Hoof Wall Separation Disease in Connemara pony (HWSD)

HWSD (Hoof Wall Separation Disease) is an inherited hoof disease in Connemara ponies. The disease is caused by a mutation in the SERPINB11 gene (c.504_505insC). In affected horses, the dorsal hoof wall breaks and separates. Clinical signs may vary between individuals. Some ponies are minimally affected; it can be seen only small areas of progressive fraying and separation of the hoof wall. On the other hand, in some horses the disease is very severe. It can lead to a state of severe lameness and the formation of local chronic inflammation. It is the chronic inflammation that leads to hoof lameness, which is very painful for the horse. In especially severe cases, euthanasia may even be necessary. The condition of the hooves can often be affected by sudden changes in the environment (for example, when going from dry to wet or vice versa). The defect affects all 4 hooves, but the degree to which they are affected can vary. Clinical signs appear during the first 6 months of the affected horse's life. In the first study (2015), the frequency of detected carriers was 14.8% of the 369 Connemara horses tested.

HWSD is an autosomal recessive genetic disorder. Healthy individuals are referred to as N/N. An individual who inherits the mutated gene from one of its parents is referred to as N/HWSD; the animal has no clinical symptoms of the disease but can pass the mutated gene on to its offspring. Only those individuals who inherit the mutated gene from both parents (referred to as HWSD/HWSD) show the above symptoms. Elimination of carriers from the breed is not recommended due to the reduction of genetic variability of the breed. Crossing a healthy individual (N/N) and a carrier (N/HWSD) theoretically produces 50% carriers and 50% healthy individuals. When mating, it is important to select the breeding pair in such a way that no pairing of two carriers occurs. When mating two heterozygotes (N/HWSD), theoretically 25% of the offspring would be healthy, 50% would be carriers and 25% would inherit both mutated genes from their parents and be affected by HWSD.

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Reference:

Finno, C. J. "Hoof wall separation disease: A review." Equine Veterinary Education (2021)

Finno, Carrie J., et al. "SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara ponies." PLoS genetics 11.4 (2015): e1005122.