Effects of foetal size, sex and developmental stage on adaptive transcriptional responses of skeletal muscle to intrauterine growth restriction in pigs

Intrauterine growth restriction (IUGR) occurs both in humans and domestic species. It has a particularly high incidence in pigs, and is a leading cause of neonatal morbidity and mortality as well as impaired postnatal growth. A key feature of IUGR is impaired muscle development, resulting in decreased meat quality. Understanding the developmental origins of IUGR, particularly at the molecular level, is important for developing effective strategies to mitigate its economic impact on the pig industry and animal welfare. The aim of this study was to characterise transcriptional profiles in the muscle of growth restricted pig foetuses at different gestational days (GD; gestational length ~ 115 days), focusing on selected genes (related to development, tissue injury and metabolism) that were previously identified as dysregulated in muscle of GD90 fetuses. Muscle samples were collected from the lightest foetus (L) and the sex-matched foetus with weight closest to the litter average (AW) from each of 22 Landrace x Large White litters corresponding to GD45 (n = 6), GD60 (n = 8) or GD90 (n = 8), followed by analyses, using RT-PCR and protein immunohistochemistry, of selected gene targets. Expression of the developmental genes, MYOD, RET and ACTN3 were markedly lower, whereas MSTN expression was higher, in the muscle of L relative to AW littermates beginning on GD45. Levels of all tissue injury-associated transcripts analysed (F5, PLG, KNG1, SELL, CCL16) were increased in L muscle on GD60 and, most prominently, on GD90. Among genes involved in metabolic regulation, KLB was expressed at higher levels in L than AW littermates beginning on GD60, whereas both IGFBP1 and AHSG were higher in L littermates on GD90 but only in males. Furthermore, the expression of genes specifically involved in lipid, hexose sugar or iron metabolism increased or, in the case of UCP3, decreased in L littermates on GD60 (UCP3, APOB, ALDOB) or GD90 (PNPLA3, TF), albeit in the case of ALDOB this only involved females. In conclusion, marked dysregulation of genes with critical roles in development in L foetuses can be observed from GD45, whereas for a majority of transcripts associated with tissue injury and metabolism differences between L and AW foetuses were apparent by GD60 or only at GD90, thus identifying different developmental windows for different types of adaptive responses to IUGR in the muscle of porcine foetuses.

Sexual dimorphism in placental development and function: Comparative physiology with an emphasis on the pig

Across mammalian species, it has been demonstrated that sex influences birth weight, with males being heavier than females; a characteristic that can be observed from early gestation. Male piglets are more likely to be stillborn and have greater preweaning mortality than their female littermates, despite the additional maternal investment into male fetal growth. Given the conserved nature of the genome between the sexes, it is hypothesized that these developmental differences between males and females are most likely orchestrated by differential placental adaptation. This review summarizes the current understanding of fetal sex-specific differences in placental and endometrial structure and function, with an emphasis on pathways found to be differentially regulated in the pig including angiogenesis, apoptosis, and proliferation. Given the importance of piglet sex in agricultural enterprises, and the potential for skewed litter sex ratios, it is imperative to improve understanding of the relationship between fetal sex and molecular signaling in both the placenta and endometria across gestation.

Associations between maternal vitamin D status and porcine litter characteristics throughout gestation

Emerging evidence suggests an important role of vitamin D in the establishment and maintenance of pregnancy, and the regulation of foetal growth across mammalian species. However, the temporal changes in maternal vitamin D status throughout gestation in the pig and the relationship between maternal vitamin D status and litter characteristics of interest across gestation remain poorly understood and under-investigated. The abundance of 25(OH)D in maternal plasma was quantified by HPLC–MS/MS at gestational days (GD) 18, 30, 45, 60 and 90 (n = 5–11 gilts/GD). Maternal plasma 25(OH)D concentrations significantly increased between GD18 and GD30 (P < 0.05). The relationship between maternal vitamin D metabolite concentrations and litter characteristics of interest including gilt weight, ovulation rate, mean litter weight, number of live foetuses, percentage prenatal survival, and sex ratio of the litter was assessed. Maternal 25(OH)D (P = 0.059) concentrations tended to be positively associated with percentage prenatal survival on GD60. On GD90, maternal 25(OH)D (P < 0.05) concentrations were inversely associated with gilt weight. Maternal plasma 25(OH)D concentrations were inversely associated with the percentage of male foetuses in the litter on GD90 (P < 0.05). This study has provided novel insights into temporal changes in maternal vitamin D status throughout gestation and the relationship between maternal vitamin D status and the economically important litter characteristics of gilt weight, percentage prenatal survival and percentage of male foetuses in the litter. Improving the understanding of the role of vitamin D across important developmental timepoints in relation to foetal growth is essential to improve reproductive success in livestock species.

Associations between testicular development and fetal size in the pig

Background

Impaired reproductive performance is the largest contributing factor for the removal of boars from commercial systems. Intrauterine growth restricted piglets represent 25% of the total number of piglets born and have impaired reproductive performance. This study aimed to improve the understanding of temporal changes in testicular gene expression during testes development in fetuses of different size. The lightest and closest to mean litter weight (CTMLW) male Large White × Landrace littermates were collected at gestational days (GD) 45, 60 and 90 (n = 5–6 litters/GD).

Results

Testes weight and testes weight as a percentage of fetal weight were not associated with fetal size at GD60 or 90. Fetal plasma testosterone was not associated with fetal size at GD90. There was no association between fetal size and seminiferous tubule area and number, number of germ or Sertoli cells per tubule. The lightest fetuses tended to have wider seminiferous tubules compared to the CTMLW fetuses at GD90 (P = 0.077). The testicular expression of KI67 (P ≤ 0.01) and BAX:BCL2 ratio (P = 0.058) mRNAs decreased as gestation progressed. Greater SPP1 mRNA expression was observed at GD60 when compared with GD45 and 90 (P ≤ 0.05). Lower expression of DMRT1 and SPP1 (P < 0.01) mRNAs was observed in testes associated with the lightest fetuses compared to the CTMLW fetuses at GD90.

Conclusions

These findings provide novel insights into the expression profiles of genes associated with testicular development and function. Further, these data suggest that programming of reproductive potential in IUGR boars occurs late in gestation, providing a platform for further mechanistic investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00678-3.

Profiling of open chromatin in developing pig (Sus scrofa) muscle to identify regulatory regions

There is very little information about how the genome is regulated in domestic pigs (Sus scrofa). This lack of knowledge hinders efforts to define and predict the effects of genetic variants in pig breeding programs. To address this knowledge gap, we need to identify regulatory sequences in the pig genome starting with regions of open chromatin. We used the "Improved Protocol for the Assay for Transposase-Accessible Chromatin (Omni-ATAC-Seq)" to identify putative regulatory regions in flash-frozen semitendinosus muscle from 24 male piglets. We collected samples from the smallest-, average-, and largest-sized male piglets from each litter through five developmental time points. Of the 4661 ATAC-Seq peaks identified that represent regions of open chromatin, >50% were within 1 kb of known transcription start sites. Differential read count analysis revealed 377 ATAC-Seq defined genomic regions where chromatin accessibility differed significantly across developmental time points. We found regions of open chromatin associated with downregulation of genes involved in muscle development that were present in small-sized fetal piglets but absent in large-sized fetal piglets at day 90 of gestation. The dataset that we have generated provides a resource for studies of genome regulation in pigs and contributes valuable functional annotation information to filter genetic variants for use in genomic selection in pig breeding programs.

