Strategies to Mitigate Enteric Methane Emissions by Ruminants

To meet the 1.5°C target, methane (CH4) from ruminants must be reduced by 11 to 30% of the 2010 level by 2030 and by 24 to 47% by 2050. A meta-analysis identified strategies to decrease product-based [PB; CH4 per unit meat or milk (CH4I)] and absolute (ABS) enteric CH4 emissions while maintaining or increasing animal productivity (AP; weight gain and milk yield). Next the potential of different adoption rates of one PB and/or ABS strategies to contribute to the 1.5°C target was estimated. The database included findings from 425 peer-reviewed studies, which reported 98 mitigation strategies that can be classified into three categories: animal and feed management, diet formulation, and rumen manipulation. A random-effects meta-analysis weighted by inverse variance was carried out. Three PB strategies, namely increasing feeding level, decreasing grass maturity, and decreasing dietary forage-to-concentrate ratio, decreased CH4I by on average 12% and increased AP by a median of 17%. Five ABS strategies, namely CH4 inhibitors, tanniferous forages, electron sinks, oils and fats, and oilseeds, decreased daily methane by on average 21%. Globally, only 100% adoption of the most effective PB and ABS strategies can meet the 1.5°C target by 2030 but not 2050, because mitigation effects are offset by projected increases in CH4 due to increasing demand. Notably, by 2030 and 2050 low- and middle-income countries may not meet their contribution to the 1.5°C target for this same reason, whereas high income countries could meet their contributions due to only a minor projected increase in enteric CH4 emissions.