Milk Casein Genetics: What Updated A2 and Kappa Casein Trends Mean for Dairy Producers

By
Tanya Eadie
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127

Milk proteins continue to influence breeding decisions in Canada and around the world. Casein traits, such as Beta Casein (A2) and Kappa Casein, affect milk digestibility, cheese yield, and the overall value of milk. With new information from Lactanet’s updated database, producers now have a clearer picture of how these genotypes are changing within different dairy breeds.

Why Casein Genetics Matter

Caseins make up most of the protein in cow’s milk. Small genetic differences can change how easily milk is digested or how well it performs during cheese making. As a result, more producers are paying attention to casein genetics.

Over the past few years, interest in A2 milk and high-yield cheese milk has grown. Because of this demand, many breeders are testing for Beta Casein and Kappa Casein and using the results in their selection programs.

Since 2022, Lactanet has received a much larger number of casein test results from A.I. companies, breed associations, and international sources. This expanded dataset allows for a more accurate look at how casein traits appear across breeds.

Beta Casein (A2): Current Frequencies and Trends

Beta Casein appears in two common forms: A1 and A2. The A2 form has gained attention because of consumer interest in A2-labelled milk products.

A2A2 Still Strong in Jersey, Guernsey, and Brown Swiss

The newest results show that the A2A2 genotype remains very common in several breeds:

  • Guernsey: 86.4%

  • Brown Swiss (global): 84.1%

  • Jersey: 77.8%

Lactanet’s database also now includes more results from Interbull, which greatly increased the number of European bulls in the Brown Swiss dataset. Because of this, the global Brown Swiss A2A2 frequency rose sharply. However, among Canadian-born Brown Swiss, the frequency is lower at 70.5%.

More Canadian Females Carrying A2

In addition, Figure 2 (referenced in the original report) shows a steady rise in the number of Canadian females carrying at least one copy of A2. This includes animals with A2A2 and A1A2 genotypes.

This gradual increase suggests that more Canadian breeders are choosing sires that will help move their herd toward A2 over time.

Kappa Casein: Effects on Cheese Yield

Kappa Casein is another important milk protein. It affects clotting, curd firmness, and cheese yield. Because of this, it is especially important for herds that ship milk to cheese processors or participate in solids-based payment programs.

There are six possible Kappa Casein genotypes: AA, AB, AE, BB, BE, and EE.

Why the BB Genotype Matters

  • The BB genotype tends to produce milk with higher fat and protein.

  • It also clots faster, which can increase cheese yield.

  • The EE genotype is the least desirable because milk from EE cows does not clot well.

Breed Comparisons

The updated data shows clear breed differences:

  • Jersey: 80.4% BB

  • Brown Swiss: 64.8% BB

These results match what many producers already see on their farms. Jersey and Brown Swiss genetics remain strong options for cheese-focused production.

How Producers Can Use Casein Genetics

Casein information can help producers improve milk quality while also supporting their long-term breeding goals.

To Increase A2 in the Herd

  • Use A2A2 or A1A2 sires.

  • Monitor carrier status in replacement heifers.

  • Consider genomic testing to guide future mating plans.

To Increase Kappa Casein B

  • Select sires with BB or AB genotypes.

  • Avoid using sires that may increase the EE genotype.

Because these traits are simple and easy to track, they fit well into both small and large breeding programs.

Accessing Casein Information

Producers can easily find their herd’s casein results through Lactanet tools:

  • A2 Report in MySite: Available each January, with herd-level and animal-level details.

  • Group Query on LactanetGen.ca: Allows producers to filter animals by Beta Casein or Kappa Casein genotype.

These tools make it easy to track herd progress and adjust breeding plans as needed.

Key Takeaways

  • Casein traits are becoming a more common part of genetic selection because of their impact on digestibility and cheese yield.

  • The A2A2 genotype is especially strong in Guernsey, Brown Swiss, and Jersey populations worldwide.

  • Canadian herds continue to show increasing numbers of A2 carriers.

  • Jersey and Brown Swiss lead in the desirable Kappa Casein BB genotype.

  • Producers can change casein frequencies in their herd by selecting sires with the right genotypes and reviewing herd reports regularly.

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