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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 E I L E E N REED  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE  FACULTY OF GRADUATE  Department  We a c c e p t  of Poultry  this  STUDIES Science  t h e s i s as conforming  to the required  standard  UNIVERSITY OF B R I T I S H COLUMBIA May ©  31,1985  Shawna E i l e e n Reed,  31,1985  In presenting advanced Library  degree  shall  agree that  this thesis at  make  the  representatives.  be  University  fulfilment of of  it freely available  permission  purposes may  in partial  for  extensive  granted by  British for  copying  copying  of  University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date; May  23.1985  and  that  an the  study. I further  this thesis  for  Department or by  scholarly his or her  or publication of this thesis  for financial gain shall not be allowed without my  Department of Poultry Science  requirements for  Columbia, I agree  reference  the Head of my  It is understood that  the  written permission.  Abstract In 1957, strains 3 and 4, two highly selected but unrelated strains of Single  Comb  Research  White  Station  Leghorn  chickens from  at Ottawa were  crossed  to establish  (strain 6). Further selection was imposed hen-housed  egg production (HHEP) based  maintenance  Agriculture  Canada's  Animal  the Agassiz strain  on strain 6 for improvements in on part-records to 273 days and  of egg weight, fertility, hatchability  1957 to 1963 were analysed utilizing the SAS There were no significant improvements  and viability. Data  from  programs. 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 days  large enough. There was a significant decrease in body weight at 365 (-4.33  selection  ±  0.48, p  within full-sibs  <  0.0009). This  decrease  for more refined  may  be  because  of  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, a l though Haugh units were increasing when measured at 450 days. The  mean  h  J  s  for HHEP  was  0.45, and the mean  h  2  s  for egg  production to 273 days was 0.20 and the mean h ^ for the same trait was 2  0.33. The mean h  2 g  and h  2 d  estimates for egg weight  0.60 and 0.50, respectively. The  mean  h  J  and h ^ 2  g  at 225 days were for age  at sexual  maturity were 0.22 and 0.33, respectively, and those for body weight at 365  ii  days  were  specific  0.53  gravity  and  0.62, respectively. The  at 225 were  mean  h  2 g  and  0.64 and 0.33, respectively  h  for egg  J d  while  those for  Haugh units at 225 days were 0.57 and 0.68, respectively. These  estimates  were  selection  consistent  differentials  with  showed  those that  found  in the literature. The  selection was  sctual  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  sires.  iii  in the downward  direction  on the  Acknowledgements I would  like  to  thank  encouragement,  and  financial  Dr. K. support  Research Council of Canada grant manuscript,  and  for  the  M.  Cheng  (Natural  for  his  Sciences  advice, patience, and  Engineering  #A-8062) during the preparation of this  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  from which this thesis was I would  also  like  to  Animal Research Centre the raw  data was  data  developed. His expertise is greatly appreciated.  thank  Drs. R. W.  Fairfull  and  R. S. Gowe  of  the  in Ottawa for making available the tapes on which  stored and for their helpful suggestions, and  the technical  assistance of Mr. L. B. Asselstine. The and  I am  the SAS  UBC  computing centre provided the funds for statistical analyses  grateful to F. Ho  M. Grieg for their technical assistance with  computer programs package.  My  thanks to my  during the course of my I would Science  and  years, and  were very  patient and  understanding  studies.  like to express  for awarding me  consecutive  family who  my  the C. W. I wish  to  gratitude to the Department  of Poultry  Roberts Memorial Scholarship for thank  my  guidance during the preparation of this thesis.  iv  thesis committee  two  for their  Table of Contents List of Tables  V l i  List of Figures 1.  Introduction  2.  Literature Review  xiv 1 .3  2.1 Selection Limits  3  2.2 Effects of Strain Crossing  6  2.3 Physiological Relationships 3.  Materials  Between  Egg Production Traits  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  4.  8  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  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 4.1.4 Control  .34  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 5.  Differentials  55  Discussion  57  BIBLIOGRAPHY  .67  APPENDIX  72  vi  List of Tables  Table  3.1.2.1.  Page  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 of variance for HHEP from  25  148 to 273 days for  strain 6. 4.1.1.2.  Estimates of the sire („' ),dam (#'.,) and S  26  u  individual (<j* ) components of variance, and of the e  heritabilities based on the sire (h ) and dam (h ^) 2  2  g  components of variance for strain 6 for egg production from 4.1.1.3.  148 to 273 days.  Estimates of the sire (<»').dam s individual  («,» ) and a  27  U' ) components of variance, and of the e  heritabilities based on the sire (h ) and dam (h ^) 2  2  g  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 s  U'^) and a  28  individual (#' ) components of variance, and of the e  heritabiIities based on the sire (h ) and dam 2  s  (h ^) 2  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 ) and 2  g  dam  29  (h ^) components of variance for egg 2  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 ) and 2  g  dam  31  (h ^) components of variance for egg weight 2  at 225, 350 and 450 days of age for strain 6. 4.1.2.2.  Heritability estimates based on the sire (h ) and 2  g  dam  (h ^) components of variance for egg  32  specific  2  gravity at 225 and 450 days of age for strain 6. 4.12.3.  Heritability estimates based on the sire (h ) and 2  g  dam  (h ^)-components 2  of variance for Haugh units  at 225 and 450 days of age for strain 6.  viii  33  4.1.3.1.  Heritability estimates based on the sire (h ) and 2  g  dam  35  (h ^) components of variance for age at 3  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 control strain, and deviations  from the control for  strain 6 for egg production from 4.3.1.2.  148 to 497 days.  Means and standard errors for strain 6 and the control strain, and deviations  39  from the control for  strain 6 for egg production from 4.3.1.3.  148 to 273 days.  Means and standard errors for strain 6 and the control strain, and deviations  38  40  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 control strain, and deviations  from the control for  strain 6 for egg weight at 225 days in grams.  ix  42  4.3.2.2.  Means and standard errors for strain 6 and the control strain, and deviations  43  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 control strain, and deviations  44  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 control strain, and deviations  45  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 control strain, and deviations  46  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 control strain, and deviations  47  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 control strain, and deviations  from the control for  strain 6 for Haugh units at 450 days.  x  48  4.3.3.1.  Means and standard errors for strain 6 and the control  49  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 control  50  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  strain for  53  strain, and  54  fertility. 4.3.3.4.  Means for strain 6 and the control hatchability.  4.3.3.5.  Means for strain 6 and the control 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  dams of strain 6 for egg production from  56  148 to  273 days, egg weight at 225 days in grams, and body weight at 365 days in decagrams from to  1963.  xi  1957  Estimates of the sire  dam  (e' ), s  and  (o' ) a  individual (a' ) components of variance, and the degrees of freedom  (df , df^ , and d f , g  g  respectively) of each component from the analyses of variance for strain 6 for 1957. Estimates of the sire (o' ), dam s  (<>') and d  individual (o' ) components of variance, and the e  degrees of freedom  (df  df^ , and d f ,  s>  g  respectively) of each component from the analyses of variance for strain 6 for 1958. Estimates of the sire (,' ), dam s  (o' )  '  anc  a  individual («' ) components of variance, and the e  degrees of freedom 3  v  (df , df . , and df , 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' ) components of variance, and the e  degrees of freedom  (df , d f g  d  , and d f , g  respectively) of each component from the analyses of variance for strain 6 for 1960.  xii  Estimates of the sire  (cr' ), s  dam  and  (cj' ) d  individual (e»') components of variance, and the e  degrees of freedom  (df , df^ , and df , g  g  respectively) of each component from the analyses of variance for strain 6 for 1961. Estimates of the sire (a'), s individual  dam  („•) and a  (<j' ) components of variance, and the e  degrees of freedom  (df , df g  rf  , and df , g  respectively) of each component from the analyses of variance for strain 6 for 1963. Estimates of the sire („' ),dam s  (<j' ) and d  individual («' ) components of variance, and the e  degrees of freedom  (df df_, and df s' d ' e'  v  respectively) of each component from the analyses of variance for strain 6 for 1957 to 1963.  xiii  List of Figures  Page  Figure  4.3.3.1  Mean body weights at 365 days vs year  xiv  51  1. INTRODUCTION In  1957, two  unrelated  strains  chickens that had apparently plateaued  of  Single  in response  productivity.  Research  Station  Animal Research Research through  (Falconer,  was  the nature to  species  of selection  selection  selection  strain in an attempt to  conducted research  at  carried  the  Agassiz  out by the  such  as  1967). Straincrosses had been  limits, and efforts  response  fruit  flies  1953a, b, 1955, 1971; Falconer  the agricultural  Leghorn  Centre, Agriculture Canada.  barriers  non-commercial  .experiment  as part of the straincross  into  these  This  White  to long-term  for egg production were crossed to create a new increase  Comb  a source  were  only  (Robertson,  to break  beginning in  1955) and  mice  and King, 1953; Roberts, 1966,  of interest  to animal  breeders in  industries as a means of increasing productivity by taking  advantage of heterotic effects. In addition, there was considerable interest in  selection  suggested  plateaux  and  crossing  strains  was  one  method  that  was  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 data  were  shipped  to Ottawa  for keypunching,  returned  Station. The  to Agassiz for  checking, and then sent back to Ottawa for analyses. The heavy in  Ottawa  selection  delayed  the analyses  of the Agassiz  on the parental strains at Ottawa  workload  data. Furthermore,  yielded  further  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 was  that  same  time  period  going through a revolution  developed constantly  for  data  being  handling updated  incompatibilities which  (early  1960's), computing  as newer and and  which  better systems  processing. lead  Computing  to  many  knowledge were being  facilities  were  software/hardware  further delayed the analyses of the Agassiz project  data. The purpose of this thesis is to utilize this set of data to 1) estimate 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  the  straincross  the parental strains. These  comparisons  and  for  communication).  