I'm new at raising chickens and I bought 17 black austrolorps that were suppost to 5 months old, but I know they had to be different ages, some were full feathered and some smaller with chic looking fuzz. I noticed bringing them home I could here some of them making a smack sound along with the usual chicken sounds. I've had them for going on 3 weeks and I've had 3 of the smaller ones to die and now have one quarenteened because its just sleeping and you can hear it breathing with no chicken sounds, its wings are drooped and she just stands there with her eyes closed. The lady I got them from said her chickens were okay and that it might be resperitory and to put some tetracycline in there water, I have done that for 3 days now haven't noticed that sound in others as much, just every now and then, Hate to loose anymore what do I need to do? I also bought 10 brown leghorn from another person (5 months old), put them in the same pen, now I've read that, that was no no, but they seem to be fine as are the older ones the I bought earlier.