PSV-2 Effects of Saccharomyces cerevisiae fermentation product and Bacillus Direct-Fed Microbials on intake and ruminal parameters of heifers fed corn silage-based diets.

Abstract This experiment evaluated dry matter intake (DMI) and ruminal fermentation and in situ parameters of beef heifers offered corn silage-based diets and supplemented with Saccharomyces cerevisiae fermentation product (SC) and Bacillus-based direct-fed microbial (DFM). Sixteen rumen-cannulated Angus heifers (initial BW = 184 ± 9.5 kg) were housed in individual dry-lot pens and allocated to an incomplete 4 × 4 Latin Square design (4 simultaneous squares). Treatments were arranged in a 2 × 2 factorial design, in which factor 1 was the inclusion or not (SC0) of 14 g/heifer daily of a SC (SC14) and factor 2 was the inclusion or not (BAC0) of 4.36 g of a DFM containing Bacillus licheniformis 809 and B. subtilis 810 (BAC4). The experiment periods last 27 days + 6 days of washout. Heifers were fed a total mixed ration (TMR) daily containing corn silage, corn grain, soybean meal, DDGS, soybean hulls, and a mineral-vitamin mix. From day 22 to 26, 9 g of TMR were placed in nylon bags, introduced through the cannulas, and incubated in triplicate in the rumen of each heifer for 0, 1, 3, 8, 12. 24, 48, 72, and 96 h. On day 27, ruminal fluid was collected prior to feeding (0 h) and at 4, 8, and 12, post-feeding to evaluate volatile fatty acids (VFA). No BAC × SC effects (P ≥ 0.99) were detected for DMI, whereas the inclusion of SC14 decreased (main effect; P = 0.04) DMI vs. SC0 heifers and BAC4 increased (main effect; P = 0.05) DMI vs BAC0 (Fig. 1). No treatments × time (P ≥ 0.40) or BAC × SC effects (P ≥ 0.38) were observed for the total VFA or molar proportion of individual ruminal VFA (Table 1). A treatment effect was observed (main effect; P = 0.04) in total VFA, which was greater for BAC4 vs. BAC0 heifers (Table 1). No BAC × SC or main effects (P ≥ 0.34) were detected for fractions A (soluble fraction), B (degradable fraction), and C (undegradable fraction), passage rate, and effective degradability of DM (Table 2). However, adding BAC4 or SC14 to the diets tended to increase (P ≤ 0.10) in situ degradability of fraction C (Table 2). Additionally, adding BAC4 to the diet increased (P = 0.02) the degradation rate vs. BAC0 heifers. Overall, the inclusion of BAC4 in the diet positively influenced ruminal digestion by increasing degradation rate, which may enhance nutrient utilization efficiency. Additionally, the tendency for BAC4 or SC14 to increase fraction C digestibility suggests potential benefits for fiber digestion, resulting in enhanced DMI and total VFA in BAC4 heifers.