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 i n 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 s ize, genotype, sex, and matching dietary nutriment to nutrient require ments for lean tissue growth. On the average, current production strat egies produce carcasses that contain excessive amounts of fat, impedin g optimized efficiency at all levels of production. Use of large-matur e-size terminal sires, feeding rumen-escape dietary protein, feeding i ntact males, and slaughtering at appropriate weights all improve compo sition of gain. Improvements of 10 to 20% in rates of gain and efficie ncy of nutrient use and similar reductions in feed cost can be achieve d with each of these management strategies. Results from several exper iments demonstrate that these effects are additive and provide a measu re 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 concu rrently reduce the amount of nitrogen waste returned to the environmen t. Potential for further manipulation of composition exists through mo re accurately defining nutrient requirements of growing lambs and thro ugh use of metabolism modifiers. Maintaining a competitive, profitable , and sustainable sheep industry depends on continued improvement of p roduction efficiency, preferably in systems with high reproductive rat es.