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

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Effects of Nesting Material Provision and High-Dose Vitamin C Supplementation during the Peripartum Period on Prepartum Nest-Building Behavior, Farrowing Process, Oxidative Stress Status, Cortisol Levels, and Preovulatory Follicle Development in Hyperprolific Sows

Hyperprolific sows often experience increased oxidative stress during late gestation and lactation periods, which can adversely affect the farrowing process and overall lactation performance. This study examines the influence of providing a coconut coir mat (CCM; 1 × 1 m) as nesting material, supplementing high-dose vit-C (HVC; 20% vit-C, 10 g/kg feed) as an antioxidant, or both on maternal behavior, the farrowing process, oxidative status, cortisol levels, and preovulatory follicle developments in sows with large litters. In total, 35 sows (Landrace × Yorkshire; litter size 15.43 ± 0.27) were allocated to the following four treatment groups: control (n = 9, basal diet), vit-C (n = 8, basal diet + HVC), mat (n = 10, basal diet + CCM), and mat + vit-C (n = 8, basal diet + HVC + CCM). A post-hoc analysis showed that compared with sows that were not provided CCM, mat and mat + vit-C groups demonstrated increased durations of nest-building behavior during the period from 24 h to 12 h before parturition (p < 0.05 for both), reduced farrowing durations, and decreased intervals from birth to first udder contact (p < 0.01 for both). The mat group exhibited lower advanced oxidation protein product (AOPP) levels during late gestation and lactation periods than the control group (p < 0.05). Sows with HVC supplementation showed longer farrowing durations than those without HVC supplementation (p < 0.0001). The vit-C group had higher salivary cortisol levels on day 1 after farrowing than the other treatment groups (p < 0.05). Furthermore, the follicle diameters on day 3 after weaning in the vit-C group tended to be smaller than those in the control group (p = 0.077). HVC supplementation prolonged farrowing and increased the physiological stress on postpartum, and no advantageous effects on maternal behavior and developmental progression of preovulatory follicles were observed. Hence, alternative solutions beyond nutritional approaches are required to address increased oxidative stress in hyperprolific sows and secure their welfare and reproductive performance. The present results substantiated the positive impact of providing CCM as nesting material for sows with large litters on nest-building behavior and the farrowing process, which could mitigate the deleterious consequences induced by peripartum physiological and oxidative stress.

Defining "Normal" in Pig Parturition

Simple Summary

The dual considerations of efficient food production and good animal welfare have never been so important nor under such strong public scrutiny as they are in current times. Intensive animal production industries play an important role in feeding an ever-growing, increasingly affluent population that is hungry for animal proteins. The efforts to improve efficiency in these production systems must not come at the cost of animal welfare. One pain point in pig production is that of parturition, where factors such as litter size and sow-housing type have been shown to influence the process and outcome. However, there are still many gaps in knowledge surrounding the normal physiology and endocrinology in a farrowing and this review seeks to summarise what is known and highlight areas where further work is required.

Abstract

Animal production industries rely on efficient and successful reproductive outcomes, with pigs being no exception. The process of parturition in pigs (farrowing) can be especially prolonged, due to the large numbers of piglets being born (on average, approximately 13 piglets per litter in Australian conditions). Difficulties in farrowing (dystocia) lead to poor piglet outcomes and health problems in sows, in turn, causing economic loss for producers and welfare concerns for the animals. Despite the importance of this topic and publications in the area stretching back nearly 50 years, there is still no consensus on the prevalence of dystocia in pigs nor on how to identify a pig experiencing the condition. Understanding the process of parturition and the factors that influence its success is a crucial step towards the early identification of sows undergoing dystocia and development of best practices to assist them. This article describes the key factors that contribute to successful farrowing and identifies areas in which more research is required before the parturition process in the pig can be fully understood.

