Effects of nitrogen sources degradability on the use of the fiber, nitrogen and starch of bovine diets

O objetivo do experimento foi avaliar os efeitos da utilização do farelo de soja ou da glutenose sobre a degradabilidade ruminal in situ dos constituintes de dietas compostas por feno, milho e as fontes nitrogenadas fornecidas para bovinos adultos com 650 kg de peso. A glutenose foi considerada fonte nitrogenada de baixa degradabilidade e o farelo de soja, de média degradabilidade ruminal. As degradabilidades potenciais obtidas para o nitrogênio foram 39,7 e 90,3% e as degradabilidades efetivas 35,7 e 62,9%, respectivamente, para glutenose e farelo de soja. Utilizou-se a fibra mordente para determinar a taxa de passagem das dietas e obtiveram-se 6,6%/h para dietas com farelo de soja e 2,4%/h para dietas com glutenose. Não houve diferença na degradabilidade potencial da matéria seca do feno, nas frações A, B, C e na taxa de degradação, mas a degradabilidade efetiva da matéria seca foi inferior para as dietas com farelo de soja (29,3 vs 40,6%). Os demais ingredientes, à exceção do milho, apresentaram acentuadas diferenças entre as dietas nas variáveis de degradabilidade, na taxa de degradação e na degradabilidade efetiva do nitrogênio, com inferioridade na dieta com glutenose. O milho diferiu apenas quanto à degradabilidade efetiva do nitrogênio, superior na dieta com glutenose (68,7 vs 56,3%). O amido do milho apresentou menor degradabilidade efetiva na dieta com farelo de soja (52,5 vs 68,0%), sendo a degradabilidade efetiva da fibra do feno também inferior para essas dietas (27,3 vs 43,2%). Concluiu-se que fontes nitrogenadas com distintas degradabilidades podem afetar tanto a degradabilidade da fibra do volumoso quanto à do amido da própria fonte nitrogenada e do milho das dietas.The objective of this experiment was to evaluate the effect of utilization of soybean meal or corn gluten meal on in situ ruminal degradabilities of diets, based on coastcross hay, corn and one of the nitrogen sources, fed to bulls, with average weight of 650 kg. Corn gluten meal was considered as a nitrogen source of low degradability and the SBM as intermediate ruminal degradability. They presented nitrogen potencial degradability of 39.7 and 90.3% and effective degradability of 35.7 and 62.9, for the corn gluten meal and soybean meal, respectively. It was used mordant fiber to determine the rate of passage of the diets and it was obtained 6.6%/h for diets with soybean meal and 2.4%/h for diets with corn gluten meal. There was no difference in the potential degradability of the dry matter of the hay, in the fractions A, B, C and in the degradation rate, but the effective degradability of dry matter was lower for diets with soybean meal (29.3 vs 40.6%). For the nitrogen the ingredients, except corn, presented marked differences among diets in the fractions of degradability, in the degradation rate and in the effective degradability, being inferior in the diet with corn gluten meal. The corn differed only in the effective degradability of the nitrogen, being superior in the diet with corn gluten meal (68.7 vs 56.3%). The corn-starch presented lower effective degradability in the diet with soybean meal (52.5 vs 68.0%) and the effective degradability of the hay fiber also was inferior for these diets (27.3 vs 43.2%). It was concluded that nitrogen sources with distinct degradabilities can affect the degradability of the fiber of the roughage, as well as the degradability of the starch of the nitrogen source or the corn of diets