title: Shortened egg reappearance after ivermectin or moxidectin use in horses in the UK.
abstract: This study reports ivermectin and moxidectin egg reappearance periods (ERP) from UK horses with persistently positive faecal egg counts (FEC), defined as positive FEC within the ERP of an anthelmintic post-treatment, or with FECs that remained positive after the normal ERP post-anthelmintic treatment. A selected population of UK pleasure horses deemed at high risk of strongyle infection was studied. The earliest ERP recorded after ivermectin or moxidectin, using first positive FEC, was 5 weeks. From 16 premises where moxidectin was used, five had ERP ≥12 weeks using two further metrics. For premises where moxidectin was administered to only one animal (present or tested), and evaluated as one group (n = 61), ERP was ≥10 weeks. For premises where ivermectin was used, the ERP was ≥5 weeks. Premises with only one horse (present or tested), dosed with ivermectin (n = 31), analysed as one group, demonstrated egg reappearance ≥6 weeks. These field data suggest shortened ERPs following macrocyclic lactone treatment compared to previously published values (8-10 and >13 weeks respectively) when these drugs were first marketed.
authors.affiliation: School of Equine Management and Science, Royal Agricultural University, Cirencester, Gloucestershire GL7 6JS, UK; School of Veterinary Medicine, University of Surrey, Guildford, Surrey GU2 7TE, UK. Electronic address: simon.daniels@rau.ac.uk.
authors.forename: S P
authors.initials: SP
authors.lastname: Daniels
authors.affiliation: School of Veterinary Medicine, University of Surrey, Guildford, Surrey GU2 7TE, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Proudman
mesh_terms: D000818:Animals; D000969:Antinematodal Agents / Q000627:therapeutic use*; D005243:Feces / Q000469:parasitology; D005260:Female; D006736:Horses; D008297:Male; D010063:Ovum / Q000187:drug effects*; D010270:Parasite Egg Count / Q000662:veterinary; D013319:Strongyle Infections, Equine / Q000453:epidemiology* / Q000469:parasitology / Q000517:prevention & control; D013320:Strongyloidea / Q000187:drug effects / Q000502:physiology*; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D000969:Antinematodal Agents
keywords: Egg reappearance; Ivermectin; Moxidectin; Resistance; Strongyles