If you live in an area that has lots of rain or snow you know that caring for pets and livestock that are out in the weather takes more than just shelter. Horses and livestock are susceptible to "rain rot" and other fungus' that thrive in moist conditions. You need to have an area where not only the animals can get out of the rain but also have a chance to dry off.
"Rain rot" takes sometimes months to get rid of once an animal has gotten it. It often takes daily shampooing of the animal with medicated shampoo to cure the condition. Prevention is the best cure for this.