I quit adding any fat to burger about 10 years ago, and haven't missed it a bit. I trim all the deer/elk/antelope/caribou whatever fat off first, then grind the meat as lean as possible. Vacuum-seal and freeze, then when I get ready to cook it I add a couple of tablespoons of olive oil per burger, more or less, and mix it up, along with whatever seasonings I find appealing at the moment. They cook up nicely on my grills, inside or outside, and have no "domestic" flavors.
Dennis