chickens will eat all the grass in their run.Best thing to do is grow chicken friendly plants for them to eat. Grow them in 5 gallon pots(preferably glass) and when they start to grow,wrap chicken wire around the entire plant including the top.You have to make this chicken proof for it to work.Then water those plants and add some fresh chicken poo to speed up the process.Soon you will have your own chicken jungle.They will eat whatever is growing and poking out of the chicken holes,and might even jump on top to contribute to growth.You will see them laying around the pots, waiting patiently for more to grow out so they can snipe up.Best plants are in the bean,or cherry tomato family..something that bushes out fast,fast,fast!