My entire flock switches back to layer when the pullets/cockerels go through puberty (voice change). At that time, I finish up what ever unmedicated feed they are on, and put them on layer. No issues with roosters, or non laying birds. My previous roo (avatar) was replaced at the age of 4 b/c he was no longer hitting the bulls eye when he was breeding the hens. many folks keep their entire flock on layer feed, in spite of mixed gender. I hear all the noise about too much calcium causing renal failure in non laying birds, but have yet to experience any such issue with my birds.
An other option to keep your birds from wasting crumble is to wet it down or ferment it. I've been fermenting for 5 years now. The fermentation process is super easy, and increases Methionine and Lysine in the feed. studies also indicate that fermentation may produce B vitamins. Super easy to do. Read the FF FAQ article in my signature for more information.
I use a combination of dog bowls, and plastic gutter feed troughs. Never seen ants at the feeders.