Pus in the foot is a very common cause of sudden, often severe, single limb lameness in the horse.
Beneath the insensitive sole there are laminae which are densely supplied with nerves. Abscess formation results in pressure between the sensitive laminae and the rigid dorsal hoof wall and hence pain. It can be compared to infection beneath the finger or toenail. Infection can be introduced; through a puncture in the sole of the foot, nail prick at shoeing, through a crack in the dorsal hoof wall or via the white line.
The affected horse is often extremely lame and may even refuse to weight bear on the affected limb. The foot is often hot and will have a bounding digital pulse. When hoof testers are carefully applied to the sole of the foot there will be a pain response in the region of the abscess. The vet or farrier will remove the horse's shoe and pare the foot to look for the track of the abscess. If this is found the track can be followed to release the pus and allow it to drain, causing reduction in local pressure and hence pain. A poultice will be applied and changed twice daily and the horse treated with non-steroidal anti-inflammatory drugs and box rest. Tetanus vaccination status should be checked and tetanus antitoxin given if the horse is un-vaccinated or if vaccination status cannot be verified. Antibiotics are rarely given as they may mask an abscess, which will return once the antibiotics are withdrawn. If the pus cannot be located then a poultice will be applied, in order to ripen the abscess and the horse re-examined in 48 hours. If there is no improvement and the horse remains lame then radiographs may be taken to identify the pocket of gas and ensure that a pedal fracture is not present. Sometimes the abscess may track further along the sole or even break out at the coronary band. Once the abscess has finished draining the sole of the foot needs to be kept clean and dry to prevent reinfection.
Prevention of foot abscesses involves; good farriery and trimming, regular picking out of the feet, avoidance of waterlogging of the feet and good diet to maintain strong horn and white lines. Any solar penetrations should be cleaned and poulticed without delay and advice sort from your veterinary surgeon. Tetanus vaccination is important as potentially fatal infection can gain access through hoof injuries.