Comparison between the characteristics of follicular fluid and the developmental competence of bovine oocytes

Seasonal variations in the metabolomic profile of the ovarian follicle components in Italian Mediterranean Buffaloes

The aim of this work was to evaluate the seasonal effect on the metabolomic profile of the ovarian follicle in Italian Mediterranean buffalo to unravel the causes of the reduced competence during the non-breeding season (NBS). Samples of follicular fluid, follicular cells, cumulus cells and oocytes were collected from abattoir-derived ovaries during breeding season (BS) and NBS and analyzed by 1H Nuclear Magnetic Resonance. The Orthogonal Projections to Latent Structures of the Discriminant Analysis showed clear separation into seasonal classes and Variable Importance in Projection method identified differentially abundant metabolites between seasons. Seasonal differences were recorded in metabolite content in all analyzed components suggesting that the decreased oocyte competence during NBS may be linked to alteration of several metabolic pathways. The pathway enrichment analysis revealed that differences in the metabolites between the seasons were linked to glutathione, energy generating and amino acid metabolism and phospholipid biosynthesis. The current work allows the identification of potential positive competence markers in the follicular fluid as glutathione, glutamate, lactate and choline, and negative markers like leucine, isoleucine and β-hydroxybutyrate. These results form a major basis to develop potential strategies to optimize the follicular environment and the IVM medium to improve the competence of oocytes during the NBS.

The effects of glutathione ethyl ester in in vitro maturation on the developmental ability of oocytes derived from cattle with liver abnormalities

The main objectives of this study was to identify the effects of a relationship of hyper-concentration of Gamma-glutamyltransferase (γ-GTP) in follicle fluid (FF) on the levels of glutathione (GSH)/reactive oxygen species (ROS) in oocytes and subsequent embryo development in cattle with abnormal livers. Furthermore, we investigated the effect of supplementing in vitro maturation medium with glutathione ethyl ester (GSH-OEt) on the subsequent developmental potential of oocytes from such cattle. We used a control group of cattle (with normal livers) and a liver disorder (LD) group, in which the liver was diagnosed as being abnormal. In experiment 1, the LD group was divided to two subgroups according to the concentration of γ-GTP in FF: a low group (≤50 IU/L; the low LD group), and a high group (>50 IU/L: the high LD group). Cumulus oocyte-complexes (COCs) were matured and fertilized in vitro and then cultured to the blastocyst stage. The levels of GSH and ROS in the matured oocytes after IVM were then assessed in each group. On day 7 after fertilization, embryo cleavage and development were assessed. We found that the rate of development to the blastocyst stage was significantly lower in the high LD group than in the control group and the low LD group. The levels of GSH in matured oocytes were significantly lower in the high LD group than in the control group and low LD group. The levels of ROS in matured oocytes was significantly higher in the high LD group than in the control group and the low LD group. In experiment 2, COCs from cattle in the high LD group were matured in m-199 supplemented with 5 mM GSH-OEt, then IVF and IVC was performed for 7 days. The GSH levels were determined in some COCs after IVM. The supplementation of media with GSH-OEt during IVM increased the levels of GSH in mature oocytes and improved the rate of blastocyst development compared with the control group. In conclusion, GSH-OEt supplementation to media during IVM can improve the developmental potential of oocytes in liver-diseased cattle with high γ-GTP concentrations in the FF by increasing intracellular GSH synthesis and scavenging ROS.

A multilevel analysis identifies the different relationships between amino acids and the competence of oocytes matured individually or in groups

High-protein diets contribute to an increase in urea follicular concentrations associated with decreased fertility. Urea has been shown to interfere with the epidermal growth factor (EGF)/EGFR system, which has been shown to have a beneficial effect during in vitro maturation (IVM) of oocytes. Of note, the number of cumulus-oocyte complexes (COCs) in the maturation medium can change the maturation and the developmental competence of COCs. Therefore, it was hypothesized that, the presence of urea and EGF may have a differential effect on the depletion/appearance of AAs and competence of COCs matured individually (I-IVM system) or in groups (G-IVM system). In the G-IVM system, COCs increased consumption (depletion) of AAs compared with other groups in the presence of high-level urea (40 mg/dl) + EGF (10 ng/ml). In the I-IVM system, the non-cleaved COCs depleted more AAs than the cleaved COCs, in particular in the presence of urea. The combination of urea and EGF increased the depletion of AAs in the G-IVM system. However, the EGF abrogated the urea-induced depletion of AAs by the I-IVM COCs. The use of N-acetyl-L-cysteine as an EGFR inhibitor canceled urea-induced depletion of AAs. This shows the inhibiting effect of urea over the EGF/EGFR system. In the presence of urea + EGF, COCs had a lower degree of developmental competence than control in both I- and G-IVM systems. Arginine had the best predictive power to identify highly competent COCs in the G-IVM system, while glutamine was the best predictor of the cleavage in the I-IVM system. In conclusion, this multi-level study shows that COCs matured individually or in groups may have different association with AAs metabolism. These findings provide new insights into the relationships between AA metabolism and the subsequent developmental competence of COCs.

