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

Follicle development in pigs: State of the art

Understanding the factors and pathways involved with recruitment, atresia, and selection of follicles in the pig, may provide insight into approaches to limit fertility failures. Antral follicles depend upon FSH to the 2-3 mm stage, become codependent upon LH at 4-5 mm, and rely on LH when >5 mm. Within the follicle, gonadotropin binding, steroids, growth factors, and inhibin interact to determine the fate of the follicle. Continuous recruitment appears likely for follicles, and once >1 mm, they may have a limited period for survival, before selection or atresia. If true, then the number of healthy follicles that can respond to a hormone signal for selection, could vary by size and development stage. Which follicles are selected may depend upon their age, numbers of capillaries, granulosa and thecal cells, and FSH and LH receptors. This might also suggest that factors such as management, nutrition, and stress in prior weeks, could affect different cohorts of follicles to determine which of those from the ovarian population will be selected.

Reproductive performance of gilts and weaned sows grouped at different days after insemination

The objective of the study was to compare the reproductive performances of gilts and weaned sows grouped at different days after insemination. The study was conducted on a sow farm in the Midwest of Paraná State, Brazil, using animals from the Camborough genetic line (PIC®, Patos de Minas, Brazil, Landrace × Large White crossbred). The groups of comparison have considered the distribution of gilts (n = 407) and sows (parity 1 to 5; n = 843) according to the day of group housing in collective pens in relation to the day of last insemination (AI). Thus, gilts were distributed in four groups of comparison: group housing on days 1, 2, 3, or 4 after the last AI (AI). Sows were distributed in three groups of comparison: group housing on the day after the last AI (0), at day 1 or 2 after the last AI. Farrowing rate (FR), the total number of piglets born (TB), and return to estrus (RE) were recorded. In a subsample (254 gilts and 622 sows), the presence and the score of skin lesions (0, no lesions; 1, low; 2, moderate; or 3, high) were evaluated 24 and 48 h after mixing. Statistical analysis was performed using the SAS^® 9.4 software using the GLIMMIX procedure. Comparisons of means were performed using the Tukey-Kramer test and frequencies by logistic regression. Group housing gilts on different days after insemination did not affect FR, TB, and RE (P ≥ 0.79). However, sows mixed 2 days after AI had a reduction in TB compared to those mixed on day 1 (P = 0.05), without differences from sows mixed on the day of the last AI. All the females had low (score 1; 60.5%) or moderate (score 2; 39.5%) skin lesions. For both female categories, the presence of low or moderate lesion scores did not affect ER, FR, and TB (P ≥ 0.25). Fights within 48 h were not severe enough to compromise reproductive performance (P ≥ 0.25). In conclusion, group housing gestating sows 2 days after breeding compromised litter size; however, mixing gilts on days 1 to 4 after breeding did not impair reproductive performance.

A systematic review of the impact of housing on sow welfare during post-weaning and early pregnancy periods

Breeder animals are an important focus in farm animal welfare assessments as they typically live the longest lives and are at the greatest risk for suffering due to their longevity. For breeding pigs, the time between the end of lactation (post-weaning) and the implantation of embryos (early gestation) is very dynamic from both a physiological and husbandry perspective. However, research to date is limited on how best to house and manage sows during this critical period of their production cycle from a welfare perspective. Previous animal-based welfare outcome measures were restricted to certain health, behavioral and physiological indicators. This systematic review used Web of Science to make in-depth comparisons among welfare-based studies that focus on sow housing during the post-weaning and early pregnancy period to identify important knowledge gaps. Only a small number of studies (n = 27) were found that met our systematic search criteria. Compared to stalls, group housing requires mixing of animals and always triggers more aggression and skin lesions at the time of mixing. The predominant use of health and physiological indicators constrained the animal-based welfare outcomes in these studies. Thus, what type of housing yields the best overall welfare outcome remains to be elucidated as none of the studies found explored the mental wellbeing of sows during this period. This systematic review defines a critical knowledge gap regarding the full impact of housing on the welfare of post-weaning and early gestation sows. This gap, and thus the true welfare impact of sow housing, will only be addressed by the use of novel, more holistic assessment methods that also capture the psychological state of the sow.

