Sk Calvert

The responsiveness of sows to their piglets in relation to the length of parturition and the involvement of endogenous opioids

Abstract The aim of this study was to describe maternal behaviour in the pig and to investigate the effect of endogenous opioids on maternal responsiveness. The behaviour of 16 Large White×Landrace female pigs was recorded around farrowing which involved recording the pigs posture and her response when piglets were present at her nose. To determine the role of endogenous opioids, sows were injected (i.m.) with either naloxone, an opioid antagonist, (1 mg kg −1 bodyweight ( n =8)) or saline ( n =8) at 3.75 h after the birth of the first piglet. Generally the initial period following the birth of the first piglet seemed to be the most active after which the sows spent almost all of the time in lateral recumbency. The results also show that farrowing sows are generally unresponsive to their piglets during farrowing. Sows receiving naloxone became more responsive towards their piglets. The changes seen in posture and responsiveness to piglets were delayed in sows with a longer parturition suggesting some involvement of cumulative piglet births on passivity. It is proposed that opioid-mediated passivity in the pig, characterised by lateral lying and unresponsiveness to piglets, may be advantageous by maximising suckling opportunities and reducing the risk of crushing piglets and of attracting predators to the nest.

Opioid-mediated changes in nociceptive threshold during pregnancy and parturition in the sow

Abstract This study aimed to investigate if pregnancy‐induced hypoalgesia occurs in the sow, and to examine the role of endogenous opioids which are known to be released in response to nociception. Sixteen Large WhitexLandrace multiparous sows were tested in straw bedded pens (2.5×2.5 m) during weeks 4, 8 and 12 of pregnancy and over the farrowing period. Testing involved thermal stimulation of eight areas on the rear‐quarters of the sows with a CO2 infra‐red laser until a physical response was seen (tail flick, leg move or muscle twitch) or for a maximum of 16 s. Over the farrowing period testing was more frequent, and at 3.75 h after the birth of the first piglet, half the sows received an injection (i.m.) of an opioid antagonist naloxone (N) (1 mg kg−1 body weight) with the remainder receiving a control dose of saline (S). Responses were recorded 15 and 30 min post‐injection. There was no significant difference between response times over weeks 4, 8 and 12 of pregnancy (P=0.152), however a significant rise was seen from week 12 to 5 days before parturition (P=0.002). Response times continued to rise until the birth of the first piglet by which time the majority of sows had stopped responding within 16 s (P<0.001). Response times fell over days 1, 2 and 7 post‐partum. After administration of naloxone response times fell compared to control animals at 15 min (P<0.001) and 30 min (P<0.01) post‐injection. These results suggest that nociceptive threshold increases during late pregnancy in the sow, perhaps as an endogenous defence against labour pain, and that during parturition this change in nociceptive threshold is, at least in part, opioid‐mediated. Oxytocin is known to be inhibited by endogenous opioids at parturition, thus future research should consider the potential role of increased nociception at birth as a negative feedback to oxytocin release.

Diversity of behaviour during novel object tests is reduced in pigs housed in substrate-impoverished conditions

Modern intensive farming conditions lack the diversity of substrates present in more natural environments and offer young animals fewer opportunities for interaction. Evidence exists that this may affect the organization of interactive patterns of behaviour, but shifts in behavioural diversity have not been measured directly. We investigated the effect of the substrate in the home pen on the diversity of behaviour in young growing pigs, Sus scrofa. Over 5 months, 26 pigs were housed singly in either substrate-impoverished (SI) or substrate-enriched (SE) conditions. Once every month we recorded the behaviour of these pigs in detail both in the home pens and in two novel object tests. In addition, we calculated the diversity of behaviour shown by SI and SE pigs in the home pen and in the novel object tests, using a relative behavioural diversity index. In the two novel object tests, SI pigs were less mobile than SE pigs and focused their behaviour on particular substrates. In addition, SI pigs showed less diverse behaviour than SE pigs. Our results show that the less diverse behaviour of SI pigs previously recorded in their home pens persists under novel conditions, supporting the hypothesis that substrate-impoverished housing conditions structurally affect the organization of behaviour in young growing pigs. Copyright 2000 The Association for the Study of Animal Behaviour.

The effect of environment on plasma cortisol and beta-endorphin in the parturient pig and the involvement of endogenous opioids.

Previous work has indicated that plasma cortisol increases during farrowing in the pig suggesting increasing physiological stress. The aim of this study was to determine changes in plasma cortisol and beta-endorphin over farrowing in the pig to obtain a more detailed profile of pituitary and adrenal release at this time and also to investigate the involvement of endogenous opioids in the mediation of the HPA axis. Indwelling jugular catheters were implanted, under general anaesthesia, in 31 Large White x Landrace gilts approximately 15 days before the expected parturition day (EPD). Gilts were moved into either a farrowing crate, without straw (n = 15), or a straw-bedded pen (n = 16) 5 days before the EPD. Samples were taken during the pre-farrowing period and then during farrowing itself. At 7.5 min after the birth of the first piglet (BFP), gilts either received naloxone, an opioid antagonist, (1 mg kg(-1) body weight, i.v.) or a control dose of saline. Plasma beta-endorphin increased following the BFP but remained fairly constant over the third and fourth hour of farrowing. Plasma cortisol continued to increase over the 4 h following the BFP. Changes seen in these hormones were generally insensitive to the environment and there was little evidence of opioid mediation of the HPA axis at parturition. From these results it is suggested that certain aspect(s) of parturition itself stimulate the HPA axis. However it is unknown if the rise in plasma cortisol is a result of some stress-inducing factor of the parturition process or whether it reflects a metabolic function. The study also demonstrates the lack of any inhibitory mediation of the HPA axis by endogenous opioids at parturition.

The Effect of Substrate-Enriched and Substrate-Impoverished Housing Environments on the Diversity of Behaviour in Pigs

In intensive farming situations, growing animals are housed in relatively barren environments. The lack of opportunity to perform substrate-interactive and manipulative behaviour patterns may affect the expression and organization of these behaviours. However, making direct comparisons of the behaviour expressed in environments of differing physical complexity is difficult. In this experiment a relative diversity index was used to compare the behavioural repertoires of pigs housed in two different environments for a period of five months. One group of pigs (substrate-enriched) had straw, forest bark and branches added to the standard pens and the other group (substrate-impoverished) did not. The pigs were individually housed, and their behaviour was focal sampled in these pens on one day each month. It was shown that the relative diversity of manipulative behaviour shown by the pigs in the substrate-impoverished environment was lower than in the pigs in the substrate-enriched environment (p < 0.05). The relative diversity of the whole behavioural repertoire shown by the pigs in the substrate-impoverished environment also tended to be lower than that in the substrate-enriched environment (p = 0.06). It is concluded that this may be due to a difference between the two groups in motivation to interact with and manipulate objects, or a function of the manipulable quality of the substrates available to them. Alternatively, exposure to substrate-impoverished environments may interfere with the ability to express manipulative behaviour. Both situations pose a threat to the welfare of growing pigs resident in barren environments.