Several different skin conditions can lead to scabbing and crusting on a horse’s lower limbs. Here are some questions to help you narrow down the cause of the problem:
Are only white areas affected? If scabs are covering only your horse’s white markings---and especially if all areas covered by white hair are affected---chances are good that what you are seeing is photosensitization. This is an intense inflammatory reaction that occurs when a horse ingests certain plants that contain phototoxic compounds. These substances enter the bloodstream and, when exposed to sunlight through pink skin, cause painful blistering and crusting. Treating photosensitization is a multi-step process. You need to identify and eliminate the causative plant (alsike clover and St. Johnswort are common culprits) and shield the horse from sunlight with UV-protective sheets and wraps or turn him out only after sundown. Severe cases may call for topical treatments or systemic medications prescribed by a veterinarian to ease your horse’s discomfort or reduce inflammation.
Are the scabs on the back of the fetlock? Skin irritation limited to this specific location of the leg is typically a case of scratches, which is chapping of the skin and associated infection. You can handle mild cases on your own by washing the area, drying it thoroughly and clipping the hair carefully. Then apply a layer of antibiotic ointment, followed by a layer of thick protective cream, such as the type used to treat diaper rash. Keeping the area dry and covered in ointment for a few days should do the trick. If it doesn’t, call your veterinarian.
Is the scabbing only on the front of the rear pasterns? Accumulated skin scurf in this area is often called “stud crud” and is thought to be a reaction to male horses splashing their legs with urine. It may also be caused by excessive oil secreted by sebaceous glands in that area. In either case, it’s harmless and can be cleared up with medicated shampoo supplied by your veterinarian.
Is there also crusting on the back and sides of the body? Diffuse scabbing on a horse’s rump or flanks as well as his limbs is likely rainrot, a condition caused by proliferation of Dermatophilus spp. bacteria that normally live harmlessly on a horse’s skin. In wet, humid weather, the bacteria multiply, irritating hair follicles and causing a distinctive type of crusting. To treat rainrot, massage mineral oil into his coat, which will encourage the scabs to slide off on their own within a day or two. Then, bathe him with a medicated shampoo. Persistent cases or those on old, ill or otherwise immune-compromised horses may require an antibiotic from your veterinarian.
This article first appeared in the June 2017 issue (#477) of EQUUS magazine