Welfare of pigs on farm

This scientific opinion focuses on the welfare of pigs on farm, and is based on literature and expert opinion. All pig categories were assessed: gilts and dry sows, farrowing and lactating sows, suckling piglets, weaners, rearing pigs and boars. The most relevant husbandry systems used in Europe are described. For each system, highly relevant welfare consequences were identified, as well as related animal-based measures (ABMs), and hazards leading to the welfare consequences. Moreover, measures to prevent or correct the hazards and/or mitigate the welfare consequences are recommended. Recommendations are also provided on quantitative or qualitative criteria to answer specific questions on the welfare of pigs related to tail biting and related to the European Citizen's Initiative 'End the Cage Age'. For example, the AHAW Panel recommends how to mitigate group stress when dry sows and gilts are grouped immediately after weaning or in early pregnancy. Results of a comparative qualitative assessment suggested that long-stemmed or long-cut straw, hay or haylage is the most suitable material for nest-building. A period of time will be needed for staff and animals to adapt to housing lactating sows and their piglets in farrowing pens (as opposed to crates) before achieving stable welfare outcomes. The panel recommends a minimum available space to the lactating sow to ensure piglet welfare (measured by live-born piglet mortality). Among the main risk factors for tail biting are space allowance, types of flooring, air quality, health status and diet composition, while weaning age was not associated directly with tail biting in later life. The relationship between the availability of space and growth rate, lying behaviour and tail biting in rearing pigs is quantified and presented. Finally, the panel suggests a set of ABMs to use at slaughter for monitoring on-farm welfare of cull sows and rearing pigs.

Analysis of Uterine Blood Flow in Breeding Sows through the Estrus and Early Diestrus, and after Artificial Insemination

This study aimed to determine uterine blood flow indices by transabdominal Doppler ultrasound in sows (n = 18) under different conditions: (i) sows after estrus detection (day 0, D0); (ii) sows 2 h after artificial insemination (AI), performed 24 h after detection of estrus (day 1, D1); (iii) sows in early diestrus (day 5, D5). Moreover, three different types of seminal doses were used for AI depending on the ejaculate fraction included (F1: doses containing only the rich fraction of the ejaculate; F2: F1 + the transition fraction between rich and poor fractions; F3: F2 and poor fraction). The statistical analysis revealed significant differences in some indices regarding the period of analysis (D0, D1, and D5). Diastolic velocity and mean velocity showed lower values at D5 in comparison with D0 and D1 (p < 0.01). On the other hand, the pulsatility index and the relationship systolic velocity/diastolic velocity indicated higher values at D5 in comparison with D0 and D1 (p < 0.01). No differences were observed regarding the type of seminal dose used in any of the time points analyzed (p > 0.05). Neither insemination per se nor the type of ejaculate fraction used immediately modified the uterine vascularity, but some indices are affected by the stage of the estrus cycle (estrus vs. early diestrus).

Does Maternal Stress Affect the Early Embryonic Microenvironment? Impact of Long-Term Cortisol Stimulation on the Oviduct Epithelium

Maternal stress before or during the sensitive preimplantation phase is associated with reproduction failure. Upon real or perceived threat, glucocorticoids (classic stress hormones) as cortisol are synthesized. The earliest “microenvironment” of the embryo consists of the oviduct epithelium and the oviductal fluid generated via the epithelial barrier. However, to date, the direct effects of cortisol on the oviduct are largely unknown. In the present study, we used a compartmentalized in vitro system to test the hypothesis that a prolonged stimulation with cortisol modifies the physiology of the oviduct epithelium. Porcine oviduct epithelial cells were differentiated at the air–liquid interface and basolaterally stimulated with physiological levels of cortisol representing moderate and severe stress for 21 days. Epithelium structure, transepithelial bioelectric properties, and gene expression were assessed. Furthermore, the distribution and metabolism of cortisol was examined. The polarized oviduct epithelium converted basolateral cortisol to cortisone and thereby reduced the amount of bioactive cortisol reaching the apical compartment. However, extended cortisol stimulation affected its barrier function and the expression of genes involved in hormone signaling and immune response. We conclude that continuing maternal stress with long-term elevated cortisol levels may alter the early embryonic environment by modification of basic oviductal functions.

