Effects of Nonstructural Carbohydrate, Urea and Soluble Protein Levels on Microbial Protein Synthesis in Continuous Culture of Rumen Contents

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Abstract
Two experiments were conducted to examine the effects of nonstructural carbohydrate levels on ruminal nitrogen utilization and to study the effects of dietary urea and protein solubility on ruminal microbial protein synthesis. In Experiment 1, three isonitrogenous diets with differing starch to cellulose ratios provided the substrate for microbial metabolism. The major nitrogen sources in the diets were peanut meal and urea. Acid detergent fiber (ADF) digestibility increased with decreasing starch levels in the diets, while dry matter (DM) digestibilities were not affected by treatments. Although digestion coefficients for dietary crude protein, which ranged from 94 to 98%, were not affected by level of dietary starch, substituting starch for cellulose decreased ammonia levels and increased microbial protein synthesis. The high starch diet in Experiment 1 was used as the basal diet in Experiment 2. Four isonitrogenous diets with differing levels of dietary urea and protein solubility supplied the substrate for microbial metabolism. There were two levels of protein solubility, low and high, each with or without urea. Protein solubility was varied by using heated or unheated peanut meal. ADF digestibilities were not affected by urea feeding or protein solubility. The DM digestion coefficients were slightly lower for the urea diets than the non-urea diets. Ammonia concentrations were higher on the urea diets than on the non-urea diets. There were no effects of urea or protein solubility on microbial growth when expressed as g crude protein synthesized per 100 g DM digested. However, grams of microbial nitrogen synthesized daily was significantly lower for the urea diets. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.