I've never had to treat my Bantams for anything. I think the periodic darkening is a sign of respiratory difficulty. I keep the coop and yard tidy, so I doubt dust is the problem. I realize stress can sometimes darken the comb, but I hear some faint wheezing. When I was clipping his nails the other day, his comb was getting almost black and became weak. He quickly recovered after I set him back down. I tried a bit of VetRX but it doesn't seem to eliminate the faint wheezing. I've used Tylan 50 before at 1cc breast muscle injections on my standard breeds. Would 1/4 cc injection be acceptable for this Bantam cock?