (TQ.) and the Phenotypic ( r p ) Correlations of 37 - 39 the MH Line f o r the Egg Production T r a i t s . '9 R e l a t i v e E f f i c i e n c y (R.E.) of D i f f e r e n t Selection C r i t e r i a 41 (UBC). 10 R e l a t i v e E f f i c i e n c y (R.E.) of D i f f e r e n t S e l e c t i o n C r i t e r i a 42 •(MH). 11 Means and Standard Deviations of Egg Component T r a i t s f o r 49 the 3 Lines. 12 Summary o f the Analyses of Variance: 50 Line and Season-Age E f f e c t on Egg Component T r a i t s . 13 Means f o r the Egg Component T r a i t s f o r Each Season-Age 52 Group (over the 3 Lines), . , 14 Summary of the Analyses of Variance f o r the Egg Component 54-T r a i t s (UBC). 15 Summary of the Analyses of Variance f o r the Egg Component 55 T r a i t s (MH). 16 Summary of the Analyses of Variance f o r the Egg Component 56 T r a i t s (BA). • .17 Means and Standard Deviations f o r the Egg Component Traits.. 57 of the UBC Line f o r the 4 Season-Age Groups. 18 Means and Standard Deviations f o r the Egg Component T r a i t s 58 of the TiH Line f o r the 4 Season-Age Groups. 19 Means and Standard Deviations f o r the Egg Component T r a i t s 59 of the BA Line f o r the 4 Season-Age Groups, 20 Phenotypic Correlations f o r the Egg Component T r a i t s (UBC 6 l and MH L i n e s ) . ' 21 Phenotypic Correlations f o r the Egg Component T r a i t s (BA 62 L i n e ) . 22 Phenotypic Correlations f o r the Egg Component T r a i t s : 63 Those t r a i t s f o r which c o r r e l a t i o n s were found s i g n i f i -c a n t l y d i f f e r e n t f o r the 4 Season-Age Groups. 23 H e r i t a b i l i t y Estimates (h 2) and Standard Errors (S.E.) of 66 Egg Component T r a i t s f o r the 3 Lines, 24 S i r e Component of Variance (s) and Progeny Within S i r e 67 (p/s) Variance f o r the Egg Component T r a i t s . 25a Genotypic and Phenotypic Correlations: 69 Egg Weight with Other Component T r a i t s . 25b Genetic and Phenotypic Correlations: 70 Yolk Weight with Other Component T r a i t s , 25c Genotypic and Phenotypic Correlations: 70 Albumen Weight with Other Component T r a i t s . 25d Genotypic and Phenotypic Correlations: 71 Between Egg Component T r a i t s . 25e Genetic and Phenotypic Correlations: 72 Egg Number with Egg Component T r a i t s , 25f Genotypic and Phenotypic Correlations: 73 Egg Mass with Egg Component T r a i t s , A G K N O W . L E ' D G M . E N T S The author i s g r a t e f u l to Dr. G. W, Roberts who provided supervision, suggestions and f a c i l i t i e s f o r t h i s study. He would a l s o l i k e to express h i s appreciation to Dr. R. G, Peterson and Mr, G. Williams f o r t h e i r valuable discussions. The author wishes to express h i s gratitude to Dr. J . B i e l y f o r h i s encouragement during the course of t h i s study. Appreciation i s also expressed f o r the assistance given by fellow students and the t e c h n i c a l s t a f f , i n p a r t i c u l a r , Mrs. Carol Ann Paulson. Thanks are al s o due to Miss Janet Gehring f o r t r a n s l a t i n g my handwriting i n t o t y p e s c r i p t . This project could not have been undertaken without the encouragement, understanding and continuing patience of my wife Laxmi and sons Sanjay and Ajay, - 1 -I N T R O D U C T I O N The selection for egg production has been mainly confined to the number of eggs a hen lays in a given period. Simultaneous consideration to egg weight and age at sexual maturity has also been given. The egg industry has made considerable progress in terms of egg number. How much of this progress belongs to which discipline of the poultry sciences i s a matter of dispute. But there i s no doubt that in the past the poultry breeder has been able to increase the genetic potentiality of birds to lay more eggs. Nevertheless, the situation in the present day poultry industry seems static. There have been several reports in the literature where authors have reported that their populations have reached a plateau for egg production after selection for a certain number of generations (Yamada et a l . 1958, Mdrris I963 and Nordskog et a l , I967), What appears to be needed in the present poultry breeding industry i s a new platform for the conventional t r a i t s and an investigation of new t r a i t s of economic importance. Today eggs are sold on the basis of number, quality and a weight gradation but the consumers should be made aware of the importance of other t r a i t s . Traits l i k e egg solid and egg protein are of special importance.. Eggs are an excellent source of protein of high biological value and are the major source of animal protein in economically underdeveloped countries. There-fore, any increase in total solids and/or protein content of eggs would be highly desirable in those countries. In this study a biometrical evaluation of egg mass was made in order to determine i t s potential as a new criterion for selection for egg produc-tion, A comparison of the response to selection of egg mass with conven-tional selection criterion such as egg number, egg weight and sexual maturity was also considered. - 2 -In a d d i t i o n , the i n v e s t i g a t i o n of the s u i t a b i l i t y of some egg component t r a i t s f o r s e l e c t i o n was evaluated. The egg component t r a i t s studied were yolk weight, percent yolk, albumen weight, percent albumen, s h e l l weight, percent s h e l l , yolk percent s o l i d , albumen percent s o l i d , yolk percent protein, albumen percent protein, yolk s o l i d and albumen s o l i d . In order to gain an understanding of the genetic d i v e r s i t y of a l l of the aforementioned t r a i t s 3. divergent l i n e s of chickens were u t i l i s e d i n t h i s study. - 3 -R E V I E W O F L I T E R A T U R E EGG PRODUCTION TRAITS  H e r i t a b i l i t y Lush (1940) discussed the h e r i t a b i l i t y of qu a n t i t a t i v e characters and he defined h e r i t a b i l i t y i n a broad and narrovr sense. In the broad sense, h e r i t a b i l i t y r e f e r s to the r a t i o of h e r i t a b l e variance to the t o t a l variance. In the narrow sense, h e r i t a b i l i t y (h^) includes the average e f f e c t of genes transmitted from parents to the progeny or i t may be considered as the r a t i o of a d d i t i v e genetic variance to the t o t a l variance. The p r a c t i c a l a p p l i c a t i o n of the h i e r a r c h a l c l a s s i f i c a t i o n on the basis of Fish e r ' s a n a l y s i s of variance, f o r the estimation o f the h e r i t a b i l i t y , has been made by Hetzer et a l , (1944) and Lerner (1950). A d e t a i l e d pro-cedure f o r estimating the variance component to obtain h e r i t a b i l i t y estimates i n poultry population was given by King and Henderson (1954a),-The a v a i l a b l e l i t e r a t u r e on the inheritance of egg production i s rather voluminous, Munro (1936) was probably the f i r s t to obtain dam-daughter regression average of seve r a l f l o c k s as 0.153; the h e r i t a b i l i t y of egg production being 0.30. Shoffner and Sloan (1948) and Lerner (1950) have reviewed the reported estimates of h e r i t a b i l i t y of egg production. King and Henderson (1954b) have given a mean of 0,31 as the h e r i t a b i l i t y of survivors* egg production which was obtained by a simple average of those reported i n the l i t e r a t u r e . In t h e i r study they obtained a h e r i t a b i l i t y estimate of su r v i v o r s ' egg production as 0.48. Kinney (1969) summarizing selected l i t e r a t u r e gave the following means and ranges of h e r i t a b i l i t y of egg production based on s i r e component of variance1 - 4 -Time Duration Mean Heritability Range Short term (270 days of age, approx.) 0.22 0.02-0.42 Intermediate term (350 days of age, approx.) 0.19 0.11-0.28 Long term (500 days of age, approx.) 0.22 0.02-0.45 However, the heritability estimates found in the literature are of a wider range than reported by Kinney. Wyatt (1954-) estimated the herit-ability of egg production as 0 and Saeki et al . (1959) as 0.66. The reported estimates of heritability of age at sexual maturity and body weight at housing as summarized by Kinney (1969) are as follows: 1. Age at Sexual Maturity Breeds Mean h2 Range a. Light breeds 0.39 0.07-0.90 b. Heavy breeds 0.39 0,06-0.45 2. Body Weight at 24 Weeks of Age Breeds Mean h 2 Range a. Light breeds 0.57 0.32-0.86 b. Heavy breeds 0.53 0.35-0.85 Most of the heritability estimates for egg weight reported in the literature indicate this trait is highly heritable. Thirteen separate estimates from 4 different sources cited by Shoffner and Sloan (19^8) ranged from 0.46 to 0.84. Lerner and Cruden (1951) found egg size to be 60 percent heritable in a flock of White Leghorns. Saeki et a l . (1959) reported that heritability of egg weight for 5 different strains, ranged - 5 -from 0.21 for a strain of White Leghorns to 0.71 for Rhode Island Reds. Baker (i960) presented a very good review on the h e r i t a b i l i t y of egg weight. Waring et a l . (1962) obtained h e r i t a b i l i t y of egg weight for 40, 55 and 65 week old hens as 0.70, 0,77 and 0.4-9 respectively. In his summary on reported h e r i t a b i l i t y estimates, Kinney (1969) presented the following mean and range for h e r i t a b i l i t y of egg weightj 1, Early Egg Weight Breed Mean h2 Range a. Light breeds 0.45 0.15-0.72 b. Heavy breeds 0.57 0.01-0.87 2. Mature Egg Weight Breed . Mean h 2 Range a. Light breeds 0.46 0.09-0.96 b. Heavy breeds O.58 0.20-1.15 Saeki et a l , (1959) were probably the f i r s t to report the he r i t a b i l i t y of egg mass. Their estimates for 5 different lines of chickens were 0.37, 0.17, 0.19, 0.32 and 0.18. Hicks (1963) mentioned that the h e r i t a b i l i t y of egg mass was equivalent to or higher than the h e r i t a b i l i t y of egg number. Waring et a l . (1962) obtained h e r i t a b i l i t y estimates of egg mass in chickens as 0.139, 0.240 and 0.409 for production up to 40, 55 and 65 weeks of age. However, egg mass as determined by these authors was based on 4 days a week trapnest record and mass was calculated by multiplying the number of eggs by an average egg weight. Selection On The Basis Of Part Production Records Dickerson and Hazel (19^4) enunciated a principle which states that the rate of progress (AG) expected under selection would be equal to the intensity . - 6 - . of s e l e c t i o n (z/b) m u l t i p l i e d by the h e r i t a b i l i t y (h 2) and divided by the i n t e r v a l "between generations ( t ) . Their main contention was that the genetic gain from s e l e c t i o n should be evaluated on the basis of the time u n i t , and that the genetic gain per u n i t of time could be increased by reducing the age of the parents, • Dempster and Lerner (194-7) proposed the use of e a r l y egg production records as a s e l e c t i o n c r i t e r i o n f o r Improving annual egg production. This theory was supported by Maddison (1954), Morris (1956) , O l i v e r et a l . (1957), Erasmus (1962) and Van Vleck and D o o l i t t l e (1964). However, the theory of s e l e c t i o n on the basis of ea r l y records has been c r i t i c i s e d by Kraszewska-Domanska (1959, 1962a, 1962b and I963), Gowe and S t r a i n (1963) and Nordskog et a l . (1967). Nordskog et a l . (1967) pointed out that the major cause of t h e i r i n a b i l i t y to demonstrate c l e a r -cut gains i n t o t a l r a t e of production over a period of 15 years was due to the i n e f f e c t i v e n e s s of i n d i r e c t ( e a r l y record), s e l e c t i o n , Morris (1964) a l s o questioned the effectiveness of ea r l y record s e l e c t i o n . T h e o r e t i c a l l y , to evaluate the r e l a t i v e merit of the ea r l y and f u l l record s e l e c t i o n the following information would be neededj 1. The h e r i t a b i l i t i e s of the two production records, 2. A knowledge of the genetic c o r r e l a t i o n s of e a r l y records with f u l l and r e s i d u a l records, 3. The duration of generation i n t e r v a l f o r the s e l e c t i o n systems. The genetic c o r r e l a t i o n between e a r l y records and f u l l records have been reported to be quite high and i'n f a c t the majority are higher than t h e i r corresponding phenotypic c o r r e l a t i o n s . For example, the estimates of genetic c o r r e l a t i o n s obtained by Lerner and Cruden (1948), O l i v e r et a l . (1957) , Jerome e t . a l . (1956), Bray et a l . (i960), King (1961), Van Vleck and D o o l i t t l e (1964), Clayton and Robertson (1966) and H i l l et a l . (1966) - 7 -ranged from 0.75 to 1.26. The genetic correlations between early and residual production, though not high, have been reported to be positive in most estimates. Some of the reported estimates were 0.55 (Abplanalp, 195?)i 0.218 (Kraszewska-Domanska, 1964), 0.20 (Morris, 1964), 0.45 (Clayton and Robertson, I966), • 0.159 (Caceres, 196?), O.58 (Bohren et a l . , 1970). In a population sub-jected to selection for about 8 years on the basis of early egg production records, Morris (1963) observed a decline in genetic correlation from O.56 to 0.14 between early and residual records. One of the most important consequences of selection for egg number i s the decline in egg weight with the corresponding gain in egg number because of the negative genetic correlation between the egg number and the egg weight. The reported estimates of genetic correlation between egg weight and survivors* production were summarized by Kinney (1969). The reports in his summary ranged from -0.4-9 to 0.07, Morris (1963) reported a mean of 3 grams per egg decrease at the end of 8 years of selection for egg number. Craig et a l . (1969) stated "There was a general tendency for the selected egg production strains and their crosses to decrease in body and egg weight at 32 and 52 weeks of age." This effect was even greater at 55 weeks of age for both the t r a i t s . Kinney et a l . (l9?0) reported a negative genetic regression of egg weight and body weight on early egg number records in 4- selection systems (individual, Sire Family, Dam Family and Index Selection) practiced by them. Because of the consistent decrease in egg weight when selection experiments were based on number of eggs produced, Bohren (1970) stressed the need of selection on the basis of egg mass, Saeki et a l . (1959) - 8 -reported the following estimates of genetic correlations between egg mass, egg number and egg weight in 5 strains of chickens. Egg Mass with Egg Mass with Egg Number with Strains Egg Weight Egg Number' Egg Weight  White Leghorn(l) 0.021 0.603 -0.402 White Leghorn(2) - 0.642 -0.321 Barred Rock 0.201 0.339 -0.440 New Hampshire 0.184 0.774 -0.291 Rhode Island Red 0.516 0.437 -0.222 Waring et a l , (1962) reported the genetic correlations between egg mass and egg number at 17, 32, 55 and 65 weeks of age as 0.541, 0.772, 0.814 and O.897 respectively. The corresponding figures for egg weight were 0.891, 0.610, 0.479 and 0.330. EGG COMPONENT TRAITS There have been a number of reports on the component parts of hens' eggs and their composition. The earliest was that of Malcolm (l90l) who reported the mean of egg weight, yolk weight, shell weight and albumen weight as 59,45, 18.21, 6,04 and 35.19 grams respectively. Romanoff and Romanoff (1949) have summarized most of the earlier reports. Smith et a l . (1954) obtained the following results for yolk, albumen and shell as percentage of the whole egg and yolk percent solid: Egg Components Mean Range % Yolk 31.5 27.7-33.7 % Albumen 59.6 56.5-63.8 % Shell 8.9 7.8-10.2 Yolk % Solid 52.0 51.1-56.3 - 9 -The estimates of nitrogen content of eggs observed by Arroyave et al . (1957) ranged from I .96 1 0,02 gms. to 2.05 - 0.02 gms. per egg for 5 different breeds of chickens. Everson and Souders (1957) presented a detailed review on the chemical composition of the hens egg from a nutritional point of view. They gave averages of 12.2% and 50.6% for solid and 10.8% and l6,J% for protein in albumen and yolk respectively. Shenstone (1968) presented an excellent review on the chemistry of yolk and albumen. Season-Age Effect The season-age effect on egg weight and its components was recognized as early as 1914, by Curtis. In her own words "From the beginning of laying until the beginning of the first breeding season the eggs increase rapidly in size and in general as egg weight increases the percentage of albumen decreases." Atwood (1914) showed that the yolks are relatively heavier in