The objective of this study was to assess the variation in the pH, ruminal ammonia, nitrogen compound balance (BN) and microbial synthesis (Nmic) of 12 Holstein cows distributed in three 4 × 4 Latin squares, fed diets containing soybeans in different forms: only soybean meal (SM - control diet), raw soybeans (RS), toasted soybeans (RST) and soybean meal plus 5% urea (SMU), using corn silage as bulk. The microbial protein synthesis was estimated using the purine derivatives in the urine and the milk. Blood samples and spot urine were collected, approximately four hours after the morning meals. There was effect of the diets on the urine volume (UV) and the urea excretion in the urine (UEU). The smallest urine volume (18.84 L) was observed with soybean meal + urea. Urea excretions in the urine were similar among the diets containing raw soybean (532.98 mg/kgPV) and toasted soybean (524.41 mg/kgPV) and differed between the soybean meal (561.56 mg/kgPV) and soybean meal + urea (575.71 mg/kgPV). The way of supplying soybean did not affect the nitrogen balance or the ureic nitrogen concentrations in the Plasma (NUP), but they had a significant effect on the ureic nitrogen in the milk (NUL) whose greatest mean was obtained with raw soybean (15.66 mg/dL). The means of alantoina in the urine (416.45 mmol/dia), milk (12.78 mmol/dia), total purine derivatives (468.30 mmol/dia), microbial protein synthesis (287.33 g/dia) and the efficiency of the microbial synthesis (133.06), expressed in g of CP/kg of consumed TNT did not differ among the diets. The diets tested did not the nitrogen balance or the microbial production, but the addition of raw soybean grains increased nitrogen levels in the milk.
milk; purines; soybean grains; urea plasma
