As stated before warts are viral, they go away by themselves. However when my filly was a baby she got a really bad case of milk warts, some were over 2cm long and her whole muzzle was covered, she wasn't a pretty pony!!
. It was recomended by my herbalist to use Thuja ointment applied as many times as possible each day. In her case they cleared up within 2 weeks. If you have access to a homeopath a better option is Thuja given internally.