Cows that are fed on a diet rich in rapeseed produce healthier milk and spreadable butter, according to the latest research.

Rapeseed contains lower levels of harmful saturated fats and high levels of unsaturated fats, which pass through the cow’s digestive system and into its milk, reported the Guardian.

The rapeseed diet also results in dairy products containing oleic acid, a fat which makes butter spreadable even when taken straight from the fridge.

Such naturally spreadable butter is already sold by UK retailer Marks & Spencer, although the research behind it has only recently been published in the Journal of the Science of Food and Agriculture, the newspaper said.

Butter has to be made entirely from milk fat. Adding vegetable oil to it to make it spreadable means it can no longer be marketed as butter.

Anna Fearon, the food chemist at Queen’s University in Belfast who led the research team, said that in this method of making spreadable butter, the vegetable oil is added at a much earlier stage so the product is still made entirely from milk fat.