respect to the total weight in the spring than in the f a l l . Jull (1924) concluded that the component parts of the egg contribute in different degrees at different times of the year toward the total egg weight. Phipott (1933), Olsson (1936) and Hafez et al . (1955) claimed that the yolk percentage increases and the albumen percentage decreases with advancement of laying, Erasmus (1954) showed that the egg size increases with the age of the pullets and that hen's eggs have a higher proportion of yolk than do pullet eggs. . _ Arroyave et al . (195?) showed small but significant differences between strains as to nitrogen content of eggs, Their strains varied as to age and although according to them age was not statistically a signifi-cant factor in the case of nitrogen, i t may be of importance in other strains than those tested. May and Stadelman (i960) found significant "time" differences for egg content weight and grams of protein per egg. - 10 -Cunningham et a l . (1960a) presented a d e t a i l e d account of the e f f e c t of age and season on egg s i z e and i t s components,. According to them egg weight varied markedly with the season; tending to be l a r g e r i n spring and smaller during periods of high temperatures. Regarding the volume of albumen and yolk they .maintained that both vary with season and age of the b i r d . In t h e i r study percent t o t a l s o l i d i n albumen also showed a d e c l i n i n g tendency (not s t a t i s t i c a l l y tested) with advancing age, • Cunningham et a l . (1960b) reported a highly s i g n i f i c a n t e f f e c t of age on albumen protein content, however, the seasonal e f f e c t was found to be no n - s i g n i f i c a n t , Marion et a l , (1964) reported no s i g n i f i c a n t d i f f e r e n c e i n the s o l i d content of eggs produced i n 2 successive years by the same b i r d s , C o t t e r i l l et a l , (1962) presented a d e t a i l e d account of the e f f e c t of age and season on egg s i z e and i t s components. According to them the r e l a t i v e d i s t r i b u t i o n of egg components was a function of both egg s i z e and age of b i r d , Chung and Stadelman (1965) reported a consistent increase i n yolk s o l i d and albumen s o l i d from January to March, Yolk s o l i d content showed a f u r t h e r increase from August to October. But albumen s o l i d content decreased from J u l y to November. K l i n e et a l , (1965) observed that within each s i z e group (egg weight) the proportion of yolk increased with increasing age of the l a y e r and f o r each age group smaller eggs had a higher proportion of yolk. They also reported a decreased proportion of s h e l l with the increased age of l a y e r . Phenotypic C o r r e l a t i o n J u l l (1924) reported c o r r e l a t i o n c o e f f i c i e n t s of 0 . 9 2 2 , 0.820 and 0.644 between egg weight and yolk weight, albumen weight and s h e l l weight r e s p e c t i v e l y , Hafez et a l , (1955) i n a f l o c k of Fayomi found c o r r e l a t i o n s between d i f f e r e n t egg components (albumen, yolk and s h e l l ) to be very high, i n the - 11 -order of 0.98 to 0.99. Arroyave et-al. (195?) observed phenotypic correlations of 0,49 between yolk weight and total solid and 0.54 between yolk weight and fat content of egg yolk. May and Stadelman (i960) reported 0.94-5 and 0,625 a s the phenotypic correlations between egg weight and its contents' weight (albumen + yolk) and egg weight and total protein. Cotterill et a l . (1962) in White Leghorns calculated the phenotypic correlation between egg size and percent shell, percent yolk, percent albumen solids and percent yolk solids as 0.19, 0.35, 0.15 and 0.01 respectively. Jaffe (1964-) in a commercial stock of White Leghorns found a phenotypic correlation of 0.553 between egg weight and yolk weight, Chung and Stadelman (1965) reported the phenotypic correlations of egg weight with albumen and yolk weight as 0,92 and 0.72 respectively. In addition, they calculated the phenotypic • correlation betvreen yolk weight and albumen weight as 0,42, Marion et al. (1966) reported following phenotypic correlation coefficients for egg component traits: Trait No. ' No. Trait 2. 3. 4. 5. 6. 1. Egg Weight -0.09 -0.34 0.37 0.21 -0.16 2. Percent Shell -0.08 -0.28 0.0? 0.01 3. Percent Yolk -0.93 -0.60 0.57 4. Percent Albumen 0.54 -0.55 5. Percent Moisture -0.60 6, Percent Lipid Heritability and Genetic Correlations Though a number of authors have reported strain differences for egg component traits, reports on the estimates of heritability and genetic - IZ -correlations are few. Strain differences have been reported for various egg component t r a i t s by Arroyave et a l . (l95?)» May and Stadelman ( i 9 6 0 ) , C o t t e r i l l et a l . (1962), Marion, W. e t . a l . (196*0, Marion et a l . (1965) and Chung and Stadelman (1965). Scheinberg et a l . (1953) obtained h e r i t a b i l i t y estimates as 0.68, 0.12 and 0.66 for albumen weight and 0.00; 0.02 and 0.12 for yolk weight, for New Hampshires, Barred Rocks and White Leghorns respectively. Yao and Skinner (1959) working with White Leghorns reported that the h e r i t a b i l i t y estimates based on f u l l - s i b correlation for albumen weight, yolk size, percent albumen and percent yolk were 0.306, O.36O, 0.301 and O.258. These authors found genetic correlations between egg size and albumen weight and egg size and yolk size to be positive and significant, Jaffe (l964) estimated h e r i t a b i l i t i e s in White Leghorns for egg weight and yolk weight from the sire component of variance as 0,715 t O.I85 and 0.428 t 0.147 respectively. He also reported the genetic correlation between these two t r a i t s to be 0.853. In a flock of White Leghorns, the h e r i t a b i l i t y estimates reported by H i l l et a l , (1966) based on sire and dam component of variance for egg weight, yolk weight, albumen weight, shell weight, yolk percent solids, albumen percent solids, yolk solids and albumen solids were 0.55 - 0.25, 0.32 ± 0.19, 0.57 ± 0.25, 0.32 .+ 0.13, 0.49 t 0.21, 0.72 t 0.35, 0.35 - 0.24 and O.87'+ 0.40 respectively. They also reported negative genotypic correlations between yolk weight, albumen weight and yolk solid with egg number and positive genotypic correlations of yolk and albumen percent solid with egg number. - 1-3 -M A T E R I A L S A N D M E T H O D S EGG PRODUCTION TRAITS F o r t h i s s t u d y 3 r a n d o m b r e d l i n e s o f c h i c k e n s , two o f S i n g l e Comb W h i t e L e g h o r n , U n i v e r s i t y o f B r i t i s h C o l u m b i a (UBC) a n d Mount Hope (MH) a n d one o f B l a c k A u s t r o l o p (BA) b r e e d , m a i n t a i n e d a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a P o u l t r y F a r m , were u s e d . I n o r d e r t o c o l l e c t some p r e l i m i n a r y i n f o r m a t i o n , i n 1968, 120 f e m a l e s f r o m e a c h o f t h e 3 l i n e s were h o u s e d i n i n d i v i d u a l c a g e s b e f o r e t h e o n s e t o f l a y i n g . I n d i v i d u a l b o d y v r e i g h t s a t h o u s i n g a n d a g e a t s e x u a l m a t u r i t y ( a g e a t 1st egg) were r e c o r d e d . T h e eggs were c o l l e c t e d i n t h e a f t e r n o o n , a n d s t o r e d i n a w a l k - i n c o o l e r o v e r -n i g h t . On t h e f o l l o w i n g m o r n i n g , t h e y were b r o u g h t b a c k t o r o o m t e m p e r a t u r e a n d e a c h egg was w e i g h e d a n d r e c o r d e d i n d i v i d u a l l y t o t h e n e a r e s t g r a m . T h i s was c o n t i n u e d d a i l y u p t o 5^0 d a y s o f a g e o f t h e b i r d s . T h u s , t h e egg number a n d egg mass ( w e i g h t o f t h e t o t a l eggs l a i d i n a g i v e n p e r i o d ) u p t o 5^ -0 d a y s o f a g e were o b t a i n e d f o r e a c h i n d i v i d u a l h e n . I n t h e f o l l o w i n g y e a r , 60 o f t h e 120 f e m a l e s a n d 15 m a l e s f r o m e a c h l i n e were s e l e c t e d a t random f o r t h e p r o d u c t i o n o f t h e n e x t g e n e r a t i o n . F o u r h e n s were b r e d t o e a c h m a l e . A r t i f i c i a l i n s e m i n a t i o n was c a r r i e d o u t . T h e p r o g e n y were h a t c h e d i n 2 l o t s , 10 d a y s a p a r t . O n l y f e m a l e p r o g e n y were k e p t , i n d i v i d u a l l y I d e n t i f i e d a n d r a i s e d i n s t a n d a r d c o n d i t i o n s . A t a b o u t 4 months o f a g e , 2 d a u g h t e r s f r o m e a c h dam were s e l e c t e d a t r a n d o m a n d h o u s e d i n i n d i v i d u a l c a g e s (N = 110, UBC; 87 , MH; a n d 93, B A ) , Some dams h a d o n l y 1 s e l e c t a b l e d a u g h t e r . I n d i v i d u a l b o d y w e i g h t s , a g e a t 1s t egg ( a g e a t s e x u a l m a t u r i t y ) , egg p r o d u c t i o n a n d t o t a l egg mass w e r e r e c o r d e d a s d e s c r i b e d e a r l i e r . T h e egg number a n d egg mass o f t h e h e n s t h a t s u r v i v e d u p t o 5^0 d a y s - 14 -of age (N = 9 0 , UBC; 70,.MH; 6 0 , BA) were evaluated at the following agess 1. 5^ -0 .days of .age (540 no., and 540 mass) 2. 3?5 days of age (375 no. and 375 mass) 3 . 325 days of age (325 no. and 325 mass) 4 . 275 days o f age (275 no. and 275 m a s s ) . For the c a l c u l a t i o n of r e l a t i v e s e l e c t i o n e f f i c i e n c y of the e a r l y and f u l l production records the egg number and egg mass of 2 early records (275 days of age and 325 days of age) were compared against the production records of 540 days of age. The r e s i d u a l production was ca l c u l a t e d by subtracting the ea r l y production record i n question from 54-0 days production record. The average egg weights f o r 4 periods were obtained by averaging the weights of the eggs, produced i n the week preceding 275, 325, 375 and 540 days of age. These egg weights obtained at 4 d i f f e r e n t periods were termed as egg weight I, II, III and IV. Within l i m i t s , the feeding and management pra c t i c e s during the laying, period were kept to recommended commercial l e v e l s . EGG COMPONENT TRAITS The egg component measurements were taken at 4 d i f f e r e n t periods each 3 months apart so that the season-age e f f e c t s could be assessed. These periods were the f i r s t f o r t n i g h t of November, February, May and August of 1969/70, In view of.the amount of work a n t i c i p a t e d , only 1 p u l l e t from each mating described e a r l i e r was selected at random f o r egg component measurements. Two eggs from each p u l l e t were measured i n each season and a mean value of the 2 was used f o r analyses. The eggs used f o r component measurements were brought to the laboratory - 15 -a f t e r t h e i r weights were recorded f o r egg mass. These eggs were again weighed to the nearest 0,01 of a gram. A f t e r the i n i t i a l weighing, the eggs were broken, and the albumen poured i n t o a beaker then the yolks vrere put on a wet paper tovrel and r o l l e d so that the adhesive albumen would be removed. These yolks were then t r a n s f e r r e d to tared p e t r i dishes, and weighed to the nearest 0,01 of a gram. The egg s h e l l s were c a r e f u l l y washed with tap water, d r i e d at 100°C - 105°C overnight i n an oven and weighed. The d i f f e r e n c e between egg weight and the weight of the yolk and dry s h e l l was c a l c u l a t e d as albumen weight. Percent yolk, albumen and s h e l l were then c a l c u l a t e d . Percent S o l i d Determination The albumen of each egg was blended slowly with a small e l e c t r i c mixer to which a t h i n f l a t c u t t i n g blade had been f i t t e d . Care was taken to minimize the amount of a i r incorporated i n t o the albumen during the blending procedure. A refractometer reading to 4 decimal places f o r each egg was obtained by p l a c i n g 2 drops of blended albumen on theBausch and Lomb refractometer previously adjusted to operating temperature of 25°C - 2?°C, The refractometer prism was cleaned with tap water and wiped with s o f t t i s s u e paper a f t e r each reading. P r i o r to taking the refractometer reading about 10 cubic centimeters of albumen from each egg was frozen at -15°F f o r f u r t h e r analyses. A f t e r weighing the yolk, i t s membrane was pinched and the contents were c o l l e c t e d i n a small beaker. The refractometer readings vrere taken i n the same manner as that of the albumen with the exception that the prism was cleaned with 0.85% s a l i n e instead of tap water. The refractometer readings thus obtained were c a l i b r a t e d separately f o r - 1 6 -y o l k and albumen i n terms o f percent vacuum-oven d r i e d s o l i d . The percent o v e n - d r i e d s o l i d were obtained a c c o r d i n g to the procedure s e t f o r t h i n the A . O . A . C . Method o f A n a l y s i s , Sec. 16.002 and 16.003 (1964)i Two p r e d i c t i o n equations (standard curves) each f o r y o l k and albumen s o l i d were obtained and were as f o l l o w s : (1) For Yolk Y = -527.1 + 409.3 R 2 = 0.8? (2) For Albumen.Y = -608.6 + 458.1 X; R 2 = 0.91 Where X = the r e f r a c t o m e t e r r e a d i n g o f a given s a m p l e , ' Y = t h e percent s o l i d , and R 2 = t he p r o p o r t i o n o f the v a r i a t i o n i n - Y e x p l a i n e d by the v a r i a t i o n i n X, Grams o f y o l k and albumen s o l i d were then c a l c u l a t e d from the percent s o l i d o b t a i n e d . .Procedure used f o r P r o t e i n Determination For p r o t e i n d e t e r m i n a t i o n , a method developed f o r meat by Moss and K i e l s m e i e r (1967), which was l a t e r modified by Gardner and Young (1969) f o r eggs, was used. The reagents and procedures were as f o l l o w s : (1) Reagents used (a) Amido B l a c k Dye 3.0 gms. (b) C i t r i c A c i d 21.4 gms. (c) P r o p i o n i c A c i d 1.0 c c . (d) D i s t i l l e d Water 1000.0 c c . (2) P r e p a r a t i o n o f dye (a) 3 grams o f Amido B l a c k Dye and 21.4 grams o f c i t r i c a c i d were d i s s o l v e d i n 1000 c c , o f d i s t i l l e d water. 1 c c . o f p r o p i o n i c a c i d was then added to the solution" and miked t h o r o u g h l y . - 17 -(b) The pH of the s o l u t i o n was adjusted to 2.2 by adding more aqueous dye or c i t r i c a c i d depending upon whether the pH was low or high. Protein Determination ' • Albumen , The aforementioned frozen albumen sample was defrosted at room tempera-ture. One h a l f cc.. of albumen was pipetted i n t o a 25 cc. t e s t tube. To t h i s 12.5 ml. of reagent dye s o l u t i o n was added and the tube was mechanically shaken f o r about 1 minute. The mixture stood at room temperature f o r about 30 to 60 minutes. The tubes then were centrifuged at 1700 G. f o r 20 minutes. One ml, of supernatent s o l u t i o n was pipetted i n t o 100 ml, volu-metric f l a s k . The s o l u t i o n then was d i l u t e d to 100 ml. with d i s t i l l e d water. The o p t i c a l density of the d i l u t e d s o l u t i o n was measured at a wavelength of 6l5 millimicrons using a Bsckman Spectrophotometer. The o p t i c a l density readings thus obtained were c a l i b r a t e d i n terms of the percent protein obtained by standard Kjeldahl method set f o r t h i n the A.0.A.G, Method of Analysis (1964). The p r e d i c t i o n equation (standard curve) obtained v i a regression was as f o l l o w s J Y = 12.72 - 0.0784 X; R 2 = 0.818 where X = the o p t i c a l density, Y = the percent protein i n albumen, and R = as described e a r l i e r . Yolk The procedure used f o r the determination of o p t i c a l density of the yolk and i t s c a l i b r a t i o n with the standard K j e l d a h l method was e s s e n t i a l l y - 18 -the same as described f o r the albumen. The only d i f f e r e n c e s vrere. the yolk samples vrere not frozen and they vrere f i r s t d i s s o l v e d i n 0,85% s a l i n e f o r the ease of p i p e t t i n g . For each gram of yolk, 1 ml. of s a l i n e was used. One h a l f ml. of t h i s s o l u t i o n was pipetted i n 25 cc. t e s t tube as described e a r l i e r . The p r e d i c t i o n equation (standard curve) f o r yolk protein was obtained as follows: Y = 21.43 - 0.1086 X; R 2 = 0.?66 where X = the o p t i c a l density, Y = the percent protein i n yolk, ' and R 2 = as described e a r l i e r . The R 2 obtained i n t h i s study f o r yolk and albumen vrere considerably lower than the one (0,99) reported by Gardner and Young (1969). Reasons f o r these lowered values are unknown. - 1 9 -S T A T I S T I C A L M E T H O D S As stated e a r l i e r , chicks vrere hatched i n 2 l o t s and the egg component t r a i t s were measured i n each of 4 d i f f e r e n t seasons. Seasons, however, were confounded with the age of the b i r d s , therefore, t h i s e f f e c t i s r e f e r r e d to as the season-age e f f e c t . The data were analysed using the l e a s t square method as described by Harvey (i960), FIXED EFFECTS, Separate analyses were performed to assess f i x e d e f f e c t s f o r egg component t r a i t s and f o r egg production t r a i t s . Egg Production T r a i t s The s t a t i s t i c a l model assumed i n the analyses of l i n e e f f e c t s f o r the egg production t r a i t s vras as follows: M + 1 i + e i j where jxn observation i n i x n l i n e , and e. In t h i s model, l i n e s vrere assumed to be f i x e d . Egg Component T r a i t s . The following s t a t i s t i c a l model vras assumed to i n v e s t i g a t e possible l i n e and season-age e f f e c t s . - 20 -Y i j k = / / + l i + a j + ( l a ) i j + e. j k where Y j j k ~ k t h individual in i t h line and season, y_/ = the overall population mean, 1± = an effect due to i t n line; i = 1 . . . 