As the cold settles in be sure to check your horses blankets, straps get broken, horses sometimes try eating their paddock mates clothes, shoulders get rubbed or they just get grungy.  The footing is starting to get slippery with the snow so the horses may not be running around as much outside. You may want to lunge them before you ride or if the arena is empty let then blow off a little steam and play in the soft footing.