Human breastmilk, goat, sheep, & water buffalo milk are all naturally A2/A2 beta-casein protein. Cows vary dependent upon their genetics and breed. There is no breed of cow that is all one or the other. While Jersey’s are an A2/A2 dominant breed there can be A1 Jerseys. The opposite applies to Holstein’s. The only way to know for sure is to lab test each animal.
All cows milk used to be A2/A2 until the industrialization of dairy when this A1 variant started appearing. Supposedly, A2/A2 milk is easier to digest. Mostly, all you will find is anecdotal evidence to support these claims, however, proponents of A2/A2 are adamant that it makes all the difference.
What we say is try it out and see what works for you. Sometimes goat or sheep milk is the best option because they are both A2/A2 and they have 10x smaller fat molecules which makes it easier on the tummy.