3 , ' = an effect due to j ^ n season-age; j = 1 . . . 4 , (la)i j = the joint effect of j"^ n season-age on i^h line holding season-age and line constant, and e i i k = a n effect peculiar to i j k t n individual assumed J to ,be NID (0,0). Both line and season-age effects were assumed to be fixed in this model. The statistical model assumed to assess the hatch, season-age and sire effects for each line was as follows: Y i j k l = ^ + a j + s k + (h a ) i d + (as) j k + e. j k l where Y i j k l = individual in the i ^ n hatch, j^h season-age and k"th sire group, = overall population mean, h ± = an effect due to i t h hatch; i = 1 . . . 2 , aj = an effect due to j ^ n season-age; j = 1. . .4- , s k = an effect due to k^n sire; k = 1 . . . 1 5 , (ha)ij =. the joint effect of i " t * 1 hatch on j t n season-age holding hatch and season-age constant, (as)jk = the joint effect of j * n season-age on k^n sire holding season-age and sire constant, and e i j k l = residual effect assumed to be NID (0,(j). All effect; except residual effect were assumed to be fixed. For a l l the above mentioned analyses the mean squares were calculated in the usual manner by dividing the sum of squares by their appropriate degrees of freedom. The F values were obtained by dividing a l l effects by - 21 -the e r r o r mean square. Wherever the effects.were found to be s i g n i f i c a n t the Duncan's (1955) New M u l t i p l e Range Test (Duncan's T e s t ) , modified by-Kramer (1956) was used. A p r o b a b i l i t y l e v e l of 5% was used to determine s i g n i f i c a n c e i n a l l analyses. The hypothesis that several r's (simple c o r r e l a t i o n s ) are from the same p . (population c o r r e l a t i o n ) was tested according to the method described by Snedecor and Cochran (1967). HERITABILITY AND GENETIC CORRELATION / . Preliminary analyses to i n v e s t i g a t e a possible season-age, hatch and season-age by s i r e i n t e r a c t i o n e f f e c t s , revealed that there was no s i g n i f i c a n t season-age by s i r e i n t e r a c t i o n present i n any of the egg component t r a i t s studied f o r a l l the 3 l i n e s . Hatch e f f e c t s and hatch by season-age i n t e r -a c t i o n e f f e c t s were a l s o n o n - s i g n i f i c a n t i n most of the t r a i t s . Therefore, hatch, season-age by s i r e i n t e r a c t i o n and season-age by hatch i n t e r a c t i o n e f f e c t s were assumed to be non existent i n the subsequent genetic analyses,, Following Henderson's (1948) Method 2 the observations were corrected f o r season-age (fixed) e f f e c t s ; and then the estimation of the s i r e component of variance and covariance were obtained from each analyses of the adjusted data f o r the c a l c u l a t i o n of h e r i t a b i l i t i e s and genetic c o r r e l a t i o n s . The following s t a t i s t i c a l model was assumed f o r the estimation of s i r e component of variance and covariance from the adjusted data, f o r each l i n e j where o v e r a l l population mean, an e f f e c t due to i ^ h s i r e ; i = 1 . . . 1 5 , assumed to be NID (0,0), and e f f e c t p e c u l i a r to j t r i i n d i v i d u a l of i z n s i r e , assumed to be NID (0,0). - 2 2 -The hierarchal analysis of variance used for estimating the sire variance component for the above model i s presented in Table 1, The sire variance component was estimated as: 2 = ms - MSp.. 0 s . K x Using sire variance component the he r i t a b i l i t y (h 2) was calculated as follows: -The standard error (S.E.) of h e r i t a b i l i t y was calculated using the formula after Swiger et a l . (1964). S. E. (h^) = 4 2 _ , ,2(N-1) ( 1-t) 2 1 + (KX - l ) t K2 (N-S)(S-l) Where t i s the intra class correlation and estimated as: t = - ^ = £ h 2 The hierarchal analyses of covariance used for estimating the sire variance component for the model given i s presented in Table 2. The following formula (Falconer, i960) was used for the calculation of genetic correlation: r Cov s ( x y ) r G ^ ( x ) The sire components of variance,needed to calculate the genetic correlation of 2 t r a i t s were taken from the comparable h e r i t a b i l i t y analyses. The standard errors for genetic correlations were calculated after Robertson's (1959) formula which was modified by Falconer (i960): - 23 -Table 1. Analyses of Variance f o r the Estimation of S i r e Variance Component Source of Va r i a t i o n Degrees of Sums of Mean Estimated Freedom Squares Squares Mean Square T o t a l ( N ) N - l SSip MS T Between S i r e s (s) S - l sss MSS ol + %crl Progeny/Sires N-S SSp MS p . Table 2, Analyses of Variance f o r the Estimation of S i r e Covariance Component Source of V a r i a t i o n Degrees of Sums of Mean Estimated Freedom squares Squares Mean Squares T o t a l (N) N-l S C P T MCPg Between S i r e s (S) S - l S C P S MCPS Cov. + K-, Cov e S J- s Progeny/Sires N-S SCP p MCPp Cov e The c o e f f i c i e n t was cal c u l a t e d as follows: • N - m 2 K ' _ N" (Becker, 1967) 1 ~ S - l - 2k -r C ^ - 4 F(h|) -0x4) Where ^ denotes standard error of genetic correlation and h 2 and h 2 are the heritabilities of the two traits considered. RELATIVE SELECTION EFFICIENCY: The relative selection efficiency of early and f u l l records as criterion of selection was calculated according to the slightly rearranged version of the formula given by Lerner and Cruden (1948). The rearranged formula is as follows: E = K h E rGEA/hA Where: E = relative selection efficiency, K = generation interval, h E = square root of the heritability of the early production records, h A = square root of the heritability of the annual production records, and r G F A = genetic correlation between the two production periods. - 25. -R E S U L T S AND D I S C U S S I O N EGG PRODUCTION TRAITS Meansand Standard Deviations The means of a l l the 18 t r a i t s studied along with t h e i r standard deviations are given i n Table 3 . Analyses of variance' c a r r i e d out to f i n d the d i f f e r e n c e s between l i n e s showed that except f o r 375 Days No,, 325 Days No. and 275 Days Mass, the l i n e s d i f f e r e d s i g n i f i c a n t l y f o r a l l the egg production t r a i t s studied (Table 4 ) . Duncan's Test showed that the non Leghorn l i n e , BA, d i f f e r e d from the MH and the UBC l i n e s more often than the White Leghorn l i n e s d i f f e r e d among themselves (Table 3 ). It i s i n t e r e s t -ing to note that the 3 l i n e s c o n s i s t e n t l y d i f f e r e d i n egg weight f o r a l l 4 periods (Table 3), Body weight at housing was s i g n i f i c a n t l y d i f f e r e n t i n a l l the 3 l i n e s , while age at sexual maturity i n the MH l i n e d i f f e r e d s i g n i f i c a n t l y from the UBC and BA l i n e . Though, s t a t i s t i c a l l y , i t i s not s i g n i f i c a n t i t i s worth noting that the MH l i n e laid, an average of 5«8 eggs l e s s than the UBC l i n e , s t i l l the egg mass f o r the MH l i n e was "}60 gms, higher than f o r the UBC l i n e . H e r i t a b i l i t y H e r i t a b i l i t i e s of a l l t r a i t s along with t h e i r standard errors are presented i n Table 5 « In a l l the l i n e s the h e r i t a b i l i t i e s f o r egg number and egg mass, f o r a given period, were in a close agreement. In general, h e r i t a b i l i t y f o r egg number was s l i g h t l y higher than egg mass. These r e s u l t s were i n general agreement vrith Saeki et a l , (1959) and Waring et a l . ( 1962) . For a l l the egg production t r a i t s the s i r e component of variances (v of a d d i t i v e genetic variance) and progeny within s i r e variances (environ-mental and non-additive genetic variance) are presented in Table .6 , In - 26 -Table 3. Means and Standard Deviations of the Egg Production T r a i t s , * UBC MH BA T r a i t Mean S.D. . Mean S.D. Mean S.D. 540 No. • 239.1a 37.0 2 3 3 - 3 a b 54.6 2 2 2 .l b 44.2 540 Mass (gms) 13980.0a 2344.0 14340.oa 3394.0 12380.ob 2516.0 375 No. I4"5.9a 16.9 139.2 a 38.2 I42 .9 a 20.3 375 Mass (gms) 8133.0 a 986.4 8208.0„ 2255.0 ?642.0b 1087.0 325 No. 119.3b 12.5 .110.5 C 32.8 1 2 9 . 9 a 20.2 325 Mass (gms) 6473.0a b 768.3 6362.ob 1872.0 6846.0a 1010.0 275 No. 84.9a 11.1 ? 5 . 9 b 24.3 82.9a 15.0 275 Mass (gms) 4496.o a 564.8 4266.o a 1317.0 4233.o a 761.4 540 - 275 No. 154.l a 32.6 157.3a 42.4 139.8 b 38.8 540 - 275 Mass (gms) 9488.0a 2090.0 10070.oa 2?68.0 8209.0 b 2257.0 540 - 325 No. 119.8 a 30.3 122.8 a 37.3 87. 2 b 27.8 540 - 325 Mass (gms) • 7512.o a 1945.0 7978.0a 2437.0 5171.ob 1643.0 Body Wt, (gms) 1601.ob 35.5 1405.0C 206.8 1705.o a 478.3 Age at l s z Egg (days) 160.4-yj 10.2 170.6 a 13.9 162.2 b 13.6 Egg Wt. I (gms) 57-5 b 3.4 6 0 . 1 a 4.3 55.2 C 3.1 Egg Wt. I I (gms) 59.5 b - 3.3 62.4 a 4.6 57.0 C 3.4 Egg Wt. I l l (gms) 61.6 b 3.4 6 3 . 8 a 4.9 58.9 C 4.1 Egg Wt. IV (gms) 63.5 b • 3.8 64-8a 4.2 60.4 C 4.1 Means i n the same row vrith the common subscripts were not s i g n i f i c a n t l y d i f -ferent from each other (Duncan's Test, P4. -0 .05) . - 2? -Table 4, Summary of Analyses of Variance: .Line Differences f o r the Egg Production T r a i t s . • T r a i t T o t a l R 2 T o t a l F i t t e d ! . S.S.2 540 No. O.036* 41.24 x 10h 540 Mass 0.104* 16.71 x 108 375 No. 0.004 13.26 x 104 375 Mass 0.052* 45.26 x 10? 325 No. ' 0.017 96.42 x io3 325 Mass 0.029* 29.77 x 10? 275 No. 0.049* 82.13 x 10^ 275 Mass 0.024 17.17 x 10? 540 - 275 No. 0.050* 30.46 x 10^ 540 - 275 Mass 0.109* 12.83 x 108 540 - 325 No. 0.050* 24.84 x 10^ 540 - 325 Mass 0.090* 10.47 x 108 Body Wt. 0.245* 21.01 x 106 Age at 1 s t Egg 0.109* 38.71 x io3 Egg Wt. I 0.200* 35.06 x 102 Egg Wt. I I 0.239* 40.73 x 102 Egg Wt. I l l 0.169* 43.81 x 102 Egg Wt. IV 0.166* 4.72 x 102 df 2 219 1 F r a c t i o n of the t o t a l sums of squares accounted f o r by f i t -t i n g the e f f e c t s i n the s t a t i s t i c a l model ( R 2 ) . Since only one e f f e c t (Line) was f i t t e d i n t h i s model, t o t a l R 2 w i l l be equal to R 2 f i t t e d f o r the e f f e c t , 2 T o t a l corrected sums of squares. * ' S i g n i f i c a n t (Pi= 0.05). 28 -Table 5« H e r i t a b i l i t y Estimates (h 2) and Standard Errors (S.E.) of the Egg Production T r a i t s , . T r a i t ..: UBG . MH BA S.E. h2 S.E. h'2 . S.E.. 540 No. 0 . 8 2 +0.46 0.58 to. 51 0.33 to. 51 5 4 0 Mass 0.75 - + 0 . 4 5 0.51 to. 50 0.31 to. 50 450 No. 0.62 +0.42 0.59 to. 51 0.36; .to.52 450 Mass 0.52 +0.41 0.72 to. 53 0..25 to. 50 375 No. 0.27 to.35 0.45 to. 49 -0.34 to. 36 375 Mass 0.58 +0.42 0.62 to. 52 -0.33 to. 37 325 No. 0.43 +0.39 0.33 to .46 -0.39 t°'35 325 Mass 0.53 +0.41 0 . 4 5 to. 49 - 0 . 4 1 • to. 34 275 No. 0.85 l o . 4 6 0.59 to. 51 -0.39 to. 35 275 Mass 0.83 +0.46 0.39 to. 47 -0.50 to. 32 5 4 0 - 275 No. 0 . 8 4 +0.46 0.31 to. 4 6 0.59 to. 55 5 4 0 - 275 Mass 0.77 +0.45 0.17 to. 4 2 O.56 to. 55 5 4 0 - 325 No. 0.75 to. 45 0.22 +0.43 0.52 to.54 5 4 0 - 325 Mass 0.71 to.44 0.13 t o .4 1 0.12 to. 47 Age at i s +- Egg 1.09 to. 49 0.01 to. 38 0.29 " "to.50 Body Wt. . 0.22 to.34 -0.29 +0.28 0.26 to. 50 Egg Wt. I . 0.44 to. 39 0.13 to. 4 1 O.56 to. 55 Egg Wt. I I 0.65 to.43' 0.69 to. 53 0.31 to. 51 Egg Wt. I l l 0.53 to. 4 1 0.94 to.56 0.77 to.57 Egg Wt. IV 0.22 to.34 0.67 to.53 • 0.58 to. 55 - 29 -Table 6 . Sire Component of Variance ( S ) and Progeny Within Sire ( P / S ) Variance for the Egg Production Traits, Trait UBC MH BA . . . S P/S S P/S S P/S 5 4 0 No. 2.82xl02 1.09x103 3.67xl0 2 2.18x103 1.39xl02 1.69xlo3 5 4 0 Mass 1.03xl06 4.45xl06 1.26xl06 8.67xl06 4.22xl0 5 5.52xio 6 4 5 0 No. 1.22xl03 5 . 7 3 x l 0 2 2.23xl02 1.29xlo3 7 . 6 6 x 1 0 1 8.43x103 4 5 0 Mass 3.39xlo5 2.28xl06 1.02xl0 6 4.65,xl06 1 . 6 4 x l 0 5 2.73xl0 6 375 No. 2 . 1 9 X 1 0 1 3.03xl0 2 1.34xl02 1.0?xl0 3 -3.58X10 1 4.37xl0 2 375 Mass 1.42X10 5 8.44xlo5 6.51xl05 3.56xl0 6 -9.58x10^ 1.19xl06 325 No, 1 . 7 3 X 1 0 1 1 . 4 2 x l 0 2 7.84X10 1 8.66xlb2 - 3.00X10 1 3.25xl0 2 . 325 Mass 6.06x10^ 3.98x10^ 3 . 3 7 x l 0 5 2.68xl06 -8.43xl0i|' 8.75xl05 275 No. 3.87X10 1 1.43xl02 1.06xl02 6 . 2 4 x 1 0 2 -2.28X10 1 2 . 4 8 x l 0 2 275 Mass 6.25x10^ 2 . 3 ? x l o 5 1.58x10^ 1 . 4 7 x l 0 6 -7.02x10^ 6,l6xl0 5 540-275 No. 2 . 2 8 x 1 0 3 8.77xl02 1 . 2 4 x l 0 2 1 . 4 8 x l o 3 2 . 0 4 x l 0 2 1.25xl03 540-275 Mass 8.63x10^ 3 . 6 4 x l 0 6 2.90x10^ 6.60xl0 6 6.39xl05 4 . l 8 x l 0 6 521O-325 No. 1 . 7 4 x 1 0 3 7.26xl0 2 7.32X10 1 1 . 2 4 x 1 0 3 1 . 4 6 x l 0 2 1 . 0 4 x 1 0 ^ 5 4 0-325 Mass 7.03x105 3.26xl06 1.79xl05 5 . 5 4 x l 0 6 1.03xl05 3.96xl06 Age at 1 s t Egg 3.00X10 1 7 . 9 8 X 1 0 1 0 . 5 1 X 1 0 1 2.11xl0 2 1 . 4 0 X 1 0 1 1.75xl0 2 Body Wt. 3.77xlo3 6.57xlOi4' - 5 . 2 8 x l o 3 7 . 8 8 x 1 0 ^ 5 . 2 8 x i o 3 7 . 4 7 x 1 0 ^ Egg Wt. I 0.12X10 1 0 . 9 9 X 1 0 1 0.06x10* 1 . 9 0 X 1 0 1 0 . 1 4 X 1 0 1 O . 8 3 X I O 1 Egg Wt. II 0.18X10 1 0 . 9 5 X 1 0 1 0.37X10 1 1.77X10 1 0 . 0 9 X 1 0 1 1.05X101 Egg Wt. I l l 0.15X101 0.99X10 1 0.57X101 1.87X101 0 .33X10 1 1 . 4 0 X 1 0 1 Egg Wt. IV 0.08X10 1 I . 3 6 X I O 1 0 . 3 0 X 1 0 1 1 . 5 0 X 1 0 1 0 . 2 5 X 1 0 1 1 . 4 5 X 1 0 1 - 30 -general, the non-additive variance was highest in the MH lin e followed by the BA lin e and the UBC l i n e . Since a l l the 3 lines were kept in a similar environment, the larger part of the variance between progeny within sires in the MH lin e may be non-additive genetic variance. The higher h e r i t a b i l i t y estimates of egg production reported here especially for the UBC and the MH lines, as compared to those found in the literature, are of interest. A l l the 3 lines have been maintained by a closed random mating system for the past 10 years. There has been no a r t i -f i c i a l selection and natural selection has been minimized. Inbreeding was reduced by using about 100 males and 300 females each year for the production of the replacement stock. A l l of these factors should assist in maintaining much of the genetic v a r i a b i l i t y which would be present in these lines. The exceptionally high h e r i t a b i l i t y estimates for the early records of egg number and egg mass in the UBC line may be related to the high h e r i t a b i l i t y of age at sexual maturity (1.09). Since, in this study, production up to a given age was considered, any genetic differences in the age at sexual maturity should have been reflected in the early production records. Lerner and Cruden (1948), Jerome et a l , (1956) and Oliver et a l , (1957) have reported h e r i t a b i l i t y to be higher for the early production up to January 1 and then i t gradually declined with time. No consistent trend, could be established in this study, either for egg number or for egg mass. However, examination of the h e r i t a b i l i t y of egg number tr a i t s in the UBC lin e at 275, 325, 375, 450 and 540 days of age showed that h e r i t a b i l i t y did decline (O.85 to 0,43 and 0,26) for the f i r s t three periods, but increased to 0,62 at 450 days of age and 0,82 at 5^ -0 days of age. These results were in partial agreement with Oliver et a l , (1957) "ho found that as age advanced the effect of age at sexual maturity declined. The increase in h e r i t a b i l i t y -. 