Stress and parturition in the pig

A. B. Lawrence, K. A. McLean, S. Jarvis, C. L. Gilbert, J. C. Petherick

Research output: Contribution to journalArticlepeer-review

Abstract

Sows are routinely housed in behaviourally restrictive crates when giving birth. In the UK there has been considerable public concern over the use of these parturition (or farrowing) crates. In attempting to objectively assess the stress experienced by sows in farrowing crates it has been necessary to consider the potential inter-relationships between behaviour, stress and the physiology associated with parturition. Evidence from behaviour and the hypothalamic-pituitary-adrenal (HPA) axis suggests that farrowing crates elicit a stress response, indicated by raised plasma Cortisol, by interfering with pre-parturient maternal behaviour (nest-construction). Cortisol concentrations, however, also rise during parturition irrespective of whether sows are housed in crates or in pens that allow greater behavioural freedom, which may indicate that parturition itself has stress-inducing aspects. The hormone oxytocin, released from the posterior pituitary is fundamentally involved in the parturition process. Recently it has become apparent that opioids play a significant role in regulating oxytocin release both centrally and at the level of the pituitary. The interaction between opioids and the oxytocin system allows for the possibility that stress can influence oxytocin release. An acute midpartum stress is highly effective at restraining oxytocin and slowing delivery rate in rats and pigs, an effect that appears largely opioid-mediated. The work reviewed here suggests that opioids also strongly regulate oxytocin release in pigs farrowing under undisturbed conditions as the opioid-antagonist naloxone elevates oxytocin in sows farrowing in crates and pens. The function of this opioid-restraint of oxytocin during normal deliveries remains unclear. The crate environment itself appears to be associated with a weak opioid-restraint of oxytocin during the late delivery phase, which may reflect a mild adverse response to giving birth in the crate. Overall, the results suggest that crates do not act to strongly elevate hypothalamicopioid tone to inhibit posterior pituitary release of oxytocin. By inference the evidence suggests that farrowing crates are not a potent source of stress for sows during actual delivery.

Original languageEnglish
Pages (from-to)231-236
Number of pages6
JournalReproduction in Domestic Animals
Volume32
Issue number5
DOIs
Publication statusPublished - 1997
Externally publishedYes

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