SCIDs Information

Severe Combined Immunodeficiency Disease (SCID)

SCID is an inherited disease specifically seen in pure and part-bred Arab horses. Foals afflicted with this condition have an enhanced susceptibility to infection and first show signs of disease at between two days and eight weeks of age. Clinical diagnosis of the disease is not straightforward as the symptoms, such as raised temperature, respiratory complications and diahorrea, are typical of new-born foals with a range of infections. SCID affected foals always die within the first six months of life, regardless of the level of veterinary care administered.

SCIDs in Arabian horses was inherited as an autosomal recessive condition, which means that one copy of the disease gene is inherited from a carrier stallion and another from a carrier mare. The foal which inherits two copies of the disease gene is affected with a lethal inability to fight infections, and dies within the first few months of life.

Matings between two clear horses as well as matings between a clear and a carrier horse will NEVER produce an affected animal. By definition, carriers of genes for autosomal recessive disorders are completely free of clinical signs of the disease. That is, carriers do not have any negative consequences to their health or performance. If two carriers are mated, there is a 25% chance that the foal will be clear, 50% chance that it will be a carrier and 25% chance that it will be affected, a chance not worth taking.

Prior to the advent of molecular genetic testing for autosomal recessive disorders, the only way an Arabian Horse was identified as carrier was when he or she produced an affected offspring. The traditional recommendation in veterinary medicine would be gelding of these animals to prevent other affected offspring being produced. This is no longer necessary and not in the best interest of the breed. Carrier horses that have desirable traits can now be mated to tested horses that are clear and never produce an affected foal. Their offspring can be tested and appropriate matings set up in the next generations without the breed suffering the loss of another foal to SCID. The breed continues to benefit from all of the outstanding traits a carrier animal may possess. The economic value of the Arabian Horse should not be affected by being clear or carrier.

SCIDs is easy to test for. There are three possible test results: Clear, Carrier, and Affected. Below is a description of what each result means to the breeder.

Although possible that there will be some clear foals when breeding "Carrier to Carrier", breeding this pair of Horses is not recommended. Some resulting foals are likely to be Carrier and some foals are likely to be Affected.

The cost of testing is a small fraction of the value invested in the horse. All breeding animals need to be tested to avoid major losses to the breed and heartache to the humans and to the breed.