31 -estimates of egg production at 450 and 540 days of age may be due to the increased v a r i a b i l i t y of persistency in the flock. This was indicated from the sire component of variance obtained for 275 days (38.7), 325 days (17.3), 375 days (21.9), 450 days (1220.0) and 540 days (282.0) of records of egg number. In this connection, results obtained by Bray et a l . (i960) were interesting. They found the h e r i t a b i l i t y of age at sexual maturity and persistency to be similar and a genetic correlation of 0,78 between these t r a i t s . They also found the genetic correlation between age at sexual maturity and rate of lay to be small and positive (0,05). This indicated that although the rate of lay was independent of age at sexual maturity, persistency w a s largely genetically associated with age at sexual maturity. The same contention could be applied to the results obtained in this study which might explain the higher h e r i t a b i l i t y estimates of the longer production records. The h e r i t a b i l i t y estimates of egg number in the MH line for different production periods were not very far apart; O.58 (540 days), 0.59 (450 days), 0.45 (375 days), 0.33 (325 days) and 0.59 (275 days). This could be expected because the h e r i t a b i l i t y of age at sexual maturity in this l i n e was low (O.Ol), In other words, the additive genetic variance for age at sexual maturity in MH line was too low (5.1) to have any effect on the he r i t a b i l i t y of egg number and egg mass of early production periods. In the BA li n e , the h e r i t a b i l i t y estimates of egg production t r a i t s for 540 days (0.33 for no. and 0.31 for mass) and 450 days (O.36 for no. and 0.25 for mass) of age were low compared to the Leghorn lines. These low herit-a b i l i t y estimates in the BA line seem to be mainly because of the lower sire component (additive genetic) of variance in this line 139.0 (540 days No.) and 76.6 (450 days no.) compared to Leghorn line 282 (UBC, 540 days no.), - 32 -367 (MH, 540 days No.), 1220 (UBC, 450 days No.) and 223 (MH, 450 days No.). The h e r i t a b i l i t y estimates for early production (egg number and egg mass) for a l l . 3* age criteria ; 275» 325 and 375 days of age were negative in the BA l i n e . While negative estimates are considered to be the results of the sampling variance, i t seems that the additive genetic variance for early records in this line may be quite low. These results appeared to be analogous to those obtained by Nordskog et a l . (1967). whereinthey found the h e r i t a b i l i t y of early records to be 0.08 and that of the f u l l records as O.267. An interpretation of these results w i l l be discussed in detail later. The h e r i t a b i l i t y estimates of egg weight obtained in this study over the 4 periods in 3 lines were within the range of estimates reported in the literature. Low estimates of mature egg weight in the UBC line and early egg weight in the MH line are of interest. In the UBC l i n e , the estimate was high for early egg weight (0.44). It stayed so in the intermediate periods (O.65 and O.53) and then declined for mature egg weight (0,22). In other words, the early egg weight appeared to have more additive genetic variation (36, 54 and 45) than mature egg weight (24). This may be a result of the relationship of age at sexual maturity and body weight. Since a considerable portion of the variation present for age at sexual maturity in the UBC line was found to be genetic, birds which came Into production late would have a large body size and thereby produce a larger egg. The her i t a b i l i t y of mature egg weight declined in the UBC l i n e because a l l birds were f u l l y grown and differences in mature body weight do not appear to influence the difference in egg weight. The low he r i t a b i l i t y of early egg weight in the MH line would again be associated with age at sexual maturity. The he r i t a b i l i t y of the la t t e r was essentially zero. The average - 33 -age at sexual maturity i n the MH l i n e was 10 days higher than i n the UBC l i n e . In other words, i n the MH l i n e the birds were r e l a t i v e l y more p h y s i c a l l y mature when they came to p h y s i o l o g i c a l maturity, Genotypic and Phenotypic Correlations The genotypic and phenotypic c o r r e l a t i o n s i n the UBC and the MH l i n e s are l i s t e d i n the Tables 7 and 8, Since, i n the BA l i n e , a negative s i r e component of variance was obtained f o r early production records, the genetic c o r r e l a t i o n s of early records vrith f u l l records could not be calculated.. The genotypic c o r r e l a t i o n s of corresponding egg mass and egg number f o r both l i n e s ranged from O.69 f o r 540 - 325 days ( r e s i d u a l production) i n the MH l i n e to O.96 a t 5^-0 days of production i n the UBC l i n e . These r e s u l t s were i n close agreement vrith those reported by Saeki et a l . (1959) and Waring et a l . (1962). Lerner and Cruden (1948), O l i v e r et a l . (1957) and Waring et a l . (1962) showed that, i n general, f o r egg number and egg mass t r a i t s the genotypic c o r r e l a t i o n s of e a r l y , f u l l and r e s i d u a l records were higher than the corresponding phenotypic c o r r e l a t i o n . In t h i s data, the genetic c o r r e l a -t i o n s between ea r l y and f u l l records and between ea r l y records and r e s i d u a l records f o r both egg number and egg mass were of the same magnitude and mostly higher than the phenotypic c o r r e l a t i o n s . This may suggest' that small p o s i t i v e or negative environmental c o r r e l a t i o n s existed between these t r a i t s (Searle , 1961). The genetic c o r r e l a t i o n s of early records of egg number vrith f u l l and r e s i d u a l records were c o n s i s t e n t l y higher than t h e i r counterparts f o r egg mass. This vras more obvious i n the UBC l i n e , as expected, since egg mass consideredboth egg number and egg weight and these two t r a i t s were g e n e t i c a l l y negatively c o r r e l a t e d i n t h i s l i n e . The estimates of genetic c o r r e l a t i o n s between d i f f e r e n t length of production records of egg number and egg mass were higher i n the MH l i n e Table 7a, The Genotypic (r G) and the Phenotypic (rp) Correlations of the UBC Line for the Egg Production Traits. Trait 540 No. 540 Mass 325 No. 325 Mass rG S.E. rp rG S.E. ' rp rG:' S.E. rP rG S.E. rP • 540 Mass ' 0.96 to. 02 0.94* 325 No. 0.98 to. 01 0.68* 0.89 to. 05 0 .52* 325 Mass O.69 to. 13 0.61* O.76 to. 11 0 .60* 0.88 to. 07 0 .61* 275 No. 0.60 +0.21 0.42* 0.53 to. 25 0.28* 0.97 tO. 02 0.42* 0.87 to.06 0.42* 275 Mass 0.37 to. 28 0.49* 0.44 to.27 0.49* 0.71 t C 21 0.49* 0.92 to. 04 0.49* 540 - 275 No. 0.98 to. 01 O.96* 0.95 to. 03 0 .93* 0.88 to. 09 . 0;.96* 0.59 to. 25 0 .96* 540 - 275 Mass 0.95 to. 03 0.91* .0.97 to. 02 0.98* 0.80 tC 14 0 .91* 0.59 to. 24 0.91* 540 •- 325 No. 1.01 0.95* 0.98 to. 01 0.94* 0.99 to. 01 0.95* 0.66 to. 20 0.95* 540 - 325 Mass 0.97 to. 20 0.90* 0.99 to. 00 O.96* 0.87 to. 09 0 .90* O.30 to. 32 0 .90* Age at 1 s t Egg -0.51 to. 29 -0.20 -O.38 to. 34 -0.04 -O.83 tO. 16 -0.18 -0.55 to. 46 -0.18 Body Wt. 0.67 to.08 -0.06 0.80 to. 03 -0.03 "0.55 to. 13 -0.06 0 . 5 4 to. 12 -0.06 Egg Wt. I -0.51 to. 16 -0.07 0.16 to. 22 0.35* - 0 . 2 5 to. 26 -0.07 O.32 to. 23 -0.07 Egg Wt. II -0.13 to. 28 -0.05 0.06 to. 29 0.26* -0.48 to.27 -0.05 0 .06 to. 32 -0.05 Egg Wt. I l l -0.24 to. 23 - 0 . 0 7 0.00 to. 25 O.23* -0.49 to. 23 -0.07 0 . 0 9 to. 29 -0.07 Egg Wt. IV -0.30 to. 14 -0.14 0.03 to. 15 0.14 -0.61 tO. 12 -0.14 0 . 0 6 to.17 -0.14 * Significant (Ho, P = 0, P 4 0 . 0 5 ) . ** These values could not be calculated. Table 7b. The Genotypic (rQ.) and Phenotypic (rp) Correlations of the UBC Line for the Egg Produc-tion Traits. Trait 275 No. 275 Mass 540 - 275 No. 54C ) - 275 Mass rG S.E. rG S.E. rP rG S.E. r P rG S.E. rp 275 No. 275 Mass 0 .81 t o . 11 0 . 7 2 * 540 - 275 No. 0 .42 ±0.27 0.20 0 .19 ±0.32 O.26* 540 - 275 Mass 0.37 ±0.27 0.13 0 . 2 2 ±0.30 0 .28* 0 .99 ±0.01 0 .97* 540 - 325 No. 0.51 +0.22 0 . 2 1 * 0 .28 10.28 0 . 2 9 * 1 .00 0 .99* 0 .99 ±0.01 0 . 9 6 * 540 - 325 Mass 0 .44 i O . 2 3 0.12 0.30 ±0.27 0 . 3 0 * 0 . 9 8 ±0.01 0 .95* 1.00 ** 0 . 9 8 * Age at lsx Egg Body Wt. - 0 . 7 4 0.40 ±0.18 ±0.12 -0 .54* 0 .14 - 0 . 7 2 0.96 ±0.19 ± 0 . 1 1 - 0 . 45* 0.20 - 0 . 3 2 0 . 5 2 .±0.35 ± 0 . 1 1 0 . 0 0 - 0 . 1 2 -0 .24 0.61 ±0.38 ±0.09 0.07 -0 .08 Egg Wt. I - 0 . 1 5 ±0.21 - 0 . 2 0 0 . 4 4 +0.18 0 . 2 5 * - 0 . 1 1 ±0.22 0.12 0.06 ±0.23 0 . 3 2 * Egg Wt. II -0 .34 ±0.25 - 0 . 3 1 * 0.15 ±0.27 0.07 - 0 . 1 5 ±0.27 0 . 0 5 0 . 0 3 ±0.29 0 . 2 6 * Egg Wt. I l l -0.28 ±0.22 -0 .24* 0.27 ±0.27 0.16 - 0 . 2 5 ±0.23 0 . 0 0 - 0 . 0 7 ±0.25 0 . 2 1 * Egg.Wt. IV - 0 . 3 0 ±0.13 -0 .24* 0.10 ±0.23 0 .09 - 0 . 1 7 ±0.14 0 . 0 6 - 0 . 0 1 ± 0 . 1 5 0 .13 * Significant (HQs p = 0 , TL 0 . 0 5 ) . ** These values could not be calculated. Table 7c The Genotypic (TQ) and the Phenotypic (rp) Correlations of the UBC Line for the Egg Production Traits. Trait 540 - 325 No. 540 - 325 Mass Age at l s ^ Egg Body Wt. rG S.E. r P S.E. rP S.E. r p rG S.E. r p 540 - 325 Mass 0.99 +0.01 0.96* Age at l s " t Egg -0.44 +0.33 -0.02 -0.34 +O.36 -0.04 Body Wt.' O.67 1*0.08 -0.07 0.78 +0.06 -0.05 -0.78 to. 05 -0.25* Egg Wt. I . -0.09 +0.23 0.15 0.09 + 0.23 0.34* 0.33 to. 17 0.26* 0.67 to.20 0.09 Egg Wt. II -0.14 +0.28 0.07 0.05 +0.28 0.2?* 0.52 to. 18 0.35* 0.36 to.40 0.08 Egg Wt. I l l , -0.23 +0.24 0.03 -0.03 +0.25 0.23* 0.46 to. 17 0.27* 0.16 +0.40 0.17 Egg-Wt. IV -0.16 ±0.15 -0.04 -0.00 •+0.16 0.15 0.54 to. 09 0.21* -0.04 to.24 0.18 Trait Egg Wt . I Egg Wt. II P &g Wt. I I I rG S.E. rG S.E. rP rG ' S.E. rp Egg Wt. II 1.05 0.88* Egg Wt. I l l 1.0? O.87* 1.04 0.90* Egg Wt. IV 1.23 0.71* 1.19 0.76* 1.06 0.81* * Significant (Ho: p = 0, P (= 0.05). ** These values could not be calculated. j Table 8a. The Genotypic ( r G ) and the Phenotypic ( r p ) Correlations of the MH Line for. the Egg Produc-i t i o n T r a i t s . i • ' ' . T r a i t 540 No. 540' Mass 325 No. 325 Mas s rG S.E. . rp rG S.E. rp rG S.E. rp . rG S.E. r p 540 Mass 0.88 to .07 0.95* 325 No. 0.98 ±0.01 0.66* 1.08 ** O.56* 325 Mass 1.01 tttt 0.70* 1.15 ** O.67* 0.93 to. 05 0.93* 275 No.. 0.93 +0.04 0.56* 0.97 tO. 02 0.40* 0.75 tO.20 0.84* 0.77 to. 13 0.79* •275 Mass I.03 tt* 0.63* 1.11 ** 0.67* 0.87 tO. 08 0.93* 0.97 to.01 0.96* 540 - 275 No. 0.96 +0.02 0.89* 0.82 to. 90 O.89* 1.50 *•* 0.27* 1.10 tttt 0.34 540 - 275 Mass 1.00 0.82* 1.02 tttt 0.92* 1.78 **• 0.21 1.86 tttt 0.34 540 - 3 2 5 No. 1.07 ** 0.80* 0.79 to. 80 0.81* 1.12 *tt 0.27* 0.86 to. 05 0.16 540 - 325 Mass 1.04 tttt 0.78* 0.85 to. 10 O.83* 1.46 ** 0.04 1.60 tttt 0.15 Age at 1 s t Egg -2.23 *•* -0.37* -2.26 *•* -0.26* -2.78 *•* -O.56* -2.85 tttt -0.53* Body Wt. **- *tt 0.15 ** *tt 0.30* ** *•* 0.23 ** tt* 0.34* Egg Wt. I 0.54 to. 10 0.06 1.17 ** 0.28* 1.32 ** 0.09 1.15 tttt 0.31* Egg Wt. II 0.13 to. 40 0.01 0.61 to. 26 0.20 0.32 to.45 0.05 O.63 to. 27 0.17 Egg Wt. I l l -0.15 to. 47 -0.08 0.30 tO.46 0.20 0.17 to. 59 -0.18 0.30 to. 49 0.04 Egg Wt. IV -0.26 to. 39 -0.00 0.20 to. 52 0.15 0.67 to. 27 -O.56* 0.78 to. 17 0.08 ! * S i g n i f i c a n t (Ho: p = 0, P ^ 0.05). ! tttt T V I P R P v a l i i p s could not be ca l c u l a t e d . Table 8b . The Genotypic (r^) and the Phenotypic (rp) Correlations of the MH Line for the Egg Pro-duction Traits. Trait 275 No. 275 Mass 540 - 275 No. 540 - 2?5 Mass rG S.E. rp rG S.E. r p rG S.E. r p rG S.E. rp 2?5 No. 2?5 Mass 0.69 to.15 0 . 8 6 * : 540 - 275 No. 1.40 •** 0.17 0.95 to. 03 0 . 2 3 * 540 - 275 Mass 1.11 ## 0.06 1.22 ** 0.21 0 .76 to. 09 ' 0 . 9 6 * 540 - 325 No. 1.53 #*• 0.05 0.77 to.17 0 . 0 8 0 . 9 9 to. 01 0 . 9 7 * 0 .60 to. 21 0 . 9 3 * 540 - 325 Mass 2.57 ** - 0 . 0 6 1.86 *# 0 . 0 5 0 . 9 9 to. 01 0 . 9 4 * 1.06 0 . 9 7 * Age at lsz -2.55 ** - 0 . 6 0 * - 2 . 5 0 *# - 0 . 6 1 * - 2 . 2 2 - 0 . 0 7 - 2 . 4 5 - 0 . 0 2 Egg Body Wt. ** *# 0.24* ** *•* 0 . 3 6 * *-* ** - 0 . 0 1 ** 0.00 Egg Wt. I 1.06 •*# - 0 . 0 3 1.30 . 0.24* 0.57 to. 13 0.04 1.30 *•* 0.24* Egg Wt. II 1.17 . ## -0.14 0.61 to. 30 0.11 0 . 0 2 to. 50 0 . 0 6 0 .73 to. 30 0 . 2 9 * Egg Wt. I l l 0.24 to. 45 - 0 . 2 5 * 0 .49 to. 43 - 0 . 0 5 - 0 . 2 7 +0.56 0 . 0 3 . 0.28 to. 71 0 . 2 6 * Egg Wt. IV 0.44 to. 32 - 0 . 2 0 0.97 to. 03 0 . 0 1 - 0 . 8 9 to, 10 0 . 0 5 -0.14 to. 62 0 . 2 3 * Significant (H 0: p = 0, ? k 0 . 0 5 ) . ** These values could not be calculated. i Table 8c, The Genotypic ( r G ) and the Phenotypic (rp) Correlations of the MH Line, f o r the Egg j Production T r a i t s . T r a i t 540 - 325 No. 5^ 0 - 325 Mass Age at I s t Egg Body Wt. S.E. rp r G S.E. r p r G S.E. r p ' rG S.E. rp 540 - 325 Mass 0.68 tO. 12 O.96* Age at 1 s t Egg - 1 . 8 9 ** - 0 . 0 0 - 2 . 2 3 ** 0.03 Body Wt. ** ** - 0 . 0 5 ** tttt -0.04 ** ** - 0 . 3 0 * Egg Wt. I . 0.48 to. 17 0.00 1.76 ** 0.15 -3.22 * * 0.10 Egg Wt. I I 0.15 to.65 0.05 0 .92 to. 09 0.23 -1.07 ** 0.17 ** ** ** Egg Wt. I l l - 0 . 2 7 to.67 0.04 0.44 to. 39 0.23 - 0 . 3 0 t2,70 0.24* ** *•* ** Egg Wt. IV -0.98 tO. 02 0.04 - 0 . 3 0 ' to. 37 0.19 . -1.64 **. 0.10 ** ** ** T r a i t Egg Wt. I Egg Wt. II Egg Wt. I I I rG S.E. rp rG S.E. rp rG S.E. r-o Egg Wt. I I 1.48 tt* 0.85* Egg Wt. I l l 1.45 ** 0.78* 1.07 tttt 0.84* Egg Wt. IV 1.54 ** 0.55* 0.94 to. 04 0.58* 0.97 to. 02 . 0 . 6 1 * * S i g n i f i c a n t (Hos p - ,0, P k 0 . 0 5 ) . ** These values could not be ca l c u l a t e d . - 4o -than i n the UBG l i n e . This seems to be more so f o r the.genetic c o r r e l a t i o n between e a r l y and r e s i d u a l records of egg number and egg mass. For example, the genetic c o r r e l a t i o n between 275 days egg number and 540 - 275 days egg number was 0.42 i n the UBG l i n e as compared to 1,40 i n the MK l i n e . These higher c o r r e l a t i o n s may be due to the f a c t that the age at sexual maturity i n the MH l i n e d i d not contribute to the a d d i t i v e genetic variance of the e a r l y production records. Therefore, i n t h i s l i n e the genetic covariance between e a r l y and f u l l and e a r l y and r e s i d u a l production was high as compared to the UBG l i n e . R e l a t i v e E f f i c i e n c y of D i f f e r e n t C r i t e r i a of Selection . Two p a r t i a l record c r i t e r i a were used i n t h i s study; production up to 275 days of age and up to 325 days of age. The former would be the usual length of time that part records are used and the l a t t e r would be the maximum length of time one can a f f o r d and s t i l l keep the generation i n t e r v a l to 1 year. For each standard deviation i n the s e l e c t i o n d i f f e r e n -t i a l the expected gain per generation w i l l be the path between genotype and phenotype of that character which i s equal to the square root of the h e r i t a b i l i t y estimate (h). To f i n d the c o r r e l a t e d response, h i s m u l t i p l i e d by the genotypic c o r r e l a t i o n between the character selected and the c o r r e l a t e d character i n question. The r e s u l t s of r e l a t i v e s e l e c t i o n e f f i c i e n c y of both egg mass and egg number are presented i n Tables 9 and 10. In general, f o r egg number and egg mass, e a r l y records showed higher gains per u n i t of time than f u l l records. For s e l e c t i o n based on 275 days of egg mass, the genetic gain per u n i t of time f o r the UBC l i n e was a l i t t l e lower than the s e l e c t i o n based on 540 days of egg mass. I t would be of i n t e r e s t to observe the c o r r e l a t e d responses when selection.pressure i s applied on egg number and/or egg mass. Two important _ 41 -Table 9. Relative Efficiency (R.E.) of Different Selection Criteria (UBC). . .. Egg Number .  No. Production Age (Days) h x TQ Gain/Generation R.E. R.E./Year 1 2?5 0.922 x 0.600 2 325 O.655 x 0.977 3 540 0.9057 0.5532 0.6408 0.9057 0.6107 0.7075 1.0000 1.2214 1.4150 1.0000 Egg Mass No. Production Age (Days) h x T Q Gain/Generation R.E. R.E./Year 1 275 0.913 x 0.43 0.3999 0.4622 0.9243 2 325 . 0.726 x 0.75 0.5484 O.6338 I.2676 3 540 O.8653 O.8653 1.0000 1.0000 - 42 -Table 10. Relative Efficiency (R.E.) of Different Selection Criteria (MH). Egg Number  No. Production Age (Days) h x rg Gain/Generation R.E. R.E./Year 1 2?5 0.764 x 0.93 0.711 0.937 1.874 2 325 • 0.576 x 0.98 O.565 0.745 1.590 3 540 0.758 - 0.758 1.000 1.000 . Egg Mass No. Production Age (Days) h x r G .Gain/Generation R.E. - R.E./Year 1 275 0.622 x 1.11* 0.622. 