What symptoms have you seen in sick birds? Many respiratory diseases are caused by viruses (infectious bronchitis, ILT, others,) and those will not respond to an antibiotic. Those usually last a month or more and run their course. Coryza, another bacterial disease, may respond to Tylan in combination with sulfa antibiotics, such as sulfadimethoxine. Symptoms may give clues on which disease you are treating. Also testing would help to diagnose. Here is a good list of all common diseases including the respiratory ones with symptoms:This afternoon will be 2 days since I have started the treatment with Tylan 50 and they are not worse and they are not better. I will continue the treatment but I need to order a broad spectrum antibiotic because I really don't know if they have MG. You mentioned Baytril but it says permanent egg withdraw? Is there any other antibacterial med out there good for a big range of possible chicken respiratory infections?
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