Backpacks measure Shropshire cows' methane levels
Backpacks have been fitted to cows in Shropshire to help monitor how much methane they emit.
Tubes slowly suck in an air sample from the loop over the cows' nose and mouth into the backpacks which are changed every 24 hours.
Researchers at Harper Adams University College in Newport want to try to reduce the amount they produce and are changing their diets.
Climate experts have said methane accelerates global warming.
Dr Liam Sinclair said: "They are getting four different diets to see if we can reduce the methane produced on an individual cow basis," he said.
"Farmers are very interested in reducing, if you like, this carbon 'hoofprint'.
"Because, if we ever end up with a situation of a carbon tax being introduced, that information will be valuable in terms of informing government and others in terms of policy making so that farmers can be rewarded for trying to do something that is beneficial to the environment."
So-called intelligent feed stations enable some cows to access certain feeds.