0.872 1.744 2 325 O.667 x 1.15* O.667 0.935 I.870 3 540 0.713 0.713 1.000 1.000 * Value of 1., 00 was used for calculation. correlated characters to be considered are egg weight and age at sexual maturity. In the UBG li n e , egg weights measured at a l l 4 periods were negatively correlated to egg number of early, f u l l and residual records (Tables 7 a, b, c This was in agreement with the results obtained by Jerome et a l . (1956), Abplanalp (1957) and Waring et a l . (1962). Any attempt made to increase egg number in the UBG li n e , whether on ' early or f u l l records, should have an adverse effect on egg weight. In fact, long term selection experiments conducted on the basis of early production records by Morris (1963), Kinney est a l . (1970) and Bohren est a l . (1970) showed a consistent decline in egg weight for each generation of selection. In fact, in the later generation of these experiments the gain in egg number seemed to be offset by a reduction in egg weight. The economic implications of the reduction of egg weight are severe especially in the early production'period because very small eggs produced by pullets during the f i r s t 15 days or so would be uneconomical in the shell egg market. I t i s of extreme interest to note that the genetic correlations between egg mass and early egg weight were positive (Table 7a) and the genetic correlations between mature egg weight and residual egg mass were very small and negative ( Table 7b), , The genetic correlation between age at sexual maturity and egg number was consistently negative for a l l production periods (Table 7). The egg mass and age at sexual maturity were also negatively correlated for similar periods but the magnitude was lower than the genetic correlation between egg number and age at sexual maturity (Tables 7 a, b). Therefore, i f selection pressure was applied to egg mass in the U3C l i n e , the h e r i t a b i l i t y of which being similar to that of egg number, the egg weight would be expected to - 44 -remain constant or increase and the rate of reduction i n sexual maturity-would be decreased. In the MH l i n e , the s i t u a t i o n was d i f f e r e n t . In t h i s l i n e , negative genetic correlations existed only between mature egg weight and f u l l and residual egg numbers (Tables 8a, b), while a l l other genetic correlations between egg number and egg weight were positive. Positive genetic correlations between egg number and egg weight are not uncommon. Results of t h i s kind have been reported by Hicks (1958), Waring et a l , (1962) and Kordskog et a l , (1967). In the MH l i n e , no decline i n egg weight would be expected, especially early egg weight, i f selection vrere applied to early egg numbers. However, the negative genetic correlations (-0,153 to -0,980) of mature egg vreight with f u l l and residual records, indicated that a decline i n mature egg vreight may be expected i n a long term selection program, even though selection would only be applied to the early production period. In the MH l i n e , the genetic correlations of egg mass vrith egg weight were a l l p o s i t i v e except f o r the ones of residual egg mass (540-275 and 540-325 days) vrith egg vreight IV, This suggests that no adverse effects would be expected on egg weight i f selection vras applied to egg mass. Since the h e r i t a b i l i t y of age at sexual maturity i n the MH l i n e vras n e g l i g i b l e (O.Ol), the very high negative correlations of t h i s t r a i t with other t r a i t s appears to be of l i t t l e significance (Tables 8a, b and c ) . Therefore, l i k e the U3G l i n e , selection i n the MH l i n e on the basis of egg mass should be more advantageous than selection on the basis of egg number especially when the h e r i t a b i l i t i e s of these t r a i t s are of the same magnitude. The preceding discussion f o r both the l i n e s (UBC and MH) indicated that selection on the basis of egg mass should be more advantageous from an economic point of view. Selection f o r egg mass would be a selection f o r egg number and egg weight both. Though eggs are not marketed by weight, the grading of extra large, large, medium etc, could be considered essentially the same. Birds selected on the basis of egg mass should provide higher profits to the poultry producers. This contention was further amplified from the data in that negative genetic correlations between egg mass and age at sexual maturity was of considerably lower magnitude than the one of egg number with age at sexual maturity. Suggesting that selection based on egg mass is preferable, i t would be desirable to discuss in detail the effect of selection on early egg production (egg number and egg mass) records, Lerner and Cruden (1948), Lerner ajid Dempster (195&)i Oliver et al. (1957), Kinney et a l . (1970), Bohren et al. (1970) and Bohren (1970) have strongly recommended the use of early egg production records while Morris (1963), Gowe and Strain (1963) and Nordskog et al. (1967) have raised doubts about its usefulness. These latter authors have found that selection on the basis of early egg number records increased the egg number in the early egg production periods but i t did not increase the residual egg number. In fact, sometimes a decrease in the residual production was observed. This usuallyoccurred in the later part of their selection program. Bohren (1970) pointed out, this could happen only when the genetic correlation between early egg production and residual egg production was negative. Morris (1963) observed a decline over 8 years of selection in the estimated genetic correlation from O.56 to 0,14 between early and residual egg numbers. However, his realized genetic correlation, in fact, changed to a negative value when the residual production declined. Bohren (1970) main-tained that the genetic correlation between early and residual records in Morris's experiment, though i t declined, was s t i l l positive. However, the - 46 -results of his experiment did show a negative genetic gain in residual produc-tion when selection was based only on the early partial records. This decline in residual egg production seems quite plausible to this author. Since selection was based on early egg. production records at a specified date, this would result in a selection for reduction in age at sexual maturity, which in fact declined by 3*0-4.0 weeks. Though according to Morris, this was not the sole cause of the increase in egg number in the early partial records, the decline in age at sexual maturity could be con-sidered a major reason for i t . The results of Bray et al, (i960) were interesting. They found a positive genetic correlation (O.78) between age at sexual maturity and persistency, and a negative genetic correlation (-0.70) between persistency and early egg production to a fixed date. Persistency a s they defined was the egg production in thelatter part of the year of laying, which in turn would approximate the residual production in Morris's study. Thus, as the age at sexual maturity decreased, as in Morris's experiment, and the early egg production increased, the persistancy or the residual production decreased. Estimates of the genetic correlations between residual and early egg number obtained by VanVleck and Doolittle (1964) also supported this contention. Kraszewska-Domanska (1964) reported 3 out of 8 estimates of genetic correlations between early and residual production to be negative. In the present study, although a l l the correlations of this kind were found to be positive, they were of lower magnitude in the UBC line than the MH line. In fact, because of the low genetic correlation, the efficiency of the selection per unit of time based on records up to 275 clays of age for egg mass was less than the one based on the f u l l records (Table 9) . Admittedly, this may well be accounted for by the standard errors for genetic correlation and herit-- 47 -a b i l i t y . Even then, this author feels that the contention of Bohren et a l . (1970) about the use of early records as a basis of selection should be taken with caution. In his argument, he has stated that the average of the 8. estimates of selection efficiency based on early records reported by Kraszewska-Domanska (1964) was more efficient per unit of time than the selection efficiency using the f u l l records. However, low individual estimates of Kraszewska-Domanska should not be ignored, for the h e r i t a b i l i -ties and the genetic correlations within a population are peculiarities of that particular population. The reason put forward by Bohren (1970) for the failure of obtaining genetic gain in the long term selection experiments of Gowe and Strain (1963) and Morris (1963) was that these authors in thelatter part of their experiment also included egg weight in their selection program. This again suggests the usefulness of egg mass as the basis of selection, rather than egg number. The failure of Nordskog et a l . (1967) to achieve more gain from selection based on early egg numbers could be due to the low he r i t a b i l i t y of this t r a i t (0.09) as compared to the he r i t a b i l i t y of f u l l records (0.26). This situation was quite similar to one obtained in this study for the BA li n e where the h e r i t a b i l i t y of production up to 540 days of age was 0.33 and 0,31 for egg.number and egg mass respectively and the he r i t a b i l i t y of early egg production was negative. The relative efficiency of the early and f u l l records after two genera-tions of selection, calculated from the Nordskog et a l . (1967) data by the method of Lerner and Cruden (1948) for individual selection, shows that selection on the basis of early records was less efficient (0,82) than f u l l records (l.OO). The authors would have been better off by selecting their - 48 -b i r d s on t h e b a s i s o f f u l l r e c o r d s . T h i s a g a i n warns us t h a t t h e g e n e t i c p arameters a r e t y p i c a l f o r a p o p u l a t i o n and t h a t a g i v e n p o p u l a t i o n s h o u l d be t h o r o u g h l y examined b i o m e t r i c a l l y b e f o r e s t a r t i n g a s e l e c t i o n program. Among t h e l i n e s s t u d i e d h e r e , a s e l e c t i o n program f o r egg number and/or egg mass i n the BA l i n e would have t o be based on f u l l r e c o r d s . The h i g h h e r i t a b i l i t y o f r e s i d u a l egg p r o d u c t i o n i n d i c a t e d t h a t s e l e c t i o n f o r p e r s i s t e n c y W6uld be most d e s i r a b l e i n t h i s l i n e . I n t h e MH l i n e s e l e c t i o n on t h e b a s i s o f e a r l y r e c o r d s s h o u l d e n a b l e t h e i n v e s t i g a t o r t o r e a l i z e a c o n s i d e r a b l e g a i n i n b o t h e a r l y and f u l l r e c o r d s . I n t h e UBG l i n e s e l e c t i o n may be s t a r t e d on t h e b a s i s o f 325 days egg p r o d u c t i o n r e c o r d s b u t n o t on t h e b a s i s o f 275 days, e s p e c i a l l y f o r egg mass. A c o n s t a n t e v a l u a t i o n o f h e r i t -a b i l i t i e s and g e n e t i c c o r r e l a t i o n s o f e a r l y , f u l l and r e s i d u a l egg produc-t i o n r e c o r d s would be d e s i r a b l e f o r each g e n e r a t i o n o f s e l e c t i o n . EGG COMPONENT TRAITS Mean and S t a n d a r d D e v i a t i o n s The means and s t a n d a r d d e v i a t i o n s p e r t a i n i n g t o a l l t h e 13 t r a i t s s t u d i e d , i n each l i n e a r e g i v e n i n T a b l e 11. The means f a l l w i t h i n t h e r a n g e g i v e n by Shenstone (1968) i n h i s r e v i e w . While t h e p e r c e n t y o l k , p e r -c e n t s h e l l and p e r c e n t p r o t e i n vrere l o w e r than t h e a v e rage r e p o r t e d by Shenstone (1968), t h e p e r c e n t albumen and y o l k p e r c e n t s o l i d vrere h i g h e r . The e s t i m a t e s o f albumen p e r c e n t s o l i d and albumen p e r c e n t p r o t e i n were l o w e r i n t h i s s t u d y t h a n r e p o r t e d by E v e r s o n and Souders (1957) i n t h e i r r e v i e w . But, t h e y o l k p e r c e n t p r o t e i n and y o l k p e r c e n t s o l i d were h i g h e r i n t h e p r e s e n t s t u d y than t h a t r e p o r t e d by E v e r s o n and Souders (1957). F i x e d E f f e c t s The l e a s t s q u a r e a n a l y s e s ( T a b l e 12) r e v e a l e d t h a t e x c e p t f o r t h e p e r -c e n t s h e l l t h e l i n e e f f e c t was s i g n i f i c a n t f o r a l l t h e t r a i t s s t u d i e d . The Duncan's T e s t showed t h a t , a l t h o u g h t h e egg vreight between UBC l i n e and t h e _ 49 -Table 11. Means and Standard Deviations of the Egg Component T r a i t s f o r the 3 Lines,* T r a i t UBC MH BA Mean S.D. Mean S.D. Mean S.D. Egg Wt. (gms) 5.09 6 l . 9 0 p C -6.60 57 .62 b 6.00 Yolk Wt. (gms) I6.8?b 2.50 l6.85 b 2.44 1 7 . 3 0 a 2.73 % Yolk 28.?5b 2.63 27.20c 2.54 29.78a 2.45 Albumen Wt. (gms) 3 ° . 5 5 b 2.94 39.58a 4.78 35.23c 3.67 % Albumen 62.43b 2.3.2 63.88a 2.74 6 l . 3 5 c 2.48 S h e l l Wt. (gms) 5.17b 0.63 5.48a O.56 5.02c 0.60 % S h e l l 8 - 8 o a b 0.85 8.88a 0.81 8 . 7 0 b 0.75 Yolk % S o l i d 53 .50 a 0.72 53 .33 b 0.71 53 .23 b 0.62 Albumen % S o l i d 11 .63 a 0.64 11.44b 0.86 11.01c 0.86 Yolk % Protein l6.89 b 0.68 17.04a 0.55 17 .03 a 0.59 Albumen % Protein >.94a O.47 9.82b 0.57 9 . 5 1 c 0.49 Yolk S o l i d (gms) 9.02b 1.33 8 - 9 9 c 1.29 9.21a 1.46 Albumen S o l i d (gms) ^ • 2 5 b 0 . 3 8 4 . 5 2 a 0.60 3.87c 0.41 * The mean i n the same row with the common subscripts were not s i g n i f i -c a n tly d i f f e r e n t from each other (Duncan's Test, P 0 . 0 5 ) . Table 12. Summary of the Analyses of Variance: Line and Season-Age Effect on Egg Component Traits. Trait/ Total Total Fitted 1 S.S.2 Main E f f e c t s 3 ' -Line Season-Age (s) Interaction 3 Line x S Egg Wt. 0.52 19511.45 0.078* 0.43* 0.002 Yolk Wt. 0.66 3405.5? 0.007* 0 . 6 4 * 0.002 % Yolk. 0.50 3906.68 0 . 1 4 0 * 0.34* 0.010 Albumen Wt. 0.38 9088.63 0.170* 0.20* 0.003 % Albumen 0.38 3773.78 0 . 1 4 0 * 0.22* 0.00? Shell Wt. 0 . 1 8 203.22 0 . 0 8 0 * 0.09* 0.005 % Shell 0.21 3 4 0 . 2 ? 0.009 0.20* 0 . 0 0 4 Yolk % Solid 0.055 252.08 0.030* 0.20* 0.010* Albumen % Solid 0.44 354.73 0.100* 0.33* 0.010 Yolk % Protein 0.19 199.37 0.010* 0.16* 0.020 Albumen % Protein 0 . 1 4 152.16 0.11* 0.02* 0.01 df. 11 520 . 2 3 6 1 Fraction of the total sums of squares accounted for by fitting the effects in the statistical model (R 2). 2 Total corrected sums of squares. 3 Fraction of the total sums of squares accounted for by each effect in the statistical model. * Significant (P L 0.05). - 51 -BA line did not differ significantly, these lines exhibited significant differences in the rest of the traits (Table n), This was in contradic-tion to Cotterill et al. (1962) and Marion, W. et al. (1964) that the differences in the egg component traits would be mainly due to the differences in egg weight. Strain differences have been reported for egg size (Morris, 1954; Cotterill et al . 1962; Marion et al. I 9 6 8 ) , yolk weight (Morris, 1954), albumen weight (Morris, 1954), percent yolk (Cotterill et al . 1962; Marion, W. et al. 1964; Marion et al . 1965)» albumen percent solid (Cotterill et al. I962), protein percent in the whole egg (May and Stadelman, i960), percent albumen and percent shell (Marion, W, et al. 1964; Marion et al., 1965). The season-age effect was also significant for a l l the egg component traits (Table 12). While the egg weight, yolk weight, percent yolk, albumen weight and yolk percent protein showed a consistent increase from the first season-age to the fourth season-age, the percent albumen, percent shell and albumen percent solid showed a definite decreasing trend. The other 3 traits; shell weight, yolk percent solid and albumen percent protein did not show any trend but had significant differences between season-age groups ( Table 13) . Interestingly enough the season-age by line interaction was not signifi-cant for any of the traits. May and Stadelman (i960) also found the strain by season-age interaction to be non-significant for egg weight, content weight, percent water and percent protein. Similar results were obtained by Marion et al. (1966) for egg weight, percent shell, percent yolk and percent albumen. Marion, W, et al , (1964) did find a significant strain by season-age interaction for egg weight and percent shell. However, in their experiment they deliberately chose lines that had been selected for large and small egg size which probably affected the results. - ^ -Table 13 . Means for the Egg Component Traits for Each Season-Age Group (over the 3 Lines). Trait Season- Season- Season- Season--Age I Age I I Age I I I Age IV Egg Wt. (gms) 53.064d 58.659c 6l.680 b 63.6l7 a Yolk Wt, (gms) 13 .74l d 17.189C l8.280b I8.998 a' Yolk % 26.027c 2 8 . ? 