As we look into the A2A2 situation we are seeing other things that can effect the production and quality of the milk produced by a cow. One of those is Leptin, the presence of Leptin shows that calves grow and wean heavier, has an impact on carcass quality, cattle that are positive for Leptin also have better feed efficiency, finish in the feedlot sooner and is shown that cows that are positive also produce more milk.
A2 has to do with an amino acid, and it is thought that people who are lactose intolerant, it may not be the lactose but the the A1 and A2 gene. A1 has been associated to increased cases of type 1 diabetes, heart conditions, autism and other health problems. People who are lactose intolerant have been told to drink goat milk. Goat milk still contains lactose, but it is high in the A2A2. So lactose intolerant people can also consume the A2A2 milk from cows with no problems.
Research studies of the effect of A2 in beef production have not been done on any large scale yet, but thoughts by many are that if the A1 milk is bad for the health of us as humans wouldn't the same hold true for the milk that a beef cow produces for her calf.
There was a time when all cows only produced the A2A2 milk, but there was a gene mutation, (don't know when) that created the A1 gene. This gene is primarily associated with the Holstein and Friesian cow. All breeds of cattle carry two copies of the genes, so you can have cows that are A1A1, A1A2 OR A2A2. Some breeds do seem to have a higher percentage of animals within those breeds to carry the A2A2 gene.
There is no way to visibly tell if animals do or do not have the presence of these genes.