Winter can be hard on horses if the proper care is not given, and this means for equines stabled inside or outside.
Horses that are stalled all winter are usually clipped and will require blankets. The clipping is helpful for those equines that are ridden hard in the winter such as for fox hunting or indoor horse shows. They cool down quicker after a work out, but clipping also leaves them defenseless for the freezing temperatures.
Horses turned out full time in the winter should have adequate shelter such as a lean-to, as well as a daily check to make sure there are no health issues.
Water should not be iced up and there are many varieties of heaters for both buckets or outdoor troughs.
More hay should be fed to horses in the winter rather than more grain.
Remember, horses (like all animals) need four things to survive:
Water - fresh, clean and preferably room temperature.
Food - roughage for horses in the form of grass or hay is more important than grain.
Shelter - indoor stalls or outdoor (make sure there is room in an outdoor lean-to for all the pastured horses)
Exercise - often forgotten in the winter, exercise is important for those horses stalled 24/7 - either turned out daily in a paddock or ridden.
See these good articles on this topic at
http://www.evergreenequinevet.com/article28.htm
http://extension.psu.edu/animals/equine/news/2012/winter-care-for-your-horse
