Which Milk is A2 Milk? A Complete Guide to Beta-Casein Proteins

December 23, 2025 •

4 min read

Originally, all cow's milk contained only the A2 beta-casein protein, but a natural genetic mutation introduced the A1 protein to many modern dairy herds. The question of which milk is A2 milk now comes down to sourcing, as it refers specifically to milk containing only this easier-to-digest protein variant.

Quick Summary

A2 milk comes from specific cow breeds that naturally produce only the A2 beta-casein protein, rather than the more common mix of A1 and A2 proteins found in regular milk. Other animal milks, like goat, sheep, and buffalo milk, are also naturally A2.

Key Points

A2 vs. A1 Proteins: A2 milk contains only the A2 beta-casein protein, whereas regular cow's milk is typically a mixture of A1 and A2 proteins.
Digestive Comfort: The A1 protein, upon digestion, can release a peptide called BCM-7 that has been linked to digestive discomfort in some people, a side effect not associated with the A2 protein.
Sourced from Specific Cows: A2 cow's milk is sourced from special herds of cows, like Jersey or Guernsey breeds, that have been genetically tested to ensure they produce only the A2 protein.
Naturally A2 Milk Sources: Other animal milks, including goat, sheep, and buffalo milk, are naturally A2 and do not contain the A1 protein.
Not for Lactose Intolerance: Despite potential digestive benefits, A2 milk still contains lactose and is not suitable for individuals with a confirmed lactose intolerance.
No Major Nutritional Differences: For those without a sensitivity to the A1 protein, A2 milk offers a very similar nutritional profile to regular milk.

The Difference Between A1 and A2 Milk

To understand which milk is A2 milk, it's essential to look at the protein composition. All milk contains a variety of proteins, but two of the most significant are casein and whey. The beta-casein protein, which makes up about one-third of the total protein in cow's milk, exists in at least 13 different forms, with the A1 and A2 variants being the most common.

The difference between the A1 and A2 beta-casein protein is a single amino acid at position 67 on its chain. This small variation can have a major effect on how the protein is digested. In a process that occurred thousands of years ago, a genetic mutation caused some cows to produce the A1 protein. Today, most commercial milk from conventional dairy cows contains a mix of both A1 and A2 proteins.

During digestion, the A1 beta-casein protein breaks down to release a peptide called beta-casomorphin-7 (BCM-7). BCM-7 has been linked to digestive issues like bloating, discomfort, and inflammation in some sensitive individuals. In contrast, the A2 beta-casein protein is broken down differently and does not release significant amounts of BCM-7. For some people, switching to A2 milk can alleviate these digestive symptoms, though it is not a solution for true lactose intolerance or a cow's milk protein allergy.

A2 Milk from Specific Cow Breeds

Since the A1 protein arose from a natural genetic mutation, it is a genetic trait passed down through cow breeds. Dairy farmers can now test their herds to identify cows that produce milk containing only the A2 protein. This process of genetic testing and selective breeding ensures that the milk labeled as A2 is free from the A1 protein.

Cow breeds that are known to have a high percentage of A2 genetics:

Jersey: Hailing from the Channel Islands, Jersey cows are well-known for producing milk with a high fat content and a very high percentage of the A2 protein.
Guernsey: Also from the Channel Islands, Guernsey cows are another breed with a historically strong A2 profile, often with over 70% of their milk containing predominantly A2 protein.
Indian Breeds: Many indigenous Indian breeds, such as Gir, Sahiwal, and Rathi, are known to be naturally rich in A2 beta-casein.
Charolais and Limousin: These Southern French breeds are also listed among those with higher A2 genetics.

Other Animal Milks That Are Naturally A2

Interestingly, the A1 beta-casein mutation is largely confined to Western cattle breeds. Most milk from other dairy-producing mammals naturally contains only the A2 beta-casein protein, making them natural A2 milk sources.

