A method of reducing the level of saturated fatty acids relative to the level of unsaturated fatty acids in milk. In particular, the genotyping and/or phenotyping of bovine cows on the basis of the amino acid residue located at position 67 of beta-casein produced in their milk. The invention is based on the finding that there is a correlation between the ratio of saturated to unsaturated fatty acids in milk and the beta-casein variants in milk.