Dietary Nitrogen Effect on Ruminant Heat Increment

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Abstract
The mean fasting metabolic rate of six mature wethers was 70.3±2.6 W.kg.0.75 kcal. Fasting measurements were made after 84 hr. post-feeding, using an R.Q. of 0.73 or lower as the indication of fasting. The heat increment of five sheep was measured on six isocaloric diets. The diets contained proteins at levels of 3.6, 9.4, 16.3 and 21.6%, and urea at levels equivalent to 9.8 and 16.3% protein. The heat increment response to increasing levels of dietary protein was curvilinear, with the highest heat increments for the intermediate level protein diets. The heat increment on protein diets was higher than on isonitrogenous urea diets. There was no relationship, among diets, between nitrogen balance and heat increment.