Activity of organophosphorus compounds against oral stages of gasterophilus intestinalis and Gasterophilus nasalis.

Controlled tests of the efficacy of bot-active compounds, dichlorvos, trichlorfon, trichlorfon butonate, and carbon disulfide on the larvae of Gasterophilus intestinalis and Gasterophilus nasalis during their migratory period in the tissue of the mouth of horses and ponies were completed on experimentally induced and naturally acquired infections. Against the experimental parasitisms in pony foals, the resin-pellet formulation of dichlorvos given on the feed at the dose level of 37 mg/kg, 2 formulations of trichlorfon given by stomach tube at the dose level of 40 mg/kg, another of trichlorfon given on the feed, and trichlorfon butonate given intragastrically at the dose level of 43 mg/kg were 100% efficacious. Against naturally acquired parasitisms in horses, a broad-spectrum gel formulation of dichlorvos given intraorally at the dose level of 36 mg/kg was quite efficacious, whereas liquid carbon disulfide given by stomach tube at the dose level of 2.4 ml/45.45 kg was ineffective.