California Air Resources Board

Principal Investigator/Author: Ermias Kebreab

Contractor: University of California, Davis

Contract Number: 17RD018

Project Status: Completed

Relevant CARB Programs: Climate Change,  AB 32 Climate Change Scoping Plan, California Greenhouse Gas Emissions Inventory Program, Dairy and Livestock Greenhouse Gas Emissions Working Group, Short-Lived Climate Pollutants

Topic Areas:  Greenhouse Gas Inventory , Short-Lived Climate Pollutant Inventory, Particulate Matter (PM) , PM2.5, State Implementation Plans (SIPs), Agriculture

Research Summary:

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 that 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 the 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, other promising additives 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), and biochar as a manure additive (up to 82.4%). 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 was 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 by 1.09 billion kg CO2e and 3NOP 2.33 billion kg CO2e annually. Further research on the additives of Mootral, macroalgae, SOP, biochar, and other emerging ones is required before recommendations for use can be made.

Keywords: methane (CH4), emissions, Senate Bill 1383 (SB 1383), dairy, manure, additives, climate change, greenhouse gas reduction strategies, methane emissions, dairy emissions