What is A2 milk?
TWO MAJOR protein groups are present in cow’s milk — approximately 82% of protein is casein and 18 per cent whey protein. Caseins are a group of proteins and beta casein is the second most abundant protein. The beta casein group has two common variants: A1 and A2. Most milk contains a mixture of these proteins. Approximately 60% of the beta casein is A2, and 40% is A1. The proportion of A2 and A1 beta casein in milk varies with different breeds of dairy cattle, but A2 milk contains only A2 beta casein.
Before domestication, cows produced the A2 beta casein protein and not A1. A natural gene mutation occurred in Holsteins 8,000 years ago, resulting in production of the A1 beta casein protein in this breed. In general, milks from Guernsey and Jersey cows, Asian herds, human milk and others (sheep, goat, donkey, yak, camel, buffalo, sheep, etc) contain mostly A2 beta casein.
Milk from Holstein Friesians contain mostly A1 beta casein. Because Holsteins are used to genetically improve the production of other dairy cattle breeds, the A1 beta casein variant became dominant in milk. But dairy herds in much of Asia, Africa and parts of southern Europe remain naturally high in cows producing A2 milk.
More than 50% of the Jersey breed carries the A2 beta casein variant, but with considerable variation among the herd, and more than 90% of the Guernsey breed carries the A2 beta casein variant. As this is genetic, it gets passed onto offspring — you can therefore breed for an entirely A2 herd once you have tested cattle and culled/bred as appropriate. Why is this important? Many people believe that they are lactose intolerant and give up dairy entirely, but some of this group may actually have an intolerance to A1 beta casein.
Drinking A2 milk and its dairy products is understood to reduce bloating and indigestion (digestive discomfort) caused by A1 milk consumption.
A2 milk contains the same amount of lactose as non-A2 milk so, in clinically diagnosed cases of lactose intolerance, A2 milk will not provide the benefits that lactose-free milk offers.