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.

Molecular determinants of a competent bovine corpus luteum: first- vs final-wave dominant follicles

Reproductive management in cattle requires the synchrony of follicle development and oestrus before insemination. However, ovulation of follicles that have not undergone normal physiological maturation can lead to suboptimal luteal function. Here, we investigated the expression of a targeted set of 47 genes in (a) a first-wave vs final-wave dominant follicle (DF; the latter destined to ovulate spontaneously) and (b) 6-day-old corpora lutea (CLs) following either spontaneous ovulation or induced ovulation of a first-wave DF to ascertain their functional significance for competent CL development. Both the mass and progesterone-synthesising capacity of a CL formed following induced ovulation of a first-wave DF were impaired. These impaired CLs had reduced expression of steroidogenic enzymes (e.g. STAR and HSD3B1), luteotrophic receptors (LHCGR) and angiogenic regulators (e.g. VEGFA) and increased expression of BMP2 (linked to luteolysis). Relative to final-wave DFs, characteristic features of first-wave DFs included reduced oestradiol concentrations and a reduced oestradiol:progesterone ratio in the face of increased expression of key steroidogenic enzymes (i.e. CYP11A1, HSD3B1 and CYP19A1) in granulosa cells and reduced expression of the HDL receptor SCARB1 in thecal cells. Transcripts for further components of the TGF and IGF systems (e.g. INHA, INHBA, IGF2R and IGFBP2) varied between the first- and final-wave DFs. These results highlight the importance of hormones such as progesterone interacting with local components of both the TGF and IGF systems to affect the maturation of the ovulatory follicle and functional competency of the subsequent CL.

The fetal ovary exhibits temporal sensitivity to a 'real-life' mixture of environmental chemicals

The development of fetal ovarian follicles is a critical determinant of adult female reproductive competence. Prolonged exposure to environmental chemicals (ECs) can perturb this process with detrimental consequences for offspring. Here we report on the exposure of pregnant ewes to an environmental mixture of ECs derived from pastures fertilized with sewage sludge (biosolids): a common global agricultural practice. Exposure of pregnant ewes to ECs over 80 day periods during early, mid or late gestation reduced the proportion of healthy early stage fetal follicles comprising the ovarian reserve. Mid and late gestation EC exposures had the most marked effects, disturbing maternal and fetal liver chemical profiles, masculinising fetal anogenital distance and greatly increasing the number of altered fetal ovarian genes and proteins. In conclusion, differential temporal sensitivity of the fetus and its ovaries to EC mixtures has implications for adult ovarian function following adverse exposures during pregnancy.

In utero exposure to cigarette chemicals induces sex-specific disruption of one-carbon metabolism and DNA methylation in the human fetal liver

BACKGROUND

Maternal smoking is one of the most important modifiable risk factors for low birthweight, which is strongly associated with increased cardiometabolic disease risk in adulthood. Maternal smoking reduces the levels of the methyl donor vitamin B12 and is associated with altered DNA methylation at birth. Altered DNA methylation may be an important mechanism underlying increased disease susceptibility; however, the extent to which this can be induced in the developing fetus is unknown.

METHODS

In this retrospective study, we measured concentrations of cobalt, vitamin B12, and mRNA transcripts encoding key enzymes in the 1-carbon cycle in 55 fetal human livers obtained from 11 to 21 weeks of gestation elective terminations and matched for gestation and maternal smoking. DNA methylation was measured at critical regions known to be susceptible to the in utero environment. Homocysteine concentrations were analyzed in plasma from 60 fetuses.

RESULTS

In addition to identifying baseline sex differences, we found that maternal smoking was associated with sex-specific alterations of fetal liver vitamin B12, plasma homocysteine and expression of enzymes in the 1-carbon cycle in fetal liver. In the majority of the measured parameters which showed a sex difference, maternal smoking reduced the magnitude of that difference. Maternal smoking also altered DNA methylation at the imprinted gene IGF2 and the glucocorticoid receptor (GR/NR3C1).

CONCLUSIONS

Our unique data strengthen studies linking in utero exposures to altered DNA methylation by showing, for the first time, that such changes are present in fetal life and in a key metabolic target tissue, human fetal liver. Furthermore, these data propose a novel mechanism by which such changes are induced, namely through alterations in methyl donor availability and changes in 1-carbon metabolism.

