Cow’s milk contains six major proteins. Four are casein proteins, the other two are whey proteins.
Casein proteins make up about 80 percent of the protein in cow’s milk.
A type of casein called beta-casein is one of the major ones, and is itself of different kinds, depending on the genetic make-up of the cow. The most common are beta-casein A1 and beta-casein A2. Milk high in beta-casein A1 is being referred to as ‘A1 milk’ while milk high in beta-casein A2 is being called ‘A2 milk’.
Milk we buy normally contains a mixture of A1 and A2 beta-caseins as it comes from mixed herds. Freisian cows produce mostly A1 milk, while Guernsey cows, sheep and goats produce mostly A2 milk.
It is beleived by many well respected people in the NZ FDA community that although not a cause of crohns, this A1 casein is the reason why many crohns sufferer's and other with digestive tract problems have difficulties with dairy products.
I kinda feel the govt line in the past has been a bit closed because NZ s dairy industry is mainly A1 herds .... very interesting research :)