Intake and total and partial digestibility of nutrients, ruminal pH and ammonia concentration and microbial efficiency in beef cattle fed with diets containing sorghum (Sorghum bicolor (L.) Moench) silage and concentrate in different ratios

The intake and total apparent and partial digestibility of nutrients, ruminal pH and ammonia concentrations and efficiency of microbial synthesis were evaluated in beef cattle fed diets containing sorghum silage and concentrate in the following ratios: 800:200, 650:350, 500:500 and 350:650 g/kg, in a total dry matter basis. Four crossbred Holstein x Zebu rumen and abomasum fistulated steers, 224 ± 23 kg-average initial live weight, were assigned to a 4 × 4 Latin square design. Chromic oxide was used as marker to estimate fecal and abomasal dry matter flows, and microbial efficiency was determined from purine basis. The intakes and total apparent digestibilities of DM, OM, CP and NFC and TDN intakes increased linearly (P < 0.01) with the increase of concentrate in the diet. NDF intake and total apparent digestibility decreased linearly (P < 0.05). The apparent ruminal and intestinal digestibilities of DM, OM, CP, NDF and NFC were not influenced (P > 0.05) by increasing the concentrate in the diet, and the mean values were 619 and 381 (g/kg); 656 and 349; 391 and 498; 902 and 79 and 600 and 399 (g/kg DM), respectively. There was a quadratic effect of collection time (P < 0.01) on the concentration of ruminal NH3–N and pH, considering maximum and minimum values of 14.89 mg/dL and 6.16 at 2.39 and 4.28 h after feeding, respectively. The efficiency of microbial synthesis, expressed in different ways was not influenced (P > 0.05) by treatments, with 11.39 g CPmic/100 gTDN on average. Although increasing concentrate levels in the diets resulted in higher intakes of almost all nutrients, this did not result in alterations in the ruminal variables evaluated.