Consumo e digestibilidade de nutrientes de novilhos a pasto, suplementados com diferentes fontes de nitrogênio não proteico associado a enzima fibrolitica

Abstract

The aim of this study was to evaluate the intake and digestibility of nutrients in steers on pasture, supplemented with different sources of non-protein nitrogen . Three crossbred steers with average body weight of 350 kg and fitted with ruminal cannula were used, kept in individual paddocks with Urochloa brizantha pasture and distributed in Latin-square design 3x3 repeated in time. The animals were supplemented with 0,3% of the body weight. The treatments were based in protein supplementation with 38% of crude protein and different non-protein sources: UC (concentrate + conventional urea) and UP (concentrate + protected urea); the control treatment was mineral supplementation (SM). All the animals received 20g of fibrolytic enzyme (Fibrozyme TM, Alltech) daily supplied directly into the rumen. The intake of the animals was determined by the relation between the dry matter in the excreted feces and with the use of the internal marker (FDNi) and external marker (TiO2). The total apparent digestibility coefficients of the dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and organic matter (OM), were obtained from the relation between the total of nutrients retained and the fecal excretion of them. The total intake of the dry matter was influenced by the used nitrogen source (P<0,05) and it was bigger in animals supplemented with protected urea (7,42 Kg) in relation to the conventional urea (5,33 Kg). No significant differences were observed in the intake to the type of the supplementation (mineral or protein), what shows the rates of 5,51 and 6,37 Kg MS/day. The protein supplementation improved the DM, CP; NDF and OM digestibility coefficients; but the non- protein nitrogen source with slow release showed better coefficients to the digestibility coefficients (P<0,05) of DM, CP and OM when compared with the conventional urea supplementation. The slow release urea inclusion in protein supplements associated with fribrolytic enzyme to young bulls under grazing was better to the conventional urea, providing a bigger intake of forage and better apparent digestibility of the nutrients.