Curvilinear Trends in Direct and Some Correlated Responses to Nineteen Generations of Selection for Part Record Rate of Egg Production in a Randombred Line of Chickens

Abstract

Direct and correlated responses to 19 generations of selection for part record rate of egg production were studied. The select line (B line) was derived from a base randombred control line (A line) which, in turn, was derived as a random sample of the Regional Cornell control population. Cumulative direct and correlated responses were computed as deviations of the generation means of the various traits from the corresponding means of the control line. Second-order polynomial regressions of the various traits reveal significant curvilinear relationships between cumulative responses and cumulated selection differentials for the selection criterion (part record rate of lay) and the correlated traits, part record egg number, full record egg number, full record rate of lay, mature body weight, 32-week egg weight, and Haugh unit.It was determined that this line attained a limit of upward selection response in the 12th generation. The genetic change in the selection criterion per generation before the attainment of the limit was 1.07% (P<.001), which gave a highly significant (P<.001) direct response of .09% per unit of selection applied. Significant negative correlated responses were obtained for 32-week egg weight and Haugh unit; a nonsignificant decrease in body weight response was observed; age at first egg, shell thickness, and laying house mortality decreased in their correlated responses to 19 generations of selection for part record rate of lay; fertility and hatchability increased .05 and .02%, respectively, although these were not significant.