The part about the skin is true. You can do it on a lot of animals, but horses it is really easy to see the results. Well hydrated skin will snap back quickly. You should also test for capillary refill time, etc.
I believe Cribbing and Weaving are learned. They result from boredom. Not sure how much FACT this is though.
Most grey horses are stalled most of their life, due to increased risks of cancer, sunburn etc from hot weather
( heard this from a friend, but grey horses, usually have black skin,not pink skin. So I don't believe that this is true,it is cruel)
I thought mud fever was scratches, that has nothing to do with the hoof. I've actually had a horse with no socks get bad scatches. Like real bad, he had them for 5 years if he hadnt died he probably would have still had them. He would go on antibiotics for injuries and the scatches didnt seem to be effected by it.