KLB dysregulation mediates disrupted muscle development in intrauterine growth restriction

Abstract

Intrauterine growth restriction (IUGR) is a leading cause of neonatal morbidity and mortality in humans and domestic animals. Developmental adaptations of skeletal muscle in IUGR lead to increased risk of premature muscle loss and metabolic disease in later life. Here, we identified β‐Klotho (KLB), a fibroblast growth factor 21 (FGF21) co‐receptor, as a novel regulator of muscle development in IUGR. Using the pig as a naturally‐occurring disease model, we performed transcriptome‐wide profiling of fetal muscle (day 90 of pregnancy) from IUGR and normal‐weight (NW) littermates. We found that, alongside large‐scale transcriptional changes comprising multiple developmental, tissue injury and metabolic gene pathways, KLB was increased in IUGR muscle. Moreover, FGF21 concentrations were increased in plasma in IUGR fetuses. Using cultures of fetal muscle progenitor cells (MPCs), we showed reduced myogenic capacity of IUGR compared to NW muscle in vitro, as evidenced by differences in fusion indices and myogenic transcript levels, as well as mechanistic target of rapamycin (mTOR) activity. Moreover, transfection of MPCs with KLB small interfering RNA promoted myogenesis and mTOR activation, whereas treatment with FGF21 had opposite and dose‐dependent effects in porcine and also in human fetal MPCs. In conclusion, our results identify KLB as a novel and potentially critical mediator of impaired muscle development in IUGR, through conserved mechanisms in pigs and humans. Our data shed new light onto the pathogenesis of IUGR, a significant cause of lifelong ill‐health in humans and animals.

Key points

Intrauterine growth restriction (IUGR) is associated with large‐scale transcriptional changes in developmental, tissue injury and metabolic gene pathways in fetal skeletal muscle.

Levels of the fibroblast growth factor 21 (FGF21) co‐receptor, β‐Klotho (KLB) are increased in IUGR fetal muscle, and FGF21 concentrations are increased in IUGR fetal plasma.

KLB mediates a reduction in muscle development through inhibition of mechanistic target of rapamycin signalling.

These effects of KLB on muscle cells are conserved in pig and human, suggesting a vital role of this protein in the regulation of muscle development and function in mammals.

Novel relationships between porcine fetal size, sex, and endometrial angiogenesis†

It is hypothesized that growth restriction occurs due to inadequate vascularization of the feto-maternal interface. Evidence exists for sexual dimorphism in placental function although associations between fetal sex and the endometrium remain poorly investigated. This study investigated the relationship between porcine fetal size, sex and endometrial angiogenesis at multiple gestational days (GD). Endometrial samples supplying the lightest and closest to mean litter weight (CTMLW), male and female Large White X Landrace conceptuses or fetuses were obtained at GD18, 30, 45, 60, and 90 (n = 5-9 litters/GD). Immunohistochemistry for CD31 revealed a greater number of blood vessels in endometrium supplying females compared to those supplying males at GD45. Endometrial samples supplying the lightest fetuses had fewer blood vessels (GD60) and uterine glands (GD90) compared to those supplying the CTMLW fetuses. Quantitative PCR revealed decreased CD31 (GD60), HPSE and VEGFA (GD90) expression, alongside increased HIF1A (GD45) expression in endometrial samples supplying the lightest compared to the CTMLW fetuses. At GD30, PTGFR, CD31, and VEGFA mRNA expression was increased in samples supplying female fetuses compared to those supplying male fetuses. Intriguingly, decreased expression of ACP5, CD31, HIF1A, and VEGFA mRNAs was observed at GD60 in endometrial samples supplying female fetuses compared to those supplying their male littermates. Endothelial cell branching assays demonstrated impaired endothelial cell branching in response to conditioned media from endometrial samples supplying the lightest and female fetuses compared with the CTMLW and male fetuses, respectively. This study has highlighted that endometrial tissues supplying the lightest and female fetuses have impaired angiogenesis when compared with the CTMLW and female fetuses respectively. Importantly, the relationship between fetal size, sex and endometrial vascularity is dynamic and dependent upon the GD investigated.

Associations between foetal size and ovarian development in the pig

It is estimated that intra-uterine growth restricted piglets represent 25 % of the total number of piglets born. Growth restricted female pigs have impaired reproductive performance postnatally. HHowever, when during gestation this phenotype arises is not known. With this study, the aim was to improve the understanding of foetal ovarian development in normal and small foetuses throughout gestation. Female Large White X Landrace foetuses were obtained at gestational day (GD) 45, 60 and 90 (n = 5-6 litters/GD). Histological analysis of GATA4 stained foetal ovaries at GD60 and 90 indicated there were fewer primary follicles (P ≤ 0.05) in the foetuses weighing the least compared to those with a weight similar to the mean for the litter (CTMLW) at GD90. Plasma oestradiol concentrations were less in the foetuses with lesser weights compared with greater weight foetuses at GD90 (P ≤ 0.05). The RNA was extracted from ovaries of the lesser weight and CTMLW foetuses at GD45, 60 and 90 and qPCR was performed to quantify relative abundance of 12 candidate mRNAs for which encoded proteins that modulate ovarian function and development. Gestational changes in relative abundances of CD31, PTGFR, SPP1 and VEGFA mRNA transcripts were observed. Relative abundance of KI67 (P = 0.066) and P53 (P ≤ 0.05) was less in ovaries of the lesser weight compared to CTMLW foetuses at GD60. There was a lesser relative abundance of PTGFR mRNA transcript in ovaries from the foetuses with lesser weight compared to CTMLW foetuses at GD45 and 60 (P ≤ 0.05). These findings indicate that postnatal differences in the reproductive potential of growth restricted females are programmed early in gestation. It is hoped that further investigation will improve the understanding of the relationship between prenatal reproductive development and postnatal reproductive performance.

Identification of appropriate reference genes for qPCR analyses of porcine placentae and endometria, supplying foetuses of different size and sex, at multiple gestational days

Recent studies suggest associations exist between foetal size and sex, and gene expression at the porcine feto-maternal interface. It is essential to identify reference genes which have stable expression throughout gestation in feto-placental units associated with foetuses of different size and sex. qPCR was performed for 11 genes within porcine placentae and endometria at gestational days (GD) 30, 60 and 90. Several reference genes were found to have stable expression in these samples. The combination of B2m1 and Tbp1, and Hprt1 and Tbp1 had the most stable expression in endometria and placentae, respectively. Reference genes identified as having stable expression were utilized in a larger experiment with placentae and endometria associated with foetuses of different size and sex at four GD. The average expression of B2m1 and Tbp1 mRNAs was suitable for the normalization of temporal changes in endometria, and comparison between endometria supplying foetuses of different size throughout gestation. The average expression of Hprt1 and Tbp1 mRNAs was suitable for the normalization of placental mRNA expression for comparison of temporal changes and sex differences between placentae supplying foetuses of different sex throughout gestation. This combination was suitable for the normalization of mRNA expression in placentas supplying GD30, GD60 and GD90 foetuses of different size. This study has identified reference genes with stable expression in placentae and endometria across multiple gestational days, in tissues associated with foetuses of different size and sex. The results of these experiments highlight the importance of selecting appropriate reference genes for the biological comparison under investigation.

Associations between fetal size, sex and placental angiogenesis in the pig

Inadequate fetal growth cannot be remedied postnatally, leading to severe consequences for neonatal and adult development. It is hypothesized that growth restriction occurs due to inadequate placental vascularization. This study investigated the relationship between porcine fetal size, sex, and placental angiogenesis at multiple gestational days (GD). Placental samples supplying the lightest and closest to mean litter weight (CTMLW), male and female Large White X Landrace fetuses were obtained at GD30, 45, 60, and 90. Immunohistochemistry revealed increased chorioallantoic membrane CD31 staining in placentas supplying the lightest compared to those supplying the CTMLW fetuses at GD60. At GD90, placentas supplying the lightest fetuses had decreased CD31 staining in the chorioallantoic membrane compared to those supplying the CTMLW fetuses. The mRNA expression of six candidate genes with central roles at the feto-maternal interface increased with advancing gestation. At GD60, ACP5 expression was increased in placentas supplying the lightest compared to the CTMLW fetuses. At GD45, CD31 expression was decreased in placentas supplying the lightest compared to the CTMLW fetuses. In contrast, CD31 expression was increased in placentas supplying the lightest compared the CTMLW fetuses at GD60. In vitro endothelial cell branching assays demonstrated that placentas supplying the lightest and male fetuses impaired endothelial cell branching compared to placentas from the CTMLW (GD45 and 60) and female fetuses (GD60), respectively. This study has highlighted that placentas supplying the lightest and male fetuses have impaired angiogenesis. Importantly, the relationship between fetal size, sex, and placental vascularity is dynamic and dependent upon the GD investigated.

