title: An investigation of anthelmintic efficacy against strongyles on equine yards in Scotland.
abstract: BACKGROUND
  Cyathostomins comprise 50 helminth species, considered the most problematic equine endoparasites. Three classes of anthelmintic are currently licensed for their control, namely the benzimidazoles (fenbendazole), tetrahydropyrimidines (pyrantel) and macrocyclic lactones (ivermectin and moxidectin). Anthelmintic resistance in cyathostomins is common. With no new classes expected in the near future, it is essential to determine the efficacy of the available anthelmintics to inform future control programmes.
  
  
  OBJECTIVE
  To determine the efficacy of all 3 anthelmintic classes against strongyles in equids on livery yards in east and central Scotland.
  
  
  METHODS
  Anthelmintic efficacy testing using the faecal egg count reduction test (FECRT).
  
  
  METHODS
  FECRTs were performed on equids with initial strongyle faecal egg counts (FECs) of ≥50 eggs per gram. Efficacy was determined by comparing pretreatment (Day 0) and 14 days post treatment (Day 14) FECs. The following chemicals were tested: fenbendazole, pyrantel, ivermectin and moxidectin. Group arithmetic mean FECR of >90% for fenbendazole and pyrantel, and >95% for ivermectin and moxidectin, represented efficacy, whereas lower mean FECR indicated potential resistance.
  
  
  RESULTS
  A total of 447 FECRTs were performed on 15 yards, as follows (the numbers in parentheses represent the number of yards each anthelmintic was tested on): 55 equids (7 yards) fenbendazole, 111 (8 yards) pyrantel, 163 (13 yards) ivermectin and 118 (10 yards) moxidectin. Fenbendazole resistance was documented on all yards (range of mean FECR, 15.8-83.4%), whereas pyrantel (90.4-99.6%), ivermectin (99.5-100%) and moxidectin (99.4-100%) treatment had acceptable efficacy.
  
  
  CONCLUSIONS
  Reduced efficacy of fenbendazole was widespread, whereas >90% efficacy was found after pyrantel, and >95% efficacy after ivermectin and moxidectin. Overall, efficacies were higher than reported previously in Europe and the USA, potentially reflecting differences in management and anthelmintic use on the yards surveyed.
  
  
  CONCLUSIONS
  The use of fenbendazole for strongyle control in Scotland should be questioned. Targeted use of pyrantel should be encouraged to reduce reliance on macrocyclic lactones. Further work to correlate management practices with the presence of anthelmintic resistance is warranted.
authors.affiliation: Royal (Dick) School of Veterinary Studies and Roslin Institute, University of Edinburgh, UK.
authors.forename: C H
authors.initials: CH
authors.lastname: Stratford
authors.forename: H E
authors.initials: HE
authors.lastname: Lester
authors.forename: K J
authors.initials: KJ
authors.lastname: Pickles
authors.forename: B C
authors.initials: BC
authors.lastname: McGorum
authors.forename: J B
authors.initials: JB
authors.lastname: Matthews
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D006376:Helminths / Q000187:drug effects*; D006734:Horse Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000469:parasitology*; D006736:Horses; D010270:Parasite Egg Count; D012606:Scotland / Q000453:epidemiology
chemical_list: D000871:Anthelmintics
keywords: anthelmintic resistance; cyathostomins; faecal egg count reduction test; horse