The thesis examines the relationships between pain, stress and behaviour of the
pig around parturition. This includes the effects of pregnancy and parturition on
maternal nociception, and environmental restriction on stress physiology and
behaviour. The main findings are:
1. Late pregnancy and parturition in the pig is associated with an endogenous
analgesic system which is, at least in part, mediated via endogenous opioids.
2. Passivity and inactivity are major components of maternal behaviour in the
pig and are suggested to be indicative of good maternal care in this species.
The thesis provides evidence of an opioid mediation of maternal behaviour
which could arise through several potential routes, namely: the action of the
analgesic system, general sedation, the inhibition of oxytocin release.
3. A rise in plasma Cortisol, ACTH and P-endorphin concentrations were found
in pre-parturient gilts housed in both straw bedded pens and conventional
farrowing crates. However crates caused further stimulation of the HPA axis
reflecting thwarting of nestbuilding behaviour in this restrictive environment.
4. The farrowing crate did not cause further HPA activity during the expulsive
phase which may reflect the inactivity of the pig at this time. A rise in plasma
Cortisol was found as the expulsive phase progressed irrespective of
environment however the thesis found that the expulsion of a piglet does not
appear to play a major role in this.
Overall the thesis has realised a better understanding of parturition in the pig by
relating the physiology and behaviour of the pig at this time. The possibility of
maternal pain influencing the progress of parturition and maternal behaviour is
discussed in relation to possible mechanisms by which this may occur. The
thesis has also highlighted welfare implications regarding the use of farrowing
crates, and provides information which may be used when considering changes to
housing for parturient pigs.