Somatic and Z-chromosome additive genetic effects on egg production were evaluated in three White Leghorn strains and their two-way crosses during the first laying cycle. Egg number of the survivors from hens housed one per cage in a randomized block design was divided into 12 periods of 28 days each, starting at age at first egg. The pattern of age changes in additive and Z-chromosome effects varied among strains, indicating genotypic differences in response to aging. These differences increased on average with age. Lifetime performance of layers may be improved by selecting animals at older ages. This favours individuals with better DNA repair capacity or those which can turn on favourable genes or mm off detrimental genes as required to buffer the negative effects of aging. 

M. C Ledur, R. W Fairfull, I. McMillan, L. Asselstine

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 24: Sheep and goats (fibre); sheep and goats (meat and milk); poultry; horses; buffaloes., , 329–332, 1998
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