American Dexter Cattle Association

DNA Testing (Genotyping)

Why do it? What to do? How do we do it?

Why do we Test?

Genotyping: The ADCA requires that the DNA Genotype of all bulls used for breeding be on file in its Registry Office before calves sired by those bulls can be registered. This is true for AI bulls as well. (While any AI bull whose blood type was on file in the Registry Office prior to January 1, 2003, is exempt from the DNA Genotyping requirement, the person who sells semen from that bull is encouraged to request DNA Genotyping for the sake of future reference or parentage questions.)

Texas A&M – Dr. Gus Cothran’s Lab – is the lab of choice for genotyping. That is where the database for genotyped animals is housed. If you test at a different lab, you must make sure that their process is compatible with that at Texas A&M in order to transfer the results to the
database. The genotype results must be sent directly from the testing lab to the A&M lab – and there is generally a small fee for that process at A&M.

Genotyping is a means of ensuring the purity of the Dexter Cattle Breed. If there is a parentage question on a calf, the genotype of the bull will already be on record and can be used to determine the sire of a calf. It is not usually difficult to determine the dam. Many people are
beginning to genotype all their animals. This will insure that the calf is both Sire and Dam Qualified. At this point, it is not mandatory to genotype the dam.

Chondrodysplasia: Dexter Cattle can carry a genetic mutation called Chondrodysplasia. This mutation causes defective bone growth which results in short legged, heavy bodied animals. Although this short legged animal is very appealing with its small stature, the gene can be lethal. If two carrier animals mate, the statistics indicate that one in four calves would be a “bulldog” calf – grossly deformed and born dead. Statistically, one in four would be a noncarrier, and two in four would be carriers.

In order to be better informed so that a breeder can establish successful breeding practices, it is recommended that animals – especially the shorter legged animals – be tested for chondrodysplasia. A well-informed breeder can then make appropriate choices in sire and dam in order to avoid calf loss due to this particular gene. If only one of the two is a carrier, then the bulldog calf will not occur. There will be a fifty-fifty chance of producing carrier calves if one or the other parent is a carrier. If neither is a carrier, then the problem is eliminated entirely.

PHA (Pulmonary Hypoplasia with Anasarca): Pulmonary Hypoplasia indicates incomplete formation of the lungs. Anasarca indicates an accumulation of fluids in tissues and body cavities. PHA-affected calves are either aborted or stillborn. Because of the anasarca, the PHA
calf may be tremendously swollen which would make delivery exceedingly difficult and potentially life threatening for the cow. The PHA affected calf occurs when the PHA gene is inherited from both the sire and the dam. If only one of the parents carry the gene, the calf will
appear normal, but can carry the PHA gene.

The statistics are similar to the chondrodysplasia carriers. When both parents are PHA carriers, there is a 1 in 4 chance of a PHA (dead) calf; a 1 in 4 chance of a non PHA carrier; and a 2 in 4 chance of producing PHA carrier calves. When a PHA non-carrier is bred to a PHA carrier, the chances are 50% of producing a PHA carrier and 50% of producing a PHA non-carrier. It is possible for a chondrodysplasia non-carrier to carry PHA. It is possible for a chondrodysplasia carrier to also carry PHA. The two genes do not appear to be related.

Testing give the breeder the knowledge of his animals’ genetic status so that he/she can make appropriate decisions on breeding practices. By breeding non-carriers to carriers, you can avoid the dead calf and potential damage to the cow. By gradually eliminating PHA carriers from your herds, you can build a herd that doesn’t carry this lethal gene. Unlike the chondrodysplasia carrier, PHA carriers cannot be identified visually. PHA carriers may be either longer or shorted legged animals.

Color Testing for Red or Dun: If a dun calf is born of parents that are not dun, or only one is dun, then the calf must be color tested for dun in order to be registered as dun. The same is true of a red calf born of parents that are not both red, or only one parent is red. The calf must be color tested for red in order to be registered as red.

A-2 Milk Testing: Of the protein found in cow’s milk, about 1/3 of it is made up of the protein called Beta Casein. There are many different forms of this protein, and the one we are looking at is one of the most common – called the A2 variant. It is believed to be the most ancestral form of the protein. That just means that the other forms are derived from the A2 variant. We are interested in the A2 variant because population based studies of people consuming milk suggest that having milk that contains the A2 variant of Beta Casein may be linked to lower rates of heart disease and type 1 (juvenile) diabetes. It may also be linked to lower rates of other diseases. We don’t yet know why this might be true, or what levels are best. Studies are ongoing on this topic. (Thanks to Eleanor Conant, Postdoctoral Research Associate, Dr. Gus Cothran’s Lab, Texas A&M University.) The test that we will do is similar to the test we do for chondrodysplasia, so we can tell if a cow or bull has 0, 1, or 2 copies of the A2 variant gene (which will then produce the protein).

