http://www.horseshoes.com/advice/essays/raymiller16/diseasesofthehoofpart2.htm

Thrush is an infective condition of the frog and its sulci which results in degeneration of the horn and the production of foul smelling gray/black discharge. In severe or neglected cases the infection can spread to involve the underlying corium. The degeneration of the horn is due to infection with keratolytic bacteria and fungi and multiple organism infections are common. Predisposing causes of thrush include wet unhygienic stable conditions, poor routine foot care, prolonged confinement, overgrown ragged frogs, and long or high heels which produce deep sulci.

Canker is a chronic hypertrophic moist pododermatitis as a result of infection of the stratum germinativum. The nature of the infection is not fully understood, although a number of bacteria have been identified in clinical cases none has been confirmed as the causal agent. The infection causes the production of rapidly growing, friable, filamentous fronds of horn. Canker usually starts in the frog region but, if it is not recognized or is left untreated, it can spread to involve the sole and wall. The condition is predisposed to by unhygienic stable condition and poor hoof care.

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After a long wet winter that dried up super fast in late spring, I have been running into subtle cases of THRUSH all summer long.

I didn't begin looking for it until mid July, after having a few horses with extremely hard to detect thrush in conjunction with distorted feet, and now that I'm looking for it?

Its everywhere. Almost 3 horses out of 4 that I look at, including horses I haven't trimmed, have thrush. These owners are shocked because these horses feet don't stink, you can't easily see the thrush. Thrush is often VERY hard to spot, and because it's dry and summer, people don't think of thrush.

Many of us hoof care providers have become over-conservative about trimming frogs, so perhaps we aren't paring away as much of the dead frog, but this is beyond barefoot... 5 typical horses came to me shod by high-end farrier's.

No matter who's caring for the feet hen we focus on the wall, its easy to ignore the frogs.

Since my immersion into the rotten world of Thrush, one of the primary symptoms I now look for is hoof distortion, poor movement or unsoundness as horses try to avoid frog discomfort.

Here is a typical example... I got an email from a net buddy in Arizona who mentioned that her hoof care person had left too much wall on the insides of both front feet,so I suggested that she check for thrush, and decided to put up a page because we are all so used to thinking of it as black gooey crud that we see in the winter, not as this hidden source of spring and summer unsoundness. Yes, her horse had a "mild" case of thrush!

Bottom line? Look for thrush if your horses feet have changed in a way that allows it to stop using his frog or foot effectively.

 

Signs of potential thrush, frog infection or bacterial problem include:

Thrush is notorious for messing up feet, and I have about a dozen horses that came into my care after years of intermittent lameness usually misdiagnosed as "navicular syndrome"  that has turned out to be nothing more than thrush. 

Horses will walk on the sides of their feet or favor their toes when they have thrush to avoid "hoof mechanism", the flexion in the hoof that enables shock absorption.

 This condition is a lot like Athletes Foot; it's painful and tough to get rid of unless you soak religiously, and even that isn't a guarantee. Using White Lightening, Clean Trax or Cow Dry udder ointment helps extreme cases.

In the winter Thrush is an obvious thick gooey mess, but in the summer it may be a thin line of dark matter buried deep in the central sulcus or at the deepest parts of the frogs commisure's, the gap between the frog and the sole.

 

The bottom line? If your horse has anything weird happening with its feet, look for thrush!!!

Soak affected feet in a warm Lysol or Borax soaking solution  (diluted to the strength used on floors) for 30 minutes a day for 2 to 5 days.

Have your hoof care provider check the frog to see if its shedding, and remove any shedding frog, flaps and tight cracks or grooves.

If soaking doesn't help, try Clean Trax or White Lightening vapor treatments. You can reduce the cost of purchasing a special treatment boot by using an IV solution bag used inside a regular boot.

Topical treatments supposedly helps with minor thrush but the only topical that has worked for tough thrush for my clients is antibiotic Dry Cow Treatment / Teat Sealant, available in Ag Catalogs. Other topical's don't get rid of severe thrush or its symptoms completely.

Soaking is cheap insurance!