Correlated Responses in Some Economic Traits from Selection for Fast and Slow Hatching

Two strains of White Leghorns which had been selected for hatching time so that they differed by 48 hr in the average time required for incubation were studied to determine if correlated genetic responses to the selection for hatching time had occurred. Significant differences between the fast and slow hatching lines were observed for average embryo weight and embryo length from three to 14 days of incubation. Significant differences between the selected lines were also observed for chick weight on day of hatch, at 25 days after die start of incubation and at three and six weeks of age. The correlated responses observed were asymmetrical because for most measures the response was a reduction of weight or length in the slow hatching line, with no significant changes from the control line in the fast hatching line. No changes which could be considered correlated genetic responses were observed for age at first egg or in rate of lay. Both selected lines matured at significantly later ages and laid at higher rates than the control line.