Towards developing support tools for sustainable control of gastrointestinal nematodes in sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, Manawatū, New Zealand
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2021
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Massey University
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Abstract
Gastrointestinal nematode (GIN) parasitism is a major animal health challenge for sheep. Parasitized animals typically display a number of clinical signs, including a reduction in voluntary feed intake, altered grazing behaviour and lethargy. The aim of this thesis was to use remote sensing technologies to advance the development of a methodology where early changes in animal behaviour can be used to help identify sheep suffering ill effects of GIN parasitism, especially in a pre-clinical situation. It was hypothesised that lambs with even modest worm burdens will be less active, graze for less time and spend more time resting than those herd mates that were less heavily parasitized.
The movement and behavioural activity of young and mature, infected and uninfected sheep were monitored in a series of studies using global positioning system (GPS) and tri-axial accelerometer sensors. Key behaviours were identified using machine learning techniques. Also assessed was the influence of host genotype on movement activity.
Accelerometry data accurately identified grazing, resting and walking activities of sheep. The sensors were able to identify the effects of GIN parasitism on movement and behaviour in sheep. Clear evidence was found that GIN were associated with reduced movement and overall activity in growing lambs, with reductions in time spent ‘grazing’ and ‘walking’ occurring concomitantly with increases in ‘resting’ activity, and before effects were recorded on growth rates. Host genotype also had an effect on movement activity of lambs in untreated sheep, but not in treated individuals. Adult sheep, however, showed no consistent changes in movement and behaviour associated with parasitism, as measured by faecal egg counts.
Overall, the findings in this thesis have demonstrated the potential value in remote monitoring of sheep as a diagnostic marker to detect the generally subtle behavioural changes associated with changing GIN infection status. Such monitoring could therefore be used as the basis for deciding whether animals need to be treated with anthelmintic on the basis of individual need, and such decisions could be taken early, i.e. before animals have failed to grow adequately or started to manifest more overt signs of clinical illness such as weight loss.
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Sheep, Parasites, Nematodes, Behavior, Monitoring, Remote sensing