By: Colleen Cargile

 

What Is The Difference Between A1 and A2 Milk?

The A1/A2 status of the cow is determined by a pair of genes of the sixth chromosome. There are two major alleles of this gene, which are the A1 and A2 beta-casein alleles. Beta-casein is produced by the CSN2 gene, which has 12 variants, these variants can be split into two main groups, A1 and A2. The A1 and A2 variants of the CSN2 gene cause changes to the amino acid sequence in the beta-casein protein, this results in a conformational difference in the folding sequence of the amino acid chain and alters the properties of the protein. The A1 and A2 alleles are a result of a natural mutation caused by a SNP at codon 67 of the beta-casein gene.

• A2 – CCT (Proline)
• A1 – CAT (Histidine)

A cow carries two copies of the beta-casein gene, she can carry two copies of either allele or one copy of each, making the possible combinations A1A1, A2A2 or A1A2. Neither allele is dominant over the other, they are codominant, which means that an A1A2 cow will produce A1 and A2 beta-casein in equal amounts.

History Of A2 Milk

Originally, all milk contained the A2 beta-casein allele, however, between 5,000 and 10,000 years ago a genetic mutation occurred which resulted in a proportion of European cattle breeds producing the A1 beta-casein. The mutation occurred more in higher producing breeds, such as the Holstein, than it did in the lower producing colored breeds. The reason the majority of our milk produced today contains the A1 beta-casein is because over the years breeders selected and bred for higher producing cattle such as Holsteins, whereas lower producing colored breeds are not quite as popular.

The different milk proteins were first discovered in the 1990’s by a New Zealand based scientist, Dr. Corrie McLachlan, who started doing research when a noticeable increase in the amount of people having problems digesting milk occurred. Dr. McLachlan later founded The a2 Milk Company and began marketing a2 milk all over the world. A2 milk was first marketed in March of 2003 in Australia, and was later marketed in the UK and Asia, but it did not hit the U.S. markets until April of 2015.

Proportion Of Cattle With A2 Milk

The proportion of A2 beta-casein varies from one breed to another, depending on where they originated and how they were selected for over the years. However, prevalence of either allele in a herd may be much different than that of the breed as a whole, depending upon the breeding program and what the farmer has chosen to select for.

• Proportion of A2 beta-casein is higher in colored breeds than black and white breeds
• The Scottish Ayrshire carries the A2 allele at well over 50%
• 40% of Holstein sires in active AI lineups have two copies of the A2 gene, and over 80% have at least one copy

How To Breed For An A2 Herd

There are a couple different strategies for converting a dairy herd to 100% A2, but either way it must be known how the genes are passed onto progeny. An A2A2 cow is guaranteed to pass the A2 allele on to her progeny, just as an A1A1 cow is guaranteed to pass the A1 allele on to her progeny. On the other hand, an A1A2 cow has a 50% chance of passing on either allele.

There are two different approaches to convert to an A2 herd, each approach involves different breeding strategies and takes a different amount of time to fully convert the herd.

1. Passive Approach
   • This approach involves only using A2A2 bulls without DNA testing your herd
   • Takes almost three years before you see any impact on your herd at all
   • A herd starting out with an A1:A2 ratio of 50:50 will see an A2 proportion increase each year of about 5%
     • Ex: Year 1 A1:A2 = 50:50, Year 2 A1:A2 = 45:55, Year 3 A1:A2 = 40:60, etc.
   • The rate of improvement gradually slows down and the herd will never reach 100% A2
2. Active Approach
   • This approach involves using only A2A2 bulls as well as testing your herd of cattle and selectively culling all A1A1 and A1A2 cattle, leaving only A2A2 cows in the herd
   • Takes about two cow generations to convert the entire herd (about 10 years)

Which approach you should use, depends on you as a producer and what your goals are. If you prefer not to incur the cost of testing all of your animals you may prefer to use the passive approach, however, this does take quite a bit longer to convert your herd. Each approach has its pros and cons. What some producers may do is test their whole herd and when they get the results back they split their herd into two, one herd will be 100% A2 cows and the other herd will be any cows containing either one or two A1 alleles. This makes it so that the farm does not have to cull their A1 cattle, but it can be costly because it requires different milk storage for the A2 cows and milking them separately.

How Are Cattle Tested for the A2 Allele?

