Note these 2 babies striping the leaves off of the weeds in preference to nibbling on grass. In some cases, weeds with their deep tap roots are considered to have more nutrients/minerals because they are pulling them up from the subsoil. Doesn't matter --- sheep will graze brambles, brush, and weeds in preference to straight grass.
Here's a history lesson regarding multiflora rose. It was once promoted by the various conservation agencies as a natural "living fence" and as a shelter plant for birds and wildlife. Louis Bromfield in his noted book, Malabar Farm, spent a page or two extolling the virtues of multiflora rose. He planned, as time permitted, to plant it on both sides of his fencelines so that by the time that the wire failed, a living fence capable of "turning cattle" woud be well established! Aaacckkkk! Hard to believe in retrospect. Other than that interlude, I LOVE the book!