The effects of natural selection on 273 day part-record egg production were examined by comparing population differentials in selected strains of laying hens. Similar differentials were also calculated for unselected control strains. Viability had the greatest effect on population differentials in both selected and control strains. In the selected strains no other effects of natural selection were evident, probably due to artificial selection for fitness traits. In control strains, the effect of viability was higher and breeders averaged higher egg production than survivors to 273 d. As the average egg production in the control populations remained constant, the difference was probably due to effects that reduced the mean of the survivor population relative to the breeder population that were not wholly genetic. The subclinical effects of some diseases might account for this. Also, hatchability significantly affected differentials for part-record egg production in the control strains.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 13–15, 1994
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