No abstract

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.

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 White x Landrace multiparous sows were tested in straw bedded pens (2.5 x 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.

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.

Previous work has shown that an acute mid-partum can inhibit oxytocin secretion and prolong delivery in the pig, an effect that is opioid-mediated (Lawrence et al., 1992). However, where gilts were given 5 days to adapt to the farrowing crate, there was little indication that the crate interfered with oxytocin secretion or the progress of parturition relative to gilts farrowing in pens with straw bedding (Lawrence et al., 1995). This experiment aimed to directly assess the extent to which crates or pens affect opioid-control of oxytocin (OT) secretion as a means of measuring stress in the parturient gilt.