We culled a hen who had stopped laying well before molt and since molt has gotten white tips on the feathers on her head, wings, and body. She was a black bird. She did not have any lice or mites, The only strange thing we noticed was that she had a layer of yellow fat surrounding her heart. I've read that this could be a sign of chronic URI. We also culled a 5 month old roo a few days before, and he had no such deposits and was healthy as a horse. Both birds went to the dogs. My concern is that if this is a URI that will keep reappearing in my old birds and passing to my young ones, is the best move to cull every bird? What about my Muscovy ducks? Thanks!