Assessing the effects of supplementation with a <i>Saccharomyces cerevisiae</i> fermentation-derived postbiotic on methane production, ruminal fermentation, and nutrient utilization in beef cattle

Yeast-fermentation products are promising feed additives to enhance ruminal fermentation, improve feed efficiency and animal performance, and potentially mitigate enteric methane (CH4) emissions. This study aimed to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation-derived postbiotic on ruminal fermentation parameters, CH4 production, and nutrient utilization in beef steers consuming a high-grain diet. Six ruminally cannulated Angus crossbred steers (783 ± 29 kg of bodyweight) were used in a crossover design (42-d period), where they received a basal diet comprised of (dry matter [DM] basis) 65.9% cracked corn, 14.4% bermudagrass hay, 9.9% dry distillers grains plus solubles, 4.9% cottonseed hulls, and 4.9% of vitamin-mineral supplement. Each day, steers were individually fed a carrier of dry distillers' grains plus solubles (250 g/d as fed) with one of the following treatments: CTL, carrier only; or SCFP, carrier plus 28 g/steer/d of a Saccharomyces cerevisiae fermentation-derived postbiotic (NaturSafe, Diamond V, Cedar Rapids, IA). Ruminal fermentation parameters, including pH, concentration of ammonia nitrogen (NH3-N), volatile fatty acids (VFA), total gas, CH4 production, and in vitro organic matter (OM) digestibility, were assessed using an ex vivo model. Additionally, in vivo measurements of pH, VFA, and NH3-N were conducted over 24 h, and apparent total tract digestibility was determined using collected feed and fecal samples. Data was analyzed as a crossover design including treatment, order, and period as fixed effects, and steer within order as a random effect. Supplementation with SCFP had no effect (P > 0.10) on the ruminal fermentation parameters assessed using the ex vivo model. Daily supplementation of SCFP in vivo showed no effect (P = 0.12) on ruminal pH or concentration of NH3-N; however, a decrease (P = 0.04) in concentration (mM) of total VFA was observed due to reduced concentration of propionate (P = 0.03) and butyrate (P < 0.01). The acetate to propionate ratio was greater (P = 0.02) in SCFP compared with CTL. Supplementation of SCFP resulted in a decrease (P < 0.01) in molar proportion (MP; mol/100 mol) of butyrate and tended to reduce (P = 0.09) MP of propionate, yet MP of acetate and valerate increased (P = 0.02). Apparent total tract digestibility of DM, OM, and starch increased (P < 0.05), with crude protein digestibility showing a tendency to increase (P = 0.08) with SCFP inclusion. Thus, supplementing SCFP at a rate of 28 g/animal/d altered ruminal fermentation in vivo and improved the digestibility in this study.