3 1 b 29.68?a 30.002a Albumen Wt, (gms) 34.2?0d 36.889c 37.978 b 39.570a Albumen % 64.6l4a 62.265b 6l.473 c 6 l . 7 4 l b c Shell Wt. (gms) 4.921c 5 .290 a b 5.391a 5.219b Shell % 9.280a 8.963b 8.66oc 8.277d Yolk % Solid 53.487 a 5 3 . 3 4 6 a b 5 3 . 2 4 9 b 5 3 . 3 4 0 a b Albumen % Solid 12.079a 11.489b 11.173c 10.780d Yolk Protein % l6.710b I 6 . 8 l 5 b 17.26la l?.386 a Albumen Protein %. - 9.8 5 8 a 9.726b 9.680b 9-8l2 a b * Mean in the same row with the common subscripts were non-significantly different from each other (Duncan's Test, P 4 0 . 0 5 ) . -53-The l e a s t square analyses f o r each l i n e (Tables 14,15 and 16) showed the hatch e f f e c t to be generally n o n - s i g n i f i c a n t f o r the egg component t r a i t s , except f o r percent s h e l l i n the UBC l i n e and the BA l i n e , yolk percent protein i n the MH l i n e and the BA l i n e and albumen percent protein i n the BA l i n e . This general lack of s i g n i f i c a n c e vras not unexpected since the hatches were only 10 days apart. Therefore, the hatch e f f e c t was .not considered i n subsequent analyses f o r the estimation of h e r i t a b i l i -t i e s and genetic c o r r e l a t i o n s . The hatch by season-age i n t e r a c t i o n was a l s o n o n - s i g n i f i c a n t i n a l l t r a i t s except f o r yolk weight i n the BA l i n e and yolk percent protein i n the MH l i n e . The season-age e f f e c t within each l i n e was s i g n i f i c a n t f o r a l l the t r a i t s except the yolk percent s o l i d i n the MH and the BA l i n e s , the yolk percent protein i n the BA l i n e , the albumen percent protein i n the UBC and the BA l i n e and the albumen s o l i d i n a l l 3 l i n e s (Tables 14, .15 and 16). Duncan's Test f o r each season-age f o r each l i n e showed that the ranking of the season-age means follow the same general trend i n a l l l i n e s (Tables 17, 18 and 19). Since no season-age by s i r e i n t e r a c t i o n s were found, then as expected, the ranking of the season-age means f o r each l i n e followed the same general trend as observed i n the pooled data of Table 13. The r e s u l t s o f season-age e f f e c t s were i n agreement with May and Stadelman(i960) f o r albumen weight and egg weight, Cunningham et a l . (1960a and b ) f o r albumen weight, yolk weight and percent s o l i d and percent p r o t e i n i n albumen, C o t t e r i l l et a l , (1962) f o r percent s o l i d i n albumen, Marion, W. et a l . (1964) f o r percent s h e l l , percent yolk, percent yolk s o l i d and percent albumen s o l i d , Marion est a l . (1966) f o r egg weight, percent s h e l l , percent yolk and percent albumen. The only r e s u l t s which cont r a d i c t t h i s study were of Cunningham et a l . (1960b. ) f o r albumen percent. Table 14. Summary of the Analyses of Variance f o r the Egg Component T r a i t s (UBC). . ; • T r a i t T o t a l F i t t e d 1 T o t a l S.S. 2 . Main Hatch (H) E f f e c t s Season-Age (s) 3 S i r e H Interactions3 x-S S x S i r e Egg Wt. 0.76 5138.07 0.0002 0.56* 0.12* 0.01 0.04 Yolk Wt. 0.83 1237.11 0.0003 0.70* 0.06* 0.004 0.02 % Yolk 0.64 1373.89 0.0004 0.49* 0.05 0.007 0.06 Albumen Wt. 0.55 I7IO.I8 0.004 0.28* 0.15* 0.012 0.059 % Albumen 0 .60 1069.34 0.006 0.40* 0.097* 0.0006 0.074 S h e l l Wt. 0.45 77.43 0.0007 0.07* 0.24* 0.001 0.13 % S h e l l Wt. 0.46 143.27 0.02* 0.15* 0.20* 0.025 0.072 Yolk % S o l i d 0.41 103.24 0.010 0.03 0.15* 0.015 0.24 Albumen % S o l i d 0.68 82.33 0.0004 0.37* 0.15* 0.0017 0.08 Yolk % Protein O.38 92.72 0.002 0.09* 0,07 0.02* 0.13 Albumen % Protein 0.39 44.42 0.004 0.02 0.19* 0.01 0.10 Yolk S o l i d . 0.82 350.97 0.00 0.68* 0.06* 0.002 0.003 Albumen S o l i d 0.38 29.11 0.002 0.016 0.21* 0.014 0.090 df 63 198 1 . 3 14 3 42 1 F r a c t i o n of the t o t a l sums of squares accounted f o r by f i t t i n g the e f f e c t s i n the s t a t i s t i c a l model (R 2) 2 T o t a l corrected sums of squares. 3 Fract i o n of the t o t a l sums of squares accounted f o r by each e f f e c t i n the s t a t i s t i c a l model. * S i g n i f i c a n t (P <= 0 . 0 5 ) . - 55 -Table 15 . Summary of the Analyses of Variance f o r the Egg Com-oonent T r a i t s ... . (MH). T r a i t ' T o t a l F i t t e d 1 T o t a l s . s . 2 Main Hatch (H) E f f e c t s Season-Age (S) 3 S i r e I n t e r a c t i o n s 3 H XfS S x S i r e Egg Wt. 0 .63 6798 .24 0 .002 0 . 2 6 * 0.16* 0.0047 0.056 Yolk Wt. 0 .85 926.27 0 .002 0 . 5 1 * 0 . 0 ? * 0.004 0.053 % Yolk 6.60 1003.31 0.000 0 . 3 2 * 0 .12* 0.0012 0.066 Albumen Wt. 0 .47 3567.60 0.000 0.11* 0 . 2 1 * 0.0035 0 . 0 ? % Albumen 0 .47 1173.82 0.000 0.16* 0 .14* 0.0032 0.11 S h e l l Wt. 0.41 48,61 0.009 0.08* 0,15 0.004 0.10 % S h e l l 0 .58 103 .00 0 .002 0.15* 0 . 2 3 * 0.0036 0.11 Yolk % S o l i d 0 .45 7 8 . 8 3 0.000 0 . 0 2 0.11 0.030 0.26 Albumen % S o l i d 0 .68 114.92 0 .006 0 . 3 3 * 0.15* 0.0028 0.11 Yolk % Protein 0.64 47.35 - 0 .020* 0 .19* 0.16* 0 .036* . 0.19-Albumen % Prot e i n 0 .61 -50.71 0.01 0 . 0 6 * 0 . 3 4 * 0.004 0.19 Yolk S o l i d 0.84 260.58 0 .001? 0 . 5 0 1 * 0 .08* 0.002 0 .06 Albumen S o l i d 0 .39 56,29 0 .0053 0.0012 0 .28* 0.006 0.097 df 63 156 1 3 14 3 41 1 F r a c t i o n of the t o t a l sums of squares accounted f o r by f i t t i n g the e f f e c t s i n the s t a t i s t i c a l model ( R 2 ) . 2 Tot a l corrected sums of squares. 3 Fraction of the t o t a l sums of squares accounted f o r by each e f f e c t i n the s t a t i s t i c a l model. . * S i g n i f i c a n t (P L0.05). T a b l e 16. Summary o f A n a l y s e s o f V a r i a n c e f o r t h e E g g Component T r a i t s ( B A ) . T r a i t T o t a l F i t t e d 1 T o t a l S . S . 2 M a i n H a t c h (H) E f f e c t s S e a s o n -Age (S) 3 S i r e I n t e r a c t i o n s 3 H x S S x S i r e E g g Wt. 0.7.2 5921.79 0.0011 0.24* 0 . 1 3 * 0.0017 0 .09 Y o l k Wt. 0.74 1224.23 0.0005 0 , 3 3 * 0.11* 0 . 0 2 1 * O.O89 % Y o l k 0.55 988.68 0.015 0 . 2 2 * 0.14* 0.002 0.13 A l b u m e n Wt, 0.60 2216.18 0.003 0.14* 0.14* 0.006 0.14 .% Albumen 0.50 1010.40 . . 0.006 0.18* 0 . 0 9 0.012 0.19 S h e l l Wt. 0.51 59.61 0.009 0 . 1 0 * 0.14* 0.025 0.17 % S h e l l 0.53 91.45 0 .059* ' 0 . 0 7 * 0.04 0.013 0.14 Y o l k % S o l i d O.36 62.91 0.002 0.005 0 .06 0 . 0 2 O.27 A l b u m e n % S o l i d 0.51 121.61 0.003 0 . 1 5 * 0 .09 0.008 0.12 Y o l k % P r o t e i n 0.51 56.96 0 . 0 2 * 0 . 0 3 0.08 0.009 0.19 Albumen % P r o t e i n 0.39 39.71 0 . 0 2 5 * 0.029 0.17* 0.013 0.11 Y o l k S o l i d 0.73 349.22 0.0004 0 . 3 3 * 0.11* 0.018 0 . 0 9 A l b u m e n S o l i d , 0.41 27.27 0.008 0.021 0.17* 0.006 0.19 d f 63 164 1 .3 14 3 41 1 F r a c t i o n o f t h e t o t a l sums o f s q u a r e s a c c o u n t e d f o r b y f i t t i n g t h e e f f e c t s i n t h e s t a t i s t i c a l m o d e l ( R 2 ) . 2 T o t a l c o r r e c t e d sums o f s q u a r e s , 3 F r a c t i o n o f t h e t o t a l sums o f s q u a r e s a c c o u n t e d f o r b y e a c h e f f e c t i n t h e s t a t i s t i c a l m o d e l , * Significant (P 4 0 . 0 5 ) . T a b l e 17. Means and Standard D e v i a t i o n s f o r the Egg Component T r a i t s o f the .UBC L i n e f o r the 4 Season-Age G r o u p s . * T r a i t Season-Age -I Season-Age I I Season-Age I I I Season-Age IV. Mean S . D . Mean S.D. Mean S . D . Mean . S . D . Egg Wt. (gms) 52.90d 3.19 58.39 c 3.16 61.53b 3.50 62,83 a 3.39 Yolk Wt. (gms) I 3 . 7 4 d 1.14 16.93C 1.13 I8.44 b 1.35 1 9 . 2 6 a 1.52 % Yolk 25.94 d I .67 29.06 c I .67 29.93b 1.90 30.84 a 2.20 Albumen Wt, (gms) 34.26 c 2.26 2.70 37 . 7 2 a 2.37 38.42 a 2.59 % Albumen 6 4 . 7 3 a I . 8 5 62.08 b 1.88 6l.32 c I . 6 3 6 l . 0 3 c 1.72 S h e l l Wt. (gms) 4.91 b 0.53 5.26 a 0.73 5.33 a . 0.58 5.23 a 0.57 % S h e l l 9 . 2 ? a 0.73 8.82 b 0.88 8.65 b 0.72 8.32 c 0.78 Yolk % S o l i d 5 3 . 6 l a O.65 53 . 4 9 a 0.67 53.35 a 0.77 53.54 a O.78 Albumen % S o l i d 12.19 a 0.44 11.69 b 0.44 11.47 c 0.48 11.01d 0.61 Yolk % P r o t e i n l 6 . 7 0 b 0.49 l 6 . 4 6 b 1.01 17.08 a 0.34 17.24 a 0.47 Albumen % P r o t e i n 9.99 a 0.51 9.84 a 0.54 9.96 a O.38 9.98 a 0.43 Yolk S o l i d (gms) . 7 . 3 7 d 0.62 9.05 c 0.62 9.83 b 0.73 1 0 . 3 l a 0.82 Albumen S o l i d (gms ) 4 . l 8 a 0.35 4.06 a O.38 ^•33 a O.38 4 . 2 3 a 0.43 * Mean i n the same row with the common s u b s c r i p t s were not s i g n i f i c a n t l y d i f f e r e n t from each other (Duncan's T e s t , P 4 0.05). - 58 -Table 18, Means and Standard Deviations for the Egg Component Traits of the MH Line for each of the 4 Season-Age Groups,* Trait Season-Age . I Season-Age II Season-Age III Season-Age IV Mean S.D. Mean S.D. Mean S.D. Mean S.D. Egg Wt. (gms) 5 5 . 7 8 c 4.86 6 l . 9 6 b 4.45 64.35a 5.95 66 . 7 1 a 5 .53 Yolk Wt, (gms) 1 3 . ? 0 d 1.09 l ? . 0 4 c 1.30 I8 .20 b 1.57 19.02 a I .25 % Yolk 24.6% 1.79 27.54b 1.76 . 2 8-^ab 2.39 28 .59a 1.80 Albumen Wt, (gms) 36.78 c 4.08 39.34b 3.42 ^•55ab 5.06 42 . 2 3 a 4 .90 % Albumen 65.85 a 2.69 63. ^ b 1.84 62,80 b 2.81 6 3 . l 8 b 2.41 Shell Wt. (gms) 5 . l 9 b 0.50 5 . 6 l a 0.52 . 5 . 5 9 a 0 .55 5 . 5 4 a 0.62 % Shell "9.32a 0.66 9 . 0 6 a 0.60 8 . 7 1 b 0.76 8.30 b 0.88 Yolk % Solid . 53.49 a 0.46 53.46 a 0.73 53.12 b 0.72 5 3 . 2 2 a b 0.86 Albumen % Solid 12.24 a 0.56 11.^3b 0.56 11 .21 b 0.72 10.69 c 0^79 Yolk % Protein 16.70 C 0.57 17.00 b 0.48 17.02 b 0.35 17.50 a 0.48 Albumen % Protein 9 . 9 7 a O.56 9.84a 0.57 9.66 b 0.56 9 . 7 6 a 0.56 Yolk Solid (gms) 7.33a 0 .60 9. l l c 0.73 9.67b 0.85 10.12 a , 0.68 Albumen Solid (gms ) 4 . 5 1 a 0.62 4 . 5 0 a O.50 ^ . 5 5 a 0.66 4.50 a O.62 *- Mean in the same row with the common subscripts were not significantly different from each other (Duncan's Test, P 4 0 , 0 5 ) , Table 19. Means and Standard Deviations for, the Egg Component T r a i t s of the BA Line f o r each of the 4 Season-Age Groups.* • / / T r a i t Season-Age I Sea^on-/ II •Age Season-Age I I I Season-Age . Mean S.D. . Mean S.D. Mean ... S.D. Mean S.D. Egg Wt. (gms) 5 l . 9 5 d 4.19 5 7 . 0 7 c 3 . 6 8 6o.6o b 4 . 6 0 ' 6 2 . 7 6 a 5^92 Yolk Wt. (gms) 14 . 3 6 C 1.18 17i59b 2.68 I 8 . 7 8 a 1.52 1 9 . 3 0 a 1,92 % Yolk 2 7 . 8 3 c 1.48 2 9 . 9 2 b 2.46 •31.01a . 1.99 3 C 9 0 a 2.39 Albumen Wt, (gms) 32.54 d 2.53 34.83c 2.78 36.44b 3.08 3 8 . 0 5 a 3.98 % Albumen 6 3 . 0 2 a 1.72 61.04b 2.38 6 0 . 1 3 b .2.55 6 0 . 7 8 b 2.45 S h e l l Wt. (gms) 4 . 7 1 c 0.45 5 . 0 5 b 0.48 5 . 3 1 a 0 . 8 0 5 . 0 6 b 0.49 % S h e l l 9.13a 0.48 8 . 8 8 a 0.55 8 . 5 1 b 0.90 8 . 1 0 b O.58 Yolk % S o l i d 5 3 . 3 0 a 0 . 6 2 53.15a 0.50 5 3.24 a 0.57 5 3 . 2 1 a O.78 Albumen % S o l i d 1 1 . 6 l a 0.52 11.16b 0.55 1 0.64 c 0 . 8 8 1 0 . 4 4 a 0.94 Yolk % Protein l 6 . 8 l b 0.55 l 6 . 8 9 b 0.55 1 7 . 0 2 b 0 . 4 4 17.51a 0.57 Albumen % Protein 9 - 5 6 a b 0.42 9 - ^ 5 a b 0.47 9 . 3 7 b 0.54 9 . 6 6 a 0.52 Yolk S o l i d (gms) 7.65c O.65 9 . 3 4 t 1.42 1 0 . 0 0 a 0 . 8 3 10.27a 1.06 Albumen S o l i d (gms ) 3 . 7 8 a 0.37 3.89a 0.40 3.81a 0.45 3.82 a 0.77 * Mean i n the same row with common subscript's were not s i g n i f i c a n t l y d i f f e r e n t from each other (Duncan's Test, P L 0 , 0 5 ) . - 60 -A most interesting feature of these analyses was that the season-age by sire interaction was found to be non-significant for a l l the tra i t s in a l l of the 3 lines. The lack of a sire by season-age interaction showed that the sire effects were relatively constant across the season-age periods. This indicated a lack of genotype by environment interaction. This was consistent for the sire effects of a l l the 3 lines. A comparable report on this subject vras that of H i l l _et_ al_. (19&6). They found a sire by season-age interaction to be significant for 3 t r a i t s ; egg weight, shell weight and albumen weight, out of 8 tr a i t s that they studied. In their study, egg vreight and shell weight showed a highly significant season-age by sire interaction effect. As H i l l et a l , (1966) pointed out, the probable cause of this interaction was the high temperature in July and August in Texas, U.S.A. However, i n British Columbia, particularly in Vancouver (Canada), temperatures do not go as high as in Texas and the temperature variation i s not as extreme. Therefore, a season-age by sire interaction effect may not be expected. This means that although no age by sire interaction may exist, season by sire interaction could be expected especially for tr a i t s l i k e egg weight and shell vreight which apparently can be influenced by seasonal temp-erature (Benion and Warren, 1933 and Noles and Tindell, 1966). Phenotypic Correlations Since the season-age effect was found to be significant for'most of the egg component t r a i t s , the phenotypic correlations between these tr a i t s for each season-age were estimated and tested for significance. For a l l those tr a i t s for which the phenotypic correlations did not d i f f e r significantly over the 4 season-ages, a pooled estimate of the phenotypic correlation (p) for each l i n e vras made. The pooled data i s presented in Tables 20 and 21 , Ta.ble 22 shows significant phenotypic correlations for k season-age groups. Table 20. Phenotypic Correlations for the Egg Component Traits (UBC and MH Lines) 1. No. Trait 1 2 3 4 5 6 7 8 9 10 11 12 13 1 Egg Wt. 1.00 0.66 -0.16 0.85 0.07 0,,6o 0.08 0.11 0.20 0.08 . 0.09 0.66 0.74 2 Yolk Wt. 0.56 1.00 0.60 0.30 -O.63 0.37 -0.02 -0.00 -0.13 -0.07 -0.06 0.99 0.17 3 % Yolk -0.48 0.45 1.00 -0.45 * -0.12 -0.08 -0.13 -0.34 -0.18 -0.19 0.57 -0.50 4 Albumen Wt. 0.95 0.32 -0.68 1.00 0.44 0.42 -0.04 0.13 0.30 .0.14 0.14 0.31 0'.90 5 % Albumen 0.46 -0.34 •* 0.71 1.00 -0.23 -0.33 0.09 0.24 0.15 0.14 -0,60 0.44 6 Shell Wt. •0,59 0.37 -0.27 0.4?; 0.02 1.00 * 0.09 0.20 0.05 0.11 0.38 0.42 7 % Shell -0.29 -0.15 0.12 -0.37 -0.39 0.60 1.00 0.03 0.22 -0.02 0.10 -0.01 0.07 8 Yolk % Solid 0.10 0.14 0.05 0.10 0.06 -0.07 -0.19 1.00 0.18 0.09 -0.12 0.17 0.18 9 Albumen % Solid 0.21 0.07 -0.17 0.22 0.14 0.16 -0.03 0.06 1.00 0.06 •* -0.10 0.69 10 Yolk % Protein -0.06 -0.09 -0.02 -0.06 -0.04 -0.01 •0.04 0.07 -0.21 1.00 0.03 -0.06 0.13 11 Albumen % Protein 0.19 0.07 -0.14 0.21 .0.16 0.06 -0.11 0.05 0.57 -0.22. 1.00 -0.08 * 12 Yolk Solid O.56 0.99 0.44 0.32 -0.32 0.35 -0.17 0.30 0.08 -0.07 0.07 1.00 0.197 13 Albumen Solid 0.86 0.29 -0.62 0.91 O.63 0.45 -0.32 0.10 0.61 -0.13 0.42 0.30 1.00 * These correlations were found to be significantly different between 4 season-age groups. They are presented in Table 22, 1 The correlations above the diagonal are for the UBC Line and below the diagonal are for the MH Line. > Table 21 . Phenotypic Correlations for the Egg Component Traits (BA Line). No. Trait 1 2 3 4 • 5 . 6 7 8 9 10 11 12 13 1 Egg'Wt. 1.00 2 Yolk Wt. 0 . 5 4 1.00 ! 3 % Yolk - 0 . 2 6 * 1.00 . 4 Albumen Wt. 0 . 8 8 0.32 - 0 . 4 7 1.00 ! 5 % Albumen 0.14 - 0 . 4 7 # 0.52 1.00 : 6 Shell Wt. 0.66 •* - 0 . 2 0 0.58 -0.04 1.00 , 7 % Shell i 0.05 0 . 0 5 0 . 0 2 - 0 . 0 6 - 0 . 2 6 * .1.00 1 J 8 Yolk % Solid .0.01 0 . 0 8 . 0 . 0 5 0.05 0.02 - 0 . 0 1 - 0 . 0 2 1 .00 9 Albumen % Solid * 0.06 * * 0.06 0 .07 - 0 . 0 0 1 .00 j10 Yolk % Protein 0.01 - 0 . 0 8 - 0 . 0 8 0 .06 0.11 - 0 . 0 9 - 0 . 2 1 0 . 0 5 0 . 0 6 1.00 ! 11 Albumen % Protein 0.14 P.09 - 0 . 0 9 0.08 # 0.07 0 . 0 7 -0.04 0 . 6 3 0 . 0 3 1 .00 j 1 2 Yolk Solid 0 . 5 3 •* . * 0.32 -0.46 * 0 . 0 5 0 .20 0 . 0 9 - 0 . 0 7 0 . 0 9 1 .00 £ 13 Albumen Solid * 0.29 - 0 . 3 7 * 0.37 0.48 0 . 0 0 0 . 0 3 0 . 6 3 0.08 0.46 0.28 1.00 * These correlations were found to be significantly different between 4 season-age groups. They are presented in Table 2 2 . - 63 -Table 22, Phenotypic Correlations for the Egg Component Traits: Those tr a i t s for which correlations were found significantly different for the 4 Season-Age groups. Correlation Of With Season-Age I Season-Age II Season-Age I I I Season' Age IV UBC % Yolk % Albumen - 0 . 9 2 - 0 . 9 1 - 0 . 7 5 - 0 . 7 7 % Shell Shell Wt. 0.82 0.14 0.85 0.87 Albumen % Protein Albumen % Solid 0.10 , - 0 . 0 1 0.18 - 0 . 1 2 Albumen Solid Albumen % Protein . 0.38 0.40 0.39 0 .52 MH-% Yolk % Albumen -0.67 - 0 . 8 9 - 0 . 9 2 - 0 . 9 0 BA Yolk Wt. % Yolk 0.51 - 0 . 5 0 0.50 0 . 6 3 % Yolk % Albumen -0.87 - 0 . 3 5 - 0 . 5 6 - 0 . 8 9 Shell Wt. Yolk Wt. 0.70 0.12 0.19 O.36 Shell Wt. % Shell O.67 0.71 - 0 . 0 0 0.55 Albumen % Solid Egg Wt. 0.32 0 .20 0.01 -0.46 Albumen % Solid % Yolk --0.26 - 0 . 3 0 0.12 0.28 Albumen % Solid Albumen Wt. O.29 0 .23 - 0 . 