Japanese Journal of Sheep Science

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The objective of the present study was to determine body weights at slaughter for ram and ewe Suffolk lambs, reared under the early rapid growth production system, to produce the carcasses desired by outlets. Those carcasses were classfied within B2 grade of the Japanese Lamb Carcass Classification.
Carcass measurements were collected from 33 ram and 23 ewe lambs. Lambs were fed concentrate and hay in confinement, and slaughtered at 20 weeks (137±17 (s.d.) days) of age on an average. Body weight at slaughter and average daily gain were 55.1±4.6 kg and 0.37± 0.06 kg for ram lambs, and, 47.6±3.2 kg and 0.32±0.05 kg for ewe lambs, respectively. The following linear regression equations for estimating carcass weight and carcass backfat depth from body weight were observed within sexes :
1. Ram lambs, carcass weight=0.59 (body weight) -6.79, (n=33 ; R²=0.86 ; P< 0.01).
2. Ram lambs, backfat depth=0.17 (body weight) -4.18, (n=33 ; R²=0.26 ; P< 0.05).
3. Ewe lambs, carcass weight=0.68 (body weight) -9.53, (n=23 ; R²=0.79 ; P< 0.01).
4. Ewe lambs, backfat depth=0.27 (body weight) - 7.29, (n=23 ; R²=0.27 ; P< 0.05).
The B2 grade carcass must have both B class (20 to 25 kg) of carcass weight and 2 class (4 to 7 mm) of backfat depth. Body weights to satisfy B class of carcass weight were estimated to be within 45 and 54 kg range from equation 1. Slaughter body weights to satisfy 2 class of backfat depth were estimated to be within 48 and 66 kg range from equation 2. It was estimated that the overlapping part of these two body weight ranges was the range which produce B2 grade carcass for ram lambs. The same procedure was applied for ewe lambs.
It was concluded that ram lambs should be slaughtered at a body weight of 48 to 54 kg, and ewe lambs at 43 to 51 kg. The derived optimal slaughter weights were limited to the Suffolk lambs reared under production system used in the present study.

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