data  from  the  two  results will  parental  strains  between  provide limited (Gowe,  personal  2. LITERATURE REVIEW  2.1 SELECTION LIMITS Typically, artificial selection has  been imposed  order to improve some production  on  domesticated  trait whether it be  wool often for a considerable number of generations additive  genetic  component  of  the  genotypic  a population gradually  may  over  time, and  variance  becomes exhausted. A  selected  alleles increases and due  to  (Falconer, 1981;  in any  one is  strain. The the  genetic  Falconer, 1981). Initially,  show positive selection response but this response  decrease  increases  eggs, milk, meat or  variance  component utillized during selection (Clayton, 1968;  animals in  eventually  limit will  as  additive genetic  reached as  the frequency  eventually becomes fixed, and  inbreeding, particularly  Falconer and  be  plateau  if the  may  population  of  homozygosity size  is small  King, 1953; Yamada et al., 1958). Although this  topic is of interest in selection experiments, selection limits have not been a  problem  seldom  in  closed  commercial to  outside  breeding  operations  introductions of  as  such  birds and  populations  lines  are  are  generally  turned over rapidly. Even variance genetic  may  additive  remain  effects. Any  environment action  though  may  genetic  constant  variance  due  to  dominance/epistatic  may  decrease,  environmental genetic  and  effects  and  interactions which were previously masked by become  relatively  more  important  contribution to the total variation (Falconer and  and  phenotypic non-additive genotype  by  additive genetic  increase  in  their  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  3  variance  to  the  phenotypic  4 variation, may  decrease  before selection was When  and  then appear to stabilize at a lower  value than  imposed.  calculated  heritabilities  remain  constant  over  other explanation for the plateau in selection response  time, then  some  must be  considered  (Lush, 1951): 1) non-additive gene action, where stabilization may  be due to  antagonistic rectional alleles  pleiotropic gene effects, selection favouring overdominance, d i -  dominance  at  low  of  alleles  frequencies  1958), 2) negative  for the  selcted  (Falconer, 1971;  genetic correlations, such  approached, pleiotropic gene interactions increase,  and  thus  cause  natural  traits, and  Roberts,  1966;  phenomenon  homeostasis'; stage  of  of  resistance  that when a selection  that  affect  selection  to  to  selection  Lerner, 1948), 3) positive  the  life  cycle  and  the total  work  selection for the characteristic in one it in another. Traits based show  response  combinations.  as  Genotype  by  is  limit is  fitness  may to  'optimum' fitness  is termed  for a  'genetic  character  at another  at  one  stage, and  4)  flock, or ecological niche, and against  largely* on  selection  selection  et al.,  antagonistically  pressure  selection  negative  recessive  Yamada  artificial selection in order to return the population to an (this  rare,  non-additive genetic effects will not  for  overdominance  environment  and  epistatic  interactions  effects that will be broken up by recombination  and  are  gene  transitory  dissipate in subsequent  generations (Falconer, 1955). Negative causes  of  a  genetic low  correlations  response  to  between  selection  components  overall  relationships trait  Pleiotropic  may gene  be  between them low,  and  interactions  the heritability  consequently, have  the  one  in multi-trait selection  Heritabilities of the individual trait or components may negative  are  the  programs.  be high, but due to  of the combination  response  potential  of  will for  be  or  weakened.  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 unfavourable combinations to  the  genetic  and may  will be fixed or lost and  covariance  combinations' portion  selection progresses, favourable and  will  decrease  increases. The  over  thus their contribution time,  genetic correlation  as  will  the  thus  mixed decrease  eventually become negative (Liljedahl et al., 1979).  Egg weight is a trait of economic importance to the poultry operator and  so, has  been  actively  maintained  showed  that  maximizing weights poorer  selected at some  eggs of  be  fitness.  selected  hatchability  than  breeding  pre-existing  and  Consequently,  birds  or were  improved  producing  complex  breeding  1950). Generally, poultry breeders are interested set  of  traits  regardless  of  high  stages of the program  smaller egg  in many  (1952)  in terms of  showing  environment  egg  due  to  colleagues. However,  there were studies that showed fertility, hatchability, and high  at least  Gunns  were the optimum  against in later their  programs, or  level. Lerner  intermediate weight  reproductive  may  for in many  viability  programs  remained  (see Lerner,  in selecting for the same  thus  the  fourth  of  Lush's  possibilities does not concern us here. Linkage can be genes but is broken during  a temporary up  selection, and  by  cause  crossing  so, is not  a  of negative correlations between  over  and  permanent  recombination fairly quickly obstacle to  selection. The  tighter the linkage , the more resistant the complex is to breaking up, particularly  in the  crossing-over units  areas  the  centromeres  is a rare event, and  during selection  unfavourable  near  allele will  (Mather depend  and on  thus these  of  the  chromosomes  'polygenes' may  Harrison, 1949). Chance the  population size, but  behave as  fixation may  where  of  an  also  be  6 caused by  linkage to another selectively  latter possibility will depend on  advantageous gene; however, this  the intensity of selection in a quantitative  situation (Roberts, 1966). Rare recombinational  events, and  new  additive genetic variance into a plateaued selection  is once  population  may  more  then  observed  continue  to  mutations may  population  (Falconer,  introduce  such that response to  1953a,b; Roberts,  increase  in  new  productivity  1966).  until  The  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  plateau  under  long-term  in response  straincross  may  to  exhibit  selection,  and  selection for  one  heterosis  to  due  are or  showing more  dominance  tendency  traits. and  effects but as already mentioned, these effects cannot be for as emphasis is on the  a  to  Initially, the  epistatic  gene  directly selected  heterozygote.  White Leghorn straincrosses exhibited higher heterosis if the parental strains  were  dominance and al.,  1983).  background  from  differing  any  backgrounds  due  to  the  increased  epistatic interactions between the different alleles (Fairfull et  Even  crosses  of  strains  derived  from  exhibited subtantial heterotic effects  gene combinations present the parents  genetic  in the  (Falconer, 1971). The  information or direct evidence  crosses were used.  the  possibly due  hybrid offspring that had  present  study  same  will not  to  genetic epistatic  been fixed in  attempt to provide  on this phenomenon since only two-way  7 Because heterosis  of  the  expected  differing  cannot  be  straincross  responses,  predicted from  the  magnitude  parental performance  of  (Fairfull,  1982). Typically, in strain and line crosses of chickens, heterotic advantages are for decreased  age  at sexual maturity, increased rate of egg  greater viability, higher body weight  and  greater egg  laying and  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 to  so continue  respond to selection at a greater rate than the parents which may  reached  a  selection  Consequently,  the  (Falconer  response  (Roberts,  1967), an  response  phase, and  initial  hybrid fitness caused alleles;  limit  however,  a  curve  King,  is sigmoid  lag(Saadeh  final  and  et  1953;  Roberts,  in shape  with  al., 1968;Falconer,  limit. There  may  be  an  have 1967).  three parts  1971), a rapid  initial  reduction in  by deleterious epistatic interactions between recessive  selection  will  quickly  reduce  the  incidence  of  the  deleterious alleles involved (Barton and Charlesworth, 1984). The linkage  initial lag portion of the response curve may  disequilibrium.  variability  present  impeded from  in the  different  hybrid  Recombination  within the  first  few  cross  generation's  lines are put  is formed. Progress  crossovers becoming  new  will  of  release  then  any  potential  (Lush, 1947). Response selection  in the repulsion will  also be caused  by  genetic will  be  as  favourable alleles  phase of  linkage when the  depend  on  available for selection. As  sufficient  recombination  numbers  of  puts genes  into the coupling phase in increasing numbers, the rapid response  phase of  selection is entered (Thoday et al., 1964; Roberts, 1967). The amount  of  limit  reached  genetic  in any  differentiation  selection between  program the  will lines  depend before  on  the  crossing  8 (Roberts, 1967). Lines are often inbred and genetic variability by recombination may  then crossed to release potential  (Lush, 1947); however, the limit  not be the highest possible due to unfavourable  along  with  selection  the  selected  alleles.  Inbreeding  reached  alleles becoming fixed  degeneration  will  oppose  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 is  constructed  genetic from  will  variance  crosses of  Robertson, 1966;  affect  due  to  the  be  response  linked  loci  seen that how  to  selection  is maximized  of  amount  in populations  Roberts,  1967). Selection within  strains  genetic  effects  construction  of  (Arthur the  or  to epistasis and  et al., 1968) whereas recurrent reciprocal selection may  method  the  and  Beck,  population  may  lines  can  also  and be  linkage (Saadeh  make better use  1974).  of  derived  lines previously selected in the same direction (Hill  ineffective in utilizing genetic variance due  non-additive  as  the population  Furthermore, contribute  to  of the the  selection limit.  