Accelerated selection for hen-housed egg production and correlated responses in White Leghorns (Gallus domesticus) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pg15bh90f

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  • The records of a population of White Leghorns at the Oregon State Agricultural Experiment Station, submitted to accelerated selection for hen-housed egg production on an individual and a family basis at 40 weeks of age for 18 years, were studied. An analysis was made to determine the relative efficiency of accelerated selection compared to direct selection for egg production based on annual records. When annual means of the production line were compared with control populations, accelerated selection proved to be effective in obtaining genetic gains in hen-housed annual production by increasing the part-year or egg production to February 1 while the residual production remained unchanged. Reliable estimates of genetic parameters obtained from the pooled analysis of the data demonstrated that accelerated selection on the basis of egg production to February 1 is justified and could provide 1.8 times as much genetic gain per year as would direct selection based on annual records. The half-sib heritability estimates for hen-housed egg production were 14 percent for production to February 1 and 11 percent for annual production. Sexual maturity had an heritability of 27 percent and body weight one of 53 percent. The estimates of heritability for egg weight and egg specific gravity averaged 32 percent and 30 percent, respectively. The full-sib estimates of heritability were generally larger than those based on half-sib estimates, indicating the presence not only of additive genetic variance in the population, but also other sources of variation such as non-additive genetic variance and maternal variance. For this reason, half-sib estimates of heritability are more reliable. The high estimate of genetic correlation, 0.86, between annual hen-housed egg production and that to February 1 justifies the use of accelerated selection. The positive correlation between residual egg production and that to February 1 indicates that there was no decline in residual production as a result of accelerated selection. Annual egg production seems to have plateaud in the last six generations, possibly due to a reduction in the additive genetic variance as indicated by the negative time trend of the heritability of hen-housed egg production to February 1. The progressive reduction in mortality indicates that the effect of inbreeding caused by restrictions in population number has not been important. Selection indices for annual and production to February 1 were derived from the estimates of genetic parameters. The results of this study demonstrate that accelerated selection for hen -housed egg production at 40 weeks of age or to February 1 has been more effective than direct selection on annual records would have been.
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