Critical tests of the antiparasitic activity of thiabendazole and trichlorfon sequentially administered to horses via stomach tube.

Thirteen critical tests were conducted in horses naturally infected with helminths and bots. Single doses of thiabendazole (44 mg/kg of body weight) and trichlorfon (40 mg/kg of body weight) powder formulations were administered as suspensions sequentially given via stomach tube to evaluate the efficacy of the combination against the large parasites of horses. Parasite removal efficacies were 100% against 2nd instar Gasterophilus intestinalis and 2nd and 3rd instar Gasterophilus nasalis and 82 to 100% against 3rd instar G intestinals. There were complete removals of mature and immature Parascaris equorum and mature Oxyuris equi. Removal efficacies against Strongylus vulgaris were 89 to 100% and against Strongylus edentatus, 82 to 100%. Of 2 horses infected with Strongylus equinus, removals were 72 and 100%. Seven of the 13 horses treated had transient, semi-liquid feces during the posttreatment hours 1 through 24.