2.3 PHYSIOLOGICAL RELATIONSHIPS BETWEEN EGG  PRODUCTION TRAITS  The  account  criteria  of  selection  should  take  into  the  biological  relationships between production traits that are being selected for, particularly with respect to the correlated responses expected As  mentioned  in the previous  section, the  lack of  in unselected traits.  response to  selection  will occur in a multi-trait selection program if selected traits are negatively 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  physiological  by  the  heritabilities  relationships between  the  traits  of may  the  traits  impose  involved. a  limit  on  The the  9 correlations and hence, the indirect response to selection. Egg  production  is often measured and expressed  ways. For example, individual egg records  obtained  in several different  over a set number of  days will not account for differences in age at first egg or winter whereas percent due  production  from  first egg to a fixed  to differences in age at sexual  maturity  factors such  as rate  date will avoid bias  (Goher et al., 1978; Bohren,  1970). On the other hand, hen-housed egg production include  pause,  of egg production  to a fixed date would  , age at first  egg, and  viability (Gowe and Fairfull, 1982b). Morris records a  (1963) postulated  production  in the residual  pullet  having  ovulation  on  part-year  egg  capacity earlier than  period. Physiologically, increased to a fixed date may  to mature earlier or increase  increasing clutch length, decreasing her  based  egg record, and thus actually decrease the  numbers from age at sexual maturity the  selection  caused a pullet to deplete her egg production  hen selected on the whole  pullet's  that  egg  be achieved  by  her rate of production  by  interclutch pauses, and hence, increasing  rate (Lerner, 1950;Liljedahl  et al., 1984). Although  quality traits can be increased concurrently along with  other egg  other traits, there is,  theoretically, a limit to the rate of response to selection because, as the rate of egg production due  increases, egg weight  tends to decrease possibly  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  the  length  mass of  the  of  time that the  yolk  in the  reproductive  ovary  and  the  system  albumen  has  to  in the  isthmus, as  well as the shell in the uterus which would influence its breaking Related  to  this  physical capacity  depletion  of the hen  of  the  egg  production  to ingest feed and  until  they  are  example, if the hen of  her  their  eggs will  low  and  and  by  the  strength. The  she  result  eggs may  internal  in decreased  amount  of  discussion  selection programs may Changes  dam  will draw on body  cease  not  quality  be  and  production. For  of  the  egg  will  that  may  be  why  response  also  eggs, poorer chick  storage  length of the  transmitted  to  to  other nutrients in her  hatchability of the in the  marketable due  therein (Bennett et al., 1981;  slow due  is the  will also influence the viability of  disease  shows  in genetic  machinery  enough calcium, the shell quality  viability, as well as a reduction  the  will  does not get enough protein and  the antibodies contained  1969). This  then  supplied with  eggs (Akbar et al., 1983). The progeny  and  decrease, and  decrease if the hen  quality  is not  breaking  diet which will  depleted  strength.  turn it into eggs. If the  necessary nutrients are not included in the diet, the hen reserves  increase  via the  Nagai and  selection  in  her egg,  Gowe,  multi-trait  to the above physiological considerations.  physiological characters  are known to  with age. Heritabilities decrease as the birds get older possibly due  occur to the  inability of the aging birds to cope with external stresses such exposure to pathogens, and ability the  internal stresses such as  increases  ratio,  of  the  environmental  additive  (Liljedahl et al., 1984;  genetic  variance  variance  to  requirements. This in-  which reduces the the  total  heritability:  phenotypic  variance  Akbar et al., 1983).  In summary, crossing two to plateau  egg-laying  unrelated  in response to selection for egg  strains that showed production  should  a tendency 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 temporarily, the selected egg production unselected  increase,  traits and also the correlated but  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  necessary  metabolites  characters  across  to transcribe DNA  (Liljedahl  differing  and thus to synthesize the  et al., 1984); consequently, comparison of  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  3.1  SELECTION  METHODS  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 'Agassiz' British  to selection  for egg production, were  strain at Agriculture  Columbia  Canada's Agassiz  (A. T. Hill, project  crossed  Research  to form the  Station,  notes). The straincross  Agassiz,  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 tion, body  weight  strains had been previously  at 365 days  and conformation  subjected of birds  to. In addiwithin  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, Leghorns Station  1985) was developed kept  from  at the Department  in Ottawa, Ontario.  This  a flock  of Agriculture's flock  had been  production since the 1940's (Gowe et al., 1954) lier  (Munro,  1936 and  bottleneck as only the  of Single  small  Animal  White  Research  selected  for  egg  and possibly even ear-  1942). In 1948, the flock  a very  Comb  went  through a  number of males was used  to sire  next generation. As a result, the Ottawa flock was considered to  have a relatively narrow genetic  base. The flock has been closed to  introductions  other flocks since  of new birds  from 12  1949 (Gowe and  13  Fairfull, 1980; Gowe et al., 1973; Gowe et al., 1959a). In  1950, a  within-family  population of White flock the  Leghorn  division  of  the  common  females was used to divide the Ottawa  into two strains. One strain became the selected other became  the random-mated  3.1.1.4). For the first  base  Ottawa  control  generation only, the males  strain  strain  were used  3, and  (see  Sec.  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  average  performance  test  (ROP test  stocks  were  had been  chosen  on the Canadian  records  for their Record  made on different  obtained from  private  apparent better than  of Performance (ROP)  farms  breeders). A  were full  compared as 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 descendants  progeny were  of  the  selected  original  without  dial lei  reference  matings to base  and stock  their origin;  therefore, no time was allowed for recombination and crossing-over to occur. Strain 4 was maintained as a closed in  flock from  its beginning  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  Agassiz strain in unpublished records) was  referred  to  as  established in 1957  the  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  the end of the regular pedigree breeding 3.1.1.4 The  strain  (also  established from  3.1.1.1.) in maintained  1950. as  a  sire and  known as the  From  1957  at  season.  Strain  other half 1950  5; Gowe and  of the  until  1959,  Ottawa the  Fairfull,  flock  control  closed, random-breeding, flock-mated  1960, the strain was scheme  of  Ottawa Control Strain  This was  in May  switched  each dam  produced  (see  Sec.  strain  was  population. In  to a random-mated, pedigreed  (using artificial insemination) such a dam  that each  1985)  breeding  sire produced  in order to minimize  a  genetic drift  (Gowe et a I., 1959b).  3.1.2  SELECTION PROCEDURES Prior to 1950, the original Ottawa White Leghorn flock had been  selected held  for egg  for two  parental  production based  years  strains  is not  performance based  on  across 1950  test Canada  more. The  full  laying  selection  known, but  on ROP  Strains 3 and kept  or  on  they  records with birds  history  had  better  of  the  than  seven average  records  4 as well as samples of the control strain were  for performance for varying  at several experimental  lengths  of  time  to 1963) as well as at the main farm  (including  branch  farms  Agassiz  from  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  at Ottawa except for strain 6 which was kept and selected at  Agassiz. Random  samples  of chicks of strains  exclusively  3 and 4 and the  control  strain were shipped to the various farms participating  genetic  and environmental  period.  The Ottawa  strains  3 and 4 to control  studies  control  conducted  strain  was  over  in  the  the 1950 to 1963  maintained  for environmental  only  concurrently  variations  with  (Gowe and  Wakely, 1954; Gowe et al., 1959a,b). Selection at  was based  on part-record  performance  from  housing  147 days to 273 days of age. The primary trait of interest was  hen-housed basis  egg production  of full  (HHEP) to 273 days, selected  and half-sib  family  records  as well  for on the as  individual  performance. Independent culling levels were used to maintain existing levels  of fertility, hatchability  were  evaluated  family  on the basis  of parental  and hatchability  records. Full  and half-sib  records were also used to select for viability in the brooding,  rearing  and laying  periods although viability  also indirectly selected  to 1952. When  of the selection  was  to the selection  females  were  records  and then  selection albumen  was  for egg size in strains 3 and 4 from  egg size dropped  generations added  in the latter period  for in the HHEP trait.  There was no selection 1950  and viability. Fertility  selected  program criteria  substantially  for the two strains, this trait for all strains. Starting  for egg weight  on their  in the first two  individual  on the basis  records  starting  in  1952,  of pedigree in 1960. No  emphasis was placed on egg quality measurements such as 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 addition, body account  weight  for strain  and  conformation  at 365  days  6 within the selected full-sib  were lighter and showed  more refined  were  taken  into  families. Birds that  conformation  were more likely  to be chosen as parents of the next generation. In with  order  to be  the residual  strains stock  were kept was  record  able  period  to compare  (274 to 497  for strain  days) and the full  record, all breeding  of age. In 1957, the first  6, birds were only  days of age because the flock was year. Therefore  performance  on test to 497 days of age, even though  selected at 273 days  keeping  the part-record  kept  year of  on test  until  424  not established until June of that  ,the full record for that year is 73 days short of the  full 497 days used in other years.  3.1.3 REARING AND All  eggs  TEST PROCEDURES  were  hatched  at Ottawa for the first  study, and the chicks were shipped Agassiz ing  by air express  year  after  hatching to  in early June of 1957. From the second generation  in the spring of 1958, individually  Agassiz.  