My Shetland do NOT get any hard feed in winter - except if a) they are in lamb AND b )the snow cover is too thick for them to scratch through it. From Xmas onwards (or earlier if really cold spell) I fill hayracks in the morning, and do not refill until next morning. They will usually still graze well. I will feed pregnant ewes in the last 4 weeks before lambing, but not huge amounts. Non-breeding animals don't get any hard feed - at all (except when I need to catch them for any treatment)
Last winter my lot went through about a small bale per day (around 40 sheep). I did not need to give any hard feed as we really did not have any snow.
They all lambed easily outside in mid-April, and I sold some shearlings at market for quite a good prize in the summer.
But I normally have quite ok grass.