225 Crude protein-content of fat-free muscle and viscera in sheep

The nutritional effects of variation in feed supply and subsequent compensatory gain can play a significant role in cattle and beef production, due to their effects on carcass quality and feed costs. A system that predicts changes in fat and protein content of muscle and viscera in animals of different life stages and nutritional histories could therefore assist management to optimize performance and reduce costs of feed. A method has been developed to simultaneously estimate body composition and nutrient requirements of ruminants. This method estimates body composition from the difference in energy balance derived from ME intake, and heat production from ME intake and protein content of muscle and viscera, but requires information on protein content of fat free mass in viscera and non-viscera “muscle” tissue. Data from the literature was combined with unpublished data from a study conducted in growing lambs. This experiment tested the effects of ad libitum intake of diets of varying energy density and added RUP on performance and carcass composition of lambs that had been previously restricted or unrestricted prior to a 12–13 week finishing phase, and both carcass and viscera components were chemically analyzed on an individual basis. On a fat-free basis, muscle crude protein averaged 20.8%; this value is in agreement with literature values, which lie between the range of 20–24% and which do not appear to vary substantially with age in postweaning sheep. In the same sheep, crude protein content of viscera averaged 15.6% on a fat-free basis; while data on visceral composition in the literature is limited, these values are within the range of available data. This data is use to parameterize functions describing growth of viscera and changes in heat production over time. This contributes to the method we have developed to estimate nutritional effects on body composition.