Use of carcase measurements to predict percentage carcase composition in crossbred lambs

Abstract

Half carcases from 108 lambs, from two sexes (wethers and ewes), six genotypes (Dorset Horn and Border Leicester rams crossed with Merino, Corriedale and Border Leicester x Merino first cross ewes) and three slaughter weights (34, 44 and 54 kg liveweight) were dissected into fat, muscle, bone and connective tissue. Measurements of carcase weight, fatness (1 2-13th and 8-9th rib fat depth), size (carcase length, chest depth and leg length) and shape (fleshing index) were recorded. Carcase weight and fat depth at the 12-13th and 8-9th rib sites were the three best single predictors of percentage fat (RSD's = 3.564,3.912 and 3.291 ), percentage muscle (RSD's = 3.1 64,2.970 and 2.948) and percentage bone (RSD's = 1.455, 1.848 and 1.467) in the carcase. The combination of carcase weight with a measure of fat depth at the 12-13th or 8-9th rib sites improved the prediction of percentage fat (RSD's = 2.845 and 2.955), percentage muscle (RSD's = 2.629 and 2.851) and percentage bone (RSD's = 1.425 and 1.342) over that of carcase weight or fat depth as single predictors (P< 0.05). The further addition of size or shape to a model already containing weight and fatness was not significant (P > 0.05). Interactions between carcase measurements and weight were significant for some measures of fatness and size in the prediction of percentage fat and bone. No interactions were significant in the prediction of percentage muscle. The effect of genotype on the prediction of percentage composition was significant for many of the measurements, whereas the effect of sex was only significant for prediction of percentage bone and not for prediction of percentage fat and muscle. It was concluded that carcase weight and fatness provided the most accurate prediction of percentage carcase composition and that additional measures of size or shape did not improve the accuracy. Using carcase weight and fatness, knowledge of genotype improved the prediction of percentage carcase composition, whereas sex was relatively unimportant.