EFFECT OF SIRE BREED (SOUTHDOWN, SUFFOLK), SEX, AND GROWTH PATH ON CARCASS COMPOSITION OF CROSSBRED LAMBS

An experiment was repeated in 2 years using 698 lambs to investigate the effects of sire breed (Southdown, Suffolk), sex (female, short-scrotum male), and growth path on lamb growth and carcass composition. The three growth paths used were high (H), high followed by maintenance (HM), or low followed by high (LH) levels of pasture availability. The Suffolk-cross lambs averaged 2.3 kg more than Southdown-cross lambs at weaning (unfasted liveweight) and gained 2.6 kg more than the Southdown-cross lambs between weaning and slaughter. The male lambs weighed 1.8 kg more than the females at weaning and gained 0.7 kg more between weaning and slaughter. When hot-carcass weight was adjusted to 17.1 kg, the Southdown-cross lambs averaged 1.6 mm higher GR than Suffolks and females averaged 1.6 mm higher GR than short-scrotum lambs. The effect of the different nutritional treatments applied in this study was not consistent on GR or any other carcass measurements. The HM lambs had the largest carcass measurements indicative of skeletal growth and the highest kidney fat weights. The results of this trial indicate that to produce lean heavy lambs, farmers should use rams from breeds with a large mature size and feed only male lambs to heavier weights. Altering carcass composition through nutritional manipulation is far less likely to produce the desired outcome.