Impact of composition manipulation on lean lamb production in the United States.

At present less than 30% of the market lambs slaughtered in the United States meet the requirements for leanness and muscling as specified in the "Certified Fresh American Lamb" program established in 1990 by the American Sheep Industry Association (ASI). Carcass composition of slaughter lambs is determined by stage of growth relative to mature size, genotype, sex, and matching dietary nutriment to nutrient requirements for lean tissue growth. On the average, current production strategies produce carcasses that contain excessive amounts of fat, impeding optimized efficiency at all levels of production. Use of large-mature-size terminal sires, feeding rumen-escape dietary protein, feeding intact males, and slaughtering at appropriate weights all improve composition of gain. Improvements of 10 to 20% in rates of gain and efficiency of nutrient use and similar reductions in feed cost can be achieved with each of these management strategies. Results from several experiments demonstrate that these effects are additive and provide a measure of the true genetic capacity for protein accretion rate in growing lambs. Adoption of these management strategies will allow lambs to be slaughtered at a younger age, which may improve meat quality and concurrently reduce the amount of nitrogen waste returned to the environment. Potential for further manipulation of composition exists through more accurately defining nutrient requirements of growing lambs and through use of metabolism modifiers. Maintaining a competitive, profitable, and sustainable sheep industry depends on continued improvement of production efficiency, preferably in systems with high reproductive rates.