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Modelling the short- and long-term impacts of drenching frequency and targeted selective treatment on the performance of grazing lambs and the emergence of anthelmintic resistance

Published online by Cambridge University Press:  01 February 2013

YAN C. S. M. LAURENSON ,
STEPHEN C. BISHOP ,
ANDREW B. FORBES  and
ILIAS KYRIAZAKIS
YAN C. S. M. LAURENSON*
Affiliation:
The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, UK
STEPHEN C. BISHOP
Affiliation:
The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, UK
ANDREW B. FORBES
Affiliation:
Merial, 29 avenue Tony Garnier, Lyon 69007, France
ILIAS KYRIAZAKIS
Affiliation:
School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
*
*Corresponding author: The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, UK. Tel: +44 131 651 9100. Fax: +44 131 651 9105. E-mail: yan.laurenson@gmail.com
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Summary

Refugia-based treatment strategies aim to prolong anthelmintic efficacy by maintaining a parasite population unexposed to anthelmintics. Targeted selective treatment (TST) achieves this by treating only animals that will benefit most from treatment, using a determinant criterion (DC). We developed a mathematical model to compare various traits proposed as DC, and investigate impacts of TST and drenching frequency on sheep performance and anthelmintic resistance. Short term, decreasing the proportion of animals drenched reduced benefits of anthelmintic treatment, assessed by empty body weight (EBW), but decreased the rate of anthelmintic resistance development; each consecutive drenching had a reduced impact on average EBW and an increased impact on the rate of anthelmintic resistance emergences. The optimal DC was fecal egg count, maintaining the highest average EBW when reducing the proportion of animals drenched. Long-term, reducing the proportion of animals drenched had little impact on total weight gain benefits, across animals and years, whilst reducing drenching frequency increased it. Decreasing the frequency and proportion of animals drenched were both predicted to increase the duration of anthelmintic efficacy but reduce the total number of drenches administered before resistance was observed. TST and frequency of drenching may lead to different benefits in the short versus long term.

Keywords

anthelmintic resistancerefugiasheepsimulation modellingtargeted selective treatmentTeladorsagia circumcincta

Information

Type
Research Article
Information
Parasitology , Volume 140 , Issue 6 , May 2013 , pp. 780 - 791
Copyright
Copyright © Cambridge University Press 2013

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