I used to add pork fat to my venison, but the taste of burgers made from it wasn't what I wanted in a hamburger. I switched to using beef fat trimmings to end up with about a 10% fat content in the uncooked meat, and am very happy with the result. It is actually best to trim away most visible venison fat from the meat prior to grinding, as venison fat just isn't that tasty. As you know, the muscle itself has very little internal marbling, but there are areas with large fat deposits, especially in well fed deer.
