Guest Post by Tom Ryan FWCF on his experience with treating an HWSS affected pony.

This paper has recently been published in Forge Magazine and is republished here with kind permission from Mr Ryan http://www.equinehoof.co.uk/hwss.php

Hoof wall separation syndrome in Connemara ponies

Tom Ryan FWCF

The first time I saw pony Liam (name changed) was just after my client had bought him. I could see that he had slightly broken up hooves but thinking like most farriers would, I expected his hooves would improve under my charge. Unfortunately, this was not to be the case and as the winter progressed his hooves gradually deteriorated and by April 2010 the stratum externum was breaking away from the stratum medium, not just in the area around the nails but also around the toe of the hoof, an area that normally stays intact when hooves break up.

Photograph 1:  Liam's broken hoof in May 2010

As all four hooves were badly affected and thinking that a bacterial infection was causing the problem I decided to ask the help of the client's vet and together we took biopsies from the affected areas of Liam’s hoof wall. The results came back as normal, no abnormal bacteria associated with breaking hooves were found in the hoof.

Photograph 2:  Broken hoof removed and hoof poulticed with iodine

We decided that the entire areas of broken hoof should be removed but doing this to all four hooves at once was out of the question as it would make the pony very lame. Instead we decided to treat one hoof per week, in this way if we encountered problems it would be with only one foot. So each week all the broken hoof from one foot was removed and for the next twenty four hours the hoof was poulticed with iodine to ensure the hoof was sterile.

Photograph 3:  Kerckheart Aluminium shoe glued to repaired hoof

The hoof was rebuilt with glue then an aluminum shoe was glued to the repaired hoof, blue children's modeling dough was used on the inner border of his shoe to prevent the glue or shoe pressing onto the sole of his foot.  This was time consuming and expensive but worked well. For the next few months the glued on shoes were replaced as they started to become loose or were lost altogether, Liam was comfortable in the shoes and they didn’t cause him any problems.

Photograph 4: All hooves repaired

I noticed his hoof reacted slightly differently to the glue, in that the surface of stratum medium adhered less well to the glue, something I had not observed in other types of broken hooves. I have experienced cases of breaking hoof walls and seedy toe in other breeds both in everyday practice and as a referral farrier at an equine veterinary practice and I can safely say that Liam’s feet were different, although at the time I wasn’t sure quite how, it certainly was not a case of severe seedy toe.

When the wall had re-grown down to the ground surface, I could still see that his hoof was still not normal but tried again using nailed shoes, unfortunately his hooves soon started to deteriorate again. In discussion with the client it was decided to try Liam barefoot as an alternative solution to the problem but Liam soon became very uncomfortable and foot sore, as all his weight was being carried by his sole, as the hoof wall was crumbling away, we realised that this was not going to solve his problem and went back to gluing his shoes.

Liam had been bought for showing but as his feet were repaired with glue and the rules for showing do not allow filled or rebuilt hooves, he could not be shown. Considering that the only way of keeping him sound was with rebuilt hooves and glued shoes, meant his hooves were going to be a perpetual and very costly problem. After a lot of soul searching, the owner in discussion with her vet decided he would have to be put down.

It was eighteen months later at a Farriers Focus Day, that a farrier who has produced a horseshoe for broken hooves called GluShu[ii] first mentioned hoof wall separation syndrome in Connemara ponies to me. Some quick research on the internet[iii] revealed that there did seem to be an ongoing hoof wall problem within the Connemara population which some were calling ‘Hoof Wall Separation Syndrome‘(HWSS). Gauging what proportions of Connemara's have had problems or how severely it has affected them was difficult to establish, certainly some severe cases have eventually resulted in euthanasia.

Some contributors reported an apparent absence of lipids in HWSS affected hooves, a type of fat normally found in hoof, its function is thought to provide protection to the hoof structure by repelling excess moisture. Reading the comments of others about HWSS, I knew that this was what I had been dealing with eighteen months earlier.

Current thinking is that HWSS is a congenital genetic problem, the genes thought to be responsible are said to be recessive within an autosomal chromosome, autosomal chromosomes are not responsible for deciding the sex of the animal and therefore both males and females can carry the defective gene. Both parents must be carriers of the defective recessive gene in order to produce a chance of a foal with affected hooves. The possible outcomes are; a 1:4 chance that the foal will have HWSS, a 2:4 chance of a foal with good hooves but still a carrier of the defective gene and a 1:4 chance of producing a foal which is not a carrier and has good hooves.

Diagram 1:  Possible outcome if both parents are HWSS carriers. 

