Generally when archery seasons begin out West, most monster mule deer will still be in the velvet stage of antler development. Many hunters want to preserve their velvet trophy, but are either not able to get it frozen and preserved or get it to a taxidermist in a timely manner. As a result, the velvet slips and they no longer have the ability to mount it with the velvet on. Here's what I've done over the years that's worked for me.
If you want to properly preserve velvet antlers IN THE FIELD, you will have to inject & brush them with formaldehyde and/or some of the new less toxic chemicals (Denatured alcohol, 4 in 1 solution,or Knobloch's antler in velvet tan). I personally prefer the 4 in 1 solution to Velvet Tan, as it was easier to use for me, however, all three will work. A very respected taxidermist whose specialty was velvet antlers taught me this technique.
First, (using rubber gloves and eye protection) take a razor blade and make small incisions at the tips of all points (less than 1/8"). Next hang the antlers upside down, allowing the blood to drain. Starting at the bases inject the solution into the veins (you'll see and feel them) that follow the antler. You will begin to see the solution "push" out blood towards the tips. Continue injecting the solution as you work the untreated blood towards the tips. When you reach the ends, make sure you've treated ALL the veins on each antler. You'll quit injecting solution when the color of the solution is the same coming out as it was going in. Once you think you're done, inject some more to make sure.
Allow the antlers to hang upside down overnight. After the solution/blood has stopped dripping out the ends, use a very fine painters brush and lightly brush the velvet with the solution. This will prevent bugs from entering the velvet that has no blood. After allowing the velvet to dry, lightly "brush" out the velvet to give it the natural uniform look. Remember; wear eye protection and gloves when using formaldehyde or any other chemicals. Slow down and don't be in a hurry to finish. If done correctly, your trophy should last forever.