Livestock-environment interactions: Methane emissions from ruminants
Livestock producers face a number of challenges including pressure from the public to be good environmental stewards and adopt welfare-friendly practices. However, environmental stewardship and animal welfare may have excitingly conflicting objectives. Examples include pasture-based dairy and beef cattle production where high-fiber diets increase methane emissions compared with grain feeding practices in confinement. Livestock account for 35-40% of global anthropogenic emissions of methane, via enteric fermentation and manure, which together account for about 80% of the agricultural emissions. Recent estimates indicate that the methane emissions from African cattle, goats, and sheep are likely to increase from their current level of about 7.8 million tons of methane per year in 2000 to 11.1 million tons per year by 2003, largely driven by increase in livestock numbers. This paper therefore reviews certain areas of CH4 emissions from ruminants, highlights on how some novel feed additives can decrease CH4 emissions from ruminants; and how some plants secondary metabolites might act as a selective inhibitor of methanogens. An enteric methane emission (which is one of the greenhouse gases) represents an economic loss to the farmer where feed is converted to CH4 rather than to product output. As developing countries are now responsible for almost three-quarters of such emissions, this has important implications in terms of mitigation strategies, because these countries are presently outside the remit of the Kyoto Protocol.
Key words: Environment, CH4 emissions, feed additives, mitigation, ruminants.