Milk from other animals that is naturally A2:

Goat Milk: As one of the most widely consumed milks globally, goat milk contains primarily A2 beta-casein protein. Many people who experience digestive discomfort with cow's milk find goat milk easier to tolerate.
Sheep Milk: This type of milk also contains predominantly A2 beta-casein. Additionally, the fat globules in sheep milk are smaller than in cow milk, contributing to its easy digestibility.
Buffalo Milk: Buffalo milk is always 100% A2 and is known for its rich, creamy texture and high nutrient density.
Human Breast Milk: For infants, human milk contains a high percentage of A2 beta-casein, which is why the structure of the A2 protein is often compared to it.

Comparison: A2 Milk vs. Regular Cow's Milk


Feature	A2 Milk	Regular Cow's Milk (A1/A2 Mix)
Beta-Casein Protein	Contains only the A2 beta-casein variant.	Contains a mix of both A1 and A2 beta-casein variants.
Digestion Byproduct	Does not produce significant levels of the BCM-7 peptide during digestion.	Produces the BCM-7 peptide, which can trigger digestive discomfort in sensitive individuals.
Protein Structure	The protein structure is different due to a single amino acid difference from A1.	Contains the A1 variant with a slightly different protein structure.
Common Sources	Sourced from specific cow breeds (Jersey, Guernsey, Indian breeds) or other mammals (goats, sheep, buffalo).	Typically sourced from conventional dairy cows like Holsteins, which produce a mix of A1 and A2 proteins.
Digestive Impact	May be easier to digest for people sensitive to the A1 protein, though it is not lactose-free.	Can cause digestive discomfort in individuals sensitive to the A1 protein, but is not the same as lactose intolerance.
Nutritional Profile	Generally similar nutritional content (vitamins, calcium, fat) to regular milk. Some sources suggest minor variations in fat and nutrient content.	Contains the same essential nutrients as A2 milk.

Conclusion: Making Your Choice

The fundamental answer to the question "which milk is A2 milk?" is milk that contains only the A2 beta-casein protein. This can be either specially-sourced cow's milk from specific breeds like Jersey or Gir, or milk from other mammals such as goats, sheep, or buffalo. While A2 milk is not a magic cure for dairy-related issues and contains the same lactose as regular milk, it may offer a path to enjoying dairy again for individuals who experience digestive discomfort linked to the A1 protein. For those with no issues consuming regular milk, there is no strong scientific evidence suggesting A2 milk is superior. The choice ultimately depends on individual dietary needs and how your body responds to the different protein variants. For further reading, consider resources on beta-casein research.

The Verdict on A2 Milk Sourcing

A2 cows are selected through genetic testing, ensuring they produce only the A2 protein.
Goat milk is naturally A2, making it a viable alternative for A1-sensitive individuals.
Sheep and buffalo milk are also naturally A2, providing other high-protein, easily digestible options.
Most regular cow's milk is a mix of A1 and A2 due to a genetic mutation in common Western dairy breeds like Holsteins.
A2 milk does not address lactose intolerance, as it still contains the same amount of milk sugar.

Frequently Asked Questions

The key difference is the type of beta-casein protein they contain. Regular cow's milk contains a mix of A1 and A2 proteins, while A2 milk comes from cows that naturally produce only the A2 protein.

Some individuals who experience digestive discomfort (e.g., bloating, gas) from regular milk report better tolerance with A2 milk. This is believed to be related to the A1 protein's breakdown into the peptide BCM-7, which A2 milk avoids.

No, A2 milk still contains lactose, the milk sugar responsible for lactose intolerance. It is a protein issue, not a sugar issue. People with lactose intolerance should still avoid it or opt for a lactose-free option.

Certain cow breeds, such as Jerseys, Guernseys, and many indigenous Indian breeds like Gir and Sahiwal, are known for producing A2 milk. These herds are identified through genetic testing.

Yes, milk from goats, sheep, and buffalo is naturally and predominantly A2. Unlike many Western dairy cows, these mammals do not have the A1 beta-casein mutation.

Milk specifically labeled as 'A2' has been sourced from cows that have been genetically tested and selected for their A2 protein production. You must look for this explicit labeling on the product.

For those with a dairy allergy or galactosemia, A2 milk is not a suitable substitute and carries the same risks as regular milk. While some studies have been funded by the industry, there are no known risks for individuals who can safely consume regular cow's milk.