Hoof Wall Separation Disease (HWSD)
In 2009 there was increasing awareness worldwide, of a problem with the hoof structure in a subset of our beloved Connemara Ponies. This ‘problem’ is Hoof Wall Separation Disease (HWSD).
With advances in electronic communication, owners and breeders of affected ponies came into contact with each other, and formed the CONNEMARA PONY RESEARCH GROUP (CPRG); a group dedicated to having serious scientific research performed on the disorder which would become known as HWSD.
The total lack of interest and acknowledgement by the Connemara Pony Breeder’s Society and the International Committee of Connemara Pony Societies (ICCPS ) that this hoof issue existed, resulted in the CPRG ‘going it alone’ in an effort to find the cause of the ‘problem’. As a result of the genetic research undertaken at Bannasch Laboratory, UC Davis, the commercial genetic test for the HWSD mutation was released in August 2014.
There are three categories of result for the HWSD test:
N/N: no copies of the mutation. Completely normal hoof structure.
N/HWSD: one copy of the mutation. The pony is referred to as a carrier. Shows normal hoof structure. MUST ONLY BE BRED TO N/N partner.
HWSD/HWSD: two copies of the mutated gene. This pony is referred to as 'affected'. It has abnormal hoof structure of varying degrees of severity. MUST ONLY BE BRED TO N/N partner.
All Connemara Pony Breed Societies worldwide now require purebred foals to be HWSD tested as part of the registration process. The CPBS instituted this ruling in 2016, however several other breed societies made the requirement much earlier. Some societies also require the testing of part-breds when the Connemara parent is N/HWSD (carrier status).
The total lack of interest and acknowledgement by the Connemara Pony Breeder’s Society and the International Committee of Connemara Pony Societies (ICCPS ) that this hoof issue existed, resulted in the CPRG ‘going it alone’ in an effort to find the cause of the ‘problem’. As a result of the genetic research undertaken at Bannasch Laboratory, UC Davis, the commercial genetic test for the HWSD mutation was released in August 2014.
There are three categories of result for the HWSD test:
N/N: no copies of the mutation. Completely normal hoof structure.
N/HWSD: one copy of the mutation. The pony is referred to as a carrier. Shows normal hoof structure. MUST ONLY BE BRED TO N/N partner.
HWSD/HWSD: two copies of the mutated gene. This pony is referred to as 'affected'. It has abnormal hoof structure of varying degrees of severity. MUST ONLY BE BRED TO N/N partner.
All Connemara Pony Breed Societies worldwide now require purebred foals to be HWSD tested as part of the registration process. The CPBS instituted this ruling in 2016, however several other breed societies made the requirement much earlier. Some societies also require the testing of part-breds when the Connemara parent is N/HWSD (carrier status).
The condition has been identified in all countries where the Connemara pony is bred, in both local and imported stock. - not 'one' country nor one bloodline.
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. 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. There are degrees of severity with HWSD; some can be managed and some ponies need to be euthanized. Environment and nutrition may be contributing factors, but are not the cause.
The cause is the malfunction of a protein called a protease inhibitor. It results in damage to the protein structures which hold the layers of the hoof wall together. (For the geeks among us, the mutation inserts a premature stop codon into the prostease inhibitor).
The science behind the HWSD test
HWSD does not respond to topical hoof applications and dietary interventions like other hoof conditions such as White Line Disease (WLD) do. HWSD is commonly confused with WLD by those people unaware off the existence of HWSD. There are NO "cures", but maintaining a steady wet or dry environment often helps to maintain the hooves, however changes between the two states can cause disintegration of the hoof in a matter of hours; particularly wet to dry changes.
HWSD has to date, NOT been found in any other breed than the Connemara pony and its derivatives.
Now that it is possible to identify carrier ponies NO HWSD affected ponies should still be being born. Sadly though, this is not the case. In countries other than Ireland, UK and France, there have been no affected ponies born since 2016. The acceptance of the science behind the test and uptake of the testing regime for breeding stock has not been voluntarily embraced in the three countries mentioned above, unlike in the other jurisdictions.
HISTORY OF HWSD
In 1996 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 what was thought to be the lipid metabolism in the extracellular matrix of the hoof wall between the tubular structures of the hoof wall. In simple terms, the affected hoof lacked the 'waterproof glue' to the hoof wall tubules together. The true cause of this malfunction was identified as a result of the UC Davis research and proved that the original hypothesis that HWSD is caused by a lipid malfunction to be incorrect. However further research into the structure of the HWSD affected hoof wall is awaiting approval to commence, so we may yet find out at why some ponies are more severely affected than others
.
