|Vavra, Martin - OREGON STATE UNIV|
Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2003
Publication Date: July 1, 2004
Citation: Ganskopp, D.C., Svejcar, A.J., Vavra, M. 2004. Livestock forage conditioning: bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail. Journal of Range Management. 57:384-392. Interpretive Summary: Bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail are 3 of the most prominent grasses on rangelands in the intermountain west. When these grasses cease growing in the middle of the summer, their nutritional value has declined to such a degree that foraging cattle and wildlife will begin losing weight. Our objective was to use grazing beef cattle as a tool to elevate late season forage quality among these grasses. Light spring grazing by cattle reduced fall forage supplies by 32 percent and heavier cattle grazing decreased fall standing crops by about 67 percent. The remaining forage, however, was of superior quality compared to the same grasses in ungrazed stands. Protein content of ungrazed grasses was about 4 percent, lightly grazed grasses about 5 percent, and heavily grazed grasses about 7 percent. Assays of fall/winter digestibility found herbage most digestible in heavily grazed pastures (mean = 59 percent, intermediate in lightly grazed pastures (mean = 53 percent) and least among ungrazed pastures (mean = 49 percent. Among the 3 grasses tested, bottlebrush squirreltail averaged 7.5 percent crude protein in the fall, Idaho fescue about 6 percent, and bluebunch wheatgrass about 5 percent. This suggested that bluebunch wheatgrass might be the most difficult of the 3 to successfully condition with livestock grazing and bottlebrush squirreltail the easiest. While these findings reveal that spring livestock grazing may decrease fall forage supplies by 32 to 67 percent, they establish that ranchers or range managers can use cattle grazing as a tool to elevate the nutritive value of fall forages in their pastures. This study will help ranchers and pasture and wildlife managers develop grazing programs that furnish higher quality forage for later use in the fall and winter.
Technical Abstract: We tested the hypothesis that spring cattle grazing may be used to positively affect subsequent fall/winter nutritional characteristics of 3 grasses. Our objectives were: 1)to evaluate fall and winter nutritional indices of bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail that were ungrazed, lightly grazed, or heavily grazed by cattle during the spring boot-stage of growth; and 2)to quantify the opportunity costs of applying these treatments on fall standing crops. Compared to ungrazed stands, light and heavy spring cattle grazing reduced September standing crop by 32 and 67 percent, respectively. For September and December periods, crude protein among heavily grazed grasses exceeded ungrazed controls (mean=3.9 percent) for 11 of 12 comparisons. The CP of lightly grazed grasses (mean=5.2 percent) were higher (P<0.05) than ungrazed controls for 6 of 12 comparisons. Among grazed treatments, fall/winter CP measures were highest for bottlebrush squirreltail (mean=7.4 percent), intermediate for Idaho fescue (5.9 percent), and lowest for bluebunch wheatgrass (mean=4.9 percent). This suggested bluebunch wheatgrass might be the most difficult of the 3 grasses sampled to successfully condition with livestock grazing. Fall/winter NDF values were 68.5, 66.6, and 63.2 percent, respectively, among ungrazed, lightly grazed, and heavily grazed treatments Assays of fall/winter IVOMD suggested herbage was most digestible in heavily grazed paddocks (mean=59 percent), intermediate in lightly grazed paddocks (mean=53 percent), and least digestible in ungrazed areas (mean=49 percent). This study establishes that grazing during the boot stage of development can augment fall and winter forage quality among bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail.