Sounds like quite a regiment, what happend to the poor flock?
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So combining them probably wont do any extra harm, I just think its a little bit much and will knock out some of the good bacteria and micro-flora the chicken wants to have in it. Honestly that's the major problem with broad spectrum antibacterial treatments for healthy animals, it kills the good stuff and makes the bad stuff stronger.
and then i'm going to dust them for mites, and trim their toenails... okay not really.

i have had a terrible time with this particular batch of chicks -- i'm sure it does sound like overkill! this is a hypothetical treatment for them, but already the latest victim seems to be recovering, thankfully. i've lost 6 out of 9 from this age group. it's absolutely unbelievable to me.
at first no one could figure out what was happening. nothing fit -- mareks, coccidiosis, respiratory infections, nothing! i called a vet, called the ag extension office, and scoured the info available online. i even had the local chicken inspector come out, and she was flummoxed. she said we could do a necropsy, but at that point the last three were recovering, so i hated to sacrifice one just for that. she said unless it's a specific disease, they wouldn't be able to tell me anything helpful for months. i believe they had a vitamin B1 deficiency... as best i can determine.
but now i just had another of that batch who i thought developed cocci. ARGH. i'm treating her with sulmet and watching her friends carefully. so far no one else shows any signs of anything. which makes me doubt it was coccidiosis, since it's supposed to be highly contagious. this morning, i began to wonder if i should be treating her with a different broad-spectrum antibiotic instead of sulmet. but by late morning, she is seeming a bit stronger. so...
thank you very much for the reply. it is good to know, just in case.