I know I keep Primitive sheep which don't respond as well as more commercial breeds to bagged feed/nuts/cake/whatever, so are raised on grass, either fresh or as hay, with very little supplementary feeding, and then only when the snow is lying. They take up to 16 months to reach a size ready for slaughter - this is not a problem for us as we have plenty of grazing.
What disturbs me is the thought of raising a sheep, which is a ruminant, on large quantities of dried feed. Primitives which are grass reared are known to have high levels of CLA (Conjugated Linoleic Acid) which is good for humans to have in their diet (good fat), and this is thought to be a result of grass rearing. Similarly, cattle fed on concentrates with no fresh grass are more likely to carry pathogenic E.coli - causing disease in humans.
We raise most of our male sheep for meat for our own consumption so there's no way I would even want to stuff them with man-made feed. I want to be eating the healthiest meat I can, and small quantities are better for health.
Just saying