A foot abscess, also known as pus-in-the-foot is an extremely common condition, and one that can cause lameness ranging from moderate to non-weightbearing. Fortunately, despite its dramatic appearance, foot abscess is usually a simple and satisfying condition to treat.
A foot abscess is a localised infection within the hoof, which forms a pocket of pus within the hoof horn. This usually develops due to a tiny penetration of the foot, for example, by a sharp stone. Bacteria are implanted into the deeper layers of the sole, and the more superficial layers then close over the top, trapping the infection. This can happen up to several weeks before any signs are seen, and usually goes totally unnoticed.
After an average of 10-14 days, the bacteria have grown, and enough pus has accumulated that there is a large pressure build up. This pressure pushes on nerves within the foot and causes often excruciating pain. There is also significant inflammation within the foot, which can be noticed as a bounding digital pulse, and a degree of heat in the hoof wall. Lameness will also develop at this point, which will often be so severe that the horse is unwilling to place their foot on the ground. This is the time at which the vet is often called.
The vet will examine your horse, and often a bounding digital pulse and heat in the foot will be detected, leading them to suspect that the lameness is originating from the foot. Hoof testers will then be applied to the foot to try and determine the location of any pain within the foot. These are large pincer like tools with blunt ends, that put pressure through the hoof wall and sole. Horses will usually react to any pain by pulling their foot away. Horses that are shod may have to have their shoe removed at this point to allow examination of the entire solar surface of the foot.
Once an area of pain has been localised, the sole of the foot is pared to try and find the abscess. When the surface of the abscess is pricked, there is usually a sudden and copious burst of foul smelling fluid. After locating the abscess, your vet will pare away any dead tissue, and create a hole through which the abscess can drain. Extensive paring can be necessary, and may be performed 24 hours after drainage is created, when the horse will be a lot more comfortable.
Having established drainage, it is now important to poultice the foot until all material has been drained from the abscess. This is achieved using poultice material (Animalintex), soaked in hot water, and then bandaged to the foot. Poultices need to be changed at least once daily, and ideally twice or more per day. After 3-5 days of wet poulticing, dry poulticing is often used to avoid over-softening the foot. Poulticing will need to be continued until no further discharge is found when changing the dressing.
Occasionally, it can be extremely difficult to locate an abscess despite a strong response to hoof testers, and adequate paring of the foot. In these cases, radiography (x-rays) may be used to try and identify the abscess site. The signs of a foot abscess are also consistent with other conditions of the foot (see list below), and radiography will help to rule them out.
The Painful Foot – What Can It Be?
- Foot Abscess
- Solar Bruising
- Nail Bind
- Pedal Bone Fracture
Although foot abscesses are a bacterial infection, antibiotics are rarely used in managing them. Firstly, the routinely available antibiotics available for use in horses do not reach the hoof in significant concentrations to be useful, and are not active against the bacteria that are commonly involved in foot abscesses. Secondly, in cases where the abscess cannot initially be drained, antibiotic use can slow down abscess maturation and prolong the course of the disease.
The provision of analgesic (pain relieving) drugs is another matter of opinion and debate. While it would seem that giving pain relief to a horse in obvious pain would seem obvious, this is not the case. In the initial stage of the disease, before the abscess has burst then even high doses of analgesics typically prove ineffective in relieving pain. Once the abscess has burst, then relief from pain is extremely rapid, even without the administration of drugs. It would seem, therefore, that at no point do analgesics actually improve the pain associated with an abscess. On the other hand, the commonly used analgesic drugs also have significant anti-inflammatory effects, that can be beneficial. The decision as to whether to treat will be made on a case by case basis.
Vaccination against tetanus is vital in cases of pus-in-the-foot, and if your horse is unvaccinated, or their vaccination status is uncertain, then immediate cover will be provided using Tetanus Anti-Toxin.
The prognosis for simple foot abscesses is excellent, and following drainage horses will return to soundness rapidly and totally. On some occasions, abscesses can re-occur if drainage seals over, and require further paring of the foot, but provided this occurs then no long term complications should be seen.
If foot abscesses are left untreated, then they may burst out at the coronary band (known as gravel). This is not a disaster, but these cases can take considerably longer to return to full soundness.
Some foot abscesses can be caused by the presence of a hoof “tumour” or abnormality of growth known as a keratoma. These cause a deviation of the white line on the sole and may allow dirt and infection to track up the wall. They have to be removed surgically.