Selection for body weight at eight weeks of age in dwarf and normal meat-type chickens originating from a common...

A study was conducted to evaluate responses to selection for 8-week body weight in normal and dwarf meat-type broiler lines originating from the same nonselected randombred population. Following three generations of selection, normal and dwarf dams were mated to males from a commercial broiler stock to compare strain cross performance of progeny from the two dam groups. The mean realized heritabilities across four generations for 8-week body weight, estimated by dividing the cumulative responses by the cumulative selection differentials, were .69 for normal lines and .59 for dwarf lines. Realized estimates from regression of population means on cumulative selection differentials were .78 +/- .10 and .74 +/- .02 for normal lines and .70 +/- .14 and .59 +/- .19 for dwarf lines. Although these estimates were not significantly different, realized heritabilities were consistently greater in normal than in dwarf lines across generations. The smaller heritability estimates observed in dwarf lines were compensated for by larger selection intensities (i), which resulted in similar selection responses in 8-week body weight for normal and dwarf genotypes. The fertility of normal and dwarf females mated to commercial broiler males was identical. However, the hatchability of fertile eggs was approximately 10% higher for dwarfs than for normal females. Body weights (8-week) of male progeny from dwarf dams mated to commercial males were 3% smaller than comparable males from normal dams. There were no differences between 8-week body weights of female progeny from normal and dwarf dams mated to commercial males.