Mixing Sows into Alternative Lactation Housing Affects Sow Aggression at Mixing, Future Reproduction and Piglet Injury, with Marked Differences between Multisuckle and Sow Separation Systems

Simple Summary

Alternative lactation housing could reduce aggression when sows are mixed. We aimed to compare the effects of mixing sows during lactation (with or without piglets) at weaning and after insemination and determine the effects of mixing strategies and lactation housing on the piglet. Sows in the multisuckle treatment were the least aggressive, had the fewest injuries around mixing, and gave birth to the most piglets at the subsequent litter, with multisuckle housing having no apparent ill effects on the piglets. There was greater aggression in sows separated from their piglets for seven hours daily in lactation (SEP) than any other method. Multisuckle housing appears to be an effective way of decreasing aggression at the point of mixing, whilst optimizing sow reproduction. The behavioural response to mixing was similar when it occurred at weaning or after insemination, with the highest incidence of aggression observed in sows mixed without their piglets during lactation.

Abstract

Alternative lactation housing could reduce aggression when sows are mixed. We aimed to compare the effects of mixing sows in lactation (with or without piglets), at weaning or after insemination, and determine the effects of lactation housing on the piglet. This study used 120 multiparous Large White × Landrace sows and 54 focal litters. The sows were mixed into groups of six and allocated to multisuckle from day 21 lactation (MS), separated from litter and housed in groups, with piglets left in the crate for seven hours daily from day 21 lactation (SEP), mixed at weaning (day 28 lactation) (WEAN) and mixed after artificial insemination (AI) (MAI; 4 ± 1 day after last AI). Behaviour, saliva for free salivary cortisol concentration and injury counts were taken on M-1 (before mixing), M0 (mixing), M1 and M6. Piglets were weighed, injury-scored and bloods taken for cortisol. There was reduced aggression, seen as fights, bites and knocks in MS compared to the other treatments on all days (p < 0.05). MS sows had no fights on M1 and M6 and had more piglets born in the subsequent farrowing. Piglet weight, cortisol and mortality were unaffected by treatment (p > 0.05). MS piglets had greater injury scores immediately after moving to multisuckle and lower injuries around weaning (p > 0.001). Multisuckle housing could decrease aggression and stress at mixing in sows, with changes in the time of peak piglet injury (at mixing rather than at weaning) but overall no negative effects on the piglets.

GnRH-agonist deslorelin implant alters the progesterone release pattern during early pregnancy in gilts

The aim of this study was to investigate the relationship of progesterone (P) and luteinizing hormone (LH) during recognition and establishment of pregnancy in the gilt. Therefore, the effects of eliminating episodic LH pulses on P patterns were determined during early pregnancy. To this end, a slow-release GnRH implant deslorelin was used for GnRH down-regulation. A group of gilts (GnRHa, n = 8) was implanted with the GnRH-agonist on Day 11 of pregnancy, while a control group (C, n = 5) was treated with a non-impregnated placebo implant. Blood was collected via a vena cava caudalis catheter at 10-min intervals for 8 hr on Day 16 and 21 of pregnancy. As expected, the GnRH implant reduced LH secretion (p < 0.01) and abolished LH pulses completely at Day 16 and Day 21 of pregnancy. On Day 16, there was no difference in P levels between the treatments. However, on Day 21, the GnRH-agonist treatment led to significantly increased P concentrations (p < 0.01) compared with the control gilts. Progesterone was secreted in a pulsatile manner in both treatment groups and no relationship between LH pulsatility and P pulsatility was observed. In conclusion, abolishment of LH pulsatility did not affect the pulsatile pattern of P secretion but led to an unexpected overall increase in P on Day 21 of pregnancy; this effect was delayed and occurred 10 days after commencing treatment with the GnRH depot agonist. The elevation of P on Day 21 of pregnancy in the GnRHa group suggests either a reduced negative feedback effect or an increased autocrine response by the corpora lutea.

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.

Effect of timing of relocation of replacement gilts from group pens to individual stalls before breeding on fertility and well-being

