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The social function of pain-related behaviour and novel techniques for the assessment of pain in lambs: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University, Turitea campus, Manawatu, New Zealand
Pain is a phenomenon that is physical and emotional. There is growing evidence to support
the idea that emotional neural systems in the brain drive future behaviour. The behavioural
reactions accompanying the pain experience are highly varied, which suggests multiple
functions. Pain-related behaviour often doesn’t occur in isolation. Instead, it is observable
by other animals, thus providing access to information about the emotional state of the
The purpose of this thesis was to investigate pain-related behaviour within a social context.
In the simplest terms, animal interactions occur in a dyad, where the animal displaying
a particular repertoire of behaviours is the actor and another viewing and potentially
responding to the actor’s behaviour is the observer. Each individual can be an actor and
Domestic sheep are a good model species for studying pain from a social perspective.
They are a social species with a strong tendency to form groups. Sheep provide us with
an opportunity to evaluate the social infl uences on pain within the context of painful
husbandry procedures normally undertaken in New Zealand such as tail docking, ear
tagging and castration. There is also some evidence that the social context affects the
behaviour and emotional state of sheep.
The social infl uences on pain perception and expression have only just begun to be
investigated and the studies contained in this thesis add a great deal to this research area.
Therefore, the literature review was presented at the end of the thesis and made reference
to the fi ndings of the previous experimental chapters of this thesis and introduced a
social/communicative function for pain related behaviour.
This other chapters then provided evidence for the social function of pain behaviour,
by investigating both sides of the actor-observer dyad. Two chapters focussed on the
actor lamb. One, which is presented as two papers, investigated novel ways pain may be
expressed by lambs. These are the fi rst studies to demonstrate changes in the ear posture
and facial expression of lambs associated with the negative experience of pain. The other
chapter, presented as another two papers, investigated what factors affect pain expression
by lambs. One study of this chapter demonstrates that the ontogeny of pain processing
appears to differ between male and female lambs, and the other demonstrates that
expression of pain behaviour depends on the relationship between the actor and observer
lamb and previous experience of the test environment.
There is also one chapter, comprised of one paper, which focussed on the observer lamb.
This paper investigated how pain expression by the actor lamb affected the behavioural
expression of the observer. This study demonstated socially facilitated behaviour of
lambs, possibly indicative of empathy, in response to conspecifi c pain using quantitative
behavioural methods, and a novel qualitative assessment technique.
This thesis culminates in a general discussion chapter which assesses the methodologies
used and their limitations, as well as drawing together the research presented in this thesis
and analyzing it in the context of the social communicative function of pain.