Thank you. I tried Google first too and it was not helpful.I did a quick Google Search and after a few unsatisfying results thought to look up Maria Hall who worked extensively with Blue Jersey Giants back when they first gained in popularity. She's very knowledgeable, and in her FAQ pages I found this...
"We feed 18% Protein Chick starter for first 2 months. We feed 16% layer feed which contains corn, oyster shells, layer supplement when the birds are of laying age. We do not know the actual formula that is used on the 16% layer. It is highly important for a person not to just feed scratch grains and/or cracked corn as a sole food as the protein level is only 8 to 10% and does not meet the nutritional needs of a Jersey Giant. When a bird free ranges this does provide additional possibilities for increased protein levels by eating grasshoppers and such."
You can see the rest of her website here:
Thank you. I tried Google first too and it was not helpful.