My Brahmas have droopy saggy bottoms, and the vent area is missing feathers. The feathers went away when winter came, I thought the molt, but they never came back. The bottom under the vent is saggy and droopy. Like a baby's diaper that needs changing, but it's clean though. No poopy butts, laying regularly, eggs look great, they are eating and solid stools, perky and happy, it just looks bad. What is causing this? Thanks