How Can Cattle Be Selectively Bred?

Farmers today use different methods to keep track of their cows, from GPS ear tags for cattle to marking them with hot or cold branding. One purpose for which different tags are used for cattle is to single out those that should be bred from the rest. That brings us to the subject of selective breeding and what it means.

Cows are selectively bred for milk production

You might have heard of the Holstein breed and the generous amounts of milk that just one single specimen can produce. While it is true that the breed of the cows used for milking and later making dairy products matters, the Holstein cow could not have been the amazing milk-yielding machine that is today.

It may take an outsider by surprise, but farmers use a lot of math in their study of how much milk they can obtain from their cattle. For decades, in the US, thousands of such people have kept records of milk production, as well as other details, such as milk composition.

All this information allowed them to establish mathematical patterns regarding how much milk a cow can deliver throughout its life span. With the help of these figures, farmers have managed to decide which cows to breed and how.

The selective breeding techniques they have used over these decades transformed the Holstein breed into what it is today. And this is just an example. To see what a long road they walked, it is enough to say that dairy cows today make four times their regular production of almost 80 years ago.

What exactly is selective breeding?

Especially the dairy industry is interested in getting cows to produce more milk, which is why farmers involved in it use selective breeding. That can be done with the help of artificial insemination, as that allows the farmers to pick the sex of the calf being born.

Therefore, they can choose to have a larger population of females. Of course, that comes with a more complicated process for separating the semen – which holds the genetic information regarding the sex of the calf – and that may not be affordable for all farms.

There is a debate on whether this selective breeding technique is not too costly. The math done so far proves that selective breeding is worth the cost as it can increase the milk production of a herd by 2.7%.

Are there any other desirable outcomes, besides milk production?

Milk composition is equally essential when it comes to selective breeding. Cows are not selectively bred only because their breeders want them to deliver more milk. Other outcomes such as milk characteristics are desired. For instance, the percentage of fat in the milk and how much protein it contains matter.

The female calves resulted from the insemination of cows with semen from selected bulls might also live longer and have better udder quality. All these factors have a decisive influence on the milk quantity and quality, and that’s why farmers appeal to genetics to ensure that their cattle can perform to the highest capacity.

What is the bull market?

That is a short name for the market dealing with bull semen that is used for selective breeding. If you search for more information on this aspect, you will discover that the value of a sample is decided by the lifetime net merit of the bull from which the semen is harvested.

All seems simple from this point of view. The key statistic mentioned means the added value provided by the genes of the bulls used for harvesting the semen. In other words, it tells farmers how much better the calves obtained from inseminating a cow with the said semen can be.

An interesting aspect is that this statistic is evaluated in US dollars. To give an example of how it works, for a cow that gives 1,000 pounds more milk over its breed’s average throughout its lifespan, after being inseminated with a semen sample, the bull from which the semen was obtained gets just an increase of 1 USD for its lifetime net merit.

How much milk does a cow produce due to selective breeding?

The idea of selective breeding started quite some time ago. In the 1940s, cows used to give around 5,000 pounds of milk. Today, on average, a dairy cow can produce more than 21,000 pounds of milk. Besides the distinct advantage for farmers who get more from each cow, there is another beneficial consequence.

Cows produce methane, which is a greenhouse gas, and they also need a lot of pasture to graze on. These aspects can impact the environment negatively. With the increasing demand for dairy products, farmers were stimulated to increase the number of heads in the herds they manage. A peak was registered in 1972 when the number of cows in the US was a bit short of 140 million heads. However, their numbers have slowly declined since, to under 100 million heads.

What is another consequence of selective breeding?

No matter how much talk is being carried on over the use of antibiotics that can make animals healthier, with increased lifespan, the most impact is delivered by the manipulation of genetics. Studies show that 22% of the Holstein genome has been modified through selective breeding over the last four decades.

In other words, the dairy cow that lives and gives milk today is different from the cow living and producing milk in the 1940s or even later. Through selective breeding, these cows become healthier, and their production is increased, as well.

Are there downsides?

While the benefits are undeniable, some other things must be mentioned. One negative consequence is that while milk production is on the rise, fertility is suffering. Low fertility rates have been reported in herds where selective breeding is used extensively.

The explanation is that the energy supply must be directed toward milk production, and not enough is left for sustaining a pregnancy. As cows are milked from the first days of calving for months, the chances of getting them pregnant again decrease.