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Estimation of genetic parameters of egg production in Single Comb White Leghorn chickens developed from… Reed, Shawna Eileen 1985

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ESTIMATION OF GENETIC PARAMETERS OF EGG PRODUCTION IN SINGLE COMB WHITE LEGHORN CHICKENS DEVELOPED FROM A STRAINCROSS by SHAWNA EILEEN REED A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of P o u l t r y Science We accept t h i s t h e s i s as conforming to the r e q u i r e d standard UNIVERSITY OF BRITISH COLUMBIA May 31,1985 © Shawna E i l e e n Reed, 31,1985 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Poultry Science University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date; May 23.1985 Abstract In 1957, strains 3 and 4, two highly selected but unrelated strains of Single Comb White Leghorn chickens from Agriculture Canada's Animal Research Station at Ottawa were crossed to establish the Agassiz strain (strain 6). Further selection was imposed on strain 6 for improvements in hen-housed egg production (HHEP) based on part-records to 273 days and maintenance of egg weight, fertility, hatchability and viability. Data from 1957 to 1963 were analysed utilizing the SAS programs. There were no significant improvements in performance for HHEP, but egg weight, fertility, hatchability and viability were maintained. The lack of response to selection for HHEP was probably due to the following reasons: 1) too many traits were considered in the selection program at the same time, 2) negative genetic correlations existed among the selected traits, 3) strict adherence to a selection scheme was not practiced, 4) most of the traits under selection had low heritabilities, 5) the duration of the study was not long enough, and 6) the population size of strain 6 may not have been large enough. There was a significant decrease in body weight at 365 days (-4.33 ± 0.48, p < 0.0009). This decrease may be because of selection within full-sibs for more refined birds with better conformation as parents of the next generation. There were significant decreases in egg specific gravity at 225 and 450 days, and in Haugh units at 225 days, al-though Haugh units were increasing when measured at 450 days. The mean hJ for HHEP was 0.45, and the mean h2 for egg s s production to 273 days was 0.20 and the mean h2^ for the same trait was 0.33. The mean h 2 g and h 2 d estimates for egg weight at 225 days were 0.60 and 0.50, respectively. The mean h J g and h2^ for age at sexual maturity were 0.22 and 0.33, respectively, and those for body weight at 365 ii days were 0.53 and 0.62, respectively. The mean h 2 g and h J d for egg specific gravity at 225 were 0.64 and 0.33, respectively while those for Haugh units at 225 days were 0.57 and 0.68, respectively. These estimates were consistent with those found in the literature. The sctual selection differentials showed that selection was positive for egg production, while those for egg weight at 225 days were zero, and those for body weight at 365 days showed that selection was in the downward direction on the sires. iii Acknowledgements I would like to thank Dr. K. M. Cheng for his advice, patience, encouragement, and financial support (Natural Sciences and Engineering Research Council of Canada grant #A-8062) during the preparation of this manuscript, and for the opportunity to learn theoretical and practical aspects of quantitative genetic research under his supervision. I am indebted to Dr. A. T. Hill for the use of his unpublished data from which this thesis was developed. His expertise is greatly appreciated. I would also like to thank Drs. R. W. Fairfull and R. S. Gowe of the Animal Research Centre in Ottawa for making available the tapes on which the raw data was stored and for their helpful suggestions, and the technical assistance of Mr. L. B. Asselstine. The UBC computing centre provided the funds for statistical analyses and I am grateful to F. Ho and M. Grieg for their technical assistance with the SAS computer programs package. My thanks to my family who were very patient and understanding during the course of my studies. I would like to express my gratitude to the Department of Poultry Science for awarding me the C. W. Roberts Memorial Scholarship for two consecutive years, and I wish to thank my thesis committee for their guidance during the preparation of this thesis. iv Table of Contents List of Tables V l i List of Figures xiv 1. Introduction 1 2. Literature Review .3 2.1 Selection Limits 3 2.2 Effects of Strain Crossing 6 2.3 Physiological Relationships Between Egg Production Traits 8 3. Materials and Methods 12 3.1 Selection Program 12 3.1.1 Background of the Strains Used in the Program 12 3.1.1.1 Strain 3 12 3.1.1.2 Strain 4 13 3.1.1.3 Strain 6 14 3.1.1.4 The Ottawa Control Strain 14 3.1.2 Selection Procedures 14 3.1.3 Rearing and Test Procedures 17 3.1.4 Traits Measured 19 32 Statistical Analyses 21 4. Results 24 4.1 Heritability Estimates 24 4.1.1 Egg Production Traits 24 4.12 Egg Quality Traits 30 4.1.3 Other Traits .34 4.1.4 Control Population 34 42 Genetic Correlations 34 4.3 The Performance of Traits Measured in Strain 6 37 v 4.3.1 Egg Production Traits 37 4.3J2 Egg Quality Traits 41 4.3.3 Other Traits 41 4.4 Actual Selection Differentials 55 5. Discussion 57 BIBLIOGRAPHY .67 APPENDIX 72 vi List of Tables Table Page 3.1.2.1. Scheme for the selection of males and females 16 as parents of the next generation. 4.1.1.1. Heritability estimates based on the sire component 25 of variance for HHEP from 148 to 273 days for strain 6. 4.1.1.2. Estimates of the sire („' ),dam (#'.,) and 26 S u individual (<j*e) components of variance, and of the heritabilities based on the sire (h 2 g) and dam (h2^) components of variance for strain 6 for egg production from 148 to 273 days. 4.1.1.3. Estimates of the sire (<»').dam («,» ) and 27 s a individual U'e) components of variance, and of the heritabilities based on the sire (h 2 g) and dam (h2^) components of variance for strain 3 for egg production from 148 to 273 days (Gowe and Fairfull, 1985). vii 4.1.1.4. Estimates of the sire („' ) dam U'^) and 28 s a individual (#'e) components of variance, and of the heritabiIities based on the sire (h2s) and dam (h2^) components of variance for strain 4 for egg production from 148 to 273 days (Gowe and Fairfull, 1985). 4.1.1.5. Heritability estimates based on the sire (h 2 g) and 29 dam (h2^) components of variance for egg production from 148 to 497 and from 274 to 497 days for strain 6. 4.1.2.1. Heritability estimates based on the sire (h 2 g) and 31 dam (h2^) components of variance for egg weight at 225, 350 and 450 days of age for strain 6. 4.1.2.2. Heritability estimates based on the sire (h 2 g) and 32 dam (h2^) components of variance for egg specific gravity at 225 and 450 days of age for strain 6. 4.12.3. Heritability estimates based on the sire (h 2 g) and 33 dam (h2^)-components of variance for Haugh units at 225 and 450 days of age for strain 6. viii 4.1.3.1. Heritability estimates based on the sire (h2g) and 35 dam (h3^) components of variance for age at sexual maturity and body weight at 365 days of age for strain 6. 4.2.1. Mean genetic correlations (r ) among traits 36 measured for strain 6. 4.3.1.1. Means and standard errors for strain 6 and the 38 control strain, and deviations from the control for strain 6 for egg production from 148 to 273 days. 4.3.1.2. Means and standard errors for strain 6 and the 39 control strain, and deviations from the control for strain 6 for egg production from 148 to 497 days. 4.3.1.3. Means and standard errors for strain 6 and the 40 control strain, and deviations from the control for strain 6 for egg production from 274 to 497 days. 4.3.2.1. Means and standard errors for strain 6 and the 42 control strain, and deviations from the control for strain 6 for egg weight at 225 days in grams. ix 4.3.2.2. Means and standard errors for strain 6 and the 43 control strain, and deviations from the control for strain 6 for egg weight at 350 days in grams. 4.3.2.3. Means and standard errors for strain 6 and the 44 control strain, and deviations from the control for strain 6 for egg weight at 450 days in grams. 4.3.2.4. Means and standard errors for strain 6 and the 45 control strain, and deviations from the control for strain 6 for egg specific gravity at 225 days. 4.3.2.5. Means and standard errors for strain 6 and the 46 control strain, and deviations from the control for strain 6 for egg specific gravity at 450 days. 4.3.2.6. Means and standard errors for strain 6 and the 47 control strain, and deviations from the control for strain 6 for Haugh units at 225 days. 4.3.2.7. Means and standard errors for strain 6 and the 48 control strain, and deviations from the control for strain 6 for Haugh units at 450 days. x 4.3.3.1. Means and standard errors for strain 6 and the 49 control strain, and deviations from the control for strain 6 for age at sexual maturity. 4.3.3.2. Means and standard errors for strain 6 and the 50 control strain, and deviations from the control for strain 6 for body weight at 365 days in decagrams. 4.3.3.3. Means for strain 6 and the control strain for 52 fertility. 4.3.3.4. Means for strain 6 and the control strain for 53 hatchability. 4.3.3.5. Means for strain 6 and the control strain, and 54 deviations from the control for strain 6 for percent laying house mortality from 148 to 497 days. 4.4.1. Actual selection differentials for the sires and 56 dams of strain 6 for egg production from 148 to 273 days, egg weight at 225 days in grams, and body weight at 365 days in decagrams from 1957 to 1963. xi Estimates of the sire (e's), dam (o'a) and individual (a' ) components of variance, and the degrees of freedom (df g, df^ , and df g, respectively) of each component from the analyses of variance for strain 6 for 1957. Estimates of the sire (o' s), dam (<>'d) and individual (o'e) components of variance, and the degrees of freedom (df s > df^ , and df g, respectively) of each component from the analyses of variance for strain 6 for 1958. Estimates of the sire (,'s), dam ( o ' a ) anc' individual («'e) components of variance, and the degrees of freedom (df , df . , and df , 3 v s' d ' e' respectively) of each component from the analyses of variance for strain 6 for 1959. Estimates of the sire («»» ),dam („' ) and s a individual (o'e) components of variance, and the degrees of freedom (dfg, df d , and df g, respectively) of each component from the analyses of variance for strain 6 for 1960. xii Estimates of the sire ( c r ' s ) , dam ( c j ' d ) and individual (e»'e) components of variance, and the degrees of freedom (dfg, df^ , and df g, respectively) of each component from the analyses of variance for strain 6 for 1961. Estimates of the sire (a'), dam („•) and s a individual (<j'e) components of variance, and the degrees of freedom (dfg, df r f , and df g, respectively) of each component from the analyses of variance for strain 6 for 1963. Estimates of the sire („'s),dam (<j'd) and individual («'e) components of variance, and the degrees of freedom (df df_, and df v s' d ' e' respectively) of each component from the analyses of variance for strain 6 for 1957 to 1963. xiii List of Figures Figure 4.3.3.1 Page Mean body weights at 365 days vs year 51 xiv 1. INTRODUCTION In 1957, two unrelated strains of Single Comb White Leghorn chickens that had apparently plateaued in response to long-term selection for egg production were crossed to create a new strain in an attempt to increase productivity. This .experiment was conducted at the Agassiz Research Station as part of the straincross research carried out by the Animal Research Centre, Agriculture Canada. Research into the nature of selection limits, and efforts to break through these barriers to selection response were only beginning in non-commercial species such as fruit flies (Robertson, 1955) and mice (Falconer, 1953a, b, 1955, 1971; Falconer and King, 1953; Roberts, 1966, 1967). Straincrosses had been a source of interest to animal breeders in the agricultural industries as a means of increasing productivity by taking advantage of heterotic effects. In addition, there was considerable interest in selection plateaux and crossing strains was one method that was suggested to break through a selection limit. Hence, this study was initiated in order to determine if a cross between two seemingly plateaued strains would result in renewed response to selection in the hybrid. Unfortunately, the data from this straincross was not fully analysed at the end of the study. The estimation of the genetic parameters for the hybrid had to be carried out at the Animal Research Centre, Ottawa, as computing facilities were not available at the Agassiz Research Station. The data were shipped to Ottawa for keypunching, returned to Agassiz for checking, and then sent back to Ottawa for analyses. The heavy workload in Ottawa delayed the analyses of the Agassiz data. Furthermore, further selection on the parental strains at Ottawa yielded response, and it was shown that the parental strains were not near a plateau at the time this 1 2 cross was made (Gowe and Fairfull, 1985; A. T. Hill, personal communication). During that same time period (early 1960's), computing knowledge was going through a revolution as newer and better systems were being developed for data handling and processing. Computing facilities were constantly being updated which lead to many software/hardware incompatibilities which further delayed the analyses of the Agassiz project data. The purpose of this thesis is to utilize this set of data to 1) esti-mate genetic parameters and response to selection for the straincross, 2) show genotype by environmental interactions, if any, as the parental strains were selected in Ottawa where the control strain was also reproduced, and the straincross was selected in Agassiz, and 3) make comparisons between the straincross and the parental strains. These results will provide limited comparisons for data from the two parental strains (Gowe, personal communication). 