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Title: The use of heart rate variability measurements as a non-invasive method of assessing affective state in horses
Author: Kay, R.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2012
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Domestic horses maintain many of their innate behavioural traits as a group-living, free-ranging herbivore that usually avoids predation by flight. Confinement, isolation, restraint, riding, training and exposure to management practices present a vastly different experience to their natural environment but the psychological need to respond to environmental factors may remain, even when the biological motivation has been removed. This disparity can lead to the development of physiological and behavioural abnormalities indicative of a negative affective state and poor welfare. The concept of animal welfare should include the animals’ physical and psychological health and harmony with their environment. There is an increasing call for subjective feelings and the assessment of emotion to be taken into account so that welfare can be enhanced by increasing the incidence of positive experiences and minimising negative ones. Reliably establishing the affective state of an animal is a challenging task but measuring physiology and behaviour in response to pleasant or unpleasant stimuli can provide evidence for the existence of affective state. Equine research has endeavoured to identify ‘reactivity’, temperament and emotionality but has not yet investigated underlying affective state in response to different stimuli, the existence of, or factors that might influence positive affective states. As such, there is no strong scientific knowledge of what equine emotional experiences are. Many physiological measures involve invasive procedures that contribute to the stress load of the individual and non-invasive methods often only determine the presence or absence of ‘stress’ or are dogged by interpretive problems. Heart rate variability (HRV) is a major growth area in the study of emotion and is an established parameter to quantify the state of the autonomic nervous system. Empirical evidence from human and animal research associates high levels of HRV with positive emotions and vice versa. This research aimed to evaluate the use of HRV alongside behavioural measurements as a non-invasive method of assessing affective state in horses. Equine HRV and behaviour were measured during anticipation of positive rewards (companionship and feeding), during a negatively valenced management procedure (sham-clipping), in four housing systems allowing increasing levels of social contact and potential factors affecting HRV were assessed. By exposing horses to housing and management conditions differing in their emotional valence it was possible to identify factors that significantly affected HRV and highlight incidences where a significant relationship existed between behaviour and HRV (significant if p≤0.05). Rewarding and contrasting circumstances were found to be significantly associated with HRV. Social interaction, ‘play’ behaviour and the provision of a haylage diet were all associated with high HRV whereas disruption to the horses’ leisure time was associated with low HRV. HRV provided an objective physiological measurement for interpreting behaviour and assessing underlying affective state; compliant behaviour in response to an aversive stimulus was not associated with low HRV and specific pre-feeding behaviours (behavioural transitions, ear movement and head nodding) could prove a useful indicator of negative affective state in future studies. Specific social and spatial factors significantly affecting HRV were also identified; tactile contact with neighbouring horses was related to high HRV and hay net position appeared to affect the horses’ capacity for environmental monitoring. A natural variation in HRV between equine sexes and between individuals was confirmed and changes in HRV were found to be situation-specific. It was possible to use these initial data to make suggestions for the establishment of a preferable habitat and management regime for horses. The importance of social interaction was highlighted, particularly ‘play’ behaviour. Horses housed in confinement and isolation may derive greater benefit from the ‘reward’ or contrast of social interaction than horses kept in more social conditions. Where negative experiences are encountered, these might be mitigated by rewarding with a preferred forage type and extending visual horizons towards neighbouring horses and the external environment. Ensuring that negative experiences are not prolonged or offsetting them with positive experiences could enhance quality of life. This study makes a unique contribution to equine welfare research as the use of HRV measurements to assess emotion in horses is a relatively new area of investigation. HRV was found to add vital physiological support to existing findings and although research of this nature is in its infancy, HRV appears to be a promising tool for assessing affective state and interpreting behavioural responses to stimuli in horses. There is extensive scope for further investigation into the use of HRV as a measure of emotional responses to management factors, environmental and ridden/training conditions in order to identify enjoyable or rewarding practices, so that the experience of positive emotion can be incorporated into management and training.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available