Comment by qq99

You can kinda tell based on their actions (sometimes). We haven't really needed to bring them to the vet for illness, but once for amputation of an infected + hurt toe. Additionally, if they get parasites (typically mites), they need anti-parasitics. My wife has done a ton of research into identifying chicken issues so she is always on the lookout.

We've had other times where one might appear a bit sluggish, but then the next day are back to normal. Probably ate something bad?