The effect of diets content 50% of corn silage and 50% of concentrate, resultant of combination of starch sources of high degradability (dried cassava hulls) and low degradability (corn), with nitrogen sources of high degradability (yeast) and low degradability (cottonseed meal and meat and bone meal), on pH, ammonia and microbial efficiency, was evaluated. Four Holstein steers (334 kg), fitted with ruminal and duodenal cannulas, in a 4 x 4 Latin Square experimental design were used. Intake was limited to 2% of live weight. The starch and N sources did not affect pH and N-NH3 concentration of ruminal fluid. The pH ranged from 6.02 to 6.67 and the average concentration of N-NH3 was 8.46 mg/100ml. Chemical composition of ruminal bacteria, the average flow of organic matter (OM), OM and N microbial did not differ among starch and N sources. The N flow was higher in diets of cottonseed meal, meat and bone meal than diets with yeast. Interactions of starch and N sources on OM truly degraded in the rumen (OMTDR) expressed as percentage of intake, were observed. The highest values of OMTDR were observed in the diet of cassava hulls and yeast, intermediate values in the diets of corn and cottonseed meal + meat and bone meal, and the lowest values of corn and yeast, cassava hulls and cottonseed meal + meat and bone meal. The microbial efficiency synthesis did not differ among starch and N sources evaluated, showing values of 57.2 and 30.9 g of microbial N/ kg of apparent and true ruminal OM degraded in the rumen.
cassava hulls; corn; cottonseed meal; microbial efficiency; nitrogen; starch
