A1 milk is a type of cow's milk that contains a specific form of beta-casein protein known as A1 beta-casein. This protein differs from A2 beta-casein, which is found in A2 milk. Some studies suggest that A1 milk may be linked to digestive discomfort in certain individuals, while A2 milk is often marketed as a gentler alternative. The primary source of A1 milk comes from breeds like Holstein and Jersey cows, which are commonly found in many dairy farms. In contrast, A2 milk is produced by cows that primarily carry the A2 gene, such as Guernsey and Ayrshire breeds.