Consumo e digestibilidade em bovinos em pastejo com forragem de baixa qualidade recebendo níveis crescentes de compostos nitrogenados suplementares / Intake and digestibility in cattle grazing a low quality grass pasture and supplemented with increasing levels of nitrogenous compounds

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The objective of this work was to evaluate the effects of supplementation with nitrogenous compounds on intake, digestibility, and microbial protein synthesis in cattle under grazing during dry season. Five Holstein x Zebu steers fitted with rumen and abomasums canullae and with average initial live weight (LW) of 236kg, were used. The animals grazed five Brachiaria decumbens Stapf. paddocks and had free access to water and mineral. The experiment was carried out according to a 5 x 5 Latin square design, with five treatments and five experimental periods. The treatments were formed according to supplementation levels of nitrogenous compounds: 0; 0.35; 0.75; 1.05 and 1.40 g of crude protein (CP)/ Kg LW. A mixture of urea, ammonium sulfate and albumin (4.5:0.5:1.0) were used as nitrogen supplement. The daily quantity of supplement was calculated on animals LW at the beginning of each experimental period. The average CP levels in the diet were 7.39, 8.92, 10.98, 12.55 and 13.62% as dry matter (DM) basis, which corresponded to supplementation levels of 0, 0.35, 0.75, 1.05 and 1.40 g CP/kg LW, respectively. Linear- response-plateau (LRP) relationships were observed between intake estimates and diet CP levels (P<0.05). The LRP pattern showed the increase of intake until CP levels close to 9%, as dry matter basis. The estimates became unchangeable from this level. The total and ruminal digestibility coefficients of DM and neutral detergent fiber (NDF) and the diet level of total digestible nutrients presented a positive linear pattern (P<0.10) according to diet CP levels. The rumen pH was not affected by CP levels (P>0.10). The rumen ammonia nitrogen (RAN) concentration was linearly increased by diet CP levels (P<0.01). This variable assumed the value of 8.00 mg/dL of rumen fluid when the intake estimates reached the maximum values (close to 9 % of CP). The urinary excretion of nitrogen, the serum urea nitrogen concentration, the apparent nitrogen balance and the relative nitrogen balance were linearly increased (P<0.01) by diet CP levels. The different CP levels in the diet did not affected (P>0.10) the estimates of abomasums flow of microbial nitrogenous compounds (NMIC) and the efficiency of microbial synthesis. The NMIC and nitrogen intake became identical on 9.46% of CP in the diet. It is recommended the nitrogenous compounds supplementation to raise the CP level of the diet to 9%, as dry matter basis. Under these circumstances, the utilization of low-quality forage by grazing animals would be optimized.

ASSUNTO(S)

nutricao e alimentacao animal pastejo nitrogenous compounds disgestibilidade grazing compostos nitrogenados digestibility

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