@Maryam, read this thread, it has pictures of how quickly enrofloxacin can work.
https://www.backyardchickens.com/threads/my-first-sinus-infection.945918/
Enrofloxacin works very quickly, as in sometimes they are noticeably better in a matter of hours. Give the enrofloxacin for two days past the cessation of symptoms. Does that make sense?
It will work better if you give it twice a day. If you have the
10 mg/kg
100 mg/ml dose = 0.1 ml per kg twice a day
50 mg/ml dose = 0.2 ml per kg twice a day
25 mg/ml dose = 0.4 ml per kg twice a day
15 mg/kg
100 mg/ml dose = 0.15 ml per kg twice a day
50 mg/ml dose = 0.3 ml per kg twice a day...
Many people do euthanize birds with respiratory infections rather than treat them, especially if it's something like Coryza, MG, MS, ILT, etc., those are diseases that have the potential to infect an entire flock. But since you have just one that is sick, there is a good chance it's not one of...
Yes, that is what I would give, it is the best for many types of bacterial respiratory infections. Do you know how much to give? It does need to be given orally or by injection, never in water. Let me know if you need help calculation a dose.