The two main types of milk proteins are the caseins and the whey proteins which make up to 80% and 20% of the protein content of cow's milk proteins respectively. Other proteins present at low levels in milk include antibodies and iron carrying proteins.

Just as animals inherit traits such as eye or coat color from their parents, cows also have traits, inherited through their genes, to produce different naturally occurring forms of their major milk proteins.

Beta casein, makes up to a third of the protein content of cows milk, and has an excellent nutritional balance of amino acids.

There are 2 main forms of beta casein protein found in the milk of dairy cows: A2 and A1 beta casein which differ from each other by one amino acid. Small differences in amino acid composition of proteins can result in the different forms of a protein having different properties.

Which beta casein genes the cow has inherited determines what form of beta casein will be produced in their milk.

One gene for beta casein production is inherited from each parent, so each cow carries 2 copies of the beta casein gene.

Of these 2 beta casein genes;

• both can be for A2 beta casein, so its milk contains only the A2 form of beta casein
• both can be for A1 beta casein, so its milk contains only the A1 form of beta casein
• one can be A1 and the other A2 beta casein so its milk contains equal amounts of A1 and A2 beta casein.

A simple DNA test, looking at the cow’s beta casein genes, allows easy identification of which of the beta casein forms it carries.

For more information on beta caseins in cows milk click here.