168. Effects of Bacillus-based and Active Dry Yeast Microbials Supplementation on Intake, Digestibility, and Ruminal Fermentation Parameters of Rumen-cannulated Angus Heifers Fed a Corn-silage-based Diet.

Abstract This study evaluated the effects of Bacillus-DFM (BAC) and active dry yeast (ADY) supplementation on dry matter intake (DMI), total-tract apparent digestibility, and ruminal fermentation parameters of rumen-cannulated Angus heifers. Sixteen rumen-cannulated Angus heifers (initial BW = 353 ± 4.5 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 (0ADY) of 0.5 g/heifer daily of a Saccharomyces cerevisiae CNCM I-1077 (1ADY) and factor 2 was the inclusion or not (0BAC) of 4.36 g of a DFM containing Bacillus licheniformis 809 and B. subtilis 810 (1BAC). 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 days 17 to 26, 5 g of titanium dioxide (TiO2) was intraruminally dosed twice daily, at 12-h intervals, as an external marker of fecal output. From days 22 to 26, fecal spot samples were collected at 12-h intervals. Samples from offer, refusals, and fecal spot were analyzed for chemical composition to calculate total-tract apparent digestibility. On the same days (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 × ADY effects (P ≤ 0.23) were observed for DMI, ruminal degradability, and total-tract apparent digestibility (Table 1). A treatment effect on DMI (main effect; P = 0.04) was observed with BAC supplementation, with a greater effect with 1BAC than with 0BAC. A tendency to increase (main effect; P = 0.06) the dry matter (DM) fraction B degradability was observed for 1ADY compared to 0ADY. The BAC supplementation tended to decrease the neutral detergent fiber (NDF) lag time (main effect; P = 0.08) and the degradation rate (kd; P = 0.07). There were no observed interactions between BAC × ADY or BAC × ADY × TIME for ruminal fermentation parameters, nor were there any main effects detected (P ≥ 0.39; Table 2). The supplementation with Bacillus-based DFM increased the DMI and tended to reduce the lag time and degradation rate of NDF without impacting the ruminal fermentation parameters, total-tract apparent digestibility, or total digested nutrients. The supplementation with ADY tended to increase the DM fraction B degradability without impacting any other variables analyzed herein. For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text.