Understanding Equine Thrush.

By

Paul Conroy BSc(hons)AWCF

Introduction.

Equine thrush is an anaerobic bacterial infection of the frog, usually affecting the central sulcus (the groove running down the middle of the frog) and the lateral sulci (the grooves either side of it). With early effective treatment this condition can be nothing more than a short-term nuisance, however, if left untreated it can lead to more serious problems than a foul smell and soreness, Sheared heels and canker, a far more serious disease of the hoof. As a farrier working in practice for over 30 years, it’s something I come across almost weekly, sometimes daily. A good farrier will usually identify thrush long before it becomes a serious problem.

Let’s look at some common causes:

Poor foot hygiene:

This is commonly cited as the main cause of equine thrush and while it’s hard to argue that isn’t the case.

The thrush bacteria is anaerobic, this means it thrives in an environment starved of oxygen, so feet that are not picked out regularly, and the exposure to wet and dirty bedding simply creates the perfect environment for the bacteria to get hold.

 That said, thrush can be found in horses that live in near perfectly ran yards with impeccable stable hygiene so poor foot hygiene can’t be the only cause.

Horses worked on stony ground:

I know this one might sound far fetched but stick with me, horses that are worked on rough stony ground develop fissures (a long, narrow opening, crack, or cleft in a surface, structure, or organ) these can be quite deep without being deep enough to make the frog bleed, but they do seem to allow dirt and bacteria to take hold, slowly leading to thrush. Rough rubble and sharp stones such as flint are best avoided when exercising your horse, smooth type stones generally don’t cause this issue.

Prolonged use of pads, packing material or heart bar shoes:

Your horse might need pads or packing for various reasons that are needed and your farrier will have fitted these, an unintended consequence of this is that, over time, they can cause thrush for the same reason discussed in the poor hygiene section, basically a lack of oxygen. The same applies to heart bar shoes for the same reasons.  

Irregular shoeing or trimming:

This causes many foot related lameness’s and problems but leaving feet long and frogs untrimmed simply creates cavities that produce the utopian environment for thrush to take hold, often remaining undiscovered for weeks when lameness becomes apparent.

Some signs to look out for:

Foul smell:

Its actually difficult for me to describe a smell that I can instantly recognise when I smell it, weirdly, the longer I have been shoeing horses, the less able I have become to smell it, I think it’s called being nose blind, but it’s happened to me at times. Let’s just say it’s one of those foul smells that you never forget once you smell it, so, if you’re not sure, ask someone on your yard that has smelt thrush before, they will recognise it, your farrier or vet will definitely recognise it. The good news is the smell is one of the first signs so to the keen horse owner, it can be an early alarm before the more serious signs arrive such as lameness.

Black discharge from the central sulci of the frog:

Thrush, unlike canker, will always remain local to the frog, canker has the ability to invade the whole hoof capsule, thrush can’t do this so it will always be found in the central sulci, a black smelly necrotic discharge is often found in this area and the horse is usually sensitive to the touch around the central sulci.

Large open or split central sulci of the frog:

I will begin by saying I have seen plenty of horses with an open central sulci that is perfectly healthy, however, for most horses the central sulci is immediately visible but, its fully closed, by that I mean it doesn’t go anywhere, its just a deep valley in the middle of the frog, with thrush, this opens up and become very deep and sore to touch, one of the dangers of thrush is that it can be very deep and remain undiscovered until the horse becomes lame, this is especially a problem for horses with naturally strong and deep hooves with strong high heel buttress’s, cob types and traditional coloureds are normal candidates for this.

Lameness:

Veterinary advise should ALWAYS be sought if this occurs as we are now at the more urgent end of treatment and where one of the more serious and long-term effects of thrush lives. When the infection is deep enough, it eats away at the internal arch in the back of the foot leading to a structural breakdown of the heels, a condition known as sheared heels and a farriery intervention is needed to stabilise this as quickly as possible. The lameness might be because it’s just a raging infection and sore for the horse, it could be that a far more serious problem is developing such as canker. In all cases I can’t stress enough the need for veterinary (first) and farriery (second) treatment. 

So, what should I do if my horse has thrush?

Well In most cases, immediate treatment on discovery and early on will irradicate the problem within a few days, however, and I can’t stress this enough, if your horse goes lame, is very sensitive around the frog area or you see blood, veterinary attendance is needed immediately.

In my opinion, the best things to treat thrush is hydrogen peroxide or copper sulphate, both are effective, I would say hydrogen peroxide is the best at treating established thrush whereas copper sulphate is better as a daily or weekly preventative measure if diluted sufficiently. Things such as Hibiscrub and iodine are generally less effective against established thrush.

Hydrogen peroxide creates an environment that is hostile to the thrush bacteria. Imagine the thrush bacteria hiding in a sealed room with all the windows shut. That's the sort of environment they like. Hydrogen peroxide is like throwing all the windows open at once and flooding the room with fresh air. Suddenly the environment they thrive in disappears. If using peroxide, care must be taken that the concentration is strong enough to be effective but not too strong to damage live healthy tissue.

Prevention

A strong daily hoof care programme is the biggest preventative measure you can take, picking feet out twice a day and removing wet bedding will reduce the risk of thrush developing significantly.

A good tip I always advise my clients (especially the ones with shoes on) is to pick your horses feet out and let them stand on a hard surface like concrete. This will allow all that free oxygen hanging around doing nothing to circulate around the bottom of the foot and frog, remember oxygen is your friend when it comes to thrush.