We used the chickens for eggs mostly and meat when they stopped laying. We used the sheep for meat every spring. We would trade with the neighbors in exchange for helping farm our vegetable crops or fresh milk from the small-ish dairy farm down the road. It wasn't the kind of thing where we were selling to a grocery conglomerate or anything.
Probably none of our farming practices would have been acceptable at scale. But that wasn't our point. It was mostly just for our family. Honestly, not the worst way to grow up. You farm your own food and slaughter your own meat. You learn a certain respect and appreciation for what sustains you.
But anyway, yeah, I don't know what the rules are if you're selling your livestock. Feeding them trash probably isn't allowed, even though it's efficient.