Rib-eye muscle (M. longissimus lumborum) area (REA) and depth (B) at the 12th rib were ultrasonically measured on 89 ram lambs from 3 sire breeds. The lambs were then slaughtered and these live measures plus carcass weight were evaluated as predictors of the corresponding carcass measures and the following two measures of muscling, based on four muscles surrounding the femur bone and the femur itself: 1. Muscle:Bone ratio (M:B), and 2: Muscularity (MUSC), defined as an index of muscle depth (square root of the weight of the four muscles per unit femur bone length) relative to a skeletal dimension (femur length). Prediction of carcass REA and B from ultrasonic REA and B, after adjusting for carcass weight, was more effective for B (partial r=0.40) than REA (partial r=0.18). The main problems with prediction arose with higher values (B>33mm), when ultrasonic values underestimated actual carcass values. REA and B (ultrasonic live and direct carcass) significantly (p<0.001) improved the prediction of MUSC or M:B over carcass weight alone, but did not account for the highly significant (P<0.001) breed effect on these traits. It is concluded that ultrasonic and carcass measures of REA and B provide useful but limited information on lamb leg muscularity.

AM, Nicol

Proceedings of the New Zealand Society of Animal Production, Volume 52, , 1-2, 1992
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