Anthelmintic resistance on goat farms in Georgia: efficacy of anthelmintics against gastrointestinal nematodes in two selected goat herds

Gastrointestinal nematode (GIN) parasitism is a major constraint to product ion of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics d uring the warm season. Overuse of anthelmintics has led to an increase in t he incidence of anthelmintic resistance in many parts of the world, but dat a on prevalence of anthelmintic resistance in GIN of goats in the southeast ern United States are very limited. To address this issue, anthelmintic eff icacy was determined in goat herds at the Fort Valley State University, Agr icultural Research Station (FVSU-ARS) and the University of Georgia, Colleg e of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) t ests and DrenchRite(R) larval development assays (LDA). At FVSU-ARS, 2-year -old Spanish goat does were randomly allocated to one of nine different tre atment groups (n = 10): albendazole (ABZ; 20 mg/kg body weight (BW)), fenbe ndazole (FBZ; 20 mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM ; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10 mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were r andomly allocated to one of five different treatment groups (n = 8): ABZ (2 0 mg/kg BW),IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FE C of treated and control animals, and percent reductions were interpreted u sing the World Association for the Advancement of Veterinary Parasitology g uidelines for resistance. For the LDA, nematode eggs were isolated from poo led fecal samples of untreated control goats in each herd and used to perfo rm DrenchRite(R) assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 7 6, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IV M, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidect in was the only drug tested that was fully effective. Results of the LDA we re in agreement with results of the FECR tests for both herds. These data d emonstrate the presence of GINs resistant to all three major anthelmintic c lasses in both goat herds. (C) 2001 Published by Elsevier Science B.V.