Pour-on formulation of eprinomectin for cattle: Fecal elimination profile and effects on the development of the dung-inhabiting Diptera Neomyia cornicina (L.) (Muscidae)

The plasma and fecal concentrations of eprinomectin were determined in cattle following topical administration at a dose rate of 0.5 mg kg(-1). The maximum plasma concentrations of 12.24 ng ml(-1) occurred 2 d after administration, and eprinomectin remained detectable in plasma 29 d after administration (0.10 ng ml(-1)). The maximum dung concentration of 350 ng g(-1) was observed 3 d after administration and thereafter for at least 29 d (4 ng g(-1)). The amount of drug recovered in dung during this period was 20.50%+/-4.31% of the total administered dose. The effects of eprinomectin against the nontarget dung-feeding Diptera Neomyia cornicina was assessed under laboratory conditions. Feces voided by cattle treated with eprinomectin were associated with high larval mortality during the first 12 d after treatment, with null emergence until day 7. The no-observed-effect concentration for N. cornicina was estimated to be close to 7+/-5 ng g(-1).