Cows and sheep happily graze on moors and other rocky areas that could not be suddenly used to grow any kind of plants for food.
Harry Metcalfe has a good video[0] about it - he keeps cows on the fields that are just too steep and too rocky to grow anything else - but it doesn't bother animals. Same applies to sheep. I imagine animals like chickens will have different considerations, because farm buildings do take land that can be used for something else.