Dr Tony Parker stands behind harvested seaweed in North Queensland, which could be the secret to reducing cattle methane emissions.

Credit: Prof. Rocky de Nys

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Farting cows may produce less methane if fed on a diet of seaweed, Australian researchers have said.

The 'Reef and Beef' project, as it is dubbed, is a Queensland-based venture attempting to reduce the impact of Australia's cattle industry on global warming. As a bonus, it will also provide an economic motive for eco-friendly disposal of aquaculture waste.

"Our project aims to decrease methane emissions by cattle, and provide a new product from aquaculture," said lead researcher Tony Parker, a livestock nutritionist from James Cook University in Townsville, Australia.

"Better management of aquaculture, a new protein source for cattle farmers to choose from and cleaner water being discharged into the Inner Great Barrier Reef are further benefits," he added.

Farts and burps from cows are thought to account for around 20 per cent of the world's human-related methane emissions. Methane is a more damaging greenhouse gas than carbon dioxide, giving our taste for beef and dairy a huge global warming footprint.

Cows produce vast quantities of methane due to the poor quality of their diet, which is typically high in indigestible types of fibre. Microbes in the cow's gut ferment and break down this fibre, producing - in addition to valuable energy and nutrients for the cow - lots of gas.

Parker got the idea of feeding seaweed to cows after hearing about sheep which live on marine plants.

"Orkney sheep are ruminants that live off seaweed and they do very well on such a diet - so the obvious question is, why can't cows?" he said.

Seaweed has less cellulose and more starch than grass, making it easier for cows to digest. Less fermentation is required, and therefore, Parker hopes, less methane is produced.

Sourcing the seaweed will be easy, he said. Some fish and crustacean farms in Queensland already use seaweed to clean their ponds. The growing seaweed takes up waste nutrients from the water, bringing nitrogen and phosphorus content down to safe levels before the water is discharged into the ocean. Currently the seaweed is then simply thrown away. Parker hopes that by making this seaweed into a valuable product, more farms will adopt the practice.

"If we can get the beef and aquaculture industries to work together on this we can not only help them reduce their impact on the environment but also improve their profitability," said Rocky de Nys, a marine biologist from James Cook University who is also involved with the project.

Parker and de Nys plan to test-drive their idea on a local herd of heifers. Encouraging the cows to eat seaweed in not likely to be a problem, Parker explained. "As a general rule ruminants love sodium. I have tested the dried algae on our cattle and they hook into it," he told G Online.

Measuring the cow's methane output, however, will be tricky. "I'm not looking forward to that part of the process," Parker admitted.

Richard Eckard, an agricultural scientist at the University of Melbourne, thinks the project has potential. "This is an excellent way of closing the nutrient loop," he said.

Eckard also predicted challenges. "Often plants fed on effluent take up luxury quantities of nutrients, which could cause problems for the cattle. The volume of seaweed needed could also be rather large," he said.

Of more serious concern is the potential for bacterial infection. "There would be a need to substantially 'clean up' the seaweed to ensure we are not feeding cows on pathogens," Eckard noted.