Doppler ultrasound can be used to monitor umbilical arterial blood flow in lightly sedated pigs at multiple gestational ages

Doppler ultrasound was performed under moderate sedation (ketamine and azaperone) for 30min to monitor umbilical arterial (UA) blood flow in one uterine horn of Large White×Landrace gilts (n=23) at Gestational Days (GD) 30, 45, 60 and 90. Gilts were scanned before they were killed to examine relationships between litter size, sex ratio and five UA parameters (peak systolic velocity (PSV), end diastolic velocity (EDV), A/B (PSV to EDV) ratio, fetal heart rate (FHR) and resistance index (RI)). In gilts in which scans were obtained from all fetuses in the scanned horn, relationships between UA parameters, and fetal weight and sex were examined. A subset of gilts were sedated, scanned and recovered (SSR) earlier in gestation (GD30 or GD45) to assess the effects of sedation on later fetal development by comparison with control litters (no previous sedation). Temporal changes were observed in all UA parameters (P≤0.001). At GD60 and GD90, FHR decreased with increasing duration of sedation (P≤0.001). Sex ratio and fetal weight affected UA blood flow, whereas litter size and fetal sex did not. SSR at GD30 and GD45 was associated with decreased fetal weight at GD60 (P≤0.001) and GD90 (P=0.06) respectively, compared with controls. These results suggest maternal sedation during gestation affects fetal development, which should be investigated further. Measuring UA blood flow in growth-restricted porcine fetuses throughout gestation may be feasible.

Association of foetal size and sex with porcine foeto-maternal interface integrin expression

Integrins regulate adhesion at the foeto-maternal interface by interacting with secreted phosphoprotein 1 (SPP1) and fibronectin (FN). It is hypothesised that impaired foetal growth of ‘runt’ piglets is linked to altered integrin signalling at the foeto-maternal interface. Placental and endometrial samples associated with the lightest and closest to mean litter weight (CTMLW) (gestational day (GD18, 30, 45, 60 and 90), of both sex (GD30, 45, 60 and 90) (n = 5–8 litters/GD), Large White × Landrace conceptuses or foetuses were obtained. The mRNA expression of the integrin subunits (ITG) ITGA2, ITGAV, ITGB1, ITGB3, ITGB5, ITGB6, ITGB8, SPP1 and FN was quantified by qPCR. Temporal changes in mRNA expression were observed, with different profiles in the two tissues. Endometrial ITGB1 (P ≤ 0.05, GD45) and SPP1 (P ≤ 0.05, all GD combined and GD60) expression was decreased in samples supplying the lightest compared to the CTMLW foetuses. Placentas supplying female foetuses had decreased expression of ITGB6 (GD45, P ≤ 0.05) and FN (GD90, P ≤ 0.05) compared to those supplying male foetuses. Endometrial samples supplying females had increased ITGB3 (P ≤ 0.05, GD60) and FN (P ≤ 0.05, GD30) expression and decreased SPP1 (P ≤ 0.05, GD60) expression compared to male foetuses. Correlations between mean within-gilt mRNA expression and percentage prenatal survival, number of live foetuses or conceptuses and percentage male foetuses were observed. This study has highlighted novel and dynamic associations between foetal size, sex and integrin subunit mRNA expression at the porcine foeto-maternal interface. Further studies should be performed to improve the understanding of the mechanisms behind these novel findings.

Associations between fetal size, sex and both proliferation and apoptosis at the porcine feto-maternal interface

Introduction

Inadequate fetal growth has severe consequences for both neonatal and adult development. It is hypothesised that the feto-maternal interface associated with the lightest and male fetuses will undergo more apoptosis and less proliferation than those supplying the closest to mean litter weight (CTMLW) and female fetuses respectively.

Methods

Placental and endometrial samples associated with the lightest and CTMLW (gestational day (GD) 18 and 30), male and female (GD45, 60 and 90) Large White X Landrace conceptuses or fetuses were obtained. The mRNA expression of candidate genes involved in apoptosis or proliferation (BAX, BCL2, P53 and KI67) was quantified by qPCR. TUNEL staining was performed on placental samples supplying the lightest and CTMLW fetuses (GD45 and 60), of both sex (GD60).

Results

Placentas associated with the lightest fetuses had decreased P53 and KI67 expression compared to the CTMLW fetuses at GD45. At GD60, P53 expression was increased in placentas supplying the lightest compared to CTMLW fetuses. P53 expression was increased in endometrial samples associated with the lightest compared to the CTMLW fetuses at GD45. At GD30 and GD60 respectively, BAX expression was increased and BCL2, P53 and KI67 expression were decreased in endometrial samples associated with females compared to their male littermates. TUNEL staining revealed no association between fetal size or sex, and apoptotic cell number.

Discussion

This study has highlighted dynamic associations between fetal size, sex, and apoptosis and proliferation at the porcine feto-maternal interface. Further studies should be performed to improve the understanding of the mechanisms behind these findings.

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Gestational day influence feto-maternal interface apoptotic mRNA expression.

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Fetal size is associated with feto-maternal interface apoptotic mRNA expression.

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Sexual dimorphism exists in feto-maternal interface apoptotic mRNA expression.

The role of dietary fibre in pig production, with a particular emphasis on reproduction

Fibres from a variety of sources are a common constituent of pig feeds. They provide a means to utilise locally-produced plant materials which are often a by-product of the food or drink industry. The value of a high fibre diet in terms of producing satiety has long been recognised. However the addition of fibre can reduce feed intake, which is clearly detrimental during stages of the production cycle when nutrient needs are high, for example in growing piglets and during lactation. More recently, fibre has been found to promote novel benefits to pig production systems, particularly given the reduction in antimicrobial use world-wide, concern for the welfare of animals fed a restricted diet and the need to ensure that such systems are more environmentally friendly. For example, inclusion of dietary fibre can alter the gut microbiota in ways that could reduce the need for antibiotics, while controlled addition of certain fibre types may reduce nitrogen losses into the environment and so reduce the environmental cost of pig production. Of particular potential value is the opportunity to use crude fibre concentrates as ‘functional’ feed additives to improve young pig growth and welfare. Perhaps the greatest opportunity for the use of high fibre diets is to improve the reproductive efficiency of pigs. Increased dietary fibre before mating improves oocyte maturation, prenatal survival and litter size; providing a consumer-acceptable means of increasing the amount of saleable meat produced per sow. The mechanisms responsible for these beneficial effects remain to be elucidated. However, changes in plasma and follicular fluid concentrations of key hormones and metabolites, as well as effects of the hypothalamic satiety centre on gonadotrophin secretion and epigenetic effects are strong candidates.

