Lamb growth performance and carcass weight from rotationally grazed perennial pasture systems compared with annual pasture systems with supplements

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Abstract
Annual pastures used to finish lambs can decline in herbage nutritive value (NV) from January to April in the temperate zone. If lambs are to be finished to market specifications for carcass weight during this period, the use of summer-active perennial pastures or supplementation of annual pastures, is required. The present study investigated liveweight (LW) gain and carcass characteristics of lambs finished on perennial pastures compared with annual pastures and supplementation. Fifty-four second-cross lambs were allocated to one of the following four treatments in an asymmetric split-plot design: perennial pasture (PP), annual pasture with hay and grain (AP), AP with flaxseed (AP+FS) and AP with flaxmeal (AP+FM). Lambs were fed for 7 weeks and weighed weekly. Blood glucose and total antioxidant status were determined before, during and at the end of the experiment. Carcass weight and GR fat were measured at 24 h post-slaughter. Lambs grazing PP had significantly higher daily LW gain (P < 0.001), slaughter weight (P < 0.001), carcass weight (P < 0.01) and GR fat (total tissue depth at 12 rib, 110 mm from midline) (P < 0.001) than did lambs grazing AP, AP+FS or AP+FM. Lambs receiving AP+FS and AP+FM grew significantly faster (P < 0.001) than lambs receiving AP. It is likely that lambs grazing the perennial pasture were actively selecting the green portion of lucerne that had higher herbage NV than that indicated by the conventional feed analysis. Results show that lambs grazing a lucerne-dominant perennial pasture performed better than did lambs grazing annual pasture with supplements during the finishing period. Further work is required to determine the efficacy of other perennial species to enable economic finishing of lambs during summer and early autumn.

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