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

Abstract

Abstract According to the Environmental Protection Agency (EPA), enteric methane (CH4) was the second largest source of greenhouse gas emissions from agriculture in 2021 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 arose from the southeastern U.S., representing 43.3% of cow-calf, 27.4% of stocker, 23.1% of feedlot, and 12.1% of dairy derived enteric CH4, according to the EPA. Previous work has demonstrated that reducing CH4 emissions represents the most promising means to limit climate change in the short-term, due to the short atmospheric lifespan of CH4. As such, developing enteric CH4 mitigation strategies for southeastern cattle producers is imperative. Enteric CH4 mitigation strategies 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 (ionophores or inhibitors); secondary plant compounds (tannins, essential oils, saponins)], and breeding strategies (e.g., selecting for low CH4 emitters; selecting for low residual feed intake). Of these options, the direct CH4 inhibitors appear to be the most promising. The largest source of enteric CH4 from the southeastern U.S. is from cow-calf production, representing 71.6% of the total. Furthermore, a 13.6% reduction in enteric CH4 from the southeastern cow-calf herd would offset more emissions than a 100% reduction in the southeastern dairy, stocker, or feedlot sectors. Despite the large gains in emission reductions that could be achieved by focusing on enteric CH4 mitigation strategies from southeastern pastoral systems, there has been relatively little research efforts in this area. 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 greater for grazing than for confined fed cattle. Additionally, there are limited and aging research into grazing management strategies effects on enteric CH4 emissions. There also exists a gap-in-knowledge of how common (e.g., supplementation) or changes in management (e.g., selecting for smaller mature cow sizes) practices could potentially influence enteric CH4 emissions. Future research is still needed to further develop enteric CH4 mitigation strategies, with efforts needed in grazing systems, especially for the southeastern U.S.