ORIGINAL: wyotimberghost
The butcher who grinds our meat adds cow fat as a percentage of the total weight of deer/elk meat we are grinding. I don't remember what percent of fat we add, but it's not enought to taste at all, and it's just enough to help the hamburger meat stick together well.
The usual ratio for burger is 3:1 venisonto beef fat , but can be as high as 30% beef fat . Try freezing your burgers before cooking them , they'll hold together much better .