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Item Summer diets of sheep grazing spotted knapweed-infested foothill rangeland in Western Montana(Montana State University - Bozeman, College of Agriculture, 2005) Thrift, Brian Douglas; Chairperson, Graduate Committee: Jeffrey C. Mosley.Spotted knapweed (Centaurea biebersteinii DC.) is a perennial, invasive forb that infests millions of hectares of private and public rangelands in western North America. Previous research indicates that spotted knapweed is nutritious and readily grazed by domestic sheep (Ovis aries), but no studies have investigated prescription grazing of spotted knapweed within different levels of infestation or on a landscape scale. This twoyear study quantified the diets of a ewe-lamb band (n almost equals 800 ewes, 1120 lambs) that prescriptively grazed spotted knapweed-infested foothill rangeland in western Montana. Sheep grazed within light and moderate infestations of spotted knapweed (13% and 36% of vegetative composition, respectively) until perennial grasses were reduced to a 5 to 8- cm residual stubble height. Diets were estimated in mid-June and mid-July by clipping current year's standing crop immediately before and after grazing. Clipped samples were analyzed for CP, NDF, and ADF to estimate nutritive quality. Relative preference indices were calculated to evaluate diet selection by sheep. Sheep ate more spotted knapweed in moderate versus light infestations (64 vs. 26% of their diets, respectively; P<0.01), and spotted knapweed averaged 45% of sheep diets between June and July (P=0.61). Within light infestations, sheep ate fewer graminoids in June than July (17 vs. 55% of their diet, respectively; P<0.01). Sheep diets in moderate infestations averaged 33% graminoids regardless of month (P=0.18). Sheep did not select for graminoids in light infestations in June, but did select for spotted knapweed leaves in moderate infestations during July. Nutritive quality of sheep diets was similar to sheep grazing uninfested rangeland. Relative utilization of graminoids averaged 15%, except under exceptionally hot and dry weather conditions. Relative utilization of spotted knapweed averaged 45%. Previous research suggests that this level of spotted knapweed utilization may render herbicide application uneconomical. My results indicate that sheep can prescriptively graze moderate spotted knapweed infestations in either June or July, but to limit graminoid consumption, light infestations should be grazed in June vs. July.Item Providing supplement, with or without peg, to reduce the effects of cnicin and enhance grazing of spotted knapweed by sheep and cattle(Montana State University - Bozeman, College of Agriculture, 2006) Cheeseman, Melany; Chairperson, Graduate Committee: Bret E. Olson.Spotted knapweed (Centaurea maculosa Lam.), an invasive forb from Eurasia, infests over 1.7 million hectares in Montana and costs millions of dollars in forage losses each year. Some wildlife and livestock graze this species, however, most large herbivores, including cattle and horses, avoid spotted knapweed and prefer native plants. Some herbivores may avoid or reduce their intake of spotted knapweed because the plant contains cnicin. Cnicin is a bitter-tasting sesquiterpene lactone that may cause negative post-ingestive consequences in the rumen. If an appropriate supplement and/or antitoxicant can be identified that will reduce the negative post-ingestive effects of cnicin to rumen microbes, sheep and cattle may consume more spotted knapweed and grazing may help control this invasive species. I determined the effects of cnicin, rates of an anti-toxicant (polyethylene glycol), and a nutrient/energy supplement, with or without polyethylene glycol, on sheep and cattle rumen microbial activity, efficiency, and mass using a modified in vitro system. Sheep and cattle rumen microbes were negatively affected by cnicin. Polyethylene glycol, at the rates provided, had limited effects on sheep and cattle rumen microbial response to spotted knapweed plant parts. The nutrient/energy supplement, with or without polyethylene glycol, enhanced sheep and cattle rumen microbial efficiency. Because the nutrient/energy supplement may reduce some of the negative effects of cnicin on rumen microbes, sheep and cattle may consume more spotted knapweed in the field when provided with the supplement. I hypothesized that providing a nutrient/energy supplement, with or without polyethylene glycol, would increase sheep and cattle intake and time spent consuming spotted knapweed in a drylot, and in the field in July and August. Animal behaviors were recorded by focal animal sampling. Providing a nutrient/energy supplement, with or without polyethylene glycol, did not enhance sheep and cattle intake or time spent consuming spotted knapweed in a drylot, or in the field in July and August. Therefore, supplementing sheep and cattle with the nutrient/energy supplement, with or without polyethylene glycol, provided in these trials, may not be an appropriate method for managing the spread of spotted knapweed.