Desempenho nutricional de bovinos de corte em pastejo suplementados com grão de milho destilado de alta proteína

Abstract

The objective of this study was to evaluate the effects of including high-protein distilled grain (DDGAP; 43% crude protein (CP), dry matter basis) in supplements for grazing beef cattle, on the intake and nutritional performance of the animals. DDGAP is one of the co-products of ethanol distillation from corn grain, and its production process guarantees DDGAP a high content of crude protein (CP). Five Nellore bulls with initial mean body weight (BW) of 413.5 ± 32 kg, were distributed in a 5 x 5 Latin square design. They were tested in five experimental periods, inclusions of 0, 70, 145, 220 and 330 g DDGAP /kg concentrate supplement (dry matter basis (DM)) for grazing beef cattle (pasture 7.46% crude protein (CP), dry matter basis) in the dry/water transition period. Concentrated supplements were provided in the amount of 6 kg/animal/day (natural matter basis), equivalent to 1.5% BW/day, once a day. The inclusion of DDGAP did not affect total DM (P = 0.76) and forage (P = 0.76) intakes, organic matter digestibilities (P = 0.33) and CP (P = 0.33) , and consequently, did not affect the consumption of digestible organic matter (P = 0.76). The inclusion of DDGAP linearly increased CP intake (P = 0.07) due to increased rumen non-degradable protein intake (PNDR; P < 0.01), as rumen degradable protein intake was not affected (P = 0.07) by the inclusion of DDGAP. Ruminal pH showed a quadratic behavior (P = 0.04) with the inclusion of DDGAP, with a maximum value observed with 220g of DDGAP /kg supplement. Although the inclusion of DDGAP linearly reduced the ruminal concentration of ammoniacal N (P = 0.03), no effects were observed on serum urea-N levels (P = 0.13), urinary urea excretion (P = 0.11), body N retention (P = 0.11), body N retention efficiency (as a proportion of ingested or absorbed N; P > 0.11), and microbial protein intestinal flow. These findings indicate that the lower ruminal ammonia production with the inclusion of DDGAP was not enough to improve the N retention efficiency, as a compensation probably occurred with the higher hepatic urea production via amino acid catabolism in animal tissue. The inclusion of DDGAP in high intake supplements (1.5% of BW/day) although increasing PNDR intake and reducing ruminal ammonia concentration, does not affect intake, diet digestibility and body N retention efficiency. It is recommended the inclusion of up to 330g DDGAP /kg DM of high consumption supplement for beef cattle grazing in the dry-water transition.