Continuing on the theme of what animals do to survive winter cold, it can be just as much of a problem being large as being small in intensely cold weather.
When you are big-bodied, there are few places to take refuge from cold temperatures and wind chill, which increases the rate of heat lost to the cold environment. In addition, large-bodied animals would need a large amount of food per day to maintain a warm temperature, and winter is typically the most difficult season in which to find it.
Their heavy winter coats insulate their core, but lots of surface area of exposed extremities could be vulnerable to high heat loss. At sub-zero F air temperatures, even large-bodied deer will have to expend energy to stay warm. Daily food consumption is too meager to support that expense, so deer have to dip into the fat reserves they built up in the fall eating energy-rich foods like acorns.
The White-tailed Deer strategy for surviving winter cold is a conservative one — reduce energy expenditures to conserve body fat. They let their extremities chill to the same temperature as their environment, so little heat is lost there. They eat snow (for moisture), which lowers their core temperature and heart rate, and thus their whole-body metabolism. They reduce their daily activity, spending less time foraging, which also saves some energy. In short, deer coast through the winter relying on their fat reserves, hoping for an early spring (don’t we all!).