Let's just say it's a point of debate. People with soy allergies seek out soy free products and it's an alternative marketing avenue which we small farmers can persue.
With that said, I have no idea the methodology by which a chicken would eat soy meal and have it passed along intact to an egg...
There are as many feed formulas as there are grains out there. You just use whatever is cheapest that month when you are milling & mixing. The protein is then coming from seed meals, which will also vary depending on where you live. Where I am, soybean, linseed, rapeseed and sometimes...