Crossbred lambs involving specialist meat breed (Expt. A) or long-woolled breeds (Expt. B) were slaughtered at ages ranging from 12 to 30 weeks. Carcasses were classified retrospectively into current export grades according to their weight and fat measurement GR. In both experiments measurement GR was related to carcass weight (r=0.57 to 0.83) and increased, on average, by just over 1 mm per kg carcass weight increase. Proportions of carcasses grading 'trimmer' or 'overfat' increased at carcass weights above 15 kg or at slaughter ages greater than 18 weeks. In Expt. A, 4% of carcasses graded 'overfat' at the 12 week slaughter age and 81% at 30 weeks. There was little difference in the grade distribution of carcasses among sire breeds in Expt. A (Southdown, Suffolk and Dorset Down) but in Expt. B lambs reared by Corriedale ewes showed higher proportions of 'trimmer' (25%) and 'overfat' (18%) carcasses compared with those reared by Romneys (10% and 2% respectively). It is suggested that the higher carcass fat of lambs from Corriedale ewes is due partly to greater milk consumption compared with those suckled by Romneys.

RW, Purchas, and RG Keogh

Proceedings of the New Zealand Society of Animal Production, Volume 44, , 219-222, 1984
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