In Vitro Evaluation of Different Dietary Methane Mitigation Strategies

Simple Summary Dietary methane mitigation strategies do not necessarily make food production from ruminants more energy-efficient, but reducing methane (CH4) in the atmosphere immediately slows down global warming, helping to keep it within 2 degrees C above the pre-industrial baseline. There is no single most efficient strategy for mitigating enteric CH4 production from domestic ruminants on forage-based diets. This study assessed a wide variety of dietary CH4 mitigation strategies in the laboratory, to provide background for future studies with live animals on the efficiency and feasibility of dietary manipulation strategies to reduce CH4 production. Among different chemical and plant-derived inhibitors and potential CH4-reducing diets assessed, inclusion of the natural antimethanogenic macroalga Asparagopsis taxiformis showed the strongest, and dose-dependent, CH4 mitigating effect, with the least impact on rumen fermentation parameters. Thus, applying Asparagopsis taxiformis at a low daily dose was the best potential dietary mitigation strategy tested, with promising long-term effects, and should be further studied in diets for lactating dairy cows. Abstract We assessed and ranked different dietary strategies for mitigating methane (CH4) emissions and other fermentation parameters, using an automated gas system in two in vitro experiments. In experiment 1, a wide range of dietary CH4 mitigation strategies was tested. In experiment 2, the two most promising CH4 inhibitory compounds from experiment 1 were tested in a dose-response study. In experiment 1, the chemical compounds 2-nitroethanol, nitrate, propynoic acid, p-coumaric acid, bromoform, and Asparagopsis taxiformis (AT) decreased predicted in vivo CH4 production (1.30, 21.3, 13.9, 24.2, 2.00, and 0.20 mL/g DM, respectively) compared with the control diet (38.7 mL/g DM). The 2-nitroethanol and AT treatments had lower molar proportions of acetate and higher molar proportions of propionate and butyrate compared with the control diet. In experiment 2, predicted in vivo CH4 production decreased curvilinearly, molar proportions of acetate decreased, and propionate and butyrate proportions increased curvilinearly with increased levels of AT and 2-nitroethanol. Thus 2-nitroethanol and AT were the most efficient strategies to reduce CH4 emissions in vitro, and AT inclusion additionally showed a strong dose-dependent CH4 mitigating effect, with the least impact on rumen fermentation parameters.