What breeds of dairy cattle produce the highest amounts of the A2 protein?
Generally it is accepted that the Guernsey breed of cattle have the highest frequency of the A2 gene, and thus Guernsey herds produce milk with high levels of A2 beta casein. Though not as high as the Guernseys, Jersey cows also produce milk containing high levels of A2. Holstein and Friesian breeds carry the A1 and A2 genes in roughly equal proportions. Sire programs and artificial insemination cattle can however greatly displace the frequency of beta casein genes from generation to generation, owing to the phenomena termed the ‘founder effect’. Thus one can only generalize about the level of A2 a herd may collectively produce until tested.
