Simple Summary: Dietary methane mitigation strategies do not necessarily make food production from ruminants more energy-efficient, but reducing methane (CH 4 ) in the atmosphere immediately slows down global warming, helping to keep it within 2 • C above the pre-industrial baseline. There is no single most efficient strategy for mitigating enteric CH 4 production from domestic ruminants on forage-based diets. This study assessed a wide variety of dietary CH 4 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 CH 4 production. Among different chemical and plant-derived inhibitors and potential CH 4 -reducing diets assessed, inclusion of the natural antimethanogenic macroalga Asparagopsis taxiformis showed the strongest, and dose-dependent, CH 4 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 (CH 4 ) emissions and other fermentation parameters, using an automated gas system in two in vitro experiments. In experiment 1, a wide range of dietary CH 4 mitigation strategies was tested. In experiment 2, the two most promising CH 4 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 CH 4 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 CH 4 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 CH 4 emissions in vitro, and AT inclusion additionally showed a strong dose-dependent CH 4 mitigating effect, with the least impact on rumen fermentation parameters.