Friesian horses



  • Hydrocephalus is an excessive accumulation of fluid in the brain.
  • It results in the appearance of a dome-shaped head.
  • There is no treatment and affected foals are aborted, stillborn, or born with severe neurological issues.
  • Hydrocephalus is inherited as an autosomal recessive disorder in Friesian horses.
  • A causative mutation has been identified in Friesians and a DNA test is available.

What is hydrocephalus?

Hydrocephalus is the excessive accumulation of cerebrospinal fluid in the brain. This results in severe distension of the head, giving it a large, domed appearance.

Hydrocephalus is inherited as an autosomal recessive disorder in Friesian horses. It is thought to occur due to an abnormal narrowing of the opening at the base of the skull. A causative genetic mutation has been identified and a genetic test is available. This mutation has also been associated with a single case of hydrocephalus in a stillborn Belgian draft horse. Further research is needed to investigate the inheritance of hydrocephalus in other breeds.

What are the clinical signs of hydrocephalus?

The primary clinical sign of hydrocephalus is an enlarged, dome-shaped head. Dystocia may occur in dams pregnant with affected foals.

How is hydrocephalus diagnosed?

Hydrocephalus is apparent by the appearance of the head. Radiographs can be used to support a diagnosis. The available genetic test can be used for a definitive diagnosis.

How is hydrocephalus treated?

There is no treatment for hydrocephalus.

What is the prognosis for hydrocephalus?

Friesian foals affected with hydrocephalus are aborted, stillborn or born with severe neurological issues that warrant euthanasia.

How can hydrocephalus be prevented?

Hydrocephalus in Friesians can be prevented by utilizing the genetic test to avoid matings that could produce affected offspring. The disorder has an autosomal recessive mode of inheritance, meaning that an affected offspring has to inherit one copy of the causative mutation from each of its parents. Carrier by carrier matings should be avoided as they have a 25% chance of producing an affected foal. The genetic test for hydrocephalus is mandatory for stallion and mare registration with The Friesian Horse Society for purebred and part-bred horses (geldings are exempt).

The genetic test is recommended for Friesians and Friesian crosses.

For more information:

UC Davis Veterinary Genetics Laboratory - Friesian Horse Hydrocephalus genetic test

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