Impact of di-ethylhexylphthalate exposure on metabolic programming in P19 ECC-derived cardiomyocytes

Di(2-ethylhexyl)phthalate (DEHP) is the most common plasticizer in plastic devices of everyday use. It is a ubiquitous environmental contaminant and primarily known to impair male gonadal development and fertility. Studies concerning the long-term effects of prenatal DEHP exposure on certain diseases [The Developmental Origins of Health and Disease paradigm (DOHaD) hypothesis] are scarce although it is proven that DEHP crosses the placenta. Rising environmental pollution during the last centuries coincides with an increasing prevalence of cardiovascular and metabolic diseases. We have investigated the effects of an early embryonic DEHP exposure at different developmental stages on cardiomyogenesis. We used an in-vitro model, the murine P19 embryonic carcinoma cell line (P19 ECC), mimicking early embryonic stages up to differentiated beating cardiomyocytes. P19 ECC were exposed to DEHP (5, 50, 100 µg ml(-1)) at the undifferentiated stage for 5 days and subsequently differentiated to beating cardiomyocytes. We analyzed the expression of metabolic (Pparg1, Fabp4 and Glut4), cardiac (Myh6, Gja1) and methylation (Dnmt1, Dnmt3a) marker genes by quantitative real-time PCR (qRT-PCR), beating rate and the differentiation velocity of the cells. The methylation status of Pparg1, Ppara and Glut4 was investigated by pyrosequencing. DEHP significantly altered the expression of all investigated genes. The beating rate and differentiation velocity were accelerated. Exposure to DEHP led to small but statistically significant increases in methylation of specific CpGs within Ppara and Pparg1, which otherwise were generally hypomethylated, but methylation of Glut4 was unaltered. Early DEHP exposure of P19 ECC alters the expression of genes associated with cellular metabolism and the functional features of cardiomyocytes.

Parental diet, pregnancy outcomes and offspring health: metabolic determinants in developing oocytes and embryos

The periconceptional period, embracing the terminal stages of oocyte growth and post-fertilisation development up to implantation, is sensitive to parental nutrition. Deficiencies or excesses in a range of macro- and micronutrients during this period can lead to impairments in fertility, fetal development and long-term offspring health. Obesity and genotype-related differences in regional adiposity are associated with impaired liver function and insulin resistance, and contribute to fatty acid-mediated impairments in sperm viability and oocyte and embryo quality, all of which are associated with endoplasmic reticulum stress and compromised fertility. Disturbances to maternal protein metabolism can elevate ammonium concentrations in reproductive tissues and disturb embryo and fetal development. Associated with this are disturbances to one-carbon metabolism, which can lead to epigenetic modifications to DNA and associated proteins in offspring that are both insulin resistant and hypertensive. Many enzymes involved in epigenetic gene regulation use metabolic cosubstrates (e.g. acetyl CoA and S-adenosyl methionine) to modify DNA and associated proteins, and so act as 'metabolic sensors' providing a link between parental nutritional status and gene regulation. Separate to their genomic contribution, spermatozoa can also influence embryo development via direct interactions with the egg and by seminal plasma components that act on oviductal and uterine tissues.

Maternal protein-energy malnutrition during early pregnancy in sheep impacts the fetal ornithine cycle to reduce fetal kidney microvascular development

This paper identifies a common nutritional pathway relating maternal through to fetal protein-energy malnutrition (PEM) and compromised fetal kidney development. Thirty-one twin-bearing sheep were fed either a control (n=15) or low-protein diet (n=16, 17 vs. 8.7 g crude protein/MJ metabolizable energy) from d 0 to 65 gestation (term, ∼145 d). Effects on the maternal and fetal nutritional environment were characterized by sampling blood and amniotic fluid. Kidney development was characterized by histology, immunohistochemistry, vascular corrosion casts, and molecular biology. PEM had little measureable effect on maternal and fetal macronutrient balance (glucose, total protein, total amino acids, and lactate were unaffected) or on fetal growth. PEM decreased maternal and fetal urea concentration, which blunted fetal ornithine availability and affected fetal hepatic polyamine production. For the first time in a large animal model, we associated these nutritional effects with reduced micro- but not macrovascular development in the fetal kidney. Maternal PEM specifically impacts the fetal ornithine cycle, affecting cellular polyamine metabolism and microvascular development of the fetal kidney, effects that likely underpin programming of kidney development and function by a maternal low protein diet.—Dunford, L. J., Sinclair, K. D., Kwong, W. Y., Sturrock, C., Clifford, B. L., Giles, T. C., Gardner, D. S.. Maternal protein-energy malnutrition during early pregnancy in sheep impacts the fetal ornithine cycle to reduce fetal kidney microvascular development.

