Hoof wall separation disease
Hoof wall separation disease, or HWSD, weakens the hoof wall so that it splits, crumbles or separates, often in a young pony. It is best documented in Connemaras. Its inherited origin does not mean every Connemara is affected, or that every cracked hoof has this cause.
Recessive inheritance
Why HWSD weakens the hoof wall
The hoof wall is the hard outer structure around the foot and helps bear weight. In HWSD, its outer part cracks and separates abnormally. As the wall becomes less able to carry the load, more weight may fall on the sole, with painful consequences.
The original 2015 study linked HWSD to a small insertion in SERPINB11, called c.504_505insC. It disrupts how the gene’s instructions are read. Researchers also found that SERPINB11 was less active in the tissue that produces the hoof wall. The exact way this gene contributes to strong hoof horn still needs further investigation; an association does not explain every step of the mechanism.
HWSD can weaken a pony’s hooves in the first months of life
Cracks usually begin in the first few months, often before six months of age, although earlier cases are described. All four feet can be involved to different degrees. The wall’s edge may look frayed while the coronary band, where hoof growth begins, appears normal.
A mild case may be easier to spot from underneath the foot. Severe loss of support can cause marked lameness. Abscesses or laminitis, a painful condition affecting the foot’s internal supporting tissues, can complicate the disease. A photograph of one hoof cannot establish the full extent of the problem or how much pain the pony is experiencing.
Ponies with two copies of the HWSD variant can have severe or hard-to-detect hoof problems
HWSD has autosomal recessive inheritance: the high-risk combination occurs when a pony receives the SERPINB11 variant from both parents. A pony with just one copy is an unaffected carrier of this form and can pass its copy to a foal. With two copies, the risk of signs is high. Limited separation and a severely painful hoof are nevertheless very different clinical situations.
The original study found signs in all two-copy ponies in its sample. Current UC Davis resources also report a two-copy pony without obvious clinical signs and describe high but incomplete penetrance: most two-copy ponies show signs, but not every pony does. These findings remind us to separate a genotype from what can be seen in one animal. A DNA result alone cannot predict an individual pony’s clinical course.
HWSD has been documented in Connemaras and horses with Connemara ancestry
Both the disease and variant are documented in Connemaras. Laboratories also identify Connemara crosses as relevant to testing. Connemara ancestry can therefore matter even when an animal is not registered as a purebred Connemara pony.
Published carrier frequencies come from particular groups sampled at particular times. They do not automatically represent every country, bloodline or present-day generation. A breed name cannot tell you whether one horse has zero, one or two copies. Likewise, a list of populations in which the variant has been documented does not prove that it is absent everywhere else.
Distinguishing HWSD from other hoof problems
A split hoof wall can have several causes. White line disease, abscesses and the consequences of laminitis can also lead to separation. HWSD is not simply another name for those problems. In its characteristic early presentation, separation is within the wall while the white line and sole can look healthy.
The vet considers when signs began, all four feet, pain, ancestry and the hoof care history. Examination and, where appropriate, further investigations assess the damage and complications. Genetic testing helps identify the inherited mechanism but does not remove the need to look for another cause or an additional condition. A genetic diagnosis and an assessment of current hoof health are complementary.
What the HWSD DNA test looks for
The test looks for the SERPINB11 variant associated with HWSD. It can identify carriers whose feet give no indication of their status. The laboratory reports zero, one or two copies; its symbols need to be read alongside its own explanation.
A negative result addresses that particular variant. It does not guarantee trouble-free feet or exclude all inherited disorders. Conversely, a two-copy result does not measure pain or predict progression by itself. Samples should follow the laboratory’s instructions and be clearly linked to the correct animal; an uncertain identity undermines the usefulness of an otherwise valid result.
What care can help a pony with HWSD?
There is no cure that corrects the inherited defect. Regular hoof care and protective or supportive options may be considered with the vet and farrier. These depend on the damage and how the pony bears weight; one shoeing or management approach is not automatically suitable for every case.
Some cases are more manageable, but care can be demanding and deterioration can occur despite close attention. Persistent pain or laminitis can seriously compromise welfare. Euthanasia may be necessary in severe cases. Prognosis needs to be reviewed through the pony’s comfort, examination and response to care, rather than being decided from the genotype alone. Initially manageable disease can still progress.
Testing the mare and stallion to reduce their foal’s risk of HWSD
If the mare and stallion each have one copy of the SERPINB11 variant linked to HWSD, every conception has a 25% chance of a foal with two copies of that variant, a 50% chance of a one-copy carrier and a 25% chance of a foal without it. The 25% describes a genotype, not a guarantee of identical clinical signs. Each pregnancy is a new event: four births need not follow that exact distribution.
For the tested variant, a carrier mated to a confirmed non-carrier cannot produce a two-copy offspring, although some foals can be carriers. This helps avoid at-risk combinations while retaining genetic diversity. A two-copy pony passes the variant to all offspring; having mild or unobvious signs does not change that inheritance.
Understanding HWSD DNA test results
These descriptions concern SERPINB11:c.504_505insC. Some reports label two copies as ‘affected’; the number of copies should still be distinguished from clinical examination.
Questions about the condition: Hoof wall separation disease
Do healthy-looking hooves rule out the HWSD variant in a pony?
No. One-copy carriers do not show this disease. Even with two copies, signs can be subtle or unobvious, so appearance cannot replace testing.
Is HWSD a contagious infection?
Its cause is inherited and it cannot be caught from another pony. Secondary infections can nevertheless complicate a damaged hoof and need assessment in their own right.
Scientific sources about the condition: Hoof wall separation disease
This article brings together the research and the university and laboratory resources listed below. Numbers after each section link to the references used. Sources consulted in November 2026.
- Finno et al. (2015) — SERPINB11 Frameshift Variant Associated with Novel Hoof Specific Phenotype in Connemara Ponies
PLOS Genetics · UC Davis / Massey University · Research
- Hoof Wall Separation Disease (HWSD)
UC Davis Center for Equine Health · University resource
- Connemara Pony Hoof Wall Separation Disease
UC Davis Veterinary Genetics Laboratory · Test documentation
- Hoof Wall Separation Disease: description and genetic test
Animal Genetics · Test documentation