This is my first winter with sheep and I will be keeping them locked up at night due to wolves and cougars. During the day I would like to put them in an ungrazed pasture with a shelter from the elements. Will they graze on the grass that is there or do I need to feed them in the snow? The grass is currently 1-2 feet tall and in some places 4-6 feet tall. I put hay in the barn at night when they come in but I want to ensure adequate nutrition thanks in advance