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Keeping it clean: Testing animals for genetic defects helps locate the healthiest genetics

Mark Allan Published on 24 February 2011

Beef producers in the United States have been able to effectively increase the amount of beef produced without increasing the number of animals overall through selective breeding for genetically superior animals and improved nutrition and management.

However, the drive to use sires and cow families with certain preferable traits has, in some instances, come with some unwanted genetic baggage.

For example, dwarfism had devastating results on British breed populations in the 1950s and 1960s, resulting in many operations being hit hard financially.

In the past, the only way to manage a genetic defect was to remove all animals from the production population that could be traced back to a known carrier, or use progeny testing to show that the animal was a non-carrier of the recessive mutation for the genetic defect.

Progeny testing is done by mating a candidate sire to known female carriers or his actual daughters, then observing the presence or absence of an affected progeny for the genetic defect.

Producers often had to cull entire families that had lineage to a known carrier without knowing the actual carrier status of the animals being culled.

This meant a lot of excellent genetics were discarded to clean up the genetic defect in their populations.

Today, producers can easily remove animals that are carriers of a genetic defect while keeping non-carrier animals from the same family.

With surgical precision, producers can go in with a simple DNA test for a known defect and find out who the carriers are, and as a result, they can now benefit from non-carrier animals they previously would have culled.

As DNA technology was introduced to the beef industry, it brought with it a new way of testing and identifying genetic defects.

Genetic defects are still costly, but we are better equipped to limit the financial impact they have on the industry at all levels.

“The advent of genome sequences allowed us to develop tools to tackle genetic defects more aggressively,” says Jonathan Beever, Ph.D., associate professor at the Department of Animal Sciences, University of Illinois.

“It may seem like genetic defects have been a big problem recently, but that’s not really the case. It’s just that we now have some tremendous ways to deal with them.”

Most recently, Beever says, tests have been developed for genetic defects, including Arthrogryposis Multiplex (AM) in December 2008, Neuropathic Hydrocephalus (NH) in March 2009 and Contractural Arachnodactyly (CA) in July 2010.

“We really try not to pay any significance to a particular breed,” Dr. Beever says. “But sometimes it just happens that way.

Once we get into a population, as producer education increases or we’re successful in doing something, people become more interested in discussing other problems. And one problem naturally takes us to another.”

Managing genetic defects

When it comes to managing genetic defects in their herds, Dr. Beever says many producers are beginning to understand and utilize DNA technology.

“With the overall awareness surrounding genetic defects, it winds up being an economic question,” Dr. Beever says. “Producers need to assess the market.

Do you want to test from a marketing standpoint? If not doing it is costing you money, then you need to test.”

If producers haven’t tested in the past and are looking to start, they really need to look at pedigrees going deeper than three generations, to understand the probability of the animal being a carrier.

Breed associations have been proactive in helping producers understand known animals that are carriers and non-carriers.

In many cases, the associations have done analyses to assist the producer in identifying potential carriers. In fact, many associations publish an animal’s carrier/non-carrier status – either as a result of DNA testing or an official progeny test.

To begin testing, it’s a good idea for producers to start with influential herd animals. For example, producers could begin by testing donor cows, herd sires and sale animals. In many cases, the best way to begin is to start small.

It also is important to remember that every breed association has its own policies surrounding genetic defects and testing for them.

For example, some breeds allow producers to register carrier females and some don’t. And if a producer does have a carrier female he or she intends to keep, the safest way to manage the offspring for the genetic defect is to test all progeny born to a known carrier female.

“It really depends on the producer’s ultimate goal,” Dr. Beever says. “If your ultimate goal is elimination of the defect, once you get to that point, there’s no more testing required.

If there’s a reason to continue to use carriers, you just have to keep up with a diligent management program to know where those animals are, that they’re mating the right way and where you’re going to direct those calves.”

Dr. Beever adds that anytime you’re planning to keep carrier animals in a breeding program, it’s going to require intensive management.

Now what?

In the end, DNA testing allows us to better manage our herds. As we continue to test animals and are keeping a vigilant eye for problems, genetic defects will continue to surface.

If we didn’t have DNA testing, it would be like operating without insurance. Genetic defects are bad news and are costly, but we now can manage them in a way that we have never been able to manage them before.

Plus, using DNA testing is not nearly as expensive as it was to throw away high-quality genetics.

“Genetic defects and the technologies should be viewed in the right perspective,” Dr. Beever says. “These are the first genomic tools.

They’re the easiest to implement and use and, down the line, we have the potential to use these same technologies to find out so much more than just genetic defects.”  end_mark

mark allan

Mark Allan

Associate Director,
Global Technical Services, Pfizer Animal Genetics

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