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and diverse population of microorganisms which break down ingested feed to produce volatile fatty acids (VFA’s), CO2 and CH4. The VFA’s produced in the rumen are absorbed and used as an energy source, but most of the CO2 and CH4 are removed from the rumen by eructation. Typically more than 80% of the CH4 is produced in the rumen and the rest in the lower digestive tract (Immig 1996; Murray et al. 1976). The majority of the CH4 produced (>95%) is released via the mouth with only a small proportion (<5%) released via the flatus (Murray et al. 1976). Typically 3.5 – 7.5% of the gross energy consumed is lost as CH4 (O’Hara et al. 2003). A second source of CH4 is that arising from voided faecal material. Emissions from this source vary considerably; in grazing animals, where faecal material is deposited directly onto pastures, only small amounts of CH4 arise from this source but in situations where manures are stored for prolonged periods in anaerobic conditions relatively large quantities of CH4 can be emitted. Steinfeld et al. (2006), using a mix of Intergovernmental Panel on Climate Change (IPCC) Tier 1 and Tier 2 approaches, estimated global enteric emissions from ruminant livestock to be of the order of 84 M t/year. Clark et al. (2005) also adopted an IPCC Tier 2 type approach and arrived at a lower estimate of 70.4 M t/ year. These two values typify the range of values found in the literature (IPCC 2001) for global enteric CH4 production. Steinfeld et al. (2006), again using a mix of Tier 1 and Tier 2 approaches, estimated global annual CH4 emissions from manure management to be in the order of 8.2 M t/year, a figure that is much higher than previous estimates (e.g. US-EPA 2005). Steinfeld et al. (2006) present a figure for all anthropogenic CH4 emissions of 5.9 G t/year CO2e which suggests that ruminant animals emit between 25 and 33% of the all anthropogenic CH4 emissions. Total anthropogenic GHG CO2e emissions are estimated to be in the order of 33 G t/year (Steinfeld et al. 2006) indicating that CH4 emissions from ruminant livestock account for between 5 and 6% of global anthropogenic emissions. However, this figure varies dramatically between countries. For many developed countries the figure will typically be 3% or less but for some developing countries, for example Uruguay, Brazil and Argentina the figure is more than 25% Abstract Globally methane emissions from ruminant livestock account for 5-6% of total anthropogenic carbon dioxide equivalent emissions. In New Zealand, methane emissions from ruminants comprise 31.5% of our total emissions putting us in a unique position within the developed world. Reducing methane emissions from ruminant livestock is technically challenging and has to be achieved against a rising demand for animal products. There is currently no price on emissions meaning that there is little incentive for farmers to adopt mitigation practices unless these practices are profitable in their own right. In the short term the mitigation opportunities already identified by researchers have limited applicability for grazing ruminants or they involve actions (e.g. reducing animal numbers) that may adversely affect profitability. In the medium and longer term direct modification of rumen microbial processes (e.g. vaccination against methanogens) and the breeding of ‘low’ methane producing animals offer promise for universal, cost effective solutions.

Methane emissions from ruminant livestock; are they important and can we reduce them?