STRATEGIES TO REDUCE METHANE EMISSIONS FROM ENTERIC AND LAGOON SOURCES

The State of California launched the short-lived climate pollutant reduction strategy (SB 1383) with the objective of decreasing methane (CH4) emissions from livestock by 40% by 2030 from 2013 levels. Considering about 50% of CH4 emissions in the State are attributed to enteric fermentation and manure, achieving significant CH4 emission reduction from these sources will be critical to meeting SB1383 goals. There are numerous mitigation options described in the literature including feed and manure additives. The objective of the study was to provide quantitative analysis, evaluate feasibility, and summarize and prioritize research gaps to guide future research in the State. Specifically the current study conducted a literature review of available mitigation strategies using additives to reduce enteric and manure methane emissions including size effect and performance analyses and used life-cycle assessment tools to estimate net greenhouse gas emissions from using potential feed additives in the dairy industry. Effect size and meta-analyses were conducted to identify the additives with greatest potential for CH4 mitigation. For feed additives, 3-nitrooxypropanol (3NOP), bromochloromethane, chestnut, coconut, distillers dried grains and solubles, eugenol, grape pomace, linseed, monensin, nitrate, nitroethane, saifoin, fumaric acid, and tannins had significant impacts on enteric emissions. For manure additives, acidification, biochar, microbial digestion, physical agents, straw, and other chemicals significantly reduced CH4 emissions. However, there were other promising additives that need further research, including Mootral, macroalgae and SOP lagoon additive (SOP). After further analysis of variance, the most effective feed additives were 3NOP (41% in dairy and 22% reduction in beef) and nitrate (14.4% reduction). Biochar as a manure additive can be effective on compost manure (up to 82.4% reduction), but may have no impact on lagoon emissions. A life cycle assessment tool was used to estimate the net reduction in enteric CH4 emissions by using the feed additives 3NOP and nitrate. The overall average net reduction rate of supplementing 3NOP and nitrate were 11.7% and 4.9%, respectively. Given the toxicity concerns of nitrate, only 3NOP is recommended for use pending FDA approval. Considering California milk production of 18 billion kg in 2017, using nitrate on California dairy cows would reduce GHG emissions 1.09 billion kg CO2e and 3NOP 2.33 billion kg CO2e annually. Further research in the additives of Mootral, macroalage, SOP, biochar and other emerging ones is required before recommendation for use can be made.