Farmers could soon be using naturally derived perfumes on cows to keep flies at bay, reducing the need for insecticides.

New Scientist magazine reported on Wednesday that scientists at Britain's Institute of Arable Crops Research were working to isolate chemicals that cows naturally secrete or exhale in order to find out which ones make them unattractive to flies.When flies feed on cows they cause stress for the animals, reducing growth and milk production, and some cows attract far more flies than others.

In an experiment, Michael Birkett and colleagues at the institute isolated 18 chemicals secreted by cows. They tested the effects of one chemical by putting it in slow-release bags and placing the bags on the two cows that had attracted flies the most in a group of six cows.

The number of flies evened out, suggesting that the chemical had repelled the insects. Birkett and his team are doing more research with a view to producing a concoction of natural substances that could be used on cows to keep flies at bay.