Variation in gilt fertility is associated with increased replacement and reduced longevity. Stress before breeding is hypothesized to be involved in reduced fertility. This study tested the timing of gilt relocation from pens to individual stalls before breeding on fertility and well-being. The experiment was performed in replicates on a commercial research farm. After detection of first estrus, gilts ( = 563) were assigned to treatment for relocation into stalls 3 wk (REL3wk), 2 wk (REL2wk), or 1 wk (REL1wk) before breeding at second estrus. Subsets of gilts from each treatment ( = 60) were selected for assessment of follicles at second estrus. Data included interestrus interval, number of services, conception, farrowing, total born, and wean to service interval. Piglet birth weight was obtained on subsets of litters ( = 42/treatment). Measures of well-being included BW, backfat, BCS, lesions, and lameness from wk 1 after first estrus until wk 16. Gilt BW at wk 5 (158.4 kg) was not affected ( > 0.10) by treatment. Measures of BCS, lameness, and lesions at breeding and throughout gestation did not differ ( > 0.10). Treatment did not affect ( > 0.10) gilts expressing a normal interestrus interval of 18 to 24 d (83.4%) but did influence ( < 0.05) the proportion expressing shorter ( < 0.001) and longer ( < 0.001) intervals. Gilts in REL3wk had a shorter ( < 0.001) interestrus interval (20.7 d) than those in REL2wk and REL1wk (22.6 d). Gilts with shorter intervals ( = 24) had fewer total born while gilts expressing longer cycles ( = 65) had reduced farrowing rates. The number of services (1.9) and number of follicles (19.7) at breeding were not affected ( > 0.10) by relocation. There was no effect of treatment on farrowing rate (85.2%), born alive (12.6), or any litter birth weight measures ( > 0.10). The percentage of sows bred within 7 d after weaning (94.4%) was also not affected by treatment ( > 0.10). These results suggest that the timing of relocation before breeding had no effect on well-being or on the majority of gilts with normal estrous cycles and their subsequent fertility. However, a smaller proportion of the gilts exhibited shorter and longer interestrus intervals in response to relocation 1 or 3 wk before breeding. In cases where gilt fertility may be less than optimal, producers that relocate gilts from pens to stalls before breeding should evaluate interestrus interval as a response criterion.

The effects of ovarian biopsy and blood sampling methods on salivary cortisol and behaviour in sows

In reproductive physiology research, experimental animals are often subjected to stressful procedures, including blood sampling and biopsy. In this present study, presence of pain or distress induced by four different procedures was examined using a measurement of salivary cortisol levels and activity observations in sows. The treatments were: 1) PAL: The ovary was palpated through the rectum without snaring, 2) TUB: transvaginal ultrasound-guided biopsy of the ovary was conducted without snaring, 3) SNA: a soft rope snare was placed around the maxilla, 4) CAT: A soft rope snare was placed around the maxilla, and an intravenous catheter was inserted through the ear vein of the sows. Activities, social cohesion and other pain-related behaviour, and salivary cortisol concentrations were recorded. Salivary cortisol concentrations in CAT sows increased in response to the procedure (P<0.05), whereas the other treatments did not trigger a significant response. The CAT sows had higher cortisol concentrations than the other groups for 10min after initiation of the procedures (P<0.01), and they maintained higher cortisol levels than the PAL and TUB groups 15min post-treatment (P<0.05). Furthermore, the CAT sows showed the highest frequency of head shaking (P<0.001) and trembling behaviour (P<0.05) during the 1h post-treatment. Summarizing, the catheterization procedure might induce a short-term pain or stress response during and after the procedure in terms of pain-related behaviour and salivary cortisol status. We suggest that TUB might not cause appreciable pain or distress.

Effect of day of mixing gestating sows on measures of reproductive performance and animal welfare

Effects of day of mixing sows after breeding were measured for reproduction and welfare on a commercial research farm. Sows (n = 1,436) were weaned into stalls for breeding, and groups of sows were assigned to 1) no mixing and housed in individual stalls (STL), 2) mixed on d 3 to 7 after breeding (D3), 3) mixed on d 13 to 17 after breeding (D14), or 4) mixed 35 d after breeding (D35). Mixed sows were moved into pens (n = 58 sows/pen) with an electronic sow feeding station and maintained as a static group. In the first 12 d after mixing or movement into STL (period 1), sows were assessed for lameness and lesions every 3 d and then every 2 wk until farrowing (period 2). Cortisol and fights were measured in period 1. Conception rates were reduced (P < 0.005) in D3 (87.1%) and D14 (89.2%) compared to D35 (92.2%) and STL (96.2%). Farrowing rates were lower (P < 0.0001) in D3 (82.8%) compared to D35 (90.5%) and STL (96.2%), but litter size was not (P ≥ 0.20) affected by mixing. The proportion of sows bred within 10 d of weaning was reduced (P < 0.05) for D14 compared to STL, but D3 and D35 did not differ among treatments. Number of fights 24 h after mixing was less (P < 0.0001) for D14 compared to D3 and D35 groups, and serum cortisol was greater (P < 0.05) for D35 compared to STL and D3. From period 1 to 2, lameness increased in D3 and decreased in D35 but did not change for D14 and STL (treatment × period, P < 0.05), whereas leg inflammation did not differ (P > 0.10) among treatments. Head and body lesion scores declined from period 1 to 2 in all mix groups, whereas vulva lesions increased in the D3 and D35 but did not change in D14 and STL (treatment × period, P < 0.0001). These results suggest STL can improve most measures of welfare compared to mixing in groups. However, when mixing sows, assessments for reproductive performance and welfare may change from gestation to farrowing. The poorest reproductive performance and welfare was observed when sows were mixed 3 to 7 d after breeding. There were few differences between the D14 and D35 treatments in reproduction or welfare, but D14--not D35--differed from STL in weaned sows rebred. Overall, results of this trial suggest that, even though any of the mixing days can result in acceptable measures of reproduction, there are clear effects of day of mixing on fertility and welfare, and special attention should be focused on the long-term reproductive and welfare consequences.