2. LITERATURE REVIEW 2.1 SELECTION LIMITS Typically, artificial selection has been imposed on domesticated animals in order to improve some production trait whether it be eggs, milk, meat or wool often for a considerable number of generations in any one strain. The additive genetic component of the genotypic variance is the genetic component utillized during selection (Clayton, 1968; Falconer, 1981). Initially, a population may show positive selection response but this response may gradually decrease over time, and eventually plateau as additive genetic variance becomes exhausted. A limit will be reached as the frequency of selected alleles increases and eventually becomes fixed, and homozygosity increases due to inbreeding, particularly if the population size is small (Falconer, 1981; Falconer and King, 1953; Yamada et al., 1958). Although this topic is of interest in selection experiments, selection limits have not been a problem in commercial breeding operations as such populations are seldom closed to outside introductions of birds and lines are generally turned over rapidly. Even though additive genetic variance may decrease, phenotypic variance may remain constant due to environmental and non-additive genetic effects. Any dominance/epistatic genetic effects and genotype by environment interactions which were previously masked by additive genetic action may become relatively more important and increase in their contribution to the total variation (Falconer and King, 1953). In other words, the cessation of response to selection does not necessarily mean that the genetic variability in a population has been exhausted. Heritability, which is a measure of the ratio of additive genetic variance to the phenotypic 3 4 variation, may decrease and then appear to stabilize at a lower value than before selection was imposed. When calculated heritabilities remain constant over time, then some other explanation for the plateau in selection response must be considered (Lush, 1951): 1) non-additive gene action, where stabilization may be due to antagonistic pleiotropic gene effects, selection favouring overdominance, di-rectional dominance of alleles for the selcted traits, and rare, recessive alleles at low frequencies (Falconer, 1971; Roberts, 1966; Yamada et al., 1958), 2) negative genetic correlations, such that when a selection limit is approached, pleiotropic gene interactions that affect the total fitness may increase, and thus cause natural selection to work antagonistically to artificial selection in order to return the population to an 'optimum' fitness (this phenomenon of resistance to selection pressure is termed 'genetic homeostasis'; Lerner, 1948), 3) positive selection for a character at one stage of the life cycle and negative selection at another stage, and 4) selection for the characteristic in one flock, or ecological niche, and against it in another. Traits based largely* on non-additive genetic effects will not show response as selection is for overdominance and epistatic gene combinations. Genotype by environment interactions are transitory effects that will be broken up by recombination and dissipate in subsequent generations (Falconer, 1955). Negative genetic correlations between components are one of the causes of a low response to selection in multi-trait selection programs. Heritabilities of the individual trait or components may be high, but due to negative relationships between them the heritability of the combination or overall trait may be low, and consequently, response will be weakened. Pleiotropic gene interactions have the potential for forming many 5 harmonious combinations but if the effect is favourable on one trait and unfavourable in another, then response will be slow. Dickerson (1955) called this phenomenon 'genetic slippage'. As selection progresses, favourable and unfavourable combinations will be fixed or lost and thus their contribution to the genetic covariance will decrease over time, as the mixed combinations' portion increases. The genetic correlation will thus decrease and may eventually become negative (Liljedahl et al., 1979). Egg weight is a trait of economic importance to the poultry operator and so, has been selected for in many breeding programs, or at least actively maintained at some pre-existing level. Lerner and Gunns (1952) showed that eggs of intermediate weight were the optimum in terms of maximizing reproductive fitness. Consequently, birds showing high egg weights may be selected against in later stages of the program due to poorer hatchability than their smaller egg producing colleagues. However, there were studies that showed fertility, hatchability, and viability remained high or were improved in many complex breeding programs (see Lerner, 1950). Generally, poultry breeders are interested in selecting for the same set of traits regardless of environment thus the fourth of Lush's possibilities does not concern us here. Linkage can be a temporary cause of negative correlations between genes but is broken up by crossing over and recombination fairly quickly during selection, and so, is not a permanent obstacle to selection. The tighter the linkage , the more resistant the complex is to breaking up, par-ticularly in the areas near the centromeres of the chromosomes where crossing-over is a rare event, and thus these 'polygenes' may behave as units during selection (Mather and Harrison, 1949). Chance fixation of an unfavourable allele will depend on the population size, but may also be 6 caused by linkage to another selectively advantageous gene; however, this latter possibility will depend on the intensity of selection in a quantitative situation (Roberts, 1966). Rare recombinational events, and new mutations may introduce new additive genetic variance into a plateaued population such that response to selection is once more observed (Falconer, 1953a,b; Roberts, 1966). The population may then continue to increase in productivity until another selection limit is reached. 22 EFFECTS OF STRAIN CROSSING Straincrosses have been a great source of interest to poultry breeders as a means of increasing genetic variation particularly when the parental strains have been under long-term selection, and are showing a tendency to plateau in response to selection for one or more traits. Initially, the straincross may exhibit heterosis due to dominance and epistatic gene effects but as already mentioned, these effects cannot be directly selected for as emphasis is on the heterozygote. White Leghorn straincrosses exhibited higher heterosis if the parental strains were from differing genetic backgrounds due to the increased dominance and epistatic interactions between the different alleles (Fairfull et al., 1983). Even crosses of strains derived from the same genetic background exhibited subtantial heterotic effects possibly due to epistatic gene combinations present in the hybrid offspring that had been fixed in the parents (Falconer, 1971). The present study will not attempt to provide any information or direct evidence on this phenomenon since only two-way crosses were used. 7 Because of the differing straincross responses, the magnitude of heterosis expected cannot be predicted from parental performance (Fairfull, 1982). Typically, in strain and line crosses of chickens, heterotic advantages are for decreased age at sexual maturity, increased rate of egg laying and greater viability, higher body weight and greater egg weight, fertility and hatchability (Jerome et al., 1956; Gowe and Fairfull, 1982a). Straincrosses are expected to have as much or more additive genetic variance as the parental populations (Saadeh et al., 1968), and so continue to respond to selection at a greater rate than the parents which may have reached a selection limit (Falconer and King, 1953; Roberts, 1967). Consequently, the response curve is sigmoid in shape with three parts (Roberts, 1967), an initial lag(Saadeh et al., 1968;Falconer, 1971), a rapid response phase, and a final limit. There may be an initial reduction in hybrid fitness caused by deleterious epistatic interactions between recessive alleles; however, selection will quickly reduce the incidence of the deleterious alleles involved (Barton and Charlesworth, 1984). The initial lag portion of the response curve may also be caused by linkage disequilibrium. Recombination will release any potential genetic variability present within the new cross (Lush, 1947). Response will be impeded in the first few generation's of selection as favourable alleles from different lines are put in the repulsion phase of linkage when the hybrid is formed. Progress will then depend on sufficient numbers of crossovers becoming available for selection. As recombination puts genes into the coupling phase in increasing numbers, the rapid response phase of selection is entered (Thoday et al., 1964; Roberts, 1967). The limit reached in any selection program will depend on the amount of genetic differentiation between the lines before crossing 8 (Roberts, 1967). Lines are often inbred and then crossed to release potential genetic variability by recombination (Lush, 1947); however, the limit reached may not be the highest possible due to unfavourable alleles becoming fixed along with the selected alleles. Inbreeding degeneration will oppose selection because of the associated reduction in fitness of the population due to the increasing homozygosity from the random fixation of alleles. From the above discussion, it can be seen that how the population is constructed will affect the response to selection as the amount of genetic variance due to linked loci is maximized in populations derived from crosses of lines previously selected in the same direction (Hill and Robertson, 1966; Roberts, 1967). Selection within strains or lines can be ineffective in utilizing genetic variance due to epistasis and linkage (Saadeh et al., 1968) whereas recurrent reciprocal selection may make better use of non-additive genetic effects (Arthur and Beck, 1974). Furthermore, the method of construction of the population may also contribute to the selection limit. 2.3 PHYSIOLOGICAL RELATIONSHIPS BETWEEN EGG PRODUCTION TRAITS The criteria of selection should take into account the biological relationships between production traits that are being selected for, particu-larly with respect to the correlated responses expected in unselected traits. As mentioned in the previous section, the lack of response to selection will occur in a multi-trait selection program if selected traits are negative-ly correlated with each other. Response in unselected traits will be deter-mined largely by the degree of genetic correlation between themselves and the selected traits, and by the heritabilities of the traits involved. The physiological relationships between the traits may impose a limit on the 9 correlations and hence, the indirect response to selection. Egg production is often measured and expressed in several different ways. For example, individual egg records obtained over a set number of days will not account for differences in age at first egg or winter pause, whereas percent production from first egg to a fixed date will avoid bias due to differences in age at sexual maturity (Goher et al., 1978; Bohren, 1970). On the other hand, hen-housed egg production to a fixed date would include factors such as rate of egg production , age at first egg, and viability (Gowe and Fairfull, 1982b). Morris (1963) postulated that selection based on part-year egg records caused a pullet to deplete her egg production capacity earlier than a hen selected on the whole egg record, and thus actually decrease the pullet's production in the residual period. Physiologically, increased egg numbers from age at sexual maturity to a fixed date may be achieved by the pullet having to mature earlier or increase her rate of production by increasing clutch length, decreasing interclutch pauses, and hence, increasing her ovulation rate (Lerner, 1950;Liljedahl et al., 1984). Although other egg quality traits can be increased concurrently along with other traits, there is, theoretically, a limit to the rate of response to selection because, as the rate of egg production increases, egg weight tends to decrease possibly due to the redistribution of the hen's egg-making efforts. If the total egg mass is limited by the physiological capacity of the digestive system to metabolize feed for nutrients and energy, and the reproductive system to synthesize the necessary egg components, then selection for higher rate of lay will result in more eggs but