Periparturient Behavior and Physiology: Further Insight Into the Farrowing Process for Primiparous and Multiparous Sows

Giving birth is a critical time for many species and is often the most painful event ever experienced by females. In domestic species, like the pig, pain associated with parturition represents a potential welfare concern, and the consequences of pain can cause economic losses (e.g., by indirectly contributing to piglet mortality as pain could slow post-farrowing recovery, reduce food and water intake, reducing milk let-down). This study investigated pain assessment and its management in primiparous (gilts) and multiparous (sows) breeding pigs, including the provision of a non-steroidal anti-inflammatory drug (NSAID) post-parturition. Individuals were randomly allocated to receive the NSAID ketoprofen (3 mg/kg bodyweight) (n = 11 gilts, 16 sows) or the equivalent volume of saline (n = 13 gilts, 16 sows) by intramuscular injection 1.5 h after the birth of the last piglet. Data collected included putative behavioral indicators of pain (back leg forward, tremble, back arch), salivary cortisol concentrations pre-farrowing and up to 7 days post-injection. In addition, post-partum biomarkers of inflammation, including the acute phase protein C-reactive protein (CRP) and 3 porcine cytokines [interleukin-1 β (IL1 β), interleukin-6 (IL6), and tumor necrosis factor α (TNF α)] were measured in plasma collected 6 h following the injection. Behaviors were analyzed using generalized linear mixed models, and physiological variables with linear mixed models. No difference in putative pain behaviors, salivary cortisol, CRP, or cytokines were found between individuals treated with ketoprofen or those administered the saline control. However, there were some differences between gilts and sows, as sows exhibited more putative pain behavior than gilts, had higher salivary cortisol on the day of farrowing and had higher plasma TNF α. Conversely, gilts had higher salivary cortisol than sows on day 3 post-farrowing and had higher CRP. This indicates that, like human females, multiparous sows experience more pain from uterine activity following birth than primiparas. This study provides useful information for developing management practices relating to post-farrowing care for breeding pigs.

Epigenetics and developmental programming of welfare and production traits in farm animals

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the 'developmental origins of health and disease' or 'DOHaD' hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems.

Sex-specific prenatal stress effects on the rat reproductive axis and adrenal gland structure

Social stress during pregnancy has profound effects on offspring physiology. This study examined whether an ethologically relevant social stress during late pregnancy in rats alters the reproductive axis and adrenal gland structure in post-pubertal male and female offspring. Prenatally stressed (PNS) pregnant rats (n=9) were exposed to an unfamiliar lactating rat for 10 min/day from day 16 to 20 of pregnancy inclusive, whereas control pregnant rats (n=9) remained in their home cages. Gonads, adrenal glands and blood samples were obtained from one female and one male from each litter at 11 to 12-weeks of age. Anogenital distance was measured. There was no treatment effect on body, adrenal or gonad weight at 11-12 weeks. PNS did not affect the number of primordial, secondary or tertiary ovarian follicles, numbers of corpora lutea or ovarian FSH receptor expression. There was an indication that PNS females had more primary follicles and greater ovarian aromatase expression compared with control females (both P=0.09). PNS males had longer anogenital distances (0.01±0.0 cm/g vs 0.008±0.00 cm/g; P=0.007) and higher plasma FSH concentrations (0.05 ng/mL vs 0.006 ng/mL; s.e.d.=0.023; P=0.043) compared with control males. There were no treatment effects on the number of Sertoli cells or seminiferous tubules, seminiferous tubule area, plasma testosterone concentration or testis expression of aromatase, FSH receptor or androgen receptor. PNS did not affect adrenal size. These data suggest that the developing male reproductive axis is more sensitive to maternal stress and that PNS may enhance aspects of male reproductive development.

A genome-wide linkage analysis for reproductive traits in F2 Large White × Meishan cross gilts

Female reproductive performance traits in pigs have low heritabilities thus limiting improvement through traditional selective breeding programmes. However, there is substantial genetic variation found between pig breeds with the Chinese Meishan being one of the most prolific pig breeds known. In this study, three cohorts of Large White × Meishan F2 cross-bred pigs were analysed to identify quantitative trait loci (QTL) with effects on reproductive traits, including ovulation rate, teat number, litter size, total born alive and prenatal survival. A total of 307 individuals were genotyped for 174 genetic markers across the genome. The genome-wide analysis of the trait-recorded F2 gilts in their first parity/litter revealed one QTL for teat number significant at the genome level and a total of 12 QTL, which are significant at the chromosome-wide level, for: litter size (three QTL), total born alive (two QTL), ovulation rate (four QTL), prenatal survival (one QTL) and teat number (two QTL). Further support for eight of these QTL is provided by results from other studies. Four of these 12 QTL were mapped for the first time in this study: on SSC15 for ovulation rate and on SSC18 for teat number, ovulation rate and litter size.

Heat shock induces interferon-TAU gene expression by in vitro-produced bovine blastocysts

PROBLEM

The type I interferon (IFN), IFN-tau (τ), is the primary embryonic signal for pregnancy maintenance in ruminants. This study determined the effects of heat shock upon IFN-τ (IFNT) gene expression by bovine blastocysts in vitro.

METHOD OF STUDY

In vitro-produced blastocyst-stage embryos were exposed to 42°C for 4 hr, and mRNA for heat-shock protein 70 (HSP70) and IFNT quantified.

RESULTS

Heat shock increased both HSP70 and IFNT expression. There was a significant correlation between HSP70 and IFNT transcript levels irrespective of whether a blastocyst had been exposed to heat shock or not.

CONCLUSION

The increase in IFNT as a result of heat shock suggests that a proportion of the variation in IFNT expression observed in blastocyst-stage embryos is a response to stress.

Genotype and fetal size affect maternal­–fetal amino acid status and fetal endocrinology in Large White×Landrace and Meishan pigs

This study compared maternal plasma amino acid concentrations, placental protein secretion in vitro and fetal body composition and plasma amino acid and hormone concentrations in feto–placental units from the smallest and a normally-sized fetus carried by Large White × Landrace or Meishan gilts on Day 100 of pregnancy. Compared with Large White × Landrace, Meishan placental tissue secreted more protein and Meishan fetuses contained relatively more fat and protein, but less moisture. Fetal plasma concentrations of insulin, triiodothryonine, thyroxine and insulin-like growth factor (IGF)-II were higher in Meishan than Large White × Landrace fetuses. In both breeds, fetal cortisol concentrations were inversely related to fetal size, whereas concentrations of IGF-I were higher in average-sized fetuses. Concentrations of 10 amino acids were higher in Large White × Landrace than Meishan gilts, while glutamine concentrations were higher in Meishan gilts. Concentrations of alanine, aspartic acid, glutamic acid and threonine were higher in Meishan than Large White × Landrace fetuses. Average-sized fetuses had higher concentrations of asparagine, leucine, lysine, phenylalanine, threonine, tyrosine and valine than the smallest fetus. This study revealed novel genotype and fetal size differences in porcine maternal–fetal amino acid status and fetal hormone and metabolite concentrations.

Efficiency of genomic selection using Bayesian multi-marker models for traits selected to reflect a wide range of heritabilities and frequencies of detected quantitative traits loci in mice

BACKGROUND

Genomic selection uses dense single nucleotide polymorphisms (SNP) markers to predict breeding values, as compared to conventional evaluations which estimate polygenic effects based on phenotypic records and pedigree information. The objective of this study was to compare polygenic, genomic and combined polygenic-genomic models, including mixture models (labelled according to the percentage of genotyped SNP markers considered to have a substantial effect, ranging from 2.5% to 100%). The data consisted of phenotypes and SNP genotypes (10,946 SNPs) of 2,188 mice. Various growth, behavioural and physiological traits were selected for the analysis to reflect a wide range of heritabilities (0.10 to 0.74) and numbers of detected quantitative traits loci (QTL) (1 to 20) affecting those traits. The analysis included estimation of variance components and cross-validation within and between families.

RESULTS

Genomic selection showed a high predictive ability (PA) in comparison to traditional polygenic selection, especially for traits of moderate heritability and when cross-validation was between families. This occurred although the proportion of genomic variance of traits using genomic models was 22 to 33% smaller than using polygenic models. Using a 2.5% mixture genomic model, the proportion of genomic variance was 79% smaller relative to the polygenic model. Although the proportion of variance explained by the markers was reduced further when a smaller number of SNPs was assumed to have a substantial effect on the trait, PA of genomic selection for most traits was little affected. These low mixture percentages resulted in improved estimates of single SNP effects. Genomic models implemented for traits with fewer QTLs showed even lower PA than the polygenic models.

