Carcass fatness in lambs grazing various forages at different rates of liveweight gain

Abstract

In three experiments, Dorset, Suffolk cross, or Coopworth lambs weighing c. 30 kg in January were offered a range of forages including high-endophyte Nui ryegrass-dominant pasture, white clover-dominant pasture, Moata or Concord ryegrasses, lucerne, rape, or chicory. Herbage allowances were adjusted to achieve target liveweight gains of 300, 200, or 120 g/day and lambs slaughtered at c. 43 kg liveweight from March to May. In Experiment 1, medium and low rates of liveweight gain were compared on both ryegrass-dominant and clover-dominant swards. In Experiment 3, the comparison was extended to include a high rate of liveweight gain (300 g/day) on clover-dominant swards. Allowances of Nui ryegrass required to achieve liveweight gains of 200 g/day were over 2 times greater than that of clover and up to 5 times greater than for chicory and lucerne. There was no effect of liveweight gain on carcass GR measurements of lambs grazing ryegrass-dominant pastures when compared at the same carcass weights but lambs growing rapidly on clover-dominant pastures were up to 3 mm fatter (P < 0.01) at the GR site than slower-growing lambs. There was no effect of forage type on leanness of lambs grown at 200 g/day nor was there any effect of forage type and liveweight gain on meat quality. Restricting the diet to maintain lamb liveweight of 43 kg for 30–53 days gave inconsistent removal of fat and can not be recommended as a strategy to produce leaner lambs.

Keywords:

• meat animals
• sheep
• lambs
• lamb meat
• meat quality
• nutrition
• composition
• fatness
• Trifolium sp
• Lolium sp