A Case of a Foot Abscess

As seen in the May 2017 edition of Horse Deals Magazine

The phone rings in reception early one morning with a distressed owner. ‘My horse has broken its leg! He was fine last night, then I went to feed him this morning and he can’t put weight on his back leg! Please help!’ On examination of the gelding, the lower limb appeared swollen, the digital pulse (blood supply to the foot) to the left hind foot was bounding. He was very reactive to hoof testers when applied to the toe, and he was reluctant to bear full weight on the affected leg. Given the rapid onset, the bounding digital pulse and the response to hoof testers, the cause of the lameness appeared to be coming from the foot. A tract of dirt and debris was located in the white line at the toe region. The tract was closely followed a few millimetres and pus started to ooze from the area.

When draining an abscess, it is important to make a small hole in the foot so that the sensitive corium surrounding the pedal bone doesn’t prolapse through the hole. Sensitive corium that has prolapsed can be very painful and can cause a prolonged treatment period.

Foot abscesses are a relatively common cause of lameness in the horse. They appear to be more frequent after a period of rain (like much of the east coast of Australia is experiencing now) or in damp, unhygienic environments such as a stall that isn’t cleaned regularly. The moist environment increases the pliability and porousness of the usually hard hoof capsule. Other factors that contribute to abscess formation include horses with long toes or suffering from chronic laminitis. They tend to have stretched and damaged white lines, allowing dirt, debris and microbes to penetrate into the sensitive tissue of the foot.

As mentioned, foot abscesses commonly start at the white line, the junction between the sole and the hoof wall. From there, the abscess can track in two directions, up the hoof wall to the coronary band or under the sole and frog, exiting the heel bulbs.

There are a variety of environmental micro-organisms that infect the foot, but most commonly anaerobic bacteria predominate. Anaerobic bacteria can only survive in environments with little oxygen. One anaerobic bacteria that can be involved in a foot abscess is also responsible for causing tetanus (Clostridium tetani) in the horse. To avoid your horse developing tetanus, which is a very serious disease, it is important to have your horse up to date with its vaccinations, especially if it develops a foot abscess.

Foot abscesses can also occur from sharp objects penetrating the sensitive tissue of the foot. These include wire, wood and nails. Infections can also occur from horseshoe nails driven too close to the white line when applying shoes. For this reason, it is a good idea to involve both your veterinarian and farrier if your horse develops a foot abscess. If detected earlier, foot abscesses entering through the white line can be treated with drainage and a poultice.

If the abscess has been ongoing or it is suspected to have occurred from a penetrating sharp object, the coffin bone, navicular bone, navicular bursa, deep digital flexor tendon or other sensitive structures of the foot may be involved. If this is the case, the treatment can be prolonged and very involved.

Complicated foot abscesses may require surgical debridement, systemic antibiotics and antibiotic regional limb perfusions. Medical grade maggots have also been used to debride severe foot abscesses.
The case discussed at the beginning of the article responded well to drainage of the abscess, a wet poultice to help draw further discharge and anti-inflammatories. Typically the poultice can be changed as needed, which maybe daily if required. After 2-3 days the limb swelling resolved, the digital pulse returned to normal and the horse was not showing signs of lameness at the walk. It can take up to a week for the inflammatory process to completely resolve, depending upon the severity of the abscess and how much of the underlying tissue is affected. Large abscesses may require therapeutic shoeing after drainage is established to shift load away from the painful region. As mentioned previously, it is important to consult with your farrier and veterinarian to develop a treatment plan that suits your horse and the problem.

Luke is a veterinary podiatrist providing a high level of service to the Australasian horse industry through affiliated veterinary practices and an online consultancy portal. Luke is the founder of Motion Equine Podiatry Consulting and is available by appointment in multiple locations along the east coast of Australia.
luke.wellssmith@gmail.com • www.motionepc.com.au

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