Page 174 - February 2021

VETERINARY VIEWS
THRUSH
by Nancy S. Loving, DVM
You’ve seen it many a time – a horse gal- lops down the track, and dirt clods fly every which way. With normal activity, horse hooves experience a natural cleansing that scours the bottom of the hoof and removes collections of debris. Any cause for inactivity, such as constraints on exercise and turnout
or due to lameness convalescence, influences how well a horse achieves the natural clean-
ing action that comes from moving across dry ground. It doesn’t require a fast run to accom- plish this; even just regular movement at a walk and trot accomplishes a good effect.
With less than optimal hygiene, infection can develop. Most cases of thrush occur in inactive horses that live in stalls. A result of standing idle doesn’t allow the foot to flex and move so it doesn’t get the opportunity to self-clean.
A horse’s environment further impacts hoof health to some degree. Certain conditions predispose to bacterial or fungal infections
of the frog that may lead to thrush. Horses
live in the presence of manure and soil where
potentially destructive organisms proliferate, particularly if dirt and debris remain trapped in the crevices (sulci) of the frog. Pads covering the sole also tend to trap moisture
in the bottom of the foot to facilitate such growth. While poor hygiene sets the stage for development of thrush, even with the best of care, infection can develop in the frog or its sulci (crevices) in excessively moist conditions. For example, horses in the arid western USA don’t tend to have nearly as many or the extent of thrush infections as those living in damp parts of the country. Thrush occurs in some
of the best cared for and managed farms, but a common denominator is that it tends to develop in horses spending a large amount of time in stalls.
Susceptibility to develop thrush varies with the configuration of the foot. A foot with an upright heel and deep crevices is a foot that has a higher risk of trapping infection. A horse with a chronic lameness condition that causes heels to contract and/or poses limitations on exercise is also prime to develop thrush. While
some affected horses have deep crevices of the frog, in other cases there is no depth to the frog clefts at all. The incidence may be higher in feet with a deeper cleft that is more likely to retain moisture, which becomes a media for bacterial growth.
WHAT DOES THRUSH LOOK LIKE?
The consistency of a normal frog is much like that of a rubber eraser, firm but pliable. Normally, the central sulcus is fairly shallow, if that. The central sulcus may deepen in a horse with limited exercise, and/or other hoof health issues. A deep crevice has limited access to air and oxygen. If debris lodges there, infection may develop, evident as a black and pasty discharge, often with an offensive odor.
A thrush infection is usually fairly superficial in its invasion of the tissues. In
the early stages, it may be difficult to identify the presence of thrush since the horse is not lame and may show no other clinical signs. At times, the first observance of a problem is that the feet stink. A more-deep seated infection
Most cases of thrush occur in inactive horses that live in stalls. Standing idle doesn’t allow the foot to flex and move, so it doesn’t get the opportunity to self-clean.
172 SPEEDHORSE February 2021
With normal activity, horse hooves experience a natural cleansing that scours the bottom of the hoof and removes debris.