R. Bras. Zootec.01/Jun/2000;29(3):921-9.
Concentrate levels in the crossbred F1 Simental x Nellore bulls diets.: 2. Nitrogenous balance, microbial efficiency and ruminal parameters
DOI: 10.1590/S1516-35982000000300038
The effects of dietary concentrate levels were evaluated on the microbial synthesis efficiency, the nitrogenous compounds balance, the ammonia concentrations and the ruminal fluid pH, the ruminal digesta passage rate and the endogenous losses of nitrogen compounds (N). Five F1 Simental x Nellore bulls fistulated in the rumen, abomasum and ileum, full fed diets with 25.0; 37.5; 50.0; 62.5; and 75.0% of concentrate and allotted to 5×5 Latin square, were used. The ammonia concentrations and the ruminal pH were determined in ruminal fluid samples immediately collected before and 2; 4; 6; and 8 hours after feeding. The unicompartimental model, using chromic oxide as indicator, determined the passage rate. The microbial synthesis efficiency, express in relation to the organic matter degraded in the rumen (OMDR), to the total carbohydrates degraded in the rumen (CHODR) and to TDN, was influenced in quadratic way by the concentrate levels in the diet, estimating maximum values of 41.22 gNmic/kg OMDR, 39.89 gNmic/kg CHODR and 17.33g CPmic/100 g NDT, estimated for 52.16, 60.44, and 56.63% of concentrate in the diet, respectively. When express in DMmic/kg CHODR, the efficiency linearly increased as the concentrate level increased. Values of 5.15 g N/kg ingested DM for the fecal metabolic nitrogen and 422 mg N/kg0,75 for the total endogenous losses were estimated. The maximum ammonia concentrations for all treatments were observed at 3,6 hours after feeding. The passage rates of .052, .052, .055, .055, and .042.h-1 were obtained for all treatments with 25.0, 37.5, 50.0, 62.5, and 75.0% of concentrate, respectively. The maximum microbial efficiency ranged from 52 to 60% of concentrate.
Keywords: concentrate; microbial efficiency; passage rate; ruminal ammonia; ruminal pH