Anyone who has owned chickens for a decent amount of time will tell you that they are most definitely NOT vegetarians. Meat or fish scraps, mice, and bugs are all considered tasty treats by chickens.
Protein is a must for chickens, especially during the annual molt. It’s usually pretty easy to tell when your flock is molting. Feathers will be just about everywhere except on your chickens. Well, almost. Feathers are made of mostly protein, so giving your flock a boost during this time is a good thing. (Add those feathers to your compost to give your garden a boost too!)