Estimating Fat Depth and Longissimus Muscle Area by Use of Ultrasonics in Beef Cattle

The research reported herein concerned the use and accuracy of ultrasonics for estimating tissue depth in cattle. The rate of fat deposition and longissimus muscle growth was estimated from measurements taken by a Branson Model 52 ultrasonic machine. Ultrasonic fat estimates were made on 63 cattle when the animals were approximately 230 days of age and at four subsequent 6-week intervals. Area estimates were made of the longissimus muscle on 10 of these cattle at the time of the fat estimate. Area estimates were made by recording dorsal and ventral depths of the muscle at numerous angles and distances from the midline. These estimates suggested that a curvilinear relationship existed between live weight and fat deposition and that the relationship between live weight and longissimus muscle growth was linear for the period studied. A correlation of 0.95 was found between the longissimus muscle estimate before slaughter and the area measured on the carcass. The longissimus muscle depth was ultrasonically measured on 207 cattle at three points: 5, 9 and 13 cm from the midline. The mean of these three measurements was multiplied by a constant, intended to relate the data more closely to the longissimus muscle area and this value was correlated with the area measured from the carcass. Correlation coefficients between predicted longissimus muscle area and carcass measurements were significant at least at the 0.05 level.