of a lower weight, and vice-versa, selection for increased egg weight will decrease rate of lay (Liljedahl et al, 1979). There is also the possibility that reducing the interovulation period 10 reduces the length of time that the reproductive system has to increase the mass of the yolk in the ovary and the albumen in the isthmus, as well as the shell in the uterus which would influence its breaking strength. Related to this depletion of the egg production machinery is the physical capacity of the hen to ingest feed and turn it into eggs. If the necessary nutrients are not included in the diet, the hen will draw on body reserves until they are depleted and then she will cease production. For example, if the hen is not supplied with enough calcium, the shell quality of her eggs will decrease, and the eggs may not be marketable due to their low breaking strength. The internal quality of the egg will also decrease if the hen does not get enough protein and other nutrients in her diet which will result in decreased hatchability of the eggs, poorer chick quality and viability, as well as a reduction in the storage length of the eggs (Akbar et al., 1983). The dam will also influence the viability of her progeny by the amount of disease that may be transmitted via the egg, and the antibodies contained therein (Bennett et al., 1981; Nagai and Gowe, 1969). This discussion shows why response to selection in multi-trait selection programs may slow due to the above physiological considerations. Changes in genetic and physiological characters are known to occur with age. Heritabilities decrease as the birds get older possibly due to the inability of the aging birds to cope with external stresses such exposure to pathogens, and internal stresses such as egg-laying requirements. This in-ability increases the environmental variance which reduces the heritability: the ratio, of additive genetic variance to the total phenotypic variance (Liljedahl et al., 1984; Akbar et al., 1983). In summary, crossing two unrelated strains that showed a tendency to plateau in response to selection for egg production should result in an 11 increase in the additive genetic variance due to the increased number of alleles available from the gene pool, and a renewed response to selection at a greater rate than the parental strains. Heterotic effects should increase, temporarily, the selected egg production traits and also the correlated but unselected traits in the direction of the sign of their genetic correlations. Age effects will influence the characters measured due to the deterioration of the aging hen's ability to transcribe DNA and thus to synthesize the necessary metabolites (Liljedahl et al., 1984); consequently, comparison of characters across differing age groups or from one period in the pullet's 'career' to a later period must take into account these possible age effects. 3. MATERIALS AND METHODS 3.1 SELECTION PROGRAM In 1957, two strains of Single Comb White Leghorns that were highly selected for egg production, and that had showed a tendency to plateau in response to selection for egg production, were crossed to form the 'Agassiz' strain at Agriculture Canada's Agassiz Research Station, Agassiz, British Columbia (A. T. Hill, project notes). The straincross progeny were hatched in the summer of 1957 and their descendants were reproduced each subsequent year (except 1962) at Agassiz for a total of six generations in floor pens. Selection was imposed on this strain in the same direction and manner as the parental strains had been previously subjected to. In addi-tion, body weight at 365 days and conformation of birds within full-sib families were also taken into account (A. T. Hill, personal communication). 3.1.1 BACKGROUND OF THE STRAINS USED IN THE PROGRAM 3.1.1.1 Strain 3 Strain 3 (also referred to as the Ottawa strain; see Gowe and Fairfull, 1985) was developed from a flock of Single Comb White Leghorns kept at the Department of Agriculture's Animal Research Station in Ottawa, Ontario. This flock had been selected for egg production since the 1940's (Gowe et al., 1954) and possibly even ear-lier (Munro, 1936 and 1942). In 1948, the flock went through a bottleneck as only a very small number of males was used to sire the next generation. As a result, the Ottawa flock was considered to have a relatively narrow genetic base. The flock has been closed to introductions of new birds from other flocks since 1949 (Gowe and 12 13 Fairfull, 1980; Gowe et al., 1973; Gowe et al., 1959a). In 1950, a within-family division of the common base population of White Leghorn females was used to divide the Ottawa flock into two strains. One strain became the selected strain 3, and the other became the random-mated Ottawa control strain (see Sec. 3.1.1.4). For the first generation only, the males were used as sires across both populations. (See Sec. 3.12 for the selection criteria and procedures used.) 3.1.1.2 Strain 4 Strain 4 (also called the New strain; see Gowe and Fairfull, 1985) was established in 1951 from seven unrelated single comb White Leghorn strains that had been chosen for their apparent better than average performance on the Canadian Record of Performance (ROP) test (ROP test records made on different farms were compared as stocks were obtained from private breeders). A full 7 x 7 dial lei cross, including the diagonal, was set up, and the progeny from these forty-nine matings were tested for performance. The progeny were then intermingled and their descendants became strain 4 in 1951. The progeny of the original dial lei matings and their descendants were selected without reference to base stock origin; therefore, no time was allowed for recombination and crossing-over to occur. Strain 4 was maintained as a closed flock from its beginning in 1950 (Gowe et al., 1973). (Selection procedures for this strain are also presented in Sec. 3.12) 14 3.1.1.3 Strain 6 As previously mentioned, strain 6 (also referred to as the Agassiz strain in unpublished records) was established in 1957 by the crossing of strains 3 and 4. Strain 3 males were shifted to the strain 4 pens, and reciprocally the strain 4 males were placed with strain 3 females. Shifting of males took place at Ottawa in May of 1957 at the end of the regular pedigree breeding season. 3.1.1.4 The Ottawa Control Strain This strain (also known as Strain 5; Gowe and Fairfull, 1985) was established from the other half of the Ottawa flock (see Sec. 3.1.1.1.) in 1950. From 1950 until 1959, the control strain was maintained as a closed, random-breeding, flock-mated population. In 1960, the strain was switched to a random-mated, pedigreed breeding scheme (using artificial insemination) such that each sire produced a sire and each dam produced a dam in order to minimize genetic drift (Gowe et a I., 1959b). 3.1.2 SELECTION PROCEDURES Prior to 1950, the original Ottawa White Leghorn flock had been selected for egg production based on full laying records with birds held for two years or more. The selection history of the seven parental strains is not known, but they had better than average performance based on ROP records Strains 3 and 4 as well as samples of the control strain were kept on test for performance at several experimental branch farms across Canada for varying lengths of time (including Agassiz from 1950 to 1963) as well as at the main farm in Ottawa from 1950 to 15 1980 (Gowe et al., 1960; Gowe and Strain, 1963; Gowe et al., 1965). The breeding stock for each strain was maintained and selected only at Ottawa except for strain 6 which was kept and selected exclusively at Agassiz. Random samples of chicks of strains 3 and 4 and the control strain were shipped to the various farms participating in the genetic and environmental studies conducted over the 1950 to 1963 period. The Ottawa control strain was maintained concurrently with strains 3 and 4 to control for environmental variations (Gowe and Wakely, 1954; Gowe et al., 1959a,b). Selection was based on part-record performance from housing at 147 days to 273 days of age. The primary trait of interest was hen-housed egg production (HHEP) to 273 days, selected for on the basis of full and half-sib family records as well as individual performance. Independent culling levels were used to maintain existing levels of fertility, hatchability and viability. Fertility and hatchability were evaluated on the basis of parental records. Full and half-sib family records were also used to select for viability in the brooding, rearing and laying periods although viability in the latter period was also indirectly selected for in the HHEP trait. There was no selection for egg size in strains 3 and 4 from 1950 to 1952. When egg size dropped substantially in the first two generations of the selection program for the two strains, this trait was added to the selection criteria for all strains. Starting in 1952, females were selected for egg weight on the basis of pedigree records and then on their individual records starting in 1960. No selection emphasis was placed on egg quality measurements such as albumen height, specific gravity and blood spots, or age at sexual Table 3.12.1. Scheme for the selection of males and females as parents of the next generation. Males 1. Sire families were ranked based on the egg production records of full and half-sib females within each sire family, and the top 5 sire families were chosen from 20 to 40 sire families available in each generation. 2. For these 5 sire families, dam families were ranked within sire based on the egg production records of full sisters (the range was 5 to 9 dam families per sire). 3. Two brothers from each of the top 2 or 3 dam families within each sire family were chosen to be sires of the next generation. In chosing these males, body weight and conformation were also taken into acccount. 4. For any given year, approximately 25 males were used as sires of the next generation (the range was 20 to 40 sires per generation). Females 1. All females were ranked by individual performance using egg production records, and the top 225 females were selected (the number of females available for each generation ranged from 400 to 1010). 2. From these 225 females, pullets from families with low fertility and low hatchability were culled as well as those females with low egg weight based on individual records. 3. For any given year, approximately 200 females were chosen as dams of the next generation. 17 maturity (except indirectly through HHEP to 273 days of age). In addi-tion, body weight and conformation at 365 days were taken into account for strain 6 within the selected full-sib families. Birds that were lighter and showed more refined conformation were more likely to be chosen as parents of the next generation. In order to be able to compare the part-record performance with the residual period (274 to 497 days) and the full record, all strains were kept on test to 497 days of age, even though breeding stock was selected at 273 days of age. In 1957, the first year of record keeping for strain 6, birds were only kept on test until 424 days of age because the flock was not established until June of that year. Therefore ,the full record for that year is 73 days short of the full 497 days used in other years. 3.1.3 REARING AND TEST PROCEDURES All eggs were hatched at Ottawa for the first year of the study, and the chicks were shipped by air express after hatching to Agassiz in early June of 1957. From the second generation on, start-ing in the spring of 1958, individually sired matings were made at Agassiz. So as to avoid the need to subdivide the pens for individually sired matings, all matings were performed by artificial insemination. For each generation, 25 sires and 250 dams were chosen by family from strain 6 as parents of the next generation. Eggs were saved for twenty days at Agassiz. Approximately 200 eggs of the control strain were sent from Ottawa to Agassiz for hatching with strain 6. Strains were randomly assigned to trays in a Jamesway incubator. As soon as the chicks were hatched, they were 18 wing-banded and intermingled under brooders. Cripples were rejected at hatching. The chicks were exposed to continuous light for the first 48 hours only, and then natural lighting thereafter. A minimum of 225 cm3 per chick was allowed until four weeks of age when the spacing was increased to 450 cm3. Each chick was allowed 4 cm of feeding space until six weeks of age when the allotment was increased to 8 cm. Weather permitting, chicks were transferred at six weeks of age to range shelters or colony houses rotated on pastures until housing. The birds were housed at 147 days of age with no culling occuring at that time. From 1957 to 1963, birds were assigned randomly to deep litter pens and trapnested five days per week. All egg records were based on five consecutive days per week but softshelled eggs were not included. Each bird was allotted 0.30 m2 of floor space in the laying houses with a minimum of 14 m2 of feeding space per 100 hens, and 35 trapnests provided per 100 hens. An all mash ration of 15.8% crude protein was fed ad libitum (Gowe et al., 1960). The ration was formulated to the Animal Research Centre's specifications at a number of local commercial feed plants. A mini-mum photoperiod of thirteen hours of light per day was provided during the laying house test. In 1962, strain 6 was not reproduced because of the leave of absence of the principle investigator; the 1961 selected parents were held over and bred in their second year to produce the 1963 Agassiz population. 