Environmental sustainability of livestock systems in the southeastern U.S.: Opportunities and research gaps

Authors: Beck, Matthew; Gunter, Stacey; Friend, Emalee; Moffet, Corey

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/16/2023
Publication Date: 3/2/2024
Citation: Beck, M.R., Gunter, S.A., Friend, E., Moffet, C. 2024. Environmental sustainability of livestock systems in the southeastern U.S.: Opportunities and research gaps [abstract]. American Society of Animal Science Southern Section Meeting. 102(Issue Supplement 1):40. https://doi.org/10.1093/jas/skae019.046.
DOI: https://doi.org/10.1093/jas/skae019.046

Interpretive Summary:

Technical Abstract: Since their estimates began in 1990, the Environmental Protection Agency (EPA) has estimated that enteric methane (CH4) is the second largest source of agricultural greenhouse gas emissions, behind nitrous oxide emissions from soil management. Cattle production in the southeastern U.S. represent a significant source of enteric CH4. In 2021, 31.5% of all cattle derived enteric CH4 in the U.S. arose from the southeastern U.S. The breakdown of the southeastern U.S. enteric CH4 contributions to the U.S. totals for various sectors were 43.3% of cow-calf, 27.4% of stocker, 23.1% of feedlot, and 12.1% of dairy, according to EPA estimates. Previous work has demonstrated that reducing CH4 emissions is the most promising means to limit global warming in the short-term, due to CH4’s high global warming potential and short atmospheric lifespan. Accordingly, developing strategies for southeastern cattle producers to reduce enteric CH4 is imperative. Mitigation strategies for reducing enteric CH4 can be grouped into diet formulations (e.g., lipid additions; feeding more grains; protein source and inclusion), feed management (e.g., grain and forage processing; grazing management; forage species), rumen manipulations (e.g., feed additives such as ionophores or inhibitors; secondary plant compounds), and breeding strategies (e.g., selecting for low CH4 emission intensity). The rumen manipulations group, primarily CH4 inhibitors, appear to be the most promising. Cow-calf sector enteric CH4 emissions account for 71.6% of the southeastern U.S. total and is the largest source. Furthermore, a 13.6% reduction in enteric CH4 from the southeastern cow-calf herd would offset more emissions than a 100% reduction from dairy, which is the next largest southeastern sector. Despite the large gains in emission reductions that could be achieved by focusing on reducing enteric CH4 from southeastern pastoral systems, there has been relatively little research effort on the topic. For example, there has yet to be any investigation into the mitigation potential of CH4 inhibitors when fed to grazing cattle. This is especially important, because the mitigation potential of inhibitors is likely much less for grazing than for confined fed cattle. This is because every mouthful of a total mixed ration should contain the inhibitor with confined fed cattle, whereas in a grazing context the inhibitor would likely need to be pulse dosed through a supplement. Additionally, there are limited and aging experimental data on how grazing management influences enteric CH4 emissions. There also exist gaps in our knowledge of how common practices (e.g., supplementation) or changes in management (e.g., selecting for smaller mature cow sizes) could potentially influence enteric CH4 emissions intensity. Future research is still needed with respect to enteric CH4 mitigation strategies, with effort particularly needed in grazing systems.