Research on Anderson and Scherzinger's hypothesis that spring cattle grazing can positively affect subsequent nutritional characteristics of grasses have generated mixed results. Our objectives were: 1) to evaluate fall/winter nutritional indices of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. & Smith), Idaho fescue (Festuca idahoensis Elmer), and bottlebrush squirreltail (Sitanion hystrix (Nutt.) Smith) in ungrazed, lightly grazed (33% utilization), or heavily grazed (69% utilization) pastures stocked with cattle at the boot stage of growth; and 2) to quantify opportunity costs of applying those treatments on fall standing crop. Compared with ungrazed stands, light and heavy spring grazing decreased September standing crop by 32 and 67%, respectively. September/December crude protein (CP) among heavily grazed grasses (x̄ = 6.9%) exceeded ungrazed controls (x̄ = 3.9%) for 11 of 12 comparisons. Crude protein of lightly grazed grasses (x̄ = 5.2%) was higher than ungrazed controls for 6 of 12 comparisons. Herbage was more nutritious during the drier of the 2 years sampled. Among grazed treatments, fall/winter CP measures were highest for bottlebrush squirreltail (x̄ = 7.4%), intermediate for Idaho fescue (5.9%), and lowest for bluebunch wheatgrass (0=4.9%). In fall/winter, herbage was most digestible in heavily grazed paddocks (x̄ = 59%), intermediate in lightly grazed paddocks (x̄ = 53%), and least digestible in ungrazed areas (x̄ = 49%). Light and heavy spring cattle grazing can augment fall/winter forage quality of bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail. Spring grazing reduces subsequent standing crop, but remaining forage will be nutritionally superior to herbage in ungrazed stands.
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Vol. 57 • No. 4