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Transmission of infectious agents from livestock reservoirs has been hypothesized to cause respiratory disease outbreaks in bighorn sheep (Ovis canadensis), and land management policies intended to limit this transmission have proven controversial. This cross-sectional study compares the infectious agents present in multiple populations of bighorn sheep near to and distant from their interface with domestic sheep (O. aries) and domestic goat (Capra hircus) and provides critical baseline information needed for interpretations of cross-species transmission risks. Bighorn sheep and livestock shared exposure to Pasteurellaceae, viral, and endoparasite agents. In contrast, although the impact is uncertain, Mycoplasma sp. was isolated from livestock but not bighorn sheep. These results may be the result of historic cross-species transmission of agents that has resulted in a mosaic of endemic and exotic agents. Future work using longitudinal and multiple population comparisons is needed to rigorously establish the risk of outbreaks from cross-species transmission of infectious agents.

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Targeted grazing by sheep or goats is a potentially useful tool for suppressing the noxious weed sulfur cinquefoil (Potentilla recta L.). However, possible transmission of weed seeds by grazing livestock is a serious ecological concern that must be addressed in any targeted grazing prescription. We investigated the effect of sheep and goat digestion on the viability of sulfur cinquefoil seeds collected from live plants growing on a foothill rangeland site in southwestern Montana. Eight sheep and eight goats (all wethers) were each gavaged with 5 000 sulfur cinquefoil seeds. Four animals of each species received immature seeds, and four animals received mature seeds. All animals were fed ground grass hay in excess daily, and intake averaged 2.0% body weight Á d À1. Total fecal collection began immediately after gavaging and continued for 7 consecutive days. Once each day, all identifiable sulfur cinquefoil seeds were recovered and counted from fecal subsamples. Seed viability before gavaging averaged 36% for immature seeds and 76% for mature seeds. Sheep and goats excreted similar numbers of viable seeds. Almost all (98%) of the viable seeds recovered from sheep and goats were excreted during Day 1 and Day 2 after gavaging. No viable seeds were recovered from either sheep or goats after Day 3. Our estimates of sulfur cinquefoil seed excretion and viability in sheep and goat feces are likely inflated compared with targeted grazing animals because gavaging with seeds bypassed mastication. Grazing livestock that consume sulfur cinquefoil seeds should be kept in a corral for at least 3 d to prevent transferring viable seeds to uninfested areas.