BREED DIFFERENCES AND GENETIC-PARAMETERS FOR BODY-COMPOSITION TRAITS IN BEEF-CATTLE

The recent scientific literature was reviewed to summarize breed diffe rences and genetic parameters for carcass traits in beef cattle. Herit ability estimates were generally moderate to large, suggesting good po tential for accurate genetic selection for a given individual carcass characteristic. However, effectiveness of multiple-trait selection for some trait combinations could be slowed by genetic antagonisms betwee n traits, suggesting the use of terminal breeding systems with complem entary sire and dam genetic types. Individual and maternal heterosis e stimates from age-constant analyses were numerically positive for most carcass traits, although estimates from weight-constant analyses were generally nonsignificant. Potential contributions to improved carcass composition from crossbreeding would primarily result from genetic co mplementarity rather than heterosis. Considerable variation exists bet ween breeds for body composition, and breed rankings vary across diffe rent traits. Studies have consistently indicated reduced meat tenderne ss for Bos indicus compared with Bos taurus breeds. Some differences i n breed rankings for marbling vs tenderness were noted. If the U.S. be ef industry shifts toward a more value-based marketing system, some ge netic concerns will include 1) an apparent antagonistic relationship b etween marbling and cutability across breeds and within some breeds, 2 ) inconsistency of beef tenderness, particularly in Bos indicus cattle , 3) the effect of increased leanness on female reproductive performan ce, and 4) the extent to which terminal breeding systems can be used.