1) Groom as little as possible
Why-If the horse isn't working hard, it's important not to remove its waxy, protective coating next to the skin. That layer helps keep them warm and waterproof in the cold, wet months of winter.
2) When it gets colder, feed more
Why-The colder it gets the higher the horse's energy requirement is to maintain its body temperature. Feed more with grass hay as opposed to more grain to reduce the risk of colic.
3) Have a plan for your manure
Why-If you have several horses and each one is producing about 50lbs of manure a day, you need definitely need a plan. Determine whether you'll be collecting and then spreading your manure or whether you'll create a compost. It has to go somewhere to keep down flies and keep your horses' living area clean and healthy.
4) Monitor water supply
Why-The cold mountain weather can often get below zero at night. Whether your water comes from a spring or whether you have to fill a trough, it's important to have a constant supply of fresh, unfrozen water for your horses.
5) Check horses for condition and injuries daily
Why-Self-explanatory. Weight loss is important to catch early. Injuries need to be addressed as soon as possible.
6) Facility/barn/tack/pasture maintenance
Why-Rail and fence maintenance, tack cleaning and stall cleaning all help to keep you and your animals safe.
7) Watch your weather
Why-Colorado weather is completely unpredictable. If you feed with big hay bales, you'll want to plan ahead of a snowstorm. You'll also need to plan your plowing so the spring melt flows into the areas you want.
For more great tips and a month-by-month guide for taking care of your horses, check out Cherry Hill's Horsekeeping Almanac and blog.