Predicting carcass composition of beef cattle using ultrasound technology

We evaluated 20 slaughtered cattle with ultrasound before hide removal to p redict fat thickness and ribeye area at the 12th rib for possible use in ca rcass composition prediction. Carcasses were fabricated into boneless subpr imals that were trimmed progressively from 2.54 to 1.27 to .64 cm maximum f at trim levels. Stepwise regression was used to indicate the relative impor tance of variables in a model designed to estimate the percentage of bonele ss subprimals from the carcass at different external fat trim levels. Varia bles included those obtained on the slaughter floor (ultrasound fat thickne ss and ribeye area; estimated percentage of kidney, pelvic, and heart [KPH] fat; and warm carcass weight) and those obtained from carcasses following 24 h in the chill cooler (actual fat thickness, actual ribeye area, estimat ed percentage of KPH fat, warm carcass weight, and marbling score). At all different subprimal trim levels, percentage KPH was the first variable to e nter the model. In the models using measures taken on the slaughter floor, ultrasound fat thickness was the only other variable to enter the model. Ul trasound fat thickness increased R-2 and decreased residual standard deviat ion (RSD) in models predicting subprimals at 2.54-cm maximum fat trim; howe ver, at 1.27- and .64-cm trim levels, R-2 and RSD increased. Models using t he same two variables (except actual fat instead of ultrasound) in the cool er were similar to those using data from the slaughter floor. However, as m ore cooler measurement variables entered the models, R-2 increased and RSD decreased, explaining a greater amount of the variation in the equation. Ul trasonic evaluation on the slaughter floor may be of limited application co mpared with the greater accuracy found in chilled carcass assessment.