US farmers' beef with Burger King over cow fart ad

Fast food chain Burger King has released an advertisement encouraging US farmers to change cow diets in order to reduce greenhouse gas emissions.

The controversial video ad features children in cowboy hats singing about the impact methane gas emitted due to cow flatulence has on global warming.

Burger King claims adding lemongrass to cow diets could ease digestion and dramatically reduce methane emissions.

But farm leaders say the ad is "condescending and hypocritical".

The ad has been trending on YouTube. It has so far been watched by more than 2 million people and drawn thousands of comments - some mocking the firm's "yodelling boy" marketing gambit, with others swearing to cut ties with the chain.

Some scientists also criticised Burger King's message and its focus on cow flatulence, instead of belching.

Prof Frank Mitloehner of University of California Davis (UC Davis)'s Department of Animal Science wrote on Twitter that it was disappointing to see the company "drop the ball" by promoting a study that was still ongoing and focusing on farts, when belching is the bigger problem.

"It's not the cow farts," he wrote. "Nearly all enteric methane from cattle is from belching. Suggesting otherwise turns this serious climate topic into a joke."