You could offer a dish of wet mash (chicken feed + water). I think chickens find that easier to swallow than dry crumbles (you mentioned issues with that in the first post). Also, chickens tend to think it is a treat, so it might encourage him to eat a little more.I suspect that is the case as well. I have not seen him drink in a while, but I offered him water (from a bucket) and he didn't want it.