These chances are random and any outcome is possible for each foal born.

If one parent is a HWSS carrier and the other is not, then there will be a 2:4 chance of the foal being a carrier but it will not have HWSS hooves.

Diagram 2: Possible outcome if one parent is a carrier

The genome for the horse was sequenced for the first time in 2007, opening the opportunity to isolate which genes may be involved in HWSS. Currently research into HWSS is being carried out by Dr. Carrie Finno, DVM, PhD at University of California Davis and is focused on identifying the genes which are associated with the production of keratin, the protein which is used to produce horn and hair. DNA samples of both normal and affected animals are currently being collected and compared. The goal of this research will be the ability to identify carriers of HWSS with a simple blood test. So they can be isolated and excluded from any future breeding program (* editor's note). Until then it will only be when an affected foal with HWSS is born that it will alert the breeder that its parents are both carries of HWSS. As this may not be the first foal from this dam and sire, previous foals may have already been produced and unknowingly sold on, as there were no indicators at that time there was a genetic problem.

When only a few ponies were carriers the chances of both parents being affected must have been small, the odd foal with poor quality hooves would have been seen as a random occurrence of bad luck. Other foals would have been born as carriers with good hooves, in this insidious way HWSS has secretly crept into the population and as the ponies have moved around the world, so has HWSS. Today cases have been reported in many countries including UK, Ireland, Sweden, New Zealand and the USA.

From the one case that I have experienced, Liam's problems were of a greater magnitude than any broken hoof I had met before. The only solution to avoid future cases of HWSS will come from revised breeding practices which acknowledge the underlying genetic causes. If the first-class reputation of the Connemara is to be upheld, then both breeders and individuals will have to address this problem in an open and honest way.

First published in the Connemara Chronicle Vol 40-2013, page 183

Anatomy notes

The hoof wall is comprised of tubules of keratin which grow downward from the Coronary band. Distribution or the density of the horn tubules reduces through the three main zones of the hoof wall, the stratum externum, stratum medium and stratum internum. The greatest density of horn tubules is in stratum externum where on the surface of the hoof wall they are slightly flattened to become oval, which is thought to help retain moisture. The stratum medium forms the bulk of the hoof wall while the inner stratum internum has the lowest number of horn tubules and forms the laminal interface with the dermal tissues, it is usually un-pigmented and can be seen as a white line on darker coloured hooves

Diagram 3, Anatomy of hoof wall

Between the horn tubules is inter-tubular horn which binds the horn tubules together, this has intermediate filaments which are laterally orientated fibres which help to bind the horn tubules together and resist cracking.

The outer stratum externum is more rigid than the more flexible stratum medium, while the stratum internum is the softest, this gradient of reducing stiffness helps the hoof capsule transfer energy smoothly between the wall and the dermis and also allows the hoof capsule to expand in shape under loading and return back to it's original shape when the load is removed. Transfer of weight from the skeletal structures is primarily from distal phalanx (pedal bone) via the hoof wall to the ground surface, the solar surface can only support a small proportion of the total weight of the horse before it causes pain.

---

Footnotes:
[i] Jameg ShoeGlu, Jameg Horseshoes, Barnby Moor Stables, Kennel Drive, Barnby Moor, Retford, Notts., DN22 8QU

[ii] GluShu, https://www.facebook.com/glushu

[iii] Google "Hoof wall separation syndrome in Connemara ponies"

* Editor's note.  Removing carrier ponies from the breeding population is not recommended as this will further reduce an already truncated genepool; the test will identify carriers.  This information will help breeders to choose non-carrier mates and therefore prevent the production of any further affected ponies.

The relevance of the Fell Pony Syndrome Research to HWSS

The situation with HWSS in presently facing the breeders of Connemara Ponies is very similar to that which The Fell Pony breeders are faced with and which they have dealt with in a positive, constructive and successful manner.   The united approach to find cause of FIS  is an example that the Connemara Pony breeding community could well do to follow.  The whole of the latest research paper has been reprinted below because it has become obvious that people are not aware of how relevant this work is.  The blog stats tell us whether people outclick to the posted links; not one outclick has been made to this paper.

The overall population numbers are different between the Fell Pony situation described here and that of the Connemara Pony situation but the level of penetrance of the relevant mutations within in each of these  populations is very similar.  Table 1 at the end of the paper  makes for very interesting reading.

