Ka McLean

The effect of environment on behaviour, plasma cortisol and prolactin in parturient sows

Nest-building in the pig is thought to be stimulated by a pre-parturient surge in prolactin. There is concern that sows in crates may experience psychological stress as a result of physical interference with nest-building. n nThirty-three gilts were implanted with jugular catheters approximately 10–14 days before expected date of parturition (EPD). On day 5 before EPD, gilts were moved into either conventional farrowing crates without bedding (treatment C; n=16) or pens allowing freedom of movement with bedding (treatment P; n=17). The animals were blood sampled on the day before and the day after introduction to the treatments. Blood and behaviour sampling was resumed 48 h before EPD and continued until 4 h post-commencement of farrowing. n nAs with previous studies gilts in both environments were more active (P<0.001) and performed more substrate-directed behaviour in the pre-parturient period (P<0.001). Gilts in pens spent considerable amounts of time in straw-directed behaviour, and gilts in crates increased amounts of floor- and fixture-directed behaviour (both P<0.001). Prolactin was not affected by treatment and increased in both environments over the same time period as this substrate-directed behaviour. However, the causal role of prolactin in nest-building must now be questioned given that a number of individuals showed no increase in prolactin over the 48 h before EPD, but still showed an increase in substrate-directed activity. Cortisol was strongly affected by treatment with treatment C having elevated total cortisol over much of the pre-parturient period (P<0.001). Cortisol also increased in penned animals during parturition. There were no consistent correlations among behaviour, prolactin and cortisol. n nThe general increase in cortisol in the early post-partum period may suggest that parturition in itself has stress-inducing aspects. The additional rise in cortisol found in the crated sows may indicate that the close confinement of the crate, by interfering with the expression of maternal behaviour, induces psychological stress. There was no evidence that the elevated cortisol response in crated gilts extended beyond the end of parturition.

Naloxone prevents interruption of parturition and increases plasma oxytocin following environmental disturbance in parturient sows

Experiments in rodents have suggested that environmental disturbance can disrupt parturition through an opioid-mediated inhibition of oxytocin secretion. To test this hypothesis in a large animal model, 14 primiparous female pigs were allowed to commence parturition in a strawed pen. Five of these gilts were allowed to continue parturition undisturbed in this pen, while the remainder were moved to a farrowing crate immediately after the birth of the first piglet. At this time, pigs were injected subcutaneously with either the opioid antagonist naloxone (n = 4; dose 1 mg/kg body weight) or saline (n = 5). Whereas the undisturbed pigs all gave birth to a second piglet within 53 min, in three of the five disturbed and saline-treated pigs no further births occurred for 2 h, at which time oxytocin was administered subcutaneously to restart parturition. By contrast, all of the naloxone-treated pigs gave birth spontaneously within 2 h, although mean interbirth intervals were still prolonged compared to undisturbed pigs. In a second experiment, nine primiparous female pigs with chronic catheters preplaced in the external jugular vein were similarly moved after the birth of their first piglet and either injected with naloxone (n = 5) or saline (n = 4). Again, parturition was interrupted in three out of four saline-treated animals for at least 2.5 h, but resumed promptly when exogenous oxytocin was administered. Plasma concentrations of oxytocin in these pigs were significantly lower than in naloxone-treated pigs, five out of six of which gave birth spontaneously to one or more piglets within 2.5 h.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of parity and environmental restriction on behavioural and physiological responses of pre-parturient pigs.

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.

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.

Vocalisations between mother and young in sheep: effects of breed and maternal experience

Abstract 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

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.

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 effects of chronic environmental stress on parturition and on oxytocin and vasopressin secretion in the pig

