Although she looked like any other Friesian, testing revealed that Marge's milk contained about one per cent fat, compared with about 3.5 per cent for whole milk.

Offspring from the cow also produce low-fat milk, showing the genetic trait is dominant, Snell said.

"Every now and then nature throws up these sorts of things and it was simply a case of us being in the right place at the right time," he said.

The company, a subsidiary of the Fonterra Co-operative Group, one of the world's largest milk companies, expects the first commercial herd of cows supplying natural low-fat milk and spreadable butter for the market by 2011.