Amid concerns that cows may be contributing to global warming through methane emissions, Irish researchers have found that including fish oil in the diet may cut those emissions by a significant amount.

The research hasn't been published yet, but details were released recently at the Society for General Microbiology's spring conference in Harrogate, England. It appears that fish oil affects the methane-producing bacteria in the rumen. In a study, researchers at University College Dublin fed three levels (0, 10 or 20 grams/kilogram of dry matter) of a novel fish oil product to the diets of beef cattle. "It was novel in the sense it included elevated levels of omega 3 fatty acids," says Tommy Boland, one of the researchers. Methane emissions were reduced by 20 percent at the high fish-oil level supplying 2 percent of dry matter intake. There was no reduction at the 1 percent level.

Asked if reduced methane emissions might be a sign of greater rumen efficiency, Boland said, "There was a linear increase in propionate production as a result of fish oil inclusion, but this does not fully explain the differences witnessed in methane output. Other proposed modes of action include reported toxic effects of free fatty acids on methanogens and protozoa. Detailed microbial analysis is ongoing to quantify this effect," he said. (Boland asked that credit also be given to his colleagues David Kenny and Kirstie Petrie.)