I have always hear aprox 50% of live weight. Here is what a butcher link says:

With an average market (live or on hoof) weight of 1,150 lbs and the average yield of 62.2%, the typical steer will produce a 715 lb. (dressed weight) carcass.

The dressed beef (or carcass) will yield approximately 569 lbs. (further details below) of red meat and trim (take home meat - which includes the average weight of 27 lbs of variety meat: liver, heart, tongue, tripe, sweetbreads and brains) and 146 lbs of fat, bone and loss. This is roughly a yield of 80% from the dressed or hanging weight - this is for a VERY LEAN Beef. A High Quality, USDA Choice Beef will yield approximately 70% of the Hanging or Dressed Weight. The yield on the take home meat weight from the live weight of the (VERY LEAN) steer is approximately 50%.

However, that is for grain fed beef. On deer/elk on native range that may not be quite as fat, you can probably figure slightly less than that.