How better-fed cows could cool the planet

Unlike antibiotics, these plant-based additives seem to have no secondary effects on milk or meat. And "measurements showed that by using them it's possible to reduce the emission of methane up to 20 percent," Professor Kreuzer says. In order to control the cows' exhalations, he puts them in respiration chambers for 48 hours, feeds them, and measures the concentration of methane from the chamber every few minutes.

The animals aren't always amused. They are not used to eating more fats. Moreover, saponins taste soapy, and tannins are bitter. For the cow, tannin is like drinking a cup of black tea, Kreuzer says: "The more you put into their feed, the merrier it is, but the more awful it tastes."

Furthermore, controlled feeding is not possible everywhere – especially not in Canada, Brazil, Australia, Argentina, and India, where huge herds of animals roam free on huge grazing lands. To reduce their burping, Prof. Winfried Drochner of the Institute of Animal Nutrition at the German University of Hohenheim proposes administering a bun-size pill filled with methane-reducing substances that would dissolve in a cow's gut over a period of months.

It would be a bitter pill for cows to swallow. But at least it wouldn't give them bad breath, as another proposal might do. Prof. Jamie Newbold, at the Institute of Rural Sciences at the University of Wales, is experimenting with a feed laced with garlic. Initial results show that the extract reduces the amount of gas produced by up to 50 percent, as the garlic directly attacks the methane-producing organisms in the cow's digestive tract. But the garlic cure could not only cause halitosis, but also odd-tasting milk and meat. Kreuzer notes that in Switzerland there's a law against feeding dairy cows garlic and onions.

Kangaroos may hold the key

One strategy that Australian scientists have embarked upon suggests not only changing the cattle's diet, but also part of their intestinal tract by making them more like a kangaroo.

Australia's heraldic animals don't emit methane from fermentation. The microbes in their stomachs – while performing functions similar to those in the digestive tracts of cows – are markedly different. A kangaroo's digestive microbes produce acetate (C2H3O2), which aids digestion.

Athol Klieve and his team from the Department of Primary Industries and Fisheries in Queensland isolated 211 bacteria from the eastern gray kangaroo's gut and screened them to determine which are best at digesting native pasture. The most promising ones could be grown in a laboratory and introduced into cattle.

If this approach succeeds, one day there could be less methane in the air – and a little bit of kangaroo in every cow.

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