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Maternal metabolic stress conditions are of growing importance in both human and dairy cattle settings as they can have significant repercussions on fertility. Upregulated lipolysis is a common trait associated with metabolic disorders and results in systemically elevated concentrations of non-esterified fatty acids (NEFAs). The effects of high NEFA concentrations on the follicular environment, oocyte and embryo development is well documented. However, knowledge on the effects of NEFAs within the oviduct, representing the initial embryonic growth environment, is currently lacking. Therefore, the experiments outlined here were designed to obtain fundamental insights into both the direct and indirect interactions between NEFAs, bovine oviductal cells and developing zygotes. Hence, zygotes were co-cultured with NEFA-pre-exposed bovine oviductal cells or subjected to simultaneous NEFA exposure during the co-culture period. The outcome parameters assessed were embryo development with cleavage (48h post insemination (pi)), morula (120–126h pi) and blastocyst (192h pi) rates, as well as morula intracellular lipid content and blastocyst quality using Bodipy and differential staining respectively. Our data suggest a direct embryotoxicity of NEFAs as well as impaired embryo development through a reduced oviductal ability to support and protect early embryo development.

We investigated whether and to which extent plasma non-esterified fatty acids (NEFAs) are reflected in oviduct fluid (OF) using an improved ex vivo flushing method. OF and plasma NEFA concentrations were respectively 0.29 ± 0.19 and 0.31 ± 0.14 mmol/L, they didnt differ significantly (P = 0.13) and tended to be positively correlated (Pearson correlation coefficient = 0.56; P = 0.07). Results suggest that OF NEFAs mirror the concentrations seen in plasma of healthy cattle.

Background: In beef cattle, changes in the periovulatory endocrine milieu are associated with fertility and conceptus growth. A large preovulatory follicle (POF) and the resulting elevated concentrations of progesterone (P4) during diestrus positively affect pregnancy rates. Amino acids (AA) are important components of maternally derived secretions that are crucial for embryonic survival before implantation. The hypothesis is that the size of the POF and the concentration of P4 in early diestrus modulate the endometrial abundance of SLC transcripts related to AA transport and metabolism and subsequently impact luminal concentrations of AA. The follicle growth of Nelore cows was manipulated to produce two experimental groups: large POF and CL (LF-LCL group) and small POF and CL (SF-SCL group). On Day 4 (D4; Experiment 1) and Day 7 (D7; Experiment 2) after GnRH-induced ovulation (GnRH treatment = D0), the animals were slaughtered and uterine tissues and uterine washings were collected. qRT-PCR was used to evaluate the expression levels of AA transporters in D4 and D7 endometrial tissues. The concentrations of AA were quantified in D4 and D7 uterine washings by HPLC. Results: Transcript results show that, on D4, SLC6A6, SLC7A4, SLC17A5, SLC38A1, SLC38A7 and SCLY and on D7 SLC1A4, SLC6A1, SLC6A14, SLC7A4, SLC7A7, SLC7A8, SLC17A5, SLC38A1, SLC38A7, SLC43A2 and DDO were more abundant in the endometria of cows from the LF-LCL group (P < 0.05). In addition, concentrations of AA in the uterine lumen were influenced by the endocrine profiles of the mother. In this context, D4 uterine washings revealed that greater concentrations of taurine, alanine and a-aminobutyric acid were present in SF-SCL (P < 0.05). In contrast, lower concentrations of valine and cystathionine were quantified on D7 uterine washings from SF-SCL cows (P < 0.05). Conclusion: The present study revealed an association between the abundance of transcripts related to AA transport and metabolism in the endometrium and specific periovulatory endocrine profiles related to the receptive status of the mother. Such insights suggest that AAs are involved in uterine function to support embryo development.

