I have a hen with a large, round, growth on her leg. It's like a large marble attached to the back of her leg at the joint, but squishy, not hard. Might be like what's wrong with your rooster? I drained bloody pus from it, but that didn't seem to help. She has a smaller, second one, too. I wonder if antibiotics would help, but have no idea which one to get for her. I'm giving her Rooster Booster in her water, soaking her leg in Epsom salts, and nothing is helping. It hurts her when I try to drain it. Her legs are clear, no mites or scales or anything like that.
Watching this thread closely for advice.