There is increasing evidence that restriction of pre-parturient behaviour in pigs is stress-inducing, characterised by an elevation in hypothalamic-pituitary-adrenal (HPA) activity in gilts. To determine whether pigs adapt to behavioural restriction, through modification of nest-building behaviour, we studied pre-parturient pigs in either farrowing crates (no bedding, n=7) or straw-bedded pens (n=7) in their first (gilts) and second (sows) parity, with physiological measurements being taken in the second parity. Observations and blood sampling were carried out during the pre-parturient phase. Crated pigs changed posture more often than penned pigs (F(1,12)=7.06, P<0.05), with the number of posture changes reducing across parities in both environments. The reduction in posture changing was more apparent in the crated sows which may indicate that attempted nest-building behaviour of sows with prior experience of farrowing crates is less fragmented. The crated pigs spent a greater proportion of time sitting across both parities (F(1,12)=9.4, P<0.01), and spent less time manipulating available substrates (F(1,12)=10.67, P<0.05). There was a tendency for penned pigs to spend a greater proportion of time standing (F(1,12)=3.77, P=0.076) with peak nesting behaviour occurring earlier in relation to parturition than in crated pigs. In addition penned sows performed more floor-directed behaviour than penned gilts, and at an earlier stage in relation to parturition. However, crated sows also performed peak nest-building earlier than crated gilts. Plasma cortisol profiles indicated elevated HPA activity in crated sows during the pre-parturient period (F(42,303)=1.43, P<0.05) suggesting increased physiological stress, however, the difference between crated and penned sows was less than that previously seen in gilts. The increased range of pre-parturient behaviours seen in the penned sows suggests that experience may result in an 'improvement' in their nest-building behaviour: earlier preparation of the nest site and then subsequent manipulation of substrates. The crated sows appeared to show some behavioural adaptation to the crate environment; earlier peak in floor directed behaviour and total substrate directed behaviour, reduced posture changing. In conclusion the nest-building behaviour of pigs is modified over parities with adaptation to the behavioural restrictions imposed by the farrowing crate. However, this adaptation, through prior experience, does not completely reduce the elevation in HPA activity previously reported in pre-parturient crated gilts.

When weaned early, piglets commonly take some time to accept solid food, resulting in a growth check and reduced welfare. The transmission of information about food between animals has been demonstrated in other species and it would be advantageous if this occurred in piglets. This experiment investigated the effects of pairing piglets that were consuming solid food with newly weaned piglets. Six litters of piglets did not receive solid food until weaning. In each litter four piglets (3 Plus 1 spare) were weaned at 21 days of age and housed together for 7 days and offered one of two foods (3 litters per food). At 28 days of age the remaining piglets were weaned and four pairs of piglets were formed, such that there were three experienced animals paired with three inexperienced observers, each pair having visual contact and varying degrees of physical contact (1: none, 2: through wire mesh, 3: housed together), and a pair of inexperienced piglets (4: housed together) to act as controls. Food intake and weight gain were recorded over a period of 7 days. There was no effect of food type on food intake or live-weight gain of the pairs but the inexperienced pigs had higher gains on food 1 than food 2. The inexperienced pairs ate less food than the other pairs and the experienced/observer pairs that were housed together had the greatest weight gain. The level of variation between piglets was such that there were no significant effects of pairing treatment on the weight gain of the inexperienced animals. Total time spent feeding increased with time from pair formation. The number of simultaneous feeding events was higher for the experienced/observer pairs housed together than for the inexperienced pairs. This experiment has indicated that food intake is stimulated when an inexperienced piglet is housed with an experienced piglet and, with further work, this could be exploited to alleviate the weaning check.

