USING ULTRASOUND TO DETERMINE FAT THICKNESS AND LONGISSIMUS-DORSI AREA ON MANCHEGO LAMBS OF DIFFERENT LIVE WEIGHT

Twenty lambs were separated randomly into two groups of 10 finishing w eights of 25 and 35 kg, respectively. Lambs were evaluated live for fa t thickness and longissimus dorsi cross sectional area between the 12t h and 13th ribs and the 3rd and 4th lumbar vertebrae using real time u ltrasound. Lambs were slaughtered using commercial slaughtering proces ses and carcasses were chilled at 6 degrees C for 24 h. Carcass measur ements of fat thickness and longissimus dorsi area were recorded over the same points as used for in vivo measurements. All ultrasound and c arcass measurements were different (P < 0.01) between lamb weight grou ps. 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 car cass measurements taken between the 12th and 13th ribs. Multiple regre ssion equations for predicting fat thickness and longissimus dorsi are a using live weight like independent variable had R-2 values ranging f rom 0.54 to 0.69 and, R-2 values from 0.60 to 0.95 when ultrasound mea surements were included. The accuracy of predicting fat thickness and longissimus muscle area on live animals could be improved by the addit ion of ultrasound measurements to live weight. Ultrasound fat thicknes s 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 ri b taken before slaughter may be accurate predictors of cold carcass we ight (R-2 = 0.70; P < 0.001) in lambs, (C) 1998 Elsevier Science B.V.