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Thrush is a very common bacterial infection that occurs on the hoof of a horse, specifically in the region of the frog. The bacteria involved is Fusobacterium necrophorum, and occurs naturally in the animal's environment — especially in wet, muddy, or unsanitary conditions, such as an unclean stall — and grow best with low oxygen. Horses with deep clefts, or narrow or contracted heels are more at-risk to develop thrush.
The most obvious sign of thrush is usually the odor that occurs when picking out the feet. Additionally, the areas of the hoof that are infected will be black in color (even on a dark-horned hoof), and will easily break or crumble when scraped with a hoof pick. When picking the hooves, around thrush areas, the differences between healthy and infected areas can be seen when there is white/gray tissue (healthy frog) surrounding a dark, smelly area (infected area).
Most horses do not become lame if infected with thrush. However, if left untreated, the bacteria may migrate deeper into the sensitive parts of the hoof, which will result in lameness. At this point, the horse may also react when his feet are picked out, and blood may be seen.
Treatment and prevention
Treatment for horses with thrush includes twice daily picking of the feet, taking special care to clean out the two collateral grooves and the central sulcus. The feet may then be scrubbed clean using a detergent and/or disinfectant and warm water, before the frog is coated with a commercial thrush-treatment product, or with iodine solution, which may be soaked into cotton balls and packed into the clefts. There are also several home remedies, such as a hoof packing of sugardine (a combination of sugar and betadine), powdered aspirin, borax or diluted bleach. It is best, however, to speak with the horse's veterinarian, to be sure that these home remedies are effective and, more importantly, safe for use on horses.
Horses with thrush, or those at risk for contracting it, are best kept in a dry, clean environment. Daily cleaning of the hooves also contributes to the prevention of thrush. In general, thrush is relatively easy to treat, although it can easily return and it can take up to a year for a fully healthy frog to regrow after a severe infection.
- Ensminger, M. E. (1990). Horses and Horsemanship: Animal Agriculture Series (Sixth ed.). Danville, IL: Interstate Publishers. p. 62. ISBN 0-8134-2883-1.