Submitted to: American Society of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: N/A
Interpretive Summary: The ability to select replacement lambs with greater muscle to bone ratios has relied solely on weight of the lambs. Conformation of different breeds would indicate that this is not the best measure of muscle to bone ratio. Measurement of lamb leg scores on hanging carcasses has been conducted in commercial settings for many years. Leg score is used to subjectively evaluated conformation of the lamb and as in indicator of carcass muscling. Two objective measures of leg width (live animal and hanging carcass measured leg width) were evaluated in addition to leg score to determine if a live measurement could accurately predict harvested leg and loin weights. As expected, carcass measurements were the most accurate predictors of leg and loin weights. The live animal measurement of leg width was comparable to carcass measures and could be used in breeding programs to select lambs with improved muscle to bone ratio.
Technical Abstract: Lamb carcass leg score (LS; 1 = low cull to 15 = high prime) is a subjective indicator of carcass muscling. Our objective for this study was to compare LS, live leg width (LL), and carcass leg width (LW) as single predictors, and in combination with live (LWT) or carcass weight (CWT), of harvested leg weight and trimmed loin (TL) weight. Lambs representing four sire breeds were reared in an extensive production system to weaning and then fed a finishing diet until harvest at a mean weight of 62.9 (SD = 9.5) kg. Before harvest, LL was determined at the widest point between hip and stifle. Wethers (n = 170) were harvested at The Ohio State University meat science laboratory, and LS and leg and TL weights were collected. The LW was measured on hanging carcasses at the dorsal tip of the visible gluteus. Means were 27.1 cm for LL, 23.9 cm for LW, 12.5 for LS, 10.0 kg for whole leg, 6.3 kg for bone-in leg, 4.4 kg for boneless leg, and 2.6 kg for TL. The range of R-square values for single prediction equations using LW was 0.60 to 0.83, LS was 0.16 to 0.32, and LL was 0.31 to 0.48. In this data set, LW was the best single-predictor of leg and TL weights. Prediction equations with CWT improved R-square. The equation with LWT had comparable R-square values as equations with CWT. When selecting for replacement animals, the prediction model with LL and LWT could be used to increase leg and TL weights. Table 1. Model R-square and root mean square error (RMSE) for predicting weights from live and carcass measurements. LS LL LW LS+CWT LL+LWT LW+CWT Whole Leg R2 0.27 0.48 0.83 0.95 0.88 0.96 RMSE (kg) 1.37 1.16 0.66 0.35 0.57 0.34 Bone-in leg R2 0.29 0.42 0.78 0.90 0.82 0.90 RMSE (kg) 0.84 0.76 0.46 0.31 0.42 0.31 Boneless Leg R2 0.32 0.39 0.78 0.81 0.70 0.83 RMSE (kg) 0.53 0.50 0.30 0.28 0.35 0.27 TL R2 0.16 0.31 0.60 0.75 0.71 0.75 RMSE (kg) 0.38 0.35 0.27 0.21 0.23 0.21