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The pros and cons of polled genetics

Chrissy Meyer Published on 24 August 2015

Polled dairy cattle trace back at least as far as pedigree records have been kept. The polled gene in dairy cattle is dominant over the horned gene, yet horned cattle are still much more prevalent in the global dairy population because few producers ever chose to select for polled cattle as part of their breeding program.

This is because the real, economic paybacks of selecting for production, health and conformation traits has traditionally trumped the desire for polled genetics.

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Genomic selection has allowed polled enthusiasts to focus on high-ranking polled animals to propagate the polled population. However, producers stressing genetic improvement in other traits are also advancing their genetics at an equally rapid rate.

You can add polled as a criteria to your genetic plan – but must keep in mind the financial repercussions of that decision in terms of the pounds of milk and components you’ll give up, and the health and fertility you may need to sacrifice, just to avoid dehorning.

The more recent public awareness about dehorning cattle has made it another hot-button topic in the industry. Naturally hornless cattle have gained popularity in recent years because of consumer opinion on the dehorning process, and the side effects they feel result from it. This perception has driven producers to create more naturally polled animals than ever in the past.

The pros of polled genetics

Many producers see the opportunity to incorporate polled genetics into their breeding program for the following reasons:

  • Avoid dehorning

You can save dollars, time and labor, and also minimize stress on your calves by forgoing the need for dehorning. The average dehorning cost varies from one farm to the next based on the chosen method of dehorning, and there is a small chance of causing additional stress on the calves during a crucial growth time.

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  • Cater to consumer perceptions

It’s a fact that consumer perception directs many aspects of the dairy industry’s reality. Animal rights activists have criticized dehorning for years, but it hasn’t been until recently that the general public has joined the activists’ view on dehorning as a detrimental process. With increased awareness about this common farm chore also comes increased consumer demands on how they feel farmers should handle it on their dairies.

We clearly don’t want animals with horns running around dairies, so the question is whether to dehorn calves or breed for polled genetics. Are consumers willing to pay a premium for milk from naturally hornless cattle? If you are not guaranteed a greater value for your milk, you should consider the dollars you could be leaving on the table by selecting exclusively for homozygous polled sires to ensure no animals are born with horns.

  • The polled gene is dominant

The basics of genetics tell us that since the polled gene is dominant over the horned gene, animals with one copy of the polled gene and one copy of the horned gene will not have horns, and a naturally hornless animal can be created in one generation. It also means it is easier to make more polled animals faster than if the polled gene was recessive.

An animal can have one of three combinations for the polled/horned gene:

  • PP = Homozygous polled means this animal has no horns, and all offspring from the animal will be born without horns.
  • Pp = Heterozygous polled means this animal does not have horns, but offspring may or may not have horns depending on their mate.
  • pp = Born with horns

If you’re starting with only horned animals in your herd, Figures 1 and 2 demonstrate your results mating cows to a polled sire. The one on the left shows that a homozygous polled bull bred to a horned cow will result in 100 percent hornless offspring.The one on the right illustrates that a heterozygous polled sire bred to a horned cow will result in only 50 percent polled offspring.

polled offspring odds

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The downside to polled genetics

While eliminating the need for dehorning may seem like the right choice for your dairy, the sacrifices you will make in order to get to that point cannot be overlooked. Whenever you add extra selection criteria to your genetic plan, you will sacrifice in other areas. Here are just a few reasons to think twice about selecting exclusively for polled genetics in your herd.

  • The continuous need for polled sires

As mentioned above, the polled gene is dominant, so you can create a polled offspring in just one generation. What many producers tend to forget is that, at this point, maintaining a population of polled cattle in your herd is much more difficult.

As the figures above show, using a heterozygous polled bull will not yield 100 percent polled offspring. To get to the point of a completely polled herd, and to maintain it once you’re there, you continually need to use only homozygous polled sires. This may not seem difficult, but it leads to the next shortcoming of using exclusively polled sires.

  • Limited availabilityand variation on polled sires

Since the prevalence of polled animals within the various dairy breeds is low, it will still take many generations to genetically eradicate horned animals from your herd if you want to maintain reasonable inbreeding levels.

Even though the number of polled bulls in active A.I. has increased substantially over recent years, the total number of sires providing that polled gene is still very limited. A.I. companies will only bring in bulls at genetic levels high enough to help you make progress in your herd.

And since selection for polled animals has only recently gained popularity, many of the polled bulls are closely related – either from a small group of elite polled cow families or with sires in common.

Yet even with selection standards in place for the elite polled animals of the dairy population, the genetic levels don’t yet match up.

  • Genetic sacrifice and compromised future performance

At this point, polled bulls don’t yet live up to the genetic levels of their horned counterparts. Table 1 shows the average of how the top 10 heterozygous polled and top 10 homozygous polled genomic sires stand up next to non-polled sires. There are some substantial genetic sacrifices you make by selecting from the best sires of either group of polled bulls.

polled cattle sacrifices

With the heterozygous polled group, 450 pounds of milk and 47 pounds of combined fat and protein is left on the table in order to guarantee a 50 percent chance at a polled calf. And with the homozygous polled sires, nearly 1,100 pounds of milk and 100 pounds of combined fat and protein is sacrificed. You must also consider your sacrifice in productive life, udders, feet and legs, fertility and calving traits.

Review your prosand cons for polled genetics

As you set your genetic plan, keep in mind the pros and cons of selecting exclusively for polled genetics. From an economic standpoint, there is a small time savings associated with eliminating the task of dehorning, but on the other hand, you will sacrifice performance and genetic advancement.

If consumer perception is driving your decision, consider whether or not you will be paid more by your milk plant for producing from an exclusively polled herd.

Regardless of your selection decision, make sure it aligns with the customized genetic plan you put in place so the genetic progress you make on your farm continues in the direction of your goals. PD

Chrissy Meyer
  • Chrissy Meyer

  • Marketing Editor
  • Alta Genetics
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