IMPLICATIONS OF GENETIC CHANGES IN BODY-COMPOSITION ON BEEF-PRODUCTION SYSTEMS

Changing the body composition of beef has implications for the entire beef production system. The dynamic nature of an animal's body composition and the production system itself make predictions of the implications of genetic change in body composition difficult. The cow-calf, stocker, and feeder segments of the production system mill be affected differently. Leaner cattle tend to be slaughtered at heavier weights. Heavier weights effectively reduce composition differences of slaughter beef to less than the genetic differences. The effects of four pricing scenarios on slaughter weight and composition were evaluated for two leaner genotypes, one with no change in marbling and one with reduced marbling. A; genetic difference of 1.0 yield grade at the same carcass weight resulted in slaughter beef that differed by .4 to 1.0 yield grade because of increased slaughter weights. Separate analyses suggested the stocker segment of beef production will be least affected by changes in body composition. Genotypes that are best fitted to slaughter requirements will have the most flexibility in types of stocker systems that can be used. The cow-calf segment of beef production has several options to adapt to leaner cattle. Management to reduce nutritional stress on leaner cows may be required by some producers. Increased selection for reproductive traits in cow genotypes may be needed. An alternative to selection for reproduction is terminal crossing to partially disassociate the slaughter animal's genotype from the cow's genotype.