Slimming diets for overfat lambs

G.J. Cruickshank, P.D. Muir, K.J.S. MacLean

AgResearch, Hawkes Bag Agricultural Research Centre, P.O. Box 85, Hastings, New Zealand

Proceedings of the New Zealand Society of Animal Production. 1992, 52: 241-242

Overseas data suggest that feeding low energy/high protein diets can increase carcass weight (and muscle mass) while reducing fat content. The potential application of this technique to maximise the returns from overfat lambs in New Zealand was studied. One hundred and sixty ewe lambs, assessed as being overfat, were allocated on a liveweight basis to one of seven treatment groups. These comprised an initial slaughter group, 2 groups offered pasture at approximately maintenance allowance, 2 groups offered pasture at approximately half maintenance plus 200g/d of a high protein pellet and 2 groups held on a bare paddock and offered ad lib straw plus 200g/d of a high protein pellet. One group from each treatment was slaughtered after 3 weeks and the second after 5 weeks of controlled feeding. Liveweight change, carcass weight and carcass fatness were monitored.

All groups lost liveweight (88-195 g/d) and estimated carcass weight (37-89g/d) over the experiment. Corrected to a common carcass weight of 15.25kg decreased GR from 11.6mm for the initial slaughter group to 9.7 and 9.2mm after 3 and 5 weeks, respectively of maintenance pasture feeding. Corresponding GR's of the supplemented groups were 9.3mm (both groups) after 3 weeks and 8.1 and 7.5mm after 5 weeks for straw and pasture based diets respectively.

Supplementation with a high protein diet was effective in reducing carcass GR measurement after 3 weeks of supplementation with a further decrease after 5 weeks. However, unsupplemented lambs also showed a decrease in GR after 3 weeks, which was not significantly different from supplemented lambs. The length of feeding required to effect a change negated the advantage of decreased GR, although economic returns could be achieved if the pellets were more readily accepted.

Keywords: NZSAPAB; Lamb; overfat; fishmeal; lean; carcass; GR

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Last Updated 25-01-1997