Question of whether chickens exist or not within FFXV. Sheep do, though we never see them (see: sheep milk). However, it’s fairly well established that people’s procurement of poultry is also satisfied by other means - Daggerquills, Dynoaevis’, Chickatrice (and presumably the other trices, even if they drop no in-game meat), and even Griffons.
That bears the question - do domesticated and wild chickens (hens, roosters, chicks and all) exist or are they just replaced with the Chickatrices, etc? That goes for other animals as well, such as pigs (ex: Gighee Ham).
Also, the interesting note that Garula are considered beef (maybe). Produce steaks and sirloins. So are Garulessa. I think.