What is Hoof Wall Separation Disease?

HOOF Wall Separation Disease (HWSD) occurs due to a genetic mutation caused by a single mutated gene, and is known as an autosomal recessive genetic disorder. If a pony has two copies of this mutated gene it makes that animal an affected (HWSD/HWSD) animal, i.e. all four hooves are affected. Defects occur in the horn of the dorsal hoof wall.

It is purely a genetic state and works in a similar way to the ‘blue-eyed cream gene’. However, the HWSD mutation can cause severe debilitation. The condition may have no obvious visible signs, or may present itself as slightly affected, to very severely affected, and it is not yet understood why the visible signs can suddenly manifest themselves.

The environment plays no part in causing the condition, however environmental conditions may help in the management of the less severely affected pony. Management in such cases is critical, and trimming and attention to the hooves may be necessary as often as at three weekly intervals. All ponies must be treated as individual cases. In very severe cases which can’t be managed euthanasia may be necessary.

What do these two photos have in common? Both ponies have HWSD!

In an affected pony the outward clinical signs of HWSD

  • are not always visible, and the hooves may look perfect, although where it is visible,
  • the hoof wall will be seen to be breaking away,
  • there may be weight bearing problems
  • the pony may be difficult to shoe and
  • there may be lameness

    • What can be done do help eradicate this disease?

    IT is important that the HWSD condition is eradicated from the herd, both from a marketing point of view and that of animal welfare. To achieve this the Connemara Pony Breeders Society have already taken several steps:

  • all foals since 2016 are tested for HWSD before registration, unless they are the progeny of CPBS recorded non-carrier parentage
  • all stallions are tested for HWSD before/at inspection unless they are the progeny of CPBS recorded non-carrier parentage;
  • all mares brought out for inspection can be tested at inspection for HWSD unless they are the progeny of Connemara Pony Breeder Society (CPBS) recorded non-carrier parentage;
  • all new registrations are tested unless they are the progeny of CPBS recorded non-carrier parentage;
  • once tested the result will be recorded in the pony’s passport;
  • if testing is not required due to the pony’s already established carrier-free status it’s CPBS passport will be stamped as being a non-carrier; and
  • to have had the test will be an important factor at sales.

    • However, the breeder must play a very important part to achieve eradication of HWSD by responsible breeding.

    Factors to consider when breeding

    Genetic testing of a pony will give one of three results:

  • 1. Affected (HWSD/HWSD)
  • 2. Carrier (N/HWSD)

    • 3. Non-Carrier (N/N)

    An Affected x Affected cross should not be considered as this will result in an affected offspring ie. HWSD x HWSD 100% result affected.

    A carrier pony alone merely carries a single copy of the gene and will not display any HWSD related disability. However, a carrier pony bred to another carrier pony, will result in the following:

    N/HWSD x N/HWSD

  • 25% of matings: likely affected
  • 50% of matings: likely result carriers
  • 25% of matings: likely result non-carriers

    • Importantly to maintain diversity in the herd it is acceptable to breed a carrier to a non-carrier:

    N/HWSD x N/N

  • 50% chance of a Non-Carrier pony or a
  • 50% chance of a Carrier pony.

    • This cross cannot result in an affected (HWSD/HWSD) pony as genetically it is not possible. It cannot be predicted which other genes will be passed on.

    It is important to note from this cross that there is then the option for the breeder to choose future breeding animals that are free of the condition, thus potentially further reducing the carrier percentage within future generations. The breeder can make a choice and this is where responsible breeding is important, the responsibility being for the good of the herd, to strive for a healthy HWSD free population.

    The Non-Carrier x Non-Carrier cross also has its part to play:

    N/N x N/N

  • 100% result Non-Carrier

    • As this cross excludes carriers it is entirely free of the HWSD gene and is therefore totally free from the genetic condition.

    Important note:

    If the N/NxN/N cross is used exclusively by breeders in the coming generations, it will limit the gene pool in an already jeopardized situation and may cause unknown and unwanted traits to manifest themselves – there is still a place for using such a cross but it should not be used exclusively if genetic diversity in the herd is to be maintained.

    Welfare is paramount

    THERE are affected ponies leading useful lives, but the welfare of the pony is paramount. This welfare comes at a price to the owner.

    It is important to realise that whilst only a small percentage of the pony population is affected, breeders must know the status of the ponies they are using to breed, breed responsibly to eradicate HWSD and preserve the herd to the breed standard. It is our duty to the Connemara pony.

    The study of HWSD is now on the syllabus of the Irish School of Farriery. Should a genetic test be required to confirm/rule out a diagnosis, please contact the Connemara Pony Breeders’ Society or visit our website at www.cpbs.ie.