Livestock Parasite Management on High-Elevation Rangelands: Ecological Interactions of Climate, Habitat, and Wildlife

Livestock parasitism on high-elevation rangeland (>1,800 m (6,000')) may not be as well documented as parasitism is at lower elevations because producers assume elevation limits parasite persistence and exposure of livestock to parasites. Certain parasites, such as horn flies, Haematobia irritans (L.) (Diptera: Muscidae), and biting midges, Culicoides spp. (Diptera: Ceratopogonidae), a vector of bluetongue virus, are restricted to lower elevations. However, some parasites are endemic to high elevations, such as the Rocky Mountain wood tick, Dermacentor andersoni (Stiles) (Acari: Ixodidae), a vector of many diseases. Multiple horse fly and mosquito species persist at various elevation gradients, with some having preference for lower or higher elevations. For example, the horse fly, Hybomitra laticornis (Hine) (Diptera: Tabanidae), occurred from 1,700-3,035 m (5,577'-9,957'), Hybomitra phaenops (Osten Sacken) (Diptera: Tabanidae) only occurred above 2,499 m (8,198'), and the western horse fly, Tabanus punctifer (Osten Sacken) (Diptera: Tabanidae), only occurred below 2,250 m (7,381'). This variable elevation range is also expressed by several mosquito species, with six of 12 known mosquito species that transmit West Nile virus at or above 1,750 m (5,740'). Furthermore, gastrointestinal roundworms can survive >1 yr at high elevations, use larvae inhibition to survive winter, and lungworm infection may increase with elevation. Evidence suggests changing weather patterns, climate variability, and animal movements could shift some parasites and diseases into higher elevations, such as mosquitoes and biting midges. Moving livestock to high-elevation ranges may also increase the opportunity for livestock-wildlife interactions, parasite and disease transmission, and exposure. Producers should develop high-elevation integrated pest management strategies, such as delaying or avoiding parasite treatment to optimize efficacy and reduce input costs, monitoring closely during wet years and periods of livestock-wildlife interactions, using elevation to avoid certain parasites, and not assuming that elevation is capable of preventing livestock parasitism.