Metabolic Profile Comparison between Follicular Fluid and Serum in Normal Cows and Those Affected by Ovarian Cysts

The aim of this study was to carry out the metabolic profile comparison between follicular fluid and serum in normal cows and those affected by ovarian cysts (OC). After slaughtering, blood samples and follicular fluids from normal and cystic animals were collected and assayed using commercial kits to determine the concentrations of metabolites (glucose, total protein, total cholesterol, cortisol, triglycerides, urea, creatinine and insulin) and the liver enzymes activity. Data showed that OC were characterized by low levels of glucose, total protein, cholesterol and cortisol in cystic fluid, while urea concentrations were high compared to normal follicular fluid (P<0.001). On the other hand, serum assays of cystic animals revealed very low values of insulin and urea, whereas cortisol levels were relatively high in comparison with the serum of normal cows (P<0.001). Significant correlations between the serum and follicular fluid concentrations of normal cows were found for glucose (r=0.49), total cholesterol (r=0.31), cortisol (r=0.38) and total protein (r=0.63). The highest correlation was found for urea (r=0.86). On contrary, weak correlations were observed between metabolites concentrations in cystic fluid and in serum for normal and cystic cows. In conclusion, OC grow and persist in a metabolic environment, which differs from follicular fluid to blood. These changes may act together and/or separately to ensure the continuous development of OC. To understand a part of the mechanism, the authors propose a deep study about blood-follicle-barrier.

Serum albumin concentration of donor cows as an indicator of developmental competence of oocytes

Adequate nutrition is required for maintenance of normal reproduction in cattle. Albumin, the best marker and fundamental part of nutrition, most abundant plasma protein and major component of fetal bovine serum, is the best predictor of malnourishment in South African cattle. The aim of this study was to determine if serum albumin concentrations of donor cows predict the developmental competence of oocytes, and if additional protein supplementation of the in vitro culture media improves embryo outcomes in oocytes from cows with inadequate serum albumin concentrations. Oocytes (n = 1024) were recovered from donors with inadequate (≤35.9 g/L), or adequate serum albumin concentrations (≥36.0 g/L). Four hundred and sixty oocytes originated from cows with inadequate serum albumin and 564 from cows with adequate serum albumin. Oocytes of these cohorts were randomly allocated to a control and supplemented fetal bovine serum in vitro embryo culture protocol. Multiple linear, logistic and Poisson regression analyses were performed to estimate the effects of different covariates on linear, binary and count data respectively. Mixed effects Poisson regression was performed for the number of oocytes that developed into blastocysts by the seventh day of culture. Adequate serum albumin concentration of donor cows independently resulted in 46% increased blastocyst formation in the control protocol (P = 0.02). Although fetal bovine serum supplementation of the culture protocol did not affect blastocyst formation in oocytes originating from cows with inadequate serum albumin, it independently reduced blastocyst formation by 30% in oocytes originating from cows with adequate serum albumin (P = 0.02). Other independent predictors of blastocyst outcome included higher serum urea nitrogen, lower beta (β)-hydroxybutyric acid concentrations and lower fat classification of donor cows. It is concluded that adequate serum albumin of donor cows is a significant predictor of developmental competence of oocytes, and that in vitro supplementation of fetal bovine serum does not improve developmental competence of oocytes and can lead to negative blastocyst outcomes. Further research is required to determine optimal protein supplementation for oocytes originating from inadequately nourished cows.

Urea influences amino acid turnover in bovine cumulus-oocyte complexes, cumulus cells and denuded oocytes, and affects in vitro fertilization outcome

High-protein diets often lead to an increase in urea concentration in follicular fluid of dairy cows, which may reduce oocyte competence. In the present study, maturation media were supplemented with urea (0, 20, 40 mg/dl), and amino acids (AAs) turnover was evaluated in the 24-h spent media of specimens (cell types), bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), or denuded oocytes (DOs). The main effects of urea and cell type, and their interaction were significant on the individual turnover (expect threonine, glycine, and tyrosine) and total turnover, depletion, and appearance of AAs. The results showed a high level of urea and DOs increased the depletion of all AAs and that of essential and non-AAs, respectively. Sensitivity analysis revealed the highest sensitivity of isoleucine, lysine, and tryptophan to urea, especially in DOs. Principal component analysis (PCA) evaluated the strong correlations between the turnover of: (1) glutamine, aspartic acid or glycine, and developmental competence and fertilization of COCs; (2) serine, isoleucine, valine or glutamic acid, and cleavage rate of DOs; and (3) serine, glutamine, aspartic acid or alanine, and CCs viability. In conclusion, urea significantly changed the turnover of AAs by COCs, CCs and DOs, and reduced the subsequent developmental competence of bovine oocytes.

