Milk is the only food for mammals at the early stage of life and serves to ensure all the necessary nutrients and protects the health. Milk is a rich source of proteins, minerals and antibodies. It is also a source of food for human even after stopping breastfeeding. Milk contains 2 major proteins: casein and whey. There are 4 types of caseins found in bovine milk: alpha s1, alpha s2, betta and kappa. Different variants of betta casein were characterized of which most common are A1 and A2, while B is less common and C is rare. Frequency of A1 and A2 beta casein varies in various dairy cattle breeds. A1 is common in Ayrshire, Red and Holstein-Friesian cattle, while A2 is common in Jersey and Guernsey. It has been reported that digestion of A1 variant beta casein in the body results in beta-casomorphine 7 (BCM-7) which may increase the risk of Diabetes Melltius 1, Sudden Infant Death Syndrome, Heart disease and Autism. Digestion of A2 does not result in forming of BCM-7, therefore, with selective breeding based on genetic tests, it is possible to reduce the A1 variant that has been linked with all the stated human diseases above. Digestion of A2 does not lead to the formation of BCM-7, so through selective breeding based on genetic testing, it is possible to reduce the A1 variant that has been linked to all of the above-mentioned human diseases.
Additional note: Due to differences in digestion physiology, it has been suggested that milk intolerance in some cases could be related to the consumption of milk containing Beta-Casein A1 proteins.