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.