Hormonal profiles and embryo survival of sows subjected to induced stress during days 13 and 14 of pregnancy

Social status and housing factors affect reproductive performance of pregnant sows in groups

Group-housing systems for pregnant sows are considered a welfare-promoting alternative to the individual stall. A major concern associated with pregnant sows housed in group pens is increased aggression at mixing and at feeding, which may cause chronic stress among some of the sows in the group due to low feed intake and social stress. Prolonged activation of the stress axis, based on elevated cortisol levels, may inhibit or impair reproductive success via disruption of the reproductive axis. Mixing sows into groups shortly after insemination evokes a stress response, which may affect fertilization and implantation due to sustained, elevated cortisol levels that disrupt reproductive processes. Yet, most studies reported minimal effects of group housing sows during pregnancy on reproduction or cortisol-related stress response. Differences between housing systems-in terms of group size, floor-space allowance, feeding system, and genetics-could account for these unexpected results. Indeed, interrupted feed intake, especially in early pregnancy, and sustained aggression in late pregnancy are two unfavorable social stresses that deserve special attention in order to achieve good reproductive performance. Unfortunately, most studies do not consider other factors, such as social rank and parity, which may interactively affect reproductive success and aggressive behavior of sows, especially in group-pen systems.

Influence of the housing environment during sow gestation on maternal health, and offspring immunity and survival

In pig husbandry, pregnant females are often exposed to stressful conditions that may affect their physiology, behaviour or health and consequently the ability of their offspring to survive and develop. This study compared two different housing systems from insemination to 106 days of gestation, a conventional (C) and an enriched one (E), for maternal cortisol and immune parameters, as well as for the immune function and survival of their offspring. The C and E systems differed essentially for the housing design (slatted floor, 2.4 m2 per sow vs a deep straw litter and 3.4 m2 per sow). Results from Expt 1 (n = 108) demonstrated that C sows had higher salivary cortisol than E sows at gestational Day 102 (DG 102). Results from Expt 2 (n = 48) showed that, at DG 102, C sows had higher granulocyte counts and total plasma immunoglobulin G concentration than E sows, whereas lymphocyte number, haematocrit and haptoglobin plasma concentration were similar. Results from Expt 3 (n = 47) showed that plasma immunoglobulin G level at 5 and 27 days of age, hematocrit, white blood cell numbers and in vitro lymphocyte proliferation of piglets at 27 days of age were not influenced by maternal housing conditions. However, reproductive data collected in Expt 2 and 3 indicated that pre-weaning mortality was higher in C than E litters. In conclusion, the C system was associated with markers of increased stress and microbial aggression in gestating sows, and with greater piglet mortality during the suckling period without identified alterations in piglet immune function.

Temporary undernutrition during early gestation, corpora lutea morphometrics, ovarian progesterone secretion and embryo survival in gilts

The present study reports effects of severe undernutrition on luteal function and pregnancy in pigs. Gilts were inseminated and either fasted on Day 10 and 11 after conception (n = 11) or fully fed throughout (n = 10). Fasting did not affect LH or progesterone pulsatile secretion pattern on Day 11 in samples taken from blood vessels draining an ovary. Ultrasonographic measurements of the size of the corpora lutea did not show any effect of fasting either. However, fasted gilts had 10 to 30 % lower systemic progesterone from Day 12 through Day 15 after conception (P < 0.05). All gilts farrowed, but fasted gilts had fewer born piglets than fully fed gilts (8.8 ± 0.8 vs 10.9 ± 0.5 respectively; P < 0.05). In conclusion, fasting during embryo elongation can compromise embryonic survival by affecting ovarian function in the days after fasting, without having an immediate effect on LH secretion and progesterone output by the ovaries.

