Well it doesn't sound like it's the feed. Rodents in the coop are never good as they do carry disease. If your lab caught one, chances are there are more that need to be evicted.
You could also try worming them as suggested by greenfamilyfarms if they haven't been wormed this spring already.
You could also try worming them as suggested by greenfamilyfarms if they haven't been wormed this spring already.