Previous work has suggested that an acute behavioural confinement in mid-partum can inhibit oxytocin secretion and prolong delivery in the pig, an effect that is opioid mediated. The present experiment investigated the effect of longer-term (chronic) behavioural confinement, that has previously been shown to elevate total plasma cortisol, on speed of delivery and on plasma oxytocin and lysine vasopressin concentrations during the peri-parturient period in primiparous pigs (gilts). Five days before their expected parturition (farrowing) date, gilts with preplaced jugular catheters were either confined to farrowing crates that severely restricted maternal behaviour, or housed in pens that permitted free movement and maternal behaviour (e.g. nest building). Blood samples were taken continuously from 24 h before the birth of the first piglet (BFP) to 6 h post-BFP, and for oxytocin on Days 1, 2, and 7 following parturition (Days P1, P2, P7). Both oxytocin and vasopressin were strongly influenced by parturition (P<0.001). There was no overall effect of chronic crating on either hormone, but crated and penned gilts did show significant differences with respect to the pattern of both oxytocin and vasopressin concentrations over time (P<0.05 in both cases). Oxytocin and vasopressin first increased in crated and penned gilts from 3 h pre-BFP (P<0.05). Crated gilts subsequently showed greater increases in both oxytocin and vasopressin over the first hour of delivery than penned gilts (mean oxytocin (pmol 1−1): 53.3±8.5 vs. 39.7±5.0 for crated vs. penned gilts; mean vasopressin (pmol l−1):4.4±0.7 vs. 2.0±04 for crated vs. penned gilts; both P<0.05). For oxytocin, crated gilts then showed subsequent declining concentrations relative to penned gilts (P<0.05). For vasopressin, penned gilts reached similar concentrations as crated gilts in the third hour post-BFP before vasopressin concentrations in both groups declined. Crated gilts also gave birth to piglets faster in the early stages of delivery (e.g. mean interval between Piglets 2 and 3 (min): 9.6±2.5 vs. 25.6±8.54 for crated and penned gilts, respectively: P<0.02). We conclude that confinement of gilts to a farrowing crate for 5 days neither adversely affects the progress of delivery in the primiparous pig nor the secretion of posterior pituitary hormones involved in parturition.

In vivo measurements of muscle volume by automatic image analysis of spiral computed tomography scans

This study investigates the accuracy of an automatic image analysis method that was developed for spiral computed tomography scans (SCTS), with the objective of calculating the volume of muscle in the hind leg (HLMV CT ) and lumbar region (LRMV CT ) in lambs. The first step in the image analysis method was the isolation (segmentation) of the muscle regions in each image of the SCTS, using a new program that was implemented in the Sheep Tomogram Analysis Routines software (STAR). Due to the differences of muscle shape in the regions investigated, the new segmentation program applies different segmentation paths in specific subregions. These were automatically identified by the program based on skeletal landmarks. After the segmentation was completed, the muscles areas were automatically measured by counting the pixels representing muscle in each image; the volumes were calculated by adding the muscle areas of each image multiplied by the depth of the image (inter-slice distance). The accuracy of these measures of muscle volume was evaluated, using regression analysis, by comparing HLMV CT and LRMV CT to the hind leg and lumbar region muscle weights measured after dissection (HLMW D , no. =240, and LRMW D , no. =50, respectively) of Texel (TEX) and Scottish Blackface (SBF) female and male lambs slaughtered in 2003-04. The effects of breed, sex and year on the association (SCTS v . dissection) were evaluated. There was a strong association between HLMV CT and HLMW D ( R 2 =97·4%), which only increased slightly ( R 2 =97·7%) when breed was included in the model. This indicates that HLMW D can be estimated directly from HLMV CT with a high degree of accuracy. For the lumbar region, the association was high ( R 2 =83·0% to 88·8% depending on the model) but lower than in the hind leg, probably because the automatic segmentation isolates only the areas of the longissimus lumborum and multifidi muscles. Breed had a significant effect on the prediction of LRMW D from LRMV CT , as well as sex in the case of the TEX lambs. The results indicated that the predictions of LRMW D from LRMV CT require different equations for very divergent breeds such as TEX and SBF.

Prediction of total body tissue weights in Scottish blackface ewes using computed tomography scanning

Thirty cull Scottish Blackface ewes were scanned three times over a period of 1 week using X-ray computed tomography (CT). Cross-sectional CT reference scans were taken at seven anatomical sites per ewe: ischium (ISC), femur (FEM), hip (HIP), 5th lumbar vertebra (LV5), 2nd lumbar vertebra (LV2), 8th thoracic vertebra (TV8) and 6th thoracic vertebra (TV6). Ewes were then slaughtered and dissection measurements collected. Results of multiple regression analyses suggested that five reference scans allow accurate prediction of total weights of bone, muscle and fat (carcass and internal). The most informative cross-sectional scans were ISC, HIP, LV5, LV2 and TV8, from which prediction equations were derived. Fat and muscle weights were predicted accurately (R 2 = 80 to 99%) but bone weight was predicted less accurately (R 2 = 56%). Repeatabilities were high for the CT measurements used to predict fat and muscle (0•82 to 0•99) but lower for those used to predict bone (0•19 to 0• 86).