Using Genomic Tests to Detect Genetic Abnormalities in Beef Cattle
Christian P. Lewis
South Dakota State University undergraduate student
Rapid advances in science and technology are appearing
throughout agriculture. One of the newest technologies that has worked its way
into the cattle industry is DNA testing and the use of genomic data.
Practical Uses of Genomic Data
Genetic abnormalities are not a common problem in beef
cattle production, but they do appear if precautions are not taken. Most
frequently, a genetic abnormality appeared because both the cow and bull were
carriers of a recessive allele that causes the abnormality. An animal is termed
a “carrier” when they have a dominant allele that is masking the recessive allele.
Figure 1 illustrates how an abnormality can appear by mating two carriers.
Genetic abnormalities will appear when a calf has two copies of the recessive
allele that it got from its sire and dam.
A
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a
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A
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AA
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Aa
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50% chance the calf will be a carrier | |||||
a
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Aa
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aa
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25% chance the calf will have the abnormality |
Figure 1: Mating two carriers (Aa) of a recessive allele (a) that is completely masked by the dominant allele (A)
Without a DNA test for an abnormality, the only way you will know an animal is a carrier or not is when you mate the suspected carrier to a known carrier and offspring with the abnormality are born. If you want to test for a genetic abnormality, the first thing that you should do is contact your breed association to see how they want DNA collected for a test and where to send DNA samples.
DNA Collecting Basics
There are three common ways to obtain DNA samples from
cattle: blood samples on FTA cards, tissue samples, and hair samples. If
testing young calves, a blood sample is often preferred. There are several
videos online that demonstrate how to collect DNA samples if you are new to DNA
testing.
Collecting blood samples
Collecting tissue samples
Collecting hair samples
Managing Known Defects
After you receive the results, there are three
possible ways to keep the tested abnormality from appearing again:
Culling the known carriers and not using carrier bulls will eliminate the abnormality from appearing in your herd again. By always using non-carrier bulls, none of your calves will ever present the abnormality. If the genetics from the known carriers are too valuable to cull, you must plan your mating decisions so that two carriers are not allowed to mate. If you use a carrier bull, all calves sired by this bull should either be sold after weaning or tested for carrier status before they are bred. Crossbreeding may be the easiest way to avoid genetic abnormalities. It’s very rare for one abnormality to segregate within two breeds, but it’s not unheard of. For example, Tibial Hemimelia (TH) segregates in both Shorthorn and Maine Anjou, as some of the same sires were used in both breeds. So, mating Shorthorn with Maine Anjou presents a risk of the TH abnormality appearing in calves. Further, if both the sire and dam share a breed (e.g., both sire and dam are Angus-influenced), mating these individuals could still result in the appearance of a genetic abnormality.
- Cull the carriers.
- Make sure not to mate two known carriers.
- Utilize crossbreeding.
Culling the known carriers and not using carrier bulls will eliminate the abnormality from appearing in your herd again. By always using non-carrier bulls, none of your calves will ever present the abnormality. If the genetics from the known carriers are too valuable to cull, you must plan your mating decisions so that two carriers are not allowed to mate. If you use a carrier bull, all calves sired by this bull should either be sold after weaning or tested for carrier status before they are bred. Crossbreeding may be the easiest way to avoid genetic abnormalities. It’s very rare for one abnormality to segregate within two breeds, but it’s not unheard of. For example, Tibial Hemimelia (TH) segregates in both Shorthorn and Maine Anjou, as some of the same sires were used in both breeds. So, mating Shorthorn with Maine Anjou presents a risk of the TH abnormality appearing in calves. Further, if both the sire and dam share a breed (e.g., both sire and dam are Angus-influenced), mating these individuals could still result in the appearance of a genetic abnormality.
DNA Test Available
Producers can often order tests for genetic
abnormalities along with other DNA tests. These DNA tests are priced based on
how many tests you want them to perform. Most DNA tests for genetic
abnormalities cost approximately $25 per head, but the cost per head may be
lower if you test for more than one genetic abnormality or purchase another DNA
testing product (e.g., Igenity Profile, PredicGEN). If you wish to learn more about genetic
abnormalities and available DNA tests for these abnormalities, you can visit
websites maintained by Zoetis Animal Genetics https://www.zoetisus.com/animal-genetics/beef/index.aspx
or Neogen Corporation http://genomics.neogen.com/en/genetic-health-and-conditions. Both of these companies provide DNA testing
services for the beef industry. A more
comprehensive list of DNA test providers can be found in the article titled
“Managing Genetic Defects” authored by Dr. Alison Van Eenennaam (see references
list).
Conclusion
In today’s production environment, it is often easier
to take precautionary steps than fix something after it becomes a problem. Genetic
abnormalities may not appear in your calf crop this year, but they could down
the road. If your cowherd is at risk (e.g. you know you have used carrier bulls
in the past), testing your cowherd for abnormalities will at the very least
give you peace of mind. It might even save a calf from developing an
abnormality, which in turn, will lead to more pounds to sell at weaning time.
References
Rolf,
M. 2015. DNA Sample Collection. http://articles.extension.org/pages/73198/dna-sample-collection
Van
Eenennaam, A. 2015. Managing Genetic Defects. http://articles.extension.org/pages/72662/managing-genetic-defects
As part of our USDA-NIFA local adaptation grant, Michael G. Gonda at South Dakota State University has developed a course titled "Applied Beef Cattle Breeding." Christian wrote this article while participating in that course.
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