True. We have a mud lot for all those times we don't put them on the pasture. That covers late fall through early spring, as well as anytime it is too wet. They can really tear the grass up with their running and sliding.This. If the grass is really thick and rich, I would section one area to make a small (<1/4 acre) dry lot to turn the horses out in in the spring. Horses can founder, colic, and other sicknesses when turned out on rich grass in the spring. Ease them onto the full pasture a couple of hours at a time starting in late spring.