There is no known mad chicken disease lol so no worries on that count!! With the mad cow disease...the whole thing is cos cows are NOT designed to ingest animal protein. They are pure herbivore. It's rare you see a cow ordering a burger you know? They would rather graze. It was never ever meant for cows to be eating feed added with animal protein.
Chickens are NOT vegetarian/herbivore...they are omnivores by design. They can deal with the animal protein better than any cow could.
Mine eat left over chicken all the time. as well as beef/pork/turkey/fish etc scraps we have hanging around. The only time I wouldn't give it to them is if it was highly seasoned or salty <ie no bacon/sausage etc> because they don't do well with higher salt levels.
I have said this before and will say it again: My grandad used to say..."Leave a dead cow in a field and the others will be as far as they can from it. Leave a dead chicken in the area and the others will come racing out with a fork and knife in each wing and a napkin round its neck ringing a dinner bell." Or something to that effect lol
I have seen an entire flock of chickens running as fast as their little feets would carry them across the pasture to get to a dead deer some poacher left. They eat frogs/birds/worms/rats/snakes/mice/carrion etc that they find. They will even kill their own chicks and I have seen them eating them as well. I have even seen them working on the chicken carcass of one of their flockmates that had been killed and remains left. That was a bit sad I have to say. Many people have seen their flock gather round at slaughter time and seeing them chickens go nuts over the bits that are dropped from it...chicken, pig, etc
I remember as a little girl laughing hysterically seeing my grandad's big rooster stealing a chicken leg fresh off the BBQ and running like heck with Grandma chasing after him. lol
But really, I have never seen any chickens fed meat that had issues from eating it. IMHO feel free to give them meat scraps etc etc, raw or cooked. I prefer cooked myself, but they don't seem to mind here how they get it.
I give my girls the hambones, leftover thanksgiving turkey carcass, and basically anything that needs to go - scraps, you name it.
They will pick the bones clean in record time.
Their favorite leftovers though, are spaghetti and ... chicken .... go figure.
We feed our pug the raw diet. At times, we'll get something that she doesn't like, and we'll feed that to the chickens. Perfect example...beef liver. I keep some in the freezer that my dog turned down, and feed it to them on hot days, as a treat. Very high protein and they eat it just as it's starting to thaw, but still very cold, and they go nuts for it.