Prediction of postweaning subcutaneous fat deposition in feedlot steers

Linear measurements of height, length, width and depth were obtained from 66 weanling feedlot steers of Angus, Hereford, Angus x Hereford and Hereford x Angus dams bred to Angus or Hereford sires. Ultrasonic fat estimates were obtained on a biweekly basis thereafter until the animals were slaughtered. Asymptotic curves were fitted through biweekly fat estimates up to 12 mm and extrapolated to predict levels of fat through 450 days postweaning. These curves were compared to curves that were fitted through all biweekly fat estimates. Deviations of the 12 mm curve from the lifetime curve were used in regression analysis. Weaning age was important (P<.05) in predicting deviations between the curves up to 20 mm. Fat estimates at weaning were related (P<.05) to deviations in postweaning days necessary to reach subsequent levels of fat on respective curves. Postweaning days necessary to reach 12 mm on the 12 mm curve was highly related (P<.001) to differences in the parameter estimates of the equations corresponding to the curves. Width at weaning was also highly related (P<.001) to these differences. Depth at weaning was related to a lesser extent (P<.01). R² for models predicting differences in parameter estimates ranged from 48 to 70%.