So  individually  as sired  to  avoid  the  need  matings, all matings  sired to were  matings were  subdivide  the  performed  of the  by  on, startmade at pens for 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 eggs  of the control strain  were  sent  from  Ottawa to Agassiz for  hatching with strain 6. Strains were randomly assigned Jamesway  200  to trays in a  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 cm of age when the spacing allowed  4 cm  allotment  was  transferred  occuring  at  that  space  until  six weeks  cm. Weather  records  were  of age when the  permitting, chicks  housed  time.  at 147  From  1957  days to  based  on  five  of age  with  1963, birds five  consecutive  days  space per 100 hens, and 35 trapnests provided mash ration of 15.8% crude protein was was  formulated  specifications at a number mum  photoperiod  fed  ad  assigned  per week but  allotted 0.30 m 2  2  of  of feeding  (Gowe et al.,  libitum  to the Animal  of light  culling  per 100 hens. An all  of local commercial  of thirteen hours  no  were  floor space in the laying houses with a minimum of 14 m  ration  houses  days per week. All  softshelled eggs were not included. Each bird was  1960). The  were  housing.  randomly to deep litter pens and trapnested egg  was  3  of age to range shelters or colony  rotated on pastures until birds were  until four weeks  increased to 450 cm . Each chick  to 8  at six weeks  The  was  of feeding increased  per chick was allowed  3  Research  feed  Centre's  plants. A  per day  was  mini-  provided  during the laying house test. In 1962, strain 6 was absence of the principle held over and bred population.  not reproduced because of the leave of  investigator; the 1961 selected parents  were  in their second year to produce the 1963 Agassiz  19  3.1.4 TRAITS MEASURED A (see  variety  of  egg  production  below) for strain  counted  as day  until end  6 and  zero and  of test at 497  age  365  related  control  was  days of age  traits  were  strain. Day  the following day days. Age  days when the first egg days) and  the  and  as day  of  recorded  hatch  one, and  at sexual maturity was  was  so  on  the age in  detected. Body weights at housing  (147  were recorded for each bird, as an aver-  of a group of birds weighed, to the nearest decagram. Age  death  and  cause of death were also noted, although  of  known accidental  deaths, e. g. predators, drowning, were eliminated from the records to avoid biasing mortality upwards. Individual egg 273,  274  to  385,  production was 386  Number of eggs laid  to  497,  recorded  148  to  497,  in each period by  for five periods, 148 to and  148  to  each hen  was  recorded, and  the percent hen-day rates of production, uncorrected and age  385  days.  corrected for  at first egg, were also calculated. Egg  quality traits were recorded  the test year, 225, 350 were  only  kept  on  and 450  test  weighed  to  gravity was specific room  the  nearest  determined  gravity  from  temperature  of  days, except for 1957  until 424  measurements were actually  1.066  on  floating to  when the birds  days. For this year, the 450  done at 424  gram by  at three different times during  a  day  days. Individual eggs were  shadograph  scale. Egg  specific  eggs in salt solutions ranging in  1.102  70°F. Albumen  by  increments  height  was  of  0.004, at a  measured  with  a  tripod micrometer as the height of the thick albumen midway between the edge of the yolk and point  where the  thick  the outer edge of the thick white at the  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), for  large  analysed  spots  (greater  than  3  mm);  however, this  trait  or '2' is  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 and  22 days, number of pips and  recorded.  not  For  some  years, the  at  18  number of fertile eggs hatched were number  of  crippled chicks  was  noted, although these chicks were not raised for the experiment.  also  21  32 STATISTICAL  ANALYSES  After obtaining the data which was stored on tapes in Ottawa, several variables  were  created  effects  of  selection.  from HHEP  the recorded  data  in order  for three  periods,  148  to calculate the  to  273  (short-term  record), 274 to 497 (residual record), and 148 to 497 days (whole record), was calculated by summing in  a family and then  the number  divided  of eggs laid by each hen housed  by the number  family. Individual egg production records used heritabilities  from  as the HHEP calculate  the sire and dam  records used  these  same  house mortality was  calculated  497 days) and expressed  from  that  to calculate the estimates of  components of variance are the same  by the Animal  estimates  of hens housed  (Fairfull,  Research personal  for the entire  Centre  in Ottawa to  communication). Laying  laying house period (148 to  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 analysis  All the SAS at  in order  to avoid  data manipulations  were transformed  bias due  each  to skewness  and statistical  of the data.  analyses were performed  using  computer programs package (SAS Institue Inc., 1982 a,b) installed  the University of British Columbia's  standard  to arcsin values before  errors, variances, and  analysis  for all traits  strain, using PROC MEANS  number  computing of valid  were generated in the SAS  resources centre. Means, observations  for strain  included in  6 and the control  package (SAS Institute Inc., 1982a,  pp. 527-532). Regression analyses were performed  on the means over  using PROC REG (SAS Institute Inc., 1982b, pp. 39-84).  time  22  Analyses traits  of  of  strain  variance  6  by  and  year  in  covariance order  to  were  performed  determine  the  on  sire  selected and  dam  components of variance, according to the following model where all variables 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  d  is the j  th  dam  nested within the i j= 1  sire; J,  th  e  is the k  th  offspring nested within the j  dam;  <ij)k  k = 1, .... K.  Because the model effects were nested and cept  the  mean), PROC  201-204). Regressions and  dam  NESTED  was  of heritabilities  used  considered to be (SAS  Institute  which were calculated  components of variance were performed  random (ex-  Inc., 1982b, pp. from  the  sire  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  on dam-family means, the model used was  reduced  calculated.  based  in the analysis of variance for HHEP  to sire effects only; therefore, dam  heritabilities could not be  23  Strain means  and  deviations thesis  6 deviations those  on time  were  calculated  of the Agassiz are presented  as the regression  as the difference  hatched  control  their  strain. Regressions  for strain 6 for all traits  coefficients are used  between  studied  of  in this  to estimate the responses to  selection. Mean period  by  heritability introducing  estimates a  again, all effects except  =  Y  year  from  overall  means  strains 3 and 4.  /  calculated  for the  ; 1 = 1,...,6) effect  into  entire  study  the model, and  the mean were considered random:  u  + g  ijkl  These  (g  were  + s  + d  /  were  used  + e (H)j  to make  (Hj)k  comparisons  to published  data  4. RESULTS  HERITABILITY ESTIMATES  4.1.1 EGG  PRODUCTION TRAITS  The  heritability  estimates  based  on  the  sire  component  of  variance (h ) for HHEP for strain 6 are reported in Table 4.1.1.1. The J  g  sire  component  of variance (o-' ) for the short-term s  egg production  period showed a large jump after two generations of selection (1959) then decreased to almost zero in 1963. The h  estimate for the entire  J  s study period from Estimates h  J  1957 to 1963 was 0.45.  of „> , -»  and «•  (progeny  and h ^ (the heritability estimate based 5  s  component of variance),  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 4.1.12. These same estimates and  for strains 3 and 4, taken  Fairfull (1985) can be found  tively,  for comparison.  estimates on time due  None  from  Gowe  in Tables 4.1.1.3 and 4.1.1.4, respecof  the  linear  regressions  for strain 6 were significantly different  to large standard  in Table  errors. With  the exception  of  of  these  from  zero  1963, the h  J g  estimates were consistently higher than those of the parental strains . The  h ^ estimates, however, fluctuated from  h^  estimates  5  2  for short-term  strain 6 are shown  and residual  year to year. The h  J g  and  record egg production for  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 24  slight  though  non-significant  Table 4.1.1.1. H e r l t a b l l l t y estimates based on the s i r e component of variance f o r HHEP from 148 to 273 days f o r strain 8. Year  Strain  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 s i r e (<J ). dam (o'g.) and Individual (<J ) components of variance, and of the h e r i t a b i l i t i e s based on the s i r e ( h ) and dam (b'^) components of variance for strain 8 for egg production from 148 to 273 days. !  !  s  E  !  s  Year  28  47  734  0.14  ± 0.04  0.23 + 0.06  1958  1957  21  90  600  0.12  + 0.06  0.51  1959  137  66  791  0.55 + 0.24  0.27  + 0.10  1960  78  40  1068  0.26 ± 0.14  0.13  + 0.10  1961  17  22  564  0.11  ± 0.11  0.14  ± 0.13  119  595  0.00 ± 0.10  0.67  + 0.25  + 0.10  1962 1963  ± S.e.  -6.47  +5.14  ± 7.82  ( p < 0.547)  56  57  mean  Linear  ± 11.43  (p < 0.602)  regression  coefficient  -16.86 ± 43. 17 (p  < 0.7 16)  745  -0.029 + 0.042  +0.035  ( p < 0.522)  (p  0.25 + 0.04  0.37  ± 0.047  < 0.496)  + 0.05  Table 4.1.1.3. Estimates of the s i r e ( o ' ) , dam ( o ) and Individual (<j' ) components of variance, and of the h e r i t a b i l i t i e s based on the s i r e (h' ) and dam (h ^) components of variance for strain 3 for egg production from 148 to !  s  d  e  1  s  273 days (Gowe and F a i r f u l l , 1985). Year  d  s  " d  1957  7  76  627  0.04  0.43  1958  2  42  521  0.01  0.30  1959  14  75  588  0.08  0. 45  19G0  13  72  654  0.07  0. 39  1961  25  1 16  765  0. 1 1  0.41  1962  2  94  812  0.01  0.4 1  1963  9  87  642  0.05  0.47  ±  s.e.  +0.61  +  1.64  ( p < 0.727)  10  1  Linear  regression  +6.36 ± 3.74 (p < 0.150)  80  e  +28.71  ± 16.25  ( p < 0.138)  658  s  +0.002 + 0.008 (p  < 0.788)  0.05  +0.011 (p  + 0.010  < 0.346)  0.41  coefficient  M  ), dam ( < J ) and individual («' ) components of variance, and of the Table 4.1.1.4. Estimates of the s i r e h e r i t a b i l i t i e s based on the s i r e ( h ) and dam (h' ) components of variance for strain 4 for egg production from 148 to 273 days (Gowe and F a i r f u l l , 1985). !  d  e  !  g  Year  b'  d  '  s  d  s  e  d  0. 25  1957  27  41  581  0.17  1958  22  39  521  0. 15  0. 27 0. 29  1959  7  45  567  0.05  1960  14  34  544  0. 10  0. 23  1961  18  50  592  0. 1 1  0. 30  1962  8  39  596  0.05  0. 