Review: Physiology and nutrition of late gestating and transition sows

The physiology during late gestation and the transition period to lactation changes dramatically in the sow, especially during the latter period. Understanding the physiological processes and how they change dynamically as the sow approaches farrowing, nest building, giving birth to piglets, and producing colostrum is important because these processes greatly affect sow productivity. Glucose originating from assimilated starch accounts for the majority of dietary energy, and around farrowing, various organs and peripheral tissues compete for plasma glucose, which may become depleted. Indeed, physical activity increases shortly prior to farrowing, leading to glucose use by muscles. Approximately ½ to 1 d later, glucose is also needed for uterine contractions to expel the piglets and for the mammary gland to produce lactose and fat for colostrum. At farrowing, the sow appears to prioritize glucose to the mammary gland above the uterus, whereby insufficient dietary energy may compromise the farrowing process. At this time, energy metabolism in the uterus shifts dramatically from relying mainly on the oxidation of glucogenic energy substrates (primarily glucose) to ketogenic energy supplied from triglycerides. The rapid growth of mammary tissue occurs in the last third of gestation, and it accelerates as the sow approaches farrowing. In the last 1 to 2 wk prepartum, some fat may be produced in the mammary glands and stored to be secreted in either colostrum or transient milk. During the first 6 h after the onset of farrowing, the uptake of glucose and lactate by the mammary glands roughly doubles. Lactate is supplying approximately 15% of the glucogenic carbon taken up by the mammary glands and originates from the strong uterine contractions. Thereafter, the mammary uptake of glucose and lactate declines, which suggests that the amount of colostrum secreted starts to decrease at that time. Optimal nutrition of sows during late gestation and the transition period should focus on mammary development, farrowing performance, and colostrum production. The birth weight of piglets seems to be only slightly responsive to maternal nutrition in gilts; on the other hand, sows will counterbalance insufficient feed or nutrient intake by increasing mobilization of their body reserves. Ensuring sufficient energy to sows around farrowing is crucial and may be achieved via adequate feed supply, at least three daily meals, high dietary fiber content, and extra supplementation of energy.

A milk-sharing economy allows placental mammals to overcome their metabolic limits

Here, we demonstrate that a naturally evolving behavior (allonursing) has greater effect on reproductive power (mass per unit of time) and output (litter mass at birth) than does artificial selection (domestication). Additionally, we demonstrate the importance of resource optimization afforded by sociality (rather than resource abundance per se) in shaping a species’ life history profile and its ability to overcome its own physiological constraints.

Maternal resource availability and metabolism have a strong limiting effect on reproductive output. Allomaternal care and domestication increase the energy available to the mother and should correlate with an increase in reproductive output. Here, we take a comparative approach to understand how this increase is accomplished (e.g., litter mass, reproductive frequency, etc.) and the strength of the effect among different forms of external energetic supplementation. We find that domestication and all forms of allocare correlate with increased fertility. All forms of provisioning correlate with larger litters without compromising offspring size. The greatest increase we observe in reproductive power is in species that practice allonursing. Our results suggest that the ultimate factor limiting reproductive output in placental mammals is maternal metabolic power rather than resource availability.

Incidence of dystocia at piglet level in cloprostenol-induced farrowings and associated risk factors

Few studies have investigated risk factors for dystocia in swine, although this birthing abnormality can compromise welfare of both sows and piglets by increasing stillbirth rate and decreasing sow productivity. This study aimed to determine risk factors associated with dystocia at piglet level in cloprostenol-induced farrowings. A dystocia event was recorded when a birth interval exceeded 45 min or when manual extraction was applied. Data were collected from 898 piglets born from 77 Landrace × Yorkshire crossbred sows, which were induced for farrowing on day 114 of gestation. Generalized linear mixed models (GLMMs) were used to evaluate the association between dystocia and parity, gestation length, litter size, relative birth order (RBO (%) = 100 ⋅ birth order/litter size), birth weight, crown rump length, body mass index, ponderal index, piglet's sex, use of oxytocin, and stillbirth. Sows nested in farrowing batches were fitted as random factors in GLMMs. Incidence of dystocia at piglet and farrowing levels was 11.0 % and 75.3 %, respectively. The final multivariate model explained 20.1 % variation of dystocia. RBO had a quadratic effect on dystocia in which incidence of dystocia decreased from RBO ≤ 40 % to RBO = 60 %–70 %, and then increased to the end of parturition. Piglets with birth weight > 1700 g and stillborn piglets had higher odds of dystocia in comparison with piglets with a birth weight of 900–1700 g (OR = 2.63; 95 % CI = 1.66–4.18) and live-born piglets (OR = 2.62; 95 % CI = 1.12–6.15), respectively. This study indicates that dystocia is very common in cloprostenol-induced farrowings and suggests that the last one-third of parturitions is the most important stage to be supervised, and selection for homogenous litters and moderate high birth weight may reduce the rate of dystocia.