The present study examined whether the effects of dietary-induced hyperlipidaemia on preimplantation embryo development depend on the predominant fatty acid (FA) type in the diet. In a combined in vivo–in vitro bovine model, two groups of cows (n = 3 in each group) were fed with three diets consecutively (4 weeks feeding for each): (1) a maintenance control diet (CONT); (2) a high-starch diet rich in saturated fat (SAT); and (3) a high-starch diet rich in omega-3 unsaturated fat (UNSAT). Two feeding sequences were used to test for carry-over effects: Group A was fed CONT, SAT1 and then UNSAT2, whereas Group B was fed CONT, UNSAT1 and then SAT2. Serum was collected after each dietary period, analysed and tested in bovine in vitro embryo culture. Introducing SAT and UNSAT diets induced hyperlipidaemia (specifically hypercholesterolaemia and elevated free FAs) and reduced insulin sensitivity. Carry-over effects in serum metabolites and FA profile were dependent on the diet and feeding sequence. SAT1 and SAT2 serum decreased blastocyst rates and altered blastocyst mRNA expression related to apoptosis and oxidative stress. UNSAT1 and UNSAT2 serum resulted in normal embryo development and quality. Other in vitro effects depended on the sequence of feeding. In conclusion, substitution of saturated fat with omega-3 fat in a high-caloric diet induced hyperlipidaemia with an FA profile yielding similar rates and quality of blastocysts compared with normolipidaemic controls.

We hypothesized that elevated non-esterified fatty acids (NEFA) modify in vitro bovine oviduct epithelial cell (BOEC) metabolism and barrier function. Hereto, BOECs were studied in a polarized system with 24-h treatments at Day 9: (1) control (0 µM NEFA + 0% EtOH), (2) solvent control (0 µM NEFA + 0.45% EtOH), (3) basal NEFA (720 µM NEFA + 0.45% EtOH in the basal compartment) and (4) apical NEFA (720 µM NEFA + 0.45% EtOH in the apical compartment). FITC-albumin was used for monolayer permeability assessment and related to transepithelial electric resistance (TER). Fatty acid (FA), glucose, lactate and pyruvate concentrations were measured in spent medium. Intracellular lipid droplets (LD) and FA uptake were studied using Bodipy 493/503 and immunolabelling of FA transporters (FAT/CD36, FABP3 and CAV1). BOEC-mRNA was retrieved for qRT-PCR. Results revealed that apical NEFA reduced relative TER increase (46.85%) during treatment and increased FITC–albumin flux (27.59%) compared to other treatments. In basal NEFA, FAs were transferred to the apical compartment as free FAs: mostly palmitic and oleic acid increased respectively 56.0 and 33.5% of initial FA concentrations. Apical NEFA allowed no FA transfer, but induced LD accumulation and upregulated FA transporter expression (↑CD36, ↑FABP3 and ↑CAV1). Gene expression in apical NEFA indicated increased anti-apoptotic (↑BCL2) and anti-oxidative (↑SOD1) capacity, upregulated lipid metabolism (↑CPT1, ↑ACSL1 and ↓ACACA) and FA uptake (↑CAV1). All treatments had similar carbohydrate metabolism and oviduct function-specific gene expression (OVGP1, ESR1 and FOXJ1). Overall, elevated NEFAs affected BOEC metabolism and barrier function differently depending on NEFA exposure side. Data substantiate the concept of the oviduct as a gatekeeper that may actively alter early embryonic developmental conditions.

Maternal metabolic disorders linked to lipolysis are major risk factors for reproductive failure. A notable feature of such disorders is increased non-esterified fatty acid (NEFA) concentrations in the blood, which are reflected in the ovarian follicular fluid. Elevated NEFA concentrations impact on the maturing oocyte and even alter subsequent embryo physiology. The aetiological mechanisms have not been fully elucidated. Therefore, in the present study, bovine in vitro maturing cumulus–oocyte complexes were exposed (24 h) to three different maturation treatments containing: (1) physiological (72 µM) NEFA concentrations (= control); (2) elevated (75 µM) stearic acid (SA) concentrations (= HIGH SA); and (3) elevated (425 µM) NEFA concentrations (= HIGH COMBI). Zygotes were fertilised and cultured following standard procedures. Transcriptomic analyses in resulting Day 7.5 blastocysts revealed that the major pathways affected are related to lipid and carbohydrate metabolism in HIGH COMBI embryos and to lipid metabolism and cell death in HIGH SA embryos. Furthermore, lower glutathione content and a reduced number of lipid droplets per cell were observed in HIGH SA-exposed oocytes and resulting morulae, respectively, compared with their HIGH COMBI-exposed counterparts. Vitrified embryos originating from HIGH SA-exposed oocytes tended to exhibit lower survival rates compared with controls. These data suggest possible mechanisms explaining why females across species suffering lipolytic disorders experience difficulties in conceiving.

