Well, you said "fermentation" and all I could think of was "wine".... shows where MY brain is.
You are not going to find any molecular biologists on here to debate this, I don't think, LOL....but it is my utterly unscientific, totally idiosyncratic hunch (is that enough qualifiers?) that it has to do with the individual animal, much as it has to do with the individual human in a shooting.
There are a zillion variables here. Is the animal ill? Has it just been bred? Does it have CWD? WHERE was it hit when it was shot? How old is it? I just saw a show on one of the outdoor channels this evening in which somebody shot a deer and it ran, but it was clear from the moment of the shot that it was a fatal injury (deer jumped up, hunched up, white tail showing). It ran off a six-foot overhand into a gully and there was found dead. The shot was a killing shot. When they found the animal, they realized it had been injured fighting and had a broken jaw (not acquired in the fall or the shoot) and it would have died that winter even if it had not been shot by the hunter. It ran. Did the pain it was already in have anything to do with it? I don't know.
Scientifically, I don't think you could tease out enough of those variables to be able to say with any certainty what's going on there. Apart from shooting twin deer who have literally had identical food, health care, etc., and seeing if they react the same, I can't imagine how to even begin to prove your hypothesis.
With humans there is always the possibility that media have "taught" a shooting victim that they are "supposed to" fall down if shot. But sometimes people who have been shot don't even realize they HAVE been! Is it possible that a deer may not recognize it's been shot until it "piles up" where it stands?
You've certainly raised an interesting question, and if y'all figure out a way to research this, I hope we get to find out the results!
Springmom