19 3.1.4 TRAITS MEASURED A variety of egg production and related traits were recorded (see below) for strain 6 and the control strain. Day of hatch was counted as day zero and the following day as day one, and so on until end of test at 497 days. Age at sexual maturity was the age in days when the first egg was detected. Body weights at housing (147 days) and 365 days of age were recorded for each bird, as an aver-age of a group of birds weighed, to the nearest decagram. Age of death and cause of death were also noted, although known accidental deaths, e. g. predators, drowning, were eliminated from the records to avoid biasing mortality upwards. Individual egg production was recorded for five periods, 148 to 273, 274 to 385, 386 to 497, 148 to 497, and 148 to 385 days. Number of eggs laid in each period by each hen was recorded, and the percent hen-day rates of production, uncorrected and corrected for age at first egg, were also calculated. Egg quality traits were recorded at three different times during the test year, 225, 350 and 450 days, except for 1957 when the birds were only kept on test until 424 days. For this year, the 450 day measurements were actually done at 424 days. Individual eggs were weighed to the nearest gram on a shadograph scale. Egg specific gravity was determined by floating eggs in salt solutions ranging in specific gravity from 1.066 to 1.102 by increments of 0.004, at a room temperature of 70°F. Albumen height was measured with a tripod micrometer as the height of the thick albumen midway between the edge of the yolk and the outer edge of the thick white at the point where the thick albumen is the widest, avoiding the chalazae. 20 Haugh units were then calculated from the above information. Blood spots were also coded as ' 1 ' for small spots (less than 3 mm), or '2 ' for large spots (greater than 3 mm); however, this trait is not analysed in this thesis. For each bird, the dam's incubation record was included. Number of eggs set, number of eggs fertile, number of embryos dead at 18 and 22 days, number of pips and number of fertile eggs hatched were recorded. For some years, the number of crippled chicks was also noted, although these chicks were not raised for the experiment. 21 32 STATISTICAL ANALYSES After obtaining the data which was stored on tapes in Ottawa, several var-iables were created from the recorded data in order to calculate the effects of selection. HHEP for three periods, 148 to 273 (short-term record), 274 to 497 (residual record), and 148 to 497 days (whole record), was calculated by summing the number of eggs laid by each hen housed in a family and then divided by the number of hens housed from that family. Individual egg production records used to calculate the estimates of heritabilities from the sire and dam components of variance are the same as the HHEP records used by the Animal Research Centre in Ottawa to calculate these same estimates (Fairfull, personal communication). Laying house mortality was calculated for the entire laying house period (148 to 497 days) and expressed as a percentage. Fertility was calculated as the number of fertile eggs divided by the number of eggs set, and expressed as a percentage. Hatchability was calculated as the number of fertile eggs hatched divided by the number of fertile eggs set, and likewise, expressed as a percentage. All percentages were transformed to arcsin values before analysis in order to avoid bias due to skewness of the data. All data manipulations and statistical analyses were performed using the SAS computer programs package (SAS Institue Inc., 1982 a,b) installed at the University of British Columbia's computing resources centre. Means, standard errors, variances, and number of valid observations included in each analysis for all traits were generated for strain 6 and the control strain, using PROC MEANS in the SAS package (SAS Institute Inc., 1982a, pp. 527-532). Regression analyses were performed on the means over time using PROC REG (SAS Institute Inc., 1982b, pp. 39-84). 22 Analyses of variance and covariance were performed on selected traits of strain 6 by year in order to determine the sire and dam components of variance, according to the following model where all varia-bles except the mean were considered random; Y = / x + s + d + e where: Y is the dependent variable, ijk H is the population mean, th s is the i sire; i = 1, „., I, / th th d is the j dam nested within the i sire; j = 1 J, th th e is the k offspring nested within the j dam; <ij)k k = 1, .... K. Because the model effects were nested and considered to be random (ex-cept the mean), PROC NESTED was used (SAS Institute Inc., 1982b, pp. 201-204). Regressions of heritabilities which were calculated from the sire and dam components of variance were performed in order to determine if they were changing over time as estimated by the regression coefficient, b, its standard error, and level of significance. Because selection was based on dam-family means, the model used in the analysis of variance for HHEP was reduced to sire effects only; therefore, dam heritabilities could not be calculated. 23 Strain 6 deviations were calculated as the difference between their means and those of the Agassiz hatched control strain. Regressions of deviations on time are presented for strain 6 for all traits studied in this thesis as the regression coefficients are used to estimate the responses to selection. Mean heritability estimates were calculated for the entire study period by introducing a year (g / ; 1 = 1,...,6) effect into the model, and again, all effects except the mean were considered random: Y = u + g + s + d + e ijkl / (H)j (Hj)k These overall means were used to make comparisons to published data from strains 3 and 4. 4. RESULTS HERITABILITY ESTIMATES 4.1.1 EGG PRODUCTION TRAITS The heritability estimates based on the sire component of variance (hJg) for HHEP for strain 6 are reported in Table 4.1.1.1. The sire component of variance (o-'s) for the short-term egg production period showed a large jump after two generations of selection (1959) then decreased to almost zero in 1963. The hJ estimate for the entire s study period from 1957 to 1963 was 0.45. Estimates of „> , -» and «• (progeny component of variance), h J s and h5^ (the heritability estimate based on the dam component of variance), and regressions of these estimates on time for strain 6 for the individual short-term egg production record (which are the same as individual HHEP in Gowe and Fairfull, 1985) are presented in Table 4.1.12. These same estimates for strains 3 and 4, taken from Gowe and Fairfull (1985) can be found in Tables 4.1.1.3 and 4.1.1.4, respec-tively, for comparison. None of the linear regressions of these estimates on time for strain 6 were significantly different from zero due to large standard errors. With the exception of 1963, the h J g estimates were consistently higher than those of the parental strains . The h 2^ estimates, however, fluctuated from year to year. The h J g and h 5^ estimates for short-term and residual record egg production for strain 6 are shown in Table 4.1.1.5. the estimates for the whole test year followed the same trend as those for the short-term record, but those for the residual record showed slight though non-significant 24 Table 4.1.1.1. Herltablllty estimates based on the sire component of variance for HHEP from 148 to 273 days for strain 8. Year S t r a i n 6 1957 0.34 ± 0.18 1958 0.19 + 0.18 1959 1.16 ± 0.45 1960 0.70 ± 0.32 1961 0.40 ± 0.24 1962 1963 0.03 ± 0.24 mean 0.45 ± 0.10 cn Table 4.1.1.2. Estimates of the sire (<J!s). dam (o'g.) and Individual (<J ! E ) components of variance, and of the heritabilities based on the sire (h ! s) and dam (b'^) components of variance for strain 8 for egg production from 148 to 273 days. Year 1957 1958 1959 1960 1961 1962 1963 28 21 137 78 17 47 90 66 40 22 119 734 600 791 1068 564 595 0.14 ± 0.04 0.12 + 0.06 0.55 + 0.24 0.26 ± 0.14 0.11 ± 0.11 0.00 ± 0.10 0.23 + 0.06 0.51 + 0.10 0.27 + 0.10 0.13 + 0.10 0.14 ± 0.13 0.67 + 0.25 ± S.e. -6.47 ± 11.43 (p < 0.602) +5.14 ± 7.82 (p < 0.547) -16.86 ± 43. 17 (p < 0.7 16) -0.029 + 0.042 (p < 0.522) +0.035 ± 0.047 (p < 0.496) mean 56 57 745 0.25 + 0.04 0.37 + 0.05 L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.1.1.3. Estimates of the sire ( o ' s ) , dam (o ! d) and Individual (<j'e) components of variance, and of the heritabilities based on the sire (h' s) and dam (h 1^) components of variance for strain 3 for egg production from 148 to 273 days (Gowe and Fairfull, 1985). Year 1957 1958 1959 19G0 1961 1962 1963 s 7 2 14 13 25 2 9 " d 76 42 75 72 1 16 94 87 e 627 521 588 654 765 812 642 s 0.04 0.01 0.08 0.07 0. 1 1 0.01 0.05 d 0.43 0.30 0. 45 0. 39 0.41 0.4 1 0.47 ± s . e . +0.61 + 1.64 (p < 0.727) +6.36 ± 3.74 (p < 0.150) +28.71 ± 16.25 (p < 0.138) +0.002 + 0.008 (p < 0.788) +0.011 + 0.010 (p < 0.346) 10 80 658 0.05 0.41 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t M Estimates of the sire ), dam ( < J ! d ) and individual («'e) components of variance, and of the Table 4.1.1.4. heritabilities based on the sire (h ! g) and dam (h' d) components of variance for strain 4 for egg production from 148 to 273 days (Gowe and Fairfull, 1985). Year 1957 1958 1959 1960 1961 1962 1963 s 27 22 7 14 18 8 15 ' d 41 39 45 34 50 39 26 e 581 521 567 544 592 596 456 s 0.17 0. 15 0.05 0. 10 0. 1 1 0.05 0.12 d 0. 25 0. 27 0. 29 0. 23 0. 30 0. 24 0.21 b' + s.e. -1.89 ± 1.23 (p < 0.183) -1 .43 ± 1 .46 (p < 0.372) -7.14 ± 9.79 (p < 0.498) -0.010 ± 0.008 (p < 0.265) -0.006 ± 0.006 (p < 0.371) 16 39 551 0.11 0. 26 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.1.1.5. Herltablllty estimates based on the sire (h' s) and dam (b ! d) components of variance for egg production from 148 to 497 and from 274 to 497 days for strain 6. 148 to 497 Days 274 to 497 Days Year h' h* h* h ! . s d s d 1957 0. 11 + 0 .03 0. 10 + 0. 1 1 0. 10 + 0 .03 0 .22 + 0.11 1958 0. 16 + 0. .07 0. 49 + 0. 10 0. 22 + 0 .07 0 .32 + 0.09 1959 0. 43 + 0. . 20 0. 30 + 0. 1 1 0. 25 + 0 . 13 0 .33 + 0.11 1960 0. 23 + 0. . 13 0. 10 + 0. 10 0. 20 + 0 . 1 1 -0 .01 ± 0.09 1961 0. 13 + 0. . 12 0. 23 + 0. 13 0. 16 + 0 . 13 0 .19 ± 0.13 1962 - - - -1963 0. 12 + 0. 13 0. 74 + 0. 24 0. 33 + 0 . 19 0 .67 + 0.24 + S.e. -0.009 + 0. 028 +0.064 + 0. 047 +0.025 + 0. .013 +0.066 + 0.044 (P < 0. .842) (P i < 0 .246) (P i < 0 . 136) (P < 0.212) mean 0. 23 + 0 .04 0. 26 + 0 .05 0. 20 + 0. 04 0. 15 ± 0.04 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t CO 30 upward trends. 4.1.2 EGG QUALITY TRAITS The h2 and h 2 estimates for the egg quality traits are S 0 presented in Tables 4.1.2.1 to 4.1.2.3 for strain 6. Heritabilities were estimated for egg weights at 225, 350 and 450 days of age. Both h 2 g and h2^ estimates for all three periods tended to show slight down-ward trends with time especially the h 2 g estimates for egg weight at 350 days (p < 0.01; Table 4.1.2.1). The mean h 2 g for egg weight at 225 days was 0.60 and the mean h 2 d was 0.50. Similar estimates for strain 3 were 0.48 and 0.64, and for strain 4, 0.59 and 0.63, respec-tively (Gowe and Fairfull, 1985). The h 2 g and h 2 d estimates for egg specific gravity are reported for 225 and 450 days of age (Table 4.1.2.2). While the heritability estimates for egg secific gravity at 225 days slightly increased with time (but were non-significant), those for egg specific gravity at 450 days did not show any consistent trends. The mean h2 and h2 estimates at 225 days were 0.64 and 0.33, and s d ' at 450 days, 0.46 and 0.25, respectively. These estimates were within range of others found in the literature (Kinney, 1969). The h 2 g and h 2 d estimates variance for Haugh units at 225 and 450 days of age are also presented (Table 4.1.2.3). These heritabilities did not change with time. The mean h 2 g for Haugh units at 225 days was 0.57, and the mean h 2 d was 0.68. For Haugh unit measured at 450 days, the mean h 2 was 0.54, and the mean h 2 was 0.55. These estimates are s ' d consistent with values reported in the literature (Kinney,1969). Table 4.1.2.1. Heritability estimates based on the sire (h* s) and dam (h* d) components of variance for egg weight at 225, 350 and 450 days of age for strain 6. 225 Days 350 Days 450 Days Year I 5 I i I I I 5 i 1957 0. 64 + 0. .20 0. 52 + 0 , 18 0. 74 + 0. 26 0. 52 + 0. . 19 0. 77 + 0 .24 0. 69 + 0. 20 1958 0. 61 + 0. .23 0. 66 + 0 . 14 0. 90 + 0. .31 0. 80 + 0 . 14 0. 82 + 0 . 29 0. 67 + 0. 14 1959 0. 69 + 0. .24 0. 45 + 0 . 11 0. 70 + 0. . 26 0. 64 + 0 . 13 0. 60 + 0, .23 0. 61 + O. 12 1960 0. 57 + 0. 22 0. 60 + 0. 14 0. 63 + 0. 23 0. 45 + 0. . 13 0. 75 + 0. . 28 0. 51 + 0.17 1961 0. 69 + 0. 24 0. 42 + 0. . 14 0. 51 + 0. 20 0. 62 + 0. . 15 0. 42 + 0 , 17 0. 75 + 0.15 1962 - - - - - , -1963 0. 40 + 0. 17 0. 33 + 0. .21 0. 39 + 0. 18 0. 33 + 0. .21 0. 48 + 0. 22 0. 53 + 0. 22 ± s.e. -0.032 + 0. 199 -0.040 + 0. .020 -0.075 + 0. 018 -0.045 + 0. .030 -0.060 + 0. 024 -0.018 + 0.02C (P < 0 . 181 ) (F I < 0 .117) (P < 0 .014) (P i < 0 .204) (P < 0 .069) (P < 0 .415) mean 0. 53 + 0. 03 0. 44 + 0. 01 0. 63 + 0. 03 0. 55 + 0. 01 0. 64 + 0. 05 0. 