I would wait because the people I respect say to treat with DiMethox or sulfadimthoxine, that it is better than Tylan for coryza. You may be seeing the worst part of his disease now. I have never treated coryza, but it takes time to get over, and it is never cured. I have read that it can last for weeks. I am glad he is doing better.These links are very helpful. Thanks for sharing. Do you think we need to move onto Tylan or should we just wait it out and keep giving him the nutri-drench?