Pus in the foot, also known as subsolar abscess, is one of the most common causes of severe, acute, lameness in horses and ponies. In this condition, a painful abscess of pus (inflammatory material) develops between the epithelial layers of the foot. The most usual route of entry of bacteria is through a break in the barrier of the sole or white line. This can be caused by external trauma, such as standing on a nail or hard flint, or separation of the white line, which can be exacerbated by laminitis. Factors such as poor hoof care or poor weather conditions can increase the risk of subsolar abscess. 

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How is pus in the foot diagnosed?

Usually, your vet or farrier will suspect a subsolar abscess based on clinical signs, namely, sudden, severe lameness, which can be as bad as being non-weight bearing, in combination with, increased digital pulses or pain on hoof testers. A definitive diagnosis is reached when pus is found by paring away the sole. In some cases, where pus cannot be found easily, nerve blocks may be used to localise the lameness to the foot, but occasionally they may only produce a partial improvement in clinical signs and will be interpreted by your vet. Occasionally radiographs may be needed to confirm the presence of pus or gas associated with an abscess. 

What are some Dos and Don’ts of subsolar abscesses?

DO:

Call your vet or farrier for advice

And do it as soon as you notice your horse is lame. Although a subsolar abscess is most likely, your vet may need to rule out other conditions, such as a fracture or an infected joint. 

Examine your horse carefully for any wounds or obvious signs of trauma

If you can, move them to a confined area and clean their legs down if necessary. 

Apply a poultice to the affected foot, if you can, while you are waiting for help

If you are unsure of how to apply a poultice, your vet or farrier will be able to show you. 

Follow your vet or farrier’s instructions on poulticing

It is advisable to keep your horse in a confined space while a poultice is necessary. Duct tape on the base of the poultice will help to prevent it from wearing away. 

Avoid mud and wet fields when poulticing 

This is because the poultice can become waterlogged with dirt, which may delay healing. 

If your horse is used to being turned out, during the period of confinement, remember to reduce the feed intake and monitor for signs of colic

Colic, particularly large colon impactions, are more common following a sudden reduction in exercise. Ensure that your horse drinks sufficient water when stabled and keep an eye on faecal output. 

Give painkillers if prescribed

Remember only a vet can prescribe pain relieving medications or analgesics. Not all cases will need analgesic treatment, but it is helpful in many cases. If your horse is not improving call your vet. 

Most cases will resolve in 2-5 days

If your horse is still lame, contact your vet as there may be an underlying problem such as a pedal bone fracture, or the drainage tract may need to be opened up further. 

Remember that it may not be possible to find pus in the early stages

So you may need a follow up visit if this is the case. This doesn’t mean anything was missed by the first vet or farrier – the pus may take some time to appear.

Monitor the affected leg 

In particular, for any swelling or inflammation; and monitor the opposite limb for signs of laminitis, which can be associated with excessive weight bearing. 

Speak to your vet about testing for Cushing’s disease (PPID)

This is a common underlying cause in cases with recurrent abscesses. 

DON’T

Give antibiotics

Most cases of pus in the foot will resolve without antibiotics. Only a vet can prescribe antibiotics and only do so when absolutely necessary, this is because some horses can experience side effects from antibiotic therapy. Additionally, overuse can lead to resistance, which can have an effect on human health. 

Give extra painkillers or treatments

Don’t be tempted to give an extra dose of pain killers or add in additional treatments without speaking to your vet first. 

Be tempted to open up a drainage tract yourself or use caustic agents on the foot

The farrier or vet will be able to advise and are trained to know how deep they can dig safely. 

Continue to poultice if the frog or skin become damaged

If the frog becomes moist and tar like, it may need treatment and time to dry out. 

Forget to check the horse

A horse undergoing treatment should be checked as frequently as possible. 

Let it get wet

When the abscess has stopped draining, don’t turn your horse out onto wet pasture or leave the foot uncovered until the defect in the sole has healed. 

Worry too much!

Don’t forget that most cases will resolve uneventfully, so try not to worry too much. Keep in regular contact with your vet and farrier to make sure that any other problems are diagnosed and treated early.

They’re common but they’re not usually serious

In summary, a subsolar abscess is the most common cause of severe, unilateral lameness, but any horse showing severe signs of lameness should be checked by a vet to rule out any other very serious conditions. It is a good idea to learn how to apply a poultice and have some poultice materials in a first aid box so that you are prepared in advance. 

While your horse is undergoing treatment, keep in regular contact with your vet to ensure that it is progressing as hoped. If you have any questions, speak to your vet who will be able to advise. 

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