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Prevalence, burden and anthelmintic resistance of gastrointestinal nematodes in the south west region of Western Australia dairy herds

Mauger, Mikayla Elizabeth (2021) Prevalence, burden and anthelmintic resistance of gastrointestinal nematodes in the south west region of Western Australia dairy herds. Honours thesis, Murdoch University.

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Anthelmintic resistance in gastrointestinal nematodes (GIN) of dairy cattle is of global importance. The objective of this study was to determine the prevalence of GIN among post-weaned replacement heifers and bull calves aged between 4 - 12 months old in Western Australia dairy farms and quantify the level of anthelmintic resistance. A secondary objective of this study was to explore pooling faecal samples for cost effective diagnostic purposes of faecal egg counts (FECs). Pre-treatment FECs were monitored on 14 dairy farms, anthelmintic resistance was assessed on 11 of the farms based on FEC of ≥500 eggs per gram (epg) in at least 10 - 15% of the samples. Control FECs were compared with anthelmintic FECs at 14 days post-treatment with doramectin (injectable), levamisole (oral), fenbendazole (oral) and, a levamisole/abamectin combination (Eclipse® combination pour-on). The results demonstrate a high level of anthelmintic resistance, with at least one class of anthelmintic failing to achieve a 95% reduction in FEC in one or more GIN species. Doramectin was fully effective against Ostertagia, but C. oncophora displayed resistance to it on 91% of the farms. Conversely, levamisole was fully effective against C. oncophora, but Ostertagia displayed resistance in 80% of the farms. Fenbendazole resistance was present in both C. onocphora and Ostertagia in 64% and 70% of the farms respectively. Trichostrongylus showed low resistance, only occurring in doramectin (14%) and levamisole/abamectin combination (14%) on the farms sampled. A high level of correlation between pooled groups of 5, 10 and 20 samples was recorded (R=0.947, 0.987, 0.972 and P=0.015, 0.002, and 0.006) respectively. This study confirms that anthelmintic resistance within Western Australian dairy farms is common and regular faecal egg count reduction testing is recommended to monitor and guide decision-making for appropriate anthelmintic usage. Utilisation of pooled FECs provides a potential cost-effective method for farmers to regularly monitor FECs.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Agricultural Sciences
Supervisor(s): Aleri, Joshua and Kelly, G.
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