24  1963  15  26  456  0.12  0.21  -0.010 ± 0.008  -0.006 ± 0.006  + s.e.  -1.89 (p  ±  1.23  < 0.183)  16  1  Linear  regression  coefficient  -1 .43 ±  1 .46  -7.14  ± 9.79  (p < 0.372)  ( p < 0.498)  39  551  (p  < 0.265)  0.11  (p < 0.371)  0. 26  Table 4.1.1.5. H e r l t a b l l l t y estimates based on the s i r e (h' ) and dam ( b ) components of variance for egg production from 148 to 497 and from 274 to 497 days f o r strain 6. !  s  148  d  t o 497 Days  274 t o 497 D a y s  Year  h'  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  1961  0. 13 + 0.. 12  0. 23 + 0. 13  0. 16 + 0 . 13  1962  -  -  1963  0. 12 + 0. 13  0. 74 + 0. 24  + S.e.  -0.009 (P  mean  1  Linear  s  + 0. 028  < 0..842)  0. 23 + 0 .04  regression  h*  d  +0.064 + 0. 047 (P  i  <  h*  0 .246)  0. 26 + 0 .05  h  s  !  -0 .01  . d  ± 0.09  0 .19 ± 0.13  -  + 0 . 19  0 .67 + 0.24  +0.025 + 0..013  +0.066 + 0.044  0. 33  (P i  <  0 . 136)  0. 20 + 0. 04  (P  < 0.212)  0. 15 ± 0.04  coefficient  CO  30 upward trends.  4.1.2 EGG QUALITY TRAITS The  h  and  2  h  in Tables  4.1.2.1 to 4.1.2.3 for strain  estimated for egg weights and  for the egg  quality  traits are  0  S  presented  estimates  2  at 225, 350 and 450 days of age. Both h  h ^ estimates for all three periods tended 2  ward trends with time  6. Heritabilities were  especially the h  350  days (p <  225  days was 0.60 and the mean h  d  g  to show slight down-  estimates for egg weight at  2 g  0.01; Table 4.1.2.1). The mean h 2  2  2 g  for egg weight at  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  specific  gravity  4.1.2.2). While  are reported  g  and h  2 d  estimates  for 225 and 450 days  for egg  of age (Table  the heritability estimates for egg secific gravity at 225  days slightly increased with time egg The  2  (but were non-significant), those for  specific gravity at 450 days did not show any consistent trends. mean h and h estimates at 225 days were 0.64 and 0.33, and s d ' 2  2  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 mean h  2  s  h  2  was  d  2 g  for Haugh units at 225 days was 0.57, and the  was 0.68. For Haugh unit measured at 450 days, the mean 0.54, and the mean '  h  2  d  was  0.55. These  consistent with values reported in the literature  estimates are  (Kinney,1969).  Table 4.1.2.1. H e r i t a b i l i t y estimates based on the s i r e (h* ) and dam (h* ) components of variance f o r egg weight at 225, 350 and 450 days of age f o r strain 6. s  d  225 D a y s Year  I  350 D a y s I  5  450 D a y s I  I  i  I  i  5  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  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  ± s.e.  mean  1  Linear  -0.032 + 0. 199  -0.040 + 0..020  -0.075 + 0. 018  -0.045 + 0..030 0 .204)  (P < 0 . 181 )  (F I  0 .117)  (P < 0 .014)  (P i  0. 53 + 0. 03  0. 44 + 0. 01  0. 63 + 0. 03  0. 55 + 0. 01  regression  <  <  -0.060 + 0. 024  ,  + 0. 14  -  0. 53 + 0. 22 -0.018 + 0.02C  (P < 0 .069)  (P < 0 .415)  + 0. 05  0. 60 + 0.02  0. 64  coefficient  OJ  Table 4.1.2.2. H e r i t a b i l l t y estimates based on the s i r e (h' ) and dam (h' ) components of variance for egg specific gravity at 225 and 450 days of age for s t r a i n 6. s  225  d  450  Days  Year  Days  h«. 0.55 ± 0.17  0. 14 + 0. 20  0. 37 + 0. 14  0.27 ± 0.22  1958  0.57 ± 0.21  0. 33  + 0. 12  0. 34 + 0. 15  0.35 ± 0.13  1959  0.70 + 0.24  0. 43  + 0. 1 1  0. 66  + 0. 24  0.23 ± 0.10  1960  0.65 ± 0.24  o. 57 + 0. 14  0. 54 + 0. 21  0.41  +0.17  0.49 ± 0.18  0. 30 + 0. 13  0. 36  + 0. 14  0.31  ± 0.09  0.87 + 0.31  0.50 + 0.19  0.46  + 0.18  -0.06  + 0.17  1957  19G1 1962 1963  b  1  ± s.e  +0.039 + 0.025 (p  mean  1  Linear  < 0.192)  0.60 ± 0.05  regression  coefficient  +0.045 + 0.028  +0.008 ± 0.029  -0.038 ± 0.027  < 0.182)  (p < 0.791)  (p  0.38 ± 0.02  0.42 + 0.04  0.20 ± 0.03  (p  < 0.226)  Table 4.1.2.3. H e r i t a b i l l t y estimates based on the s i r e (h' ) and dam ( h ) components of variance f o r haugh units at 225 and 450 days of age for strain 6. J  s  225 Year 0. 75  0,,53  s  'd ± 0. 19 ± 0. 16  h  'd  0..54 ± 0. 18  0..46  + 0. 21  0..71  0..43  ± 0. 13  ± 0. 26  0. 44 ± 0. 19  0. 86  1959  0. 58 + 0. 21  0..56 ± 0. 12  0, 48 + 0. 18  0..40 ± 0. 1 1  1960  0. 37 + 0. 17  0..87 + 0. 17  0. 44 + 0. 19  0. 82 ± 0. 20  1961  0. 53  + 0. 19  0. 48 ± 0. 14  0. 54 ± 0. 20  0. 46  ± 0. 13  0. 73  + 0. 28  0. 75  ± 0. 23  -  1963  1  + 0. 21  h  Days_  1958  1962  b  _450  Days  s  1957  d  +  +0.007 + 0.035  S . G .  regression  0. 52 ± 0. 23  +0.009 + 0.040  -0.014 + 0.020  < 0.852)  (p < 0.829)  (p  0.49 + 0.06  0.62 ± 0.03  0.48  (p  Linear  0. 75 ± 0. 22  < 0.521)  + 0.10  +0.050 ± 0.034 (p  < 0.211)  0.47  + 0.06  coefficient  to CO  34  4.1.3 OTHER TRAITS The weight h^  h  and h ^ estimates for age at sexual maturity and body  3  2  s  at 365 days are reported in Table 4.1.3.1. The mean h  3 g  and  estimates for age at sexual maturity were 0.22 and 0.33 both of  2  which were lower  than other estimates found  in the literature (Kinney,  1969). For body weight at 365 days, the mean h  2  and h ^ were 0.53 2  g  and  0.62, respectively, both of which were consistent with the average  h  estimate  2 s  of 0.52 and h  estimate  2 d  of 0.59 reported  by  Kinney  (1969).  4.1.4 CONTROL POPULATION The the  h  entire  J  s  and h  period  2  d  estimates for the control strain were based on  they  were  housed  at the Animal  Research  Ottawa, (Gowe and Fairfull, 1985), and these were used of the control populations kept  Centre,  as estimates  in Agassiz. The mean h  2  and h ^ for 2  g  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 h ^ estimate was 0.56.  The  h  2  2 s  estimate  for egg weight  at 225 days was 0.54, and the h ^ 2  estimate was 0.78.  4.2 GENETIC CORRELATIONS The  mean genetic correlations (r ) among traits measured for strain 6 are  presented Kinney age  in Table  (1969). The genetic correlation of HHEP from  at sexual  reported  4.2.1, and are compared to those  maturity  was  estimates  148 to 273 days with  -0.40, and was higher than  in the literature (-0.62). The r  found in  other  estimates  for HHEP and egg specific gravity  Table 4.1.3.1. H e r i t a b i l i t y estimates based on the s i r e ( h ) and dam (h'^) components of variance for age at sexual maturity and body weight at 365 days of age f o r strain 6. !  g  Age Year  1  maturity  Body  d  h  weight  a t 365  's  days h  'd  1957  s 0 . 18 ± 0.. 10  0. 58 + 0.. 23  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. 66  + 0. 14  0..52 + 0. 17  1961  b  at sexual  h>  0. 20 + 0. 10  1962  -  1963  -0. 04 ± 0. 06  + s.e.  -0.042 + 0.041 (p  mean  Linear  0.,37 ± 0. 14  0..48 + 0. 21  0. 60 ± 0. 15  0. 30 +  o. 22  -0.013 + 0.055  0. 37 ± O. 19  -0.028 + 0.035  ± 0. 19  0. 81  +0.033  ± 0. 24  + 0.026  < 0.358)  ( p < 0.823)  (p < 0.471)  (p < 0.266)  0.26 + 0.05  0.25 ± 0.05  0.54  0.59 ± 0.06  regression  coefficient  + 0.08  Table  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 9  measured  with  forstrain  6.  Tra i ts  Correlated  HHEP from 148 to 273 days  HHEP from 148 to 497 days  +0.97  HHEP from 274 to 497 days  +0.82  age at sexual  maturity  -0.40  egg weight at 225 days  -0.07  egg s p e c i f i c g r a v i t y at 225  -0.07  g  days  body weight at 365 days  Haugh u n i t s a t 225 days  +0.09  body weight at 365 days  -0. 17  egg weight at 225 days  +0. 38  egg s p e c i f i c g r a v i t y at 225  -0.03  days  age at sexual  maturity  egg s p e c i f i c g r a v i t y at 225  Haugh u n i t s at 225 days  +0.06  age at sexual  maturity  +0. 22  egg weight at 225 days  +0.06  egg spec 1 f i c ' g r a v i t y  -0.01  Haugh u n i t s at 225 days  +0. 23  egg weight at 225 days  +0.11  Haugh u n i t s at 225 days  -0.08  egg weight at 450 days  +0.95  days  egg weight at 225 days  37 was  -0.07, which  literature. On compared  was  in contrast  the other  hand, r  to negative estimates  g  to positive for HHEP  estimates  and Haugh  found units  in the  was 0.10  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 than and r  9  egg specific most  gravity  at 225 days was -0.01 which  reported estimates  was  (0.29). The r^ for egg weight  much  at 225 days  450 days was 0.95 which was slightly higher than expected for short-term  HHEP with  the residual  HHEP was  lower  (0.83). The  0.82, and with the  whole record HHEP, 0.97.  4.3 THE PERFORMANCE  4.3.1  OF TRAITS MEASURED IN STRAIN 6  EGG PRODUCTION TRAITS In order to make comparisons of egg production between strain  6 and the control strain possible, deviations of the phenotypic for strain 6 from  that of the control were used  basis. The individual HHEP from control  strain,  as  well  as  on a year to year  1957 to 1963 for strain  the deviations  mean  from  6 and the  the control are  presented in Tables 4.3.1.1 to 4.3.1.3. The linear regression coefficients of  these  selection not  deviations are also as estimated  significantly  for  egg production  in the tables. Response to  by the coefficients  different  production periods from  included  from  zero  of linear  for strain  regression were 6  for the egg  1957 to 1963. The regressions of the means  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 from the control f o r s t r a i n 6 for egg production from 148 to 273 days. Strain  Year  6  Control  Strain  Deviations  from  1.02  6 7 . 1 0 ± 1.96  +14.20  ± 0.89  70.60 ± 1.71  +20.84  85.85 ± 0.90  71.97  + 1.64  +13.84  1960  82.11  ±  1.10  66.34  ± 2.05  +15.77  1961  95.83  + 0.81  73.58  + 1.73  +22.25  77.44  ±  +18.68  1957  81.30 ±  1958  91.44  1959  Control  1962 1963  96 . 12 ±  b'  1.14  1.82  + 1 .45 + 0.63 ( p < 0.08)  Linear  regression  +0.66 + 0.75 ( p < 0.43)  coefficient  CO  oo  Table 4.3.1.2. Means and standard errors for strain 8 and the control strain, and deviations from the control f o r strain 6 for egg production from 148 to 497 days. Year  Strain  6  Control  Strain  Deviations  from  1957  180.06 ± 2.43  154.80  ±4.98  +25.26  1958  232. 13 ± 2.67  194.15 + 5.28  +37.98  1959  218.98 ± 2.63  200.94  +5.23  +18.04  1960  212.71  194.01  ± 6.37  +18.70  1961  240.56 + 2.41  205.54 ± 5.31  +35.02  241.20 ± 3.02  207.50  +33.70  ± 3.09  Control  1962 1963  b'  +6.86 ± 2.92  + s.e.  Linear  regression  ±5.39  ( p < 0.08)  +0.97 ± 1.94  ( p < 0.65)  coefficient  CO to  Table 4.3.1.3. Means and standard errors for strain 6 and the control strain, and deviations from the control f o r strain 6 for egg production from 274 to 497 days. Year  Strain  6  Control  Strain  Deviations  from  1957  98.76 ± 1.67  87.68 ± 3.41  +11.08  1958  140.70 ± 2.11  123.52 + 3.97  +17.18  1959  133.16 + 2.00  128.98 ± 4.01  1960  130.58 + 2.31  127.67 ± 4.77  + 2.91  144.69 + 1.93  131.99 + 4.20  +12.70  145. 12 + 2.41  130.08 + 4.05  +15.04  1961  Control  + 4 . 