Most folks are told to pick their horses feet everyday or every time they take their horse out and then when they return. The purpose is to make sure there are no stones or foreign obstacles that may be jammed in the foot to make for lameness. However, there are others that say you shouldn't pick their feet - that the mud and dirt act as a cushioning effect for the feet.
I went back and forth on this for several years but never knew anyone that didn't pick out the hooves, but I gave it a try and haven't picked my horses feet (13 of the little darlings) for 7 or 8 years and have never had a problem with lameness. Some horse owners that come here think I'm terrible for not doing it.
It is a decision that should be made by you - you do what feels okay to you.
Just wanted you to know both sides of the story.
http://www.RideNYS.com Adventure Horse Riding in NYS