Eight days ago, I received 18 Isbar chicks from an auction I won. When I got them, I realized they weren't all "day old" chicks--some were likely hatched within the previous day or two, but some were 10-14 days old, some maybe a week old. I was surprised, but didn't give it a lot of thought. As of now, ALL of the youngest ones are dead, leaving only the older ones (7, I think, though my brain just hiccuped and it could be 9). Most of them died within the first 72 hours after arrival. They appeared to be fine--no pasty butt, no symptoms of any kind that we could find, then an hour later, we would find another one or two dead. Unfortunately, when these chicks first arrived, I was in a rush and hadn't prepared their own brooder for them yet. So when we got them out of the box, I put them in another brooder with my BLRW's that I had hatched just two days before. All those BLRW's were looking great and they had never been anywhere other than the incubator and their brooder in my spare bedroom. The Isbars were in there for a few hours while we set up another brooder and got a few other things situated. Now all the BLRW's are dying. They started dying 2 days ago (so about 6 days after they had contact with the Isbars). We have had several die, and when I left for work, at least 6 more were dropping their wings down and acting very inactive. So, unlike the Isbars, the BLRW's are at least somewhat symptomatic. With the Isbars, we tried vitamin supplementation and ACV in the water. When that appeared to do no good, I discontinued that in the concern that it might have been making it worse. Didn't seem to make a difference either way. There are other chicks in the same room (ones I have hatched and some from Greenfire Farms), but in different brooders. None of them have died or are showing any symptoms. None of them had any contact whatsoever with the Isbars. We habitually use alcohol rub on our hards when moving from brooder to brooder in general cares (what can I say, I'm an ICU nurse!). I have no idea what to do here. I don't dare put the remaining Isbars anywhere near my remaining chicks. The ones that are left appear to be fine and no more have died in 2 days--just the BLRW's they had contact with. Does anyone have any idea what might be causing this? Is there something besides pasty butt that might kill off only the younger chicks and not the older ones? And, more improtantly, any suggestion on what I can try in order to save the remaining BLRW's? As far as I know, these chicks weren't vaccinated for anything. I'm hoping for something I can pick up at the local feed store in the morning when I get off work for these little ones. I'm also hoping I don't get home and find a pile of dead chicks.