One more note to add to this info... Cape your animal in the field and get the cape on ice.
Then you can actually milk most of the blood out of the veins toward the bases. You'll see the blood drain out of the base of the antlers. This is much more effective with the cape off so the blood can escape. Be careful if it's later in the year as the velvet becomes more delicate. In August you should have no worries though. I like to milk the horns dry, then inject them (alcohol works in a pinch by the way...), milk them, inject again and allow it to fully evaporate out on its own. And pay special attention to the rubbery tips. Inject these areas thoroughly. I prefer not to cut the tips because it creates an opening that can shrink and expose the hard antler tips when the horns dry. I like to keep the velvet as intact as possible.
Freeze drying produces great results for velvet preservation, but probably isn't necessary if you do them this way.
Coop