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¹ Wildlife Science Group, University of Washington, Box 352100, Seattle, Washington 98195 USA;
² Department of Fisheries and Wildlife Sciences, University of Missouri, 302 Natural Resources Building, Columbia, Missouri 65211 USA;
³ Custer State Park, HC 83 Box 70, Custer, South Dakota 57730 USA
⁵ Corresponding author (email: EGoldstein{at}state.nm.us)

ABSTRACT:   Most wild Rocky Mountain big-horn sheep (Ovis canadensis canadensis) in northern latitudes are infected with lungworms. Indirect effects of lungworms on bighorn sheep are unknown, but high pulmonary burdens might increase stress (i.e., elevated glucocorticoid levels), and chronic stress could in turn decrease fitness. We hypothesized that high lungworm burdens in Rocky Mountain bighorn ewes increase stress, thereby increasing lamb mortality. To test our hypothesis, one subherd of bighorn sheep in Custer State Park, South Dakota was provided a free-choice loose mineral mix containing the anthelmintic fenbendazole every six weeks from March 1999 to August 2000 to eliminate lungworms; another subherd served as the control. Daily, individually marked ewes were located telemetrically from the ground and uniquely marked animals were observed until they defecated. After the herd moved from the area, fecal samples were collected and stored at –23 C. A consistent number of samples per season per herd ( =16.56±3.99 samples) were collected. Fecal larval lungworm levels (LPG) in the treatment subherd were lower than levels in the control subherd; however, there was no difference in fecal glucocorticoid metabolite (FGM) levels between the two subherds. Fecal glucocorticoid metabolite levels varied by season in both subherds, with levels in winter lower than during the other three seasons. Lamb:ewe ratios were not different between the control and treatment subherds at the end of summer 1999. In contrast, the treatment group had a lower lamb:ewe ratio at the end of summer 2000 despite having lower LPG. However, this result was attributed to lower ewe production, not lower lamb survival. The LPG levels were not correlated with FGM concentrations; instead, FGM levels might reflect normal seasonal patterns. Other factors, including contagious ecthyma, were more important for determining lamb mortality than LPG and FGM levels during our study. We suggest further experimental work over a longer duration to address these relationships.
  Key words:  Bighorn sheep, fecal corticosterone, glucocorticoid metabolites, lamb recruitment, lungworm, South Dakota, stress.

⁴ Present address: New Mexico Department of Game and Fish, 1 Wildlife Way, Santa Fe, New Mexico 87507 USA;

This article has been cited by other articles:

				J. D. Rogerson, W. S. Fairbanks, and L. Cornicelli ECOLOGY OF GASTROPOD AND BIGHORN SHEEP HOSTS OF LUNGWORM ON ISOLATED, SEMIARID MOUNTAIN RANGES IN UTAH, USA J. Wildl. Dis., January 1, 2008; 44(1): 28 - 44. [Abstract] [Full Text] [PDF]