I've been using A2 dairy for quite awhile. Not quite ready yet to make the switch back to A1 to see if there's any negative reaction. The A1 protein in cow milk was due to a spontaneous genetic mutation in certain northern European cattle a thousand or two years ago from my understanding. Dairy from sheep and goats is always A2. A raw milk dairy sort of near me has done genetic testing on all their cows so you can pick which you want. I think about 90 percent of their Jersey cows are A2. They don't own any Holsteins (the classic big black and white cows) which are likely to carry the gene for A1 milk. Drawback is the farm's high quality grass-fed product is expensive.