Controlled evaluation of ivermectin in Shetland ponies.

Ivermectin was injected IM into 12 yearling Shetland ponies. The following reactions in percentages of parasites recovered from ponies given 200 microgram/kg or 300 microgram/kg, as compared with the parasitic population in those given the vehicle at 1 week after injection, were as follows: Otobius megnini nymphs--no reduction; Gasterophilus intestinalis--100% and 99.9%; G nasalis--100% and 99.9%; Parascaris equorum adults--100% and 96%; Strongylus vulgaris adults--100% and 100%; S edentatus adults--100% and 100%; cyathostome adults of the genera Gyalocephalus, Cylicocyclus, Cyathostomum, Cylicostephanus, and Poteriostomum--99.9% and 100%; 4th-stage larvae--97.3% and 96.8%; Oesophagodontus robustus adults--100% and 100%; Triodontophorus spp--adults--100% and 100%, 4th-stage larvae--95.1% and 100%; and Oxyuris equi adult males--66.7% and 77.7%, adult females--96.5% and 100%, and 4th-stage larvae--94.1% and 96.9%. Other parasites encountered were too few in number to estimate drug efficacy.