An investigation into physiological correlates of equine personality

Objective equine personality tests enable the selection of horses for roles based on their typical behavioural responses to challenges. In humans and rodents, non-behavioural correlates of personality such as physiological reactivity to stressors and cognitive style have been identified. These traits are relevant to equine welfare and performance, yet little is known about their relationship with equine personality. Therefore, it is currently unclear what impact selection for personality has on these factors. This thesis aimed to address this gap by investigating potential neurophysiological correlates of equine personality. First, the Equine Personality Test (EPT) was evaluated for internal consistency, inter-rater reliability and test-retest reliability. This demonstrated that the EPT produces valid and reliable evaluations of the equine personality factors Agreeableness, Neuroticism, Extraversion and Gregariousness towards People. Following this, autonomic and HPA axis reactivity to stressors, chronic HPA axis activity and tonic striatal dopamine were investigated as potential neurophysiological correlates of equine personality measured by the EPT. They were measured through cardiac and salivary cortisol responses to experimental stressors, hair cortisol concentration and spontaneous blink rate, respectively. Although these physiological parameters have been established as correlates of personality in human and rodent models, no similar associations were identified in the horse. The EPT did not have predictive validity for physiological reactivity to stressors, suggesting that horses identified as non-reactive to stressors on a behavioural basis did not have equally low physiological stress sensitivity. Hair cortisol concentration was positively associated with Agreeableness, suggesting that compliant horses may experience greater HPA axis activity. These results raise concerns on the welfare of compliant, non-behaviourally reactive horses. Should they be confirmed by future research, these findings should inform the choice of methods used to select horses for roles, with a view to safeguard not only human safety but also equine welfare

Dually investigated: the effect of a pressure headcollar on the behaviour, discomfort and stress of trained horses

The Dually™ is a control headcollar designed to improve equine behaviour during handling challenges by applying greater pressure than a standard headcollar. Previous research indicated it did not improve compliance in naïve horses but did result in higher Horse Grimace Scale scores (HGS) indicative of discomfort. However, subjects had not been trained to step forward to release the pressure applied by the headcollar. The current study aimed to determine the effect of training on behaviour and physiology of horses wearing the Dually™ headcollar during handling challenges. To this end, subjects received three training sessions prior to completing two handling tests in which they crossed distinct novel obstacles, one wearing a Dually™ with a line attached to the pressure mechanism and one attached to the standard ring as a control. Behaviour was coded by hypothesis blind researchers: time to cross the obstacle and proactive refusal (moving away from the obstacle) were recorded as indicators of compliance and the Horse Grimace Scale was used to measure discomfort caused by each configuration of the device. Infrared thermography of ocular temperature, heart rate variability (RMSSD and low/high frequency ratios (LF/HF)) and salivary cortisol were measured as indicators of arousal. Data from the previous study on Naïve horses was also included to compare responses to the Dually in Naïve and Trained horses. Training resulted in a decrease in RMSSD (p = 0.002) and an increase in LF/HF (p=0.012), compared to rest, indicating arousal. As per the original study, horses did not complete the tests more quickly in the Dually, compared to control (p=0.698). Trained horses from this study tended to be more proactive in the Dually compared to Controls (p=0.066) and significantly more so than Naïve horses from the previous study (p=0.002) suggesting that behaviour becomes less desirable during early Dually training. Yet, stress and HGS indicators were not higher in the Dually compared to Control during testing. Results suggest the Dually has a negative effect on behaviour but not on stress or discomfort during short handling challenges. Further research is warranted to determine the long-term effect of Dually experience on behaviour and welfare

Cognitive Bias in Ambiguity Judgements:Using Computational Models to Dissect the Effects of Mild Mood Manipulation in Humans

Positive and negative moods can be treated as prior expectations over future delivery of rewards and punishments. This provides an inferential foundation for the cognitive (judgement) bias task, now widely-used for assessing affective states in non-human animals. In the task, information about affect is extracted from the optimistic or pessimistic manner in which participants resolve ambiguities in sensory input. Here, we report a novel variant of the task aimed at dissecting the effects of affect manipulations on perceptual and value computations for decision-making under ambiguity in humans. Participants were instructed to judge which way a Gabor patch (250ms presentation) was leaning. If the stimulus leant one way (e.g. left), pressing the REWard key yielded a monetary WIN whilst pressing the SAFE key failed to acquire the WIN. If it leant the other way (e.g. right), pressing the SAFE key avoided a LOSS whilst pressing the REWard key incurred the LOSS. The size (0-100 UK pence) of the offered WIN and threatened LOSS, and the ambiguity of the stimulus (vertical being completely ambiguous) were varied on a trial-by-trial basis, allowing us to investigate how decisions were affected by differing combinations of these factors. Half the subjects performed the task in a 'Pleasantly' decorated room and were given a gift (bag of sweets) prior to starting, whilst the other half were in a bare 'Unpleasant' room and were not given anything. Although these treatments had little effect on self-reported mood, they did lead to differences in decision-making. All subjects were risk averse under ambiguity, consistent with the notion of loss aversion. Analysis using a Bayesian decision model indicated that Unpleasant Room subjects were ('pessimistically') biased towards choosing the SAFE key under ambiguity, but also weighed WINS more heavily than LOSSes compared to Pleasant Room subjects. These apparently contradictory findings may be explained by the influence of affect on different processes underlying decision-making, and the task presented here offers opportunities for further dissecting such processes

