The Importance of Coggins

Contributed by: Valerie Mellema, Gray Horse Publishing

The Coggins test. It’s required everywhere we take our horses – shows, clinics, boarding barns, racetracks, and on the highways. Unfortunately, there are those who don’t take this test as serious as they should and some don’t understand exactly what it is and why it’s important.

The Coggins test was developed in the sixties by Dr. Leroy Coggins and tests for Equine Infectious Anemia (EIA). EIA is a viral disease for which there is no cure or vaccine.

There are three phases to this disease:

  1. Acute form – Depressed, uncoordinated and feverish horse. This phase may last several days. This is when many horses will spread the disease because they are not yet anemic and may appear to just be "off" to the owner.

  2. In this phase, the horse loses wait, has recurring fevers and is generally weak. Anemia may also be present. Many horses do not survive the second stage.

  3. In the third phase, the horse enters the chronic stage. Pregnant mares may abort. Mares can also spread the disease to their foals at this stage. The horse may be mildly anemic and appear to be poor keepers.

Horses that are infected with the EIA virus will be carriers for life. Horses that are chronic may appear to be normal but will often become ill under stress.

The disease is transmitted from horse to horse by biting insects, typically horseflies and deerflies. Because horses will swat with their tail, twitch or bite at them, the "bloodmeal" is interrupted and the flies move on to another horse. The infected blood is then transmitted to the second horse, spreading the disease.

The Coggins test detects the antibodies of the virus in the horse’s blood. The antibodies are present for life after the horse has been infected. If a horse is found to be positive, there are strict quarantine rules. The horse must be confined in a screened stall and at least 200 yards away from all other horses.

It is a life of strict isolation and the horses cannot travel to events or other states. Because of this and the chronic illness these horses may undergo, many owners elect to euthanize.

Most states require that horses six months and older have a negative Coggins test in order to cross state lines. Many shows and events require a negative Coggins. If you do travel with your horses, you may consider testing more than the required once per year to ensure your horse hasn’t become infected while traveling. The same is true if you board your horse at a farm with frequent travelers and turnover.

To stay up to date with the latest equine disease outbreaks in the United States, visit


Valerie Mellema is the owner of Gray Horse Publishing & Marketing.

She has been in the equine industry for over 25 years and is a published author of multiple horse care books. She is also the owner of Mellema Thoroughbreds, a thoroughbred breeding farm. She shows her OTTB, Mistic Gray, in hunter/jumpers.

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