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Modelling the impacts of pasture contamination and stocking rate for the development of targeted selective treatment strategies for Ostertagia ostertagi infection in calves

Lookup NU author(s): Zoe Berk, Professor Ilias Kyriazakis



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© 2017 The Authors. A simulation study was carried out to assess whether variation in pasture contamination or stocking rate impact upon the optimal design of targeted selective treatment (TST) strategies. Two methods of TST implementation were considered: 1) treatment of a fixed percentage of a herd according to a given phenotypic trait, or 2) treatment of individuals that exceeded a threshold value for a given phenotypic trait. Four phenotypic traits, on which to base treatment were considered: 1) average daily bodyweight gain, 2) faecal egg count, 3) plasma pepsinogen, or 4) random selection. Each implementation method (fixed percentage or threshold treatment) and determinant criteria (phenotypic trait) was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The impact of pasture contamination on optimal TST strategy design was investigated by setting the initial pasture contamination to 100, 200 or 500 O. ostertagi L3/kg DM herbage; stocking rate was investigated at a low (3calves/ha), conventional (5 calves/ha) or high (7 calves/ha) stocking rates. When treating a fixed percentage of the herd, treatments according to plasma pepsinogen or random selection were identified as the most beneficial (i.e. resulted in the greatest BPR) for all levels of initial pasture contamination and all stocking rates. Conversely when treatments were administered according to threshold values ADG was most beneficial, and was identified as the best TST strategy (i.e. resulted in the greatest overall BPR) for all levels of initial pasture contamination and all stocking rates.

Publication metadata

Author(s): Berk Z, Laurenson YCSM, Forbes AB, Kyriazakis I

Publication type: Article

Publication status: Published

Journal: Veterinary Parasitology

Year: 2017

Volume: 238

Pages: 82-86

Print publication date: 30/04/2017

Online publication date: 28/03/2017

Acceptance date: 27/03/2017

Date deposited: 03/05/2017

ISSN (print): 0304-4017

ISSN (electronic): 1873-2550

Publisher: Elsevier BV


DOI: 10.1016/j.vetpar.2017.03.025


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