Thirty-five castrate or intact Holstein male calves, ranging in weight from 122 to 210kg, were used in the study. On study Days -15 and -14, all study calves were treated with
fenbendazole 10%
paste at 10mg/kg to remove existing
nematode infections. All cattle had zero egg counts on Day -1. Experimental
infections of a mixed species inoculum were administered to all calves on Day 0. The inoculum consisted of Cooperia spp. (primarily C. punctata, but also C. pectinata, C. spatulata, C. oncophora and C. surnabada-total 40,961); Ostertagia ostertagi-1550; Trichostrongylus colubriformis-4996; and Oesophagostomum radiatum-38. Necropsy results from two of three monitor calves slaughtered on Day 6 after
infection indicated that Day 6 was an appropriate time to evaluate efficacy of
moxidectin against fourth larval stages (L(4)). The remaining 32 calves were randomly allotted to four groups of eight based on
body weights. Eight calves (Group 1) were treated with
moxidectin 0.5% pour-on at 0.5mg/kg on Day 6 to evaluate efficacy against nematode larval stages; eight control calves (Group 2) were matched with these principals. Eight calves (Group 3) were also treated with
moxidectin pour-on at the same dosage on Day 23 in order to determine efficacy against adult nematodes; eight control calves (Group 4) were matched with these principals. In both cases, principals and controls of the Days 6 and 23 treatments were necropsied at 14-15 days
after treatment. C. punctata was the only species found in a sufficient number of controls to evaluate
moxidectin efficacy against the L(4).
Moxidectin pour-on was not effective (P<0.05) against C. punctata L(4) by arithmetic means, but was highly effective based on geometric means. Regardless of whether arithmetic or geometric means were used for percent efficacy calculations,
moxidectin pour-on was demonstrated to be highly effective (>99%) against the adult stages of C. oncophora, C. punctata, C. spatulata, C. surnabada, Cooperia spp. adult females and T. colubriformis adults.