Horses commonly have hair loss in various areas and sometimes the cause can be difficult to determine. Hair loss and skin disease in horses can be caused by multiple conditions. One of the more common conditions we see is called scratches, which is commonly found on the rear legs at the front part of the cannon bone. These horses will have hair loss in some instances and scabs. Some horses will also have swelling on the legs in this area and inflammation down around the pastern area.
There are many different causes of this condition and I believe a lot of horses develop these lesions due to allergy or flies affecting the lower legs. It may also be related to irritation from horses walking through tall grass or weeds, but something must irritate the area to start the process. Then infection develops. The infection may be bacterial or fungal. Scabs form with infection underneath them. Regardless of the cause, treatment involves clipping the hair off the legs and then removing the scabs. This can be painful, and in many cases requires your veterinarian to sedate the horse, then use a chlorhexidine shampoo to soak off the scabs and gently remove them. In recurring cases, your vet may need to culture the area to determine the bacterial organism and which antibiotic to use, as well as doing a microscopic exam of the tissue and testing for fungus. After the scabs have been removed, treating with an antibacterial, antifungal and anti-inflammatory cream is usually effective. Some cases will also require fly ointment to control flies, and those with deeper infections and swelling of the legs may require oral antibiotics plus temporarily wrapping the legs.