60 + 0.02 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t OJ Table 4.1.2.2. Heritabillty estimates based on the sire (h' s) and dam (h' d) components of variance for egg specific gravity at 225 and 450 days of age for strain 6. Year 1957 1958 1959 1960 19G1 1962 1963 b 1 ± s.e mean Days 450 Days h«. 0. 14 + 0. 20 0. 37 + 0. 14 0. 33 + 0. 12 0. 34 + 0. 15 0. 43 + 0. 1 1 0. 66 + 0. 24 o. 57 + 0. 14 0. 54 + 0. 21 0. 30 + 0. 13 0. 36 + 0. 14 0.27 ± 0.22 0.35 ± 0.13 0.23 ± 0.10 0.41 +0.17 0.31 ± 0.09 225 0.55 ± 0.17 0.57 ± 0.21 0.70 + 0.24 0.65 ± 0.24 0.49 ± 0.18 0.87 + 0.31 +0.039 + 0.025 (p < 0.192) 0.60 ± 0.05 0.50 + 0.19 +0.045 + 0.028 (p < 0.182) 0.38 ± 0.02 0.46 + 0.18 +0.008 ± 0.029 (p < 0.791) 0.42 + 0.04 -0.06 + 0.17 -0.038 ± 0.027 (p < 0.226) 0.20 ± 0.03 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.1.2.3. Heritabillty estimates based on the sire (h' s) and dam (h J d) components of variance for haugh units at 225 and 450 days of age for strain 6. 225 Days Year s h ' d s 1957 0. 75 + 0. 21 0, ,53 ± 0. 19 0. .54 ± 0. 18 1958 0. 44 ± 0. 19 0. 86 ± 0. 16 0. .71 ± 0. 26 1959 0. 58 + 0. 21 0. .56 ± 0. 12 0, 48 + 0. 18 1960 0. 37 + 0. 17 0. .87 + 0. 17 0. 44 + 0. 19 1961 0. 53 + 0. 19 0. 48 ± 0. 14 0. 54 ± 0. 20 1962 - - -1963 0. 73 + 0. 28 0. 75 ± 0. 22 0. 52 ± 0. 23 _450 Days_ h ' d 0. .46 + 0. 21 0. .43 ± 0. 13 0. .40 ± 0. 1 1 0. 82 ± 0. 20 0. 46 ± 0. 13 0. 75 ± 0. 23 b 1 + S . G . +0.007 + 0.035 (p < 0.852) +0.009 + 0.040 (p < 0.829) -0.014 + 0.020 (p < 0.521) +0.050 ± 0.034 (p < 0.211) 0.49 + 0.06 0.62 ± 0.03 0.48 + 0.10 0.47 + 0.06 L i n e a r r e g r e s s i o n c o e f f i c i e n t to CO 34 4.1.3 OTHER TRAITS The h 3 s and h2^ estimates for age at sexual maturity and body weight at 365 days are reported in Table 4.1.3.1. The mean h 3 g and h 2^ estimates for age at sexual maturity were 0.22 and 0.33 both of which were lower than other estimates found in the literature (Kinney, 1969). For body weight at 365 days, the mean h 2 g and h2^ were 0.53 and 0.62, respectively, both of which were consistent with the average h 2 s estimate of 0.52 and h 2 d estimate of 0.59 reported by Kinney (1969). 4.1.4 CONTROL POPULATION The hJ and h2 estimates for the control strain were based on s d the entire period they were housed at the Animal Research Centre, Ottawa, (Gowe and Fairfull, 1985), and these were used as estimates of the control populations kept in Agassiz. The mean h 2 g and h2^ for short-term egg production were 0.28 and 0.33, and for whole year egg production were 0.18 and 0.39, respectively. The mean h 2 g estimate for age at sexual maturity was 0.38, and the mean h2^ estimate was 0.56. The h 2 s estimate for egg weight at 225 days was 0.54, and the h2^ estimate was 0.78. 4.2 GENETIC CORRELATIONS The mean genetic correlations (r ) among traits measured for strain 6 are presented in Table 4.2.1, and are compared to those estimates found in Kinney (1969). The genetic correlation of HHEP from 148 to 273 days with age at sexual maturity was -0.40, and was higher than other estimates reported in the literature (-0.62). The r for HHEP and egg specific gravity Table 4.1.3.1. Heritability estimates based on the sire (h ! g) and dam (h'^) components of variance for age at sexual maturity and body weight at 365 days of age for strain 6. Age at sexual m a t u r i t y Body weight at 365 days Year h> s d h ' s h ' d 1957 0 . 18 ± 0. . 10 0. 58 + 0. . 23 0. ,37 ± 0. 14 0. .48 + 0. 21 1958 0, .26 ± 0 . 12 0. . 26 + 0. . 13 0 .80 + 0. 30 0 .74 ± 0. 14 1959 0. ,60 ± 0. 21 0. 28 + 0. 08 0. .61 + 0. 22 0. .60 + O. 13 1960 0. 15 + 0. .07 -o. .12 + 0. 08 0. .49 + 0. 19 0. .51 ± 0. 19 1961 0. 20 + 0. 10 0. 66 + 0. 14 0. .52 + 0. 17 0. 60 ± 0. 15 1962 - - -1963 -0. 04 ± 0. 06 0. 30 + o. 22 0. 37 ± O. 19 0. 81 ± 0. 24 b 1 + s.e. -0.042 + 0.041 -0.013 + 0.055 -0.028 + 0.035 +0.033 + 0.026 (p < 0.358) (p < 0.823) (p < 0.471) (p < 0.266) mean 0.26 + 0.05 0.25 ± 0.05 0.54 + 0.08 0.59 ± 0.06 L i n e a r r e g r e s s i o n c o e f f i c i e n t T a b l e 4.2.1. Mean g e n e t i c c o r r e l a t i o n s ( r ) among t r a i t s measured f o r s t r a i n 6. 9 Tra i ts Correlated with g HHEP from 148 to 273 days HHEP from 148 to 497 days HHEP from 274 to 497 days age at sexual maturity egg weight at 225 days egg s p e c i f i c gravity at 225 days Haugh units at 225 days body weight at 365 days +0.97 +0.82 -0.40 -0.07 -0.07 +0.09 -0. 17 body weight at 365 days egg weight at 225 days egg s p e c i f i c gravity at 225 days Haugh units at 225 days age at sexual maturity +0. 38 -0.03 +0.06 +0. 22 age at sexual maturity egg weight at 225 days egg spec 1fic'gravity Haugh units at 225 days +0.06 -0.01 +0. 23 egg s p e c i f i c gravity at 225 days egg weight at 225 days Haugh units at 225 days +0.11 -0.08 egg weight at 225 days egg weight at 450 days +0.95 37 was -0.07, which was in contrast to positive estimates found in the literature. On the other hand, r g for HHEP and Haugh units was 0.10 compared to negative estimates reported elsewhere. The r^ for HHEP and body weight at 365 days was -0.17, contrary to positive estimates reported elsewhere. The r^ between body weight and age at sexual maturity was 0.22 which was higher than other estimates. The r^ for age at sexual maturity and egg specific gravity at 225 days was -0.01 which was much lower than most reported estimates (0.29). The r^ for egg weight at 225 days and 450 days was 0.95 which was slightly higher than expected (0.83). The r for short-term HHEP with the residual HHEP was 0.82, and with the 9 whole record HHEP, 0.97. 4.3 THE PERFORMANCE OF TRAITS MEASURED IN STRAIN 6 4.3.1 EGG PRODUCTION TRAITS In order to make comparisons of egg production between strain 6 and the control strain possible, deviations of the phenotypic mean for strain 6 from that of the control were used on a year to year basis. The individual HHEP from 1957 to 1963 for strain 6 and the control strain, as well as the deviations from the control are presented in Tables 4.3.1.1 to 4.3.1.3. The linear regression coefficients of these deviations are also included in the tables. Response to selection as estimated by the coefficients of linear regression were not significantly different from zero for strain 6 for the egg production periods from 1957 to 1963. The regressions of the means for egg production on time (1957 to 1963) for the control strain Table 4.3.1.1. Means and standard errors for strain 6 and the control strain, and deviations for egg production from 148 to 273 days. from the control for strain 6 Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 81.30 ± 1.02 91.44 ± 0.89 85.85 ± 0.90 82.11 ± 1.10 95.83 + 0.81 96 . 12 ± 1.14 C o n t r o l S t r a i n 67.10 ± 1.96 70.60 ± 1.71 71.97 + 1.64 66.34 ± 2.05 73.58 + 1.73 77.44 ± 1.82 D e v i a t i o n s from C o n t r o l +14.20 +20.84 +13.84 +15.77 +22.25 +18.68 b' + 1 .45 + 0.63 (p < 0.08) +0.66 + 0.75 (p < 0.43) L i n e a r r e g r e s s i o n c o e f f i c i e n t C O oo Table 4.3.1.2. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 6 for egg production from 148 to 497 days. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 180.06 ± 2.43 232. 13 ± 2.67 218.98 ± 2.63 212.71 ± 3.09 240.56 + 2.41 241.20 ± 3.02 C o n t r o l S t r a i n 154.80 ± 4 . 9 8 194.15 + 5.28 200.94 +5.23 194.01 ± 6.37 205.54 ± 5.31 207.50 ± 5 . 3 9 D e v i a t i o n s from C o n t r o l +25.26 +37.98 +18.04 +18.70 +35.02 +33.70 b' + s.e. +6.86 ± 2.92 (p < 0.08) +0.97 ± 1.94 (p < 0.65) L i n e a r r e g r e s s i o n c o e f f i c i e n t CO to Table 4.3.1.3. Means and standard errors for strain 6 and the control strain, and deviations for egg production from 274 to 497 days. from the control for strain 6 Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 98.76 ± 1.67 140.70 ± 2.11 133.16 + 2.00 130.58 + 2.31 144.69 + 1.93 145. 12 + 2.41 C o n t r o l S t r a i n 87.68 ± 3.41 123.52 + 3.97 128.98 ± 4.01 127.67 ± 4.77 131.99 + 4.20 130.08 + 4.05 D e v i a t i o n s from C o n t r o l +11.08 +17.18 + 4 . 18 + 2.91 +12.70 +15.04 +5.43 ± 2.82 (p < 0.13) +0.30 + 1.33 (p < 0.83) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t o 41 showed slight but non-significant upward trends (Tables 4.3.1.1 to 4.3.1.3). 4.3.2 EGG QUALITY TRAITS The egg quality traits, egg weight at 225, 350 and 450 days, egg specific gravity at 225 and 450 days, and Haugh units at 225 and 450 days for strain 6 are presented in Tables 4.3.2.1 to 4.3.2.7. Egg weight remained stable for strain 6 (Tables 4.3.2.1 to 4.3.2.3). However, egg specific gravity showed significant downward trends (Tables 4.3.2.4 and 4.3.2.5). The egg quality trait regressions were not significantly different from zero for the control strain, neither did they show any consistent upward or downward trends (see Tables 4.3.2.1 and 4.3.2.7). 4.3.3 OTHER TRAITS The regression of age at sexual maturity on time for strain 6 showed that this trait remained stable over time (Table 4.3.3.1). Age at sexual maturity for the control strain tended to decline with time al-though it was non-significant (Table 4.3.3.1).. The deviations of body weight at 365 days from the control increased significantly over time for strain 6 (Table 4.3.32). Body weight of the control strain showed an upward trend over time (Table 4.3.3.2). On the other hand, body weight of strain 6 decreased over time (see Figure 4.3.3.1). Since fertility and hatchability traits were measured in two different locations (Agassiz and Ottawa) based on parental records, deviations from the control would not be useful for comparison and so are not presented here. Only the means for strain 6 and the con-trol strain are shown in Tables 4.3.3.3 and 4.3.3.4. Table 4.3.2.1. Means and standard errors for strain 6 and the control strain, and deviations from the control for strain 8 for egg weight at 225 days In grams. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 51.0 ± 0.1 54.7 + 0.1 53.9 ± 0.1 52.3 + 0.1 51.7 ± 0.1 51.8 + 0.1 C o n t r o l S t r a i n 51.7 ± 0.3 55.5 ± 0.2 54.6 ± 0.2 52.5 + 0.3 53.5 + 0.3 52.4 ± 0.3 D e v i a t i o n s from C o n t r o l -0.7 -0.8 -0.7 -0.2 -1.8 -0.6 ± s.e. -0.14 + 0.33 (p < 0.69) -0.03 ± 0.12 (p < 0.79) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.3.2.2. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for egg weight at 350 days In grams. Year 1957 1958 1959 1960 1961 1962 19<53 S t r a i n 6 56.8 ± 0.1 59.2 ± 0.1 59.5 ± 0.1 58.7 + 0.1 57.9 + 0.1 58.5 ± 0.2 C o n t r o l S t r a i n 58.0 ± 0.3 59.8 + 0.3 60.0 ± 0.3 59.4 ± 0.4 59.4 + 0.3 59.3 ± 0.4 D e v i a t i o n s from C o n t r o l -1.2 -0.6 -0.5 -0.7 -1.5 -1.3 ± s.e. +0.16 ± 0.15 (p < 0.34) -0.08 ± 0.09 (p < 0.37) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t to Table 4.3.2.3. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for egg weight at 450 days In grams. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 59.0 ± 0.2 60.6 ± 0.2 60.6 + 0.1 59.9 + 0.2 59.7 + 0.2 59.2 ± 0.2 C o n t r o l S t r a i n 60.1 ± 0.4 61.4 ± 0.3 60.9 ± 0.3 60.3 + 0.6 60.9 + 0.3 60.4 ± 0.4 D e v i a t i o n s from C o n t r o l -1.2 -0.8 -0.3 -0.3 -1.2 -1.2 • s.e. -0.02 + 0.11 (p < 0.84) -0.04 ± 0.10 (p < 0.70) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.3.2.4. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for egg specific gravity at 225 days. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 91.1 ± 0 . 2 88.5 + 0.2 88.1 ± 0 . 2 88.2 ± 0.2 87.5 ± 0.2 87.4 ± 0.2 C o n t r o l S t r a i n 89.4 + 0.4 87.1 ± 0.4 87.0 ± 0.4 88.3 ± 0.4 88.2 + 0.4 87.8 ± 0.3 D e v i a t i o n s from C o n t r o l + 1.7 + 1.4 + 1.1 -0. 1 -0.7 -0.4 ± s.e. -0.08 ± 0.20 (p < 0.71) -0.42 ± 0.10 (p < 0.02) L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.3.2.5. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for egg specific gravity at 450 days. Y e a r 1 9 5 7 1 9 5 8 1 9 5 9 1 9 6 0 1961 1 9 6 2 1 9 6 3 S t r a i n 6 8 2 . 1 ± 0 . 2 8 1 . 4 + 0 . 2 8 0 . 2 + 0 . 2 7 7 . 1 + 0 . 2 7 8 . 4 + 0 . 2 7 7 . 4 ± 0 . 3 C o n t r o l S t r a i n 8 0 . 6 + 0 . 4 8 0 . 4 ± 0 . 4 7 9 . 9 ± 0 . 4 7 6 . 4 + 0 . 4 7 8 . 2 + 0 . 3 7 8 . 6 ± 0 . 5 D e v i a t i o n s f r o m C o n t r o l + 1 . 5 + 1 . 0 + 0 . 3 + 0 . 7 + 0 . 2 - 1 . 2 + s . e . - 0 . 4 5 ± 0 . 3 0 ( p < 0 . 2 0 ) - 0 . 4 2 ± 0 . 0 6 ( p < 0 . 0 0 3 ) L i n e a r r e g r e s s i o n c o e f f i c i e n t CD Table 4.3.2.6. Means and standard errors for strain 6 and the control strain, and deviations from the control for strain 8 for haugh units at 225 days. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 86.2 + 0.2 83.0 ± 0.2 85.2 ± 0.2 85.7 ± 0.2 82.5 * 0.2 81.7 ± 0.2 C o n t r o l S t r a i n 89.0 + 0.4 85.9 ± 0.4 88. 1 ± 0.4 89.4 ± 0.4 85.9 + 0.4 85.0 ± 0.4 D e v i a t i o n s from C o n t r o l -2.8 -2.9 -2.9 -3 . 7 -3.4 -3.3 ± s.e. -0.50 ± 0.35 (p < 0.23) -0.11 ± 0.06 (p < 0.16) L i n e a r r e g r e s s i o n c o e f f i c i e n t Table 4.3.2.7. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for haugh units at 450 days. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 77.3 ± 0.3 75.9 ± 0.3 76.5 ± 0.3 73.0 + 0.4 72.7 + 0.3 80.4 + 0.3 C o n t r o l S t r a i n 80.1 + 0.5 79.0 ± 0.6 80.0 ± 0.6 74.8 + 1.0 75.4 + 0.7 82.3 ± 0.6 D e v i a t i o n s from C o n t r o l -2.8 -3 . 1 -3.5 -1.8 -2.7 -1.9 ± s.e +0.05 + 0.68 (p < 0.94) +0.19 + 0.12 (p < 0.20) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t oo Table 4.3.3.1. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for age at sexual maturity. