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.
|50% chance the calf will be a carrier
|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.
Managing Known Defect
After you receive the results, there are three possible ways to keep the tested abnormality from appearing again:
- 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.