Paternal low protein diet affects adult offspring cardiovascular and metabolic function in mice

Although the association between maternal periconceptional diet and adult offspring health is well characterised, our understanding of the impact of paternal nutrition at the time of conception on offspring phenotype remains poorly defined. Therefore, we determined the effect of a paternal preconception low protein diet (LPD) on adult offspring cardiovascular and metabolic health in mice. Male C57BL/6 mice were fed either normal protein diet (NPD; 18% casein) or LPD (9% casein) for 7 wk before mating. At birth, a reduced male-to-female ratio ( P = 0.03) and increased male offspring weight ( P = 0.009) were observed in litters from LPD compared with NPD stud males with no differences in mean litter size. LPD offspring were heavier than NPD offspring at 2 and 3 wk of age ( P < 0.02). However, no subsequent differences in body weight were observed. Adult male offspring derived from LPD studs developed relative hypotension (decreased by 9.2 mmHg) and elevated heart rate ( P < 0.05), whereas both male and female offspring displayed vascular dysfunction and impaired glucose tolerance relative to NPD offspring. At cull (24 wk), LPD males had elevated adiposity ( P = 0.04), reduced heart-to-body weight ratio ( P = 0.04), and elevated circulating TNF-α levels ( P = 0.015) compared with NPD males. Transcript expression in offspring heart and liver tissue was reduced for genes involved in calcium signaling ( Adcy, Plcb, Prkcb) and metabolism ( Fto) in LPD offspring ( P < 0.03). These novel data reveal the impact of suboptimal paternal nutrition on adult offspring cardiovascular and metabolic homeostasis, and provide some insight into the underlying regulatory mechanisms.

The expression, regulation and function of secreted protein, acidic, cysteine-rich in the follicle–luteal transition

The role of the tissue remodelling protein, secreted protein, acidic, cysteine-rich (SPARC), in key processes (e.g. cell reorganisation and angiogenesis) that occur during the follicle–luteal transition is unknown. Hence, we investigated the regulation of SPARC in luteinsing follicular cells and potential roles of SPARC peptide 2.3 in a physiologically relevant luteal angiogenesis culture system. SPARC protein was detected mainly in the theca layer of bovine pre-ovulatory follicles, but its expression was considerably greater in the corpus haemorrhagicum. Similarly, SPARC protein (western blotting) was up-regulated in luteinising granulosa but not in theca cells during a 6-day culture period. Potential regulatory candidates were investigated in luteinising granulosa cells: LH did not affect SPARC (P>0.05); transforming growth factor (TGF) B1 (P<0.001) dose dependently induced the precocious expression of SPARC and increased final levels: this effect was blocked (P<0.001) by SB505124 (TGFB receptor 1 inhibitor). Additionally, fibronectin, which is deposited during luteal development, increased SPARC (P<0.01). In luteal cells, fibroblast growth factor 2 decreased SPARC (P<0.001) during the first 5 days of culture, while vascular endothelial growth factor A increased its expression (P<0.001). Functionally, KGHK peptide, a SPARC proteolytic fragment, stimulated the formation of endothelial cell networks in a luteal cell culture system (P<0.05) and increased progesterone production (P<0.05). Collectively, these findings indicate that SPARC is intricately regulated by pro-angiogenic and other growth factors together with components of the extracellular matrix during the follicle–luteal transition. Thus, it is possible that SPARC plays an important modulatory role in regulating angiogenesis and progesterone production during luteal development.