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 163.79 ± 0.57 157.59 ± 0.48 159.65 ± 0.57 154.69 + 0.56 154 . 13 ± 0.38 156.55 ± 1.09 C o n t r o l S t r a i n 174.53 + 1.53 17 1 .27 ± 1.08 174.64 ± 1.23 172.80 ± 1.79 171.30 ± 1.16 169.32 ± 1.42 D e v i a t i o n s from C o n t r o l -10.74 -13.68 -14.99 -18. 11 -17.17 1 2 . 7 8 • s.e. -0.72 ± 0.32 (p < 0.09) -0.43 ± 0.60 (p < 0.51) ' L i n e a r r e g r e s s i o n c o e f f i c i e n t CD Table 4.3.3.2. Means and standard errors for strain 8 and the control strain, and deviations from the control for strain 8 for body weight at 365 days in decagrams. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 210.43 ± 0.88 215.53 ± 1.00 209.98 ± 0 . 8 2 206.91 ± 0.91 206.76 ± 0 . 9 2 200.64 + 1 .04 C o n t r o l S t r a i n 208.05 ± 1.80 218.43 ± 1.91 221 . 1 1 ± 2.08 217.77 ± 2.09 225.24' ± 2.38 224.22 ± 2.03 D e v i a t i o n s from C o n t r o l + 2 . 38 -2 .90 -11.13 -10.86 -18.48 -23.58 + S.e. +2.32 + 0.85 (p < 0.05) -4.33 + 0.48 (p < 0.0009) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t o + IP • 0) PJ Table 4.3.3.3. Means for strain 6 and the control strain for fertl l I t y . Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 85 . 25 94.43 88.74 96. 15 85.48 C o n t r o l S t r a i n 90.97 90.56 90.56 97 .64 95.07 ( rO Table 4.3.3.4. Means for strain 8 and the control strain for hatchability. Year 1957 1958 1959 1960 1961 1962 1963 S t r a i n 6 78.28 89.81 61 .02 86.40 68 . 38 C o n t r o l S t r a i n 87 . 33 83.90 83 .90 92.31 73.78 CO Table 4.3.3.5. Means for strain 8 and the control strain, and deviations from the control for strain 8 for percent laying house mortality from 148 to 497 days. Y e a r 1 9 5 7 1958 1 9 5 9 1 9 6 0 1961 1 9 6 2 1 9 6 3 S t r a i n 6 1 3 . 6 1 2 . 3 1 6 . 1 1 6 . 1 9 . 3 7 . 5 C o n t r o l S t r a i n 22 . 0 2 1 . 9 1 8 . 0 2 2 . 3 1 6 . 7 1 1 . 8 1 . 6 3 ± 0 . 5 1 ( p < 0 . 0 3 ) D e v i a t i o n s from C o n t r o l - 8 . 4 - 9 . 6 - 1 . 9 - 6 . 2 - 7 . 4 - 4 . 3 + 0 . 5 8 + 0 . 5 B ( p < 0 . 3 8 ) 1 L i n e a r r e g r e s s i o n c o e f f i c i e n t cn 55 Percent laying house mortality from 148 to 497 days for strain 6 and the control strain, as well as deviations from the control for strain 6 are reported in Table 4.3.3.5. The means showed a downward trend, and this trend is also reflected by the linear regression of the response to selection on time. This trend was similar for the control strain. 4.4 ACTUAL SELECTION DIFFERENTIALS The actual selection differentials (SD's) for the sires and dams of strain 6 for egg production from 148 to 273 days, egg weight at 225 days, and body weight at 365 days in decagrams from 1957 to 1963 are presented in Table 4.4.1. The SD's for the sires were based on their full and half sisters' records while those for the dams were based on their own individual records. The SD's were calculated as the mean of the selected parents minus the mean of the population. The SD's for egg production from 148 to 273 days for both the sires and the dams were positive which is in accordance with the positive selection pressure applied to this trait. The SD's for egg weight are, in practice, zero. The SD's for body weight at 365 days are slightly positive for the sires due to the selection pressure placed on this trait in the selection of sires but not dams. Table 4.4.1. Actual selection differentials for the sires and dams of strain 6 for egg production from 148 to 273 days, egg weight at 225 days In grams, and body weight at 365 days In decagrams from 1957 to 1983. Egg_product i o n from 148 to 273 Ecra weiqht a t 225 days Body welqht a t 365 days days Year S i r e s Dams S i r e s Dams S1 r e s Dams 1957 +20. 2 +22.2 -0. 1 +0.4 +0.51 + 1 .00 1958 + 14.7 + 12.6 -0.4 -0.5 -2.39 -2.30 1959 + 13.9 + 16.4 -0.3 +0.4 -3.04 + 1.51 1960 + 19.6 + 18.9 -0.3 +0. 1 -1 .03 -0.69 1961 + 14.6 + 4.7 + 1 .9 +0.7 -8.18 +0.33 1962 1963 5. DISCUSSION When this study was first initiated the parental strains used were thought to have plateaued in response to selection for HHEP; However, as selection continued in strains 3 and 4 at Ottawa, it became apparent that they had not reached a selection limit (Gowe and Fairfull, 1985; A. T. Hill, personal communication). Therefore, no great increases in the additive genetic component (o* ) were expected as the cross was not expected to behave as it might have had the parental strains been at a plateau. The crossing of two previously selected strains that were not related with regards to genetic origin may yield new sources of genetic variation, particularly in (<j* ) which is the component that shows response to selection (Falconer, 1981; Dickerson, 1969). In this study, h J g for the main trait under selection, HHEP from 148 to 273 days, for strain 6 was consistently higher than either parental strain. High h J g in the straincrosses will reflect the amount of genetic difference between the parental lines as unrelated lines selected in the same direction may not be fixed for the same alleles at various loci affecting the selected traits (Roberts, 1967). Although not necessarily plateaued in response to selection for HHEP, strains 3 and 4 were still highly selected. Consequently, increases in «' were found in HHEP and other related traits in strain 6. Falconer and King (1953) found that a cross between two unrelated mouse strains that were plateaued in response to selection for high 60 day body weight showed increased *' and a renewed response to selection, at a greater rate. Similar results were found by Roberts (1967) in his crosses of previously selected, unrelated lines of mice. Robertson (1955) was able to obtain further progress in body size in Drosophila by crossing two lines that had stabilized for body size. 57 58 After two generations of selection in strain 6, h } g for short-term HHEP increased drastically and remained high for the next two generations. This increase may be caused by crossing-over between and break up of linkage groups that had been fixed in the parental strains (Roberts, 1967; Thoday et al., 1964; Falconer, 1981). Initial crossing would put genes into the repulsion phase and then, as recombination occured to put genes into the coupling phase, increasing numbers of crossovers would become availa-ble over the next few generations. As sufficient numbers of crossovers occured and new genetic combinations became available, selection would act on them in an increasing proportion of the total such that response to selection would increase (Roberts, 1967). The purpose of crossing before selection has often been to generate segregation and allow genetic differentiation of lines through recombination (Falconer, 1981). This dramatic increase seen in the h : estimates for strain 6 for short-term HHEP is s likely to be due to reshuffling of the genome through recombination because it was not seen until two generations after the cross and this would be sufficient time to allow heterotic effects, if any, to dissipate. However, the large increase in the h 2 g estimate to a value greater than one in 1959 may still be biased upward due to genotype-environment interactions and the low number of sires (approximately 20) used per gen-eration (Dickerson, 1969). Since HHEP is a composite of the rate of egg production, age at sexual maturity, and viability (Liljedahl et al., 1984), the combination of new sources of additive genetic variance for these three characteristics, due to recombination, could have inflated the 1959 heritability estimate. Both age at sexual maturity and short-term egg production are known to be highly heritable (0.39 and 0.33, respectively; Liljedahl et al., 1984; Kinney, 1969); 59 however, laying house mortality which is used to measure viability generally has a low heritability (0.08; Kinney, 1969). If the relative impor-tance of additive by additive gene interactions between the components of HHEP increased due to temporary linkage disequilibrium then this heritability estimate could be biased upward as it contains at least one-quarter of these type of interactions (Dickerson, 1969). However, since this experiment was not designed to estimate the above genetic parameters, it is not pos-sible to distinguish between these hypotheses. Given such a pattern of h J g over time, one would expect strain 6 to have shown response to selection for higher HHEP. However, this was not the case. The lack of response to selection over the six generations of this study for strain 6 was probably due to selection for other traits besides HHEP and the negative genetic correlations between these traits and HHEP. HHEP generally has a low heritability estimate due to the combination of characteristics that constitute this trait, such as age at sexual maturity, rate of egg production and viability. Estimates, from various sources (Kinney, 1969) show that egg weight has a high heritability. This trait is known to be negatively correlated with HHEP (Lerner, 1948). As a consequence, the selection emphasis on maintaining egg weight will affect the response of HHEP to selection. Since HHEP has a low heritability, response to selection will not be as great per generation as that for a trait with a higher heritability estimate, and will be further reduced if antagonistic traits are included in the selection scheme. Although body weight has a negative genetic correlation with HHEP and some emphasis was given to smaller and more refined birds, it also has a positive genetic correlation with egg weight (Kinney et al., 1970). The interaction between these three traits would further hinder progress for HHEP. Selection so as 60 to maintain acceptable levels of fertility, hatchability and viability may also have contributed to the lack of response to selection for HHEP. Furthermore, the duration of this study may not have been long enough to show any responses to selection. Early performance in straincrosses of Drosophila were found to be a poor guide to later phenotypic behaviour (Bell et al., 1955). Even when a single trait was se-lected, Roberts (1967) found that eight generations were required for a mouse straincross to show significant responses to selection, and Robertson (1955,1956) found that 6 to 7 generations were required for Drosophila. This lag is mainly due to the need to allow recombinational events to occur in sufficient numbers for selection to act on them (Roberts, 1967). Plant breeders do not select superior crosses based on their performance until the second generation or later in order to allow recombination to occur and heterotic effects to dissipate (Falconer, 1981). In the present study, strain 6 showed a large increase in the «' for HHEP and related traits, and may have had the potential for response to selection in tater years. After 1959, the tendency for h J g estimates to stabilize at a level which indicates that there is still «' existing (Yamada et al., 1958; Dempster et al., 1952) also implies that natural selection is working against artificial selection through such mechanisms as antagonistic pleiotropy (Roberts, 1967; Falconer, 1981; Rose, 1982) in order to return, or keep, the organism at an optimum fitness level (Lerner, 1948). Birds from strain 6 were not reproduced in 1961 but were held over and reproduced in 1962 to provide the 1963 generation. The low hJ for 1963 was caused by a decrease in the ration of the <?» to the total a phenotypic variance (Falconer, 1981). Any number of environmental factors such as building modifications (project 51.11.11 notes), disease exposure, and 61 differences in management routines (the principal investigator was away in 1962 and had just returned in 1963) could have been responsible, or the increased age of the birds at the time of breeding could have caused the decrease in the «' . a The estimates of «'d and h 2 d for HHEP and individual egg production remain relatively stable except for 1963. The increase in the relative impor-tance of the «'d for that year is related to the decrease in the relative proportion of the c' An increase in «'d also reflects the increase in maternal effects due to the older age of the dams of that generation, such as greater congenital transmission of disease, e. g. lymphoid leucosis which was present in the Agassiz flocks and which is known to decrease egg production (pathology reports, project 51.11.11 notes; Liljedahl et al., 1984; Bennett et al., 1981; Akbar et al., 1983). The h 2 d estimates for these traits generally fall midway between the parental strain values (Gowe and Fairfull, 1985). Dominance and epistatic gene effects, and maternal influences do not appear to affect these egg production traits to any large degree (other than 1963 as explained) as the h 2 d estimates remain at a level consistent with the initial generations of the h 2 g estimates. Consequently, heterotic effects are not expected to be significant in this particular straincross for these traits (Falconer, 1981; Hartl, 1980; Jerome et al., 1956). Strains 3 and 4 have different magnitudes of «' and «' (see Gowe a na v and Fairfull, 1985) compared to strain 6. From the data presented here, strain 6 has a higher proportion of »' to as compared to the parental strains, especially for HHEP genetic parameters. It is therefore likely that sizable genetic differences do exist between these strains, although phenotypic differences