GENETIC-RELATIONSHIPS BETWEEN PERFORMANCE-TEST TRAITS AND FIELD CARCASS TRAITS IN JAPANESE BLACK CATTLE

Genetic relationships between body measurements and growth traits at p erformance testing of bull calves and field carcass traits in Japanese Black cattle were estimated using a two-trait sire and maternal grand sire model with REML procedure. Covariances between performance test a nd carcass traits were obtained from across environment analyses. Perf ormance test traits included wither height, chest girth, chest depth, thurl width, body weight, and daily gain. For field carcass traits car cass weight, longissimus muscle area, rib thickness, subcutaneous fat thickness, yield estimate, and beef marbling score were measured on 83 29 steers and heifers. Heritabilities for performance test traits rang ed from 0.13 to 0.36, and for carcass traits from 0.39 to 0.55. The ba sis of selection at performance testing, daily gain, did not correlate well with carcass beef marbling score, the breeding goal, indicating that genetically superior bull calves in marbling may be culled at the end of testing. Chest girth at the middle and the end of testing corr elated well in the desired directions with all carcass traits. It is p ossible to improve total merit of the carcass by introducing chest gir th into performance testing.