Considerations for the control of equine cyathostomes in arid areas.

Internal parasites of horses are ubiquitous but that does not suppose that the level of infection does not vary with climatic conditions. Climate determines the limits of where a parasite species can survive the external environment and weather determines the transmission pattern within the climatic bounds [Levine, N.D., 1963. Adv. Vet. Sci. 8, 215-261]. Arid areas have a more limited exposure potential to important parasites but the level of exposure can nonetheless lead to disease. It must be remembered that, even in arid areas, it does rain and irrigation, overflow from water troughs, dew dripping off buildings and on the vegetation can also provide the medium to allow escape of larval cyathostomes from feces to forage. How horses earn their living is most important in determining the level of exposure to cyathostomes. Recreational grazing, which surely does more for the soul of the owner than for the nutrition of the horse, almost absolutely insures that horses will encounter larvae. To be certain, in arid areas there may be an opportunity for horses to spatially separate grazing and dunging areas but not all horses are so disposed, and even if they are they may not be able to do so.