Body composition and organ weights in fleeceweight-selected and control Romney rams

Abstract

Abstract Rams from the Massey University fleeceweight-selected (FW) and control (C) lines of Romney sheep (13 per line) were slaughtered at 16 months of age to determine responses in body composition to 35 years of single trait selection for greasy fleeceweight. FW rams were heavier than C rams and, at a common liveweight, had heavier hearts, livers, thymus glands, and adrenal glands but a lower reticulo-rumen weight. Carcasses of FW rams were heavier and longer than those of C rams but there was no difference between the lines in dressing-out percentage. At a common carcass weight, FW and C rams had a similar content of water, protein, and fat in the carcass. Subcutaneous fat depths and soft tissue depth GR were generally lower in FW rams and there was a redistribution of tissue in the carcasses of these rams compared with C rams such that hind leg weight was increased at the expense of the shoulder, loin, and rack. Hind legs of the FW rams had higher weights of dissectible muscle and bone, lower weights of dissectible fat, a heavier and longer femur, and lower muscularity (depth of muscle relative to length of an adjacent bone) at a common carcass weight than those of C rams. It is concluded that responses in body composition to selection for greasy fleece-weight are small but generally favourable, except for the decrease in muscularity.