I use pork back fat for mine. You can pick it up at the meat markets here pretty cheap and it grinds nice. Most of the sausage I make I will add 20% fat to 80% venison. Some recipies call for a little more. Just experiment and have fun. I have yet to make any myself that I didn't eat however I did have the processor make some and it was terrible. That would be why I process all my families deer myself now. They just would not get enough of the deer fat out of it and would not get around to processing in time IMO