My buddy killed a bull in Colorado a few years ago on our November deer hunt. Temps were into the single digits at night. It was a bad 6 miles out and required multiple trips. We figured it was plenty cold, so to keep the meat from freezing we left the hide on but gutted and propped himopen, then skinned as we boned out. The next day on our second trip, we rolled him over to bone out the other side and that ground side had bone sour started in the hind quarter. Lesson learned. It's never cold enough
I had a different experience in almost the same situation. Colorado, November, freezing temps at night probably 40 or so during the day.
I was 7 miles in when I killed the bull. I came into this canyon from a different one and never had hunted it before. I knew a road was 3-4 miles away at the mouth to this canyon so I told my dad to wait for me there. I got both quarters off one side boned and in my game bags. It was starting to get dark, the area has lots of cliffs and since I had never been down this canyon before I loaded the front and hind quarter and headed out right before dark. Turned out to not be to bad of a pack. The next day my dad and I hunted our way into the canyon the same way as I did the day before and we finished cutting up that elk about mid morning. There was no spoilage on that bull. And it rested on the on side over night with the bone in.
It's funny how some people get spoilage and some don't.
We've also hung quarters overnight bone in and not had a problem in warmer temps. Maybe some bulls just have more bacteria in them or something?