Efeito de um aditivo microbiano dietético à base de bacillus no desempenho, parâmetros sanguíneos, características fecais, morfometria ruminal e expressão gênica intestinal de touros de corte em terminação

Abstract

Feed additives are an efficient strategy to improve performance and nutrient utilization in beef cattle. Among these alternatives, Direct-Fed Microbials (DFMs) have demonstrated potential to modulate ruminal and intestinal microbiota, promoting benefits for both animal health and productivity. The effects of a DFM containing Bacillus licheniformis and Bacillus subtilis on performance, ruminal morphometrics, intestinal gene expression, and blood and fecal parameters of feedlot bulls were evaluated. Nelore × Angus bulls (n = 144; initial body weight = 401 kg ± 45.5 kg) were randomly distributed into 36 pens (4 bulls/pen and 18 pens/treatment) following a completely randomized design. A finishing diet based on ground corn was offered for ad libitum intake twice daily for 84 days, containing the following treatments: 1) control (no DFM); 2) DFM (B. licheniformis and B. subtilis) at 6.4 × 10⁹ CFU (2 g) per animal. Data were analyzed using the MIXED procedure of SAS, with pen as the experimental unit, treatment as a fixed effect, and pen nested within treatment as a random effect. For fecal parameters (two collections), the effect of collection and its interaction with treatment were included in the model. Statistical differences were considered significant at p ≤ 0.05. Trends were mentioned if p-value was greater than 0.05 but less than or equal to 0.10. Bulls receiving DFM treatment reduced dry matter intake (P ≤ 0.01), did not differ in average daily gain (ADG; P = 0.39), and improved feed efficiency (P = 0.05) by 6% compared to the control. Other performance variables, final weight, hot carcass weight, and hot carcass yield, did not differ (P > 0.10). Regarding blood parameters, animals receiving DFM had a 6.2% reduction in plasma urea (P = 0.02). Glucose, haptoglobin, and lipopolysaccharides did not differ (P > 0.10). Ruminal morphometrics were not influenced by treatment (P > 0.10). DFM use tended to reduce fecal starch (P = 0.06). The collection period influenced fecal pH and starch (P < 0.01), with higher starch and lower pH in the second collection. DFM increased gene expression of tryptophan hydroxylase 1 (P = 0.02) and superoxide dismutase 1 (P =0.03) in the duodenum of the animals. Supplementation with DFM based on B. licheniformis and B. subtilis for Nelore × Angus bulls in the finishing phase reduces dry matter intake, does not influence ADG, improves feed efficiency, and increases the expression of genes important for duodenal function.