0 9 -0.48 Albumen % Solid % Albumen 0.25 0.14 - 0 . 2 1 - 0 . 3 1 Albumen % Protein % Albumen 0.18 . 0.25 - 0 . 3 9 - 0 . 1 2 Yolk Solid % Yolk 0.99 0.25 0 . 9 9 0 . 9 9 Yolk Solid Albumen Wt. 0.50 - 0 . 3 1 0 . 5 2 0 . 6 2 Yolk Solid Shell Wt. 0.70 0 . 0 1 0.16 0.36 Albumen Solid Egg Wt. O.83 0.79 0 .66 0.45 Albumen Solid, Albumen Wt. 0.91 0 . 8 8 0 . 6 8 . 0.51 - 64 -The only t r a i t s which showed significantly different phenotypic correlations over the 4 season-ages for a l l 3 lines were percent yolk and percent albumen. This was the only correlation which "was-significantly different over 4 season-ages in the MH l i n e . While in the UBC l i n e there were 3 phenotypic correlations showing-significant differences over the 4 season-ages, the BA line had 14 of such phenotypic correlations (Table 2 2 ) , A l l the weight tr a i t s namely yolk weight, albumen weight, shell weight, albumen solid and yolk solid had high positive signigicant correlations with egg weight in a l l the 3 lines (,Tables20, 21 and 2 2 ) , These correlations for the UBG, MH and BA lines were 0 . 6 6 , O.56 and 0 . 5 4 for yolk weight, O .85, 0 .95 and 0 . 8 8 for. albumen weight, 0 . 6 0 , 0.59 and 0 .66 for shell weight, 0 . 6 6 , O.56 and 0 .53 for yolk solid and 0 . 7 4 , 0 . 8 6 and 0 .73 for albumen solid. The correlations of egg weight with albumen weight and albumen solid were higher than those of egg weight with yolk weight and yolk solid. This probably was because the albumen i s the larger component of egg weight. The phenotypic correlations between yolk vreight and yolk solid per se for the UBG, MH and BA lines were 0,99» 0.99 and 0 . 9 9 respectively and that of albumen weight and albumen solid per se were 0 . 9 0 , 0.91 and 0.81 respectively. The correlations of egg weight with the t r a i t s expressed in percentage vrere generally quite low and only a few of them were significant. Among the nonsignificant were those of yolk percent protein in a l l the 3 lines, albumen percent protein in the UBG and BA li n e , yolk percent solid in a l l the 3 lines, albumen percent solid in the BA l i n e , percent albumen in the UBG line and percent shell in the UBC and the BA lines. The phenotypic correlation between percent yolk and egg weight-was significantly negative in a l l the 3 lines: - 0 . 1 6 (UBC), - 0 . 4 8 (MH) and - 0 . 2 6 (BA) while the one of the percent albumen with egg weight vras positive in a l l the 3 lines: 0.07 (UBG), 0.46 (MH) and 0.14 (BA). Highly s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n s vrere found between yolk weight and percent yolk, albumen weight and percent albumen, s h e l l weight and percent s h e l l , yolk weight and s h e l l weight, yolk weight and albumen weight. These c o r r e l a t i o n s ranged from 0.30 to 0,65. Highly s i g n i f i c a n t negative c o r r e l a t i o n s were found betvieen percent yolk and percent albumen. For the 3 l i n e s , these c o r r e l a t i o n s were -0,86 (UBC), -O.87 (MH) and -0.74 (BA), Highly s i g n i f i c a n t negative c o r r e l a t i o n s were also obtained between yolk weight and percent albumen and albumen weight and percent yolk. The phenotypic c o r r e l a t i o n s between yolk weight and yolk percent s o l i d , yolk weight and yolk percent p r o t e i n , albumen weight and albumen percent s o l i d , albumen weight and albumen percent protein, albumen percent s o l i d and yolk per-cent s o l i d and yolk percent s o l i d and yolk percent protein were a l l of low magnitude and, i n general, n o n - s i g n i f i c a n t . H e r i t a b i l i t y and Genetic Correlation The h e r i t a b i l i t y estimates (h 2) and t h e i r standard e r r o r (S.E.) of the egg component t r a i t s are presented i n Table 23. These estimates f o r the 3 l i n e s were not consistent and f l u c t u a t e considerably f o r most of the t r a i t s . For example, the h e r i t a b i l i t y of yolk weight: -0.02 (UBC), 1.09 (MH) and 0.68 (BA), Sampling errors would appear to be one of the probable reasons f o r explaining the lack of consistency N = 57 (UBC), N = 43 (MH) and N = 49 (BA). The sample s i z e was more or l e s s d i c t a t e d by the length of time needed to perform chemical analyses. Another a t t r i b u t a b l e reason f o r these f l u c t u a t i o n s i n the h e r i t a b i l i t y estimates could be the presence of higher or lower between progeny within s i r e variance i n one l i n e or another (Table 24). For example, the non-additive variance f o r yolk weight'was 0,76 i n the MH l i n e and 1,62 i n the BA l i n e , while the s i r e component of variance ({- a d d i t i v e variance) vras 0.29 and 0.33 f o r the MH and the BA l i n e s r e s p e c t i v e l y . This l e d to the h e r i t a b i l i t y estimates of 1,10 in. MH l i n e - 6 6 -Table 23. H e r i t a b i l i t y Estimates (h 2) and Standard Errors (S.E.) of Egg Component T r a i t s f o r the 3 Lines. T r a i t . UBC K BA h 2 S.E. h 2 S.E. h 2 S.E. Egg Wt. 0.74 ±0.58 0.16 ±0.68 0.51 ±0.63 Yolk Wt. -0.02 ±0.47 1.09 ±0.?3 0.68 ±0.65 % Yolk 0.01 +0.47 -0.18 ±0.64 0.4? ±0.63 Albumen Wt. 0.73 + 0.58 -0.11 to.65 0.17 ±0.59 % Albumen 0.24 ±0.52 -0.14 to. 64 0.10 ±0.58 S h e l l Wt. 0.92 ±0.60 -0.02 to. 66 0.34 ±0.62 ' % S h e l l . 0.39 ±0.54 0.96 ±0.73 -0 .91 ±0.34 Yolk % S o l i d 0.77 ±0.59 -0.41 ±0.59 0.90 ±0.66 Albumen % S o l i d 1.31 ±0.61 0.67 . ±0.72 -0.23 ±0.52 . Yolk % Protein 0.33 ±0.53 0.79 ±0.73 0.25 ±0.60. Albumen % Protein 0.99 ±0.60 1.54 ±0.70 0.11 ±0.58 Yolk S o l i d -0.01 ±0.47 1.14 ±0.72 0.48 ±0.63 Albumen S o l i d 1.84 to. 60 0.05 ±0.6? 0,07 ±0.58 Table 24. Sire Component of Variance (s) and Progeny Within Sire (P/s) ... Variance, for the Egg Component Traits, Trait UBC MH BA S P/S S P/S S P/S Egg Wt. 1.45 .6.38 O.87 20.93 1.82 12.53 Yolk Wt. -0.01 1.15 0.29 0.76 0 . 3 3 1.62 % Yolk . 0.00 2.28 -0 .11 2.61 0.20 1.74 Albumen Wt, 0.75 3.35 -0.41 15.70 0.26 5 .91 % Albumen • 0.14 2.13 - 0 . 1 3 3.90 0.04 . 1.81 Shell Wt. 0 . 0 5 0.18 - 0 . 0 0 0 .22 0.01 0.15 % Shell Wt. 0.04 0.39 0 .09 0.28 -0.04 0.20 Yolk % Solid 0.04 0.1? -0.02 0.19 0 . 0 3 • 0.10 Albumen % Solid 0.06 0.12 0.04 0.20 -0.02 0.33 Yolk % Protein 0.01 0.14 0.02 0.07 0.01 O .I5 Albumen % Protein 0.06 0.17 0.07 0.12 0 . 0 0 0.14 Yolk Solid -0.00 0 . 3 2 0.09 0 . 2 2 0.08 0.48 Albumen Solid 0 . 0 3 0.07 0 .00 0.28 0 . 0 0 0.11 - 68 -and 0,68 i n BA l i n e without any applicable d i f f e r e n c e i n the proportion of the ad d i t i v e genetic variance, A s i m i l a r s i t u a t i o n existed f o r albumen weight be-tween the UBG l i n e and the BA l i n e , albumen percent s o l i d between the UBC l i n e and the MH line,, yolk percent protein between the UBC l i n e and the MH l i n e and between the MH l i n e and the BA l i n e and yolk s o l i d between the MH l i n e and the BA l i n e , Whenever a negative s i r e component of variance was obtained, the genetic c o r r e l a t i o n of that t r a i t with other t r a i t s could not be ca l c u l a t e d . The estimates of genetic c o r r e l a t i o n s and phenotypic c o r r e l a t i o n s (obtained a f t e r c o r r e c t i n g the data f o r season-age e f f e c t ) are presented i n Table 25, Most of these estimates seem to be reasonably consistent f o r the 3 l i n e s . L i ke phenotypic c o r r e l a t i o n s , the genotypic c o r r e l a t i o n s of egg weight with yolk weight, albumen weight, s h e l l weight, albumen s o l i d and yolk s o l i d vrere very high and. p o s i t i v e , t h i s can be compared to the genotypic c o r r e l a t i o n s of egg vreight with percent components which vrere low and of indeterminate sign. The r e s u l t s obtained by H i l l et a l . (1966) also followed the same pattern f o r the t r a i t s that they studied. While the genetic c o r r e l a t i o n s of yolk vreight with percent yolk s o l i d was negative (-0.93 ( B A))» that of yolk vreight with yolk s o l i d vras p o s i t i v e and near unity. The. genetic c o r r e l a t i o n s of albumen weight and albumen percent s o l i d vras p o s i t i v e (0,52 (UBC)), but lower than the one of albumen vreight with albumen s o l i d (0.89 (UBC) and 1.26 (BA)). The albumen percent protein showed a p o s i t i v e genetic c o r r e l a t i o n with egg weight: 0.21 (UBC), 0.25 (MH) and 0.93 (BA). But the r e s u l t s of genetic c o r r e l a t i o n s between yolk percent protein with egg weight were inconclusive: 1.16 (UBC), -I.30 (MH) and -1.28 (BA). The genetic c o r r e l a t i o n of yolk vreight with yolk percent protein was - 69 -Table 25 a. Genotypic and Phenotypic Correlations: Egg Weight.with Other Component Trai t s . 1 Trait UBC MH BA rG S.E. . rP rG S.E. rP rG S.S. rP Yolk Wt. ** •** 0.64* 1.68 #-* 0.59* 0.79 ±0.20 0.66* % Yolk -8.41 *•* -0.1?* *# -0.59* 0.37 ±0.37 -0.21* Albumen Wt. 0.96 ±0.03 0.88* ** ** 0.96* 1.20 *# 0.94* % Albumen 0.59 ±0.14 0.04 ** **• 0.55* -O.54 ±0.13 0.09 Shell Wt. 0.82 ± 0.15 0.68* ** *# O.62* 0.79 ±0.29 0.74* % Shell 0.80 ±0.10 0.20* -1.60 •X* -0.28* *# ** 0.06 Yolk % Solid 0.25 +0.40 0.13 ** 0.18* -0.62 ±0.37 0.09 Albumen % Solid 0.51 10.42 0.15* 0.59 ±0.6? 0.32* #-* **• -0.02 Yolk % Protein 1.16 0.07 -1.30 ** -0.00 -1.28 ±0.28 -0.80* ' Albumen % . Protein 0.21 ±0.46 0.08 0.25 ±1.40 0.33* 0.93 ±0.15 0.11 Yolk Solid ** 0.66* 1.88 0.60* 0.80 ±0.15 O.67* Albumen Solid 0.87 ±0.12 0.73* 1.02 0.92* 0.96 ±0.14 0.?6* 1 The Phenotypic Correlations were calculated after correcting the data for season-age effect. * Significant (K 0jp= 0, P L 0.05). ** These values could not be calculated. - y u -Table 25b, Genetic and Phenotypic Correlations: Yolk Weight with Other Component Traits, Trait UBC MH BA rG S.E. rP rG S.E. rP rG S.E. rP % Yolk ** ** 0 . 6 1 * ** ** 0.3Q* 0.84 t o . 11 0 . 3 0 * Albumen Wt. *•* **• 0 . 2 9 * ** ** 0 . 3 7 * 0.81 t o . 07 0 . 4 7 * % Albumen ** ** - 0 . 6 6 * ** ** 0 . 2 8 * - 1 . 5 9 ** - 0 . 5 1 * Shell Wt. ** ** 0.37* ** ** 0 . 4 5 * 0 . 9 3 tO. 04 0V50* Yolk % Solid ** ** -0 .10 ** tttt 0.16 - 0 . 9 3 t o . 07 0,04 Yolk % Protein ** . ** - 0 . 2 1 * -0.24 t o . 4 9 -0 .11 -0.14 tO. 26 -0.08 Yolk Solid tttt ** 0 . 9 9 * 1,00 0 . 9 9 * 0 .99 to.01. 1 .00* Table 25c , Genetic and Phenotypic Correlations: Albumen Weight with Other Component Traits,"*" UBC MH BA rG S.E. rP rG ' S.E. rP rG S.E. r p % Yolk - 8 . 3 0 ** - 0 . 5 1 * ** ** - 0 . 7 5 * 0 .62 t o . 45 - 0 . 4 4 * % Albumen 0.76 ±0.09 0.42* ** ** 0 . 7 5 * -1.24 ** 0 . 3 9 * Shell Wt. 0.79 ±0.18 0 .54* ** ** 0 . 4 9 * 0.97 tO. 04 O .69* Albumen % Solid 0.52 + 0 .41 0 . 3 0 * ** ** 0 . 2 7 * ** ** -0.04 Albumen % Protein 0.10 to. 48 0 . 0 8 ** ** 0 . 3 1 * 1.77 *•* 0.06 Albumen Solid 0.89 tO. 06 0 . 8 9 * ** ** . 0 . 9 3 * 1.26 ** 0 . 7 9 * ' 1 The Phenotypic Correlations were calculated after correcting the data for season-age effect. * Significant (H Q: p = 0 , P 4 0 . 0 5 ) . ** These values could not be calculated. Table 25d. Genotypic and Phenotypic Correlations: Between Egg Component Traits.^ Correlation UBC MH BA Of With r G S.E. r p r G S.E. r p r G S.E. r P Albumen % Yolk % Solid Solid ' >0.27 + 0.51 • 0.22* ** ** 0.13 ** ** 0.01 Yolk % Yolk % Protein Solid 0.71 ±0.13 0.14 ** ** 0.40* -0.46 ±0.19 0.15 Albumen % Albumen % ' Protein Solid 0.18 ±0.36 0.12 1.01 ** 0.82* ** ** O.69* • Yolk Yolk % Solid Solid ** ** 0.03 . ** . ** 0.28* -0.93 +0.04 0.12 Albumen Albumen % Solid Solid O.85 ±0.10 0.12 1.54 ** 0.60* ** ** . 0.57* % Yolk '% Albumen -0.48 ±0.19-0 .88* ** ** -0.90* -0.73 + 0.09 -O.76* 1 The Phenotypic Correlations were calculated after correcting the data for season-. age effect. • , • * Significant (H Q: f) = 0, P4 0.05). ** These values could not be calculated. - 72 -Table 25e, Genetic and Phenotypic Correlations! :Egg. Number with Egg Component T r a i t s . 1 Trait UBC MH- BA r G S.E. rP rG S.E. . r p rG S.E. Egg Wt. O.56 +0.22 -0.02 2.51 ** 0.14 -O.89 ±0 .05 -O.I3 Yolk Wt. ** ** -0 .26* -0 .03 +0 , 3 5 0 .03 -0.25 ±0.21 -0 .09 % Yolk -7.42 ** -O.29* ** #* -0.13 0 .03 to. 26 0 .06 Albumen Wt, 0 .90 +0.06 0 .15* ** ** 0 .19* -1.15 *•* -0.20* % Albumen •1.8? ** 0.33* ** *#• 0 .27* 1 .25 *-* -0.1?* Shell Wt. -0.14 +0.29 -0.01 #* ** -0.07 -1.12 ** -0 .06 % Shell -1.10 ** -0 .03 -0.55 t0.22 -O.23* ** ** -0.08 Yolk % Solid 1.14 ** 0.20* ** *# 0.08 1.58 •** 0 .30* Albumen % Solid 0.00 to. 25 0.43* -O.63 tO.22 0.08 -*# ** 0.14 Yolk % Protein 1.85 ** 0.00 -1.45 ** 0 .19* -3.68 ** 0.14 Albumen % Protein 0 . 0 5 to.28 -0.13 -0.00 ±0.24 0.15 I . 6 9 #* 0.18* Yolk Solid ** ** -0 .23* 0 .09 t0.28 0.04 -0.14 1 0 . 2 5 0.08 Albumen Solid 0.56 +0 . 1 9 0 .32* 3.77 *# 0.18* -1.68 ** 0.0? 1 The P.-henotypic Correlations were calculated after correcting the data for season-age effect, * Significant ( H Q ! p = 0, P£ , 0 . 0 5 ) . ** These values could not be calculated. - .73 -Table 2 5 f . Genotypic and Phenotypic Correlations: Egg Mass with Egg Component T r a i t s . ^ T r a i t UBC MH BA rG S...E. r p rG S.E. rp rG S.E, rp Egg Wt. 0.67 t o . 23 0 .15* 2.06 ** 0.42* - 0 . 0 3 t o . 36 0.08 Yolk Wt. ** •** - 0 . 1 5 * 0.34 tO. 42 0.19* 0 .30 t o . 29 0 .03 % Yolk - 6 . 9 0 *.* - 0 . 3 4 * **• ** - 0 . 3 1 * 0 .01 to, 37 - 0 . 0 3 Albumen Wt, 0 . 9 8 + 0 . 0 2 0 . 3 1 * •x-x- ** 0.47* - 0 . 0 0 t o . 60 0.00 % Albumen 1.50 ** 0 . 3 5 * ** ** 0 . 4 3 * 0 .52 t o . 58 -0 .11 S h e l l Wt. 0 . 0 5 t o . 39 0.10 ** ** 0.13 - 0 . 3 0 tO. 40 0,11 % S h e l l - 0 . 7 1 +0.28 0.00 - 0 . 6 9 t o . 23 - 0 . 2 9 * #* ** - 0 . 0 1 Yolk % S o l i d - 0 . 9 7 t o . 03 0 . 2 5 * ** ** 0.14 1.14 *# 0 . 3 0 * Albumen % S o l i d O.07 t o . 33 0.46* -0.17 t o . 49 0 . 2 2 * #* *# 0.17* Yolk % Protein ' 1.57 #* 0.04 -1.15 ** 0.16* - 2 . 9 0 ** 0.09 Albumen % Protein 0.15 to. 37 0.11 0 .22 t o . 31 0 . 3 0 * 1.39 ** 0 . 2 2 * Yolk S o l i d ** ** - 0 . 1 2 0.46 t o . 30 0 . 2 0 * 0.42 t o . 30 .0.05 Albumen S o l i d O.32 to. 33 0.46* 2.90 0 . 4 7 * - 0 . 5 4 t o . 64 0.11 1 • The Phenotypic Correlations were calculated a f t e r c o r r e c t i n g the data f o r season-age e f f e c t . * S i g n i f i c a n t (Ho: p = 0 , P 4 0 . 0 5 ) . ** These values could not be cal c u l a t e d • - 74 -negative: -0.24 (MH), -0.14 (BA). V/hile the genetic c o r r e l a t i o n of albumen weight with albumen percent protein was found to be p o s i t i v e : 0.10 (UBC), 1.77 (BA). The albumen percent protein showed a p o s i t i v e genetic c o r r e l a t i o n with albumen percent s o l i d : 0.18 (UBC), 1.01 (MH), and the genetic c o r r e l a t i o n of yolk percent protein with yolk percent s o l i d was 0.71 i n the UBC l i n e and -0.46 i n the BA l i n e . From the aforementioned r e s u l t s some i n t e r e s t i n g points should be noted. The h e r i t a b i l i t y o f yolk weight (-0.02 (UBC), 1.10 (MH) and 0.68 (BA)) and albumen weight (0.73 (UBC), -0 .11 (MH) and 0.17 (BA)) seem to be higher than percent yolk (0.01 (UBC), -0.18 (MH) and. 0.41 (BA)) and albumen percent (0.24 (UBC), -0.14 (MH), 0.10 (BA)). Yao and Skinner (1959) a l s o obtained s i m i l a r r e s u l t s . This seems to be very meaningful because, as reported e a r l i e r , the genetic c o r r e l a t i o n s of yolk weight and albumen weight with egg vreight were high and p o s i t i v e (l . 6 8 (MH) and 0.79 (BA)) while those of yolk percent with egg weight were low (0.37 (BA) and -8.41 (UBC)). Yao and Skinner (1959) also reported a negative genetic c o r r e l a t i o n between percent yolk and egg vreight ( -0,36). From a human n u t r i t i o n a l standpoint, yolk s i z e would be more important than the amount of albumen because the yolk contains 50 "to 54 percent s o l i d as compared to 10 to 12 percent i n albumen, In a d d i t i o n , many e s s e n t i a l n u t r i e n t s are present i n the yolk. Therefore, i t would be d e s i r a b l e to have a higher yolk y i e l d r e l a t i v e to albumen. This could be achieved e i t h e r by s e l e c t i n g f o r percent yolk or by s e l e c t i n g f o r yolk s i z e disregarding the egg s i z e . S e l e c t i o n of percent yolk vrould cause a decrease i n percent albumen because of the high negative genetic c o r r e l a t i o n between percent yolk and percent albumen: -0,48 (UBC) and -0 ,73 (BA), This r a i s e s a fundamental question as to what i s a b i o l o g i c a l - 75 -base l i n e f o r the proportion of albumen and yolk i n order to obtain optimum h a t c h a b i l i t y . A commercial egg destined f o r human consumption may not match up i n every respect with a hatching egg, Scott and Warren (l9hl) showed that a r a t i o of albumen to yolk weight between 2,14 to 2,33 does not a f f e c t h a t c h a b i l i t y but when r a t i o goes to as high as 2,37 or as low as 2,11 i t s u b s t a n t i a l l y reduced h a t c h a b i l i t y . I t should be noted that an increase i n yolk s i z e .would be automatic when s e l e c t i o n pressure vras applied to egg weight. This would be the consequence of the high p o s i t i v e genetic c o r r e l a t i o n between these t r a i t s : 1 .68 (MH) and 0.79 (BA). Therefore s e l e c t i o n on the basis of yolk weight may not be j u s t i f i e d . Another method could be to s e l e c t on the basis of yolk mass ( t o t a l •amount of y o l k . l a i d by a hen i n a production period). This should be a se l e c t i o n f o r both yolk number and yolk s i z e . I t would be of i n t e r e s t to know the genetic c o r r e l a t i o n of egg mass with- yolk mass. This c o r r e l a t i o n could not be cal c u l a t e d from the data a v a i l a b l e i n the present study. How-ever, the genetic c o r r e l a t i o n of egg mass with yolk weight was p o s i t i v e : 0 . 