I think it's real. There is the obvious scapula moving with each step, but slow it down to half speed and look at the back half of the wound on the bottom flap of skin. You can see the edge rolling over and bouncing/trembling. That is some real attention to detail if it's a fake and it just looks TOO good. Even movies with multi million dollar budgets don't do CGI injuries that good. A practical effect artist could make something that good but good luck getting the deer to hold still. Remember also that we don't know how long it had been or how far it went after the injury. For all we know it had just been injured a short ways away and fell dead a short time later. A buck could definitely make it farther than you think with horrific injuries.