Brewer’s Grains on Growth Performance, Nutrient Digestibility, Blood Metabolites, and Fecal Microbiota in Simmental Crossbred Cattle Finished in Feedlot

This study was conducted to evaluate the impacts of brewer’s grains (BG) on growth performance, apparent nutrient digestibility, immunity, antioxidant capacity, and fecal microbiota of Simmental crossbred cattle and the economic benefits. A completely randomized design was adopted in our study. Twenty-four 15-month-old finishing Simmental crossbred male cattle (body weight, 433.43 ± 32.47 kg) were randomly assigned to three groups: control group (basal diet), 10% BG group (supplemented with 10% BG on a dry matter basis), and 15% BG group (supplemented with 15% BG on a dry matter basis). The trial lasted for 48 days, with serum samples collected on days 24 and 48 and fecal samples collected from days 46 to 48. Diets did not influence the average daily gain, dry matter intake, feed efficiency, and serum antioxidant parameters ( p > 0.05). The 15% BG group showed significantly higher acid detergent fiber digestibility ( p < 0.01) and elevated serum albumin levels on day 48 ( p = 0.047) compared with the control group. As for fecal microbiota, there was a lower Chao index ( p = 0.040) and a higher abundance of Romboutsia in the 15% BG group ( p = 0.025). Moreover, the feed costs of cattle fell by 9.34% and 14.66% after 10% and 15% BG supplementation, respectively. On the whole, BG supplementation demonstrated no significant effects on growth performance or animal health in finishing cattle. The 15% inclusion level demonstrated the greatest cost reduction potential. We, therefore, recommend adopting 15% BG supplementation as the optimal strategy to enhance economic returns in cattle production systems.