Fecal egg count reduction and control trial determinations of anthelmintic efficacies for several parasiticides utilizing a single set of naturally infected calves.

In this study, a single set of naturally infected calves was used for the conduct of a fecal egg count reduction test (FECRT) immediately followed by a control trial; all, to evaluate the efficacies of several commonly used, non-generic anthelmintics. Ten animals were allocated into each of the five treatment groups; untreated control (UTC), injectable 1% moxidectin given at 0.2 mg kg(-1)BW (MXD), injectable 1% ivermectin given at 0.2 mg kg(-1)BW (IVM), 9.06% oxfendazole given orally at 4.5 mg kg(-1)BW (OXF), and 10.0% fenbendazole given orally at 5.0 mg kg(-1)BW (FBZ). Confinement of animals to clean, concrete-floored pens was initiated on day -7 and continued until animal necropsy (2 animals were necropsied per treatment group per day on days 35-39 for nematode collections). All treatments were given on day 0, and the FECRT was conducted on all animals until necropsy. From days 2 to 14, FECR %'s for the combined strongyle egg counts were >or=90% for all anthelmintic groups. At the time of necropsy, FECRT %'s for the combined strongyle egg counts continued to be >or=90% for all treatments with the exception of IVM (84%). After adjustment of the strongyle egg counts in accordance with coproculture larvae percentages, FECRT %'s at the time of necropsy for Haemonchus, Ostertagia and Cooperia were found to be >or=94% for MXD and OXF, but <90% for FBZ (Ostertagia) and IVM (Haemonchus and Cooperia). At necropsy, more than six of the ten untreated animals were infected with Ostertagia ostertagi (adults, EL(4) and LL(4)), and adult Haemonchus placei, Trichostrongylus axei, Cooperia oncophora, C. surnabada and C. punctata. Based on geometric means: all of the above populations were removed by >or=96% by MXD; were removed by >or=90% by IVM except for O. ostertagi LL(4) (81.9%), C. oncophora and C. surnabada adults (77.4%) and C. punctata adults (84.8%); were removed by >or=90% by OXF except for O. ostertagi adults, EL(4) and LL(4) (89.9, 70.2 and 48.1%, respectively); and were removed by >or=90% by FBZ except for O. ostertagi adults, EL(4) and LL(4) (72.5, 0.0 and 21.9%, respectively). Judging from the above data, FECR and control trial results can be extremely similar given the proper experimentation and, despite varied degrees of nematode resistance, targeted nematode burdens commonly carried by Midwestern beef cattle are effectively removed by the parasiticides that are available today.