Approximately two million sheep graze the native ranges of Utah each year. These animals are on the range most of the year and their food supply must come from range plants as they are normally selected. The nutritive value of range forage is often borderline or deficient in essential nutrients, yet, sufficiently adequate to prevent obvious physiological disorders. These mild deficiencies may affect the productive efficiency of the animal even though no symptoms are apparent.
Cook, C. Wayne and Harris, Lorin E., "Bulletin No. 342 - The Nutritive Content of the Grazing Sheep's Diet on Summer and Winter Ranges of Utah" (1950). UAES Bulletins. Paper 303.