Effects of active dried yeast (Saccharomyces cerevisiae), a non-ionic surfactant, or their combination on gas production, rumen microbial fermentation and methane production in vitro

Abstract

Several feed additives have been assessed for their potential to reduce enteric methane (CH4) emissions from ruminants. It has been suggested that combination of individual dietary enteric CH4 mitigation strategies may results in larger increases compared when each individual strategy is applied alone. In this study, the aim was to determine the effects of increasing doses of active dry yeast Saccharomyces cerevisiae (ADY), surfactant, or their combination on rumen microbial fermentation and CH4 production using in vitro batch culture. For this purpose, 24 h batch cultures of ruminal fluid incubations were conducted in a complete randomized block design (repeated 3 times) that included a negative control (no additive), a positive control (monensin, 10 mg/L), ADY (15, 30, 60, 150, 600, 1200 mg/L), surfactant (0.03, 0.06, 0.12, 0.30, 0.60 and 2.00 mL/L), and 6 mixtures resulting from the combination of each level of S. cerevisiae and the surfactant. Compared with the negative control, monensin increased propionate at the expense of acetate, decreased ammonia (NH3) concentration and CH4 production (−28%). The addition of ADY at 600 and 1200 mg/L increased total gas production and total volatile fatty acid (VFA) concentration and lowered media pH. These ADY doses, did not affect propionate concentration but increased acetate concentration, CH4 production (up to 18% increase), and NH3 concentration. At the doses of 0.30, 0.60, and 2.00 mL/L, the surfactant decreased total gas production, total VFA and acetate concentrations, but increased propionate concentration. At doses ≥ 0.30 mL/L, surfactant decreased CH4 production by up to 70%. When the mixture consisted of doses of ADY ≥ 150 mg/L and surfactant ≥ 0.30 mL/L, changes in fermentation characteristics and CH4 production were similar to the doses observed when the surfactant was supplied alone at the same concentrations provided in the mixture. In conclusion, under the experimental conditions of this in vitro study, results show that surfactant has the potential to mitigate enteric CH4 emissions. However, ADY supply increased CH4 production and NH3 concentration. An increase in ruminal NH3 may increase urinary N excretion, which may result in greater ammonia and nitrous oxide emissions. No benefits can be therefore expected from combining ADY with surfactant to alter favorably rumen microbial fermentation to reduce enteric CH4 emissions. However, given the differences between in vitro and in vivo methodologies, validation of our findings in vivo is warranted.