I'm sure our chickens get some protein from bugs they find in the run, but by and large they've been on organic layer feed (and grass when we let them roam the yard) for years with no health issues.
Ummm, good eggs!
One food show had the host visiting a cheese farm in France. The “best” cheeses were made from Summer milk, when the cows were grass and wild flower fed, versus Winter milk when the cows were fed hay.