Reducing methane

About Methane

The largest source of greenhouse gas emissions from dairy farms is methane from the rumen. 6-10% of energy consumed by cows is converted to methane and released via breath. Forage quality has a major impact on methane production, being highest with low forage quality. It is a major source of energy loss for the cow, and if it could be avoided, milk production would likely increase.

Because of its strength as a greenhouse gas, methane is multiplied by 25 to give CO2 equivalents in the national greenhouse gas inventory.

Methane has natural and man-made sources. It is released during the breakdown of organic matter low oxygen environments like swamps, and in the gut of ruminant animals such as cattle. Man made sources include burying garbage and burning natural gas. Since the start of the industrial revolution, methane in the atmosphere has doubled.

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Possible Options for Reducing Methane on dairy farms

Herd based strategies

Reduce herd size

Reducing herd/cow numbers would reduce emissions but this option is challenged by the overall need to increase world food production to meeting the needs of an increasing world population. At the margins however, a smaller number of high producing cows will produce less methane per litre of milk production than a larger number of lower producing cows.

Reduce the number of unproductive animals

Reducing the number of replacement heifers and dry cows (either between lactations, or those carried over due to a failure to get back in calf) can increase profitability and reduce emissions.

Retaining cows longer in the herd can reduce the number of replacement heifers needed. Strategies like extended lactation (for example, cows might be milked for 15 months and calve every 18 instead of annually) can theoretically reduce emissions by up to 10% but this has not been proven.

Each farm must weigh up the pros and cons of these strategies. For example, retaining older cows to reduce the number of heifers can slow genetic gain, and older cows are likely to have more health problems.

Animal breeding

Some studies show heritable differences in rumen methane production between dairy cows, so theoretically, a breeding program could reduce methane emissions. However there is currently no attempt to include reduced methane in dairy breeding programs and bulls are not assessed for methane production. While not a viable option now, it may be in the future.  

Rumen manipulation

Methanogens (microbes that produce methane) are a small proportion of the total rumen microbial population. Reducing the numbers of methanogens in the rumen can reduce methane production, apparently without detriment to the digestion process.

A vaccine that acts against the methanogens reduces methane by up to 7.7%, however this Australian study has not been able to be repeated, perhaps because rumen populations are influenced by a range of location and diet factors. New Zealand researchers are currently working on a vaccination based strategy.

Biological control strategies where ‘predators’ of the methanogens are introduced or encouraged are possible, but this research is only in its very early stages.

Antibiotics (such as rumensin) added to the diet of ruminants can reduce methane production. However the effect is not reliable, can be short lived and there is low public acceptance for routinely using antibiotics in animal production systems.

Feed based strategies

Maximise diet quality/digestibility

Digestion of ‘roughage’ causes methane production, and ruminants have an evolutionary advantage by being able to digest relatively fibrous plant material. This suggests that methane production is deeply embedded in the evolution of ruminants and therefore may be difficult to alter.

Any strategy that improves diet quality will tend to reduce methane production per litre of milk, such as:

• improving pasture quality through grazing management
• switching from C4 (subtropical) grasses such as paspalum or kikuyu to C3 (temperate) species such as ryegrass or fescue
• adding grain to a forage diet

However, while improvements in diet quality can reduce methane emissions per litre of milk produced, they often act to increase total farm methane emissions. This is because milk production per cow increases, but cow numbers often go up to take advantage of the higher quantity and quality of feed.

Pasture breeding

Traditionally, pasture breeding has focussed on increasing dry matter yields and the longevity of sown pastures. These are still vital traits, but now that the ability to manipulate plant genes has dramatically increased, plant breeders in Australia are working on mechanisms that significantly increase the digestibility of pasture species. Though many years away, increasing the digestibility of ryegrass is being investigated, with studies on fescue and C4 grasses to follow.

Feeding fats and oils

This has long been common practice in some herds – usually through high protein meals that are by-products from oilseed crops, and direct feeding of whole cotton seed. A review of 17 feeding experiments showed that for each 1% increase in dietary fat, methane production was reduced by 5.6%. Inclusions of fats can boost production, and reduction emissions.

The suppression of methane emissions seems most pronounced when pasture quality declines – ie summer and autumn in southern Australia, and this is likely to be the time when production responses to fats and oils are greatest. This strategy is limited by the fact that if total diet fat content (including the fat contained in the pasture and other forage supplements) exceeds 6-7% then intake and milk production will be suppressed.

Feeding condensed tannins

Condensed tannins (often extracted from wattle bark) can reduce methane production because they have a directly toxic effect on methanogens. However even at relatively low concentrations in the diet, condensed tannins suppress voluntary food intake, reduce diet digestibility and therefore reduce milk production.

It is the condensed tannins in some legumes that make them ‘bloat safe’ and there have been breeding efforts since the early 1990s (focussed on lucerne and white clover) to increase the tannin content of these species to reduce their potential to cause bloat in grazing cattle. If these breeding programs are successful, then these bloat safe legumes might also act to reduce methane production. 

The farming systems reality

Rumen methane production per litre of milk differs across farming systems – under best practice management, the range is from about 6 t CO2-e/t MS (tonnes of CO2e of methane per tonne of milk solids) in a feedlot, to about 10 t CO2-e/t MS in a fully grazed situation with very little supplementation. However, best practice for production efficiency and profit give the best outcome for methane abatement for any particular farming system. It remains to be seen whether the financial incentives to reduce emissions via the Carbon Farming Initiative will be sufficient to drive changes in farming practice.

Currently, well managed dairy farms have few options to reduce methane emissions without significant changes to their farming or feeding system– making changes to reduce emissions would require analysis of the impacts on productivity and profit.

To make matters more confusing, many innovations that reduce emissions per litre of milk, increase whole farm emissions. For example, if grain supplementation is increased then 3 things tend to happen concurrently – pasture consumption per cow goes down, milk production per cow goes up, and stocking rate is increased to take advantage of the extra pasture. In this example while methane per litre of milk almost certainly falls, methane per cow and per farm can rise.

The concept applies to the whole industry. An analysis of the US dairy industry showed that in 1944 there were 25.6 million dairy cows that produced 53 billion kg of milk. By 2007 US dairy herd had fallen to 9.2 million animals, producing a total of 84 billion kg of milk. The high producing cows in 2007 were each producing 66% more CO2e than the low producing cows of 1944 because of the greatly increased feed intake and milk production. However, the opposite was the case per litre of milk, with a reduction from 3.6 kg CO2e/kg of milk in 1944 to 1.35 kg CO2e/kg of milk in 2007.

Over a shorter time frame, the figures below (Moate pers comm.) show the increased milk production per cow from 1979/80 through to 2001/10 and the decrease in methane production per litre of milk.

 

This means that reducing emissions intensity (emissions per litre of milk) is potentially a win:win for the dairy industry – any improvement in productivity and/or production efficiency is likely to give an associated reduction in emissions per litre of milk. However, the national target is to reduce total emissions (not emissions intensity), and the Carbon Farming Initiative is focussed on reducing total farm emissions and these differences are yet to be resolved.

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References and resources

Eckard, RJ, Grainger C, and de Klein CAM (2008) Options for the abatement of methane and nitrous oxide from ruminant production – a review.

J. L. Capper, R. A. Cady and D. E. Bauman (2008) Increased production reduces the dairy industry’s environmental impact - Department of Animal Science, Cornell University, Ithaca, NY

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