A Study Assessing Forage Quality and Desert Bighorn Sheep (Ovis Canadensis Nelsoni) Diet in Central Nevada Using Microhistology and Molecular Analysis

Desert bighorn sheep (Ovis canadensis nelsoni) populations in central Nevada have suffered from die-offs although biologists and wildlife managers have struggled to determine the exact cause of these population declines, making population management difficult. An important, often overlooked and under researched element of desert bighorn sheep health is diet and the quality of forage consumed. Using data collected in the Clan Alpine mountain range (a range that supports a population of healthy desert bighorn sheep in central Nevada), this research attempted to first, determine quality of collected forages (grass, shrubs and forbs) collected at five study sites in the range. Forage quality was compared between sites and seasons. Forage types collected were also compared between sites and seasons and correlated to forage quality data. Micro histological analysis and PCR analysis determined the frequency of forage types in desert bighorn sheep fecal samples collected throughout the Clan Alpines. Forage types found in fecal samples were compared seasonally and diversity indices were compared to sites of collection. In general, nutritive values and, with the exception of Selenium, mineral content met minimum domestic sheep nutrient requirements, although some variation was apparent. Collected forage did not vary between sites, but did vary seasonally. Grasses and forbs were collected more in summer than any season and less forage was collected in winter. Shrubs were collected consistently throughout the year. Grass occurred more often in fecal samples collected in spring than any other season according to microhistological analyses. Shrubs varied significantly in spring and winter. Not surprisingly, more forbs were observed in fecal samples collected in spring and summer. In order to compare sites of collection, diversity indices were calculated for project sites and for microhistological results. Diversity indices in both sites and microhistological samples declined in fall and winter. More forbs were determined using PCR analysis than any other forage type. The sample size for PCR analysis was small and significant variation between seasons was not quantifiable. However, it is suggested that because of PCR's ability to identify forage types at a more taxonomically specific level than microhistology (six sequences were identified to species), it was used in combination with microhistological analysis to further determine the diet of desert bighorn sheep. This preliminary data provides a baseline example of nutrition requirements and diet of desert bighorn sheep in the Clan Alpine range. Additionally, the variation in plant collection, nutrient values and mineral quality of forage, as well as the variety of forage types found in bighorn sheep fecal samples reminds managers and biologists alike that a diverse plant community is important for maintaining healthy bighorn sheep herds.