A methyl-deficient diet fed to rats during the pre- and peri-conception periods of development modifies the hepatic proteome in the adult offspring

A methyl-deficient diet (MD) lacking folic acid and the associated methyl donors choline and methionine, fed to the laboratory rat during the periods of oocyte and embryo development, has been shown to programme glucose metabolism in the offspring. The hepatic proteome of the male offspring of female rats fed MD diets for 3 weeks prior to mating and for the first 5 days of gestation has been examined by 2-dimensional gel electrophoresis. Three groups of differentially abundant proteins associated with energy metabolism, amino acid metabolism and antioxidant defence were identified in the soluble proteins extracted from the liver from the MD offspring at both 6 and 12 months of age. Altered mitochondrial activity in other programming models leads to a similar pattern of differential protein abundance. Two of the differentially abundant proteins were identified as GAPDH and PGK-1 by mass spectrometry. Western blotting showed that there were multiple isoforms of both proteins with similar molecular weights but different isoelectric points. The differentially abundant spots reduced in the MD offspring corresponded to minor isoforms of GAPDH and PGK-1. The levels of PPAR-alpha, SREBP and glucocorticoid receptor mRNAs associated with other models of prenatal programming were unchanged in the MD offspring. The data suggest that a diet deficient in folic acid and associated methyl donors fed during the peri-conception and early preimplantation periods of mammalian development affects mitochondrial function in the offspring and that the posttranslational modification of proteins may be important.

Development of a broad spectrum polymer-released antimicrobial coating for the prevention of resistant strain bacterial infections

More than 400,000 primary hip and knee replacement surgeries are performed each year in the United States. From these procedures, approximately 0.5-3% will become infected and when considering revision surgeries, this rate has been found to increase significantly. Antibiotic-resistant bacterial infections are a growing problem in patient care. This in vitro research investigated the antimicrobial potential of the polymer released, broad spectrum, Cationic Steroidal Antimicrobial-13 (CSA-13) for challenges against 5 × 10(8) colony forming units (CFU) of methicillin-resistant Staphylococcus aureus (MRSA). It was hypothesized that a weight-to-weight (w/w) concentration of 18% CSA-13 in silicone would exhibit potent bactericidal potential when used as a controlled release device coating. When incorporated into a polymeric device coating, the 18% (w/w) broad-spectrum polymer released CSA-13 antimicrobial eliminated 5 × 10(8) CFU of MRSA within 8 h. In the future, these results will be utilized to develop a sheep model to assess CSA-13 for the prevention of perioperative device-related infections in vivo.

Impact of endocrine-disrupting compounds (EDCs) on female reproductive health

Evidence is accumulating that environmental chemicals (ECs) including endocrine-disrupting compounds (EDCs) can alter female reproductive development, fertility and onset of menopause. While not as clearly defined as in the male, this set of abnormalities may constitute an Ovarian Dysgenesis Syndrome with at least some origins of the syndrome arising during foetal development. ECs/EDCs have been shown to affect trophoblast and placental function, the female hypothalamo-pituitary-gonadal axis, onset of puberty and adult ovarian function. The effects of ECs/EDCs are complex, not least because it is emerging that low-level, 'real-life' mixtures of ECs/EDCs may carry significant biological potency. In addition, there is evidence that ECs/EDCs can alter the epigenome in a sexually dimorphic manner, which may lead to changes in the germ line and perhaps even to transgenerational effects. This review summarises the evidence for EC, including EDC, involvement in female reproductive dysfunction, it highlights potential mechanisms of EC action in the female and emphasises the need for further research into EC effects on female development and reproductive function.

Preconception folic acid use modulates estradiol and follicular responses to ovarian stimulation

BACKGROUND

Folate is a methyl donor. Availability of folate affects DNA methylation profiles and thereby gene expression profiles. We investigated the effects of low-dose folic acid use (0.4 mg/d) on the ovarian response to mild and conventional ovarian stimulation in women.

METHODS

In a randomized trial among subfertile women, 24 and 26 subjects received conventional and mild ovarian stimulation, respectively. Blood samples were taken during the early follicular phase of the cycle prior to treatment and on the day of human chorionic gonadotropin administration for determination of serum total homocysteine, anti-Müllerian hormone (AMH), estradiol, and folate. Folic acid use was validated by questionnaire and serum folate levels. Preovulatory follicles were visualized, counted, and diameters recorded using transvaginal ultrasound. The relation between folic acid use and ovarian response was assessed using linear regression analysis.