Risk factors associated with dystocia in swine

Background and Aim:

Dystocia in swine can increase the stillbirth rate; however, its importance in pig-breeding systems has been underestimated. Until now, few studies have investigated dystocia and associated risk factors. Therefore, in this study, we aimed to evaluate the effects of various risk factors on dystocia in swine.

Materials and Methods:

Out of 5,557 piglets, we included 4,997 piglets in risk analysis study. The dependent variable was dystocia, which was recorded when a birth interval exceeded 45 min or when obstetric assistance was applied. The independent variables were parity, gestation length, litter size, birth order, gender, presence of a dead piglet, birthweight, crown rump length, body mass index, ponderal index, and oxytocin use. We used generalized linear mixed models to examine the associations between potential risk factors and dystocia at the piglet level.

Results:

A total of 6% of the piglets were born with a dystocia event, and 47.2% of the farrowing experienced at least one event. Dead piglets and piglets with a crown rump length of >31 cm were associated with an increased dystocia rate. This rate decreased from birth order 2 to 7, stabilized to 11, and then increased till the end of the fetal expulsion process.

Conclusion:

Dystocia is common in swine. Therefore, this condition should be carefully addressed by veterinarians and farrowing house personnel so that its adverse effect on welfare and productivity of sows and survivability of piglets can be reduced. Further studies investigating dystocia status and risk factors in different swine farrowing systems should be undertaken to provide more knowledge about this neglected condition.

Effects of various procedures for synchronisation of parturition in sows

Objective: The effects of various parturition controlling measures in sows on the relevant parameters for parturition were investigated. Material and methods: A total of 1975 study animals were divided into five groups: control group: A (n = 710); trial groups: B (n = 719), C (n = 180), D (n = 175), E (n = 191). The control group (A) included sows that spontaneously farrowed until day 114 of gestation. The remaining sows were administered a PGF2α-analogue (175 µg cloprostenol) on day 114. All sows that farrowed within 24 hours after prostaglandin-medication were summarised in trial group B. Dams that did not farrow until day 115 were either administered oxytocin (20 IU i. m., group C) or carbetocin in two different doses (70 µg, group D or 35 µg, group E). The sows were monitored during the peripartal period over 24 hours. Results: 83.8% of the farrowings were without any complications. The percentage of dystocia varied between the individual groups. Given a complication-free farrowing the expulsion stage began 13.0 hours (group B), 2.4 hours (group C), 1.6 hours (group D) and 1.4 hours (group E) after medication. The expulsion interval of the farrowing of two piglets decreased from 21.1 minutes with spontaneous farrowings (group A) to 18.6 minutes (group E) as a result of the administration of 35 µg carbetocin. The rate of stillborn piglets as well as the incidence of puerperal disorders and the losses of the suckling piglets also gradually, partly even significantly (p 0.05) decreased from group A to E. Conclusion and clinical relevance: The results of this study show that the use of the long-acting oxytocin carbetocin has advantages compared to oxytocin (e. g. shortened duration of birth, reduction of stillbirths). The tested dosages of carbetocin (35 µg or 70 µg) proved to be equally effective. Administration of the lower dose is recommended, since this reduces use of the active ingredient.

Non-infectious factors associated with stillbirth in pigs: a review

The main objective of this review is to provide current information regarding non-infectious risk factors associated with stillborn piglets. These factors can be roughly categorized as genetic, maternal, piglet and environmental factors, but also interactions exist between several factors. An understanding of this multifactorial problem should help practitioners and farmers implementing a more effective farrowing management to obtain a high reproductive efficiency. From the papers studied in this review, it can be concluded that litter size, parity, sow's body condition and farrowing supervision/birth assistance seems to be the most relevant risk factors associated with stillborn piglets.

