Which cow's milk is A1?

December 4, 2025 •

4 min read

The majority of commercially available dairy milk in countries like the United States, Australia, and much of Europe contains both A1 and A2 beta-casein proteins. This mix is largely due to the widespread use of certain cow breeds, leaving many to wonder, "Which cow's milk is A1?" The answer lies in the genetic makeup of the dairy cattle itself.

Quick Summary

A1 milk is produced by specific breeds of cows, primarily those of northern European descent like Holstein and Friesian. It contains the A1 beta-casein protein, which has been linked to digestive issues in some individuals. This differs genetically from A2 milk, sourced from indigenous cows or special herds bred for the A2 protein.

Key Points

Northern European Breeds Produce A1 Milk: Cows like Holsteins, Friesians, and Ayrshires, originally from northern Europe, are primary producers of milk containing the A1 beta-casein protein.
A1 Protein is a Genetic Mutation: The A1 variant is the result of a genetic mutation that occurred in dairy cattle several thousand years ago, differentiating it from the original A2 protein.
Commercial Milk is Often A1/A2 Mixed: Standard store-bought milk from larger dairies is typically a mix of both A1 and A2 proteins because it is collected from diverse herds.
A1 Digestion Releases BCM-7: When digested, the A1 beta-casein protein can release a peptide called BCM-7, which has been associated with digestive discomfort and other health concerns in some individuals.
A2 Milk is an Alternative: For people with sensitivities, A2 milk—sourced from specific breeds that produce only the A2 protein—may be easier to digest and is often marketed as a gut-friendly alternative.
Scientific Debate is Ongoing: While some studies suggest links between A1 milk and health issues, the broader scientific community and regulatory bodies often find the evidence inconclusive, highlighting the need for more research.

Understanding the A1 vs. A2 Protein Difference

To truly understand which cow's milk is A1, one must first grasp the core difference between the A1 and A2 milk proteins. These variants are different forms of beta-casein, a major protein found in cow's milk. The distinction boils down to a single amino acid at position 67 of the protein chain. A2 milk contains proline at this position, while A1 milk has histidine due to a natural genetic mutation that occurred in European dairy herds thousands of years ago.

This small change in structure affects how the body digests the protein. When A1 beta-casein breaks down, it can release a peptide called beta-casomorphin-7 (BCM-7). This peptide has been linked to potential digestive discomfort and inflammation in some people. In contrast, the A2 protein, with its proline amino acid, breaks down differently and does not typically release BCM-7.

Breeds That Produce A1 Milk

Most conventional dairy milk is a blend of both A1 and A2 proteins because it is collected from a mix of dairy herds. However, the predominance of the A1 protein can be traced back to the widespread breeding of cattle originally from northern Europe. Breeds known for producing high quantities of A1 beta-casein include:

Holstein Friesian: This black-and-white breed is the most common dairy cow in the world and is a primary source of A1 milk. Historically bred for high milk volume, the A1 variant is prevalent in Holstein populations.
Ayrshire: Originating from Scotland, this breed is also known to produce milk with a high frequency of the A1 allele.
British Shorthorn: This breed, and its crosses, contributes to the A1 milk supply in many commercial dairy operations.
Other European Breeds: While percentages vary, many other breeds with northern European ancestry carry the A1 gene.

The A1/A2 Distribution Among Cow Breeds

It's important to note that the presence of the A1 gene isn't absolute in any breed. A cow can have one of three genetic combinations for beta-casein: A1A1 (produces only A1 protein), A2A2 (produces only A2 protein), or A1A2 (produces both). The percentage of cows with the A1 gene is higher in northern European breeds compared to indigenous cows from other parts of the world.

A1 vs. A2 Milk: A Comparison


Feature	A1 Milk	A2 Milk
Sourced From	Breeds of northern European origin, such as Holstein Friesian, Ayrshire, and British Shorthorn.	Indigenous Indian breeds (e.g., Gir, Sahiwal), Channel Islands breeds (e.g., Guernsey), and specially-selected A2 herds.
Beta-Casein Protein	Contains the A1 variant and often a mix of A1 and A2 proteins.	Contains only the A2 beta-casein protein.
Digestion	Can release the BCM-7 peptide during digestion, potentially causing digestive discomfort in some individuals.	Breaks down more like human breast milk, potentially making it easier to digest for sensitive individuals.
Popularity	Dominant in the commercial milk market across the US, Europe, and Australia due to high milk yield in producing breeds.	A growing niche market, specifically targeting consumers concerned about digestive health and inflammation.

The Health Debate Surrounding A1 Milk

The discussion around A1 and A2 milk gained prominence with claims that the BCM-7 peptide released from A1 protein digestion could be linked to various health issues. Some research has explored potential correlations between A1 milk consumption and conditions such as:

Digestive Issues: Symptoms like bloating, gas, and abdominal pain are reported by some sensitive individuals after drinking regular (A1-containing) milk.
Inflammation: Some studies suggest that BCM-7 may contribute to gut inflammation, potentially leading to gastrointestinal discomfort.
Other Conditions: While more research is needed, some epidemiological studies have suggested links between A1 milk and conditions like type 1 diabetes and heart disease, though regulatory bodies often view the evidence as inconclusive.

However, the scientific community is still debating the conclusive impact of A1 milk on human health. A major European Food Safety Authority (EFSA) review found insufficient evidence to link BCM-7 in A1 milk to chronic diseases. As with any dietary choice, individual reactions and genetic predispositions play a significant role. For those who experience digestive troubles with standard milk, switching to a pure A2 milk product may offer a noticeable difference.

Conclusion: Making an Informed Choice

The question of which cow's milk is A1 is fundamentally a question of genetics and breed history. The vast majority of standard, commercial milk contains the A1 beta-casein protein, sourced from popular, high-yield European dairy breeds like the Holstein. This contrasts with A2 milk, derived from specific herds or indigenous cow breeds that produce milk containing only the A2 protein. While ongoing scientific debate exists regarding the potential effects of the A1 protein's digestion by-products, many consumers with milk sensitivities find relief by switching to A2 milk. Understanding the source and protein type of your dairy can empower you to make a more informed and personalized dietary choice.

For additional information on the science behind A1 and A2 beta-casein, you can consult research from the National Institutes of Health.

Frequently Asked Questions

The difference is based on the type of beta-casein protein in the milk. A1 milk contains the A1 beta-casein protein, while A2 milk contains only the A2 beta-casein protein. This difference is due to a single amino acid variation in the protein structure.

A1 milk is primarily produced by cows of northern European origin, including the common Holstein Friesian, Ayrshire, and British Shorthorn breeds.

Most conventional, commercially available cow's milk in the US, Europe, and Australia contains a mix of both A1 and A2 proteins. Only specially marketed A2 milk products are guaranteed to be free of the A1 protein.

The health effects of A1 milk are still a subject of scientific debate. Some studies suggest a link between the BCM-7 peptide released from A1 protein and digestive discomfort, while other major reviews have not found conclusive evidence to link it to chronic diseases.

It is not possible to visually determine if a cow is an A1 or A2 producer. The distinction is genetic and requires DNA testing to confirm the cow's genotype for beta-casein production.

Some individuals report experiencing symptoms such as bloating, gas, and digestive discomfort after consuming milk containing the A1 protein. These symptoms are often mistakenly attributed to lactose intolerance.

The A1 gene variant became widespread due to a natural genetic mutation that occurred thousands of years ago. It spread through modern dairy herds largely because of breeding practices that favored high milk yield, particularly among northern European cattle breeds.