Mucking out is ok left until the spring if you have mechanical means of doing it. Otherwise I do it once a week. Straw on shavings. Personally I find sheep beds left for a while compact down and really hard to move with a fork.
Agreed - if you are talking about keeping sheep inside on a commercial scale.
But we are talking about 4 sheep in a stable!
If you leave it till spring you will find that the bottom layers have started to rot down and stay moist and friable.
If you keep the bedding damp for a while after the sheep have gone back outside, it will rot down with considerable steam and heat like a compost heap and will reduce in volume as it rots down, to about a quarter. With only 4 sheep the resultant reduced compost is not unsurmountable to remove with a wheelbarrow. In addition, the heat generated in rotting down should effectively destroy any malignant bacteria.