Using Ultrasound, Linear Measurements and Live Fat Thickness Estimates to Determine the Carcass Composition of Market Lambs

Abstract

Thirty lambs were evaluated live for compositional differences by use of real-time ultrasound, linear measures and by fat thickness estimations by a trained livestock evaluator. The lambs were slaughtered using conventional methods and, after chilling for 24 h, USDA yield and quality grades as well as longissimus muscle area between the 12th and 13th ribs were recorded. The carcasses then were fabricated into primals, trimmed to .64 cm of fat, cut into retail cuts, trimmed to .25 cm and finally to boneless and semi-boneless retail cuts. Weights were recorded at each step of fabrication. Neither ultrasound fat thickness nor ultrasound longissimus muscle area was highly correlated (r = .62 and .36, respectively) to its corresponding carcass measurement Regression equations for predicting yield of closely trimmed retail cuts using ultrasound and linear measures had R² values ranging from .29 to .41 without estimated fat thickness and R² values from .36 to .57 including estimated fat thickness. Ultrasound fat thickness was much more useful for predicting composition when the carcass cutability endpoint evaluated was closely trimmed retail cuts. Copyright © 1989. American Society of Animal Science . Copyright 1989 by American Society of Animal Science