Prediction of components of steer carcasses using tritiated body water space, fat depth and fasted liveweight or carcass weight

Abstract

Chemical and dissectable components of the carcasses of 23 Hereford steers were related to whole body tritiated water space (T), fat depth at the 12/13th rib (FD), age, and 24 h fasted liveweight (LW) or cold carcass weight (CW). Fifteen steers were taken at intervals from a grazing experiment and were 15-22 months of age and 189-461 kg LW at slaughter. Six younger and two older steers were also used to expand the range to 3-33 months and 90-517 kg. All steers were taken from pasture 3 h after sunrise and deprived of feed and water thereafter. After 4 h, tritiated water was given intramuscularly and 20 h later blood was collected and the animals were weighed and slaughtered. One side of the carcass was minced and analysed for water, ash, nitrogen and fat. The other side was dissected into bone and boneless fractions. For each component the best single predictor and combinations of predictors which contributed significantly in the stepwise regression analysis (P < 0.05) are given. The use of T with LW or CW appreciably improved the precision of estimation of water, dry matter and chemical fat in the carcass. FD with LW or CW also improved the estimation of water, dry matter, fat and nitrogen. The combination of T, FD and CW best predicted water and fat. T, FD and LW best predicted fat in the carcass component of the live animal. The residual standard deviation of this regression was 3.3 kg v. 3.6 kg for LW and T, 6.1 kg for LW and FD, or 8.0 kg for LW alone.