may not reflect the genetic differences to the same degree. The deviation from the control of the phenotypic mean for 62 individual egg production remained stable over the period under considera-tion (1957 to 1963) for strain 6 for the short-term, residual and whole egg records. Strain 6 was being selected in an environment different to that in which the parental strains were being selected and the selection program was slightly different making phenotypic comparisons difficult. Also, since the control strain was reproduced in a different environment, this strain may have been inadequate in reflecting changes between locations (Ottawa and Agassiz) and within the Agassiz environment itself (Hill, 1972). There may have been differential responses to environmental influences between the control and strain 6. An unselected control strain may be unsuccessful in removing the effect of year to year environmental fluctuations (W. G. Hill, 7972) on the selected strain. The viability of strain 6 appears to be higher in the laying house period as compared to the control strain. Differences in viability were ex-pected to arise between the selected and the control strain as selection for HHEP also indirectly selects for better viability during the laying-house period (Gowe and Fairfull, 1980,1985). Egg weight at 225 days was another trait under selection. The aim was to maintain egg weight rather than attempt to increase it. This goal was realized in strain 6 as egg weight remained phenotypically stable over time. The selection pressure, however, was strong enough to effect a slight decrease in hJ and h s. estimates for egg weight at 225, 350 and 450 S Q days. Since the mean h1 for egg weight for strain 6 is consistent with s those for strains 3 and 4 (all of which are high; Gowe and Fairfull, 1985) there is still a significant proportion of »* present for this trait. The h 2 d estimate for strain 6 is lower than either strain 3 or 4 but it is consistent with the hJ . These estimates further support the hypothesis that dominance 63 and epistatic effects, and maternal influences are negligible in affecting egg weight. Generally speaking, maternal and non-additive genetic effects are not as important for traits with high heritabilities as they affect such traits to a lower degree relative to those traits with lower heritabilities (Falconer, 1981; Dickerson, 1969). Egg specific gravity and Haugh units, both measured at 225 and 450 days, were not traits under selection. There was a significant decline in the straincross' performance for egg specific gravity for both test dates. The heritability estimates for egg specific gravity, however, remained stable. Haugh units measured at 225 days and at 450 days, remained stable over time for strain 6. Unfortunately, no estimates of genetic paramters for strains 3 and 4 for the latter egg quality traits are available other than some h J s estimates obtained through a different project by Nagai and Gowe (1969). The h J s estimate for age at sexual maturity for strain 6 showed the same curvilinear pattern as that for individual egg production. The increases in the er» in 1959 for both of these traits in combination could have a caused the increase in the h J g estimate for HHEP as these traits are components of HHEP. Phenotypically, age at sexual maturity for strain 6 did not show a significant decrease. One' way of increasing egg production is by lowering the age of first egg. The long-term results for age at sexual maturity for strains 3 and 4 (Gowe and Fairfull, 1985) showed significant decreases in this trait although the year to year change was not significant. The duration of this study was probably not long enough to show similar responses in strain 6. Although there was no systematic selection on body weight, body weight at 365 days of the hens was the only trait that showed a 64 significant phenotypic change over time (probably because of the manner in which the parents were chosen). The higher h'd estimates, as compared to the h 2 estimates, indicate the presence of «' and maternal effects s na (Roberts, 1967). However, heritability estimates for body weight are not available for the parental strains for comparison. No conclusions concerning fertility and hatchability of the straincross can be drawn as there was no adequate control. Fertility and hatchability of the control strain were measured based on parental performance in Ottawa. Therfore they cannot be compared with the performance of strain 6 which was measured at Agassiz. The fertility of the 1961 generation of strain 6 which were not bred until their second year was reduced due to the older age of these birds at breeding. The gradual lowering of the age at sexual maturity, and the slight upward trend in overall egg production of the control strain can be attributed to the improvements in management and nutrition that had been made over the course of the study as genetic drift is an unlikely cause (Gowe and Fairfull, 1985). Keeping in mind that the control strain has not been selected for egg production yet is fed the same nutritionally excellent diet as the selected strains, the increase in body weight of the controls over generation is probably due to the tendency to put on fat as these birds are not as energetically efficient in converting feed to eggs as the selected strains (Fairfull, personal communication). Mortality among all strains has gradually decreased due to better disease control management and vaccination procedures. The egg quality traits, egg weight, egg specific gravity and Haugh units, have, remained stable for the control strain for the duration of this study as can be seen from the regressions of these traits on time which are not significantly different from zero. 65 The actual selection differentials (SD's) for the sires and dams for strain 6 for egg production from 148 to 273 days are positive as was ex-pected from the amount of selection pressures applied to. this trait. However, the selection pressure was not enough to effect a significant change in the phenotypic value for egg production. The SD's for egg weight at 225 days were practically zero which is in accordance with the maintenance of this trait at the same level throughout the selection study. The SD's for body weight for the sires were slightly posistive for all but the first year of the study but these figures may not adequately reflect the true SD's of the sires as the birds were weighed in groups and an av-erage taken. Consequently, the smallest bird with the best conformation in the group may have been chosen as a sire for the next generation in which case he would have had a body weight lower than the average of the group he was weighed in. The SD's for the dams fluctuate around zero as would be expected if the dams were being chosen without regard for their body weight or conformation as was the case in this study. The low SD for egg production from 148 to 273 days for the parents selected in 1961 reflects the delay in breeding of these birds for one year. This particular occurrance appears to confirm that as the age of the parents increases, the response to selection decreases partially due to the decrease in the actual SD. This phenomenon is caused by changes in the reproductive function of the parents with increasing age and by the use of inferior birds as replacements for superior birds that died in the interval between selection and breeding (Liljedahl et al., 1984). Exposed to six generations of selection after the initial straincross in 1957, strain 6 remained phenotypically stable for all but one of the traits under selection. HHEP, egg weight, fertility, hatchability and viability 66 remained constant throughout the selection period while body weight declined significantly and showed no signs of abating. The other traits measured but not considered in the selection program were egg specific gravity, Haugh units, and age at sexual maturity. These traits did not show any consistent trends in performance. The lack of phenotypic response to selection was probably due to the following reasons: 1) there were too many traits considered in the selection program at the same time resulting in a lack of response to selection, 2) some of the traits selected were negatively correlated with one another, 3) strict adherence to a selection scheme was not practiced, 4) most of the traits under selection had low heritabilities, 5) the duration of the study was probably not long enough, and 6) the population size of strain 6 may not have been large enough. Furthermore, some traits that were being selected such as fertility and hatchability may not have an adequate control in the strain sent from Ottawa. As a result, no conclusions could be drawn for these traits. This particular situation reflects the need for adequate controls to be included in selection studies. BIBLIOGRAPHY Akbar, M. K., J. S. Gavora, G. W. Friars, and R. S. Gowe, 1983. Composition of eggs by commercial size categories: effects of genetic group, age and diet. Poultry Sci. 62:925-933. Arthur, J. A., and W. J. Beck, 1974. Linear estimates of heritabilities and genetic correlations for body weight, egg weight, and shell colour in chickens. XV World's Poultry Congress and Exposition, Proceedings and Abstracts, Aug. 11-16, New Orleans, pp. 28-29 Barton, W. H., and B. Charlesworth, 1984. Genetic revolutions, founder effects, and speciation. Ann. Rev. Ecol. Syst. 15: 133-164. Bell, A. E., C. H. Moore, and D. C. Warren, 1955. The evaluation of new methods for the improvement of quantitative characteristics. Cold Spring Harbor Symposia on Quantitative Biology XX:197-212. Bennett, G. L., G. E. Dickerson, R. S. Gowe, A. J. McAllister, and J. A. B. Emsley, 1981. Net genetic and temporary epistatic or maternal environmental responses to selection for egg production in chickens. Genetics 99:309-321. Bohren, B. B., 1970. Genetic gains in annual egg production from selection on early part-records. World's Poultry Sci. J. 26:647-657. Clayton, G. A., 1968. Some implications of selection results in poultry. World's Poultry Sci. J. 24:37-57. Dempster, E. R., I. M. Lerner, and D. C. Lowry, 1952. Continuous selection for egg production in poultry. Genetics 37:693-708. Dickerson, G. E., 1955. Genetic slippage in response to selection for multiple objectives. Cold Spring Harbor Symposia on Quantitative Biology XX:213-224. Dickerson, G. E., 1969. Techniques for research in quantitative animal genetics. In Techniques and Procedures in Animal Production Research , Amer. Soc. of An. Sci., Wash., D. C. Fairfull, R. W., 1982. Combining ability, heterosis and reciprocal effects for first and second year performance in six selected leghorn strains crossed in a complete diallel. Proc. of the 31st Annual National Breeders' Roundtable May 6-7, St. Louis, Missouri, pp. 119-137. Fairfull, R. W., R. S. Gowe, and J. A. B. Emsley, 1983. Diallel cross of six long-term selected leghorn strains with emphasis on heterosis and reciprocal effects. Br. Poultry Sci. 24:133-158. Falconer, D. S., 1953a. Assymetrical response in selection experiments. /. U. B. S. Symposium on Genetics of Population Structure, Pavia, Italy, Aug. 20-23, pp. 17-41. 67 68 Falconer, D. S., 1953b. Selection for large and small size in mice. J. Genetics 51:470-501. Falconer, D. S., 1955. Patterns of response in selection experiments with mice. Cold Spring Harbor Symposia on Quantitative Biology XX: 178-196. Falconer, D. S., 1971. Improvement of litter size in a strain of mice at a selection limit. Genet. Res., Camb. 17^245-235. Falconer, D. S., 1981. Introduction to Quantitative Genetics 2nd ed. Longman Inc., New York. Falconer, D. S., and J. W. B. King, 1953. A study of selection limits- in the mouse. J. Genetics 51:561-581. Fisher, R. A., 1930. The Genetical Theory of Natural Selection. Clarendon Press, Oxford. Goher, N. E., J. J. Rutledge, W. H. McGibbon and A. B. Chapman, 1978. Evaluation of selection methods in a poultry breeding program. I. Selection for rate of egg production on the basis of part-year record with and without full-sibbing. II. Correlated responses. Egypt. J. Genetics and Cytology 7;79-90;9l-107. Gowe, R. S., and R. W. Fairfull, 1980. Performance of six long-term multi-trait selected leghorn strainsand three control strains, and a strain cross evaluation of the selected strains. Proc. of the 1980 South Pacific Poultry Science Convention, World's Poutry Sci. Assoc. Oct. 13-16, Auckland, N. Z., pp. 141-162. Gowe, R. S., and R. W. Fairfull, 1982a. Heterosis in egg-type chickens. 2nd World Congress on Genetics Applied to Livestock Production, Oct. 4-8, Madrid, Spain, pp. 228-242. Gowe, R. S., and R. W. Fairfull, 1982b. Some lessons from selection studies in poultry. In Proceedings of the World Congress on Sheep and Beef Cattle vol. I: Technical , R. A. Barton and W. C. Smith (eds.), Dunsmore Press Ltd., N. 2. Gowe, R. S., and R. W. Fairfull, 1985. The direct response to long-term selection for multiple traits in egg stocks and changes in genetic pa-rameters with selection. Poultry Genetics and Breeding , W. G. Hill, J. M. Manson and D. Hewitt (eds.), Longman Group, Harlow. Gowe, R. S., A. S. Johnson, R. D. Crawford, J. H. Downs, A. T. Hill, W. F. Mountain, J. R. Pelletier, and J. H. Strain, 1960. Restricted versus full-feeding during the growing period for egg production stock. Br. Poultry Sci. 1:37-56. Gowe, R. S., A. S. Johnson, J. H. Downs, R. Gibson, W. F. Mountain, J. H. Strain, and B. F. Tinney, 1959a. Environment and Poultry Breeding Problems. 