Not sure if this was brought up before, below is page 53 of a...

Not sure if this was brought up before, below is page 53 of a University of Missouri Study. mentions A2M in particular.
http://dairy.missouri.edu/revitalization/Value_Chain_Marketing_and_Processing.pdf

“For some people, consuming dairy products isn’t a good option because they feel discomfort as their bodies try to digest such products. Generally, choosing A2 beta-casein dairy leads to easier digestion regardless of whether a consumer has milk tolerance problems (Berry 2014d). The A2 milk also leads to less bloating (Hoard’s Dairyman 2014). In addition to affecting gastrointestinal health, the A1 protein has been linked to beta-casomorphin 7, or BCM-7, levels. A1 protein consumption and BCM- 7 levels have been linked to health problems such as heart disease, sudden infant death syndrome, autism and schizophrenia (Kaminski, Cieslinska and Kostyra 2007). A2 beta-casein gained attention after the book Devil in the Milk debuted in 2007 (Snowville Creamery).
Of the protein found in milk, about 30 percent is beta-casein. Historically, cows produced A2 beta- casein. However, a mutation that occurred over time led to some cows having a gene that programmed a different beta-casein amino acid sequence and caused cows to produce A1 beta-casein. Commonly, Holstein and Friesian breeds have the mutation. Depending on a cow’s genes, it may produce only A1 beta-casein, only A2 beta-casein or a combination of the two. Guernseys typically produce more A2 beta-casein (Snowville Creamery). The A2 gene is rarer (Hoard’s Dairyman 2014).
Based in North Sydney, Australia, The a2 Milk Co. has already recognized A2 beta-casein products as an opportunity to pursue. It’s sold its a2 milk products in New Zealand and Australia since 2003 (Berry 2014d). In Australia, A2 milk has captured a 9 percent share of fluid milk sales (Hoard’s Dairyman 2014). After experiencing success in its current markets, The a2 Milk Co. plans to launch its fresh milk products within the U.S. sometime during 2015 (Berry 2014d). This wouldn’t be the first effort to introduce a2 beta-casein milk to the U.S. Prairieland Dairy, a dairy collective located in southeast Nebraska, has collaborated with The a2 Milk Co. to produce a2 milk. In 2007, Prairieland started selling a2 milk at regional Hy-Vee stores with assistance from The Original Foods Co., a distributor. Relative to commodity milk, a2 milk carries a premium to compensate producers for needing to test their cows for A2 genetics and segregating the A2 milk production stream from the A1 milk production stream (Toner 2007).
U.S. companies interested in pursuing A2 milk production as a niche market will face challenges, considering that The a2 Milk Co. has already secured 11 U.S. patents, which protect cattle genetic testing and A1-free marketing claims. Until 2034, The a2 Milk Co. will have active U.S. patents (Hoard’s Dairyman 2014). Several farms, however, already promote that their milk would contain high A2 levels and educate consumers about the different beta-casein forms. Yoder Farm, which is a Pennsylvania farm that markets Golden Guernsey milk, describes a high A2 beta-casein concentration as a benefit of its Guernsey milk (Yoder’s Country Market 2014). Cedar Summit Farm explains that its breeding efforts have emphasized producing milk with high A2 beta-casein levels (Cedar Summit Farm 2014).”