CONCLUSIONS

Genomic selection generally performed better than traditional polygenic selection, especially in the context of between family cross-validation. Reducing the number of markers considered to affect the trait did not significantly change PA for most traits, particularly in the case of within family cross-validation, but increased the number of markers found to be associated with QTLs. The underlying number of QTLs affecting the trait has an effect on PA, with a smaller number of QTLs resulting in lower PA using the genomic model compared to the polygenic model.

Pre-natal social stress and post-natal pain affect the developing pig reproductive axis

This study assessed the effect of pre-natal social stress and post-natal pain on the reproductive development of young (approximately day 40) pigs. Male pigs carried by sows that were stressed by mixing with unfamiliar older sows for two 1-week periods during mid-pregnancy had lower plasma testosterone (0.54 vs 0.86 ng/ml, s.e.d.=0.11; P=0.014) and oestradiol (E2; 22.9 vs 38.7 pg/ml, s.e.d.=7.80; P=0.021) concentrations compared with males carried by unstressed control sows. Although there was no effect of pre-natal stress on female E2 concentrations, female pigs carried by stressed sows had fewer primordial ovarian follicles (log −4.32/μm2 vs −4.00/μm2, s.e.d.=0.136; P=0.027). Tail amputation on day 3 after birth reduced E2 concentrations in female (4.78 vs 6.84 pg/ml, s.e.d.=0.86; P=0.03) and in male (25.6 vs 34.9 pg/ml, s.e.d.=3.56; P=0.021) pigs and reduced both testis weight (0.09% of body weight vs 0.10% of body weight, s.e.d.=0.003; P=0.01) and the percentage of proliferating Leydig cells (1.97 vs 2.12, s.e.d.=0.114; P=0.036) compared with sham-amputated littermate controls. There was a significant (P=0.036) interaction between the effects of pre-natal stress and post-natal pain on testicular expression of the steroidogenic enzyme 17α-hydroxylase, such that amputation increased expression in pigs born to control sows, but reduced expression in animals born to stressed sows. This study shows that stressful procedures associated with routine animal husbandry can disrupt the developing reproductive axis.

Nutritional effects on oocyte and embryo development in mammals: implications for reproductive efficiency and environmental sustainability

The environment in which a breeding female lives prior to conception and during the early stages of her pregnancy has striking effects on oocytes developing in the ovarian follicle and on early embryos in the reproductive tract. Of the various environmental factors known to affect oocyte and embryo development, altered nutrition during this critical period has been particularly well studied. Alterations in the quantity of food consumed or the composition of the diet imposed solely during the pre-mating period affect oocyte maturity, blastocyst yield, prenatal survival and the number of offspring born alive. Importantly, nutrition at this time also affects the quality of embryos and resultant offspring, with increasing evidence from a variety of species showing that peri-conception nutrition can alter behaviour, cardiovascular function and reproductive function throughout post-natal life. In livestock species, it is important to devise nutritional strategies that improve reproductive efficiency and the quality of offspring but that do not add to the environmental footprint of the production system and which recognize likely changes in feedstuff availability arising from predicted changes in climate.

Glucocorticoid exposure and tissue gene expression of 11beta HSD-1, 11beta HSD-2, and glucocorticoid receptor in a porcine model of differential fetal growth

Glucocorticoids play a critical role in fetal development, but inappropriate exposure is associated with reduced fetal growth. We investigated cortisol exposure and supply in a porcine model of differential fetal growth. This model compares the smallest fetus of a litter with an average-sized sibling at three stages of gestation. At day 45, small fetuses had reduced plasma cortisol (16.8 +/- 3.4 ng/ml) relative to average fetuses (34.4 +/- 3.4 ng/ml, P < 0.001). At day 65 levels had reduced in small and average fetuses to similar concentrations (5.7 +/- 1.0 vs 4.8 +/- 0.5 ng/ml, P = 0.128). By day 100, elevated levels were found in small fetuses (10.7 +/- 1.5 vs 7.6 +/- 0.7 ng/ml, P < 0.001). Maternal plasma cortisol was unchanged over gestation (day 45, 56.7 +/- 21.6 ng/ml; day 65, 57.8 +/- 14.4 ng/ml; day 100, 55.7 +/- 6.5 ng/ml). We examined the cause of altered cortisol by investigating the fetal hypothalamic-pituitary-adrenal axis through the measurement of adrenocorticotropic hormone and assessing exposure to maternal cortisol by quantifying placental 11beta-hydroxysteroid dehydrogenase-isoform 2 (11beta HSD-2) gene expression. These data suggest that altered cortisol supply was of fetal origin. We examined organ glucocorticoid (GC) metabolism by the measurement of GC receptor (GR) and 11beta-hydroxysteroid dehydrogenase-isoform 1 (11beta HSD-1) gene expression. We found that fetal organs have different temporal patterns of 11beta HSD-1 and GR expression, with the liver particularly sensitive to cortisol in late gestation. This study examines GC exposure in naturally occurring differential growth and simultaneously explores tissue GC sensitivity and handling, at three key stages of gestation.

Altered muscle development and expression of the insulin-like growth factor system in growth retarded fetal pigs

We have used a porcine model of spontaneous differential fetal growth to investigate the effects of fetal size on muscle development. We hypothesized that altered muscle development may occur in small fetuses as a consequence of modified expression of selected genes of the insulin-like growth factor system. We examined the development of the Longissimus muscle (m. Longissimus) in small fetuses and their average sized littermates. We collected small for gestational age fetuses and their average sized sibling on days 45, 65 and 100 of gestation (term is 113-116 days). Small fetuses had significantly lower body weight at all three stages of gestation (p<0.05) and significantly reduced secondary to primary muscle fibre ratio in m. Longissimus on day 100 (p<0.05) compared to their littermates. On day 65, the expression of insulin-like growth factor receptor 1 and insulin-like growth factor binding protein 3 were significantly higher (p<0.05) in m. Longissimus of the small fetuses compared with their average sized littermates. On day 100, the expression of insulin-like growth factor receptor 1 remained significantly higher (p=0.001), in addition to significantly higher levels of insulin-like growth factor receptor 2 and insulin-like growth factor binding protein 5 in the small fetuses (p<0.05). No difference in levels of myogenin was observed between the small and average sized littermates. In conclusion, we demonstrate that reduced fetal muscle development is associated with an increased expression of several genes of the insulin-like growth factor system in small fetuses in mid to late gestation.

Ovine fetal development is more sensitive to perturbation by the presence of serum in embryo culture before rather than after compaction

The effects on subsequent fetal development of the presence or absence of serum at different times during IVC of ovine zygotes were studied. Zygotes, recovered from superovulated ewes 36h after intrauterine AI using semen from a single sire, were cultured for 5 days in synthetic oviductal fluid (SOF) media supplemented with either BSA and amino acids (SOF-) or with 10% (v/v) steer serum (SOF+). Serum was present or absent during the first two and last 2 days of IVC giving four treatments (SOF-/SOF-; SOF-/SOF+;SOF+/SOF- and SOF+/SOF+). In total, 224 embryos, including 26 in vivo controls, were transferred singly at day 6 post-AI to synchronous recipients and the products of conception recovered at day 125 of gestation. Presence of serum during IVC had a biphasic effect on embryo development. The inclusion of serum during the first 2 days of IVC retarded early embryo development while the inclusion of serum during the last 2 days of IVC produced more blastocysts by day 6. These effects were independent of each other. The presence of serum during the first 2 days of IVC resulted in increased weights of gravid uterus, placenta, fetus, fetal heart and liver. The incidence of fetuses whose total or organ weights were greater than three standard deviations above the corresponding mean weights of control fetuses was also greater when serum was present during the first 2 days of IVC. However, even when serum was absent throughout IVC there was still an infrequent incidence of fetal weights greater than three standard deviations above the mean for control fetuses. These observations provide evidence that it is the early pre-compaction stages of embryo development that are particularly sensitive to perturbations leading to abnormal fetal development.

