LAMB FAT THICKNESS AND LONGISSIMUS MUSCLE AREA MEASURED BY A COMPUTERIZED ULTRASONIC SYSTEM

Sixty lambs of Manchego, Merino and lie de France x Merino (20 lambs p er 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 usi ng real-time ultrasound in vivo and on the carcass after slaughter. Co rrelations 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 bet ween sex and among breeds, but the accuracy of ultrasound fat thicknes s predictor was lower for females than males as indicated by higher ab solute 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 l ongissimus muscle area taken before slaughter combined with video imag e analysis may be accurate predictors of final carcass fat thickness a nd longissimus muscle area in lambs. (C) 1997 Elsevier Science B.V.