Foal immunodeficiency syndrome

Veterinary advice should be sought before applying any treatment or vaccine.

Foal Immunodeficiency Syndrome

Fell Pony Syndrome

Foal immunodeficiency syndrome (FIS), formally known as fell pony syndrome, is an inherited condition of progressive anemia and immunodeficiency in foals. Initially FIS was thought to occur only in the Fell Pony breed of horse, but in 2009 a case was reported in a Dales breed pony. A mutation associated with FIS in both the Fell and Dales Pony breeds was identified in 2011. Other at risk breeds of FIS are the Clydesdale, Highland Pony, Exmoor Pony, Welsh Pony, and colored horses and ponies.

Affected foals appear normal at birth but at 2 to 8 weeks of age begin to develop severe anemia and immunodeficiency.


Weight loss
Failure to suck
Pale mucous membranes
Nasal discharge
Watery diarrhoea
Rapid heart rate


  • History
  • Clinical signs
  • Physical exam
  • Genetic test


Supportive therapy, however the syndrome is ultimately fatal to the foal.


Poor, there is usually 100% mortality by the time the foal is 3 months old.

Scientific Research References

Good Overviews

Age Range

Young foals 3-4 weeks of age of the Fell Pony breed