Cattle can be tested for the A2 allele by taking either a tissue, hair or blood sample and sending it to a lab to be analyzed. One particular company that does these type of genetic evaluations is Neogen. If a herd already genomically tests their herd, they can just add on the A2 test, if they do not genomically test a herd can just request the A2 test without getting a genomic evaluation. An A2 test alone cost $12 per animal from Neogen.

The science behind testing for the A1 and A2 alleles is fairly simple. The DNA from the cells is isolated and millions of copies are produced by PCR. The PCR machine is loaded with two special primers, one of which is complementary to the A1 allele, while the other is complementary to the A2 allele. A primer is a short sequence of DNA that binds to a complementary sequence in a gene and starts DNA replication. Each primer contains a fluorescent dye.

What are the Benefits of A2 Milk?

The reason that A2 milk has taken off over the last 10 years is because research has shown that it has an array of health benefits that A1 milk does not. However, some of the research behind a few of these claimed health benefits has been highly controversial and it is difficult to prove whether or not A2 milk is a direct health benefit for such claims as heart disease, Type I diabetes, autism or schizophrenia. Although certain claims are more controversial than others, the claim that A2 milk is easier for some people to digest, which is the major marketing angle of A2 milk, has actually been thoroughly tested and proven in human trials. Consumers that suffer from digestive problems such as nausea, diarrhea or bloating from drinking “normal”, or A1 milk,  are better able to digest A2 milk. A total of 1 in 4 people have trouble digesting normal milk, which is why this is such a big marketing tool for A2 milk. However, this does not apply to people that are lactose intolerant because A2 milk does not contain any less lactose than A1 milk.  A1 and A2 beta caseins digest differently, when A1 beta-casein is digested it releases large amounts of BCM7, which is a powerful opioid and oxidant of LDL (bad cholesterol). LDL has been associated with an increased build up of plaque on arterial walls and BCM7 has been associated with various diseases. A2 milk does not release BCM7 when digested, which is why research has shown that by drinking A2 milk instead of A1 milk it results in less plaque build up on artery walls. In addition to these benefits, research has also shown that consumption of A1 milk is associated with an increase in cases of Type I diabetes, heart disease, autism, and schizophrenia.

Figure 1: Countries that have a higher consumption of A1 beta-casein have more new cases of Type 1 Diabetes each year

Figure 2: Countries that have a higher consumption of A1 beta-casein have more deaths per 100,000 males age 30-69 due to heart disease.

Downfalls of Selecting for A2

There are a few downfalls on the herd level when selecting for A2 milk. When selecting for A2 milk, this means that you are only using A2 bulls which significantly decreases the amount of bulls to choose from when making mating selections. Although selecting for A2 does not directly have adverse effects on production or health traits, the smaller pool of bulls to select from may limit genetic progress. Also, selecting for A2 may also limit profitability, especially if you are not receiving a premium for your milk, because it is quite costly to test the entire herd and limited genetic progress may decrease production, as well.

Companies Marketing A2 Milk

There is one company that is a major marketer of A2 milk which is The a2 Milk Company. This is the company that started it all, it was founded by the New Zealand scientist that first discovered the A2 milk protein. This is the largest company that globally markets A2 milk, they market milk to Australia, New Zealand, Asia, UK, and the U.S. This company invested $20 million dollars over the course of three years to fund the U.S. market entry in April of 2015. In the U.S. this company sources its product from four A2 certified dairies with a combined 2,000 cows. Because A2 milk is such a new market in the U.S. there are not many other major companies in the country trying to market A2 milk. One of the few U.S. based companies marketing A2 milk is Prairieland Dairies, which is a 1,300 cow dairy in Nebraska. This dairy markets half of the milk produced with its own brand in Nebraska, the other half of the milk is sent to NY to be processed by Byrne Dairy and marketed by The a2 Milk Company.

A2 milk has become an important niche market over the years and has continued to grow in popularity. This could be an option for more dairy farmers in the future, especially if prices for regular milk continue to stay as low as they are. Farmers who sell their milk to companies such as The a2 Milk Company receive a premium for their milk, which may convince more farmers to convert their herds to A2. Popularity of A2 milk will most likely continue to grow as long as consumers are willing to pay for it. A half gallon of A2 milk can be sold in stores for about $4-$4.50 per gallon, which is still cheaper than a half gallon of milk from Organic Valley.

 

                             

 

 

Sources:

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