18  1962 1963  +5.43 ± 2.82 ( p < 0.13)  1  Linear  regression  +0.30 + 1.33 ( p < 0.83)  coefficient  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  different  from  egg  quality  trait  regressions  were  not  significantly  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 a l 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 different deviations  fertility  locations from  and  hatchability  (Agassiz  and  the control would  traits  were  Ottawa) based not be  on  measured parental  in  two  records,  useful for comparison  and  so are not presented here. Only the means for strain 6 and the control strain are shown in Tables 4.3.3.3 and 4.3.3.4.  Table 4.3.2.1. Means and standard errors f o r strain 6 and the control strain, and deviations from the control f o r strain 8 for egg weight at 225 days In grams. Year  Strain  Control  6  Strain  Deviations  from  1957  51.0 ±  0.1  51.7  ±  0.3  -0.7  1958  54.7  +  0.1  55.5  ±  0.2  -0.8  1959  53.9 ±  0.1  54.6  ±  0.2  -0.7  1960  52.3  +  0.1  52.5  +  0.3  -0.2  1961  51.7  ±  0.1  53.5  +  0.3  -1.8  51.8  + 0.1  52.4  ±  0.3  -0.6  Control  1962 1963  -0.14  ± s.e.  1  Linear  regression  coefficient  + 0.33  (p <  0.69)  -0.03  ± 0.12  (p <  0.79)  Table 4.3.2.2. Means and standard errors for strain 8 and the control strain, and deviations from the control for s t r a i n 8 for egg weight at 350 days In grams. Strain  Year  Control  6  Strain  Deviations  from  1957  56.8  ± 0.1  58.0  ± 0.3  -1.2  1958  59.2 ± 0.1  59.8  + 0.3  -0.6  1959  59.5  ± 0.1  60.0  ± 0.3  -0.5  1960  58.7  + 0.1  59.4 ± 0.4  -0.7  1961  57.9  + 0.1  59.4 + 0.3  -1.5  58.5  ± 0.2  59.3  -1.3  Control  1962 19<53  +0.16  ± s.e.  1  Linear  regression  ± 0.15  ± 0.4  ( p < 0.34)  -0.08  ± 0.09  (p < 0.37)  coefficient  to  Table 4.3.2.3. Means and standard errors f o r strain 8 and the control strain, and deviations from the control f o r strain 8 for egg weight at 450 days In grams. Year  Strain  Control  6  Strain  Deviations  from  1957  59.0 ±  0.2  60.1  ±  0.4  -1.2  1958  60.6  ±  0.2  61.4  ±  0.3  -0.8  1959  60.6  +  0.1  60.9  ±  0.3  -0.3  1960  59.9 +  0.2  60.3  +  0.6  -0.3  1961  59.7  +  0.2  60.9  +  0.3  -1.2  59.2  ±  0.2  60.4  ±  0.4  -1.2  Control  1962 1963  -0.02  • s.e.  1  Linear  regression  coefficient  + 0.11  (p <  0.84)  -0.04  ± 0.10  (p <  0.70)  Table 4.3.2.4. Means and standard errors for strain 8 and the control strain, and deviations from the control f o r strain 8 for egg specific gravity at 225 days. Year  Strain  6  Control  Strain  Deviations  from + 1.7  1957  91.1  ±0.2  89.4 + 0.4  1958  88.5  + 0.2  87.1  ±  0.4  + 1.4  1959  88.1  ±0.2  87.0 ±  0.4  + 1.1  1960  88.2 ±  88.3  0.4  -0. 1  1961  87.5  ± 0.2  88.2 + 0.4  -0.7  87.4 ± 0.2  87.8 ± 0.3  -0.4  0.2  ±  Control  1962 1963  ± s.e.  Linear  -0.08 ± 0.20  regression  coefficient  ( p < 0.71)  -0.42 ± 0.10  (p <  0.02)  Table 4.3.2.5. Means and standard errors f o r strain 8 and the control strain, and deviations from the control for strain 8 for egg specific gravity at 450 days. Strain  Year  Control  6  Strain  Deviations  from  1957  82 . 1 ± 0 . 2  80.6  + 0.4  + 1.5  1958  81.4  + 0.2  80.4  ± 0.4  + 1.0  1959  80.2  + 0.2  79.9  ± 0.4  +0.3  1960  77.1  + 0 . 2  76.4  + 0.4  +0.7  1961  78.4  + 0.2  78.2  + 0.3  +0.2  77.4  ± 0.3  78.6  ± 0.5  -1.2  Control  1962 1963  + s . e .  Linear  -0.45  regression  ± 0 . 3 0 (p < 0 . 2 0 )  -0.42  ± 0.06 (p <  0.003)  coefficient  CD  Table 4.3.2.6. Means and standard errors for strain 6 and the control strain, and deviations from the control f o r strain 8 for haugh units at 225 days. Year  Strain  6  Control  Strain  Deviations  from  0.4  -2.8 -2.9  1957  86.2 + 0.2  89.0 +  1958  83.0 ±  0.2  85.9 ±  0.4  1959  85.2 ±  0.2  88. 1 ±  0.4  -2.9  1960  85.7 ±  0.2  89.4  0.4  -3 . 7  1961  82.5 * 0.2  8 5 . 9 + 0.4  -3.4  81.7 ±  85.0 ±  -3.3  ±  Control  1962 1963  0.2  ± s.e.  Linear  -0.50 ± 0.35  regression  coefficient  0.4  (p <  0.23)  -0.11 ± 0.06  (p <  0.16)  Table 4.3.2.7. Means and standard errors f o r strain 8 and the control strain, and deviations from the control f o r s t r a i n 8 for haugh units at 450 days. Year  Strain  6  Control  Strain  Deviations  from  1957  77.3 ±  0.3  80.1  +  0.5  -2.8  1958  75.9 ±  0.3  79.0 ±  0.6  -3 . 1  1959  76.5 ±  0.3  80.0 ±  0.6  -3.5  1960  73.0 +  0.4  74.8  +  1.0  -1.8  1961  72.7  +  0.3  75.4  +  0.7  -2.7  80.4  +  0.3  82.3  ±  0.6  -1.9  Control  1962 1963  ±  s.e  1  Linear  +0.05 + 0.68  regression  (p <  0.94)  +0.19  + 0.12  (p <  0.20)  coefficient  oo  Table 4.3.3.1. Means and standard errors for strain 8 and the control strain, and deviations from the control for s t r a i n 8 for age at sexual maturity. Year  Strain  6  Control  Strain  1957  163.79 ±  0.57  174.53 +  1958  157.59 ±  0.48  17 1 .27 ±  Deviations  from  -10.74  1.53 1.08  -13.68  1959  159.65 ±  0.57  174.64 ±  1.23  -14.99  1960  154.69 +  0.56  172.80 ±  1.79  -18. 11  1961  154 . 13 ±  171.30 ±  1.16  -17.17  169.32 ±  1.42  12.78  0.38  Control  1962 1963  156.55 ±  1.09  -0.72 ± 0.32  • s.e.  ' Linear  regression  (p <  0.09)  -0.43 ± 0.60  (p <  0.51)  coefficient  CD  Table 4.3.3.2. Means and standard errors for strain 8 and the control strain, and deviations from the control f o r strain 8 for body weight at 365 days in decagrams. Strain  Year  6  Control  Strain  1957  210.43 ±  0.88  208.05 ±  1.80  1958  215.53 ±  1.00  218.43 ±  1.91  1959  209.98  1960  206.91  1961  206.76  ±0.82 ±  0.91  ±0.92  221 . 1 1 ±  Deviations  from + 2 . 38 -2 .90  2.08  -11.13  ±  2.09  -10.86  225.24' ±  2.38  -18.48  224.22  2.03  -23.58  217.77  Control  1962 1963  200.64  +  1 .04  +2.32 + 0.85  + S.e.  1  Linear  regression  ±  (p <  0.05)  -4.33 + 0.48  (p < 0.0009)  coefficient  o  +  IP  • 0)  PJ  Table 4.3.3.3. Means f o r s t r a i n 6 and the control strain for fertllIty. Year  Strain  6  Control  Strain  1957  85 . 25  90.97  1958  94.43  90.56  1959  88.74  90.56  1960  96. 15  97 .64  1961  85.48  95.07  1962 1963  (  rO  Table 4.3.3.4. Means for strain 8 and the control s t r a i n for hatchability. Year  Strain  1957  78.28  6  Control  87 . 33  Strain  1958  89.81  83.90  1959  61 .02  83 .90  1960  86.40  92.31  1961  68 . 38  73.78  1962 1963  CO  Table 4.3.3.5. Means f o r s t r a i n 8 and the control strain, and deviations from the control f o r strain 8 for percent laying house mortality from 148 to 497 days. Strain  Year  Control  6  Strain  Deviations  from  1957  13.6  22 . 0  -8.4  1958  12.3  21.9  -9.6  1959  16. 1  18.0  -1.9  1960  16. 1  22.3  -6.2  1961  9.3  16.7  -7.4  7.5  11.8  -4.3  Control  1962 1963  1.63  1  Linear  regression  ± 0.51  (p < 0 . 0 3 )  +0.58  + 0.5B (p < 0 . 3 8 )  coefficient  cn  55 Percent laying 6 and the control  house mortality from strain, as well  148 to 497 days for strain  as deviations from  the control for  strain 6 are reported in Table 4.3.3.5. The means showed trend, and this trend is also response to selection  reflected  a downward  by the linear regression of the  on time. This trend was similar  for the control  strain.  4.4 ACTUAL  SELECTION DIFFERENTIALS  The  actual  selection  for  egg production  differentials (SD's) for the sires and dams of strain 6 from  148 to 273 days, egg weight  body weight at 365 days in decagrams from Table  4.4.1. The SD's for the sires  sisters'  records  individual  while  those  were  at 225 days, and  1957 to 1963 are presented in based  for the dams  records. The SD's were calculated  on their  were  based  full on  and half their  own  as the mean of the selected  parents minus the mean of the population. The  SD's for egg production  sires and the dams were positive selection  from  148 to 273 days  for both the  which is in accordance with the positive  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  selection of sires but not dams.  pressure  placed  on this  trait  in the  Table 4.4.1. Actual selection d i f f e r e n t i a l s for the sires and dams of strain 6 f o r 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  t o 273  Ecra w e i q h t a t 225  days  Body w e l q h t a t 365  days  days Year  Sires  Dams  Sires  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  1961  + 14.6  1962 1963  + 4.7  -0.3  +0. 1  -1 .03  -0.69  + 1 .9  +0.7  -8.18  +0.33  5. DISCUSSION When this study  was  thought to have plateaued selection continued  first  initiated  the  parental  in response to selection for HHEP; However, as  in strains 3 and  4 at Ottawa, it became apparent that  they had  not reached a selection limit (Gowe and  personal  communication).  genetic  component  strains used were  Therefore,  no  great  (o* ) were expected  Fairfull, 1985;  increases  in  as the cross was  A. T. Hill,  the  not  additive  expected to  behave as it might have had the parental strains been at a plateau. The  crossing of two  with regards particularly  to genetic origin may in  (<j* ) which  selection (Falconer, 1981; trait  under  previously selected strains that were not related  is  yield new  the  sources  component  of genetic variation,  that  shows  Dickerson, 1969). In this study, h  selection, HHEP  from  148  to  273  response  to  for the main  J g  days, for  strain  6  was  consistently higher than either parental strain. High difference same  h  in the  J g  between  direction  the  may  affecting  the  plateaued  in response  highly  straincrosses will  reflect  parental  unrelated  not  selected  be  fixed  traits to  lines  as  for the  (Roberts,  1967).  in «'  other related traits in strain 6. Falconer and unrelated  Roberts  to  at  Although  were  and  found  greater  (1967) in his crosses  by crossing two  of  in the loci  necessarily 4  were  still  in HHEP  and  King (1953) found that a cross  rate. Similar results  previously  in response to and a renewed were  found  by  lines  of  selected, unrelated  able to obtain further progress  in body size in  lines that had stabilized for body size.  57  genetic  various  not  body weight showed increased *'  selection, at a  mice. Robertson (1955) was Drosophila  alleles  3  of  selected  mouse strains that were plateaued  selection for high 60 day response  same  amount  lines  selection for HHEP, strains  selected. Consequently, increases  between two  the  58 After  two  generations  of  selection  in strain  6, h  for short-term  } g  HHEP increased drastically and  remained high for the next two  This  by  increase may  be  caused  linkage groups that had Thoday et al., 1964; the  ble  over  occured on  fixed  and  next  and new  in the parental strains (Roberts,  then, as recombination  few  generations. As  occured  genetic combinations  sufficient  of  1967;  put genes into  to put  genes into  in an  increasing proportion of  selection  would  increase (Roberts, 1967). The  has  often  been  to  differentiation of lines through seen  in the  h  the  generate  total  such  purpose  of  crossovers  that response  of  segregation  recombination  estimates  :  numbers  became available, selection would act  them  increase  break up  phase, increasing numbers of crossovers would become availa-  the  selection  and  Falconer, 1981). Initial crossing would  repulsion phase  the coupling  been  crossing-over between  generations.  