April 13, 2013 | Veterinary Record
Foal immunodeficiency syndrome: carrier testing has markedly reduced disease incidence

S. D. Carter, L. Y. Fox-Clipsham, R. Christley, J. Swinburne

Foal immunodeficiency syndrome (FIS), a fatal autosomal recessive disease found in three breeds of horses, was first reported (in the Fell pony) in 1996, and it soon became apparent that significant numbers of syndrome foals were being born each year. In each FIS case, the foals are clinically normal at birth, but start to weaken at 2–8 weeks (Scholes and others 1998) as they develop profound anaemia (Dixon and others 2000) and do not have the ability to produce their own antibodies (Thomas and others 2005), due to the almost total lack of B lymphocytes in the circulation or tissues (Thomas and others 2003), but with apparently normal levels of functional T lymphocytes (Bell and others 2001). The outcome is persistent opportunistic infections with no effective treatment; euthanasia is the preferred option. FIS has also been reported in Fell ponies in The Netherlands (Butler and others 2006), Germany (May and others 2011) and USa (Gardner and others 2006). In 2009, we confirmed a case of FIS in a Dales pony foal (Fox-Clipsham and others 2009).

The search for the genetic lesion thus became paramount, as the carrier parents were clinically normal, and it was feared that there could be high carrier rates in breeding Fell and Dales ponies. In 2009, we identified a single nucleotide polymorphism (SNP) in a sodium transporter (SlC5a3) which was completely associated with FIS and was homozygous in FIS foals and heterozygous in FIS carriers (Fox-Clipsham and others 2011a). The SNP is a functional alteration in an exon within the SlC5a3 gene, and within three months, we developed and launched a diagnostic test (available at http://www.animaldnadiagnostics.co.uk) based on PCR and sequencing to identify FIS carriers and early syndrome foals. This was made available to all equine owners and can be performed simply on pulled hair samples, removing the need for blood sampling.

The acquisition of the FIS test meant that we could identify carriers and make recommendations concerning the possible outcomes of specific breeding combinations, for instance, a carrier breeding with a normal pony, or two carriers breeding together. We regularly met with Fell and Dales pony owners to explain how they should use the FIS test to avoid producing a syndrome foal, and stressed the need to use the FIS test to avoid carrier-carrier matings. Concerns about depletion of the gene pool in pony breeds were soon quelled once it was explained that they could still safely use carrier ponies to breed with normal ponies. Indeed, it was pointed out that owners and breeders actually needed to widen their use of stallions to reduce the numbers of FIS foals and to preserve the gene pool.In the first year of testing, our fears were confirmed when the FIS carrier rates were shown to be 39 per cent in breeding Fell ponies and 18 per cent in breeding Dales ponies. Broadening the testing to other at-risk breeds (known to crossbreed with Fell and Dales ponies), showed that 1 per cent of a coloured pony population were carriers (Fox-Clipsham and others 2011b). There may be other breeds containing FIS carriers; only further population testing will confirm or deny this possibility.

The next key question was how effective the carrier test would be in reducing the numbers of FIS foals being born in subsequent years. There have now been two breeding seasons (2011 and 2012) prior to which the 

owners could avail themselves of the test and avoid carrier-carrier matings. The test findings (Table 1) provide considerable hope for the future.The FIS carrier rate in breeding adult Fell and Dales ponies varies over the three years of testing, but this variation was statistically significant (X2(2df) p=0.3, and Fisher’s Exact Test p=0.6, respectively). 

Importantly, there was a lower number of FIS-positive (diseased) Fell pony foals in 2011 and 2012 (although this only approached statistical significance (X2(2df) p=0.1, X2for trend (1df) p=0.08) and no FIS 

cases in Dales ponies in 2011 or 2012. Obviously, the datasets may be skewed because of the animals selected for testing, which may introduce some bias. However, as many carriers will have been identified previously from breeding records, there is no reason to suppose that FIS-positive breeding stock would be preferentially submitted. It is clear that the owners and breeders have taken the advice we provided about avoiding carrier-carrier matings, and that this has led to a major reduction in the number of syndrome foals born in the last two year. Although the definitive figures are not available, the total  number of breeding Fell ponies that have been FIS tested in the last three years (n=1171) comprise a large proportion of the breeding population, and the testing has been done to guide breeding strategies. By the same measure, the 284 Dales ponies tested represent a large part of  the breeding population of that breed.

