If you have horses, the chances are you'll see thrush firsthand sooner or later. Thrush in horses is a degenerative infection of the central and collateral grooves of the frog.
With its black, foul-smelling discharge, it's easy to spot - and smell - as you clean the grooves along the sides of the frog. The grooves may also look deeper than normal if thrush has set in. If the infection is severe and has penetrated sensitive tissues, the horse will flinch when the area is cleaned or pressed with a hoof pick. In very severe cases, the horse can be lame. Otherwise the horse often appears unperturbed by its affliction, with no apparent discomfort or lameness evident.
Traditionally, thrush has commonly been blamed on bad stable management. This is not always the case. Some horses kept in poor underfoot conditions are unaffected, while others in perfect accomodation are. The individual susceptibility of the horse seems to be a major factor.
What causes thrush in horses?
Unhygienic environmental conditions: Soiled, sodden bedding or constantly damp, marshy pasture provide the perfect environment for the anerobic bacteria (those needing a low-oxygen environment) which cause thrush to flourish.
Poor foot care: Not regularly picking out and cleaning the feet. Thrush can also occur towards the end of a shoeing cycle, when flaps of the frog grow over the grooves and trap dirt and moisture.
Poor foot conformation: A deep cleft in the frog may become packed with sand after working in an arena. If not carefully cleaned this could lead to irritation and allow bacteria to enter. Horses with contracted heels can be prone to thrush because their hoof conformation narrows the grooves so dirt and manure aren't as easily dislodged.
Treatment of thrush in horses
If a horse has thrush the underlying cause needs to be identified and removed. The horse should be moved to a clean, dry environment and the feet cleaned daily.
Treatment may need to be carried out by a vet or farrier and can be time consuming as all dead and/or damaged tissue needs to be pared away on at least one occasion until healthy tissue is reached. After paring, topical treatment with a caustic material such as 10% formalin, chlorine bleach, phenol or providone iodine follows. An antibiotic solution or spray should then be applied and if the trimming has been extensive, bandaging may be necessary.
The hoof and its environment should be kept as dry and clean as possible. Keep stables clean with plenty of good-quality, dry bedding. Paper or a shaving bed may be preferable and if the horse is turned out it should only be on a well draining paddock, or it can be brought in to stand in the dry for several hours each day. If horses are in for long periods, bank the beds during the day to allow them to stand on an area of clean, dry concrete.
Antibiotics may be needed if the infection has spread. Ensure the feet are properly trimmed and shod, especially if there are any contributory foot issues.
As the bacteria are killed by oxygen, regular use of the hoof pick will allow air to the foot and reduce the ability of the bacteria to take hold.
If your horse is troubled with frequent bouts of thrush, please consult your vet or farrier.