Using ultrasound to determine fat thickness and longissimus dorsi area on Manchego lambs of different live weight

Abstract

Twenty lambs were separated randomly into two groups of 10 finishing weights of 25 and 35 kg, respectively. Lambs were evaluated live for fat thickness and longissimus dorsi cross sectional area between the 12th and 13th ribs and the 3rd and 4th lumbar vertebrae using real time ultrasound. Lambs were slaughtered using commercial slaughtering processes and carcasses were chilled at 6 °C for 24 h. Carcass measurements of fat thickness and longissimus dorsi area were recorded over the same points as used for in vivo measurements. All ultrasound and carcass measurements were different ( P < 0.01) between lamb weight groups. The highest correlation found was between ultrasound fat thickness ( r = 0.90 for 25 kg and r = 0.92 for 35 kg) and its corresponding carcass measurements taken between the 12th and 13th ribs. Multiple regression equations for predicting fat thickness and longissimus dorsi area using live weight like independent variable had R 2 values ranging from 0.54 to 0.69 and, R 2 values from 0.60 to 0.95 when ultrasound measurements were included. The accuracy of predicting fat thickness and longissimus muscle area on live animals could be improved by the addition of ultrasound measurements to live weight. Ultrasound fat thickness at 12–13th rib was the best predictor of fat thickness ( R 2 = 0.92; P < 0.001). Results suggest that ultrasonic measurements at 12–13th rib taken before slaughter may be accurate predictors of cold carcass weight ( R 2 = 0.70; P < 0.001) in lambs.