Nutritional and host effects on methanogenesis in the grazing ruminant

Concentrations of methane (CH4) in the atmosphere have almost doubled since the mid 1700s, and it is estimated that ∼30% of the global warming experienced by the planet in the last century and a half can be attributed to CH4. Between 25% and 40% of anthropogenic CH4, emissions are estimated to arise from livestock farming. Mitigating absolute emissions from livestock is extremely challenging technically and is made more difficult because of the need to increase food production to meet the demands of a burgeoning world population. Opportunities for manipulating the diet of intensively managed ruminant to reduce absolute CH4 exist, but in grazing livestock the opportunities are constrained practically and economically. Mitigating emissions per unit of product is more tractable, especially in the short term. Although the formation of CH4 is an anaerobic microbiological process, the host animal does seem to exert an influence, as animals differ in the quantity of CH4 they emit when fed the same diet. The reasons for this are not yet clear, but evidence is accumulating that these differences are consistent and have a genetic basis. Exploiting these between animal differences by animal breeding is an attractive mitigation option as it is potentially applicable to all animals and is open to continuous improvement. However, identifying the desired phenotype poses severe practical constraints. Vaccinating the host animal to produce antibodies that can modulate the activities of the organisms responsible for CH4 formation also presents a novel mitigation option.