Sheep nuts are high in protein and can be too large for some breeds, and too rough on the teeth for elderly ladies, which need to keep their teeth for up to 20 years. We do feed a little to the old dears when snow is lying, but we use coarse mix which is lower in protein than nuts, much more interesting for them to pick around in, but still rattles encouragingly in a bucket.
Many breeds of sheep, not just the primitives, like to browse as well as to graze, and they take in natural minerals and trace elements from eating bark and leaves of plants such as willow, fruit tree prunings, cow parsley and various non-toxic trees. One of the many advantages of using browse to supplement grass, and in stead of nuts, is that it keeps the sheep occupied while being no higher in calories than grass.