Breeders have tightly inbred Friesian horses over the last 100 years to preserve the breed's qualities, so buyers should be aware of potential genetic defects when purchasing Friesian horses. The breed's popularity has led to increased breeding and an increase in the number of horses with genetic defects.
Dwarfism is a common genetic defect in Friesian horses. These horses have normal-sized bodies and heads, but severely stunted legs with fetlock hyperflexion and long, narrow hooves. Approximately two foals per 1,000 births suffer from hydrocephalus, which is cerebrospinal fluid build-up in the horse's brain. Over half of Friesian broodmares retain placentas during foaling, and the condition only occurs in two to 10 percent of the overall broodmare population.