Anyone please tell me why soy is bad for chickens. Thank you.
Beats me! 10-15 years ago, soybeans were magic beans, and presented as being far better at being meat than meat ever was. Now they're the devil.
Me, I always figured that they're just beans, and about as interesting as beans ever are (not very), and about as much like meat as beans can be (not much). To use soybeans as a meat substitute in chicken feed, you have to add about a zillion other ingredients to make up for soy's innumerable deficiencies vis-a-vis meat. People do this because meat's expensive, so it pays to jump through all the hoops.
At the same time, the commodity poultry industry has wonderful hatchability with soybean-based rations. The most sensitive test of any diet is whether adult animals given it produce healthy offspring, so as far as I can tell, the early warning signs of an inferior feed just aren't there.
Back in the old days, meat byproducts like steamed beef scrap and meat-and-bone meal of high quality were affordable. These had all the balanced protein and all the minerals (except enough calcium for hens in full lay) a chicken needed. Feed rations were simple then. But meat byproducts cost a fortune now. It takes a complex spreadsheet to create a balanced ration that people can afford.
My best guess about all this stuff is that people take the nutrition fads that are intended to make humans live forever, and apply them to short-lived livestock.
I mean, suppose my hens were all chain smokers, spending all their time rolling and smoking cigarettes out behind the barn. Presumably, in fifty years or so, some would develop lung cancer. But in the 2-3 years they actually live, what would be the effect on their eggs? I don't know, but I'd bet that eating the eggs of a chain-smoking chicken is in no way comparable to being a chain-smoker yourself. Not that someone wouldn't try to make a buck-buck-buck out of the false parallel.