Resumo

FRANCO, Gumercindo Loriano; ANDRADE, Pedro de; BRUNO FILHO, José Roberto  e  DIOGO, José Mauro da Silva. Ruminal parameters and NDF forage disappearance of supplemented steers under grazing, during the rainy season . R. Bras. Zootec. [online]. 2002, vol.31, n.6, pp. 2340-2349. ISSN 1806-9290.  http://dx.doi.org/10.1590/S1516-35982002000900024.

The objective this work was to evaluate the effect of protein supplements varying in ruminal degradabilities (high-75%, medium-55% and low-35%) fed at three levels (0.5, 1.0 and 1.5 kg/day) on ruminal pH, N-NH₃ and NDF degradability of forage, with steers grazing Brachiaria brizantha cv. Marandu during rainy season. The experiment design was a randomized complete block with three replications (grazing periods) and the supplemented treatments were arranged in a factorial 3 x 3. Ten rumen-fistuled crossbred steers with 463 kg live weight, were used. The nylon bag technique and grazing simulation were used to verify the forage and supplement ruminal degradation. Ruminal pH and N-NH₃ were determined along two consecutive days. There were no differences between the treatments (supplement source and level) on forage NDF degradability. However, there were differences for the incubation times, with the higher degradability (67.58%) at 96 hours of incubation. No difference for the ruminal pH and time x treatment interaction were observed, but there were differences for the time of sampling. The pH varied ranged from 5.7 to 7.4, with an average of 6.48. The N-NH₃ values were higher for the supplements with high protein degradability. The first hours after supplementation showed the highest values of N-NH₃, and the peaks of N-NH₃ in the morning were higher than the peaks of the afternoon. Fiber degradation was not affected by rumen N-NH₃ concentrations.

Palavras-chave : degradability; NDF; N-NH₃; nylon bag; protein; tropical forage.