Critical tests of the anthelmintic febantel in the horse: activity of a paste formulation alone or with a trichlorfon...

Critical tests were carried out in 10 horses to evaluate the antiparasitic activity of febantel given alone or with trichlorfon. Paste formulations were administered intraorally at dose levels of 6 mg of febantel (active ingredient)/kg and 35 mg of trichlorfon (active ingredient)/kg. In 5 tests with febantel alone, removal of 100% was recorded for mature or immature Parascaris equorum from 2 infected horses. Strongylus vulgaris from 4 infected horses, S edentatus from 5 infected horses, and mature Oxyuris equi from 1 infected horse; and removal of 96% was recorded for small strogyles from 1 horse tested, and bots in 5 infected horses were not affected. In 5 horses treated with both compounds, removal of 100% was recorded for mature P equorum from 2 infected horses, immature P equorum from 1 infected horse, S vulgaris from 5 infected horses, Sedentatus from 5 infected horses, mature O equi from 2 infected horses, immature O equi from 1 horse tested, 2nd Gasterophilus intestin-equi from 1 infected horse, 2nd-instar C nasalis from 1 infected horse, and 3rd-instar C nasalis from 4 infected horses. Removal of 98% was recorded for small strongyles from 1 horse tested, and removal of 65% to 100% for 3rd-instar C intestinalis from 5 infected horses. In the aggregate, removal of 3rd-instar C intestinalis was 99%. Untoward effects of treatment were quite limited. Only a transient softening of feces in 1 of 5 horses given the trichlorfon paste plus the febantel paste was recorded.