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  • Author or Editor: Thomas H. Terrill x
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Objective—To determine prevalence of resistance to all anthelmintics that are commonly used to treat gastrointestinal nematodes (GINs) in goats.

Design—Prospective study.

Animals—777 goats.

Procedure—On each farm, goats were assigned to 1 of 5 treatment groups: untreated controls, albendazole (20 mg/kg [9.0 mg/lb], PO, once), ivermectin (0.4 mg/kg [0.18 mg/lb], PO, once), levamisole (12 mg/kg [5.4 mg/lb], PO, once), or moxidectin (0.4 mg/kg, PO, once), except on 3 farms where albendazole was omitted. Fecal samples were collected 2 weeks after treatment for determination of fecal egg counts (FECs), and percentage reductions were calculated by comparing data from anthelmintic-treated and control groups. Nematode populations were categorized as susceptible, suspected resistant, or resistant by use of guidelines published by the World Association for the Advancement of Veterinary Parasitology.

Results—Resistance to albendazole was found on 14 of 15 farms, and resistance to ivermectin, levamisole, and moxidectin was found on 17, 6, and 1 of 18 farms, respectively. Suspected resistance to levamisole and moxidectin was found on 4 and 3 farms, respectively. Resistance to multiple anthelmintics (albendazole and ivermectin) was found on 14 of 15 farms and to albendazole, ivermectin, and levamisole on 5 of 15 farms. Mean overall FEC reduction percentages for albendazole, ivermectin, levamisole, and moxidectin were 67, 54, 94, and 99%, respectively.

Conclusions and Clinical Relevance—Anthelmintic resistance in GINs of goats is highly prevalent in the southern United States. The high prevalence of resistance to multiple anthelmintics emphasizes the need for reexamination of nematode control practices. (J Am Vet Med Assoc 2003;223:495–500)

Full access
in Journal of the American Veterinary Medical Association


Objective—To determine prevalence of anthelmintic resistance on sheep and goat farms in the southeastern United States.

Design—Cross-sectional study.

Animals—Sheep and goats from 46 farms in 8 southern states, Puerto Rico, and St Croix in the US Virgin Islands.

Procedures—Parasite eggs were isolated from fecal samples, and susceptibility to benzimidazole, imidathiazole, and avermectin-milbemycin anthelmintics was evaluated with a commercial larval development assay.

ResultsHaemonchus contortus was the most common parasite on 44 of 46 farms; Trichostrongylus colubriformis was the second most commonly identified parasite. Haemonchus contortus from 45 (98%), 25 (54%), 35 (76%), and 11 (24%) farms were resistant to benzimidazole, levamisole, ivermectin, and moxidectin, respectively. Resistance to all 3 classes of anthelmintics was detected on 22 (48%) farms, and resistance to all 3 classes plus moxidectin was detected on 8 farms (17%).

Conclusions and Clinical Relevance—Findings provided strong evidence that anthelmintic resistance is a serious problem on small ruminant farms throughout the southeastern United States. Owing to the frequent movement of animals among regions, the prevalence of resistance in other regions of the United States is likely to also be high. Consequently, testing of parasite eggs for anthelmintic resistance should be a routine part of parasite management on small ruminant farms.

Full access
in Journal of the American Veterinary Medical Association