Use caution when growing grass for your poultry as they can eat to much, to fast and before you know it, impacted crops. I grow food grade (dunno if it makes a difference) but the wheat, oat and winter rye that you can buy, we grow it for the cats in plant pots, I will cut a handful for the girls and just be cautious.
When the birds get impacted crops, you have to remove the "plug" and from what I gather, its often a surgery that is expensive and/or one of those I don't want to do.
If you look under emergency's and illness, you will find a "impacted crop" for you to see what it intales.
Good luck- but in the mean time, lettuce, cucumber peelings and all those veggie peels are great for them. I also cook my potato peelings and left over cooked veggies with Oatmeal and left overs.
Hope I helped...oh, you can also sprout seeds, they love them!