Contents In many countries, fat supplementation in the diet has become common in the dairy industry. There are several ideas as to how dietary fat could influence reproductive performance. Saturated fatty acids, such as palm oil, can increase milk yield but may aggravate negative energy balance and thus may impair fertility when fed during the first week post-partum. However, priming the lipid oxidation in the liver by feeding saturated fats during the dry period has recently been shown to be a potentially promising strategy to mitigate fat mobilization and liver accumulation post-partum. Furthermore, polyunsaturated fats (omega-3 fatty acids and conjugated linoleic acids) are fed to reduce the de novo' fat synthesis in the udder and thus the milk fat content, which may be of modest benefit for overall energy balance. Furthermore, omega-6 and omega-3 polyunsaturated fatty acids are reported to alter follicular growth, steroid synthesis and prostaglandin metabolism in the ovary and endometrium, respectively. Omega-6 fatty acids are believed to have pro-inflammatory and thus PGF2-stimulating properties rendering them extra value as nutraceutical' early post-partum, while omega-3 fatty acids can weaken this inflammatory potency, leading to a higher chance of survival of the embryo when supplemented during the periconceptual period. Unfortunately, research results rarely provide a consensus in this perspective. The consequences of these fat-feeding strategies on oocyte and embryo quality remain an intriguing issue for debate. Fat feeding may alter the microenvironment of the growing and maturing oocyte of the early and older embryo and thus may affect reproductive outcome. We recently reported that dietary-induced hyperlipidaemic conditions can be harmful for embryo development and metabolism. However, to date, research results remain somewhat conflicting most probably due to differences in fat sources used, in diet and duration of supplementation and in experimental set-up in general.

Reduced oocyte and embryo quality are recognised as major factors in the problem of disappointing fertility in high producing dairy cows. This review aims to shed more light on the importance of the intrafollicular environment in the subfertility problem in dairy cows. Metabolic disturbances associated with negative energy balance (NEB) early postpartum are associated with ovarian dysfunction. Changes in the growth pattern of the ovarian follicle during a period of NEB can indirectly affect oocyte quality. Furthermore, a maternal metabolic disorder (linked with NEB or nutritionally induced) may alter the endocrine and biochemical composition of the follicular fluid, the micro-environment of the growing and maturing female gamete. The maturing oocyte is very sensitive to any perturbation in its direct environment and in vitro maturation models revealed that some of these metabolic changes reduce the oocyte’s developmental competence. Also, embryo quality is significantly reduced due to maturation in adverse conditions. Well balanced and timed oocyte metabolism and gene expression are crucial to safeguard an optimal oocyte development. In that perspective, metabolome and transcriptome parameters of the oocyte may serve to predict reproductive success rates. Finally, there is growing evidence that adverse conditions for oocyte growth and maturation may also jeopardise the health and performance of the offspring.

Elevated concentrations of serum non-esterified fatty acids (NEFA), associated with maternal disorders such as obesity and type II diabetes, alter the ovarian follicular micro-environment and have been associated with subfertility arising from reduced oocyte developmental competence. We have asked whether elevated NEFA concentrations during oocyte maturation affect the development and physiology of zygotes formed from such oocytes, using the cow as a model. The zygotes were grown to blastocysts, which were evaluated for their quality in terms of cell number, apoptosis, expression of key genes, amino acid turnover and oxidative metabolism. Oocyte maturation under elevated NEFA concentrations resulted in blastocysts with significantly lower cell number, increased apoptotic cell ratio and altered mRNA abundance of DNMT3A, IGF2R and SLC2A1. In addition, the blastocysts displayed reduced oxygen, pyruvate and glucose consumption, up-regulated lactate consumption and higher amino acid metabolism. These data indicate that exposure of maturing oocytes to elevated NEFA concentrations has a negative impact on fertility not only through a reduction in oocyte developmental capacity but through compromised early embryo quality, viability and metabolism. © 2011 Van Hoeck et al.