So, if a bull has 2 copies, then his offspring should have at least 1 copy of the A2 variant.

At this point, it is really important to know that, if both parents have been tested as non-carriers of chondrodysplasia or PHA, it is unnecessary to test the offspring. They will be “Obligates” as non-carriers. If you don’t own the parents, you can go to the online pedigree on the ADCA website ( and check the status of the sire and dam. If you look at their individual pedigrees, it should indicate if non-carrier status has been obtained through testing.

To DNA test your animals for any of the above tests, you should acquire the appropriate paperwork – downloadable from the ADCA website. If you do not have computer access, you may request that the forms be sent to you by the ADCA liaison. (Currently the liaison is Pam
Malcuit, 936-394-2606) There are also copies of all the A&M forms in this handbook. Please keep them to make master copies so you may copy and print them whenever needed. They are included in this handbook for your convenience. Go to the ADCA website:, and click on DNA testing. You will find different tests listed. If you click on the blue lettered text titles, the necessary forms and information will pop up for you to download or print.

Presently, Texas A&M is the lab of choice for chondrodysplasia testing, DNA genotyping, Color factor (red and/or dun) and A-2 milk testing. This lab has not yet received licensing for doing the PHA testing. Those labs are Pfizer, Igenity, and AgriGenomics – also listed online on the DNA testing tab at the ADCA website.

Once you download the forms, please fill them out carefully and neatly. Make sure you include all information requested. If the animal is not yet registered (pending testing) simply put “pending” under the registration number. You MUST have a permanent ID for the animal –
either specific brand or tattoo that is unique to that animal. No two animals should have the same tattoo or brand number or there is no way to differentiate them if there is ever a question regarding paternity, etc. This unique tattoo number will be listed on the database along with
the animal’s registered name (or the exact name under which it WILL be registered if registration is currently pending awaiting test results) and the test results.

Now it is time to acquire the hair samples used for the DNA testing. DNA material is contained in the root bulbs (follicles) of the hairs. Make sure to PULL out the hairs in order to include the follicles. Do NOT cut the hair off of the animal or you won’t have the follicle needed for testing.

  1. Use a separate paper envelope or resealable plastic baggie for each animal’s sample. Before collecting the samples, label each bag with the complete name of the animal. There is a form for this that will be included in your downloaded information. Fill out
    this form completely and attach it to your hair sample envelope or baggie. If, for some reason, your sample gets detached from your form at the lab, then this complete identification will enable the folks at the lab to know the identity of the hair sample.
  2. Thoroughly wash your hands and the scissors, pliers, hemostat, etc., that you will be using to pull the hairs. Have a roll of paper towels ready near your sample bags or envelopes.
  3. Use clean (no manure) coarse hairs from the switch at the end of the tail for your sample. Pull hairs from the switch using a sharp, jerking motion (using sterilized pliers or a hemostat) and make sure that the root bulbs or follicles are attached to most of
    them. It is best to pull about 10-15 hairs at a time, so you will need several pulls to obtain the 30-50 hairs required for a sample. It is often easier to twist the hairs around your tool before you jerk the hairs out as it seems to keep them from slipping through
    and gives you a better hold on them for pulling. Collect them on a clean paper towel – aligning the root ends as you lay them down.
  4. Using scotch tape, tape the hairs into a bundle – about 4 inches from the root ends. Then, using your clean scissors, trim the excess ends off and dispose of them – being sure to keep the bundle that includes the root ends.
  5. Place the bundle of root ends/hairs into your envelope, gently press out most of the air, and seal the bag.
  6. Clean your hands and the instruments before taking the next sample and before each successive sample. You can use rubbing alcohol or antibacterial handwash for this sterilization process. The goal is to keep each animal’s DNA sample untainted by another animals or by your DNA. It is MOST important that you not touch the actual root bulbs or follicles as this is the target area for the lab to extract the DNA. Once you have finished with hair collection, you will need to mail the samples (with the sample identification form attached to each sample) along with the completed applications for the desired testing, a STAMPED SELF-ADDRESSED ENVELOPE (for the test results to be sent to you) and a check for the necessary fees payable to the ADCA.

    You will receive two certified copies of each result, so plan your postage accordingly on
    your SASE. Usually 4 sheets of paper will go for the standard rate – or the results of 2 tests. It generally takes 2-3 weeks to get results from Texas A&M.

    Once you receive your results, you then send one certified copy to the ADCA Registrar, Jill Delaney, for recording on the animal’s pedigree – or accompanied with a registration form for any new registrations. Keep the other copy for your records on that animal.

DNA Testing Forms

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American Dexter Cattle Association

1325 W Sunshine #519
Springfield, MO 65807



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