New test can identify carriers of gene behind Connemara hoof condition

Hoof Wall Separation Disease is distressing to both Connemara ponies and their owners.
Hoof Wall Separation Disease is distressing to both Connemara ponies and their owners.

A test is now available to identify Connemara ponies that carry a mutated gene responsible for a distressing foot condition characterised by fragile hoof walls.

The test, which can be conducted on mane hair, opens the way for breeders to better manage Connemara Hoof Wall Separation Disease (HWSD), previously known as Connemara Hoof Wall Separation Syndrome.

Researchers in the Bannasch Laboratory, at the University of California, Davis, identified the genetic basis of the disease, characterized by a hoof wall that easily breaks and cracks, and a normal-looking coronary band.

The breaks and cracks begin to occur in young ponies. In severe cases, the pony bears weight entirely on the sole of the foot which can lead to severe lameness.

The gene found to be responsible is inherited as an autosomal recessive trait. It means that carriers are completely normal and only animals with two copies of the mutation will show clinical signs of the disease.

The calloused sole typical of HWSS and the result of walking on the sole. If the callousing is left alone the pony will stay paddock sound but will usually not be capable of any work.
The calloused sole typical of HWSD and the result of walking on the sole. If the callousing is left alone the pony will stay paddock sound but will usually not be capable of any work.

HWSD appears to occur only in the Connemara pony and the carrier frequency has been estimated at about 14.8 percent.

The DNA test developed for this specific mutation, which costs $US40 per animal, can determine if ponies are normal or if they carry one or two copies of the mutation.

Ponies that carry two copies of the mutation are highly likely to be affected with the disease. Some cases are milder while others are more severe.

The researchers, led by Dr Carrie Finno, identified at least one case where the pony did not appear to have clinical signs associated with having two copies of the mutation. This indicated that the mutation is not fully penetrant. However, it has very high penetrance of 96.8 percent.

While carriers are completely normal, when two of them are bred there is a one in four chance the offspring will be affected.

The research carried out at the laboratory on behalf of the Connemara Pony Research Group began about three years ago, with confirmation in 2012 that the disease has a genetic basis.

The very existence of the syndrome and that it was of genetic origin had, until then, been questioned by many people throughout the Connemara Pony breeding world.

Those who had not seen or personally experienced the condition were reluctant to accept that such a serious problem could exist within the breed.

Affected hoof cross section.
Affected hoof cross-section.

It has been stressed that carriers can still be safely bred to non-carriers in order to help maintain diversity within the breed and to maintain other positive attributes.

Finno travelled to Clifden, in County Galway, Ireland, in mid-August to present the findings of her team’s research to Connemara breeders.

Poster presentations at the meeting described the distressing nature of the disease to both affected ponies and their owners.

Breeders described their ongoing battle to improve hoof health, at times to no avail.

The breeders of one such mare, Rosewood Witchcraft, known as “Crafty”, described one such battle.

“The first two years seemed so hopeful, but as she grew her feet could no longer support her,” they reported.

“Crafty had given up, so we had to give up for her as well. I could not bear to see this lovely filly suffer.”

Others described the ongoing hoofcare required for sufferers. Some were ultimately euthanised; for others the condition has proved manageable.

The Connemara Pony Research Group, in a recent blog reporting on the meeting, said: “As a direct result of this meeting significant ‘movers and shakers’ from the Connemara Pony breeding world now positively accept that HWSD does exist and that it is a unique, verifiable and testable disease.”

The major take-home message was that “the sky is not falling” in terms of the breed.

“Carrier ponies must not be removed from the gene pool,” the group stressed.

Distal hoof wall lesions, characteristic of HWWS.
Distal hoof wall lesions are characteristic of the disease.

“If the ponies are of breeding quality they have to be kept within the breeding programme.

“Knee-jerk reactions of culling animals because of carrier status is both stupid and counterproductive to the breed.

“It is not a personal reflection upon breeders if they find out that their pony/ies are HWSD carriers.”

The group reported that genetic testing of ponies was already under way. “Results are already being made public. Educated buyers are going to want to know the HWSD status of potential breeding stock before they decide to purchase.”

The disease is typified by the dorsal hoof wall splitting away from the underlying structures.

Affected animals can suffer considerable pain, as the condition results in affected ponies having to support their weight on the sole of the hoof. Even if initially controllable, ponies can develop laminitis over time.

There has been increasing awareness worldwide of the hoof syndrome within the breed over the last 15 years.

The condition has been identified in several different countries, in both local and imported stock – not one country nor one bloodline.

Its manifestations can be seen in foals as young as 2 -3 weeks of age.

Information on the testing can be found here


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