I think cooler weather is just more comfortable for them, with a standing body temp at 100 degrees plus (101.3 iirc) Much movement at the body temp rises (why I'm a believer in gutting, or quarter ASAP). When it is real cold, I think they balance extra movement to raise their temps, but forage for high energy with minimal effort diets. Ever notice young deer on a cool am, or pm run and play? cool weather and they feel "frisky".
This is the main benefit to whole corn (good quality with no cracks). IIRC from a class I took years ago at UoG, each whole un-cracked, quality kernel of corn, has the equivalent of 1 BTU of energy, if the shell is breached, that energy is released. Corn is also harder on a deer's gut and it takes a little time for their system to adjust to it and is why they recommended feeding it in small amounts year round.
“Never be afraid to try something new, or diy. Remember, amateurs built the Ark, professionals built the Titanic”
Friends don't let Friends drink and post.......
The first 5 day's after the weekend, are the hardest....