Oxytocin plays an important role at parturition due to its involvement in uterine contractions, foetal expulsion and the onset of maternal behaviour. The role of the related neurohypophysial hormone, vasopressin, is less clear; however, there is some evidence that it is also involved in maternal behaviour and its role in osmotic regulation is well established. The aim of this study was to investigate the inhibitory effects of endogenous opioids on these hormones during the expulsive phase of parturition in the pig, and to examine how opioid restraint interacts with environmental restriction. The subjects of this study were 31 Large Whitex Landrace primiparous sows (gilts). An indwelling jugular catheter was implanted under general anaesthesia at 12 days before the expected parturition day (EPD). From 5 days before the EPD 15 of the gilts were individually housed in a restrictive parturition crate without straw and 16 were individually housed in a straw-bedded pen. Blood samples were taken with increasing frequency towards and during parturition through a catheter extension to reduce disturbance. At 7.5 min after the birth of the first piglet half of the gilts in each environment received a dose of the opioid receptor antagonist naloxone (1 mg/kg, i.v.) with the remaining gilts receiving saline as a control. Overall, there was no effect of environment on either circulating oxytocin or vasopressin. However, both oxytocin and vasopressin were inhibited by endogenous opioids during the expulsive phase. The inhibitory effects of opioids on these hormones did not appear to have any adverse effects on the progress of parturition as judged by cumulative piglet birth intervals. The regulation of the opioid inhibition of oxytocin and vasopressin during parturition is discussed in relation to other neurotransmitters and whether opioid inhibition of these neurohypophysial hormones is part of the 'normal' physiological response to parturition or whether it is stress-induced.

In a previous experiment the provision of straw to group-housed pigs increased the number of daily feeder visits. This effect of straw is comparable with conditions of reduced social competition for access to the feeder. The aim of this experiment was to investigate if changing straw provision within a pen resulted in similar and reversible effects in this behaviour. One hundred and twenty male pigs (41.1 (s.e. 0.43) kg) were used in three blocks each of four pens of 10 pigs. In each block of 42 days duration one pen had no straw throughout (treatment 1); one pen had no straw for 21 days (period 1) followed by straw for 21 days (period 2) (2); one pen had straw followed by no straw (3) and one pen had straw throughout (4). The pens were situated in a naturally ventilated building with light from 06.00 to 20.00 h. Each pen had a kennel, a lying area and a single-space computerized feeder for recording feeding behaviour. The pigs' activity was recorded on video in the 2nd and 5th weeks of each block. The number of feeder visits was slightly higher for pigs with straw (1: 9.69 v. 4: 10.46) but this was not significant (P > 0.05). The effect was more marked for treatment 2 where the visits increased (P < 0.01) from period 1 (8.52) to period 2 (10.64) and for treatment 3 where they decreased (11.20 v. 10.10). Pigs without straw (treatment 2) spent more time in the kennel than those with straw (treatment 4) (P < 0.05). For treatment 2 the proportion of time spent in the kennel fell from 0.607 in period 1 to 0.288 in period 2 (P < 0.01). There was a general trend for more activity and more lying outside the kennel when straw was provided. The effect of straw provision was not as marked as that seen previously; nevertheless changing straw provision (treatments 2 and 3) did result in all increase in feeder visits with straw, probably related to the increase in general activity and lying outside in the area adjacent to the feeder.

ContentsPrevious studies have shown an increase in plasma cortisol in gilts over farrowing irrespective of environment suggesting that factor(s) associated with parturition itself cause physiological stress. Factors involved in mediating the hypathalomo–pituitary–adrenal (HPA) axis at parturition are not well understood. This study examines the effect of piglet expulsion on the pituitary–adrenal axis by measurement of plasma cortisol, adrenocorticotropic hormone (ACTH) and β‐endorphin. The effect of farrowing environment in modulating the acute response to piglet expulsion is also investigated. Twelve second parity sows, with indwelling jugular catheters, were moved into either a farrowing crate or a straw‐bedded pen 5 days before their expected parturition date (EPD). Blood samples were taken from each sow during a prefarrowing baseline period and then rapid samples (2.5 mins) were taken for 10 min following the birth of two piglets. No effect of environment was found on any of the hormonal variables which reinforces the hypothesis that the physiological stress seen in parturient pigs is due to some intrinsic factor of parturition. Plasma cortisol, ACTH and β‐endorphin did not change significantly in the period following piglet expulsion suggesting that individual piglet expulsions do not play a major role in ‘parturition stress’. There was however, an increase in plasma cortisol, ACTH and β‐endorphin in response to increasing piglet number which is consistent with previous studies of general farrowing in which cortisol increased as farrowing progressed. Therefore this study reinforces the hypothesis that physiological stress increases with ongoing parturition although this does not appear to be a result of piglet expulsion. The potential role of other factors which may be involved in causing ‘parturition stress’ should be investigated.

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 pig's 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.

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 β-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×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 β-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.