Plasma oxytocin concentrations during late pregnancy and parturition in the dog

While oxytocin is widely used in the treatment of dystocia in dogs, there is little information about its secretion before and during normal unassisted whelping. We therefore measured plasma oxytocin concentrations during late pregnancy and the expulsive stage of parturition. Blood samples were collected from eight dogs at 3-min intervals during a 42-min period between the 2nd and 14th day before whelping and during parturition after the birth of 1-3 pups. The litters consisted of 5-15 pups and the progression of the expulsive stage was linear and nearly parallel in the eight bitches. The overall mean (+/-S.D.) plasma oxytocin concentration during late pregnancy was 3.6+/-2.1pg/ml. Mean values in individual dogs ranged from 1.2 to 7.4 pg/ml, but the intra-animal variation was rather small. During the expulsive stage the overall mean (+/-S.D.) plasma oxytocin concentration was 12.9+/-13.9 pg/ml, with mean values in individual dogs ranging from 3.5 to 46 pg/ml. The mean area under the oxytocin curve for parturient dogs was significantly higher (P<0.05) than for pregnant dogs. During the expulsive stage, the peak plasma oxytocin level in individual dogs ranged between 10 and 117 pg/ml. In six of the eight dogs a pup was born during blood collection and in five of these animals the plasma oxytocin concentration increased temporarily during periods of abdominal straining and expulsion. However, straining efforts and expulsion were not consistently associated with a rise in the circulating oxytocin level. It is concluded that in the dog plasma oxytocin levels are higher and more variable during the expulsive stage of parturition than during late pregnancy. Interrelationships between the secretion pattern of oxytocin, the level of uterine contractility, and the progress of fetal expulsion in dogs need further exploration.

Factors affecting duration of the expulsive stage of parturition and piglet birth intervals in sows with uncomplicated, spontaneous farrowings

Modern pig farming is still confronted with high perinatal piglet losses which are mainly contributed to factors associated with the progress of piglet expulsion. Therefore the aim of this study was to identify sow- and piglet factors affecting the duration of the expulsive stage of farrowing and piglet birth intervals in spontaneous farrowing sows originating from five different breeds. In total 211 litters were investigated. Breed affected duration of the expulsive stage significantly: the shortest duration was found in Large White x Meishan F2 crossbred litters and the longest duration in Dutch Landrace litters. No effect of parity on the duration of the expulsive stage was found. An increase in littersize (P<0.01), an increase in number of stillborn piglets per litter (P<0.05) and a decrease of gestation length (P<0.05, independently of littersize) all resulted in an increased duration of the expulsive stage of farrowing. A curvilinear relationship between birth interval and rank (relative position in the birth order) of the piglets was found. Besides that, piglet birth intervals increased with an increasing birth weight (P<0.001). Stillborn (P<0.01) and posteriorly presented (P<0.05) piglets were delivered after significantly longer birth intervals than liveborn and anteriorly presented piglets. The results on sow- and piglet factors affecting duration of the expulsive stage and piglet birth intervals obtained in this study contribute to an increased insight into (patho) physiological aspects of perinatal mortality in pigs.

Increased plasma concentrations of vasopressin, oxytocin, cortisol and the prostaglandin F2alpha metabolite during labour in the dog

AIM

This study investigated if the plasma vasopressin concentration increases during labour in the dog and whether the change in vasopressin correlates with that of oxytocin, 15-ketodihydro-PGF2alpha and cortisol.

METHODS

Five beagle dogs each delivered three to seven puppies. Blood samples were taken from a catheter inserted into the cephalic vein during labour and by venepuncture during the other periods.