Beneficial effects of a high fibre diet on oocyte maturity and embryo survival in gilts

The present study examined the effects of feeding gilts a high fibre diet from the third post-pubertal oestrus until either day 19 of the same cycle or insemination at the following oestrus on oocyte maturity, embryo survival and associated changes in reproductive hormone concentrations. Gilts fed with the high fibre diet had lower circulating oestradiol concentrations on days 17, 18 and 19 of the cycle and increased LH pulse frequency on day 18. More oocytes recovered on day 19 from gilts receiving the high fibre diet were at metaphase II after 46-h culture in medium containing 10% of their own follicular fluid, despite fewer large (>7 mm) follicles in these gilts when compared with control animals. There was no effect of diet on ovulation rate, corpora lutea size or progesterone concentrations on days 10–12 after insemination, but embryo survival on days 27–29 after insemination was higher in gilts that received the high fibre diet. This study demonstrates that a high fibre diet that increases embryo survival also improves oocyte maturity and provides information on endocrine correlates that may shed light on underlying mechanisms.

Effects of cobalt/vitamin B12 status in ewes on ovum development and lamb viability at birth

Scottish Blackface ewes from cobalt-deficient farmland were fed a diet containing 0.06 mg cobalt per kg dry matter from approximately 30 days before embryo recovery/transfer until lambing. Ewes remained untreated (–Co; n = 82) or were given an intraruminal cobalt-containing bolus to compensate for the dietary deficit (+Co; n = 82). Ewes used as embryo donors (–Co, n = 17; +Co, n = 16) were artificially inseminated with semen from a single Suffolk sire. Day 6 embryos obtained from –Co and +Co donors were transferred in singleton to –Co and +Co recipients in a 2 × 2 factorial-designed experiment to determine the effects of cobalt/vitamin B12 status during the periconception period (factor 1) and pregnancy (factor 2) on lamb viability at birth. Mean (± s.e.m.) circulating concentrations of vitamin B12 in –Co and +Co donors at ovum recovery were 182 ± 10 and 1288 ± 64 pmol L–1, respectively (P < 0.001), and the number of corpora lutea per ewe ovulating was 9.9 ± 1.6 and 14.4 ± 1.3, respectively (P < 0.05). Treatment did not affect the proportion of recovered ova that contained >32 cells (viable) or the median stage of development (late morula), but viable ova recovered from –Co v. +Co ewes had a better morphological grade (2.0 ± 0.1 v. 2.20 ± 0.04, respectively; P < 0.01). There was no effect of treatment on the proportion of recipient ewes that became pregnant. Circulating concentrations of vitamin B12 were lower in –Co than +Co ewes during pregnancy (P < 0.001) and at birth in lambs born to –Co ewes compared with those born to +Co ewes (P < 0.001). There was no effect of donor or recipient cobalt/vitamin B12 status on lamb birthweight, neonatal vigour or neonatal rectal temperatures, but lambs derived from +Co v. –Co embryo donors were more active in the first 3 days after birth (P < 0.05). Results show that sub-clinical cobalt/vitamin B12 deficiency reduces ovulatory response in superovulated ewes and that periconception nutrition can affect neonatal lamb behaviour.

Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction

Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using alpha(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P < 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 x essential amino acids), SNAT2 mRNA levels showed further significant (P < 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P = 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adapt in vitro to nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

Effect of alterations in the quantity and composition of the pre-mating diet on embryo survival and foetal growth in the pig

This trial examined the effects of feeding six diets, which varied in either amount or composition, during the oestrous cycle prior to insemination on embryo survival and foetal development on day 27+/-2 of pregnancy in gilts. Ten or 11 gilts per group received either a maintenance (M) diet, 1.8 x M, 2.6 x M or nutritionally balanced diets in which the content of fibre, protein or starch was increased. Of the six diets tested, only the high fibre diet significantly increased embryo survival when compared to its 1.8 x M isoenergetic control (88.20+/-1.96% versus 81.25+/-2.67%; P<0.05). More litters from gilts fed the 1.8 x M and the starch diets had foetuses defined as intra-uterine growth retarded (IUGR; 50% and 62.5 of litters, respectively), compared to the other four groups in which 0-12.5% of litters contained IUGR foetuses (P<0.05). There was no effect of dietary treatment on foetal or placental size or on the within-litter variability in foetal and placental size. Plasma concentrations of oestradiol and progesterone on days 4-8 of the oestrous cycle and on day 27+/-2 of pregnancy were unaffected by treatment. Feed intake was positively related to mean plasma IGF-1 concentrations on days 4-8 of the cycle (P<0.01) and to mean leptin concentrations on days 4 and 5 (P<0.001). Leptin concentrations were unaffected by alterations in the composition of the diet, whereas IGF-1 concentrations were higher in gilts fed the starch diet compared to the M control (159+/-9.52 versus 127+/-7.65 ng/ml; P<0.05). These data demonstrate that alteration to the composition of the feed consumed during the cycle before insemination can affect both embryo survival and the distribution of foetal size within the litter. The underlying mechanism(s) remain to be determined, but probably involve dietary-induced changes in concentrations of reproductive hormones and/or intermediary metabolites that in turn affect ovarian follicular and oocyte development.

Cortisol stimulates system A amino acid transport and SNAT2 expression in a human placental cell line (BeWo)

Both placental system A activity and fetal plasma cortisol concentrations are associated with intrauterine growth retardation, but it is not known if these factors are mechanistically related. Previous functional studies using hepatoma cells and fibroblasts produced conflicting results regarding the regulation of system A by cortisol. Using the b30 BeWo choriocarcinoma cell line, we investigated the regulation of system A by cortisol. System A function was analyzed using methyl amino isobutyric acid (MeAIB) transcellular transport studies. Transporter expression [system A transporter (SNAT)1/2] was studied at the mRNA and protein levels using Northern and Western blotting, respectively. Localization was carried out using immunocytochemistry. The [(14)C]MeAIB transfer rate across BeWo monolayers after preincubation with cortisol for 24 h was significantly increased compared with control. This was associated with a relocalization of the SNAT2 transporter at lower cortisol levels and significant upregulation of mRNA and protein expression levels at cortisol levels >1 microM. This is the first study to show functional and molecular regulation of system A by cortisol in BeWo cells. It is also the first study to identify which system A isoform is regulated. These results suggest that cortisol may be involved in upregulation of system A in the placenta to ensure sufficient amino acid supply to the developing fetus.

Zygote donor nitrogen metabolism and in vitro embryo culture perturbs in utero development and IGF2R expression in ovine fetal tissues

Tests were made of the effects of altering nitrogen metabolism in zygote donor ewes on fetal development and expression of the gene encoding the type II insulin-like growth factor receptor (IGF2R) following the transfer of ovine embryos cultured from these zygotes, either in the absence or presence of serum. Zygotes, recovered from superovulated ewes (32 on a urea supplemented (30 g urea/kg) diet (high N) and 32 on a control diet (low N)) 36 h after intrauterine AI using semen from a single sire, were cultured for 5 days in synthetic oviductal fluid (SOF) media either with BSA and amino acids (SOF-) or with 10% (v/v) steer serum (SOF+). In total, 166 embryos, including 30 in vivo controls, were transferred singly at day 6 post-AI to synchronous recipients and the products of conception recovered at day 125 of gestation. Elevated plasma urea concentrations in zygote donors were associated with accelerated early embryo development, low pregnancy rates (16%) for embryos from the high N, SOF+ treatment, and significantly influenced fetal development and the expression of IGF2R in the fetal heart at day 125 of gestation. Importantly, the culture of sheep zygotes under serum-free conditions led to a high incidence of aberrant conceptus development and IGF2R expression. Consequently, maternal nitrogen metabolism prior to zygote recovery and in vitro culture can influence fetal development and the expression of an imprinted gene following embryo transfer, and these data support the notion that environmental effects on the follicle-enclosed oocyte may contribute to the etiology of the Large Offspring Syndrome.