to  crossing before  and  allow  genetic  (Falconer, 1981). This dramatic  for strain  6  for short-term  HHEP is  s likely  to  be  because would  due  it was be  to  not  reshuffling  seen  sufficient  time  until to  of  two  1959  may  interactions and  still  be  allow  the low  biased  genome  generations heterotic  However, the large increase in the h in  the  2 g  through  after  the  recombination cross and  effects, if any, to  dissipate.  estimate to a value greater than  upward  due  to  this  one  genotype-environment  number of sires (approximately  20) used per gen-  eration (Dickerson, 1969). Since  HHEP  is a composite  of the  rate of  egg  production, age  sexual maturity, and viability (Liljedahl et al., 1984), the combination sources  of  of additive genetic variance for these three characteristics, due  new to  recombination, could have inflated  the  1959  at sexual  egg  production are known to be highly  heritable  maturity (0.39  and  and 0.33,  short-term  heritability estimate. Both  at  respectively; Liljedahl  et al., 1984;  age  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 importance 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 Given such a pattern of h have shown response  study  over time, one would expect strain 6 to  J g  to selection for higher HHEP. However, this was not  the case. The lack of response this  hypotheses.  for strain  6 was  to selection  probably  over  the six generations of  due to selection  for other  traits  besides HHEP and the negative genetic correlations between these traits and HHEP.  HHEP  combination  generally  has  a  of characteristics  low  that  heritability  constitute this  estimate  due  trait, such  to the  as age at  sexual maturity, rate of egg production and viability. Estimates, from various sources trait  (Kinney, 1969) show that egg weight  is known to be negatively correlated with HHEP (Lerner, 1948). As a  consequence, the selection the  response  response trait  with  weight  of HHEP  emphasis on maintaining egg weight will affect  to selection. Since  to selection will  antagonistic  was  has a high heritability. This  a higher traits  has a low heritability,  not be as great per generation  heritability  are included  has a negative  HHEP  estimate, and will in the selection  genetic correlation with  as that for  be further reduced if scheme. Although  body  HHEP and some emphasis  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  a  60 to  maintain acceptable levels of fertility, hatchability and viability may  have contributed to the lack of response Furthermore, the enough  to  show  straincrosses phenotypic  of  any  of  were  to selection for HHEP.  this  responses  Drosophila  behaviour  lected, Roberts  duration  study  to  may  not  selection.  found  to  be  have  Early a  sufficient breeders  (1967) found  poor  guide  the second and  not  for  that  selection  select  eight  generations  were  required  to selection, and  effects  to  act  on  or to  later  in order  dissipate  to  have had the potential for response  which  later se-  for a  Robertson This  Drosophila.  1959, the tendency  indicates that  there  is  (Roberts,  on  for h still  J g  1967). Plant  their performance until  allow  recombination  (Falconer, 1981). In the  strain 6 showed a large increase in the «'  After  them  superior crosses based  generation  heterotic  may  to  in  due to the need to allow recombinational events to occur in  numbers do  long  performance  (1955,1956) found that 6 to 7 generations were required for is mainly  been  (Bell et al., 1955). Even when a single trait was  mouse straincross to show significant responses  lag  also  to  occur  present  study,  for HHEP and related traits, and  to selection in tater years. estimates  «'  to  existing  stabilize  (Yamada  at  et  a  level  al., 1958;  Dempster et al., 1952) also implies that natural selection is working against artificial  selection  (Roberts, 1967;  through  such  Falconer, 1981;  mechanisms  Rose, 1982)  as  antagonistic pleiotropy  in order to return, or keep, the  organism at an optimum fitness level (Lerner, 1948). Birds from strain 6 were not reproduced and 1963  reproduced was  phenotypic  in 1962  caused  by  to provide the a  decrease  in the  variance (Falconer, 1981). Any  1963  in 1961  but were held over  generation. The  ration number  of  the  low  h  <?» to the a  of environmental  J  for total  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 «' and h d  for HHEP and individual egg production  2 d  remain relatively stable except for 1963. The increase in the relative importance of the «' for that year is related to the decrease d  proportion  of the c'  An  increase  in «'  d  also  reflects  in the relative the increase in  maternal effects due to the older age of the dams of that generation, such as greater congenital transmission was  present  production  in the Agassiz  (pathology  of disease, e. g. lymphoid leucosis which  flocks and which  is known  to decrease egg  reports, project 51.11.11 notes; Liljedahl et al., 1984;  Bennett et al., 1981; Akbar et al., 1983). The h  estimates  2 d  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 1963  as explained) as the h generations  2 d  traits to any large degree (other than  estimates  the  initial  of the h  are  not expected to be significant  2 g  remain at a level consistent with  estimates. Consequently, heterotic effects 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  strain 6 has a higher proportion of »' to strains, especially for HHEP genetic sizable  genetic  differences  phenotypic differences may degree. The  deviation  do  the data  presented  here,  as compared to the parental  parameters. It is therefore likely that  exist  between  these  strains,  although  not reflect the genetic differences to the same  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 was the may and may  slightly different control  strain  making phenotypic  was  reproduced  have been inadequate Agassiz) and  the selection program  different  environment, this  strain  in reflecting changes between locations (Ottawa  within the Agassiz  strain 6. An  in removing the effect  and  comparisons difficult. Also, since  in a  environment  have been differential responses  the control and  selected  itself  to environmental  (Hill, 1972). There influences between  unselected control strain may  of year  to year  environmental  be unsuccessful  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 pected for  to arise between the selected  and  the control  HHEP also indirectly selects for better viability  strain  as  were exselection  during the laying-house  period (Gowe and Fairfull, 1980,1985). Egg  weight  at 225  days was  another  trait under selection. The  weight rather than attempt  aim  was  to maintain egg  was  realized in strain 6 as egg weight remained phenotypically stable over  time. The  selection pressure, however, was  decrease  in h  and  J  S  h.  estimates  s  to increase it. This goal  strong enough to effect a slight  for egg  weight  at 225, 350  and  450  Q  days. Since the mean h  for egg  1  weight for strain 6 is consistent with  s those for strains 3 and 4 (all of which are high; Gowe and there is still a significant proportion of »*  Fairfull,  present for this trait. The  1985) h  2 d  estimate for strain 6 is lower than either strain 3 or 4 but it is consistent with the h  J  . 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  heritability estimates for egg specific gravity, however, remained  dates. The 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 a  caused  the increase  in the h  of these J g  traits  estimate  in combination  for HHEP  could have  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 weight  there was no systematic selection  at 365 days  of the hens  was  the only  on body trait  weight, body  that  showed  a  64 significant phenotypic  change over time (probably because of the manner in  which the parents were chosen). The the  h  estimates,  2  s  (Roberts,  indicate  the  higher h'  presence  1967). However, heritability  estimates, as compared to  d  of  «' na  estimates  and  maternal  for body  weight  effects are  not  available for the parental strains for comparison. No can  be  of  the  conclusions concerning  fertility and  drawn as there was  no  control  measured  strain  were  hatchability of the straincross  adequate control. Fertility based  on  and  parental  hatchability  performance in  Ottawa. Therfore they cannot be compared with the performance of strain 6 which  was  measured  at Agassiz. The  strain 6 which were not bred  fertility  of  the  1961  until their second year was  generation reduced  due  of to  the older age of these birds at breeding. The upward  gradual  trend  in  lowering overall  of the age egg  at sexual  production  of  the  attributed to the improvements in management and  strain  can  nutrition that had  the course  (Gowe and  Fairfull, 1985). Keeping in mind that the control strain has  diet over  as  control  the slight  made over  been selected for egg  of the study  maturity, and  is an  been  unlikely cause not  production yet is fed the same nutritionally excellent  as the selected strains, the increase in body weight of the controls generation  is probably  due  to the tendency to put  birds are not as energetically efficient selected  strains  strains has and  genetic drift  be  (Fairfull,  personal  on  fat as  these  in converting feed to eggs as the  communication).  Mortality  among all management  gradually decreased  due  to better disease control  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  strain 6 for egg production from pected  from  the amount  However, the selection change weight  148 to 273 days are positive as was ex-  of selection  pressure was  in the phenotypic  value  pressures  not enough  applied to effect  for egg production. The  to. this  SD's for body weight  the first  trait.  a significant SD's for egg  at 225 days were practically zero which is in accordance  maintenance of this trait at the same level throughout The  and dams for  with the  the selection study.  for the sires were slightly posistive for all but  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 average taken. Consequently, the smallest bird with the best conformation in the  group  may  have been  chosen  as a sire  which case he would have had a body weight  for the next lower  generation in  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  parents selected one  for egg production  from  148 to 273 days  for  the  in 1961 reflects the delay in breeding of these birds for  year. This particular occurrance appears to confirm that as the age of  the parents increases, the response the decrease  to selection decreases partially due to  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 under  selection.  