I haven't looked into it lately, but I remember MuscleMeds using collagen in their Carnivor RTD's. Collagen can be any damn thing/part of an animal, like hooves, ears, nose, etc. It's the most common and abundant biological tissue in mammals, and often an inferior source of protein.
On the other hand, I've always had good luck with Optimum Nutrition products. I haven't bought too much from them since Costello sold the company, but if I had to choose...
