1. Is Pain Expression Linked to Personality in Horses?
Carrie Ijichi, Lisa Collins & Robert Elwood
School of Biological Sciences, Queen’s University Belfast
Introduction
To assess the subjective pain experience of an animal, we often rely on behavioural indicators such as lameness
This assumes that pain expression is proportional to damage and does not take individual differences into account
Thus pain may be under, or over-estimated, having a serious impact on analgesic dosage, treatment and decisions on humane euthanasia
Aims
Test whether lameness accurately predicts the underlying severity of tissue damage and quantify any individual differences in pain expression
Test hypotheses founded on previous work [1,2,3] concerning how personality would be expected to link with Stoicism and pain behaviour
Methods
An experienced equine veterinarian scored 21 horses for lameness and severity of tissue damage using either x-ray or ultrasound during the course of normal diagnosis in a clinical setting
Stoicism was calculated as severity score minus lameness score
Personality was quantified using a validated questionnaire [1] completed by owners who also gave their subjective opinion on how tolerant the horse was to pain using a 1-5 likert scale
Data was analysed using Principal Component Analysis based on polychoric correlation matrix and individual relationships were confirmed using Spearman rank correlation
Results
Principal Component Analysis
Neurotic
Extrovert
0.0
1.0
0.5 -
Emotionally Stable
Introvert -
Figure adapted from two PCA outputs (accounts for 90% of total variance) illustrating the relationships between variables and personality factors. The length of the arrow represents the approximate strength of the loading on both dimensions whilst its direction denotes its relationship with the personality axis. -
Tolerance
Lameness
Severity
Stoicism - +
Spearman Rank Correlations -
Contrary to common assumptions, there was no correlation between scores for lameness and severity (p=0.26)
Neuroticism negatively correlated with Stoicism which was derived from clinical data (p=0.04), confirming PCA findings
In support of PCA, Neuroticism also had a tendency to correlate negatively with Tolerance as rated by owners (p=0.08)
SRC did not confirm a relationship between Neuroticism and Severity (p=0.18)
Extroversion was positively correlated with lameness (p=0.03), in agreement with PCA + + +
Conclusions
This research challenges accepted practice in veterinary, pain and welfare fields, as lameness was not a reliable indicator of the severity of damage or degeneration
In addition, we provide preliminary evidence that personality plays a role in the expression of animal pain
More neurotic horses were less stoical and less tolerant, which suggests they may be more stressed by pain
More extrovert horses were more lame, regardless of actual tissue damage, suggesting their behavioural indicators of suffering are clearer
These findings offer preliminary support for our hypothesis that individual differences may confound behavioural measures of subjective states [2], with Neuroticism relating to sensitivity and Extroversion relating to how that is expressed
Although the extrovert response to pain was identified, knowledge gaps remain in how introvert individuals express pain
Because they are not as lame, pain may be more difficult to identify in introverts yet they may suffer more [3], making exploration and documentation of their pain response crucial for improved welfare
References
Acknowledgements
1. Ijichi, C., Collins, L., Creighton, E. & Elwood, R. 2013a. Harnessing the power of personality assessment: Subjective assessment predicts behaviour in horses. Behavioural Processes, 96,
2. Ijichi, C., Collins, L. & Elwood, R. 2013b. Evidence for the role of personality in stereotypy predisposition. Animal Behaviour, 85,
3. Koolhaas, J.M., De Boer, S.F., Coppens, C.M. & Buwalda, B Neuroendocrinology of coping styles: Towards understandings the biology of individual variation. Frontiers in Neuroendocrinology, 31,
We are indebted to the staff and clients at Tullyraine Equine Clinic, in particular Hugh Suffern (MVB, MRCVS), without whom this study would not have been possible.