A long-term poultry egg-stock selection study, conducted at the Animal Research Centre, has been used as a basis for considering some issues in breeding. Gains of 2 eggs and 0.3 g egg size per generation were made over 29-30 generations without significant changes in fertility, hatchability or viability. During the last 10 generations, egg specific gravity and Haugh units were improved while body weight was reduced without a significant increase in percentage of eggs with blood spots. This was achieved with populations of 1100 pullets housed/strain/year. All sires were from sire families (half-sib) above average for egg production. About VS of the sires contributed sires to the next generation to avoid rapid inbreeding or the loss of desirable low frequency genes. Inbreeding in the selected strains averaged 0.7-0.8% per generation. Each selected trait should be clearly defined, particularly complex traits like egg production: Closely related traits, hen- housed egg production and hen-day rate from first egg, gave different direct and indirect responses when used as the principal trait of selection. There was no evidence of decreases in genetic variation of egg production or any other trait over the thirty years. Also, the genetic correlations changed little during the study. However, heritabilities of selected strains were lower than those of the control implying that change had taken place. Changes in selection objectives and the value of control strains are discussed.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XII. Biotechnology, selection experiments, parameter estimation, design of breeding systems, management of genetic resources., , 152–167, 1986
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