Predictably, our breeding recommendations to use carrier-clear matings have not had a rapid impact on the large numbers of FIS carriers in the breeding populations of both breeds. Reducing carrier numbers will either take much longer using the current breeding approach, or a change in breeding strategy to avoid breeding from carriers at all. With the carrier rate so high in the Fell ponies, such a restrictive recommendation would probably be unacceptable to many  breeders, and would risk depleting the gene pool. On the other hand,  the breeders who choose carrier-clear matings will need to test their offspring to see if their foal is a carrier. The results are consistent with uptake of the FIS carrier test by the owners of at-risk ponies, and suggest that they have also taken our advice about breeding strategies to reduce the numbers of FIS-positive foals. This is a significant and swift impact of modern genomic technologies in clinical veterinary medicine, and is a healthy indicator of veterinary scientists and animal breeders working well together to improve animal welfare.

TABLE 1: Foal immunodeficiency syndrome (FIS)-positive test results in Fell and Dales ponies (adults and foals) (N/A=not applicable)

Year	Number tested	Normal (%)	FIS Carriers (%)	FIS Diseased (%)
(A) Fell ponies
Adults        2010	565	290 (51)	275 (49)	N/A
2011	179	103 (58)	76 (42)	N/A
2012	106	60 (57)	46 (43)	N/A
Foals          2010	142	72 (51)	58 (41)	12 (8)
2011	108	60 (56)	39 (36)	1 (1)
2012	71	32 (45)	38 (54)	1 (1)
(B) Dales Ponies
Adults 2010	180	158 (88)	22 (12)	N/A
2011	53	44 (83)	9 (17)	N/A
2012	36	32 (89)	4 (11)	N/A
Foals 2010	10	9 (90)	0 (0)	1 (10)
2011	4	3 (75)	1 (25)	0 (0)
2012	1	1 (100)	0 (0)	0 (0)

References
BELL, S. C., SAVIDGE, C., TAYLOR, P., KNOTTENBElT, D. C. & CARTER, S. D.
(2001) an immunodeficiency in Fell ponies: a preliminary study into cellular responses.
Equine Veterinary Journal 33, 687–692
BUTLER, C. M., WESTERMANN, C. M., KOEMAN, J. P. & SLOET VAN
OLDRUITENORGH-OOSTERBAAN, M. M. (2006) The Fell pony immunodeficiency syndrome also occurs in the Netherlands: a review and six cases. Tijdschrift Voor Diergeneeskunde 131, 114–118
DIXON, J. B., SAVAGE, M., WATTRET, A., TAYLOR, P., ROSS, G., CARTER, S. D.,
KELLY, D. F., HAYWOOD, S., PHYTHIAN, C., MACINTYRE, A. R., BELL, S. C.,
KNOTTENBELT, D. C. & GREEN, J. R. (2000) Discriminant and multiple regression
analysis of anaemia and opportunistic infection in Fell pony foals. Veterinary Clinical
Pathology 29, 84–86
FOX-CLIPSHAM, L., BROWN, E. E., CARTER, S. D. & SWINBURNE, J. E. (2011b)   Population screening of endangered horse breeds for the foal immunodeficiency syndrome mutation. The Veterinary Record 169, 655–655
FOX-CLIPSHAM, L., CARTER, S. D., GOODHEAD, I., Hall, N., KNOTTENBELT, D. C., MAY, P. D. F., OLLIER, W. E. & SWINBURNE, J. E. (2011a) Identification of a
mutation associated with fatal foal immunodeficiency syndrome in the Fell and Dales pony. PLoS Genetics 7 135, e1002133
FOX-CLIPSHAM, L., SWINBURNE, J. E., PAPOUlA-PEREIRA, R., BLUNDEN, A. S., MALALANA, F., KNOTTENBELT, D. C. & CARTER, S. D. (2009) Immunodeficiency/anaemia syndrome in a Dales pony. The Veterinary Record 165, 289–290
GARDNER, R. B., HART, K. a., STOKOl, T., DIVERS, T. J., FLAMINIO, M. J.,
JElINEK, F., FALDYNA, M. & JASURKOVA-MIKUTOVA, G. (2006) Fell pony syndrome in a pony in North america. Journal of Veterinary Internal Medicine 20,
198–203
MAY, A., LEIPIG, M. & GEHlEN, H. (2011) Case report of a Fell pony immunodeficiency syndrome foal in Germany. Pferdeheilkunde 27, 507–513
SCHOlES, S. F., HollIMAN, A., MAY, P. D. & HOLMES, M. A. (1998) a syndrome of anaemia, immunodeficiency and peripheral ganglionopathy in Fell pony foals. The Veterinary Record 142, 128–134
THOMAS, G. W., BELL, S. C. & CARTER, S. D. (2005) Immunoglobulin and peripheral B-lymphocyte concentrations in Fell pony foal syndrome. Equine Veterinary Journal 37, 48–52
THOMAS, G. W., BELL, S. C., PHYTHIAN, C., TAYLOR, P., KNOTTENBELT, D. C.
& CARTER, S. D. (2003) Aid to the antemortem diagnosis of Fell pony foal syndrome by the analysis of B lymphocytes. The Veterinary Record 152, 618–621

