Heterosis, maternal and direct effects in double-muscled and normal cattle: II. Carcass traits of young bulls

Data on 135 young bulls from a two-breed group diallel experiment involving double-muscled (DM) and normal (N) cattle were analyzed to obtain estimates of heterosis, maternal and direct effects for carcass traits. When carcass traits were adjusted to a constant age at slaughter (398.5 d), significant positive heterosis was observed for slaughter and carcass weights, carcass length and s.c. fat thickness. Maternal effect was relatively unimportant for the traits studied. The progeny of N sires and DM straightbreds were heavier at slaughter and had higher carcass weight, s.c. fat thickness and carcass length (P less than .01), whereas DM-sired progeny and DM straightbreds had higher dressing percentage (P less than .05) and cutability (P less than .01). Heterosis was significant for all the 10-11-12th rib joint dissection traits except for percentage of muscle. Although there was negative heterosis for percentage of bone, there was positive heterosis for rib joint weight, fat weight and percentage, muscle weight and muscle:fat and muscle:bone ratios. For direct effect and straightbred differences, N-sired progeny and N straightbreds, respectively, had significantly larger values for rib joint weight, fat weight and percentage and bone weight. The DM-sired progeny and DM straightbreds had larger values for percentage of muscle, muscle:fat and muscle:bone ratios. When the carcass and dissection traits were adjusted to a constant carcass (303.7 kg) and rib joint (4,812 g) weight, respectively, the results were similar to those observed on age constant basis except for rib eye area, for which DM-sired progeny and DM straightbreds had larger values.