I'm sorry but you already know what this guy is about from past dealings with him. IMO he going to look at any complaint you have about the same way he dealt with the horse issue.
Personally I would take a couple chickens at a time and fry them up. If he doesn't get the hint as their numbers dwindle then he will eventually lose them all.
It is not your responsibility to fatten up his chickens for his benefit. The way I see it is if you are fattening them up it best be for your benefit.