You don't need to cook veggies for hens, but there are certain ones that either aren't good for them or they don't eat. I wouldn't give mine raw potatoes in any form - whole OR peelings. Mine get a steady supply from a friend but I check what's in the bag before tipping it on the ground for them - they like pecking around so I just scatter it and anything that isn't eaten in a couple of hours gets lifted and composted.