A French cattle feed company on Tuesday unveiled a novel form of carbon credits aimed at incentivising farmers to stop cows from emitting climate-changing farts.

Grass-chewing farm animals are an often-overlooked contributor to global warming, as their emissions are of methane, a gas that is two dozen times more efficient than carbon dioxide in trapping solar heat.

In France, cattle account for five percent of the country's carbon output.

At a press conference, the company Valorex said it would offer a carbon-credit bonus to farmers who join the "Bleu-Blanc-Coeur" (Blue-White-Heart) initiative, which promotes food products with higher levels of the valued protein Omega 3.

Valorex sells a trade mix that comprises corn, soy, lupin and linseed, which it says means cows emit 64-percent less methane, deliver better quality milk and need fewer vet bills.

A credit of 100 euros ($134) will be awarded for every tonne of CO2-equivalent gas that is saved from entering the atmosphere, said Valorex president Pierre Weill.

The credit cannot be used on the European carbon market, where the CO2 has collapsed to just a few euros (dollars) a tonne.

Instead, it has to be exchanged for goods and services provided by other companies which are part of a long-running "Bleu-Blanc-Coeur" (Blue-White-Heart) initiative.

The new scheme, certified as bona fide by the French government and the UN Framework Convention on Climate Change (UNFCCC), has so far notched up 8,365 tonnes of averted carbon.

Out of France's 72,000 milk producers, 500 have joined Bleu-Blanc-Coeur, which requires them to follow strict guidelines.