Behavioural response of sheep to forage resources and parasite risk in an extensive grazing system

  • Caroline L Liddell

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Understanding parasite-host interactions is vital for managing domestic and wild animal populations under future scenarios of increased parasitism and anti-parasitic drug resistance. This thesis used extensively grazing sheep on an upland area in the UK to investigate aspects of habitat selection and associated behaviour relevant to parasite infection risk. Newly available technologies for animal tracking and remote sensing were utilised, with the aim to develop fundamental understanding of ungulate grazing patterns in relation to resource health trade-offs; to seek insights that might improve the efficiency, sustainability and health of extensive sheep farming systems; and to trial methods and approaches for transfer to studies of free-living wild ungulates. Spatial variation in parasite risk and forage distribution across grazing landscapes presents herbivores with complex choices when trading off maximising food intake versus minimising infection risk. Overall, I found sheep had used sites with higher quality vegetation more than cattle and horses grazing the same landscape, likely due to their small size and foregut fermenting digestive system, which is less able to process low-quality, high fibre vegetation. However, I further found that the trade-off in foraging decisions varied between individual sheep based on their health status, with healthy individuals prioritising forage intake and less healthy individuals prioritising parasite avoidance. It is increasingly being acknowledged that individuals of the same species within a population differ consistently in their behavioural responses to the same environmental stimuli, such as forage resources. These responses are a result of personality-specific and state-dependent behaviours where an individual’s state describes any intrinsic factors (such as in this study parasitic infection) which affect the costs and benefits of its behavioural decisions. These individual and collective patterns in habitat use should be considered when studying factors that affect the distribution of grazing animals, as important processes could be concealed in population-level studies.
Date of Award28 Sept 2021
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorChristos C Ioannou (Supervisor) & Richard Wall (Supervisor)

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