Mud fever is caused by a buildup of moisture behint the pastern and under the fetlock. The best way to prevent it is to always remember to dry your horses legs whenever they get wet.
Try to keep there grazing source longer so that there are not desperately seeking out food. Keeping them well fed and their minds busy would be a good start, it is rare.
Mud fever is caused by the bacterium, Dermatophilus congolensis. It can enter skin that has been compromised by injury, abrasion, or chapping. To avoid infection, keep skin clean and dry.
Mud fever occurs in horses that live or work in wet, muddy conditions.It affects the skin over the pasterns and heels. Infections make it very painful for the horse.