What they are:
Abscesses are an accumulation of pus under the skin or in the deeper tissues. Abscesses can occur anywhere on a horse’s body and are caused when a foreign body or infection stimulates white blood cells to congregate in one place. The white blood cells form pus and then the body starts to seal off the site of the infection by walling off the infected area.
Initially an abscess is just a hard-ish swelling that is painful when touched, but it will quickly grow bigger and typically within about a week a centre, head or tip of the swelling can be identified. When they occurs on the skin of the horse, it is likely that the abscess will burst through the skin.
To begin with, some vets may try and treat a small abscess with antibiotics. However, if the abscess is large or contains a foreign body, they will commonly proceed straight to drainage and removal of the foreign body as necessary. Once an abscess has formed a centre, head or tip to its swelling, it is ready to drain. The abscess cavity will be drained and then flushed out for the next few days to prevent it closing and trapping more pus inside. Draining an abscess is much better normally than simply waiting for it to burst, as upon bursting the abscess can damage surrounding tissues and the infection can more easily spread. Draining is much more controlled and therefore safer all round.