Single-space feeders used in pig selection may favour those pigs which control access to the feeder. This was not the case when straw bedding was provided (Nielsen et al. 1995). However, straw may have modified behaviour and masked the effects of aggression. Therefore an experiment was conducted to examine the influence of straw bedding on behaviour and performance of pigs fed via a single-space feeder. The food intake, growth rate, feeding and social behaviour of 8 pens of 10 pigs (start weight 40 kg) with or without straw (4 pens/treatment) were recorded over a period of 35 days. Food was supplied by one single-space computerised feeder in each pen and this equipment provided records of feeding behaviour. Social behaviour and activity was observed by video recording on two occasions in week 2 and week 4 of the experiment. Each pen had an enclosed kennel. The provision of straw increased the number of visits to the feeder (13.11 vs. 9.22; P<0.05) and these were of a shorter duration (4.34 vs. 6.18 min; P<0.05). The pigs on straw had a higher growth rate than those without (803 vs. 741 g/d; P<0.05). Pigs with straw had a lower proportion of observations in the kennel (0.470 vs. 0.683; P<0.001) and spent less observations lying (0.765 vs. 0.806; P<0.05). The number of aggressive incidents initiated was higher with straw (14.8 vs. 8.8; P<0.05). The modified feeding pattern with straw may have been due to a higher general level of activity or a combined effect of low ambient temperature and the position of the feeder relative to the kennel. Thus this effect of straw may be confined to cold environments.

This experiment was designed to investigate the function of vocalisations of the parturient ewe to her lambs in two breeds of sheep, a highly selected lowland breed (Suffolk), and a less selected hill breed (Scottish Blackface). Sheep have a specific lambing vocalisation, the low-pitched bleat or "rumble", that is made almost exclusively to the lamb. The hypothesis was that this "care-giver" bleat will be important in the formation of the ewe-lamb bond. Ewes also make high-pitched bleats, considered to be "protest" or distress bleats, after the birth of the lamb. Vocalisation data were collected from inexperienced and experienced ewes of both breeds, and their lambs. Additionally, an embryo transfer study between the two breeds was carried out to investigate interactions between ewe and lamb bleating. Low-pitched bleating was higher in primiparous ewes than multiparous ewes, and highest in primiparous Blackface ewes (mean bleat rate: primiparous Blackface=7.04, multiparous Blackface=2.73, primiparous Suffolk=3.99, multiparous Suffolk=2.18; P<0.005). An increase in litter size, or raising lambs of a different breed, had no effect on the rate of low-pitched bleating. The number of Suffolk ewes making high-pitched bleats was greater than Blackface ewes (61.4% vs. 35% for Suffolk and Blackface ewes respectively, P<0.01) and the rate of bleating increased with twin litters. Suffolk lambs had a higher bleat rate than Blackface lambs (mean bleat rate: Blackface=0.252, Suffolk=0.622, P<0.01), and lambs born to a primiparous ewe had a higher bleat rate than lambs with a multiparous dam (P<0.05). Birth of the second twin lamb caused a doubling in individual lamb bleat rate in both breeds. Ewe low-pitched bleat rate is, therefore, affected by intrinsic factors, ewe breed and experience, but not by characteristics of the lamb in the immediate postnatal period. The function of the bleat may be to strengthen bonding with the lamb, and the higher rate in primiparous ewes may reflect both the immaturity of the system in inexperienced animals and a slower rate of bond formation. High-pitched bleating is affected by ewe breed and may reflect the likelihood of separation of the ewe from the lamb. Lamb vocalisations are modified by their rearing experience, and appear to represent a signal of need. Increased domestication of the Suffolk breed may have led to an increase in lamb vocalisations.

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.

Previous work has suggested that gilts housed in a crated environment, without bedding, are more physiologically stressed over the pre-parturient period as characterised by elevated cortisol levels (Lawrence et al, 1994) compared to those housed in a straw bedded pen. β-endorphin and Adrenocorticotropic Hormone (ACTH) are released concomitantly from the adenohypophysis (Guillemin et al, 1977) and have been shown to increase during parturition in humans (Fajardo et al, 1994), with ACTH being involved in the stress response, and β-endorphin possibly playing a role in an endogenous defence against the pain of parturition. This study aimed to demonstrate the pre-parturient changes in these plasma hormonal concentrations and activity levels in relation to two different farrowing environments.