Effects of Bacillus licheniformis 809 and Bacillus subtilis 810 supplementation on in situ degradation of a high-concentrate byproduct-based diet in forage-fed beef cows

Abstract This study evaluated the effects of Bacillus-based direct-fed microbial (DFM) supplementation on in situ nutrient disappearance and degradability of high-concentrate diets. Fifteen rumen-cannulated cows were used in a completely randomized design. Treatments consisted of a forage-based diet plus 500 g of protein-mineral (390 g dried distillers grain + 110 g vitamin-mineral mix; as-fed basis) supplement mixed with 1) 3 g (as-fed basis) of a Bacillus-based DFM containing Bacillus licheniformis 809 and B. subtilis 810 (BAC; n = 7; 2.2 × 109 CFU of the mixture/g; Bovacillus, Novonesis, Lyngby, Denmark), or 2) without BAC (CON; n = 8). Samples of four high-concentrate, byproduct-based diets (A, B, C, and D) were collected from a commercial feedlot in South Africa. These diets were composed of hominy chop, corn silage, Eragrostis hay, cottonseed cake, molasses syrup, urea, limestone, salt, and a mineral–vitamin premix, and subsequently dried for analysis. From days 28 to 32, each diet was placed in Dacron bags and introduced through the cannulas. Residuals were dried, and DM, NDF, and ADF content were determined. No treatment × hour interactions were detected (P ≥ 0.11) for nutrient disappearance in any of the diets. Dry matter and NDF disappearance were greater (P ≤ 0.05) in diets A, C, and D for cows fed BAC compared with CON, whereas no differences were observed in nutrient disappearance from diet B (P ≥ 0.33). Similarly, ADF disappearance was greater in diet A (P = 0.04) and tended to be greater in diet C (P = 0.07) in BAC vs. CON and was unaffected by treatment in diets B and D (P ≥ 0.13). Combining all four diets, degradation of fraction B (degradable fraction; total pool disappearing at a measurable rate) of DM was greater for BAC vs. CON (P = 0.02), whereas degradation of fraction C (undegradable fraction; total unavailable pool in the rumen) tended to be lower for BAC than CON (P = 0.08). Evaluating NDF degradation across diets, the degradation of fraction B tended to be greater for BAC vs. CON (P = 0.10), whereas effective degradability was greater for BAC compared with CON (P = 0.02). No treatment effects were observed on NDF fraction C (P = 0.18) or degradation rates (% per h; P = 0.92) between treatments. Collectively, feeding a Bacillus-based DFM improved in situ disappearance and the potentially degradable nutrient pool of a high-concentrate byproduct diet in forage-fed beef cows.