Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: June 13, 1996
Publication Date: N/A
Technical Abstract: A model was developed on the premise that in growing cattle, the ME requirement for maintenance is the sum of ME required to maintain the animal in a weight constant state, plus a fraction of the ME consumed above this requirement. The first requirement is referred to as the weight maintenance requirement (WMR), and the second as the production maintenance requirement (PMR). It is proposed that PMR is used to maintain additional metabolic and physiological machinery associated with greater amounts of ME intake. A time lag in changes in maintenance requirement with changes in nutrition is also proposed. Data on calves, 15 mo-old steers, and mature cows, that were fed different diets to maintain constant BW, were used to estimate WMR (kcal/kg BW). A published body composition model was used to predict PMR (kcal/kg BW) from data on rate of growth and ME consumption of steers. Results suggest that within diet, breed estimates of WMR were proportional to BW from birth to maturity, and estimates of PMR were proportional to ME intake expressed as a multiple of WMR. The body composition model was reformulated to use ME intake as its input, estimate ME for production (MEP) using breed estimates of WMR and PMR, and predict daily gain and composition from MEP. This model was evaluated on its ability to predict observed final weight in experiments where ME intake was recorded. Residual SD for six observed and predicted treatment means was 2.12 kg. Response in maintenance ME requirement and BW of mature cows fed to lose BW, then realimented, was similar to observed data on heat production and BW obtained at MARC. The model also works in a reverse manner to predict feed requirements to achieve a predetermined level of performance.