A2 milk

A2 milk is a variety of cows' milk that predominantly contains the A2 form of β-casein proteins (as opposed to A1 milk, which contains mostly A1 β-casein proteins). Cows' milk like this was brought to market by The a2 Milk Company and is sold mostly in Australia, New Zealand, China, and the United States. It was sold in the United Kingdom between 2012 and 2019. Non-cow milk, including that of humans, sheep, goats, donkeys, yaks, camels, buffalo, and others, also contain mostly A2 β-casein, and so the term "A2 milk" is also used in that context.

The a2 Milk Company and some companies producing goat's milk products claim that milk containing A1 proteins is harmful, but there has been no widely accepted scientific work identifying a direct link between A1 protein and any adverse effect on health.

A1 and A2 beta-casein are genetic variants of the beta-casein milk protein that differ by one amino acid. A genetic test, developed by the a2 Milk Company, determines whether a cow produces A2 or A1 type protein in its milk.