The mane factor: compliance is associated with increased hair cortisol in the horse

Equine personality tests enable the selection of horses for roles based on their habitual behavioural responses to challenges, aiming to maximise performance and safeguard equine welfare. However, existing research has identified that behavioural responses to acute challenges do not correlate well with stress physiology in the horse. The aim of this study was to investigate whether chronic stress physiology is related to habitual compliance in horses. Hair cortisol concentration (HCC), a long-term biomarker of hypothalamic–pituitary–adrenal axis activity and stress, was assayed in mane hair from the withers, midpoint of the neck and poll of 24 riding school horses (66% male, mean age 13 ± 4 years). Three caregivers provided scores for Agreeableness, Neuroticism, Extroversion, Gregariousness Towards People and Gregariousness Towards Horses for all subjects using a validated equine personality questionnaire. A gamma GLMM was used to model HCC as a function of personality scores and potential confounders of HCC (age, sex, hair colour and sampling location). Individual horses were fitted as random intercepts in the model. Manual backward selection was used to identify the best-fitting plausible model. Mean HCC was 3.8 ± 1.2 pg/mg. The final model only retained Agreeableness and sampling location as explanatory variables of HCC. A positive association was found between Agreeableness (reflecting habitual compliance) and hair cortisol concentration (t = 2.7, p = 0.01). Basal cortisol levels are known to drive sensitivity to punishment in humans. Therefore, horses with higher basal cortisol may be more sensitive to the aversive cues associated with negative reinforcement and consequently be more compliant. However, it is also possible that habitually compliant behaviour leads to higher chronic stress levels through increased exposure to stressors, as more subtle expressions of discomfort are not recognised by handlers. This result has important implications for welfare in the context of horse-human interaction and warrants further investigation to clarify whether a causal link exists between habitual compliance and higher levels of chronic stress. There was also a weaker but significant impact of sampling location (t = 2.1, p = 0.03; higher HCC at the poll), highlighting the importance of carefully standardizing sampling location for HCC analysis

Do you see what I see? Investigating the validity of an equine personality questionnaire

Subjective equine personality questionnaires have the potential to predict a range of industry-relevant outcomes including fear reactivity, compliance with human cues, pain expression and susceptibility to stereotypies, in a time- and cost-efficient manner. However, to produce meaningful measures of target animals’ behavioural tendencies, subjective personality assessment tools must satisfy four criteria: internal consistency, predictive validity, inter-rater reliability, and test-retest reliability. The Equine Personality Test (EPT) has been developed to assess horses on five personality factors based on trait ratings from a familiar observer. While the EPT has been shown to have predictive validity, it has not been assessed for internal consistency, inter-rater reliability or test-retest reliability. To this end, three experienced primary caregivers and three riding instructors assessed 25 familiar horses using the EPT. The internal consistency, inter-rater reliability and test-retest reliability of the five subscales of the EPT were investigated using Cronbach’s α and intra-class correlation (ICC) analyses. The Agreeableness, Neuroticism, Extroversion and Gregariousness towards People subscales had high Cronbach α and inter-rater and test-retest ICC coefficients (α> 0.7; ICC>0.8). By contrast, the Gregariousness towards Horses subscale had low Cronbach α (α=0.39) and inter-rater ICC coefficient (ICC=0.498), and an adequate test-retest ICC coefficient (ICC=0.784). Primary caregivers had higher ICC coefficients than instructors for most subscales and questionnaire items. The EPT therefore provides internally consistent and highly reliable measures of Agreeableness, Neuroticism, Extroversion, and Gregariousness towards People in equines, although measures of Gregariousness towards Horses should be interpreted with caution. The reliability of EPT scores can be further improved by targeting primary caregivers as raters. Taken together with previous findings demonstrating predictive validity for the questionnaire, these results contribute to making the EPT the only subjective equine personality questionnaire to have been checked against all four criteria of a valid and reliable personality assessment tool. This positions the EPT as a highly relevant equine personality assessment tool that may be used to predict behavioural tendencies in industry or research settings alike

Cognitive biases: dissecting the influence of affect on decision-making under ambiguity inhumans and animals

There have been many battles about how best to formalise the affective states of humans andother animals in ways that can be self-evidently tied to quantifiable behaviours. One recent suggestion isthat positive and negative moods can be treated as prior expectations over the future delivery of rewardsand punishments, and that these priors affect behaviour through the conventional workings of Bayesiandecision theory (Mendl et al., 2010). Amongst other characteristics, this suggestion provides an inferentialfoundation for a task that has become a widely-used method for assessing mood states in animals (Hardinget al., 2004). This so-called ‘cognitive bias’ task extracts information about affect from the optimistic orpessimistic manner in which subjects resolve ambiguities in sensory input. Here, we describe experimentsin humans and rodents aimed at elucidating further aspects of this notion. The human studies assessed theextent to which subjects can incorporate information about explicitly-imposed external loss functions intotheir inference about ambiguous inputs, and the way this incorporation interacts with mood. Subjects foundit hard to integrate these sources of information well, which was unexpected given their apparently admirablecapacities in related circumstances (Whiteley & Sahani, 2008), so we are exploring modifications. Therodent studies sought to examine the interaction between the experimenter-imposed instrumental demandsof the task and inherent Pavlovian effects, such as ineluctable approach and avoidance in the face of theprospect respectively of rewards and punishment (Guitart-Masip et al. 2014). The latter might provide anaccount of the differences between rats and mice that we were surprised to observe

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