If by Grain, you mean specifically Chicken Feed, they should have all that they can eat. Feed is mixed with the correct grain ratios to provide all their dietary needs, including protein. I sometimes give my B's cheese, crumbled boiled eggs and cooked meats as protein treats
I also keep layer pellets available 24/7. For a protein boost I offer black oil sunflower seeds (BOSS), cheese, scrambled or hard boiled eggs, and yogurt. My girls also free range so they find alot of protein on their own in the form of bugs, mice, frogs and what have you. I think they'd eat one of the crows that hang around if they could catch em.