A 25 years experience of group-housed sows-reproduction in animal welfare-friendly systems

Since January 1 2013, group housing of sows has been compulsory within the European Union (EU) in all pig holdings with more than ten sows. Sows and gilts need to be kept in groups from 4 weeks after service to 1 week before the expected time of farrowing (Article 3(4) of Directive 2008/120/EC on the protection of pigs). The legislation regarding group housing was adopted already in 2001 and a long transitional period was allowed to give member states and producers enough time for adaptation. Even so, group housing of sows still seems to be uncommon in the EU, and is also uncommon in commercial pig farming systems in the rest of the world. In this review we share our experience of the Swedish 25 years of animal welfare legislation stipulating that sows must be loose-housed which de facto means group housed. The two most important concerns related to reproductive function among group-housed sows are the occurrence of lactational oestrus when sows are group-housed during lactation, and the stress that is associated with group housing during mating and gestation. Field and clinical observations in non-lactating, group-housed sows in Sweden suggest that by making basic facts known about the pig reproductive physiology related to mating, we might achieve application of efficient batch-wise breeding without pharmacological interventions. Group housing of lactating sows has some production disadvantages and somewhat lower productivity would likely have to be expected. Recordings of behavioural indicators in different housing systems suggest a lower welfare level in stalled animals compared with group-housed ones. However, there are no consistent effects on the reproductive performance associated with different housing systems. Experimental studies suggest that the most sensitive period, regarding disturbance of reproductive functions by external stressors, is the time around oestrus. We conclude that by keeping sows according to the pig welfare-friendly Directive 2008/120/EC, it is possible to combine group-housing of sows with good reproductive performance and productivity. However, substantially increased research and development is needed to optimize these systems.

Effect of gestating sow body condition, feed refusals, and group housing on growth and feed intake in grower-finishing pigs

The main focus of this study was to identify sow gestation features that affect growth rate (GR) and feed intake (FI) of their offspring during grower-finishing stage. Because the sow provides a specific environment to her offspring during gestation, certain features (e.g., BW of the sow), feed refusals or gestation group, may affect her ability to deliver and feed a healthy litter. Data on 17,743 grower-finishing pigs, coming from 604 sires and 681 crossbred sows, were obtained from the Institute for Pigs Genetics. Sow gestation features were collected during multiple gestations and divided into 3 clusters describing i) sow body condition (i.e., BW, backfat, and gestation length), ii) sow feed refusals (FR), the difference between offered and eaten feed during 3 periods of gestation: 1 to 28, 25 to 50, 45 to 80 d, and iii) sow group features (i.e., number of sows, and average parity). Sow gestation features were added to the base model 1 at a time to study their effect on GR and FI. Significant gestation features (P < 0.1) were fitted simultaneously in animal model to investigate whether they could explain common litter and permanent sow effects. Gestation length had effect on GR [1.4 (g/d)/d; P = 0.04] and FI [6.8 (g/d)/d; P = 0.007]. Body weights of the sow at insemination [0.07 (g/d)/kg; P = 0.08], at farrowing [0.14 (g/d)/kg; P < 0.0001], and after lactation [0.1 (g/d)/kg; P = 0.003] had effect on GR. Sow parturition-lactation loss in backfat thickness and weight were not significant for GR and FI. Days with FR during 25 to 50 and 45 to 80 d of gestation and average FR during 45 to 80 d of gestation had negative effect on GR and when substantially increased had also a positive effect on FI. Sow FR from 1 to 28 d of gestation were not significant. Number of sows in gestation group had effect on FI [-9 (g/d)/group member; P = 0.04] and day sow entered group had an effect on GR [-0.9 (g/d)/day; P = 0.04]. Sow gestation features explained 1 to 3% of the total variance in grower-finishing pigs. Gestation features did explain phenotypic variance due to permanent sow and part of phenotypic variance due to common litter effects for FI but not for GR.

Reproductive issues in welfare-friendly housing systems in pig husbandry: a review

In Europe, housing conditions of sows are currently changing, related with a larger emphasis on pig welfare. As a result, sows are and will be less kept in crates, but more so in loose housing systems (farrowing, lactation) and group housing systems (pregnancy, lactation, weaning-to-oestrus interval). These changes in housing conditions may affect reproductive functioning of the sows. Group housing of sows may decrease farrowing rate and litter size when stress levels rise or when feed intake in early pregnancy is not fully secured. Loose housing during farrowing results in an improved farrowing process, but may increase piglet mortality by crushing during early lactation. Further, group housing during lactation may increase the risk of lactational oestrus. Thus, new - welfare friendly - housing systems require increased attention to management to ensure optimal reproductive performance.

