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Grazing sheep on improved pastures during winter offers an economically attractive alternative to supplementation in sage-brush steppe ecosystems. We studied diet selection and nutrition of sheep grazing in crested wheatgrass (Agropyron desertorum) and crested wheatgrass-shrub (Kochia prostrata, Atriplex canescens, Purshia tridentata, Artemisia tridentata, Chrysothamnus nauseosus, Ceratoides lanata) pastures during early-January (period 1), mid-January (period 2), and late-January (period 3). Diet selection by esophageally fistulated sheep differed during each of the 3 periods because the amount of available forage changed with snow depth, trampling, and utilization. Sheep grazing crested wheatgrass (CW) pastures consumed diets that were about 55% mature grass and 45% green vegetative growth during periods 1 and 2, and 93% mature grass and 7% green vegetative growth during period 3. Sheep grazing crested wheatgrass-shrub (CWS) pastures consumed diets that were about one-half grass and one-half shrub during all periods. Organic matter intake (g kg BW ^ -.075), determined from total fecal output and in vitro digestibility estimates, were higher (P = 0.036) for sheep grazing CWS pastures than for sheep grazing CW pastures during periods 1 (38 vs. 28) and 3 (31 vs. 27), but were similar (P<0.10) during period 2 (28 vs. 26). Diets of sheep grazing CWS pastures contained more (P = 0.002) crude protein (%) than diets of sheep grazing CW pastures during periods 1 (9.0 vs. 5.8), 2 (7.3 vs. 6.6), and 3 (7.9 vs. 4.6). In vitro organic matter digestibilities (%) of diets of sheep in CW and CWS pastures were similar during period 1 (45 vs. 48), but higher (P = 0.001) for sheep grazing in CW pastures during periods 2 (46 vs. 29) and 3 (32 vs. 24). We stocked pastures heavily to accentuate differences between sheep diets in CW and CWS pastures during period 1-3; we believe results from period 1 best represent the potential nutritional benefits of shrubs on snowy winter ranges. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020