RESULTS

Vasopressin concentration increased from 2 +/- 0 pmol L-1 (anoestrus) to 26 +/- 11 pmol L-1 at the birth of the first puppy, remained high at the birth of the second puppy and then decreased. Oxytocin increased from 63 +/- 5 pmol L-1 (anoestrus) to 166 +/- 19 pmol L-1 at the birth of the first puppy and remained elevated throughout labour. The PGF2alpha metabolite concentration increased from 0.2 +/- 0.0 nmol L-1 (anoestrus) to 66 +/- 17 nmol L-1 at the birth of the first puppy and remained elevated 1 h after the completion of parturition. The cortisol concentration increased from 49 +/- 9 nmol L-1 (anoestrus) to 242 +/- 35 nmol L-1 at the birth of the first puppy, remained high during the birth of the second puppy and then declined.

CONCLUSIONS

The plasma level of vasopressin was strongly correlated with that of cortisol but less with that of the PGF2alpha metabolite, and not significantly with the concentration of oxytocin. This indicates that the four hormones play different roles during labour in the dog.

Pituitary-Adrenal Activation in Pre-Parturient Pigs (Sus Scrofa) is Associated with Behavioural Restriction Due to Lack of Space Rather than Nesting Substrate

Previous research has shown that pre-parturient primiparous pigs (gilts) housed in behaviourally restrictive farrowing crates without straw redirect their nest-building behaviour to non-manipulable substrates such as the bars of the crate. These gilts also show elevated plasma adrenocorticotropic hormone (ACTH) and Cortisol levels, particularly around the peak of nest-building activity, when compared to gilts in larger pens that have been provided with a manipulable substrate (straw). It remains unclear whether these behavioural and physiological responses to crating result from the lack of a suitable nesting substrate or from the restricted space. This study investigated the effects of space (crate [C] versus pen [P] and straw (straw [S] versus no straw [NS]) using a 2 × 2 factorial design. Thirty-four gilts were implanted with an indwelling jugular catheter at around 12 days before parturition. They were moved to one of the four environments five days before parturition, and blood sampling and recording of behaviour were carried out during the pre-parturient period. Penned gilts (P), irrespective of straw availability, spent more time standing and walking and performed more total substrate-directed behaviour than crated (C) gilts. When straw was not available to penned gilts, a large proportion of their substrate-directed behaviour was redirected to the floor. Space also had an effect on ACTH and Cortisol levels across the entire pre-parturient phase, with C gilts having higher levels than P gilts irrespective of straw availability, but particularly so at the peak of nest-building activity. There was no effect of straw on ACTH or Cortisol levels. Overall, it appears that increased space, perhaps through allowing locomotion, increases substrate-directed behaviour of pre-parturient gilts. When space is available but straw is absent, pre-parturient gilts redirect their nest-building behaviour to the floor. The ability to express substrate-directed behaviour as a result of increased space is reflected in lower levels of indicators of physiological stress.

Endogenous opioid regulation of oxytocin and ACTH secretion during pregnancy and parturition

Progress of parturition in the rat is optimal when there is increased oxytocin secretion, thus ensuring quick birth and otherwise risking adverse neonatal health. To ensure that the mechanisms for this are available, oxytocin neurons adapt in pregnancy and this includes development of a tonic inhibition by endogenous opioids. Endogenous opioid inhibition of oxytocin secretion increases in pregnancy, initially acting on the nerve terminals in the posterior pituitary and later on oxytocin cell bodies and their inputs. This inhibition enhances stores of oxytocin and enables restraint of oxytocin neuron responsiveness to selected excitatory inputs. The hypothalamic neurons which mediate stress also adapt in late pregnancy so that hypothalamo-pituitary-adrenal axis and oxytocin secretory responses to stressor exposure are attenuated. This is also partly due to endogenous opioid inhibition. Thus, in pregnancy oxytocin and hypothalamo-pituitary-adrenal axis secretion in response to stimulation is restrained, protecting the unborn fetus(es) from premature delivery and glucocorticoid exposure and preparing the oxytocin neurons for their important secretory role during parturition. In parturition itself, endogenous opioids continue to inhibit these neurons. Stress exposure during parturition delays births, probably due to endogenous opioid inhibition of pulsatile oxytocin secretion. On the other hand, basal ACTH and corticosterone secretion are reduced in parturition through inhibition by endogenous opioids. So, opioids continue to regulate the activity of oxytocin and hypothalamo-pituitary-adrenal mechanisms in labor; inhibition of oxytocin neurons at this time may control the spacing of pup births.

