by Todd Byrem, Ph.D. Director, AntelBio
Judging by recent inquiries at NorthStar the story surrounding A2 milk must be reaching new heights. Questions such as; can we test our milk for A2, how can we transition our herd to A2 milk, and are there really beneficial health effects to drinking A2 milk are but a few we have fielded lately. Current science can only answer some of these questions; the rest, only time will tell.
What is A2
Scientifically the term A2 refers to a specific variant of a milk protein called beta-casein, which makes up 30 percent of the total protein in milk. Overall, caseins, including alpha-, beta-, gamma- and kappa-casein, are the major protein in milk, that after processing we enjoy as curds, on pizzas, and in the glue we ate in kindergarten. There are multiple forms of beta-casein, each unique due to a variation in the beta-casein gene, but the two most predominant in bovine milk are A1 and A2.
Phylogenetic analysis has shown that the original beta-casein gene in bovines encoded the A2 form and that between 8,000-10,000 years ago a mutation resulted in the emergence of the A1 form. Over time the A1 form has increased in frequency, particularly in Holsteins, until today where 60 percent of beta-casein in milk is A1 and 40 percent is A2. The mutation in the original A2 beta-casein gene resulted in a single amino acid substitution in the final protein. The result of this amino acid change is that upon digestion in humans, the A1 form releases a bioactive peptide (fragment). This bioactive peptide, if it escapes further digestion and is absorbed into the blood stream, can interact with our cells and affect their function.
Identifying A1 & A2 in your herd
The easiest and least costly way of determining if a single cow is producing the A1 or A2 protein or both is to run a genetic test on her DNA from hair, blood or tissue samples. Although there is a difference in the protein itself, the difference is so small that the cost of finding the difference in a milk assay is prohibitive. Either way, both DNA- and protein- based assays have been patented by The a2 Milk Company® and are available only through partnering laboratories that have licensed rights to the test (Neogen® GeneSeek® and UC Davis Veterinary Genetics Laboratory). With genetic testing, if the cow is homozygous A1/A1, she produces the A1 protein. If she is homozygous A2/A2, she produces the A2 protein. If she is heterozygous, she produces both forms.
The decision to transition a herd to A2 milk should be carefully considered. The entire A2 milk story is yet to be written as there are many uncertainties surrounding the health implications and future demand for it. In addition to patenting the tests for genotyping, The a2 Milk Company has trademarked “a2 Milk®,” which adds both significant complexity to the marketing and sales in this market. That said, the inheritance and production of beta-casein variants obey simple Mendelian genetics, so transitioning a herd to produce solely A2 milk is not complicated.
Making an A2 herd
There are many routes to breed for the production of A2 milk. A low-cost, passive route would be to select homozygous A2/A2 sires for mating. Elimination of the A1 gene in a herd using this route would take many generations. Although there are numerous A2/A2 sires available for selection, a strictly A2 lineup would be limited for the improvement in other traits that may have a more certain economic future (Net Merit, Productive Life, Wellness, etc)
A more active and much costlier route would be to genomically test females and mate A2/A2 females with female-sorted A2/A2 sires for replacements. Coupled with IVF, a herd could eliminate the A1 gene in as little as two years. With the uncertainty in the direction of the market for A2 milk, the costlier, more aggressive route will carry greater risks for payoff.
As with any deviation from the commercial norm, the return on investing in A2 breeding will depend on the success of this niche market. Clearly, the consumption of A1 milk and milk products is not solely detrimental to human health. As with any source of essential nutrients, the benefits of consuming today’s milk products greatly, greatly exceed the risks. Similarly, there are no specific health benefits that can be ascribed solely to the consumption of A2 milk. There is scientific evidence that the digestion of A1 beta-casein, but not A2 beta-casein, produces a bioactive peptide that can alter cellular function in humans. However, our further digestion, absorption and reaction to the bioactive peptide is influenced by so many genetic, environmental, and behavioral factors that findings from population health studies are and will forever remain inconclusive.
Still, there is nothing wrong with special branding of milk products. It would behoove the dairy industry to produce an array of products that can meet the demands of as many consumers as possible. In some people that have demonstrated an intolerance to milk consumption, A2 milk has fulfilled their desire to include milk products in their diet. Imagine fearing the consequences of a sundae – the horror! There is a market for A2 Milk, but science may have little to do with its eventual size and potential for US dairy producers.