4. The value of a random-bred control strain in a selection study. Poultry Sci. 38:443-462. 69 Gowe, R. S., A. S. Johnson, and E. S. Merritt, 1954. Poultry breeding unit. In Poultry Division Progress Report 1949-1954 , Dept. of Agric., Canada, Exp. Farms Service. Gowe, R. S., W. E. Lentz, and J. H. Strain, 1973. Long-term selection for egg production in several strains of White Leghorns: performance of selected and control strains includoing genetic parameters of two con-trol strains. 4th Europ. Poultry Conf., London, pp. 225-245. Gowe, R. S., A. Robertson, and B. D. H. Latter, 1959b. Environment and Poultry Breeding Problems. 5. The design of poultry control strains. Poultry Sci. 38:462-471. Gowe, R. S., and J. H. Strain, 1963. Effect of selection for increased egg production based on part year records in two strains of White Leghorns. Can. J. Genetics and Cytology 5:99-100(abstract) Gowe, R. S., J. H. Strain, R. D. Crawford, A. T. Hill, S. B. Slen, and W. F. Mountain, 1965. Restricted feeding of growing pullets. 2. The effect on costs, returns and profits. Poultry Sci. 44:717-726. Gowe, R. S., and W. J. Wakely, 1954. Environment and Poultry Breeding Problems. 1. The Influence of several environments on the egg production and viability of different genotypes. Poultry Sci. 33:693-703. Hartl, D. L., 1980. Principles of Population Genetics. Sinauer Assoc., Inc., Sunderland, Mass. Hill, A. T., 1957-1963. Project P5l.11.11 notes. Hill, W. G., 1972. Estimation of genetic change. II. Experimental evaluation of control populations. A. B. A. 40:193-213. Hill, W. G., and A. Robertson, 1966. The effect of linkage on limits to artficial selection. Genet. Res., Camb. 8:269-294. Jerome, F. N., C. R. Henderson, and S. C. King, 1956. Heritabilities, gene interactions, and correlations associated with certain traits in the domestic fowl. Poultry Sci. 35:995-1013. Kinney, T. B. Jr., 1969. A summary of reported estimates of heritabilities and of genetic and phenotypic correlations for traits of chickens. Agric. Handbook no. 363, Agric. Res. Service, U. S. D. A. Kinney, T. B. Jr., B. B. Bohren, J. V. Craig, and P. C. Lowe, 1970. Responses to individual, family or index selection for short term rate of egg production in chickens. Poo/try Sci. 49:1052-1064. Krause, E.. Y. Yamada, and A. E. Bell, 1965. Genetic parameters in two populations of chickens under reciprocal recurrent selection. Br. Poultry Sci. 6:197-206. Lerner, I. M., 1948. Genetic Homeostasis . Oliver and Boyd, London, Eng. 70 Lerner, I. M., 1950. Population Genetics and Animal Improvement . Cambridge University Press, Cambridge, Eng. Lerner, I. M., and C. A. Gunns, 1952. Egg size and reproductive fitness. Poultry Sci. 31:537-544. Liljedahl, L. E., N. Kolstad, P. Sorensen, and K. Maiala, 1979. Scandinavian selection and crossbreeding experiment with laying hens. I. Background and general outline. Acta Agric. Scandinavica 29:273-286. Liljedahl, L. E., J. S. Gavora, R. W. Fairfull, and R. S. Gowe, 1984. Age changes in genetic and environmental variation in laying hens. Theor. Appl. Genet. 67:391-401. Lush, J., 1947. Family merit and individual merit as bases for selection, I, II. Am. Nat. 91:241-379. Lush, J., 1951. The effectiveness of selection. J. Animal Sci. 10:3-21. Mather, K., and B. J. Harrison, 1949. The manifold effect of selection. Heredity 3;1-52;131-162. Morris, J. A., 1963. Continuous selection for egg production using short term records. Australian J. Agri. Res. 14:909-925. . Munro, S. S., 1936. The inheritance of egg production in the domestic fowl. I. General considerations. Sci. Agric. 16:591-607. Munro, S. S., 1942. Further data on the relation between shell strength, potential hatchability and chick viability in the fowl. Sci. Agric. 22:698-704. Nagai, J., and R. S. Gowe, 1969. Genetic control of egg quality. I. Sources of variation. II. Selection for maximum rate of improvement. Br. Poultry Sci. 10:337-350;351-358. Roberts, R. C., 1966. The limits to artificial selection for body weight in the mouse. I. The limits obtained in earlier experiments. II. The genetic nature of the limits. Genet. Res., Camb. 8:347-360; 361-375. Roberts, R. C, 1967. The limits to artificial selection for body weight in the mouse. III. Selection from crosses between previously selected lines. Genet. Res., Camb. 9:73-85. Robertson, F. W., 1955. Selection response and the properties of genetic variation. Cold Spring Harbor Symposia on Quantitative Biology XX:166-177. Robertson, F. W., 1956. The use of Drosophila in the experimental study of animal breeding problems. A. B. A. 24:218-224. Rose, M. R., 1982. Anatagonistic pleiotropy, dominance, and genetic variation. Heredity 48:63-78. 71 Saadeh, H. K., J. V. Craig, L. T. Smith, and S. Wearden, 1968. Effectiveness of alternative breeding systems for increasing rate of egg production in chickens. Poultry Sci. 47:1057-1072. SAS Institute Inc., 1982a. SAS User's Guide: Basics. SAS Institute Inc., Box 8000, Cary, N. C. 27511. SAS Institute Inc., 1982b. SAS User's Guide: Statistics. SAS Institute Inc., Box 8000, Cary, N. C. 27511. Thoday, J. M., J. B. Gibson, and S. G. Spickett, 1964. Regular responses to selection. II. Recombination and accelerated response. Genet. Res., Camb. 5:1-19. Yamada, Y., B. B. Bohren, and L. B. Crittenden, 1958. Genetic analysis of a White Leghorn closed flock apparently plateaued for egg production. Poultry Sci. 37:565-580. APPENDIX 72 Table 6.1. Estimates of the sire ( c ' s ) , dam («'d) and individual ( o ' e > components of variance, and the degress of freedom (df s, d f d , and df e, respectively) of each component from the analyses of variance for strain 6 for 1957. T r a i l d ' a * ' s d f d * ' d d f e HHEP t o 2 7 3 d a y s 3 8 35 - - 2 7 2 3 7 5 E g g p r o d u c t i o n f r o m 38 28 2 7 0 47 4 7 1 7 3 4 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 38 9 3 2 7 0 8 6 4 7 1 3 1 5 7 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 38 48 2 7 0 3 8 4 7 1 1 9 3 8 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 38 2 261 2 3 8 8 8 d a y s E g g w e i g h t a t 3 5 0 3 8 3 2 6 4 2 3 6 4 9 d a y s E g g w e i g h t a t 4 5 0 38 4 2 6 0 3 3 2 2 12 d a y s E g g s p e c i f i c g r a v i t y 38 4 261 1 3 8 8 24 a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y 38 2 2 6 0 1 3 2 2 21 a t 4 5 0 d a y s H a u g h u n i t s at 2 2 5 3 8 5 261 4 3 8 8 19 d a y s H a u g h u n i t s a t 4 5 0 38 6 2 6 0 5 3 2 2 3 5 d a y s A g e a t s e x u a l 38 11 2 6 9 3 5 4 4 4 196 m a t u r 1 t y B o d y w e i g h t a t 3 6 5 3 8 52 2 6 7 6 7 4 13 4 3 8 d a y s Table 8.2. Estimates of the sire U' s), dam (o-'d) and Individual («'e) components of variance, and the degrees of freedom (df , df,. , and df , respectively) of each component from the analyses of variance for strain 8 for 1938. S O © T r a i t d f g „ ' s d f d « ' d d f f i * ' e HHEP t o 2 7 3 d a y s 19 521 - - 188 3 4 3 E g g p r o d u c t i o n f r o m 19 21 188 9 0 6 9 3 6 0 0 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 19 112 188 3 3 4 6 9 3 2 2 8 2 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 19 2 0 0 188 2 9 4 6 9 3 3 2 0 8 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 19 2 185 2 6 1 7 9 d a y s E g g w e i g h t a t 3 5 0 19 4 180 3 5 6 0 9 d a y s E g g w e i g h t a t 4 5 0 19 4 176 4 5 3 0 13 d a y s E g g s p e c i f i c g r a v i t y 19 3 185 2 6 1 7 19 a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y 19 2 176 3 5 3 0 24 a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 19 5 185 9 6 1 7 29 d a y s H a u g h u n i t s a t 4 5 0 19 11 176 7 5 3 0 46 d a y s A g e a t s e x u a l 19 13 186 13 177 6 7 0 m a t u r 1 t y B o d y w e i g h t a t 3 6 5 19 164 183 152 6 1 1 501 d a y s v l Table 8.3. Estimates of the sire („' s). dam.<„'„) and Individual („'„) components of variance, and the degrees of freedom (df df and df respectively) of e a c h component from the analyses of variance for strain 6 for 1959. T r a i t d f d f d « ' d d f „ 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 19 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 19 2 8 2 d a y s A g e a t s e x u a l 19 m a t u r 1 t y B o d y w e i g h t a t 3G5 19 109 182 108 d a y s 189 2 8 0 HHEP t o 2 7 3 d a y s 19 1 4 7 1 E g g p r o d u c t i o n f r o m 19 137 185 6 6 1 0 0 8 7 9 1 4 0 8 185 2 8 7 1 0 0 8 3 1 0 2 185 3 6 3 1008 3 7 7 8 181 1 8 4 6 9 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 19 2 d a y s E g g w e i g h t a t 3 5 0 19 3 1 ? 9 d a y s E g g w e i g h t a t 4 5 0 19 3 178 3 7 0 9 14 d a y s E g g s p e c i f i c g r a v i t y 19 4 181 a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y 19 6 178 a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 19 4 1 8 1 d a y s H a u g h u n i t s a t 4 5 0 19 8 178 7 8 0 10 8 4 6 18 7 0 9 2 8 8 4 6 2 2 7 0 9 51 57 184 27 9 4 1 2 9 7 8 5 1 5 0 3 Table 6.4. Estimates of the sire (<J's), dam ( o ' d ) and Individual (a' e) components of variance, and the degrees of freedom (df s, d f d , and d f e > respectively) of each component from the analyses of variance for strain 6 for I960. T r a i t s d f . d f . HHEP t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 d a y s E g g w e i g h t a t 3 5 0 d a y s E g g w e i g h t a t 4 5 0 d a y s E g g s p e c i f i c g r a v i t y a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 d a y s H a u g h u n i t s a t 4 5 0 d a y s A g e a t s e x u a l m a t u r 1 t y B o d y w e i g h t a t 3 6 5 d a y s 19 19 19 19 19 19 19 19 19 19 19 19 19 1002 78 2 3 4 2 4 2 11 1 1 8 7 178 178 178 176 175 174 174 174 174 176 176 177 4 0 112 2 0 9 0 178 7 7 9 7 7 9 7 7 9 5 8 9 5 5 0 4 8 5 5 8 9 4 8 5 4 8 5 5 8 9 7 3 6 6 5 1 3 2 2 1068 3 9 3 3 4 5 0 8 12 15 14 2 5 6 6 26 2 8 6 5 3 3 C D Table 6 . 5 . Estimates of the sire U' s). dam ( „'d) and individual («'e) components of variance, (df s, d f d , and , respectively) of each component from the analyses of variance for T r a i t d f s <'s d f d « ' d H H E P t o 2 7 3 d a y s 24 2 7 6 - -E g g p r o d u c t i o n f r o m 24 17 174 2 2 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 24 76 174 1 3 0 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 24 123 174 148 2 7 4 t o 4 9 7 d a y s 1 E g g w e i g h t a t 2 2 5 24 2 174 d a y s E g g w e i g h t a t 3 5 0 24 2 173 2 d a y s E g g w e i g h t a t 4 5 0 24 2 173 3 d a y s E g g s p e c i f i c g r a v i t y 24 3 173 2 a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y 24 3 173 3 a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 24 4 174 4 d a y s H a u g h u n i t s a t 4 5 0 24 8 173 7 d a y s A g e a t s e x u a l 24 7 174 22 m a t u r i t y B o d y w e i g h t a t 3G5 24 94 174 109 d a y s d f e 174 147 7 2 9 5 6 4 7 2 9 2 0 9 8 7 2 9 2 8 1 4 6 4 7 8 5 8 6 10 5 2 3 13 6 4 7 18 5 2 3 31 6 4 7 2 3 5 2 3 44 7 2 0 105 6 6 5 5 2 4 Table 8.8. Estimates of the sire (<r's). dam (o-'jj) and Individual (<r'e) components of variance, and the degrees of freedom (df s > df r f , and df e, respectively) of each component from the analyses of variance for strain 8 for 1983. T r a i t d f a' d f . «« d f a' s s d d e e HHEP t o 2 7 3 d a y s 24 3 2 8 - - 128 3 1 6 E g g p r o d u c t i o n f r o m 24 1 123 119 4 0 0 5 9 5 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 24 6 5 123 4 0 6 4 0 0 1734 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 24 2 3 3 123 4 7 9 4 0 0 2 1 5 8 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 24 1 120 1 351 7 d a y s E g g w e i g h t a t 3 5 0 24 1 117 1 3 2 6 12 d a y s E g g w e i g h t a t 4 5 0 24 2 116 2 3 0 7 13 d a y s E g g s p e c i f i c g r a v i t y 24 6 120 4 351 19 a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y 24 4 116 - 1 3 0 7 34 a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 24 6 120 6 351 19 d a y s H a u g h u n i t s a t 4 5 0 24 6 116 9 3 0 7 34 d a y s A g e a t s e x u a l 24 - 7 2 7 3 4 8 3 9 3 6 0 0 m a t u r 1 t y B o d y w e i g h t a t 3 6 5 24 5 3 2 7 3 117 3 7 6 4 0 5 d a y s Co Table 8.7. Estimates of the sire (<»'), dam io'M) and Individual (#• ) components of variance, and the degrees of freedom S O 8 (df s > d f d , and df e, respectively) of each component from the analyses of variance for strain 8 for 19S7 to 1983. T r a i t d f . s df H H E P t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 148 t o 2 7 3 d a y s E g g p r o d u c t i o n f r o m 148 t o 4 9 7 d a y s E g g p r o d u c t i o n f r o m 2 7 4 t o 4 9 7 d a y s E g g w e i g h t a t 2 2 5 d a y s E g g w e i g h t a t 3 5 0 d a y s E g g w e i g h t a t 4 5 0 d a y s E g g s p e c i f i c g r a v i t y a t 2 2 5 d a y s E g g s p e c i f i c g r a v i t y a t 4 5 0 d a y s H a u g h u n i t s a t 2 2 5 d a y s H a u g h u n i t s a t 4 5 0 d a y s A g e a t ' s e x u a l m a t u r 1 t y B o d y w e i g h t a t 3G5 d a y s 143 143 143 143 143 143 143 143 143 143 143 143 143 4 3 56 188 192 2 0 9 7 I 1 18 I I 18 1 1 18 1097 1088 1077 1097 1077 1097 1077 1 112 1 106 5 7 2 1 5 149 8 19 105 1 127 4 0 8 0 4 0 8 0 4 0 8 0 3 4 3 8 3 1 6 6 2 8 7 6 3 4 3 8 2 B 7 6 3 4 3 8 2 8 7 6 3 9 0 4 3 5 6 7 3 0 4 7 4 5 2 8 1 4 3 2 7 7 10 14 18 2 7 2 3 4 7 2 5 8 4 9 4 v l CO 

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