This invention relates to a method for determining whether a bovine animal possesses a gene for .beta.-casein A.sup.2 or the gene for .beta.-casein A.sup.1 in its milk by testing the DNA of the bovine animal for the presence of at least one DNA marker (excluding those DNA markers present in the sequence of the genes themselves). In particular, the method uses SNPs as DNA markers for the .beta.-casein A.sup.2 and .beta.-casein A.sup.1 genes.