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Half of Holstein heifer calves could be polled by 2034

Ben Dorshorst Published on 17 January 2014

Dehorning cattle has become a standard practice in modern dairy operations to prevent injury to humans and animals alike. Dehorning is one of the sometimes unpleasant tasks that must be performed on the average dairy farm.

But what if you could eliminate this task simply by choosing the “right” bull? Selecting genetically hornless or “polled” sires will allow you to incorporate the polled trait into your herd and permanently eliminate dehorning from your to-do list.

Origin of polled
Polled refers to animals that are naturally hornless. If an animal has the polled gene, it will not grow horns. The origin of the polled trait is difficult to pinpoint but likely predates modern breed formation, being present in breeds originating from a wide geographic area in Europe.

This suggests that this trait was already present when cattle more commonly fulfilled a dual-purpose role of meat and milk production.

In modern cattle, the polled trait is most commonly thought of in association with beef breeds. However, polled dairy cattle have been in existence for as long as pedigree records have been kept, tracing back to the early 1900s in the North American Holstein population.

The difference in accessibility of calves at a young age between dairy and beef cattle management systems is the likely reason beef breeders have placed more emphasis on selecting for polled in the past.

Current availability of polled dairy cattle
The interest in polled dairy cattle has changed dramatically over the past few years, aided in part by the development of new genomic selection strategies in dairy cattle and fueled by an increasing consumer concern with animal welfare.

Genomic selection has helped to more easily identify the genetically elite polled animals to use as sires and dams of the next generation, speeding genetic progress. The manner in which animals are raised and cared for is increasingly important to the average consumer, to the point that long-accepted animal husbandry practices are under new scrutiny.

Although the polled gene remains at a low frequency in the U.S. Holstein population, it is increasing at a relatively fast rate. The number of available polled A.I. Holstein bulls has doubled over the past year, with 96 listed in the December 2013 genetic evaluations.

The number of polled females registered with Holstein Association USA has increased by a factor of 10 in the last decade. At this rate, 50 percent of the registered Holstein females born per year in the U.S. could be polled in just over 20 years.

This may seem like an unbelievably fast change but is reflective of the current interest in breeding for polled and the ease of spreading a genetically dominant trait. Future selection intensity on polled will ultimately dictate how rapidly dairy cattle populations transition from horned to polled.

The historical association of the polled trait with beef breeds has fostered the misconception that polled is directly associated with production characteristics that are undesirable in dairy breeds.

However, an analysis of the genetic merit of registered Holsteins in the U.S. over the past 35 years shows that the polled segment of the population is remarkably similar in all major production traits to horned counterparts.

Historically, polled animals have lagged one to two years behind horned animals in genetic merit, but this is not surprising given the small number of polled animals that were available for breeders to select from. With the current rapid growth in the polled segment of the population, the genetic merit gap between horned and polled animals will continue to decrease.

This is evident by again looking at the December 2013 genetic evaluations, for which there is at least one polled bull in the top 10 percent of the entire A.I. Holstein bull population for 37 out of 38 production, reproduction and conformation traits.

The increase in demand for polled dairy cattle is evident in the registered cattle breeding market, where polled animals have been receiving above-average prices at public auction and are often the top sellers.

This is carrying over into the male side of the dairy breeding industry, with more polled bulls entering A.I. units than ever before. This, in turn, creates more polled females to select from when producing the next generation, setting up a pattern for rapid growth in the polled segment of the dairy breeds.

Cost vs. benefit of polled
The cost of dehorning a calf is quite variable between farms and can depend on how, when and by whom the dehorning is done.

If done properly, there should be minimal adverse effects on the calf, but this is still a procedure that may predispose the calf to other infections or setbacks in calf growth. Occasionally it may be necessary to treat a calf that has a particularly difficult time after dehorning.

Researchers at the USDA and Purdue University compared the total management cost of dehorning to that of using polled semen by accounting for the cost of dehorning, a premium price for polled semen and likelihood of animals requiring veterinary treatment due to dehorning.

Under all the scenarios they evaluated, dehorning was always more expensive than using polled genetics. They estimated that on average a farmer could spend an additional $7.50 on polled semen and break even by eliminating the cost of dehorning. These results indicate that there is likely to be a financial incentive to using polled semen on most farms.

Using polled in your herd
When deciding to use polled bulls in your herd, there are two options that you will be presented with: to use heterozygous (Pp) or homozygous (PP) polled bulls. There are typically more heterozygous polled bulls to choose from as they are easier to generate, requiring only one of their parents to be polled.

Heterozygous polled bulls will also typically be of slightly higher genetic merit than homozygous polled bulls, although this difference is becoming smaller with every generation.

The decision between heterozygous or homozygous polled bulls depends primarily on the goal you set for your herd. A homozygous polled bull has the advantage that every single calf born will be polled, but homozygous bulls of the same caliber of heterozygous polled bulls are more difficult to find.

Conversely, heterozygous polled bulls will typically be of higher genetic merit, with the downside that only half of their calves will be polled.

If it is important to you to be using bulls that are at the very top of the genetic merit rankings, you will want to use heterozygous polled bulls. If you are prepared to make a small sacrifice in genetic merit rankings, homozygous polled bulls guarantee you every calf will be polled and you can retire that dehorning iron for good.

With the increased emphasis on breeding for polled dairy cattle (especially in the Holstein breed), the difference in genetic merit between horned, heterozygous polled and homozygous polled animals is shrinking rapidly. It may be a while before a polled bull sits in the No. 1 spot in any of the major index rankings, but they are certainly climbing the list.

If you decide to use heterozygous polled bulls, you will still have to dehorn half your calves in the first generation. In subsequent generations, half of your cows will already be heterozygous polled (Pp), which when combined with any horned bull (pp) will result in 50 percent Pp and 50 percent pp calves.

Mating these same Pp cows to heterozygous polled bulls will result in 25 percent PP, 50 percent Pp and 25 percent pp calves. By balancing the use of horned and polled bulls, you can maintain genetic progress while at the same time increasing the frequency of the polled gene in your herd.

If you desire to keep track of which animals are polled versus those that were dehorned in order to aid in breeding and culling decisions, a few options are available. Others have described various systems in which a notched ear tag corner or small button tag indicates if an animal is polled or has been dehorned.

These can easily be applied as part of the standard ear tagging or dehorning protocol on your farm. It is also possible to submit a sample for genetic testing if you are unsure if an animal is polled or has been dehorned. Genetic testing can also be used to differentiate homozygous from heterozygous polled animals, both of which will be hornless.

Summary
Polled dairy cattle have been in existence for as long as we have been keeping pedigree records. Recent advances in animal selection techniques have dramatically increased the quality and number of polled dairy cattle to choose from.

Likewise, researchers have uncovered the specific genetic mutations associated with polled, giving us a better understanding of how this trait works and more accurate genetic tests.

The dual benefit of removing costs associated with dehorning and taking a proactive stance on a growing animal welfare issue makes utilizing polled genetics something every dairy producer should consider. PD

Ben Dorshorst


Ben Dorshorst

Assistant Professor of Genetics
Department of Animal and Poultry Sciences
Virginia Tech

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