Re-modelling the piggery breeding unit may affect the farrowing rate

The objective of this retrospective cohort study was to clarify the effect of re-modelling the breeding unit on farrowing rate. The original study population included 63 sow herds that participated in the Finnish herd surveillance system. In these herds, the breeding units were re-modelled between 1995 and 2002. Information about the production system and other herd data for the last year before and the second year after re-modelling were available for 47 herds. The herds had an average of 68.5 (SD 45) sows per herd. Data were collected during one farm visit per herd. Initially, all herds had individual cages in their breeding units. The piggeries had either re-modelled their cages or switched to a group housing system with deep-litter, solid or slatted (partly or totally) floors. Farrowing rates were gathered from the national database, and data were tested with a linear regression model. Re-modelling did not have an effect on farrowing rate if initial reproductive performance of the herd was neglected. However, when farms were stratified according to performance prior to the beginning of study, namely into 'farms with initially high farrowing rate' (HF) and 'farms with initially low farrowing rate' (LF), the re-modelling had a significant effect on farrowing rate. In the HF farms, re-modelling caused a decrease in farrowing rate. Correspondingly, farrowing rate increased after remodelling in the LF farms. Farrowing rate was also influenced by mean parity of sows and by proportion of sows culled because of leg problems. This study could not show a profound impact of the design of the breeding unit on the fertility of the sow in the modern commercial production environment if the farm's reproductive performance before re-modelling was neglected. However, when initial performance was taken into account, re-modelling revealed significant, although varying effects on farrowing rate.

Stress and its influence on reproduction in pigs: a review

The manifestations of stress, defined as a biological response to an event that the individual perceives as a threat to its homeostasis, are commonly linked to enhanced activity of the hypothalamo-pituitary-adrenal (HPA) axis and the activation of the sympathetic adreno-medullary (SA) system. Activation of the HPA system results in the secretion of peptides from the hypothalamus, principally corticotropin releasing hormone (CRH), which stimulates the release of adrenocorticotropic hormone (ACTH) and beta-endorphin. ACTH induces the secretion of corticosteroids from the adrenal cortex, which can be seen in pigs exposed to acute physical and/or psychological stressors. The present paper is a review of studies on the influence of stressors on reproduction in pigs. The effects of stress on reproduction depend on the critical timing of stress, the genetic predisposition to stress, and the type of stress. The effect of stress on reproduction is also influenced by the duration of the responses induced by various stressors. Prolonged or chronic stress usually results in inhibition of reproduction, while the effects of transient or acute stress in certain cases is stimulatory (e.g. anoestrus), but in most cases is of impairment for reproduction. Most sensitive of the reproductive process are ovulation, expression of sexual behaviour and implantation of the embryo, since they are directly controlled by the neuroendocrine system.

Housing during early pregnancy affects fertility and behaviour of sows

From 1.1.2013 EU legislation will permit stall-housing of dry sows for only 4 weeks post-service. Stalls are associated with compromised animal welfare, but group housing comes with risks from social confrontations. Studies on housing effects on fertility have produced contradictory results as systems are inconsistently defined. Effects of housing on pregnancy rate 28 days post-service (P28), early disruption of pregnancy (EDP) and behaviour were investigated in 12 replicates of 40 sows. Half of the animals were stalled (treatment S, mean parity 2.4) and half group-housed adjacent on 5.1 m(2) deep litter per sow (treatment G, mean parity 2.3). Pregnancy was detected using real-time ultrasound. An EDP-diagnosis required a drop of salivary progesterone concentration from >15.9 to <15.9 mmol/l in a series of samples taken on days 17, 20, 24 and 27 post-service. Behaviour was scan sampled on day 27 for 120 min with 10-min intervals. Data was analysed using mixed regression models in MLwiN. Treatment S increased the odds for P28 with 2.3 and the pregnancy rate of a treatment group with 0.1 compared with G. G increased the odds for EDP with 4.6. Treatment did not affect total exploratory or total passive behaviour. S sows explored floor and fixtures (not bedding) more and performed more passive sitting than G sows. Social stress may have caused the impaired reproductive performance in G sows. S sows showed behavioural signs of decreased welfare, but no corresponding reproductive effects. An interdisciplinary approach is needed when evaluating the appropriateness of housing systems.