BACKGROUND: Obesity is associated with female reproductive abnormalities. Hyperlipidaemia might alter the embryonic micro-environment and potentially result in reduced fertility. We aimed to induce hyperlipidaemia nutritionally and investigate the consequences of hyperlipidaemic culture conditions on bovine in vitro embryo development, embryo quality and gene expression patterns. METHODS: Bovine zygotes (n = 1545) were cultured in synthetic oviductal fluid medium supplemented with serum from heifers (n = 3), each fed three successive dietary treatments: (i) control serum, following a hay-based diet, (ii) hyperlipidaemic serum, following a carbohydrate and protected palm-oil-rich diet (FatCh) or (iii) hyperlipidaemic serum, following a protected palm-oil-rich diet (Fat). Blastocysts were evaluated for development, cell count, picnotic and mitotic indexes and cryotolerance. Selected mRNA transcripts were measured by quantitative RTPCR. RESULTS: FatCh and Fat diets approximately doubled the total cholesterol concentrations, compared with controls (167.1 ± 11.9, 150.0 ± 12.8 versus 83.4 ± 13.7 mg/dl, respectively, P < 0.05), and fatty acid concentrations (8146.60 ± 214.61, 6935.56 ± 1081.04 versus 3944.0 ± 425.07 µmol/l, respectively, P < 0.05). Supplementation of culture media with FatCh and Fat serum significantly reduced blastocyst rates, compared with controls (27.8, 23.4% versus 36.2%, respectively, P < 0.01), total cell number (103.3 ± 30.1, 95.6 ± 28.2 versus 146.9 ± 34.2, respectively, P < 0.01), mitotic index (1.3 ± 1.1, 1.7 ± 2.4 versus 3.6 ± 2.2%, respectively, P < 0.01) and hatching rates after vitrification (20.4, 13.8 versus 35.7%, respectively, P = 0.03). Embryos in FatCh and Fat groups exhibited significantly higher mRNA levels for genes related to apoptosis and metabolism, compared with controls. CONCLUSIONS: This combined in vivo and in vitro model indicates that the exposure of preimplantation embryos to hyperlipidaemic conditions may result in reduced embryo quality and developmental potential, possibly resulting in poorer fertility.

Although fragmented and sometimes inconsistent, the proof of a vital link between the importance of the physiological status of the mother and her subsequent reproductive success is building up. High-yielding dairy cows are suffering from a substantial decline in fertility outcome over past decades. For many years, this decrease in reproductive output has correctly been considered multifactorial, with factors including farm management, feed ratios, breed and genetics and, last, but not least, ever-rising milk production. Because the problem is complex and requires a multidisciplinary approach, it is hard to formulate straightforward conclusions leading to improvements on the ‘work floor’. However, based on remarkable similarities on the preimplantation reproductive side between cattle and humans, there is a growing tendency to consider the dairy cow’s negative energy balance and accompanying fat mobilisation as an interesting model to study the impact of maternal metabolic disorders on human fertility and, more specifically, on oocyte and preimplantation embryo quality. Considering the mutual interest of human and animal scientists studying common reproductive problems, this review has several aims. First, we briefly introduce the ‘dairy cow case’ by describing the state of the art of research into metabolic imbalances and their possible effects on dairy cow reproduction. Second, we try to define relevant in vitro models that can clarify certain mechanisms by which aberrant metabolite levels may influence embryonic health. We report on recent advances in the assessment of embryo metabolism and meantime critically elaborate on advantages and major limitations of in vitro models used so far. Finally, we discuss hurdles to be overcome to successfully translate the scientific data to the field.

The detrimental consequences of elevated serum nonesterified fatty acid concentrations (NEFA) typical in negative energy balance, obesity, or type II diabetes have previously been demonstrated in ovarian follicles. However, regardless its key role in reproduction, the consequences of elevated NEFA on oviductal physiology are unclear. Therefore, the aim of this study was to 1) determine whether serum NEFAs can be found in the oviductal microenvironment using a polarized oviductal epithelial cell culture and more specifically to 2) study the effect of the BSA gradient and the direction of the NEFA gradient. Bovine oviductal epithelial cells from slaughterhouse oviducts in Day 3 to 5 of the luteal phase were mechanically isolated and cultured for 7 days in a flask. Cells were transferred in a polarized oviductal epithelial cell culture-system (Snapwell® polyester membrane, pore size 0.4 µm, 4 × 106 pores cm–2) with an apical (A) and basal (B) medium supporting cell growth until the transepithelial electric resistance reached 700 Ωcm2 (Day 6). Then, cells were exposed to a transmembranary BSA (0.75 or 3% BSA) or NEFA gradient (0 or 360 µM NEFA: 115 µM oleic acid, 140 µM stearic acid, 105 µM palmitic acid) for 48 h in 4 experimental setups: 1) A and B containing 0.75% BSA and B supplemented with NEFA, 2) same as in 1 but NEFAs were added in A, 3) A containing 0.75% BSA and B supplemented with 3% BSA and NEFA, 4) same as in 3 but with 3% BSA + NEFA in A and B contained 0.75% BSA. Samples were analyzed for total NEFA and specific fatty-acid concentrations by photometric and gas chromatographic assays. In total, 72 wells in 4 replicates were cultured and analyzed. Data were processed by paired sample t-tests and student t-tests. Exposure to NEFA did not alter the transepithelial electric resistance. In Exp. 1, the total NEFA concentration in A increased with 0.013 µM (21.11%) over 48 h of NEFA exposure in the basal compartment explained by a significant rise of stearic (8.52 µM, 20.68%) and oleic acid (12.86 µM, 45.17%) accompanied with only a 19.45% decrease of total NEFA in B (P

