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Genetics and A2 milk: what you need to know

As consumers continuously look for new ways to eat healthy, A2 milk is a trend that emerges on their radar. A2 milk has been a common brand in Australia and New Zealand for several years. It only made its entry to the US marketplace in 2015.

It’s a new concept for many people, so before you join in on the A2 hype, here are a few answers to questions you may have.

What is A2 milk?

A2 milk is produced only from cows having two copies of the A2 gene for beta casein.

To explain further, cows’ milk is about 87 percent water. The remaining 13 percent is a combination of lactose, fat, protein, and minerals that make up the solids in milk.

If we focus on the protein within milk, the major component of that protein is called casein. About 30% of the casein within milk is called beta casein. The two most common variants of the beta casein gene are A1 and A2, so any given bovine will be either A1A1, A1A2 or A2A2 for beta casein.

In the United States nearly 100% of the milk contains a combination of both A1 and A2 beta casein.

What is the benefit of A2 milk?

Researchers believe that A2 is the more natural variant of beta casein, and A1 was the result of a natural genetic mutation that occurred when cattle were first domesticated. With that in mind, studies have been done to see if people digest or react to true A2 milk differently than regular milk.

Some of those studies have found that people drinking milk exclusively from cows producing A2 milk were less susceptible to bloating and indigestion – leading some to conclude that A2 milk is a healthier option than regular milk. The exact science behind the difference in A1 versus A2 milk is complicated, but research has shown that digestive enzymes interact with A1 and A2 beta-casein proteins in different ways. Because of that, A1 and A2 milk are processed differently within the body.

Can you breed for A2 milk?

Yes, in fact the only way to have cows that produce A2 milk is to breed for it.

True A2 milk can only be produced from cattle possessing two copies of the A2 gene in their DNA. Each animal receives one copy of the gene from its sire and one copy from its dam. So for a chance to get an animal with the A2A2 makeup, you must breed a bull with at least one copy of the A2 allele to a cow with at least one copy of the A2 allele.

To ensure with 100% certainty that a female will produce A2 milk once she freshens, she must be the result of mating a cow with two copies of the A2 gene to a sire that also has two copies of the A2 gene.

Does A2 milk only come from colored breeds of dairy cattle?

Traditionally, colored breeds of dairy cattle, such as Jerseys and Guernseys have been the poster children for the A2 gene. Those two breeds still have a higher proportion of A2A2 animals. However, some of the popular Holstein sires of recent years have increased the prevalence of A2A2 sires in the black and white breed as well.

You may be surprised that about 40% of the Holstein sires in active AI lineups, including numerous household names, have two copies of the A2 gene. In addition, over 80% of Holstein sires have at least one copy of the A2 gene.

Is A2 milk the answer for people with lactose intolerance?

A2 milk contains the same amount of lactose as non-A2 milk. So in clinically-diagnosed cases of lactose intolerance, A2 milk will not provide the benefits that lactose-free milk would offer.

Since most cases of lactose intolerance are self-diagnosed, some doctors believe the cause of indigestion in those cases is actually linked to an A1 aversion rather than lactose intolerance. In those cases, drinking A2 milk may help prevent the side-effects otherwise experienced from drinking regular milk.

Should you select for A2 in your breeding program?

With this new information at hand, it may seem compelling to produce only true A2 milk. Many A2A2 sires are available, but you still have an opportunity cost by selecting only A2A2 sires.

When A2A2 is a limiting factor in your genetic selection, you’ll eliminate about half of all bulls available. That means you will likely miss out on pounds of milk, extra health and improved fertility traits.

Regardless of your selection decision around A2 sires, make sure it aligns with the customized genetic plan you put in place on your farm so you can maximize profitability and genetic progress in the direction of your goals.
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Inbreeding: manage it to maximize profit

Inbreeding is a hot topic…

Are you concerned about whether genomics is creating too much inbreeding in the dairy cattle population? Many producers express their concern that sire options to prevent negative inbreeding effects continues to dwindle. We certainly don’t want to mate an animal to her father or brother, but we do need to ask what the real goal is in terms of inbreeding. Should we aim for zero percent inbreeding or rather manage it to maximize profit?

The linear effect of inbreeding depression

As animals become more related to each other, inbreeding depression, or sub-par productive performance, can occur. Inbreeding depression is not ideal. Yet you should still weigh the negative effects against the added profit you could see from greater genetic gains.

Many producers buy in to the common misconception of a magic level of inbreeding that we should never exceed. In reality, we’ve seen results from numerous studies over time that show the effects of inbreeding depression to be linear.

For every 1% increase in inbreeding for a mating, you will realize $22-24 less profit over the life of the resulting offspring. You will see the same cost, or loss, when going from 9% to 10% inbreeding as you see between 1% and 2%.

Genetic progress

It’s well-documented that inbreeding has risen each year since the mainstream adoption of AI. Despite this increase, dairy cattle have made significant strides in production traits like milk, fat, and protein. It’s safe to say that producers would not trade today’s high producing cows for the less inbred, but also lower producing, cows of the 1960’s.

Inbreeding and milk production graph

Real-herd examples

Let’s look into the records of a random cross-section of 10 upper Midwest dairies averaging 1,500 cows, who implement a mating program on their farm. This analysis shows how cows with superior genetics are more productive than cows with inferior genetics, despite the more highly productive group also being more inbred.

In this analysis, cows born between 2005 and 2010, with at least one lactation on record were included. Each individual herd was first analyzed separately, and cows were split into quartiles based on their individual level of inbreeding.

Total # of cows% InbredNM$Milk Deviation1st Lact 305-Day MilkPTA DPRAvg. 1st Lact Preg RatePTA PL
25% MOST inbred from each herd38107.0158649282580.422.51.4
25% LEAST inbred from each herd37844.5121296278750.422.60.9

Here, you can see the difference in genetics, 1st lactation milk production, and NM$ between the top 25% most inbred from each herd and top 25% least inbred animals from each herd. The most highly inbred quartile of cows was also the most genetically superior group of cows in each of these ten herds.

When we measure actual performance, genetics more than make up for inbreeding depression. The NM$ levels, pounds of milk and milk deviations were all favorable for the more highly inbred, but also more genetically superior group.

This doesn’t mean that a mating resulting in 25% inbreeding is the best option. Rather, when managed properly as part of a program, excellent genetics can outweigh the results of inbreeding depression.

You may not realize that current proof values already account for the bull’s level of predicted future inbreeding. Outcross sires see favorable adjustments. Whereas, PTA’s on sires that are more closely related to the average population are negatively impacted because of these adjustments.

Determining matings

Let’s check out an example to see how managing, rather than avoiding, inbreeding is the best route.

The example below shows three sire options to use for a mating in your herd. Sire 1 and sire 2 both offer high Net Merit $ levels. However, their 8% and 6.5% inbreeding levels would be above the suggested 6.25% industry standard. That alone could eliminate them as potential mating sires in many breeding programs. Sire 3 would be a logical outcross mating in this example, resulting in a mere 1% inbreeding.

Sire OptionSire NM$Inbreeding % with cow being bredEconomic loss due to inbreedingAdjusted NM$ for level of inbreeding
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