Prediction of traits at constant finish for performance-tested beef cattle

The relationships of performance in time-constant intervals to that in the full feedlot phase of production and of bulls to steers were studied. Monthly records on 43 bulls and 48 steers for gain, ultrasonic backfat, weight and hip height were collected in the period postweaning to an estimated 6 to 7 mm subcutaneous backfat. Information gathered in the first 140 d (performance test) was used to predict feedlot performance to Canada grade A1 finish (7 mm backfat). Traits predicted were days to market finish (DM), weight at market finish (WM), relative growth rate (RGR) and economic rate of maturing (Ke). Economic maturing rate was derived as an estimator of growth relative to weight at fixed body composition (7 mm backfat). Prediction equations were developed by stepwise regression which explained 91, 92, 83 and 79% of the variation in DM, WM, RGR and Ke, respectively. Ratios for steer to bull values for DM and WM were .901 and .928, respectively. It was concluded that accurate prediction of DM, WM, RGR and Ke is possible from information on weight and backfat measurements as currently gathered in many test stations. Prediction of RGR and Ke could be improved by inclusion of heart girth measurements. Differences among animals in Ke are easier to estimate than are differences in rate of maturing, and may be of greater relevance for the genetic improvement of livestock.