Nutritional Mitigation of Greenhouse Gases

Methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and halocarbons are greenhouse gases (GHG) that are able to trap heat in the atmosphere by radiating less heat into the space and increase the effect of solar and thermal radiation on surface and atmospheric temperatures (Knapp et al., 2014). In 2014, total U.S. GHG emissions measured 6,870 million metric tons of CO2 equivalents. Agricultural activities contributed about 9% of total GHG emissions (U.S. EPA, 2016). Enteric CH4 generated during feed digestion accounts for most of livestock’s direct impact on total GHG emissions representing about 28.6% of U.S. GHG emissions from agricultural activities in 2014 (U.S. EPA, 2016). Although CH4 constitutes only about 10.6% of total emissions, it has greater impact because it has 28 times the global warming potential of CO2 over a 100yr timespan (Myhre et al., 2013). With an energy content of 55.22 MJ/kg (Brouwer, 1965), CH4 represents a loss of dietary energy from the animal and typically accounts for about 6-12% of the total gross energy consumed by ruminants (Johnson and Johnson, 1995). Thus, CH4 production by cattle is both an environmental concern and a potential loss in cattle efficiency. Reducing CH4 losses is an environmentally sound practice with potential to improve production efficiency. Several comprehensive reviews have been published on strategies for CH4 mitigation (Beauchemin et al., 2008; McAllister and Newbold, 2008, Hristov et al., 2013; Knapp et al., 2014). This paper will focus only on nutritional strategies to reduce enteric CH4 emissions.