Actually collagen rendered commercially from hooves, bones and hide is very nutritious. Chicken soup from boiled bones is tasty and nutritious, for example.When McDonalds says "100% beef" they mean it - fur, hooves, bones and all.
The actual meat may not be bad but it’s preparation may be so. Somewhat like school lunch cafeterias tend to suck.

The Truth About McDonald's Meat - Mashed
Considering that McDonald's sells more hamburgers than anybody else on the planet, it's not surprising that their beef gets a lot of attention. Unsettling rumors aside, one still has to wonder just how McDonald's goes about handling its meat.