Genetic effects of aging on egg production traits in the first laying cycle of White Leghorn strains and strain crosses.

Three White Leghorn strains, their two-way crosses, and two commercial lines were used to evaluate the effects of aging on mean heterosis, reciprocal, additive, Z-chromosome, and heterotic effects and their variances in two egg production traits during the first laying cycle. Egg number of the survivors (EPF) and egg number including mortality and morbidity (EPM) were evaluated from hens housed one per cage in a randomized block design. For analyses, egg number was divided into 12 periods of 28 d each.