Chickens are thin. I have feeders filled 24-7 and never let them run out. All have been wormed with Valbazen. All act great and seems to be fine but are under weight. They never seem to have much in their crop when inspected. They seem to not like purina flock raiser. I switched to laying pellets and they don't seem to like it. What can I give them to stimulate their appetites?