Behavioural, endocrine and immune responses to repeated social stress in pregnant gilts

Pregnant sows are exposed to various stressors in intensive pig husbandry that may have negative consequences on their health, reproductive performances and welfare. Social stress is one of these challenges, because gestating sows have to be housed in groups according to EU guidelines (2001/88/CE). The purpose of this study was to determine the consequences of repeated social stress in pregnant female pigs on their behavioural, endocrine and immunological responses and on pregnancy outcome. Pregnant gilts were submitted to a repeated social stress procedure induced by housing unfamiliar gilts in pairs changed twice a week between days 77 and 105 of gestation (S group, n = 18). Control gilts were housed in stable pairs during the same period (C group, n = 18). Agonistic behaviour was observed during the first 3 h after each grouping. Skin lesions were numbered 2 h after each grouping. Salivary cortisol was measured before and repeatedly during the 4 weeks of grouping. Gilts were immunized against keyhole limpet haemocyanin (KLH) on days 81 and 95 of gestation. Immunoglobulins G against KLH, proliferative responses to concanavalin A, lipopolysaccharide, pokeweed mitogen and KLH and peripheral blood leukocyte numbers were evaluated 1 week before the first grouping and 3 days after the last one. Agonistic interactions and skin lesions were observed in S gilts at each grouping, although there was a decline between the first and the last grouping (P < 0.05). The repeated social stress induced a sustained endocrine response as shown by elevated salivary cortisol levels from 1 to 48 h after grouping in S gilts compared to C gilts. The cellular as well as the humoral immunity and the leukocyte numbers were not influenced by social stress. Gestation length tended to be shorter in S gilts (P = 0.09), but litter size, piglet weight or mortality at birth were not affected. Variability of the response of S gilts to groupings was partly explained by their average success value determined according to the outcome (defeat or win) of all the groupings. In conclusion, our study demonstrates that the application of repeated social stress to pregnant gilts during the last third of their gestation repeatedly activates their hypothalamo-pituitary-adrenal axis but does not impair their immune function and pregnancy outcome.

Comparative effects of a prenatal stress occurring during early or late gestation on pig immune response

The aim of this work was to investigate the immune effects of prenatal stress (PNS) in pigs, when maternal stressor is applied during early or late gestation. In two separate experiments, gilts were submitted to a social-stress routine between either days 24 and 48 (stress (S) group, n=8 vs. control (C) group, n=6) or days 79 and 103 of gestation (S group, n=10 vs. C group, n=7). During the first month of life of the piglets, their cortisol levels were assessed in basal state and after stressful events (castration, new environment, and weaning). Piglets were immunized against ovalbumin (OVA) at 7 (D7) and 19 (D19) days of age. Lymphocyte proliferation in response to OVA and mitogens was investigated in blood in both sexes from D5 to D29 as well as in the spleen, thymus and crural lymph nodes from females euthanized on D5 and D26. On D27, the cytokine response of male piglets to an injection of lipopolysaccharide was investigated. Special care was taken to minimize the stress at blood sampling and euthanasia. We found that early gestational stress only affected the relative weight of adrenals on D5 (S<C, P<0.05). On the contrary, late gestational stress increased the proliferation index of blood cells regardless of the age, in both sexes in response to PHA (P=0.06), and in females only in response to ConA (P<0.01) and PWM (P<0.05). Overall, the effects of PNS in pigs seem to depend on the stage of gestation, gender and the immune compartment.

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.

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.