Mixing gilts in early pregnancy does not affect embryo survival

There is general acceptance that mixing sows during the first 3 weeks of gestation is detrimental to embryo development and survival. However, there is a paucity of data describing the influence of group housing and remixing during the first 14 days of gestation on pregnancy outcomes. Using 96 purebred maternal (Large White)/terminal (Duroc) line gilts, the current study determined the effects of regrouping, and the timing of regrouping, during the pre-implantation period on embryo mortality. The study was conducted in 2 blocks, with 12 gilts allocated to each of 4 treatments in each block. At 175 days of age, the combination of PG600 and 20 min of daily physical boar contact was used to stimulate puberty, with boar contact resuming 12 days after first detection of oestrus and gilts receiving two artificial inseminations (AIs), 24 h apart, at their second oestrus. After their first AI gilts were allocated to one of four treatment groups (n=12 gilts/treatment). Gilts in one treatment group were housed individually in stalls (STALL). The remaining gilts continued to be housed in their pre-AI groups and were either not remixed (NOMIX), or remixed to form new groups on day 3/4 (RMIXD3/4) or day 8/9 (RMIXD8/9) of gestation (day 0=day of first detection of second oestrus and first insemination). Group-housed gilts were housed in groups of 6, with a space allowance of 2.4 m2/gilt. All gilts were fed once a day (2.2 kg/gilt). Reproductive tracts were collected on day 26.6+/-0.13 of gestation, and the number of corpora lutea (CL) and viable embryos counted. Pregnancy rate was similar across all treatments, averaging 94.5% across the four treatment groups. The number of embryos present on day 26 of gestation was unaffected by housing treatments (P>0.05); gilts in the STALL, NOMIX, RMIXD3/4 and RMIXD8/9 groups possessed 13.2+/-0.67, 12.9+/-0.66, 14.1+/-0.46 and 13.8+/-0.57 embryos, respectively. Similarly, embryo survival rates were 0.91+/-0.04, 0.85+/-0.04, 0.91+/-0.02 and 0.87+/-0.05 for the STALL, NOMIX, RMIXD3.4 and RMIXD8/9 groups, respectively (P>0.05). In conclusion, the current data indicate that individually housing gilts immediately after their first AI does not improve embryo survival. There also appear to be no adverse effects on embryo development or survival when group-housed, mated gilts are remixed during the first 10 days of gestation.

Stress, behaviour and reproductive performance in female cattle and pigs

Female farm animals are exposed to a great variety of environmental and management related stressors. As a consequence, their reproductive and maternal abilities may be compromised through mechanisms acting on the hypothalamic, pituitary, ovarian and uterine function. Responses to short- and long-term stressors may differ as short-term stressors often fail to affect reproduction or even may have stimulatory effects. Thus, the stress response induces diverse neuroendocrine reactions that can either increase or decrease the probability of an animal reproducing depending on the specific situation. The aim of the present review is to summarise the current knowledge on the stress concept and its implications on behaviour and reproductive performance in cows and female pigs as phenomena reported in laboratory animals are unable to explain all effects encountered in domesticated farm animals.

Effect of repeated stress treatments during the follicular phase and early pregnancy on reproductive performance of gilts

In pig husbandry, stress is being considered an important cause of impaired reproductive performance. Therefore, an experiment was performed to quantify effects of repeated stressors during the follicular phase and/or during early pregnancy on reproductive performance of gilts. Eighty-one cyclic gilts were assigned to one of four treatments, namely, stress treatment during the follicular phase (n = 20), stress treatment during early pregnancy (n = 20), stress treatment during both phases (n = 21) and no stress treatment (n = 20). All gilts were housed individually, but gilts in the stress treatments had no opportunity for visual or physical contact with other gilts. Further, animals in a stress-treatment were grouped for half an hour at the start of the treatment and during the treatment period nose-sling and an unpredictable feeding scheme were applied regularly. The extent of stress was monitored using heart rate measurements, behavioural observations and saliva cortisol levels during nose-sling fixation. Of the 81 gilts, 93% showed oestrus and were inseminated. Of these, 93% were pregnant at day 35, having 17.9 +/- 0.3 ovulations and 15.6 +/- 0.3 foetuses. These parameters were not affected by treatment. The stress treatment during the follicular phase tended to shorten cycle length (stress: 20.8 +/- 0.20; control: 21.2 +/- 0.17 days, p = 0.07) and weight of foetuses at day 35 (stress: 4.47 +/- 0.08 g; no stress: 4.69 +/- 0.08 g, p = 0.06); stress during early pregnancy did not affect any of the reproduction parameters. Percentage stereotypic behaviour, heart rate and saliva cortisol levels varied greatly between animals and between days, but did not differ between the treatments. No relationships were found between any of the reproductive parameters and any of the stress parameters (heart rate, cortisol, stereotypic behaviour). These results indicate that the repeatedly applied acute stressors did not generate a chronic stress-response and that these stressors during the follicular phase and/or during early pregnancy did not affect reproductive processes. It is not clear how these findings relate to suggested effects of stress(ors) on reproductive performance in pig husbandry.

