Many times after it rains, my horse gets very muddy around her legs. I then proceed to hose her off after it stops raining. Is there any real side-effects to being real muddy?

I can't see real effect coming from the mud. But what I could see that will really affect the horse is what is in the mud. Bacteria might infect the skin of the horse if it will not be cleaned immediately. And also the horse will not be comfortable having the mud drying up its feet.

A horse that isn't cared for will have other problems, but just being generally muddy isn't going to have a real impact. lol