Sounds like I should keep the acorns to <20% of the diet due to tannins in the nut. That works for me as I don't care to spend loads of my time picking and smashing acorns
Some light reading on the subject:
http://www.atk.ke.hu/index.php?mid=60&did=181
One more forage item you could save for later when they don't have anything due to that dreaded cold.
Hens go broody when you don’t want them to… and won’t go broody when you do. 