I've learned from other bird owners that it can take a long time for symptoms of damage to a bird's respiratory system to show up. Air sac carcinoma can develop over many years time and it's difficult to know without CT scans that it's there, and even then, if it's too small to see it won't show up. Zinc poisoning also is a cumulative thing. I would rather not take the chance. I do everything I can to protect my pets.