Causes, Symptoms, Prevention and Treatment

Thrush is a common bacterial infection of the frog of a horse’s foot. The infection “eats away” at the tissues of the frog, sole and heel and if untreated will eventually result in loss of foot structure, increasing sensitivity, progressive lameness, and bleeding.

Causes of Thrush

The causative agent is a common anaerobic bacterium that thrives in the low oxygen environment of the deep clefts surrounding the frog and heel areas. The microbes causing thrush are opportunistic and are commonly found in soil contaminated with moist organic material.

High humidity or wet environments predispose horses to thrush. Once the organisms begin dividing in the frog sulci, the stage is set for a progressive invasion and subsequent infection of the frog tissue.

The Importance of Oxygen for Thrush

Blocking oxygen flow to the tissue of the frog and surrounding areas creates an environment for thrush to develop. Oxygen can be blocked to the foot tissue from packed debris, foot pads, boots, or the application of grease and oils to the foot.

Strong astringents such as formaldehyde, copper sulfate, and chlorine are caustic to live tissue. These chemicals denature the proteins in the external layer of the tissues and thereby reduce the ability of oxygen to penetrate.

Symptoms of Thrush

The exudate associated with thrush is usually black in color and characteristically has a highly unpleasant odor. Infection of the frog and surrounding tissues often leads to lameness.

Prevention of Thrush

Effective thrush prevention involves a combination of :
1) Maintaining a clean, dry (but not too dry) environment
2) Cleaning the feet on a routine basis
3) Adequate exercise
4) Proper nutrition and supplementation can create denser and healthier frog and sole tissue that is more resistant to infection.

Treatment of Thrush

If the horse develops thrush, provide the horse with a clean and dry environment to stand. Clean the bottom of the foot and frog area by removing any debris and wash the area thoroughly. Do not utilize a thrush remedy that contains caustic chemicals such as turpentine, formaldehyde, copper sulfate, or chlorine. Hoof disinfectants containing tame iodine are ideal. “Sugardine” treatments utilizing sugar-betadine solutions packed into the frog sulci have been found to be effective in many cases. Surgical debridement of affected frog tissue is sometimes necessary.

Recommended topical for thrush:

Farrier’s Finish^®

J. Frank Gravlee, DVM, MS, CNS
Founder of Life Data Labs, Inc.
H. Scott Gravlee, DVM, CNS
Equine Nutrition Consultant