The effects of branches on prepartum nest building in gilts with access to straw

Sows farrowing in a semi-natural environment terminate nest building 1-7 h prior to parturition after having built a nest for which a variety of materials are used. No nest-building behaviour occurs during parturition and the sows remain lying in the nest throughout most of the farrowing. In contrast, many intensively housed sows are restless during farrowing. To investigate whether gilts housed indoors would use branches for nest building and whether access to branches would affect the termination of nest building and parturient behaviour, we studied gilts housed individually in pens designed to stimulate natural nest building. The control group (n=21) had unlimited access to straw and the experimental group (n=21) had unlimited access to straw and branches. During nest building all the gilts used straw and all the experimental gilts also used branches. In the experimental group the interval from termination of nest building to birth of the first piglet (BFP) was significantly longer than in the control group (132 versus 58 min, P=0.04). In the experimental group, nest-building behaviour was also performed by fewer individuals during the interval from BFP until 2 h after than in the control group (38% versus 71% of the gilts, P=0.03). Gilts that performed nest building during this interval carried out more postural changes (P<0.001) and spent less time in lateral recumbency (P=0.001) than gilts which did not perform nest building. On average, gilts that performed nest building behaviour after BFP (n=26) spent 54% of the first 2 h of parturition in lateral recumbency and carried out 16 postural changes. Gilts that did not perform nest building behaviour during this interval (n=16) spent 85% of the time in lateral recumbency and carried out five postural changes. In 10 gilts that were selected randomly from the experimental group nest building was studied in more detail. In these gilts nest building peaked between 17 and 6 h prepartum. There was no difference in amount of behaviour directed towards straw and amount of behaviour directed towards branches.The results indicate that the termination of nest building in sows is under environmental feedback control. When only straw was provided the nests did not have much of a lasting structure. However, when gilts had access to straw and branches more structured and functional nests could be built. These nests may have been more effective in reducing the motivation for nest building prior to the onset of parturition.

The timing of parturition in the pig is altered by intravenous naloxone

This experiment tested the hypothesis that opioid antagonists could influence the timing of the onset and progress of parturition in the pig. Primiparous pigs (gilts) received a jugular catheter on Days 104 to 106 of pregnancy. At 1400 h on Day 112 the gilts received 10 mg PGF2alpha, i.m. to induce parturition. At 1000 h on Day 113 (i.e., 20 h later) gilts received either saline (n=6), 1 mg/kg, i.v. naltrexone (n=4) or 1 mg/kg, i.v. naloxone (n=5). Blood samples were taken daily from Days 108 to 116. On Day 113, blood samples were taken hourly from 0500 to 0900 h and then every 30 min until 2400 h, or until the birth of the last piglet (BLP) (whichever was sooner) and assayed for progesterone, oxytocin (OT), cortisol and PRL. Additional blood samples for OT and cortisol assay were taken every minute from 0930 to 1100 h on Day 113 and for 30 min during parturition. Naloxone, but not naltrexone, delayed the onset of parturition relative to saline controls (by 14 h 21 min; P<0.05). Duration of parturition and rate of births were not significantly affected by treatment. Mean plasma OT increased in the 4 h following naloxone but not saline treatment, during which time OT plasma pulse amplitude was reduced in naloxone and naltrexone-treated animals relative to saline treated controls. The PRL secretion rose following treatment in saline treated animals, consistent with approaching parturition, but failed to rise in opioid antagonist treated animals. Progesterone concentrations remained elevated in naloxone-treated animals for longer than in the other groups. These data suggest that a rapid change in overall effect of parenteral administration of naloxone to parturient pigs occurs from delaying its onset when administered as in these experiments, to facilitating its progress when given during parturition (earlier experiments). The delay of onset of parturition may be mediated by interference with hypothalamic control of OT or PRL 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.

