A2/A2 Genetics: Breeding Considerations

Some milk buyers and brands want milk from cows that carry two copies of the A2 form of a milk protein gene. If you are thinking about it, treat it as a marketing and breeding decision, not a shortcut.

Key points

A2/A2 is a gene status, tested with a sample, and passed on from both parents.
Check the market and the contract before you change breeding plans.
Compare A2/A2 bulls on the same health and production traits as any other bull.
Keep records and plan how separate milk would be handled.

What A2/A2 refers to

Cattle carry two copies of a gene that controls one of the proteins in milk. The gene has more than one common form, and the two forms are often called A1 and A2. A cow can carry two A2 copies, two A1 copies, or one of each.

A cow with two A2 copies is called A2/A2. Her calves will receive at least one A2 copy from her. Whether they get two depends on the sire. Say plainly to your family and employees what the plan is, so no one is surprised by changes in how cows are grouped.

A2/A2: two A2 copies
A1/A2: one of each
A1/A1: two A1 copies

Why farms ask about it

Some processors and brands market milk from A2/A2 cows as a separate product. Whether that is available to you, and whether it pays more, depends entirely on your milk buyer and your region.

This article does not make claims about the health effects of either protein form. Questions like that belong with qualified researchers and regulators, and the rules on what can be said on a label differ. Your milk buyer and your state department of agriculture can explain what applies to you.

If you sell to a processor that does not run a separate A2 program, there is little reason to change your sire list for this trait alone. Genetic progress in health and fertility traits usually pays better over the long run.

Start with the milk market

Before you change a single mating, find out whether anyone will buy A2/A2 milk from you, how they will verify it and what they pay. Premiums and program terms change over time, so get everything in writing.

If there is no buyer in your area, selecting for A2/A2 may be of little economic benefit, even though it can still be done alongside your other goals.

Who is the buyer and what do they require?
Do they test every cow or just a sample?
How is the milk kept separate from other milk?
How long is the contract and how can it change?

Testing cows and bulls

The A2 status of a cow or bull is found with a genetic test, usually done on a hair or tissue sample, through a lab or your genetics supplier. Many AI bulls have the result listed in their sire information.

Test heifers and replacements so you know what you have. Keep the results with the animal's other records and make sure each sample is labeled carefully, since mix-ups are easy to make.

Use only a lab or supplier that your milk buyer or breed association accepts. A result from an unknown source may not count if a buyer later asks for proof.

Choosing sires without giving up other traits

The A2 form is only one gene. A bull can be A2/A2 and still be poor for fertility, feet or udder health. Compare A2/A2 bulls on the same overall index, health traits and conformation you would use for any other sire.

If the best sires for your herd are not A2/A2, you might choose to use A2/A2 bulls on a share of the herd and watch results. Quick, sweeping changes can reduce overall genetic progress.

Whatever you decide, write the plan down. A simple page that lists your goals, the sires you will use and the share of matings involved is easier to follow than a plan kept in your head.

Keeping the milk separate

If a buyer pays for A2/A2 milk, you will have to keep that milk apart, which usually means a separate group of cows, separate handling and records that prove it. That may take management changes and extra labor.

Work out the practical side before you commit. Where will those cows be housed, and how will they be milked? How will the milk be tracked from the parlor to the truck?

Records, planning and next steps

Keep a simple record for every animal: test result, date, lab, sire and dam status. Over several generations, your herd will shift toward the status you aim for, and the records will make planning easier.

Review your plan with your genetics supplier and milk buyer each year. Programs change, and so do the bulls available to you. Revisit your milk buyer's rules every year, since terms can change without much notice.

When to get help: Ask your milk buyer what premium programs exist and what they require, and check with your state department of agriculture about labeling rules. Your veterinarian and genetics supplier can help with sampling and records.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

More in Breeding, Genetics & Reproduction

← Polled Genetics in Dairy Herds Color and Breed Standards in Dairy →