Lamb fat thickness and longissimus muscle area measured by a computerized ultrasonic system

Sixty lambs of Manchego, Merino and Ile de France × Merino (20 lambs per each) breeds were divided randomly in groups by sex up to finishing weights ranging from 22 to 28 kg. Fat thickness and longissimus dorsi cross-sectional area between the 12th and 13th ribs were measured using real-time ultrasound in vivo and on the carcass after slaughter. Correlations between actual and ultrasound measurements were higher for longissimus muscle area (r = 0.88; P < 0.001) and fat thickness (r = 0.74; P < 0.001) than for longissimus muscle depth (r = 0.56; P < 0.001). No differences were found for longissimus muscle area and depth between sex and among breeds, but the accuracy of ultrasound fat thickness predictor was lower for females than males as indicated by higher absolute differences (P < 0.05), whereas the accuracy for prediction for Manchego and Merino was lower and not significant than for crossbreds. Results indicate that ultrasonic measurements of fat thickness and longissimus muscle area taken before slaughter combined with video image analysis may be accurate predictors of final carcass fat thickness and longissimus muscle area in lambs.