Investigation of the relationship between farrowing environment, sex steroid concentrations and maternal aggression in gilts

Maternal oestrogen and progesterone have been shown to be important in the initiation of maternal behaviour. Thirty-three Large White x Landrace gilts, housed in groups during pregnancy, were observed and aggressive interactions recorded. Individuals had jugular catheters implanted 14.5 (s.e. 0.34) days before their expected parturition date (EPD). Five days before EPD gilts were randomly allocated and moved to either a conventional farrowing crate (C; without straw, 16 gilts) or a pen (P; 2.1 x 3.1 m2; with straw bedding, 17 gilts). Blood samples were taken at frequencies determined by the proximity to farrowing onset. Piglets were removed at birth and returned 2 h after placental expulsion. The reaction of each gilt to her piglets was monitored. Gilts savaging piglets were sedated with azaperone (n = 8). There was no overall effect of farrowing environment on oestradiol and progesterone concentrations. The pre-farrowing ratio of progesterone to oestradiol was higher for (P) gilts (0.45 vs. 0.25, (P) vs. (C); S.E.D. 0.085, P < 0.05) as was their overall maximum oestradiol level (3.39 vs. 2.29 ng/ml, (P) vs. (C); S.E.D. 0.39, P < 0.01). In contrast to progesterone, oestradiol patterns varied considerably between individuals. Dominance rank value during pregnancy, but not levels of aggression, correlated positively to pre-farrowing oestradiol concentrations. Treatment with azaperone was not related to farrowing environment, piglet weight or litter size. Azaperone treated gilts showed a higher pre-farrowing oestradiol to progesterone ratio (0.55 vs. 0.29, +/- azaperone; S.E.D. 0.10, P < 0.05), significantly higher levels of oestradiol post-partum (0.7 vs. 0.19 ng/ml, +/- azaperone; S.E.D. 0.20, P < 0.001) and significantly lower levels of aggression during pregnancy (1.68 vs. 2.23 aggressive interactions/h, +/- azaperone; S.E.D. 0.15, P < 0.001). The results indicate that there are no major effects of farrowing environment on sex steroid concentrations. Maternal aggression under these conditions appears to be negatively related to aggression during pregnancy, but this is not reflected in plasma concentrations of sex steroids around parturition.

Restricting maternal space during parturition in the pig. Effects on oxytocin, vasopressin and cortisol secretion following vagino-cervical stimulation and administration of naloxone

This experiment studied the effects on endocrine and birth parameters of parturient pigs produced by restricting maternal freedom of movement without otherwise altering environment. Six primiparous pigs (gilts) were each given a jugular catheter under anaesthesia 7 days before parturition and commenced birth in a strawed pen, 2.0 m x 1.5 m in size. Continuous automated blood sampling (3 ml min-1) from unrestrained gilts began following the birth of the first piglet (stage 1) and continued for 2 h. After at least 30 min of blood collection, maternal space was reduced to 2.0 m x 0.55 m by placing rails across the pen (stage 2). The scope for movement in stage 2 was similar to that offered by a farrowing crate. After at least 25 min each gilt was given the opioid antagonist naloxone (1 mg kg-1 i.v.: stage 3). At each stage, vagino-cervical stimulation (VCS) was applied to mimic foetal ejection. Non-cervically stimulated oxytocin (OT) secretion between stages 1 and 2 was unchanged (P > 0.05) but increased significantly relative to both stages 1 and 2 following naloxone treatment for 15-20 min (P < 0.05, paired t-tests on log10 data). Following VCS in all stages plasma OT rose (P < 0.05) for 1-2 min in a similar way to that seen previously following foetal ejection, the increases being proportionally similar irrespective of stage or baseline secretion. Cortisol secretion did not increase as a consequence of space restriction (mean +/- SEM concentrations were 28.6 +/- 8.51 pmol l-1 and 32.3 +/- 11.8 pmol l-1 in stages 1 and 2, respectively). In addition, VCS did not significantly affect cortisol output. Lysine vasopressin concentrations were not affected as a consequence of either stage or VCS. Parturition was not interrupted following space restriction of gilts. These data suggest that reducing maternal space allowance during parturition is not stressful when the process does not involve the movement of animals to novel surroundings.