Hoof Wall Separation Syndrome (HWSS)
Over the past 15 years there has been increasing awareness worldwide of a problem with the hoof structure in a subset of our beloved Connemara Ponies.
With advances in communication, owners and breeders of affected ponies have come in contact with each other, and have recently formed the CONNEMARA RESEARCH GROUP dedicated to having serious scientific research done on the disorder, which the group has called “Hoof Wall Separation Syndrome (HWSS)”.
The condition has been identified in several different countries, in both local and imported stock. - not 'one' country nor one bloodline. Currently HWSS is still not recognised by the breed societies but we are working hard at educating and spreading the word of this serious condition.
Hoof Wall Separation Syndrome results in the weight bearing borders of the hoof wall breaking away from the underlying structure which then leaves the pony to bear weight on the sole of the hoof. This appears to be a congenital condition, if the pony is going to have this condition, it will be born with it, and it can be seen in foals as young as 2 -3 weeks of age. It is not an acquired condition. We are unsure why, but there seems to be consensus that there are degrees of severity with this condition; some can be managed and some of these ponies need to be euthanized. Environment and nutrition may be contributing factors, but do not appear to be the cause.
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Robert Eustace of the Laminitis Trust (UK) originally described the condition as “coconut-matting hooves” as the borders of the hoof wall appears rough and frayed. Hoof samples of affected Connemara Ponies which had been referred to the Trust for treatment were analysed at the University of Edinburgh, where they found a malfunction of lipid metabolism in the extracellular matrix of the hoof wall between the tubular structures of the hoof wall. In simple terms, there seems to be a lack of 'waterproof glue' holding the hoof wall tubules together.
Figure 1. Seven month Connemara filly with HWSS showing typical lesions. This pony is walking on the sole not the wall as is normal.
Figure 2. The peeling walls near the bearing border. Note the abnormal periople and the lack of shine on the hoof wall indicating that hoof wall is permeable.
Figure 3. 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 usually not capable of any work.
If the condition is caused by a simple recessive gene (which is the current hypothesis), this means it can only occur when two carrier ponies are bred to each other.
If pedigree analyses turn out to be correct, then carriers of the condition are likely to be extensive and widespread in the Connemara breed. To prevent further breeding of affected ponies, a genetic test is needed for screening breeding stock. Such a test would allow, over time, the level of HWSS within the population to be reduced or eliminated without compromising genetic diversity. Genetic diversity is a concern with an already small gene pool. In other words, we wouldn’t have to throw the baby out with the bath water!
The horse genome was completely sequenced in 2007, and since then there has been rapid progress in locating and mapping genetic markers. UC Davis was approached by the research group, and has agreed to undertake a Genome Wide Association Study (GWAS) to attempt to find the faulty gene responsible for the condition.
Care is required that only ponies with true Hoof Wall Separation Syndrome are included in the study, and there are protocols already in place for identifying ponies, and submitting materials for research.
Additionally, work to either confirm or disprove the proposed lines of inheritance will be done on the pedigrees of affected ponies. The work will also establish an estimate of the percentage of carriers within the worldwide population of the Connemara Pony Breed.
The research group now has the support of some highly respected research groups, but now needs funding to make further progress. The cost of performing a Genome Wide Association Study on our Connemara Ponies is USD $13,000 for the first phase and another USD $5,000 to analyze the data. Donations from breeders and societies would be greatly appreciated!
A Research Fund has been established and people can send their donations to the Center for Equine Health, One Shields Ave, Davis, Ca 95616. They should send a letter accompanying their cheque stating that the donation should be directed to Connemara DNA research.
This report is a brief overview, For more detailed information, please contact the Connemara Research Group. All information, ponies & people are kept confidential. Our e:mail is:
