We have two roosters that we keep in cages (with wire floors) for breeding purposes. One is a white silkie that is 3yrs old. Last winter (we only have this problem in the winter) the feathers under his vent became a nasty smelling, matted mess. He seems healthy, eats well, behaves normally, poo otherwise looks normal, but he (his butt) looks and smells awful! Last winter I even brought him into the house and bathed him. He lived with no ill effects but here we are again this winter (and a second rooster of a DIFFERENT breed) and they both have the same problem. They eat the same food as the other birds... any clues or suggestions?