Metabolic disorders, like negative energy balance and obesity, are characterized by elevated serum non-esterified fatty acid (NEFA) concentrations, due to upregulated lipolysis. We previously showed that short-term (24-h) NEFA exposure of bovine oocytes during their final maturation is detrimental to oocyte and embryo quality (Van Hoeck et al. 2011 PLoS ONE 6, e23183). However, the typical chronic exposure as present in diseased females has never been studied before. Therefore, we aimed to use a murine preantral follicle culture model to study the effect of long-term NEFA exposure on folliculogenesis, antrum formation, and the developmental competence of the enclosed oocyte. Early secondary murine follicles (n = 629) from 13-day-old B6CBAF1 mice were individually cultured for 12 days. Follicles were exposed to 4 treatments containing physiological or pathological concentrations of stearic acid (SA), palmitic acid (PA), or oleic acid (OA) for 12 days: BASAL (72 µM NEFA mix, n = 154), high SA (280 µM SA, n = 160), high OA (210 µM OA, n = 159), and NEFA (720 µM NEFA mix, n = 156). Oocytes were routinely fertilized 20 h after a final maturation stimulus [hCG, epidermal growth factor (EGF)]. Presumptive zygotes were denuded and cultured until the blastocyst stage (Day 5 pre-implantation). Data were analyzed with a mixed-model ANOVA or binary logistic regression. The SA-exposed follicles displayed a reduced Day-12 antrum formation, compared to BASAL and NEFA follicles (68 v. 78 and 83%, P = 0.03 and P

In humans, diets rich in carbohydrates and saturated fatty acids are common and the subsequent altered metabolism has been linked to reduced fertility. Also, modern dairy cows are fed milk-stimulating diets rich in starch and fatty acids. The pre-implantation embryo is vulnerable to nutritionally induced changes in its micro-environment. We have shown that a dietary induced hyperlipidemia has detrimental consequences on development, quality and gene expression patterns of the pre-implantation embryo (Leroy et al. 2010 Hum. Reprod. 25, 768–778). Hyperlipidemia was induced by feeding starch- and saturated-fat-rich diets and the collected serum was added during bovine embryo culture. In the present study, we hypothesized that changing the saturated into a polyunsaturated fat source could alleviate these negative effects. We furthermore hypothesized that the sequence in which the different fat sources are given can affect embryo development and quality. Therefore, in the first setup: bovine zygotes (n = 1104; 4 replicates) were cultured in SOF medium supplemented with 10% serum collected from 3 synchronized heifers after 3 successive dietary treatments each fed during 4 weeks: control serum after a hay-based maintenance diet, saturated serum (SAT1) after a carbohydrate rich diet supplemented with saturated fatty acids (twice maintenance, C16 : 0, palmitic acid, 4.5% total fat), or unsaturated serum (UNSAT1) after a carbohydrate-rich diet supplemented with unsaturated fatty acids (twice maintenance, C18 : 3, linolenic acid, 4.45% total fat). In the second setup (n = 1483; 5 replicates): bovine zygotes were cultured in SOF medium supplemented with 10% serum from 3 synchronized heifers successively fed the 3 same dietary treatments in different order: control, unsaturated (UNSAT2), or saturated serum (SAT2). Day 7 blastocyst developmental competence (binary logistic regression), total cell number, and apoptotic cell ratio (ACR) (mixed model ANOVA) were evaluated. Supplementation of SAT1 serum in culture significantly reduced blastocysts from cleaved zygotes (36.7% v. 44.7%) and significantly increased ACR (0.1% ± 0.05 v. 0.06% ± 0.04) compared to controls (P

