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Strongyle Egg Reappearance Periods following Moxidectin Treatment in Horses in Southeast England
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  • Tim Mair,
  • Rebecca Opie,
  • Michelle Moreton-Clack,
  • Tim Parkin,
  • Jacqui Matthews
Tim Mair
Bell Equine Veterinary Clinic

Corresponding Author:[email protected]

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Rebecca Opie
Bell Equine Veterinary Clinic
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Michelle Moreton-Clack
Bell Equine Veterinary Clinic
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Tim Parkin
University of Bristol
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Jacqui Matthews
Austin Davis Biologics Ltd
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Background: A reduction in the Egg Reappearance Period (ERP) has been suggested to be an early indication of emerging anthelmintic resistance in strongyles. Objective:To measure the strongyle ERP following moxidectin treatment of horses in the southeast of England. Study Design: Prospective study. Methods: Horses with a faecal egg count (FEC) of > 400 strongyle eggs per gram (EPG) in a routine screening sample were enrolled into the study. Moxidectin (400 mcg/kg) was administered per os and FEC tests repeated every 2 weeks for 16 weeks. Results: Forty-eight horses completed the study. The mean EPG prior to treatment was 1047 (range 375 – 2137 EPG). In all but two horses, FEC was 0 EPG 2 weeks after moxidectin administration. In the remaining two, the FECs were 12.5 EPG (97.8-98.3% reductions compared to pre-treatment FEC). At 4 weeks post-treatment, 6 horses had positive FECs (96.6-99.2% reductions). At 6 weeks, 11 horses had positive FECs (83.8% reduction in one horse; >90% reduction in 10). At 8 weeks, 21 horses exhibited positive FECs (<90% reduction in 2). At 10 weeks, 27 horses had positive FECs (<90% in 6). At 12 weeks, 31 horses had positive FECs (<90% reduction in 11). At 14 weeks, 34 horses had positive FECs (<90% reduction in 13). At 16 weeks, 38 horses had positive FECs (<90% reduction in 17). Limitations: Weights of some horses were estimated using weigh tapes rather than a weighbridge. Dosing of the horses with moxidectin was carried out by owners. Conclusions: The results indicated acceptable efficacy of moxidectin at 14 days after treatment; however, the ERP pattern measured across the group suggest that this anthelmintic has a considerably shorter suppressive effect on strongyle egg shedding than measured when it was first introduced ( >13 weeks and up to 24 weeks).
22 Apr 2023Submitted to Equine Veterinary Education
24 Apr 2023Submission Checks Completed
24 Apr 2023Assigned to Editor
24 Apr 2023Reviewer(s) Assigned
12 May 2023Review(s) Completed, Editorial Evaluation Pending
22 May 2023Editorial Decision: Revise Minor
02 Jun 20231st Revision Received
05 Jun 2023Submission Checks Completed
05 Jun 2023Assigned to Editor
05 Jun 2023Review(s) Completed, Editorial Evaluation Pending
05 Jun 2023Editorial Decision: Accept