Methane emissions from animals have been identified as a major contributor to global warming and could soon have a major impact on livestock farming. While some researchers are investigating livestock diets that can reduce methane emissions, others are perfecting methods that turn manure into electricity. Roelof Bezuidenhout reports.
With warnings about global warming getting scarier by the day, farmers can be sure that the pressure on them to reduce greenhouse gases will increase sharply. And with environmentalists believing it could be easier, quicker and cheaper to reduce greenhouse gases by targeting methane rather than carbon dioxide, there could be shriller calls for a methane tax on livestock. But as Seranne Howis of Rhodes University’s Department of Botany writes in an essay published on the internet, farmers would prefer alternative methods to reduce methane production – ideally those that also boost production. For example, the Canadian Cattlemen’s Association claims that oilseed that’s not fit for human consumption can play a greater role in rations to improve the performance of beef cattle, improve meat quality characteristics, and reduce methane gas production by cattle. They point out that research has found that feeding whole sunflower seeds as a supplement can cut methane emissions by 22%, and that even a 15% reduction in methane gas among 2,5 million head of feeder cattle would result in a reduction of 17,6 million kilograms of this gas per year.
According to Howis, 9% to 12% of the energy that a cow consumes is turned to methane that is released either through flatulence or burping. “A huge number of factors affect methane emission, including diet, barn conditions and whether the cow is lactating, but an average cow in a barn produces 300 litres of methane a day, and even more when out in a field. Australia’s 140 million sheep and cattle are estimated to produce one-seventh of the nation’s total greenhouse gas emissions,” she says. North America has 100 million cattle.
Worldwide, ruminant livestock – including cattle, sheep, goats, and buffalo – produce about 80 million metric tons of methane per year, accounting for 22% of anthropogenic methane emissions. These emissions, she ventures, can possibly be reduced by genetically engineering cattle, or the bacteria they carry that produce the methane.
Other suggestions include better management of animals in extensive grazing systems, and feeding protected feeds. “There has been some development of a vaccine that changes the population of microorganisms in the animal’s stomach and discourages the methanogenic bacteria that break down and ferment fodder during digestion,” she says. But Howis thinks that new diets could be the easiest course, either by means of feeding the cattle less volatile fodder or by adding substances to the feed. “The addition of a bacterium to cow feed has shown some small-scale success. The organism uses oxygen to convert methane into carbon dioxide and in doing so stimulates the microbial activity in the animal’s gut that aids the digestive processes, thus leading to a more productive cow.” While there’s still no practical way of collecting the gas animals burp into the air, many larger US farmers who can afford the installations already collect the methane given off by fermenting cow manure and use it to generate electricity.
The Haubenschilds’ dairy farm in Princeton, Minnesota, is often quoted as a prime example of a green farm using this technology. Their 1 000-unit dairy herd produces enough manure to generate 20 000kW of power a week – good for their own electricity needs plus enough surplus to supply 80 other homes in the area. The manure or other organic matter is collected in methane digesters (big tanks) where it is converted into biogas through anaerobic digestion. In this process, bacteria decompose the organic matter in the absence of oxygen, producing a gas composed of 60% to 70% methane and 30% to 40% carbon dioxide. This biogas can then be used to power an engine generator or used in a modified hot water heater. Farmers can sell excess power generated to the grid. At the same time the leftover manure, which would otherwise pollute surrounding water, is compressed; fluid is drained away and used as fertiliser; and the solids are dried out and used as bedding for the herd and compost.
In the US, biomass from plants and animal waste already supplies 15 times as much energy as wind and solar power combined, but utility companies are not always keen to allow farmers to pump extra energy into their grids. However, organisations such the California Energy Commission make funds available to support farmers’ efforts to generate their own electricity. The situation in South Africa is unclear. According to Dr Robin Meeske of the Outeniqua Agricultural Research Station at George in the Western Cape, the country no longer has the necessary apparatus to measure methane emissions from animals. “But generally speaking, the more digestible the diet is, the less methane will be produced,” he told Farmer’s Weekly. |fw
