Inbreeding Effects on Traits with and Without Selection for Part Record Rate of Lay in Chickens

Data from inbred lines, one (D) selected for part record rate of lay and the other (C) unselected for any trait, were analyzed. After 19 generations of continuous full sib matings, the C line showed significant decreases in part record egg number, 32-week egg weight, shell thickness, full record egg number and part record rate of lay but nonsignificant decreases in hatchability, full record rate of lay, and laying house mortality. Age at first egg, Haugh unit and mature body weight showed significant increases in this line. The D line was similar to the C line in its response to the same intensity of inbreeding for all traits except full record egg number, part record rate, and fertility, each of which showed a significant decrease, and Haugh unit and full record rate of lay, which showed nonsignificant increases. Results indicated that the small advantages selection conferred on the inbred line in part record rate of lay (the selection criterion), full record egg number, and full record rate of lay were accompanied by undesirable changes in other traits, resulting in later sexual maturity, larger body weight, lower Haugh unit, fertility, and hatchability compared with the unselected line.