The effect of a Bacillus-based probiotic on feed intake and digestibility of a forage and a feedlot diet in Bos indicus steers

Ionophores are commonly used in feedlot rations to improve feed efficiency and reduce acidosis risk, particularly during the transition from forage to cereal-rich diets. With increasing concerns over non-therapeutic antibiotic use, interest in probiotics as potential alternative has grown. This study evaluated the effect of a Bacillus-based probiotic on feed intake and total tract nutrient digestibility in Bos indicus steers. Two diets were tested: a high-fibre forage diet (Rhodes grass hay, 690 g/kg neutral detergent fibre (NDF)) and a feedlot diet (20 % Rhodes grass hay, 40 % finisher pellet, 30 % peanut hull fibre pellet, 10 % ground barley, 470 g/kg NDF). Twelve steers (267 ± 7.5 kg) were blocked by body weight and randomly assigned to a control (n = 6) or a probiotic-supplemented group (n = 6) receiving 3 g per steer of Bacillus licheniformis 809 and Bacillus subtilis 810 (3.2 × 10⁹ CFU/g) for the trial duration. Each diet was fed for 34 days, followed by a 7-day sampling period for total faecal and urine collection. Probiotic supplementation increased organic matter digestibility by 7.8 % and NDF digestibility by 8.4 %, resulting in a significant increase (P < 0.05) in digestible fibre intake on the forage diet. No effects on intake or digestibility were observed on the feedlot diet. Probiotic supplementation did not affect nitrogen metabolism. While intake was unchanged, improved fibre digestibility suggests Bacillus-based probiotics can enhance nutrient utilisation in forage-based diets, potentially improving performance in high-fibre diets.