3 4 (MH) and 0 .30 (BA). The h e r i t a b i l i t y estimates obtained f o r each l i n e f o r yolk percent s o l i d and yolk s o l i d , albumen percent s o l i d and albumen s o l i d were quite v a r i a b l e and no d e f i n i t e trend could be established ( Table 25d), However, i t seems that the h e r i t a b i l i t y of percent s o l i d and s o l i d per se f o r yolk and albumen were not much d i f f e r e n t within each l i n e ( Table 23). This vras i n agreement with H i l l _et a l . (1966). The estimates of genetic c o r r e l a t i o n s between egg weight and percent s o l i d both f o r yolk ( 0 . 2 5 , UBC and - 0 . 6 2 , BA) and albumen (,0.51,UBC and 0 . 3 9 , MH) i n the present study were much lower than the genetic c o r r e l a t i o n s between egg weight and s o l i d per se i n the yolk ( l , 8 8 , MH and 0.80, BA) and the albumen (O.87, UBC; 1.02, MH and O.96, BA). Of additional interest was the negative genetic correlation between yolk weight and yolk percent solid (-0.93i BA) and the high positive genetic correlation between yolk weight and yolk solid (l.OO, MH and 0.99> BA). In the case of albumen, the genetic correlations of albumen weight with albumen percent sol i d and albumen solid were positive, but the correlation of albumen weight with albumen solid (0.89 UBC and 1.26, BA) was twice as large as that of albumen weight with albumen percent solid (0,52, UBC). Therefore, i f selection were to be on the absolute weight of either the egg, yolk or albumen the high positive genetic correlation should result in an increase in total solid or yolk solid or albumen solid respectively. However, i f the genetic gain were to be desired in the percent solid t r a i t , that t r a i t may have to be included within the selection program. Percent so l i d as a t r a i t i s more important for the eggs marketed to the breaking plants. A regula-tion of the Canada Department of Agriculture requires that Canada Grade A melange entering the interprovincial market shall contain not less than 25.8% total solids (Rose et a l . 1966). Here again, the question comes up as to what would be the optimum ratio of solid to water in the egg for maximum hatchability. Although water in the egg i s of minimal importance from a human nutrition point of view, i t i s very important for the developing chick embryo. Therefore, a better method may be to select on the basis of total solid l a i d by a hen in a given production period and l e t the hen adjust in terms of the amount of water she puts in the egg. Considering percent protein in yolk and albumen, i t appears that the he r i t a b i l i t y of percent protein in albumen (0 .99, UBC; I . 5 2 , MH and 0.11;-BA) was higher than the h e r i t a b i l i t y for percent protein in yolk (0.33t UBC; - 77 -0.78, MH) and 0.24, BA). The h e r i t a b i l i t y estimates of percent protein i n • albumen were quite close to percent s o l i d i n albumen within each.of the 3 l i n e s . The same was true f o r the genetic c o r r e l a t i o n s of these t r a i t s with egg weight. This would be expected since most of the s o l i d i n albumen would be p r o t e i n . Since i t i s e a s i e r to determine the percent s o l i d i n albumen than the percent protein i n albumen, an i n d i r e c t s e l e c t i o n program may be quite f e a s i b l e . I f gain i n the albumen percent protein i s desired, s e l e c t i o n f o r albumen percent s o l i d should r e s u l t i n an increase i n albumen percent p r o t e i n . The genetic c o r r e l a t i o n s of yolk percent protein with egg weight and yolk weight are rather inconclusive due to the v a r i a b i l i t y of the estimates. However, the moderate h e r i t a b i l i t y of yolk percent protein would seem to j u s t i f y i t s i n c l u s i o n i n a s e l e c t i o n program i f a gain i n yolk percent protein vras desired. However, some caution i s advised. I t has been shown that the t o t a l v a r i a t i o n i n the s o l i d s and protein t r a i t s i s not great, and progress due to s e l e c t i o n would be r e l a t e d to the a d d i t i v e genetic v a r i a t i o n . No matter how high the h e r i t a b i l i t y estimates are, a reasonably good amount of phenotypic v a r i a t i o n would be needed i n order to make progress. However, the s i t u a t i o n does not appear to be that disappointing, because there has been shown a considerable amount of v a r i a t i o n between the s t r a i n s . Therefore, the between l i n e v a r i a t i o n coupled vrith the vrithin l i n e v a r i a t i o n should enable the researcher to make considerable progress e s p e c i a l l y i f the a c t u a l population under s e l e c t i o n was a r e s u l t a n t mixture of 2 or more l i n e s . Within each l i n e the genetic and phenotypic c o r r e l a t i o n s of the egg component t r a i t s with egg mass and egg number showed that these c o r r e l a t i o n s vrere i n general higher vrith egg mass than with egg number (Tables25e and 25d), The estimated genetic c o r r e l a t i o n between 5^0 days number and the egg - 78 -component t r a i t s are i n general agreement with, those reported by H i l l et. a l . (1966) f o r yolk weight (-0.76), s h e l l vreight (-0.25), yolk p e r c e n t / s o l i d (0.26), and yolk s o l i d (-0,38). The genetic c o r r e l a t i o n s of egg number and egg mass with albumen weight, albumen percent s o l i d and albumen s o l i d were quite v a r i a b l e from one l i n e to another. I t i s important to note that the genetic c o r r e l a t i o n s between 5^0 days number and yolk weight were negative (-0,03, MH and -0.25, BA), The genetic c o r r e l a t i o n s of egg mass (5^0 days mass) with egg vreight were p o s i t i v e (0.34, MH and 0,30, BA)» vrhich again supported the idea that egg mass rather than egg number should be used as a c r i t e r i o n of s e l e c t i o n f o r f u r t h e r improvement i n poultry egg production stock. - 79 -S U M M A R Y A N D C O N C L U S I O N S This study vras conducted to make a biometrical evaluation of egg mass (vreight of the t o t a l eggs'laid i n a given period) i n order to determine i t s p o t e n t i a l as a new c r i t e r i o n f o r s e l e c t i o n as .compared to the conventional s e l e c t i o n programs based on egg number (early and f u l l production records). In a d d i t i o n , t h i s i n v e s t i g a t i o n evaluated the s u i t a b i l i t y of s e l e c t i o n on 12 egg component t r a i t s i yolk weight, albumen vreight, percent yolk, percent albumen, s h e l l weight, percent s h e l l , yelk percent s o l i d , albumen percent s o l i d , yolk percent protein, albumen percent protein, yolk s o l i d and albumen s o l i d . . The aforementioned t r a i t s vrere measured on 3 randombred l i n e s of chickens, 2 of which being the s i n g l e comb White Leghorn (UBCr and MH) breed and 1 of which being the Black Austrolop (BA) breed. The egg component t r a i t s vrere assessed i n quarterly periods (season-age) throughout the l a y i n g year, EGG PRODUCTION TRAITS " The h e r i t a b i l i t y estimates of egg number and egg mass f o r any given period (275 , 325 , 375, 4-50 and 540 days of age) vrere found to be i n c l o s e agreement. That i s , the h e r i t a b i l i t y estimates of egg number i n general, were s l i g h t l y higher than the h e r i t a b i l i t y estimates of egg mass. In the MH l i n e , the h e r i t a b i l i t y estimates of egg number and egg mass were consistent f o r d i f f e r e n t production periods. These estimates f o r 5^0 days No. and Mass, 450 days No. and Mass, 375 days No. and Mass, 325 days No. and Mass, and 275 days No, and Mass were O.58 and 0.51, 0.59 and 0.72, 0.45 and 0.62, 0.33 and 0.45, and 0.59 and 0.39 r e s p e c t i v e l y . In the UBC l i n e , the h e r i t a b i l i t y estimates were quite high f o r 275 days number (0.85) and mass (O.83), and decreased at 325 days (0.43 (number) and 0.53 (mass)) and 375 , 80 -days of age ( 0 , 2 ? (number) and O.58 (mass)). The h e r i t a b i l i t y of f u l l records, however, increased to 0 ,82 f o r egg number and 0 .75 f o r egg mass. In the BA l i n e , the h e r i t a b i l i t y estimates of egg production f o r 5^0 days ( 0 . 3 3 f o r number and 0.31 f o r mass) and450 days ( 0 . 3 6 f o r number and 0 . 2 5 f o r mass) of age were low compared to the Leghorn l i n e s . The h e r i t a b i l i t y estimates of ea r l y production (275, 325 and 375 days of age) were negative i n the BA l i n e . The genotypic c o r r e l a t i o n s of egg number with egg mass f o r the UBC and the MH l i n e (genotypic c o r r e l a t i o n s f o r the BA l i n e could not be c a l c u l a t e d because of the negative s i r e component of variance f o r a l l the ea r l y production records) ranged from O .69 f o r 540 - 325 days (residual) production i n the MH l i n e to O .96 at 540 days of production i n the UBC l i n e . The genotypic c o r r e l a t i o n s between early and f u l l records and e a r l y and r e s i d u a l records were, i n general, higher i n the UBC l i n e than i n the MH l i n e . However, i n most cases, the genotypic c o r r e l a t i o n s were higher than t h e i r corresponding phenotypic c o r r e l a t i o n s i n both the l i n e s . For egg number and egg mass, s e l e c t i o n from e a r l y production records showed higher gains per u n i t of time than f u l l production records; the exception being the s e l e c t i o n based on 275 days egg mass i n the UBC l i n e where the s e l e c t i o n e f f i c i e n c y vras a l i t t l e lower than s e l e c t i o n based on 540 days of egg mass. Because of the negative genetic c o r r e l a t i o n s between egg number t r a i t s and egg weight t r a i t s and p o s i t i v e c o r r e l a t i o n s between egg vreight t r a i t s and egg mass t r a i t s , a s e l e c t i o n f o r egg mass was recommended f o r the UBC l i n e . A s i m i l a r conclusion was drawn f o r the MH l i n e . In view of the r e s u l t s obtained f o r the 3 l i n e s , r e l a t i v e merit of - 81 -s e l e c t i o n based on e a r l y or f u l l egg records was discussed. I t was concluded that the d e c i s i o n as to which c r i t e r i o n should be used would have to depend upon the genetic properties of the population i n question. Therefore, a thorough examination of any population f o r i t s genetic parameters was strongly recommended p r i o r to i n i t i a t i n g a s e l e c t i o n program f o r the gain i n egg production t r a i t s . EGG COMPONENT TRAITS Line e f f e c t s vrere found to be s i g n i f i c a n t f o r a l l the egg component t r a i t s studied, except percent s h e l l , A season-age e f f e c t vras also found to be s i g -n i f i c a n t i n a l l the t r a i t s studied. While egg weight, yolk weight, percent yolk, albumen vreight and yolk percent protein showed a consistent increase from the f i r s t season-age to the fourth season-age, the percent albumen, percent s h e l l and albumen percent s o l i d showed a d e f i n i t e decrease. Season-age by l i n e i n t e r a c t i o n vras found to be n o n - s i g n i f i c a n t f o r a l l the t r a i t s studied. The within l i n e analyses showed that season-age by s i r e i n t e r a c t i o n vras found to be n o n - s i g n i f i c a n t f o r a l l the t r a i t s i n a l l the 3 l i n e s . A l l ' the weight t r a i t s : yolk weight, albumen weight, s h e l l weight, albumen s o l i d , and yolk s o l i d , had high, p o s i t i v e , s i g n i f i c a n t , phenotypic c o r r e l a t i o n s with egg vreight f o r a l l of the three l i n e s . The phenotypic c o r r e l a t i o n s of egg weight with the t r a i t s expressed i n percentages were generally quite low and only a few of them were s i g n i f i c a n t . Percent yolk vras negatively c o r r e l a t e d with egg vreight, while percent albumen had a p o s i t i v e phenotypic c o r r e l a t i o n with egg weight. The h e r i t a b i l i t y estimates obtained f o r most of the egg component t r a i t s were quite v a r i a b l e from one l i n e to another. The probable explanations put forward f o r the v a r i a t i o n i n h e r i t a b i l i t y estimates were: d i f f e r e n t amounts of a d d i t i v e genetic variance, d i f f e r e n t magnitudes of progeny within s i r e variance, and sampling error due to the sample size,, • The genotypic c o r r e l a t i o n s of egg weight with yolk weight, albumen weight, s h e l l weight, albumen s o l i d and yolk s o l i d were very high and p o s i t i v e . This can be compared to the genotypic c o r r e l a t i o n s of egg weight with percent yolk, s h e l l and albumen which were low and of indeterminate s i g n . The genetic c o r r e l a t i o n of yolk weight vrith yolk percent s o l i d was negative: - 0 . 9 3 ' (BA) and that of yolk weight vrith yolk s o l i d per se vras p o s i t i v e and near unity. The genetic c o r r e l a t i o n of albumen vreight and albumen percent s o l i d was p o s i t i v e : 0,52 (UBC), but lovrer than those of albumen weight with albumen s o l i d : 0.89 (UBG) and 1.26 (BA). The albumen percent protein showed a p o s i t i v e genetic c o r r e l a t i o n with egg weight: 0.21 (UBC), 0.25 (KH) and 0.93 (BA). But the r e s u l t s of genetic c o r r e l a t i o n betvreen yolk protein with egg weight vrere inconclusive: 1.16 (UBG), -1,30 (MH) and -1.28 (BA). The genetic c o r r e l a t i o n of yolk weight with yolk percent protein was negative: -0,24 (MH) and -0.14 (BA). However, the genetic c o r r e l a t i o n of albumen weight with albumen percent protein was found to be p o s i t i v e : .0.10 (UBC) and 1,77 (BA). The albumen percent protein showed a p o s i t i v e genetic c o r r e l a t i o n vrith albumen s o l i d : 0.18 (UBC) and 1.01 (MH) and the genetic c o r r e l a t i o n of yolk percent protein with yolk percent s o l i d vras 0,71 i n the UBG l i n e and -.46 i n the BA l i n e . The d e s i r a b i l i t y of increasing yolk s i z e vrithin an egg from a human n u t r i t i o n a l standpoint vras discussed. In view of the negative genetic c o r r e l a t i o n between percent yolk and percent albumen, and a probable necessity of an optimum r a t i o f o r maximum h a t c h a b i l i t y , a s e l e c t i o n program based on t o t a l yolk vreight produced by a hen i n a given period (yolk mass) - 83 -was suggested as a more f e a s i b l e method. In view of the importance of the water as an e s s e n t i a l n u t r i e n t f o r the developing chick embryo, i t was suggested that s e l e c t i o n be made on the egg s o l i d p_er se or egg s o l i d mass ( t o t a l amount of s o l i d l a i d by a hen i n a given period) and l e t the hen adjust i n terms of the amount of water she puts i n the egg. The h e r i t a b i l i t y estimates of albumen percent s o l i d and albumen percent protein were high and of the s i m i l a r magnitude. This was expected because most of the s o l i d i n albumen i s protein and i t was, therefore, suggested that s e l e c t i o n f o r percent protein i n albumen could be achieved through the s e l e c -t i o n of egg percent s o l i d which i s e a s i e r to determine. The phenotypic v a r i a -b i l i t y f o r egg s o l i d and egg protein t r a i t s was not great. 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