Grassland parasites and community dynamics under climate change

Abstract

Within temperate grassland systems, control of parasitic gastrointestinal nematodes (GINs) is a major veterinary, economical and agricultural challenge, that currently relies heavily upon the application of anthelmintics. However, anthelmintic resistance within ruminants is increasing, alongside societal and political pressures for chemical-free production lines and the development of sustainable agricultural practices. Nematode transmission is influenced by biological interactions with free-living parasite lifecycle stages, that may provide opportunity for biocontrol and alleviate pressure on anthelmintic usage. To develop understanding of these processes, this thesis investigates the agricultural factors that influence various components of the soil fauna and then considers their action upon the free-living stages of agricultural parasites and consequences for epidemiology.

In chapter one, the life stages of GINs of livestock are considered, along with the approach of nature-based solutions to control parasite transmission, leading to the thesis aims. The abiotic and biotic factors influencing GIN transmission are addressed systematically in chapter two, and a schematic is developed to integrate the interactions between soil and dung organisms and their influences on parasite development and survival. In chapter three the impact of agricultural management on soil fauna is considered, by correlating pasture sward type and earthworms. Results show that more diverse, multispecies pastures have higher earthworm biomass, specifically through greater abundance of deep-burrowing anecic species. This chapter also shaped experimental design in chapter four, a two-year mesocosm investigation that measured how GINs on herbage surrounding individual dung pats are impacted by exclusion or augmentation of earthworm and dung beetle populations. Nematode recovery was found to be significantly impacted by dung beetles, with delayed appearance on herbage but had inconsistent effects across replicates, while earthworms had no discernible effect. Experimental burial of cultured Haemonchus contortus larvae in a soil column showed that migration to the surface was possible from depths up to 56 cm, but recovery rate decreased with increasing burial depth. Chapter five further considers how agricultural practices might influence soil fauna using data collected following long-term slurry application, finding that slurry application rate impacts free-living nematodes while slurry source largely impacts earthworms. Results overall are used in chapter six to evaluate the potential for biological control or bio-augmentation using selected soil and dung organisms to contribute to the management of GINs of ruminants in temperate grassland settings.

Thesis is embargoed until 31 December 2024.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Natural Environment Research Council & NERC QUADRAT
Supervisor	Thomas Fleming (Supervisor) & Eric Morgan (Supervisor)