What is a hoof abscess?
A hoof abscess, sometimes referred to as ‘a drop in the foot’ is a localised accumulation of pus located in the horse’s foot.Most abscesses are found around the perimeter of the sole at the junction with the hoof wall. Where does the abscess break out?
The abscess or infection usually takes the line of least resistance.It may travel up the inside of the hoof wall and drain at the coronary band, but usually it breaks out on the sole of the hoof. An abscess can also occur under the bars of the hoof.What does a hoof abscess or ‘drop’ look like when opened up by the treating veterinary surgeon?
In contrast to the appearance of ordinary pus, this is seen as a greyish black fluid coming from the affected point or centre of the problem area. How does the abscess form within the foot?
When a foreign body gets into the foot, it sets off an inflammatory reaction in the hoof tissue. This is the body defence mechanism trying to fight off infection. The bacteria multiply and white cells grow around the foreign body.The inflamed area is then quickly walled off with a thin layer of fibrous tissue to form an abscess.The inflammation and the pressure from the accumulation of the pus in the surrounding tissue increases the pressure within the enclosed hoof and this leads to the clinical signs and severe pain associated with a hoof abscess. What are the usual causes that result in a hoof abscess?
Causes include the following:
A foot abscess can be caused by a particle of sand or soil entering the softer white line area, becoming engrained in the sensitive laminae underneath the hoof wall, resulting in an infection inside the hoof. Where there is a break in the white line which lies between the sole and the wall of the foot, infection can enter and an abscess can result.A misplaced nail or a nail prick: The infection can enter as a result of a nail driven into or near the white line or a ‘close nail’. It may take seven to 14 days or even longer before clinical symptoms or discomfort is observed following the placement of a ‘close nail’.Bruised sole.A puncture wound in the sole of the foot. Where there is a penetration of the sole by a sharp object infection usually follows within three days.Bacteria can gain entry into any cracks, defects or fissures in the ‘white line’, through a hoof defect or hoof separation.Horses that have been shod and then go bare foot tend to have an increased chance of developing hoof abscess until the hoof becomes stronger.Flat-footed horses have a greater tendency.What are the signs?
Signs of hoof abscess include sudden and severe lameness and pain. The degree of lameness varies from being subtle in the early stages to non-weight bearing. Usually the horse bears very little weight on the affected limb or may tend to walk on its toe if the abscess is towards the heels.Increased digital pulse or ‘throb’ in the limb – the pulse will be much stronger on the side of the foot where the abscess is located.Swelling of the leg is usually not present. However, If the abscess is long standing, there may be soft tissue swelling in the pastern or above the fetlock on the side of the limb corresponding to the side of the foot where the abscess is located.In rare cases, the tendons in the affected leg may become painful and swollen due to congested blood vessels.The temperature may be slightly elevated, though not in all cases.As the abscess progresses, the infection and pressure of the pus accumulation in the hoof can cause severe pain until the infection works its way up the hoof wall towards the coronary band or the bulb of the heel or until it drains out the sole.The site of pain can be localised to a small focal area and identified through the careful use of hoof testers. In some cases with acute lameness, the pain will be noted over the entire foot with hoof testers and, in this case, the treating veterinary surgeon will check for conditions such as laminitis, a severe bruise or even a possible fracture of the pedal bone in the foot (also known as the distal phalanx).How is hoof abscess diagnosed?
The hoof is examined for heat and severe pain. Presence of pronounced digital pulse or ‘throb’.If the horse is shod, the shoe is removed and the hoof cleaned out.Hoof testers are used to test the horse’s sensitivity to pressure in specific areas of the hoof to locate the point of origin.The treating veterinary surgeon will check the hoof using a hoof tester to determine the point of entry and the location of the abscess. This is sometimes identifiable as a black line which can be followed to locate the seat of infection. Using a hoof knife or a loop knife, a very small hole is made in the sole of the hoof to allow for drainage and to provide relief of the pressurised fluid.When the pressure of the trapped pus is released from the hoof capsule, a black or greyish exudate will drain from the site and the horse will experience some relief immediately. If the origin of the abscess cannot be identified or the infection is too deep in the hoof, for example the abscess deep in the heel, frog or bars region, no cutting or holes will be made as it may cause more harm than benefit in treatment.Where the veterinary surgeon decides that a drainage hole is not made or does not fully function to drain the abscess, then the pus will travel to the coronary band to drain there. This is a slow and painful process for the animal.