An evaluation of the 'Scanogram' as an ultrasonic aid in assessing carcase composition of live sheep

Abstract

An evaluation of the Scanogram as an aid in assessing carcase composition of live sheep was made using 23 Dorset Horn rams. Live animal measurements included tracings from Scanogram photographs taken at the 12th rib, tuber coxae and shoulder sites and an 18-hour fasted liveweight. Half carcases were dissected into fat, muscle, bone and connective tissue. Repeatability of photograph interpretation was of the order of 0.75 for fat depth at the 12th rib and tuber coxae sites and M. longissirnus area, but low for shoulder fat depth. Correlations between scan and carcase measurements made at the same site were of the order of 0.7 for 12th rib and tuber coxae fat depth and low and non-significant for shoulder fat depth and M. longissirnus area.Scanogram measurements of fat depth at the 12th rib and tuber coxae sites were the best predictors of percentage fat, and when considered in combination with liveweight provided the best estimate of total carcase fat weight. Liveweight was the best predictor of total muscle weight and the addition of Scanogram measurements to liveweight did not improve the accuracy of prediction. From examination of confidence intervals about predicted means it was concluded that the value of the Scanogram, as an aid to assessing carcase composition, was limited to differentiating between individual animals of widely differing carcase composition, or selecting groups of animals where confidence was required in the group mean.