Genetic architecture of carcass composition in chickens.

A cross-sectional diallel experiment was used to estimate the contribution of various types of genetic variation for the chemical components of the chicken carcass. Populations tested included a commercially developed sire line (CM), a fertility-selected broiler line (FS), and the pureline Jersey Giant (JG). Average line effects were significant for body weight and total carcass water, fat, and protein. Line effects were significant only for percentage fat and water. Maternal effects and additive sex linkage were not significant for any carcass component on an absolute or percentage basis. Significant average heterosis and sex by heterosis interactions were observed for abdominal fat pad weight and total carcass fat. Male hybrids exhibited a 29% decrease in abdominal fat pad size, but female hybrids exhibited a 7% increase. Significant heterosis was observed among females, but not males, for percentage carcass fat. Changes in carcass fat via hybridization produced the largest percentage change among males due to heterosis of the sex chromosomes. In the present experiment, negative heterosis for abdominal fat among male progeny accounted for approximately 65% of the overall reduction in fat content of the carcass.