RESULTS

Folic acid use modified the ovarian response to ovarian stimulation treatment. The estradiol response was higher in nonfolic acid users receiving conventional treatment [β(interaction) = 0.52 (0.07-0.97); P = 0.03], and this effect was independent of serum AMH levels and the preovulatory follicle count. In the conventional treatment, the mean follicle number was also greater in nonusers compared with the users group (14.1 vs. 8.9, P = 0.03).

CONCLUSION

Low-dose folic acid use attenuates follicular and endocrine responses to conventional stimulation, independent of AMH and follicle count. The nature of this observation suggests that the effect of folic acid is most prominent during early follicle development, affecting immature follicles. Deleterious effects of folate deficiency, like DNA hypomethylation and oxidative stress, can help to explain our observations.

A methyl-deficient diet fed to rat dams during the peri-conception period programs glucose homeostasis in adult male but not female offspring

Methyl deficiencies have been implicated in metabolic programming during the periods of oocyte and embryo development. Semisynthetic methyl-deficient diets (MD) with no folic acid, 0.05% choline, and approximately one-half the recommended content of methionine were fed to female rats for 3 wk prior to mating and for the first 5 d of gestation. During the period of MD feeding, plasma homocysteine concentrations were approximately twice those of rats fed the complete (CON) diet. From d 5, both groups received a complete semipurified AIN diet until birth. On d 8, plasma homocysteine concentrations did not differ between the 2 groups. Thereafter, dams and offspring were fed a nonpurified diet for the remainder of the experiment. At 6 mo of age, the homeostatic model assessment (HOMA) index of the male MD offspring tended to be 32% higher (P = 0.053) and peak insulin during an oral glucose tolerance test (oGTT) was 39% higher (P < 0.05) compared with the male CON offspring. There was no difference in the response to an oGTT in the female offspring at 6 mo of age. The increased HOMA index of male MD offspring persisted to 12 mo of age. The peak glucose concentration during oGTT was 23% higher (P < 0.05) in MD compared with the CON males despite 39% greater (P < 0.05) peak insulin concentrations. This study shows that in rats, a physiologically relevant methyl-deficient diet fed during the period of oocyte maturation and preimplantation development programs gender-specific changes in glucose handling by the offspring.

Effects of omega-3 and -6 polyunsaturated fatty acids on ovine follicular cell steroidogenesis, embryo development and molecular markers of fatty acid metabolism

We previously reported increased follicular fluid progesterone (P(4)) concentrations in ewes fed an n-3 compared to an n-6 polyunsaturated fatty acid (PUFA)-enriched diet, but detected no differential effect of n-3 and n-6 PUFA-enriched high-density lipoproteins (HDL) on granulosa cell (GC) steroidogenesis in vitro. Moreover, net n-6 PUFA-enriched HDL reduced early embryo development, but in the absence of a net uptake of FA. Consequently, we hypothesised that a) effects of n-3 PUFA on ovarian steroidogenesis are mediated by theca rather than GCs and b) during embryo culture lipids are acquired solely from the albumin fraction of serum, so that albumin-delivered n-3 and n-6 PUFA exert a greater differential effect on embryo development than either low-density lipoprotein (LDL)- or HDL-delivered PUFA. Data confirmed that n-3 PUFA increases P(4) production solely in theca cells and that this is associated with an increase in STAR transcript expression. Furthermore, LDL- and HDL-delivered n-3 PUFA are equally efficacious in this regard during the first 96 h of culture, but thereafter only HDL-delivered n-3 PUFA induces this effect in partially luteinised theca cells. We also demonstrate that albumin is the sole serum fraction that leads to a net uptake of FA during embryo culture. PUFA-enriched serum and albumin increased the yield of morphologically poorer quality blastocysts with increased transcript expression for the antioxidant enzyme SOD1. Important differential effects of n-3 and n-6 PUFA on ovarian steroidogenesis acting solely on theca cells are identified, but differential effects of PUFA on embryo development are less apparent.

