You can add pork fat but I usually add pork ,such as pork shoulder that has a fair amount of fat in it.You really have to do it to your taste and that goes for spices too.My favorite is 1/2 venison, 1/2 pork,salt ,pepper,nutmeg. There are various grinders available .For typical home use a hand grinder or better a grinding attachment for a Kitchen-Aid mixer.

When you make ground deer do you add anything to it to make it a little less lean and easier to cook, Maybe some pork or fatty hamburger?