This picture shows our white mare trotting through the snow in our back pasture after a snow fall in December of the 2006. Our horses were happy to get turned outing and played happily in the soft fetlock seep snow. Notice our Chestnut mare, Lucy, following close behind!
Some types of snow are perfectly safe to turn a horse out on- it provides a soft bust somewhat supportive footing. On other types of snow, horses should not be allowed out, because the danger of slipping is too great. Generally ice or hard frozen snow on top of mud provides unsafe footing for horse turnout or riding, but soft snow covering footing that is safe and well drained is fine to ride on or allow horses to play on. Be careful and watch areas around troughs and stock tanks, and this area can be dangerous- particularly if it is trampled and partially thawed in the day, and frozen again overnight.