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.