It can spoil that quickly. As stated above, on an animal that size, get it dressed, quartered, skinned, and hung so the air can circulate. I had a friend kill and elk up the Snake river canyon a few years ago. He did a good job field dressing it. It was cool when he left it with some rain. By morning there were several inches of snow so the air was cool. We hiked up and started boning it out to pack. This is getting unto 12 hours after the animal died. The meat around the hip joints was still fairly hot. The meat on that animal turned out okay, but you want to get meat cooled all the way through or you risk souring.