S. D. Carter, BSc, PhD, FRCPath
L.Y. Fox-Clipsham, BSc, PhD
R. Christley, BVSc, MVCS, PhD, 
DipECVPH, MRCVS
Department of Infection Biology,
Department of Epidemiology and
Population Health,
Institute of Infection and Global Health,
School of Veterinary Science, University
of Liverpool, Liverpool, UK
L. Y. Fox-Clipsham, BSc, PhD
Centre for Preventative Medicine,
Animal Health Trust, Newmarket, UK
J. Swinburne, BSc, PhD
Animal DNA Diagnostics Ltd,
William James House, Cowley Road,
Cambridge CB4 0WX, UK
E-mail for correspondence:
scarter@liv.ac.uk
Provenance: Not commissioned;
externally peer reviewed
Accepted February 14, 2013

Research Update

• A descriptive case report covering the clinical signs of HWSS and the pedigree research has been submitted for publication to the relevant, top peer reviewed journal available.  This paper has been accepted subject to some re-writing requests by the peer reviewers.  Such re-writing requests is normal procedure for peer reviewed publications.  Once the research paper has been published the on-line address for the abstract will be posted on this blog.

• a paper written by Tom Ryan (FWCF)  has been accepted for publication by Forge.  Forge the industry magazine for farriers and is sent to all farriers in the UK and by subscription to others around the world.  Tom has indicated that once publication in Forge has occurred he will be sending the paper to be circulated via this blog.  In his paper he deals with the issues of  hoof care to maintain quality of  life for HWSS affected ponies.

• The Havemeyer Foundation sponsored  10th International Equine Genome Mapping Workshop   is taking place in July in Portugal.   The Bannasch Laboratory will be there presenting their latest research on the HWSS issue.  Participants are invited to this prestigious workshop; just getting an invite to attend is an honour in itself.  To be one of the presenters validates the research work done to date.

• Over the summer the humongous quantity of data generated by the genomics work will be analysed in depth.  The computing requirements for such work is in the multi-terabyte arena, which is way beyond the capacity of all but a few computers in the world.  To access such a facility computer time has to be booked in advance. Booking ahead is a best guess option as to time scale and is judged on when a facility was needed in similar areas of research. As it turns out because the initial answers were so cut and dried on the HWSS project, the research has run ahead of the expected schedule. Further rapid progress has been constrained because of the need to wait for this pre-booked computer access.

• Another native pony breed with a genetic problem - The Fell has posted an update on their progress.  Their research to find the genetic marker commenced in 2005 with the mutation being located in 2009.  The test became available 3 years ago in 2010.If you wish to read more about the Fell pony research below are some links.  The process is quite proscribed. 

1. The first step is to publicise the emergence of a new condition to the veterinary profession; Immunoglobulin and peripheral B-lymphocyte concentrations in Fell pony foal syndrome.  
2. One then demonstrates that the problem is not confined to one geographical area but extends through the total genepool; The Fell pony immunodeficiency syndrome also occurs in the Netherlands: a review and six cases. 
3. The genetic research is performed and reported and published; Identification of a mutation associated with fatal Foal Immunodeficiency Syndrome in the Fell and Dales pony.
4. Having found the mutation the effects at the cellular level can be established; Fell Pony syndrome: characterization of developmental hematopoiesis failure and associated gene expression profiles.
5. The outcome; Foal Immunodeficiency Syndrome: carrier testing has markedly reduced disease incidence or put another way A recent report shows what can be achieved when scientists and horse breeders work together

• When one looks at the timescale involved with the  HWSS research much has been achieved in a very short time.  Unlike the situation with HWSS, the Fell Pony Syndrome (FPS) research had the backing, financially, morally and ethically from the Fell Pony Society and the Rare Breeds Trust; it also involved a large 'buy in' from the breeders themselves. 

The Connemara Pony Research Group would like to think that the scientific progress in this research is now sufficiently advanced that all societies, breeders and owners will now take this problem seriously and start making plans on how we as a community are going to use this information to preserve and protect our beloved Connemara pony. It is our hope that the CPBS and the ICCPS will see fit to invite Dr Carrie Finno to Ireland this year to present her HWSS research at an open public forum during  the Clifden Festival in August 2013.

Feel free to offer comment and helpful suggestions on the HWSS Facebook page.HWSS (Hoof Wall Separation Syndrome)