http://edis.ifas.ufl.edu/pdffiles/PS/PS04700.PDF
Each of our states has an Agricultural division, the one above comes from Florida.
The one below is from Oregon.
Hope these help
http://extension.oregonstate.edu/catalog/pdf/pnw/pnw477.pdf
Maybe you can get your vet to come to the BYC page
My chickens also are free range and do not over eat. Sometimes my daughter will give them extra feed because she like to pet them when they come to eat. If I have recently fed them, they will not come and eat again.
Maybe we can find you some...