Abstract
Gastrointestinal nematodes (GINs) represent a globally significant problem for grazing ruminants, adversely affecting productivity and health. Chemical anthelmintics are not as effective as they once were due to the development of anthelmintic resistance (AR) which is becoming a widespread issue in the UK and Ireland. Multispecies swards (MSS), which contain plant secondary metabolites (PSMs), have been reported to reduce parasite burdens in sheep and cattle, hence protecting bodyweight, compared to grazing on perennial ryegrass (PRG) dominated swards.This thesis investigates the practical implementation of MSS and targeted selective treatment (TST) to mitigate parasite burdens in sheep and cattle and reduce anthelmintic usage, prolonging anthelmintic efficacy. Chapter one reviews the benefits, limitations, and strategic timing of alternative strategies to optimise impacts on parasites and animal performance. The progressing AR situation in the UK was assessed in chapter two, investigating changes on sheep farms over five years. Results showed increased multidrug and multi-species resistance, highlighting the need for effective alternative control strategies. Trials of sheep grazing MSS or PRG swards were analysed in chapter three. Results showed inconsistent anthelmintic effects when grazing MSS but showed promise in improving sheep performance. Most studies on MSS have focused on sheep, however, in chapter four, the influence of grazing MSS on cattle was investigated. It was found that MSS can delay anthelmintic treatment when employing TST and improve performance for first grazing season cattle. The effect of MSS on methane emissions was investigated in chapter five as PSM in MSS have been shown to mitigate enteric methane emissions from ruminants, as well as offset increased emissions from parasitised animals. Neither sward type nor parasite burden had any observable impact on methane intensity. In chapter six, it is summarised that when integrated with TST, MSS offer a powerful tool for improving livestock productivity and reducing anthelmintic use.
Thesis is embargoed until 31 July 2027.
| Date of Award | Jul 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Sponsors | Department of Agriculture, Environment and Rural Affairs, Forest Service Northern Ireland |
| Supervisor | Francis Lively (Supervisor), Katerina Theodoridou (Supervisor) & Eric Morgan (Supervisor) |
Keywords
- Parasite
- anthelmintic resistance
- bioactives
- grasslands
- greenhouse gas emissions/methane emissions
- cattle
- sheep