Severe Combined Immunodeficiency (SCID)

Severe Combined Immunodeficiency Disease

Turnaround: 3-5 days

US: $45.00 | UK: £35.00

Breeds: Andalusian/Arabian, Anglo-Arabian, Arabian, Arabian Cross, Arabian/Dutch Warmblood, Arabian/Friesian Cross, Arabian/Paint, Arabian/Pinto, Arabian/Quarter Horse, Arabian/Saddlebred, Arabian/Thoroughbred, Arabian/Warmblood, Egyptian Arabian, Half-Arabian, Hispano-Árab, Karabakh Horse, Lusitano, Part Bred Arabian, Shagya Arabian


Severe Combined Immunodeficiency Disease (SCID) is an inherited disease seen in pure and part-bred Arab horses. Animals with this inherited condition have an enhanced susceptibility to infection and begin to show signs of the disease between two days and eight weeks of age. Clinical diagnosis of the disease is not as straightforward as the symptoms. Symptoms can range from raised temperatures, respiratory complications, and diarrhea. These symptoms are typical of new-born foals with a range of infections.

Foals affected by SCID always die within the first six months of life. This happens regardless of the level of veterinary care. SCID is therefore an extremely distressing condition for the affected animal and the owners or caregivers. SCID frequently results in financial loss due to dead foals and veterinary expenses.

This disorder is recessive. This means that a horse must have two copies of the defective gene in order to present symptoms of SCID. Consequently, both the sire and the dam must possess at least one copy of the mutated gene and pass these onto their offspring in order for the foal to be afflicted. Horses with one copy of the disease are known as carriers, and do not present symptoms of SCID. If two carriers are bred together, there is a 25% chance per foal born that they will develop symptoms of SCID. There is a 50% chance per foal born that they will also become carriers of the disease.

A number of studies have attempted to estimate the frequency of SCID carriers in the Arab horse population. Most sources speculate that the percentage of Arab foals that die of SCID is 2-3%. If breeding is random, then this percentage would imply that roughly 28-35% of Arab horses are carriers. However, in reality, most breeding is highly selective. This makes the true frequency of carriers in the population somewhat unclear.

Animal Genetics UK offers DNA testing and detection of the gene mutation responsible for Severe Combined Immunodeficiency (SCID). This is an important tool while breeding in order to ensure that two carriers are not being bred together, so as to avoid producing a foal with SCID.

Possible Results

SCID/SCIDAffected: Horse has two copies of the SCID gene mutation and will exhibit signs of the disorder.
n/SCIDCarrier: Horse has one copy of the SCID gene mutation and can pass this gene on to any offspring.
n/nClear: Horse is negative for the SCID gene mutation.