In recent years, high nonesterified fatty acid (NEFA) concentrations have been intensively discussed as an important metabolic cue linking negative energy balance in high yielding dairy cows early postpartum to disappointing fertility. Previous research has shown that high NEFA concentrations during in vitro oocyte maturation not only induce significant negative effects on the developmental capacity of oocytes but also reduce the quality and viability of the subsequent embryos that do survive until 7 days post-insemination. Because NEFA are known to regulate gene expression, the objective of this study was to investigate the effect of NEFA exposure during bovine in vitro oocyte maturation on the relative transcript abundance in the resultant day 7 blastocysts. This study focused on key genes related to embryonic quality, apoptosis, adaptation to stress, metabolism, DNA methylation, growth factors, and fatty acid synthesis. During a serum-free maturation period of 24 h, bovine cumulus–oocyte complexes were exposed to maturation medium (0.75% BSA) supplemented with 1) physiological NEFA concentrations (control; 150 μM of total NEFA, i.e. oleic, stearic, and palmitic acid), 2) elevated stearic acid concentrations (HSA; 75 μM of stearic acid), and 3) elevated NEFA concentrations (HCOMBI; 425 μM of total NEFA). Following IVF using semen from a bull of proven fertility, zygotes were cultured in SOF (+5% of FCS) medium for 7 days. Studied mRNA transcripts were quantified by real-time quantitative RT-PCR. Experiments were conducted to determine levels of each transcript relative to H2AZ in every sample. Relative mRNA abundance differences among groups were analysed by one-way ANOVA. Significant increases (P

High non-esterified fatty acid (NEFA) concentrations in the blood, associated with negative energy balance (NEB), obesity or diabetes Type II are known to alter the follicular micro-environment. These environmental changes have been associated with disappointing fertility outcome through disabled ovarian cell function and oocyte’s developmental competence. Our hypothesis was that elevated NEFA concentrations during final oocyte maturation might hamper the quality of the pre-implantation embryo as well. To assess embryo quality, the present study focused on total cell number and apoptotic index in 7-day-old embryos. Applied NEFA concentrations in the maturation medium were based on analyses in the follicular fluid of high yielding dairy cows early post partum during NEB. Bovine cumulus-oocyte complexes were exposed to 1) physiological NEFA concentrations, i.e. a combination of basal palmitic (25 μM), stearic (50 μM) and oleic acid (75 μM) concentrations (CONTROL), 2) elevated NEFA concentrations, i.e. a combination of high palmitic (75 μM), stearic (150 μM) and oleic acid (200 μM) concentrations (HIGH COMBI) and 3) elevated palmitic acid (75 μM) concentrations (HIGH PA). Palmitic acid has been recognized as a major saturated fatty acid in terms of cellular toxicity. After serum-free in vitro maturation (24 h) and fertilization (22 h), zygotes were cultured in SOF medium with 5% serum for 7 days. Blastocysts were evaluated for developmental competence, total cell number (by Propidium Iodide staining) and apoptotic index (by TUNEL detection kit). In total, 684 oocytes were cultured in 3 replicates. Data were analyzed with binary logistic regression and a mixed model ANOVA. Preliminary research showed that maturation in a combination of basal NEFA concentrations has no effect on oocyte’s developmental competence compared to the standard serum free maturation system. In the present study, maturation in HIGH COMBI resulted in significantly lower blastocyst rates (21.4%) compared to CONTROL (30.1%) (P = 0.03). No significant effect of HIGH PA maturation on blastocyst rate (24.1%) could be found. Also total cell number tended to be lower in the HIGH COMBI (104.7 ± 26.1) compared to CONTROL (125.8 ± 29.4) (P = 0.08). The apoptotic index was significantly increased in the HIGH PA group (0.22 ± 0.12) compared to the CONTROL group (0.11 ± 0.07) (P = 0.02) and tended to be higher than the HIGH COMBI group (0.14 ± 0.12) (P = 0.06). Maternal metabolic conditions, leading to increased lipolysis and high NEFA concentrations, can hamper fertility through a reduction of the oocyte’s developmental competence. The data of the present study furthermore suggest that elevated NEFAs might induce a negative carry over effect from the oocyte during its maturation to the embryo quality. This may ultimately lead to embryonic mortality and thus to a disappointing fertility outcome. Veerle Van Hoeck is supported by the Special Research Fund, University of Antwerp (Grant 22590).