TROUBLE afoot

An abscess in the foot can develop quickly, and is one of the usual suspects when a horse becomes lame, be it gradually or suddenly. Kieran O'Brien MRCVS explains why they occur and how they are treated

- Kieran O'Brien

THE horse's hoof can be imagined as a semi-flexible "thimble" attached by very firm bonds to the internal structures of the foot. These attachments the laminae in the wall and the corium of the sole - are intimately bound to the hoof and separate from it only in extreme circumstances, for example in cases of laminitis.

But if infection gains entry through a defect in the hoof wall or sole, or if these structures are penetrated, this attachment can be partially separated, resulting in pus accumulating in the separated area. This may be under the sole, under the hoof wall, or sometimes under both.

The pus is trapped and cannot escape, and as the hoof is in effect a rigid box that cannot swell to accommodate the increasing volume of pus, pressure builds up, and the horse soon becomes very lame.

Infection can gain entry via several routes. The most common is via a small defect in the white line, the normally very tight junction between the sole and the wall. This appears as a dark area (possibly just a spot or a longer area) when the sole is trimmed, for example in preparation for shoeing.

Penetration by a foreign body (including blackthorns and shoeing nails) or treading on a sharp stone causing a small fracture in the sole provide other entry points. Hoof cracks occurring when the hooves become brittle in dry weather or when parts of the hoof wall are subjected to abnormal forces (for example in underrun heels) may also allow bacteria to enter the hoof "thimble".

A corn - a focal area of bruising in the sole at the side of the frog at the heel - can get infected if the integrity of the overlying hoof is compromised.

SIGNS OF TROUBLE