The special seaweed diet for cows that could reduce NZ's methane levels

Scientists are researching a special diet for cows that could help to reduce the amount of damaging greenhouse gases they burp into the atmosphere every day.

Farmers at Lansdowne Valley Farm near Christchurch have already cracked onto something, feeding their cows seaweed.

The dried out extract is left out by farmer Roger Beattie, in a ploy that could be helping to save the planet.

"There's been a number of studies done on methane, and they seem to be pointing in the same direction; you feed some kelp and it has a methane mitigation benefit," he says.

Currently, researchers from UC Davis University in California are trying to decipher if it does in fact make cows less gassy.

They're claiming the diet has the potential to dramatically reduce the amount of methane cows burp into the atmosphere.

But Mr Beattie has been harvesting seaweed or kelp commercially off the coast of Akaroa for the past eight years.

His small team, including marine biologist Peter Randrup, harvest 500 tonnes every year by hand.

According to Mr Randrup, seaweed's reproductive organs are at the bottom - so when harvested, you can simply cut the top and then it all regrows.

Seaweed is one of the most sustainable ecosystems on earth, and that's because it grows so fast - in fact, if grass grew as fast as seaweed does, you'd have to mow it seven times a day.

The seaweed harvested by Beattie and his team is then dried out and sold to dairy farmers, under the brand Zelp.

Mr Beattie has been feeding it to his cattle for years, and while he doesn't test for methane, he says you can see the change.

"The kelp is just one of those things - if you've got an animal that's in a poorer condition, you give them kelp, and very shortly afterwards, they pick up in condition," he says.

While the science is still underway, seaweed could be the pill that helps New Zealand rein in its big methane problem.