The present paper deals with the effects of ageing on the expression of the genetic variation in relation to the environmental variation for rate of lay and egg weight in three selection lines of White Leghorn birds from Gen. 1-8 of the Scandinavian Selection and Crossbreeding Experiment with Laying Hens. The results showed that the estimates of the phenotypic variance and its genetic and environmental components increased markedly with age of the birds for an egg production trait like rate of lay, but not for a trait like egg weight when the effects of scale were corrected for by calculating the coefficients of variation.
The increase of the genetic variance for rate of lay during the egg production period of the layers was found to be approximately proportional to the parallell increase of the environmental variance, indicating that new genetic variation was induced in response to an increase of the environmental variation. These results are in close agreement with those found by Liljedahl et al. (1984).

L.-E. Liljedahl, G. Engstrom

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 514–519, 1986
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