EFFECTS OF DIETARY ENERGY INTAKE AND SEX ON CARCASS TISSUE AND OFFAL GROWTH IN SHEEP

Forty crossbred lambs (20 rams, 20 ewes) were penned in two groups (equal numbers of each sex) and fed a pelleted ration either ad libitum (H) or 70% of expected ad libitum intake (70% H). Ten lambs (5 rams, 5 ewes) from both groups (H and 70% H) were slaughtered after 40 days on feed while the remaining lambs were slaughtered after 61 days on feed. All lambs were measured for carcass leanness using an EMME machine immediately prior to slaughter. The offal components were weighed fresh and the alimentary tract was emptied of digesta. One side of each carcass was broken into four cuts (leg, loin, rib, shoulder) which were further separated into fat, muscle and bone. EMME numbers only marginally increased the amount of explained variation in the prediction of lean weight over that provided by liveweight alone. Growth coefficients between sexes and intake groups (H, 70% H) for the offal components relative to empty body weight were homogeneous, indicating that sex and dietary energy intake did not affect the relative growth of the offal components. Ram lambs had heavier heads and smaller intestines than ewe lambs, but contained less caul and mesenteric fat than ewe lambs at the same empty body weight. Lambs fed H had a greater weight of pelt, liver and caul fat, but had a lower warm carcass weight and less mesenteric fat than lambs fed 70% H at the same empty body weight. Growth coefficients between sexes and intake groups for the carcass tissues relative to physically separated tissue weights (muscle, bone, fat) were homogeneous, which indicated that sex and intake did not affect the relative growth of the carcass tissues. Ram lamb carcasses had a greater weight of muscle in the shoulder and less muscle in the leg than ewe lamb carcasses at the same carcass muscle weight. Dietary energy intake had small but statistically significant effects on carcass muscle distribution. Lambs fed 70% H produced carcasses with proportionally more muscle in the leg and less muscle in the loin and shoulder than lambs fed H at the same carcass muscle weight. Sex and dietary energy intake had minor effects on carcass bone and fat distribution. Key words: Lambs, carcass, offal, fat, EMME