Nutrition of Sheep Grazing Crested Wheatgrass Versus Crested Wheatgrass-Shrub Pastures During Winter

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