One by one, this is what happens: Chick gets lethargic, then one leg goes limp, then curls uselessly. Bad leg eventually straightens, and then hyperextends in a backward direction, by which time chick is lying spread out, panting. I've culled them all at this point. Does anyone know what could possibly be going on? The unaffected chicks are strong and vigorous, everyone eating and drinking and pooping normally...until someone succumbs to the mystery ailment. I'm holding out hope that I just culled the last one, and the rest will be fine. ETA: These chicks are 2 days old.