My chickens get pretty much anything leftover in the kitchen (that the dogs won't eat first). Occasionally there is something they don't much care for, and since they are pretty well fed, overall, they aren't inclined to eat anything that they don't consider acceptable. I don't throw them onions/garlic because I don't want the eggs tainted with that flavor !
Chickens are opportunists. They eat a huge variety of things, including each other, as disgusting as that may seem to us. So feeding them small quantities of leftover meat (any kind), is acceptable.
As to mad cow disease ... think of it this way: if a horse/cow/sheep/goat died in the pasture, no matter HOW hungry the remaining horses/cows/sheep/goats would be, they would not eat it. They would also starve to death. So when we 'formulate' some food to feed back to these animals it is TOTALLY unnatural. If a chicken dies in a flock, if left there, the other chickens would soon devour it, and that is normal.
This also holds true with feline. For centuries, cats were used to control rodents in grain bins, because they never ate the grain, only the rodents. Now we formulate feed to 'trick' them into eating grains. Now domestic house cats often end up with urinary, kidney, and other problems associated with their unnatural diet. Dogs are a little more tolerant. While they prefer meat, they will naturally eat some vegetable/grain matter, though not much as much as some commercial foods provide.
Commercially, we want to feed meat to cows and grain to cats! Isn't that just plain silly?