All of the pictures which follow are of ponies which tested as HWSD/HWSD. Figures 1 - 3 are of Rosewood Witchcraft. Her story can be found here:
The cause is the malfunction of a protein called a protease inhibitor. It results in damage to the protein structures which hold the layers of the hoof wall together. (For the geeks among us, the mutation inserts a premature stop codon into the prostease inhibitor).
The science behind the HWSD test
HWSD does not respond to topical hoof applications and dietary interventions like other hoof conditions such as White Line Disease (WLD) do. HWSD is commonly confused with WLD by those people unaware off the existence of HWSD. There are NO "cures", but maintaining a steady wet or dry environment often helps to maintain the hooves, however changes between the two states can cause disintegration of the hoof in a matter of hours; particularly wet to dry changes.
HWSD has to date, NOT been found in any other breed than the Connemara pony and its derivatives.
Now that it is possible to identify carrier ponies NO HWSD affected ponies should still be being born. Sadly though, this is not the case. In countries other than Ireland, UK and France, there have been no affected ponies born since 2016. The acceptance of the science behind the test and uptake of the testing regime for breeding stock has not been voluntarily embraced in the three countries mentioned above, unlike in the other jurisdictions.
IF YOU ARE THINKING OF BUYING A CONNEMARA PONY OR PARTBRED CONNEMARA INSIST ON VIEWING THE HWSD TEST RESULTS BEFORE PURCHASING.
HISTORY OF HWSD
In 1996 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 what was thought to be the lipid metabolism in the extracellular matrix of the hoof wall between the tubular structures of the hoof wall. In simple terms, the affected hoof lacked the 'waterproof glue' to the hoof wall tubules together. The true cause of this malfunction was identified as a result of the UC Davis research and proved that the original hypothesis that HWSD is caused by a lipid malfunction to be incorrect. However further research into the structure of the HWSD affected hoof wall is awaiting approval to commence, so we may yet find out at why some ponies are more severely affected than others
.
All of the pictures which follow are of ponies which tested as HWSD/HWSD. Figures 1 - 3 are of Rosewood Witchcraft. Her story can be found here:
Figure 1. 7 month old Connemara filly with HWSD showing typical lesions. This pony is walking on the sole, not the wall as is normal.
HWSD is caused by a simple recessive gene (known as autosomal recessive). This means that the disease state can only occur when two carrier ponies are bred to each other.
The pedigree analyses, which was the precursor of the genetic research has been proven to be correct; carriers of HWSD are presently around the low 20% of the population in Ireland. Some countries have a higher carrier rate which reflects the status of their original imports. Lack of accessible data prevents further analysis in this area.
To prevent breeding of affected ponies, ALL breeding stock in ALL countries need to be tested. All breeding stock should be required to be tested before before being bred, which presently is not the case in some countries.
By instituting and enforcing such an adult testing scheme in all countries, over time the level of the HWSD mutation within populations can be reduced or even eliminated, without compromising genetic diversity.
Genetic diversity is an immediate concern with the breed already suffering from an already small gene pool. If we do not ensure that there is no further loss in genetic diversity now, mutations with potentially worse effects than HWSD are likely to be 'lying in wait' in the Connemara Pony population. Further research in this area has already commenced.
Figure 2. Showing the peeling of the hoof wall at the weight bearing borders. NOTE the abnormal periople and the lack of shine on the hoof wall.
Figure 3. The calloused sole often seen in the HWSD affected hoof as the result of walking on the sole. If the callous is left alone the pony may remain paddock sound but is unlikely to be capable of any form of work.
Figure 4: Another foal with HWSD but see that this one does not have a sole callous. In all likelihood because the environment is wetter and softer underfoot than is the case in California where Rosewood Witchcraft lived. This foal was euthanised. Photo credit: J Mulligan
Figure 5. Same foot as Figure 4 above.
The pedigree analyses, which was the precursor of the genetic research has been proven to be correct; carriers of HWSD are presently around the low 20% of the population in Ireland. Some countries have a higher carrier rate which reflects the status of their original imports. Lack of accessible data prevents further analysis in this area.
To prevent breeding of affected ponies, ALL breeding stock in ALL countries need to be tested. All breeding stock should be required to be tested before before being bred, which presently is not the case in some countries.
By instituting and enforcing such an adult testing scheme in all countries, over time the level of the HWSD mutation within populations can be reduced or even eliminated, without compromising genetic diversity.
Genetic diversity is an immediate concern with the breed already suffering from an already small gene pool. If we do not ensure that there is no further loss in genetic diversity now, mutations with potentially worse effects than HWSD are likely to be 'lying in wait' in the Connemara Pony population. Further research in this area has already commenced.
This report is a brief overview, For more detailed information, please contact the Connemara Pony Research Group. All information about ponies & people is kept confidential. Our e:mail is: Remove parentheses to use email
