Belching cows and pigs could start costing farmers money if a proposal to charge fees for air-polluting animals becomes law.

Farmers so far are turning their noses up at the notion, which is one of several put forward by the US Environmental Protection Agency after the Supreme Court ruled in 2007 that greenhouse gases emitted by belching and flatulence amounts to air pollution.

Download the new Independent Premium app Sharing the full story, not just the headlines

"This is one of the most ridiculous things the federal government has tried to do," said Alabama Agriculture Commissioner Ron Sparks, an outspoken opponent of the proposal.

It would require farms or ranches with more than 25 dairy cows, 50 beef cattle or 200 pigs to pay an annual fee of about $175 for each dairy cow, $87.50 per head of beef cattle and $20 for each pig.

The executive vice president of the Wyoming Farm Bureau Federation, Ken Hamilton, estimated the fee would cost owners of a modest-sized cattle ranch $30,000 to $40,000 a year.

He said he has talked to a number of livestock owners about the proposals, and "all have said if the fees were carried out, it would bankrupt them".