Mine get almost anything including pizza. But no raw onions, citrus, uncooked beans, uncooked potato skins, and anything moldy. Plus there's a few more no go foods not allowed. I have about 50 chickens, 14 ducks and 4 guineas that share the treats. Moderation is the key and I don't give treats in the first half of the day so they fill up on layer pellets first, they get treats only a few hours before roost time.
My ducks and a few of my chickens.
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Oh, and their guard dogs next door.