The white line can be found on the bottom of the horse’s hoof close to the edge as a lighter area of horn where the hoof wall and sole meet. Like any join or seam, it is a potential weak spot.
White line disease occurs when the external hoof wall separates from the underlying laminae, which hold the pedal bone in position. The horn along the white line becomes crumbly and soft. This can allow bacteria and fungi to gain entry and cause further damage. The disease can occur anywhere on the hoof, although the toe is most common area, hence the common name of seedy ‘toe’. While the outside of the hoof may appear normal, when tapped it may sound hollow when compared to unaffected areas.
Your farrier can manage mild cases caught early, which rarely cause lameness, during their regular visits. The biggest concern with seedy toe is that in severe cases, when significant lameness will be seen, the internal support of the pedal bone can be compromised, leading to movement of the pedal bone, similar to laminitis cases.
Which horses are most at risk?
White line disease can be found in all sizes, types and breeds of horse, although donkeys are particularly susceptible to it. Horses with poor quality hoof horn may be more likely candidates.
A study of 1,700 racehorses in Japan1 found it was more frequently found in older horses, and in the forelegs.Owners should not confuse white line disease with hoof wall separation syndrome, which is a genetic condition found in the Connemara pony breed.
Causes of white line disease
White line disease is typically associated with poor hoof conformation or trimming, such as long toes and under run heels, which put abnormal levels of stress on the hoof wall. Prolonged soaking in wet weather weakens the white line and makes it more vulnerable to bacterial or fungal infection
Diagnosis of white line disease
Your vet or farrier will make an initial diagnosis by examining the hoof. X-rays may be used to confirm the location and extent of the separation and whether any movement of the pedal bone has occurred.
Treatment of white line disease
It is normal to trim away the hoof wall that has separated from the underlying structures until only healthy wall that is firmly attached remains, leaving the rest open to the air.
Once the diseased wall has been removed, topical treatment with either pevidine (Iodine-based antiseptic) or sugardine (an pevidine and sugar mix which is popularly used) is typically applied daily for a number of days to help harden the exposed area. Commercial equine hoof formulations that produce chlorine dioxide can also be used.
Corrective shoeing is required to provide support to the remaining hoof wall, while removing pressure from the affected areas. A heart bar or egg bar shoe with hoof packing may be required to help support the sole if there is a risk of the pedal bone moving. If a substantial amount of the hoof wall has been removed, your vet or farrier may use acrylic material to rebuild the wall to give extra stability to the hoof.
The hoof should be kept as clean and dry as possible while the healthy hoof wall grows down. Topical disinfectants (eg povidone iodine, hydrogen peroxide or zinc sulfate) in solutions or sprays can be useful to reduce microbial contamination. As the hoof wall typically grows down at approximate 1cm per month it may take a considerable length of time for the hoof wall to become fully formed again.
If the horse is not up to date with vaccination against tetanus, a booster should be given.
Prevention of white line disease
- Maintain excellent hoof hygiene, checking the hooves daily
- Do not leave the horse standing in dirty or wet bedding
- Ensure regular farrier visits, no more than six weeks apart
- Horses that have previously had white line disease should be monitored extra carefully as it has a tendency to reoccur
- Provide nutritional support to encourage growth of health hoof horn
1. https://www.ncbi.nlm.nih.gov/pubmed/10596935 – A survey of white line disease in Japanese racehorses – November 1999