Quick facts
- Beta-casein, which makes up 30% of milk protein, exists in two forms: A1 and A2.
- A2A2 cows produce milk with only the A2 protein.
- One way to determine the A1/A2 status of your herd is to genomic test your cows and heifers.
- Claims that A2 milk is easier for humans to digest and improves health have not been proven by science.
- Overall, the industry needs more data to confirm if there are added benefits to A2A2 genetics that go beyond the potential for easier human digestibility.
What is A2 milk?
Beta-casein, which makes up 30% of milk protein, exists in two forms: A1 and A2. A2 milk only contains the A2 variant of beta-casein protein. Cows with the A2A2 gene produce only A2 milk. Jersey, Guernsey, Normande and Brown Swiss breeds have a higher percentage of A2 genes than Holstein.
There have been claims that A2 milk is easier for humans to digest, improves health and lowers the risk for some diseases. Many of these claims have not been proven by science. The most promising claim is for easier human digestibility.
Testing your herd
Some farmers have transitioned to A2 herds, but this can take many generations, depending on the status of your herd. One way to determine the status of your herd is to genomic test your cows and heifers.
If you are already genomic testing, A2 status can be determined for about $5 per animal. If you choose to transition to an A2 herd, you can determine which cows and heifers to keep or cull once you receive your genomic results.
An A2A2 animal bred to another A2A2 animal will always have an A2A2 offspring. A2A2 cows produce milk with only the A2 protein. Cows that are A1A1 will produce milk with only the A1 protein. Cows that are A1A2 will produce milk that contains both A1 and A2 protein.
Breeding for A2 milk
The University of Minnesota’s research dairy herd at the West Central Research and Outreach Center in Morris, Minn. uses Holstein, Jersey, Montbéliarde, Normande and Viking Red in their breeding program. Many A.I. studs have been marketing A2A2 bulls and more information can be found online or in published bull catalogs.
The entire UMN dairy herd was genotyped in 2019. More than 50% of the Holsteins in the herd are A2A2, which was not expected because the trait has not been actively selected for. The 1964 genetic line Holsteins had a lower percentage of animals that were A2A2 at 26%. The crossbred cows and heifers ranged from 36 to 50% of animals that were A2A2.
A2 status of the University of Minnesota dairy herd in Morris, Minn.
| Breed | Number of cows | % A2A2 | % A1A2 | % A1A1 |
|---|---|---|---|---|
| Holstein | 114 | 56 | 33 | 11 |
| 1964 Holstein | 82 | 26 | 48 | 26 |
| Holstein-sired crossbred | 65 | 49 | 34 | 17 |
| Jersey-sired crossbred | 51 | 47 | 45 | 8 |
| Montbéliarde-sired crossbred | 98 | 36 | 47 | 17 |
| Normande-sired crossbred | 56 | 50 | 45 | 5 |
| Viking Red-sired crossbred | 136 | 45 | 40 | 15 |
Should you care about A2 milk?
If the industry pays a premium for A2 milk, then you might consider selecting your herd for A2A2 animals and even start using A2A2 bulls. However, remember that selecting from the top Net Merit bulls is essential to maximize farm profitability, so be sure to check that list when placing an emphasis on A2 genetics.
Are there added benefits of A2A2 genetics?
Potentially. Work done by the University of Minnesota in collaboration with Penn State looked at approximately 3,000 cows and evaluated production and productive life in relation to A2 status. The study saw a difference in production and productive life when comparing A2A2 animals to A1A1 animals, but saw no difference between A2A2 animals and A1A2 animals. There was potential bias identified in the study from culling criteria in some participating farms including A1 vs. A2 status.
Overall, the industry needs more data to confirm if there are added benefits to A2A2 genetics that go beyond the potential for easier human digestibility.
Reviewed in 2022