Scientists in New Zealand are breeding a herd of cows which naturally produce low-fat milk after the chance discovery of a gene mutation in one animal.

Milk from the cows is also high in health-boosting omega-3 fatty acids and makes butter that spreads as easily as margarine even when chilled, biotechnology company Vialactia said on Monday.

Scientists discovered a cow, later named Marge by researchers, carrying the mutant gene in a dairy herd they were testing in 2001, Russell Snell, Vialactia's chief scientist, said.