Associative effects of external buffers and plant secondary metabolites on ruminal fermentation during an induced subacute ruminal acidosis challenge in beef steers

Subacute ruminal acidosis (SARA) is a prevalent problem in cattle consuming highly fermentable diets. It was hypothesized that a novel feed additive (BRIC) containing alkaline salts and traces of plant secondary metabolites may modulate ruminal fermentation. The experiment evaluated four treatments during an induced SARA protocol. Treatments were (DM basis): 1) sodium bicarbonate at 1.2% (BICARB), 2) a commercial buffer at 1.2% (BRIC), 3) a blend of tannins and saponins at 0.15% (BXS), and 4) a combination of 1.2% BRIC plus 0.15% BXS (BRIC-BXS). Eight ruminally cannulated steers were used in a replicated 4 × 4 Latin square with four 16 d periods and ad libitum access to a basal diet (DM basis: 35.5% corn silage, 22.0% bermudagrass hay, 21.5% corn grain, 18.7% cottonseed meal, 1.0% mineral-vitamin premix and treatment supplements). For the BXS and BRIC-BXS, dietary ingredients were proportionally increased to achieve 100% of the diet DM minimizing changes in basal diet TMR composition. The study included baseline measurements (3 d), treatment adaptation (7 d), feed restriction (1 d at 50%), SARA challenge (1 d), recovery (4 d), and washout (20 d). An ex vivo batch culture incubation was conducted on the last day of baseline and the last day of recovery. Ruminal fluid was collected daily pre-feeding (0 h) and postfeeding (4 h), and every 2 h for 14 h during the SARA challenge to evaluate pH, volatile fatty acids (VFA), and ammonia nitrogen concentration (NH3-N). Data were analyzed as a replicated 4 × 4 Latin square, with data collected during the SARA challenge analyzed as repeated measures. Feeding BRIC and BRIC-BXS led to greater NH3-N (P < 0.01) in the ex vivo incubations. Postfeeding ruminal pH was lower during adaptation (P = 0.02) and feed restriction (P = 0.01) for BXS compared with the buffers. During pre-feeding feed restriction, NH3-N and butyrate were greater (P < 0.05) for BRIC compared with BXS. Additionally, BXS exhibited greater propionate and lower branched-chain VFA (P < 0.05) compared with the buffers. During SARA, butyrate proportions were greater (P < 0.01) for BRIC compared with BICARB. The responses indicate that BRIC favored butyrate production, potentially enhancing ruminal epithelial function, whereas BXS favored propionate, potentially supporting glucogenic pathways.