This meta-analysis examined the effects of mitigation strategies on enteric CH4 emission (CH4E, g/d), Ym (CH4 energy, % of gross energy intake), CH4 yield [g/kg dry matter intake (DMI)], CH4 emission intensity [Ei, g/kg milk yield (MY) or average daily gain (ADG)], DMI (kg/d), ADG (kg/d), MY (kg/d), and neutral detergent fiber digestibility (NDFD, %) in ruminants. The database consisted of data reported in 437 published studies (1963 to 2018) using cattle (65% of the data) and small and other ruminants (35%). Mitigation strategies were classified into 3 main categories: animal and feed management, diet formulation, and rumen manipulation, and up to 5 subcategories (99 total mitigation strategy combinations, which are not discussed here). A random-effects meta-analysis weighted by inverse variance was carried out (Comprehensive Meta-Analysis, V3.3.070). Mitigation effects were based on the relative mean ratio (treatment over control) to standardize effects across studies. Significance was based on α = 0.05 with values adjusted for multiple comparisons. Daily CH4 emissions were analyzed in 783 mean comparisons, followed by number of mean comparisons in descending order by DMI (706), CH4 yield (598), ADG (376), Ym (354), CH4 Ei (260), MY (245), and NDFD (206). Rumen manipulation decreased (P ≤ 0.05) CH4E (−11%), Ym (−10%), CH4 yield (−12%), and CH4 Ei (−12% for ADG) and increased (P ≤ 0.01) DMI (+1%). Diet formulation decreased (P ≤ 0.01) CH4E (−7%), Ym (−10%), CH4 yield (−10%), and CH4 Ei (−10% and −8% for ADG and MY, respectively) and increased (P ≤ 0.01) DMI (+2%) and MY (+7%) but it also decreased NDFD (−3%; P ≤ 0.01). Animal and feed management increased (+7%; P ≤ 0.01) CH4E, but it also increased (P ≤ 0.01) DMI (+17%), ADG (+27%), MY (+11%), and NDFD (+6%) and thus decreased (P ≤ 0.01) Ym (−7%) and CH4 Ei (−10% for MY). Specific practices within these main mitigation strategies effectively decreased CH4 emission without compromising animal productivity. The practical implementation of mitigation strategies will depend on proven long-term effects, economic feasibility, government policies, and consumer acceptance.
- enteric methane