The Role of Ruminant Livestock

Domesticated ruminant animals (cattle, buffalo, goats, sheep) play an essential role in the livelihoods of millions of farming families.  They contribute to household food security by supplying essential macro- and micro-nutrients, providing manure and draught power, and generating income.  In fact, an estimated 430 million of the 729 million poor people living in rural and marginal areas depend upon ruminants as a major source of household income.

Ruminants convert low quality feed unusable by humans into high value, high protein food products for human consumption (meat and milk). They also provide important non-food benefits such as capital assets, traction, manure for fuel and fertilizers, and fiber (wool).

• Ruminants supply 51% of global animal protein, of which 67% is from milk and 33% is from meat.
• Cattle supply 80% of ruminant protein, buffalo 11%, sheep 5% and goats 4%.

Ruminants are raised in diverse livestock production systems ranging from extensive pastoralist systems in developing countries to the types of intensive dairy and beef operations in more developed countries.  The types of feed consumed by the animals, and the proportion of feed consumed by grazing pasture lands, are the key defining factors in this diversity.  Other important factors include the type and breed of the animals being used, animal feeding and management practices, the integration of livestock and cropping systems, the proportion of household income derived from ruminants, and finally, access to markets for livestock and livestock products.

Enteric Methane Production and Emissions Intensity

Domesticated ruminants are the largest source of anthropogenic methane, contributing an estimated 28% of annual global methane production.  Methane is a naturally occurring by-product of the ruminant digestive tract, which is made up of four separate stomachs: the rumen, the reticulum, the abomasum, and the omasum. The largest and most important of these is the rumen. The rumen functions as a fermentation vessel and allows the animal to consume and draw nutrients from plant material that would be indigestible by humans. The rumen contains large populations of microorganisms which break down the plant material. Methane is given off by the microorganisms and expelled from the animal through eructation (burping).

The amount of methane expelled by the animal is directly related to the quantity (energy value) and quality (digestibility) of feed consumed. The amount of feed consumed is influenced by the type and quality of feed, animal weight, level of productivity, reproductive status, and temperature.  Increased feed consumption increases the energy available for conversion into methane.  However, as feed digestibility increases, the percentage of energy converted to methane decreases, with between 3% to 8% of  the energy consumed lost as methane.

Ruminant livestock in developed countries are generally kept in well managed production systems and fed diets high in digestibility and nutrients. The result is very efficient production (milk or meat) relative to the amount of methane emitted.  Conversely, ruminant livestock in developing countries tend to be fed diets low in both digestibility and nutrient content. This leads to both diminished productivity and greatly increased methane emissions.

The inefficiency resulting from low quality diets has global implications.  The United Nations Food and Agriculture Organization (FAO) statistics indicate that developing nations have more than 76% of the world’s cattle/buffalo population, yet account for only 32% of global livestock production.  Developing countries tend to increase the size of their herds/flocks to increase milk and meat production, as opposed to increasing production per animal.  Livestock production in developing countries is primarily in the hands of small-scale producers who have traditionally been overlooked in efforts to promote increased per animal productivity. Their low levels of productivity result in high levels of methane emissions per unit of product.  As a result, increased demand for milk and meat in developing countries tends to greatly increase methane emissions from livestock.

Ruminant production systems with low productivity use more energy to produce each unit of animal product than those with high productivity. Therefore, high productivity systems produce less methane per unit of production (also referred to as ‘emissions intensity’) than low productivity systems.  Increasing productivity increases food security, improves livelihoods, and mitigates emissions intensity.  The relationship between animal productivity and enteric methane emissions offers large opportunities for low-cost mitigation and widespread social and economic benefits.

In conclusion, relative to other global greenhouse gas abatement opportunities reducing enteric methane through productivity gains is the lowest cost options and has a direct economic benefit to farmers[1].

[1] Gerber, P. J., Steinfeld, H., Henderson, B., Mottet, A., Opio, C., Dijkman, J., Falcucci, A. & Tempio, G. (2013). Tackling climate change through livestock: a global assessment of emissions and mitigation opportunities. Food and Agriculture Organization of the United Nations (FAO).