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Targeted selective treatment strategies for sustainable nematode control and delay of anthelmintic resistance in adult Merino sheep in a Mediterranean environment

Cornelius, Meghan (2016) Targeted selective treatment strategies for sustainable nematode control and delay of anthelmintic resistance in adult Merino sheep in a Mediterranean environment. PhD thesis, Murdoch University.

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Abstract

‘Targeted selective treatment’ (TST) is the concept of targeting anthelmintic treatments to individual animals that will benefit from treatment, rather than giving whole flock treatments. The purpose of TST is to delay the onset of anthelmintic resistance in nematode populations. Two key issues that have delayed the utilization of TST are; a) the need for a convenient and reliable method for identifying animals less likely to cope with nematode challenge; and b) the risk that some animals will be left with nematode burdens sufficient to cause sub-clinical disease that compromises production and welfare. To investigate these issues, this thesis tested the hypothesis that body condition can indicate the ability of mature sheep to better cope with nematodes (and therefore remain untreated), thereby providing a convenient selection method for TST strategies in a Mediterranean climate, where Trichostrongylus spp. and Teladorsagia circumcincta are the predominant nematode parasites. The risk of loss of production and welfare by leaving some animals untreated was examined by modelling simulations, based on data derived from field studies, and on computer models, with various proportions of the flock remaining untreated to determine the threshold proportions of sheep to leave untreated. This approach indicated the trade-offs between delaying anthelmintic resistance with production loss and animal welfare associated with nematode burdens resultant from leaving animals untreated. Further to this, an investigation of Western Australian sheep producers (farmers) identified factors associated with the acceptance of sustainable nematode control practices, especially those likely to facilitate the adoption of TST and act as the basis for the development of communication strategies to producers. The findings of this research provide evidence-based recommendations for the sheep industry regarding sustainable nematode management strategies utilising TST in Mediterranean environments and the facilitation of adoption of TST strategies. In conclusion, the general hypothesis was shown to be applicable, that a body condition score-based TST control program can be practical to implement and will delay anthelmintic resistance in adult Merino sheep in a Mediterranean environment.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Jacobson, Caroline and Besier, R. Brown
URI: http://researchrepository.murdoch.edu.au/id/eprint/34857
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