OPTIMUM TEST PERIOD AND ASSOCIATIONS BETWEEN STANDARD 140-DAY TEST PERIOD AND SHORTER TEST PERIODS FOR GROWTH-RATE IN STATION TESTED BEEF BULLS

The records of 2034 beef bulls representing 931 sire families from ten breeds tested at Ellerslie Test Station, Alberta, Canada, from 1974 t o 1987 were analyzed to investigate the feasibility of selecting a sho rter test period and study the associations between the growth rate in the standard 140-day test period and that in shorter test periods for accurate evaluation of growth potential of young beef bulls in test s tation. The results indicated that the period between day 28 and day 1 12 of the standard test was less affected by herd of origin compared w ith the standard 140-day test period and therefore could be considered as the short optimum test period. Average daily gain in this period w as least affected by herd of origin, and had relatively high heritabil ity which would ensure satisfactory selection response. In order to pr operly evaluate growth potential of beef bulls and economically make u se of the testing facilities, it would be appropriate to have an adjus tment period of 56 days (original 28 days plus the first 28-day period of the standard test) followed by a test period of 84 days (between d ay 28 and day 112 of the standard test). Such a test would result in r eduction in management costs while providing a more accurate evaluatio n of growth potentials of young beef bulls.