The Guernsey breed currently lays claim to the highest percentage of A2 animals of any of the traditional cattle dairy breeds in the world. Guernsey breeders have long known that there was something special about Guernsey milk and now, in addition to the Golden Guernsey color and higher levels of solids and beta carotene, it is clear that the Guernsey breed is the single best source for A2 milk.
Over 300 Registered Guernsey males and females in the US population have been A2 tested. Those results show 78% A2A2, 20% A1A2 and 2% A1A1. This means that, on average, 88% of Guernsey milk is A2 milk. Many breeders have chosen to select for the A2 gene in their breeding programs. This is very easy to do in the Guernsey breed as there is a wide selection of proven and young sires with known A2 status. Keep in mind that, regardless of breed, there is really no way to truly know the status of an individual cow or group of cows unless they are DNA tested.
Follow this link for the complete list of US Guernsey bulls that have been tested and are available for AI.
There is a massive amount of information about A2 available on the web. The AGA encourages you to do your research and make your own decisions on whether A2 milk is the right choice for you. If you decide it is, look to Guernsey cows to supply it for you!