CARCASS FATNESS IN LAMBS GRAZING VARIOUS FORAGES AT DIFFERENT RATES OF LIVEWEIGHT GAIN

In three experiments, Dorset, Suffolk cross, or Coopworth lambs weighi ng 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 allo wances were adjusted to achieve target liveweight gains of 300, 200, o r 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 co mpared on both ryegrass-dominant and clover-dominant swards. In Experi ment 3, the comparison was extended to include a high rate of liveweig ht gain (300 g/day) on clover-dominant swards. Allowances of Nui ryegr ass required to achieve liveweight gains of 200 g/day were over 2 time s greater than that of clover and up to 5 times greater than for chico ry and lucerne. There was no effect of liveweight gain on carcass GR m easurements of lambs grazing ryegrass-dominant pastures when compared at the same carcass weights but lambs growing rapidly on clover-domina nt pastures were up to 3 mm fatter (P < 0.01) at the GR site than slow er-growing lambs. There was no effect of forage type on leanness of la mbs grown at 200 g/day nor was there any effect of forage type and liv eweight gain on meat quality. Restricting the diet to maintain lamb li veweight of 43 kg for 30-53 days gave inconsistent removal of fat and can not be recommended as a strategy to produce leaner lambs.