Dietary omega-3 and -6 polyunsaturated fatty acids affect the composition and development of sheep granulosa cells, oocytes and embryos

The evidence that omega-3 (n-3) and -6 (n-6) polyunsaturated fatty acids (PUFAs) have differential effects on ovarian function, oocytes and embryo quality is inconsistent. We report on the effects of n-3 versus n-6 PUFA-enriched diets fed to 36 ewes over a 6-week period, prior to ovarian stimulation and follicular aspiration, on ovarian steroidogenic parameters and embryo quality. Follicle number and size were unaltered by diet, but follicular-fluid progesterone concentrations were greater in n-3 PUFA-fed ewes than in n-6 PUFA-fed ewes. The percentage of saturated FAs (mostly stearic acid) was greater in oocytes than in either granulosa cells or plasma, indicating selective uptake and/or de novo synthesis of saturated FAs at the expense of PUFAs by oocytes. High-density lipoproteins (HDLs) fractionated from sera of these ewes increased granulosa cell proliferation and steroidogenesis relative to the FA-free BSA control during culture, but there was no differential effect of n-3 and n-6 PUFAs on either oestradiol or progesterone production. HDL was ineffective in delivering FAs to embryos during culture, although n-6 PUFA HDL reduced embryo development. All blastocysts, irrespective of the treatment, contained high levels of unsaturated FAs, in particular linoleic acid. Transcripts for HDL and low-density lipoprotein (LDL) receptors (SCARB1 and LDLR) and stearoyl-CoA desaturase (SCD) are reported in sheep embryos. HDL reduced the expression of transcripts for LDLR and SCD relative to the BSA control. The data support a differential effect of n-3 and n-6 PUFAs on ovarian steroidogenesis and pre-implantation development, the latter in the absence of a net uptake of FAs.

Endogenous folates and single-carbon metabolism in the ovarian follicle, oocyte and pre-implantation embryo

Maternal B-vitamin status at conception can affect fertility and the health of offspring. This study details transcript expression for genes encoding key enzymes in the linked methionine/folate cycles in the bovine oocyte, somatic cells of the ovarian follicle and pre-implantation embryo. Transcripts for all 12 enzymes that were studied and for the two folate receptors (FOLR1 and FOLR2) and reduced folate carrier (SLC19A1) were expressed in liver cells, but transcripts for betaine-homocysteine methyltransferase and methionine adenosyl transferase 1A were absent in all ovarian cells, and transcripts for FOLR2 were absent in embryonic cells. Transcripts for glycine methyltransferase were also absent/weak in cumulus and granulosa cells. The absence of these enzymes could have a profound effect on single-carbon metabolism within the ovary and pre-implantation embryo. Immunocytochemical analysis revealed SLC19A1 protein expression on the plasma and basal-lateral membranes of the pre-implantation embryo. The folate antagonist methotrexate (MTX) enters the cell via SLC19A1, and in the current study, MTX inclusion in bovine/ovine culture media at either 1 or 10 microM from the 1-cell stage inhibited embryo development beyond the 8-cell stage. Hypoxanthine and thymidine (100 microM) increased the proportion of embryos that developed to blastocysts, but the cell number was reduced by 20%. The reduced uptake of [(35)S] methionine into intra-cellular S-adenosylmethionine and S-adenosylhomocysteine pools, together with reduced uptake of glutamate and tryptophan, was consistent with depleted intra-cellular pools of reduced folates. These data provide an insight into the importance of maternal dietary folate/B-vitamin status during the peri-conceptional period.

Effect of the early-life nutritional environment on fecundity and fertility of mammals

The early-life developmental environment is instrumental in shaping our overall adult health and well-being. Early-life diet and endocrine exposure may independently, or in concert with our genetic constitution, induce a pathophysiological process that amplifies with age and leads to premature morbidity and mortality. Recently, this has become known as ‘programming’ but is akin to ‘maternal effects’ described for many years in the biological sciences and is defined as any influence that acts during critical developmental windows to induce long-term changes in the organisms' phenotype. To date, such delayed maternal effects have largely been characterized in terms of susceptibility to cardiovascular or metabolic disease. Here, we review evidence from experimental animal species, non-human primates and man for an effect of the early-life nutritional environment on adult fecundity and fertility. In addition, using a database of pedigree sheep, we also specifically test the hypothesis that being born small for gestational age with or without post-natal growth acceleration directly programmes fertility. We conclude that there is a lack of compelling evidence to suggest pre-natal undernutrition may directly reduce adult fecundity and fertility, but may exert some effects secondarily via an increased incidence of ‘metabolic syndrome’. Possible effects of being born relatively large on subsequent fecundity and fertility warrant further investigation.

