I so agree with speckledhen, and hope you spread the word. Antibiotics should never ever be given unless a) you know exactly the type of thing for which you're treating, b) the antibiotics are appropriate (most times they're not - especially if recommended by random feedstore people), c) the antibiotics, once started, are continued until the complete recommended duration of treatment, d) they're followed up by probiotics if antibiotics are given orally, or e) if the bird is likely to die anyway, separate from the others, and there's really no loss.
I have seen so many times poor caring bird owners told "give this here packet of antibiotics - that'll fix it" for just about anything. droopy bird? Give antibiotics. Bird won't lay? Give antibiotics. Want the bird to grow faster? Give antibiotics. No kidding, people actually recommend that.
It's not the owner's fault, but I have a little mini-crusade to get that information fixed for as many people as possible.
I was a victim of it once, and now I've learned so I share with other people. Pass it on.
OK, my rant is over. /big grin