The effect of fetal pig size and stage of gestation on tissue fatty acid metabolism and profile

The fetus requires an adequate supply of fatty acids for optimum growth and development. It has been hypothesized that reduced activity of enzymes of fatty acid metabolism could contribute to inadequate fetal growth. In a porcine model of differential fetal growth we examined heart and liver fatty acid synthase, delta5-desaturase and delta6-desaturase gene expression and measured hepatic fatty acid profile to assess long-chain polyunsaturated fatty acid status. On gestation days 45, 65 and 100 sows were killed and tissues extracted from an average-sized fetus and the smallest fetus from each litter. As early as day 45, considerable hepatic delta5- and delta6-desaturase was detected, and this expression significantly increased as gestation progressed. In contrast, cardiac desaturase expression remained stable with time. Fatty acid synthase expression was greatest at day 65 in the liver, but was not expressed in the heart. Overall, the smallest fetus did not exhibit reduced tissue delta5- or delta6-desaturase expression or compromised polyunsaturated fatty acid status at any stage. In fact, small fetuses expressed more cardiac delta5-desaturase than their average-sized siblings, possibly in response to a stress to the heart. It is clear from this study that fatty acid metabolism changes markedly as gestation progresses, and reduced fatty acid supply does not cause inadequate growth in this porcine model of fetal development.

Oocyte-somatic cell-endocrine interactions in pigs

Oocyte-somatic cell communication is bi-directional and essential for both oocyte and follicular granulosa and theca cell function and development. We have shown that the oocyte secretes factors that stimulate porcine granulosa cell proliferation in serum-free culture, and suppress progesterone production, thereby preventing premature luteinisation. Possible candidates for mediating some of these effects are the bone morphogenetic proteins (BMPs) that belong to the transforming growth factor beta family. They are emerging as a family of proteins critical for fertility and ovulation rate in several mammals, and they are expressed in various cell types in the ovary. We have evidence for a functional BMP system in the porcine ovary and BMP receptors are present in the egg nests in the fetal ovary and in the granulosa cells, oocytes and occasional theca cells throughout subsequent development. In addition to paracrine interactions in the ovary, the porcine oocyte and its developmental potential can also be influenced by nutritional manipulation in vivo. We have demonstrated that feeding a high plane of nutrition to gilts for 19 days prior to ovulation increased oocyte quality compared to control animals fed a maintenance diet, as determined by oocyte maturation in vitro. This was associated with a number of changes in circulating reproductive and metabolic hormones and also in the follicular fluid in which the oocyte is nurtured. Further studies showed a similar increase in prenatal survival on Day 30 of gestation, demonstrating a direct link between oocyte quality/maturation and embryo survival. Collectively, these studies emphasise the importance of the interactions that occur between the oocyte and somatic cells and also with endocrine hormones for ovarian development, and ultimately for the production of oocytes with optimal developmental potential.

Placental transport of leucine in a porcine model of low birth weight

Low birth weight is a major factor in neonatal morbidity and mortality in humans and domestic species and is a predictor of physiological disorders in adulthood. This study utilised the naturally occurring variation in pig fetal size within a uterus to test the hypothesis that placental amino acid transport capability is associated with fetal growth. Leucine uptake by trophoblast vesicles prepared from placentas supplying an average-sized fetus and the smallest fetus in the uterus was assessed. On days 45 and 65 of gestation, uptake of leucine by the porcine placenta was predominantly sodium independent and was inhibited by the non-metabolised leucine analogue 2-amino-2-norbornane-carboxylic acid, indicating that uptake occurs via system L. By day 100 the uptake of leucine by placentas supplying average-sized fetuses had changed from being predominantly sodium independent to involving both sodium-dependent (system B0) and -independent (system L) pathways. This change was not seen in placentas supplying the smallest fetus, which continued to display predominantly sodium-independent uptake. In conclusion, these data show gestational- and fetal size-dependent changes in the transport of leucine across the porcine placenta.

Patterns of fetal growth within Large White x Landrace and Chinese Meishan gilt litters at three stages of gestation

Low birthweight piglets have an increased incidence of mortality and morbidity. As there are few opportunities to remedy the detrimental consequences of low birthweight after birth, it is important to understand the nature of fetal growth retardation and to identify when low birthweight fetuses deviate from the growth trajectory of their normally grown siblings. The aims of this study were to identify the nature, timing and possible causal factors influencing inadequate fetal growth in Large White x Landrace (LW) and Chinese Meishan (MS) gilts at three stages of pregnancy. Thirty-six per cent of litters contained inadequately grown fetuses. Both intrauterine-growth-restricted (IUGR) and small-for-gestational-age (SGA) fetuses could be identified as early as Day 30 in MS and LW litters and the percentage of litters containing inadequately grown fetuses was similar throughout gestation. MS fetuses, placentas and piglets had less within-litter variation in weight at all stages studied. Inverse relationships were observed between litter size and both minimum and mean weights of MS neonates. No other relationships between fetal size and either uterine position or litter size were observed.

Effect of different nutritional regimens before ovulation on plasma concentrations of metabolic and reproductive hormones and oocyte maturation in gilts

This study examined the effect of feeding either a maintenance (1.35 kg day(-1)) or high (3.5 kg day(-1)) plane of nutrition for 19 days after oestrus on oocyte maturity and both reproductive and metabolic hormone concentrations in gilts. Blood samples were collected each day from oestrus until slaughter on day 19 and during two pulse bleeds (15 min samples for 8 h) conducted on day 12 and day 18. After slaughter, oocytes were recovered from the presumed ovulatory population of follicles, matured in vitro for 46+/-2 h with 10% of their own follicular fluid, and then fixed and stained to determine the stage of nuclear maturation of the oocyte. Gilts fed the high diet had a higher proportion of oocytes that reached metaphase II than gilts fed the maintenance diet (88.3+/-2.71% versus 68.2+/-6.48%; P=0.013). Circulating concentrations of insulin-like growth hormone I (IGF-I) and the number of LH pulses were lower (P<0.05) in gilts fed the maintenance diet compared with gilts fed the high diet on day 12 and day 18. Mean oestradiol and progesterone concentrations were higher (P<0.05) for gilts fed the maintenance diet compared with gilts fed the high diet. Leptin concentrations were also higher on day 19 in gilts fed the high diet (2.16+/-0.26 ng ml(-1) (n=9) versus 3.20+/-0.32 (n=11), P=0.025). The results of this study indicate that improved oocyte quality (increased proportion of oocytes that reached metaphase II) is associated with a number of changes in reproductive and metabolic hormones. Further studies are required to indicate which hormonal mechanism may, in turn, lead to increased embryo survival and eventual litter size.

Sodium transport across the chorioallantoic membrane of porcine placenta involves the epithelial sodium channel (ENaC)

The properties of chorioallantoic membrane derived from Large White Landrace sows at 45, 65 and 100 days gestation are examined. Under short circuit conditions positive charge flows from fetal to maternal sides of the tissue. Na+ is shown to be the sole charge carrier as the short circuit current is inhibited reversibly by fetal applications of amiloride and replacement of Na+ by choline in the Ringer solution, and irreversibly by both fetal and maternal applications of ouabain. The initial short circuit current is smaller at day 100 compared to days 45 and 65. The dose responses to amiloride indicate that the epithelial sodium channel (ENaC) is involved in the movement of Na+ and that it is accessible on the fetal side of the tissue only. Immunostaining shows that the ENaC-alpha subunit is present in both the allantoic membrane and the trophoblast. Uptake studies using microvillous (apical) membrane vesicles suggest it is either inactive or only weakly active at this site. The trophoblast at day 100 has a higher content of ENaC than at days 45 and 65. This is the first report of the presence of ENaC in placental tissues. The effects of ouabain indicate the presence of a Na+ pump that is more readily inhibited by applications of the drug on the maternal aspect of the tissue than on the fetal side. Differential mechanisms may be present that would allow net movement of Na+ in either direction across the chorioallantoic membrane according to the changing demands of the developing fetus.

