DNA TESTS CAN HELP BREEDERS IN TRAIT SELECTION

by: Heather Smith Thomas

Originally used in the livestock industry to identify individual animals and verify parentage for breed registry purposes, DNA testing is now being used in a wide variety of ways to help cattle producers select for certain desirable traits. It can also be used to find out if an animal carries defective genes—before that animal is used for breeding. This is a great help to cattlemen in avoiding defects that might be detrimental to future offspring. Other applications that have recently come into use include determining the sires of calves produced in multi-sire breeding groups, to identify which bulls are doing the best job and which ones may need to be culled.

Tom Holm, Business Development Manager for MMI Genomics (a company that does DNA testing for a number of cattle breed registries) says the individual differences in DNA regarding coat color, size, growth and all the traits that cattle breeders measure can now be used for many purposes. Parent verification is probably still the most commonly used application today, in various breed registries, but other uses are swiftly increasing.

“DNA technology is the most powerful tool known for resolving questions of parentage and individual identity. It provides a great benefit to breeders. We're seeing an increase in the number of parentage verification cases we have done, in all of our breed associations' clients. A DNA test increases the validity and value of the pedigree,” he says. The breeder can guarantee the bloodline represented in that pedigree, and that makes any animal more valuable. There are also instances, however, in which any stockman might wish to know the sire of certain calves—to determine which of the bulls being used in multi-sire breeding groups are doing the best job, or the poorest.

Looking At DNA Testing From The Commercial Cattleman's Point Of View -- We normally think of parentage verification or trait detection as a tool for the seedstock producer rather than the commercial cowman. “All registries have some requirements regarding which animals should be DNA tested. Basically it would include the AI bulls, embryo donor dams, etc. Some registries also do spot-checking. The genetically elite animals will usually be tested to prove their pedigree because they have the most value,” says Holm.

“But we've found that this technology can also be important to the commercial cattleman. It can be helpful to those who run multiple bulls in a single pasture. The resulting calves may have a lot of differences in growth, weaning weight, carcass traits, etc. It is therefore hard for the commercial producer to get a handle on which bulls are producing the kind of calves preferred. DNA technology can provide a way to do that. If we get a DNA profile on all the bulls that were used in that pasture, you don't necessarily have to do DNA typing on the entire calf crop in order to get an idea which bulls are doing the best job,” he says. You can take a sampling (even just 20 percent) of the best calves and the poorer ones, and find out who their sire was.

“Another thing you can find out is the serving capacity of these bulls. We have a lot of data to back this up. If you have five or six bulls, for instance, in a breeding group of 150 cows, there may be just one or two that may be siring the majority of the calves. The bottom two or three may be siring less than 10 percent, combined,” he says. This may be due to fertility issues, social dominance issues or other factors.

“If you do a random sampling of the calves, the commercial cattleman can get an idea about which bulls are breeding the cows. Hopefully the ones that are doing most of the breeding are the ones that have the best traits that you want in growth, etc. This gives the rancher some idea about how to manage his bulls to ensure that he can make a profit,” says Holm.

An example is for ranchers who've had difficulty with large birthweight calves. You can't always depend on EPD statistics to guarantee that a certain bull will sire exactly the birthweight you are shooting for. Some bulls throw calves that are larger or smaller than their predicted birthweight, and some are all over the board with inconsistent birthweights. If a rancher is experiencing too many large calves that end up dead at birth (or he has to be out there to assist the cows/heifers in order to have live calves), DNA testing can be done to see which bulls are siring the problem calves.

“Maybe one or two of the bulls have predominantly produced all the large birthweight calves. This gives the rancher an idea which bulls he may want to cull in order to eliminate this problem,” says Holm, or which ones to not use on heifers.

Applications For The Seedstock Producer -- “We've done a lot of work on multi-sire groups at the seedstock level. Some of our seedstock clients use multiple bulls in a pasture. Depending on what part of the country they live in, this may be their most effective management situation. We've had breeders in Colorado in mountain country where they use large pastures and multiple bulls. They are seedstock producers, so they want to know the sire of every calf. But it is difficult to run single sire groups in such large pastures and have all the cows covered. So they use multi-sire breeding and still get the genetic benefit of identifying each sire for each calf, for its pedigree,” says Holm. This works very well, if the sires are not too closely related. Bulls that are half brothers or father and sons or any other close relationship may have the same markers.

“We can still differentiate between them, but it takes more markers, and this means more cost,” says. It may still be cost effective, however, due to the benefits of using multi-sire pastures.

Some of the benefits of using more than one bull in a group include the fact that every cow should get bred. “If a cow ends up open, you certainly can't blame the bulls. Some people use multi-sire groups because it is more efficient to use large pastures this way.” And some bulls will be more aggressive and breed more cows if they have competition from other bulls.

Often a producer will use artificial insemination and then follow with a clean-up bull to settle any cows that did not become pregnant. The calf may be born between dates (even if you waited three weeks before turning in the cleanup bull). A calf may be up to 10 days late or 10 days early and you won't really know whether he was from the AI breeding or the bull, unless you use a clean-up bull of a different breed or color that makes it obvious which sire it was. If a producer doesn't want to switch breeds/colors, however, DNA testing could be done to determine whether it was the AI sire or the cleanup bull.

Testing For Defects Or Specific Traits -- Sometimes a defect crops up in a certain breed or bloodline, and DNA testing can determine whether an individual is free of that defect or might possibly pass it to offspring. Also, there may be instances in the future when we start testing animals for other traits that we have not yet thought about today. With the DNA database, a person can go back and check for these traits or defects in the ancestors of certain animals, as well as in current calf groups.

“In our business, we archive all samples we receive. You can have those forever, and it doesn't matter if an animal is dead or alive; we still have a sample on file for that animal. Even if it is alive, if you want to test for something else, you don't have to go through the hassle of collecting a new sample. We just retrieve it from archives,” explains Holms.

This technology can be very helpful in dealing with genetic defects. “The Angus breed now has the problem with AM (Arthrogryposis Multiplex, also called curly calf). We've been able to save our customers a lot of time and hassle by going back into our database and pulling archived samples instead of having them resubmit new samples to test for this genetic defect,” says Holm. DNA testing is a great tool for checking potential breeding stock to see whether or not they might pass on a defect to offspring.

DNA markers are thus used for various purposes—whether to verify parentage or certain traits, or locate a defect. “Markers are signposts for certain locations of the genome. The signpost of a marker might be very close to a gene, as an example, that has a huge effect for increasing marbling. In other words, as signposts, the markers can mark the location of genes that control various traits, and thereby be used for selection purposes when breeding animals. Our company and others are now testing for a large number of traits including marbling, tenderness, feed efficiency, etc. Where DNA testing can help a lot is in checking for traits that are difficult to measure, such as tenderness, or traits that are difficult to make progress in through standard genetic evaluation techniques. Some of these traits include fertility and reproduction efficiency. This is where markers really have the most promise—in traits that are difficult to measure and traits with low heritability,” he says.

DNA tests allow a breeder to assess the genetic potential of his animals for that trait at a very early age. “Otherwise, you have to wait until that animal gets to be a year old to do ultrasound, for instance, which still may not be that accurate. And you don't have to wait four or five years for the animal to have a group of progeny for measuring marbling in those offspring. If you have an accurate DNA test for marbling, you can do very early selection of breeding stock for marbling, if that's an important trait in your breeding objective.”







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