HHEP,  phenotypically stable for all but one of the traits egg  weight,  fertility,  hatchability  and  viability  66 remained declined measured  constant  throughout  significantly  the selection  and showed  but not considered  no  signs  period  while  body  weight  of abating. The other  in the selection  program  were  traits  egg specific  gravity, Haugh units, and age at sexual maturity. These traits did not show any consistent trends in performance. The the  lack of phenotypic  following reasons:  selection  program  selection, 2) some one  response  1) there were  at the same of the traits  time  to selection was probably too many resulting  traits  considered  due to in the  in a lack of response to  selected were negatively correlated  with  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  strain were  6 may being  adequate  not long enough, and 6) the population size of  not have been  selected such  control  in the  large enough. Furthermore, some  as fertility strain  sent  and hatchability from  Ottawa.  may As  traits that  not have an 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 Abstracts, Aug. 11-16,  Poultry Congress and Exposition, New Orleans, pp. 28-29  Proceedings  Barton, W. H., and B. Charlesworth, 1984. Genetic revolutions, effects, and speciation. Ann. Rev. Ecol. Syst. 15: 133-164.  and  founder  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. 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Combining ability, heterosis and reciprocal effects for first and second year performance in six selected leghorn strains crossed  in a  Breeders'  Roundtable  complete  Proc.  diallel.  May 6-7, St. Louis,  of  the 31st Annual  Missouri,  National  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 B.  S. Symposium  on Genetics  of  in selection experiments. /. U.  Population  20-23, pp. 17-41.  67  Structure,  Pavia,  Italy,  Aug.  68 Falconer, D. S., 1953b. Selection Genetics 51:470-501.  for large  and small  in mice. J.  size  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  Inc.,  New  to Quantitative  Genetics  2nd ed. Longman  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  Auckland,  Poultry  Science  Convention,  World's  Poutry  Sci. Assoc.  Gowe, R. S., and R. W. Fairfull, 1982a. Heterosis in egg-type World  Madrid,  Oct.  13-16,  N. Z., pp. 141-162.  Congress  on Genetics  Applied  Spain,  pp. 228-242.  to Livestock  Gowe, R. S., and R. W. Fairfull, 1982b. Some lessons from in poultry. In Proceedings Cattle vol. I: Technical  of  the  World  Congress  , R. A. Barton  chickens. 2nd  Production,  selection studies  on Sheep  and W.  Oct. 4-8,  and  C. Smith  Beef  (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 parameters 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 control 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 Sunderland, Mass.  of  Population  Genetics.  Sinauer  Assoc., Inc.,  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 genetic and phenotypic correlations for traits  of heritabilities of chickens.  and  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 Poultry  Sci. 31:537-544.  and reproductive fitness.  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 II. Am. Nat. 91:241-379. Lush, J., 1951. The effectiveness of selection.  J. Animal  Mather, K., and B. J. Harrison, 1949. The manifold Heredity 3;1-52;131-162.  for selection, I,  Sci.  effect  10:3-21. of selection.  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 8000, Cary, N. C. 27511.  SAS  Institute Inc., 1982b. SAS User's Box 8000, Cary, N. C. 27511.  User's  Guide:  Guide:  Basics.  SAS Institute Inc., Box  Statistics.  SAS  Institute Inc.,  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 s i r e freedom ( d f , d f s  T r a i l  HHEP Egg  d  to  273 days  273  s  ) ,  dam («' ) and individual d  (o'  e  >  components of variance, and the degress of  , and d f , respectively) of each component from the analyses of variance f o r s t r a i n 6 for 1957. e  d '  production  ( c '  a  *'  s  d f  d  * '  d  d f  e  38  35  -  -  272  375  from  38  28  270  47  471  734  from  38  93  270  86  471  3157  from  38  48  270  38  471  1938  148  to  Egg  production  148  to  Egg  production  274  to  Egg  weight  at  225  38  2  261  2  388  8  weight  at  350  38  3  264  2  364  9  weight  at  450  38  4  260  3  322  12  gravity  38  4  261  1  388  24  gravity  38  2  260  1  322  21  497  497  days  days  days  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  38  5  261  4  388  19  units  at  450  38  6  260  5  322  35  38  11  269  35  444  196  38  52  267  67  4 13  438  days Haugh days Age  at  sexual  matur1ty Body days  weight  at  365  Table 8.2. Estimates of the s i r e U ' ) , dam (o-' ) and Individual («' ) components of variance, and the degrees of freedom (df , df,. , and df , respectively) of each component from the analyses of variance f o r strain 8 f o r 1938. s  S  O  Trait  HHEP Egg  to  273 days  148  to  Egg  production  273  497  g  „ '  s  d f  d  -  « '  d  df  f i  * '  e  19  521  -  188  343  from  19  21  188  90  693  600  from  19  112  188  334  693  2282  from  19  200  188  294  693  3208  days  148  to  Egg  production 497  e  ©  d f  production  d  days  274  to  Egg  weight  at  days 225  19  2  185  2  617  9  weight  at  350  19  4  180  3  560  9  weight  at  450  19  4  176  4  530  13  gravity  19  3  185  2  617  19  gravity  19  2  176  3  530  24  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  19  5  185  9  617  29  units  at  450  19  11  176  7  530  46  19  13  186  13  177  670  19  164  183  152  611  501  days Haugh days Age  at  sexual  matur 1t y Body  weight  at  365  days  vl  Table 8.3. Estimates of the s i r e („' ). 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 s t r a i n 6 f o r 1959. s  Trait  df  HHEP  to  273  days  Egg  production  148  to  Egg  production  273  19  from  19  from  19  from  19  d f  1  4  7  d  «'  df„  d  1  280  137  185  66  1008  791  408  185  287  1008  3102  185  363  1008  3778  846  9  780  10  709  14  846  18  709  28  days  148  to  Egg  production  497  days  497  2  8  2  274  to  Egg  weight  at  225  19  days  weight  at  350  19  3  weight  at  450  19  3  2  181  1  days Egg  189  1  ?  9  days Egg  178  3  days Egg at  specific 225  Egg at  19  gravity  19  181  4  days  specific 450  gravity  6  178  days  846  Haugh  units  at  225  19  days Haugh  units  at  450  19  4  1 8  2  2  1 709  8  178  57  184  27  109  182  108  51  days Age  at  sexual  19  matur1ty Body days  weight  at  3G5  19  941  851  2  9  7  503  Table 6.4. Estimates of the s i r e (<J' ), dam ( o ' ) and Individual (a' ) components of variance, and the degrees of freedom ( d f , d f , and d f respectively) of each component from the analyses of variance f o r strain 6 f o r I960. s  s  d  Trait  HHEP  d  s to  273  production  148  to  Egg  production  148  to  Egg  production  273  497  497  df.  df.  19  1002  178  322  from  19  78  178  40  779  1068  from  19  234  178  112  779  3933  from  19  242  178  779  4508  days  Egg  e  e >  days  days  274  to  Egg  weight  at  days 225  19  176  589  weight  at  350  19  175  550  12  weight  at  450  19  174  485  15  gravity  19  174  589  14  gravity  19  174  485  25  485  66  176  589  26  736  286  651  533  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  19  units  at  450  19  11  174  20  days Haugh days Age  at  sexual  19  1 1  176  19  87  177  matur1ty Body days  weight  at  365  90  CD  components of variance, Table 6 . 5 . Estimates of the s i r e U ' ) . dam ( „' ) and individual («' ) analyses of variance for from the , respectively) of each component ( d f , d f , and s  s  Trait  d  HHEP Egg  to  273  days  production 273  d  e  d  148  to  Egg  production  f  s  24  <'s  d  276  f  d  -  «'d  f  e  -  174  147 564  from  24  17  174  22  729  from  24  76  174  130  729  2098  from  24  123  174  148  729  2814  days  497  d  148  to  Egg  production  days  274  to  Egg  weight  at  225  24  2  174  1  647  8  weight  at  350  24  2  173  2  586  10  weight  at  450  24  2  173  3  523  13  gravity  24  3  173  2  647  18  gravity  24  3  173  3  523  31  497  days  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  24  4  174  4  647  23  units  at  450  24  8  173  7  523  44  24  7  174  22  720  105  94  174  109  665  524  24  days Haugh days Age  at  sexual  maturity Body days  weight  at  3G5  Table 8.8. Estimates of the s i r e (<r' ). dam (o-'jj) and Individual (<r' ) components of variance, and the degrees of freedom (df df , and d f , respectively) of each component from the analyses of variance for strain 8 f o r 1983. s  s>  rf  Trait  HHEP  df  to  273 days  Egg  production  148  to  Egg  production  273  497  e  e  s  a'  s  24  328  from  24  from  from  df . d  ««  d  df  e  a'  e  -  -  128  316  1  123  119  400  595  24  65  123  406  400  1734  24  233  123  479  400  2158  days  148  to  Egg  production  274  to  Egg  weight  at  225  24  1  120  1  351  7  weight  at  350  24  1  117  1  326  12  weight  at  450  24  2  116  2  307  13  gravity  24  6  120  4  351  19  gravity  24  4  116  -1  307  34  497  days  days  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  24  6  120  6  351  19  units  at  450  24  6  116  9  307  34  24  -7  273  48  393  600  24  53  273  117  376  405  days Haugh days Age  at  sexual  matur1ty Body  weight  at  365  days  Co  Table 8.7. Estimates of the s i r e (<»'), dam io' ) M  (df  s >  df  S  to  273  days  production  148  to  Egg  production  148  to  Egg  production  273  497  497  8  e  df  df. s  Egg  and Individual (#• ) components of variance, and the degrees of freedom  , and d f , respectively) of each component from the analyses of variance f o r strain 8 f o r 19S7 to 1983.  d  Trai t  HHEP  O  from  143  1 127  304  57  4080  745  I I 18  215  4080  2814  1 1 18  149  4080  3277  43 I 1 18  143 56  days from  143 188  days from  143 192  274  to  Egg  weight  at  days 225  143  1097  3438  weight  at  350  143  1088  3166  10  weight  at  450  143  1077  2876  14  gravity  143  1097  3438  18  gravity  143  1077  2B76  27  3438  23  8  2876  47  19  3904  258  105  3567  494  days Egg days Egg days Egg at  specific 225  Egg at  days  specific 450  Haugh  days  units  at  225  143  1097  units  at  450  143  1077  days Haugh days Age  at'  sexual  143  20  143  97  1 112  matur1ty Body  weight  at  3G5  1 106  days  vl CO  

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