Influence of repeated regrouping on reproduction in gilts

It is generally assumed that stress around oestrus and during early pregnancy reduces reproductive performance of pigs. In our experiment, late prepuberal gilts (age at arrival 225+/-6 days) were housed in groups of four. Stress treatment consisted of once weekly regrouping and twice weekly feed competition of the 28 Stress gilts during 6 consecutive weeks, starting 13 days after arrival. Control gilts (n=28) were not treated. During the 0.5-1.5h after regroupings, Stress animals fought consistently more than the Control animals; up to 13 of the Stress animals fought for at most 60% of the time compared to one Control animal fighting for at most 3.3% of the time. The day before first regrouping, gilts had on average 4.0+/-0.9 skin scratches. By week 6, this number had reduced to 2.1+/-1.0 in Control, but remained 4.0+/-1.3 in Stress gilts (P<0.05). In the afternoon after regroupings, skin scratches increased up to 6.3+/-1.6 in the Stress gilts. Saliva cortisol in the afternoon before regrouping did not differ between weeks 1, 3 and 6, nor did it differ between Stress and Control. In Stress gilts, saliva cortisol was increased in the afternoon of first regrouping, in Batch 2 only (from 1.8+/-0.4 to 4.1+/-0.9 ng/ml; P<0.05). Animals showing a second oestrus within 5 weeks after arrival were inseminated. Duration of second oestrus of these animals was 2.48+/-0.66 days in the Stress gilts (n=24) and 2.21+/-0.58 days in the Control gilts (n=22; P>0.10). At Day 35 after insemination, pregnancy rate was 100% in both groups. Ovulation rate and number of total and vital fetuses was similar (P>0.10). The Stress treatment during a 6-week period around insemination consistently resulted in fighting but did not result in long term effects on cortisol levels and did not impair reproductive performance.

Lower birth weight and attenuated adrenocortical response to ACTH in offspring from sows that orally received cortisol during gestation

Prenatal stress is known to affect several offspring characteristics, but its effects depend among other factors on the period of gestation in which it is applied. In the present study, oral administration of hydrocortisone-acetate (HCA) was used to elevate cortisol concentrations in pregnant sows to levels also observed after psychological stress. HCA was administered during three different periods of gestation (115 days in pigs): period 1: 21-50 (P1, n = 10), period 2: 51-80 (P2, n = 10) and period 3: 81-110 (P3, n = 10) days after insemination. Control sows (n = 11) received vehicle from 21-110 days after insemination. When P1-, P2- and P3-sows did not receive HCA, they also received vehicle. During gestation, weekly saliva samples were taken from the sows to determine salivary cortisol concentrations. Treatment effects on sow, litter and piglet characteristics were determined. In addition, two female piglets per litter were subjected to an ACTH-challenge test at 6 weeks of age to determine the adrenocortical response to ACTH. Pigs were slaughtered at 6 months of age and slaughter weight, back fat thickness and percentage of lean meat were analysed. During the period of treatment with HCA, salivary cortisol concentrations were increased in P1-, P2- and P3-sows compared to control sows (P < 0.01). The total number of piglets born per litter did not differ among treatment groups (P > 0.30), but pooled HCA-litters had a higher percentage of live born piglets (P < 0.05) and fewer mummies than control litters (P < 0.05). Gestation length did not differ among treatment groups (P = 0.21), but did affect treatment effects on birth weight. Overall, HCA-piglets weighed less at birth, and remained lighter until weaning (P < 0.05). The salivary cortisol concentrations after i.m. injection of ACTH (2.5 IU/kg) were lower in P1- and P3-piglets compared to control piglets. At slaughter, HCA-treatment indirectly decreased lean meat percentage and increased back fat thickness. In conclusion, elevated peripheral cortisol concentrations in pregnant sows affect both litter characteristics and piglet physiology, the latter depending on the period of gestation during which concentrations were elevated. Underlying mechanisms require further investigation.