Reading the back of a carton of Davis Gelatine it says: Gelatine derived from New Zealand Beef Skin, Perservative 220. -sounds like hide glue to me
In my experience, Davis Gelatine works just as well as Knox, and both work at least as well as hide glue (and smell better).
I have tried to make glue from ground up hooves, maybe I was doing something wrong, but all i got was dirty scummy water
james