Synchronous onset of oestradiol-17beta secretion by Meishan conceptuses

The response of Meishan conceptuses to an exogenous precursor for oestradiol-17beta biosynthesis was investigated in vitro, to determine whether gestational age or morphological stage of development elicit changes in hormone metabolism. Conceptuses were recovered on days 11, 12, 13 or 15 after the onset of oestrus and cultured for 6 hours at 37 degrees C, in the presence or absence of testosterone. On days 12 and 13 after the onset of oestrus spherical conceptuses were recovered from some gilts, whereas others yielded elongated or filamentous conceptuses. All conceptuses recovered on day 15 after oestrus had elongated. The number of cells per individual conceptus increased from days 11 to 13 after the onset of oestrus (P < 0.001), as did conceptus surface area (P = 0.038). Supplementing culture media with testosterone, as a substrate for oestrogen biosynthesis, significantly increased conceptus oestradiol-17beta secretion in vitro on days 12, 13 and 15, regardless of whether pre- or post-elongation conceptuses were cultured. However, on day 11 oestradiol-17beta was only detected at significant concentrations in the culture media of four testosterone supplemented conceptuses and only one gilt produced conceptuses capable of secreting oestradiol-17beta in the absence of testosterone. Therefore, the onset of conceptus oestradiol-17beta secretion is apparently limited by the expression of aromatase enzymes that are activated synchronously, irrespective of the stage of morphological development, within Meishan litters. Once established, Meishan conceptus oestradiol-17beta secretion in vitro is increased in the presence of exogenous testosterone.

Consequences of manipulating gametes and embryos of ruminant species

During the past 12 years, ruminants have provided a focus for some significant advances in mammalian reproductive biotechnologies. Lambs were the first offspring generated after nuclear transfer of fetal or adult cells to enucleated oocytes, and many calves of pre-determined gender are today the result of commercialized semen sexing. In 1990, the birth of one calf provided living proof that even 'dead' spermatozoa can be paternal, whereas, more recently, a short-lived gaur calf and viable mouflon lamb represented a novel option for conservation of endangered species. As well as highlights, hazards have emerged, resulting in setbacks or developmental anomalies, such as those associated with the large offspring syndrome which encompasses a range of adverse fetal, placental and post-natal phenomena expressed in ruminants. In this review, the developmental and other consequences of applying manipulative procedures, such as assisted fertilization, semen sexing, cloning and gene transfer, to gametes and embryos from bovine, ovine and caprine species are considered. Although assisted fertilization techniques can overcome mammalian infertility, they also usurp natural gamete selection safeguards, but not always with impunity. In the case of manipulations such as cloning, and to a lesser extent gene transfer, it is evident that nuclear-cytoplasmic interactions and nuclear-mitochondrial DNA interdependences are at least partially damaged or destroyed with a view to reconstruction. Therefore, among surviving zygotes and embryos it is inevitable that the legacy is frequently one of altered genetic, epigenetic or cellular programmes and processes.

Causes and consequences of fetal growth retardation in pigs

In pigs, as in other species, fetal growth retardation is associated with reduced birth weight and increased risk of fetal and neonatal death. As there are few opportunities after birth to remedy the detrimental effects of low birth weight, it is important to understand both the intrinsic and extrinsic factors associated with inadequate fetal growth and to determine when growth retarded fetuses deviate from the growth trajectory of their normal sized littermates. Inadequately grown pig fetuses can be identified statistically as early as day 30 of the 114 days of gestation, indicating that limited uterine space is not a primary determinant of fetal growth. Comparisons of the smallest fetus within a litter with a normal sized sibling reveal that inadequately grown fetuses have altered endocrine status and lower circulating concentrations of many essential amino acids. In addition, the placenta supplying the smallest fetus is disproportionately small and has a reduced capacity to transport amino acids. Understanding the timing and the causes of fetal growth retardation in pigs may help us to devise appropriate strategies to reduce the incidence and hence the detrimental postnatal consequences of runting.

Vitamin A deficiency during rat pregnancy alters placental TNF-alpha signalling and apoptosis

PROBLEM

Vitamin A is important for immune function and deficiency is associated with adverse pregnancy outcome. In the rat, vitamin A deficiency reduces both foetal number and neonatal survival. The role of the placenta is uncertain. The effects of maternal vitamin A deficiency on placental cytokines and apoptosis have been investigated.

METHOD OF STUDY

Pregnant rats were fed either control or vitamin A free (VAF) diets (n = 4/group) from 8 weeks prior to and throughout pregnancy. Day 20 placentas from viable foetuses were examined for immunoexpression of (a) cytokines: tumour necrosis factor-alpha (TNF-alpha), TNFR1 receptor (p55), leptin and leptin receptor, (b) apoptosis: TdT-mediated dUTP nick end-labelling (TUNEL) positive cells, bax and bcl-2.

RESULTS

Placentas from VAF rats, but not controls, exhibited an infiltrate of neutrophils positive for TNF-alpha and leptin. The number of TNFR1 (p55) and TUNEL positive trophoblast cells was increased specifically in areas of neutrophil infiltration. Trophoblast giant cells in VAF placentas exhibited reduced bax but no change in bcl-2.

CONCLUSIONS

Maternal vitamin A deficiency is associated with abnormal placental apoptosis induced by neutrophil derived TNF-alpha acting through the TNFR1 (p55) and/or a change in the bcl-2/bax ratio in the trophoblast giant cells. These changes may underlie the effects of vitamin A deficiency on foetal development.

Micronutrient programming of development throughout gestation

Vitamins and minerals serve essential roles in cellular metabolism, maintenance and growth throughout life. They are also central components of many enzymes and transcription factors. However, the need for optimum amounts of key micronutrients at critical stages during the periovulatory period and subsequent embryonic and fetal life has become the focus of sustained research activity only recently. In addition to folic acid, the minerals zinc, iron and copper and the antioxidant vitamins A and E are of particular importance during pregnancy. Both excesses and deficiencies of these micronutrients can have profound and sometimes persistent effects on many fetal tissues and organs in the absence of clinical signs of deficiency in the mother. The consequences of micronutrient imbalance on the developing conceptus may not be apparent at the time of the nutritional insult, but may be manifest later in development. However, supplementary micronutrients provided later in gestation or during postnatal life cannot completely reverse the detrimental effects of earlier micronutrient imbalance. Importantly, deficiency of a specific micronutrient, such as zinc, during pregnancy can result in a greater incidence of fetal malformation and resorptions than general undernutrition. Given the range of micronutrients that affect development, the number of developmental stages susceptible to inappropriate micronutrient status and the diverse biochemical systems and types of tissue affected, it is challenging to propose a unifying hypothesis that could explain the effects of micronutrient imbalance on programming throughout gestation. Micronutrient imbalance can affect pregnancy outcome through alterations in maternal and conceptus metabolism, as a consequence of their essential role in enzymes and transcription factors and through their involvement in signal transduction pathways that regulate development. Micronutrient-induced disturbances in the balance between the generation of free oxygen radicals and the production of antioxidants that scavenge free radicals may provide an additional mechanistic explanation. The detrimental effects of many micronutrient deficiencies, particularly zinc and copper, can be alleviated by supplementary antioxidants, whereas deficiencies of antioxidant vitamins A and E are likely to reduce defence against free radical damage.