Is this a male horse? Is the scabbing on the back of the front legs? Do you ever get it cleared up or is it constant? Is there any swelling or pitting of the legs?
The first thing to try with any skin condition on the legs is daily cleaning with betadine or chlorhexidine, drying thoroughly (you may have to clip the legs if the horse has feathers, but getting the legs really really dry is important) and then apply a layer of diaper rash ointment.
Usually the factor that allows for skin infections is chronic wetting of the skin---rain, mud, dew, urine splash in male horses, etc. You have to protect the skin from damp conditions to allow it to heal.
Licensed Veterinary Technician