Dietary regulation of developmental programming in ruminants: epigenetic modifications in the germline

Ruminants have been utilised extensively to investigate the developmental origins of health and disease, with the sheep serving as the model species of choice to complement dietary studies in the rat and mouse. Surprisingly few studies, however, have investigated delayed effects of maternal undernutrition during pregnancy on adult offspring health and a consistent phenotype, together with underlying mechanistic pathways, has not emerged. Nevertheless, when broad consideration is given to all studies with ruminants it is apparent that interventions that are initiated very early in gestation, and/or prior to conception, lead to greater effects on adult physiology than those that are specifically targeted to late gestation. Effects induced following dietary interventions at the earliest stages of mammalian development have been shown to arise as a consequence of alterations to key epigenetic processes that occur in germ cells and pluripotent embryonic cells. Currently, our understanding of epigenetic programming in the germline is greatest for the mouse, and is considered in detail in this article together with what is known in ruminants. This species imbalance, however, looks set to change as fully annotated genomic maps are developed for domesticated large animal species, and with the advent of 'next-generation' DNA sequencing technologies that have the power to globally map the epigenome at single-base-pair resolution. These developments would help to address such issues as sexually dimorphic epigenetic alterations to DNA methylation that have been found to arise following dietary restrictions during the peri-conceptional period, the effects of paternal nutritional status on epigenetic programming through the germline, and transgenerational studies where, in future, greater emphasis in domesticated ruminants should be placed on traits of agricultural importance.

Assisted reproductive technology, epigenetics, and long-term health: a developmental time bomb still ticking

Live birthrates following assisted reproduction account for 1 to 3% of pregnancies in developed countries, and these figures seem set to rise. Concerns regarding the safe use of assisted reproductive technology (ART) for the treatment of infertility have been voiced for several years, yet, to date, the vast majority of children conceived using these techniques are apparently normal. Controversy surrounding reports of epigenetic alterations to genomic imprinting following human ART in recent years has fueled the ongoing debate. In contrast, both the incidence and severity of such anomalies are more apparent following ART in comparative animal species. The reasons for this are not known. By and large, the confounding effects of infertility and advanced maternal age do not apply to animal studies, which report better pregnancy rates following embryo transfer. Perhaps the incidence of imprinting disorders is increased when procedures such as ovarian stimulation, in vitro maturation, or both are used in conjunction with extended periods of embryo culture; this frequently occurs in animal but rarely in human ART. The focus of attention on imprinting, however, may have served to distract the scientific community from more subtle epigenetic modifications to nonimprinted loci in gametes and the preimplantation embryo, with health-related consequences that do not manifest until adulthood. Accumulating evidence from animal studies indicates that such effects, not yet apparent in human subjects, exist; and this may ultimately transpire to be the true developmental legacy of human ART. This article discusses these issues in the context of epigenetic and developmental abnormalities following ART in animals.

Oocyte quality in lactating dairy cows fed on high levels of n-3 and n-6 fatty acids

Different fatty acid (FA) sources are known to influence reproductive hormones in cattle, yet there is little information on how dietary FAs affect oocyte quality. Effects of three dietary sources of FAs (supplying predominantly palmitic and oleic, linoleic (n-6) or linolenic (n-3) acids) on developmental potential of oocytes were studied in lactating dairy cows. A total of 12 Holstein cows received three diets containing rumen inert fat (RIF), soyabean or linseed as the main FA source for three periods of 25 days in a Latin-square design. Within each period, oocytes were collected in four ovum pick-up sessions at 3-4 day intervals. FA profiles in plasma and milk reflected profiles of dietary FA sources, but major FAs in granulosa cells were not affected. Dietary FA source did not affect plasma concentrations of leptin, insulin, IGF1, GH, or amino acids. RIF led to a higher proportion of cleaved embryos than soya or linseed, but blastocyst yield and embryo quality were not affected. It is concluded that the ovary buffers oocytes against the effects of fluctuations in plasma n-3 and n-6 FAs, resulting in only modest effects on their developmental potential.