On Abscesses

I haven't posted here in an age but I saw a post from someone on a Facebook page about dealing with a hoof abscess. As is common with most issues relating to horse health and management, there were many opinions.

An abscess is a cavity in the body that is filled with pus – a liquid consisting of serum, living and dead white blood cells, tissue debris and, in a septic abscess, a pathogen, most commonly some sort of bacteria.

Septic abscesses are caused by an external pathogen such as bacteria being introduced into the vascular tissue in the horse’s hoof, ie the solar, wall or frog corium. 

This usually happens as a result of a penetrating injury, including a farrier breaching the white line with a nail. Sometimes pathogens gain access to the vascular tissue via damage to the white line, or frog etc. 

There are also sterile abscesses which occur when the body is attempting to expel inert tissue, such as its own dead tissue, for example, a region of corium (aka the hoof quick) that has died as a result of persistent pressure or bruising from such things as long under-run heels or bars that run across the sole.

 

In both types of abscess, inflammation results as the body walls off what its immune system has registered as a foreign body. Serum, containing white blood cells, floods the area and because the hoof (like our nails) cannot stretch in the way that skin can, the pressure from the build of fluid is extremely painful.

 

The white blood cells attempt to break down the invader, and as wound serum dissolves protein, it gradually eats through the skin and is expelled as pus. (This capacity can be seen in the scalding of skin around a wound that is oozing wound serum.)

 

If an abscess breaks internally, ie through the tissue walling it off from the wider body rather than out via the skin, eg by bacteria multiplying faster than white blood cells can kill them, or by the abscess being lanced incorrectly, the infection can become systemic.

 

A hoof abscess typically finds an exit point between horn and skin, at the coronet or at the heel bulb. Occasionally it is resorbed.

The pain from a hoof abscess can be severe enough to mimic a major traumatic injury, or be so mild it is not noticed. 

Fore limb hoof abscesses are always more painful than hind because of the differences in load bearing between fore and hind limbs.

 

Sometimes, in a sub solar abscess, opening the sole can release the pus which usually provides immediate pain relief. 

However, breaching the sole also exposes the blood rich corium to external pathogens, and if the abscess was not “ripe” it can reoccur.

 

Abscesses that are tracking up through the wall are not as easily located or relieved by excision, and the possibility of faster relief from pain has to be weighed against the degree of longer term damage to the hoof.  

On the other hand, a large abscess exit at the coronet in the toe region can take 6 months or more to reach ground level.

 

Swelling in the lower leg may be due to a septic abscess in in the hoof having become systemic but it may equally be due to oedema, “stocking up”, as a result of the horse not moving or loading the hoof.

 

Antibiotics are are unwarranted if the abscess is sterile; and as an abscess is “walled off” from the rest of the body, they may not be effective if a septic abscess.

However, if it is known or suspected that the abscess is septic, prophylactic use of antibiotics may be advisable in case it becomes systemic. (There will be wider clinical signs such as elevated temperature, inappetence etc.)

 

Vets may prescribe nonsteroidal anti-inflammatories (NSAIDs) as analgesia on the grounds that not relieving the severe pain of an abscess or injury is inhumane, but as the inflammatory response which is causing the pain is part of the body’s defences and healing processes, their use can be counter-productive. 

Typically NSAIDs are no longer used in human medicine where wound healing is a priority. 

 

The pain relief used for horses is most typically phenylbutazone, or ‘bute, as it is much cheaper than new generation NSAIDs. 

 

It’s important to know that NSAIDS work by affecting the prostaglandin synthesis that is involved in inflammation, but even modern NSAIDs can also affect prostaglandin synthesis that is involved in vital functions, such as the maintenance of the lining of the gut, blood vessels and the tubules of the kidneys.

 

There is good reason to be wary of NSAID use (especially the old type of NSAID), in horses which are blood volume depleted because of blood loss and/or dehydration, or which have known to have gut problems or kidney issues.

 

Soaking in cold water, padding the hoof, and encouraging the horse to move are important for resolution of the abscess, and for wider health.