Studies on lysophosphatidic acid action during in vitro preimplantation embryo development

Assisted reproductive technologies, including in vitro embryo production (IVP), have been successfully used in animal reproduction to optimize breeding strategies for improved production and health in animal husbandry. Despite the progress in IVP techniques over the years, further improvements in in vitro embryo culture systems are required for the enhancement of oocyte and embryo developmental competence. One of the most important issues associated with IVP procedures is the optimization of the in vitro culture of oocytes and embryos. Studies in different species of animals and in humans have identified important roles for receptor-mediated lysophosphatidic acid (LPA) signaling in multiple aspects of human and animal reproductive tract function. The data on LPA signaling in the ovary and uterus suggest that LPA can directly contribute to embryo-maternal interactions via its influence on early embryo development beginning from the influence of the ovarian environment on the oocyte to the influence of the uterine environment on the preimplantation embryo. This review discusses the current status of LPA as a potential supplement in oocyte maturation, fertilization, and embryo culture media and current views on the potential involvement of the LPA signaling pathway in early embryo development.

Development of in vitro produced porcine embryos according to serum types as macromolecule

This study was conducted to establish an in vitro maturation (IVM) system by selection of efficient porcine serum during porcine in vitro production. To investigate the efficient porcine serum (PS), different types of PS [newborn pig serum, prepubertal gilt serum (PGS), estrus sow serum, and pregnancy sow serum] were used to supplement IVM media with or without gonadotrophin (GTH) and development rates of parthenogenetic activation (PA) and in vitro fertilization (IVF) embryos were then compared. The maturation rates of the PGS group was significantly higher when GTH was not added. Additionally, during development of PA embryos without GTH, the PGS group showed significantly higher cleavage and blastocyst formation rates. Moreover, the cleavage rates of IVF embryos were significantly higher in the PGS group, with no significant differences in the blastocyst formation. However, when GTH was supplemented into the IVM media, there were no significant differences among the four groups in the cleavage rates, development rates of the blastocyst, and cell number of the blastocyst after PA and IVF. In conclusion, PGS is an efficient macromolecule in porcine IVM, and GTH supplementation of the IVM media is beneficial when PS is used as macromolecule, regardless of its origin.

Liver condition affects bovine oocyte qualities by changing the characteristics of follicular fluid and plasma

The liver is an important organ that contributes to milk production in dairy cows. The aim of this study was to examine whether liver conditions affect the characteristics of blood plasma and follicular fluid (FF) and whether supplementing in vitro maturation medium with FF from either cows with damaged livers (DL) or those with healthy livers (HL) affects oocyte developmental competence. Biochemical characteristics of FF were significantly correlated with those in plasma. As such, the characteristics of both plasma and FF were similarly affected by liver conditions in that the concentrations of total protein and inorganic phosphorus were higher for the DL cow group than for the HL cow group, whereas the concentrations of albumin, lactate dehydrogenase and calcium were lower for DL cows than for HL cows. In addition, supplementing the medium with DL-FF retarded the progression of the nuclear maturation of oocytes collected from the HL cows. On culturing oocytes in maturation medium containing HL-FF, DL-FF or foetal calf serum, the highest developmental rate to the blastocyst stage was observed in the HL-FF group, while the lowest developmental ratio was observed in the DL-FF group. The growth factor array of the FFs revealed that 10 growth factors were significantly downregulated in the DL-FF compared with those in HL-FF. In conclusion, the characteristics of plasma and FF are affected by liver conditions in a similar way. Concentrations of several growth factors were low in DL-FF, as was the ability of DL-FF to support oocyte maturation compared with that of HL-FF.

Effect of the stage of estrous cycle on follicular population, oocyte yield and quality, and biochemical composition of serum and follicular fluid in Anatolian water buffalo

This study was designed to investigate the effects that the different stages of the estrous cycle had on the number of surface ovarian follicles and oocyte yield and quality of Anatolian water buffalo during peak breeding season. Assessments were made on the basis of ovarian morphology, serum and follicular fluid concentrations of variety of biochemical parameters. Following slaughter, blood samples were collected from each animal. The stage of estrous cycle was classified as either the luteal or follicular phase, and surface ovarian follicles were classified as small, medium, or large. The follicular fluid was aspirated, and oocytes were evaluated microscopically for classification into four categories. No statistical differences (p>0.05) were observed regarding the total number of follicles or quality of oocytes relative to the stage of the estrous cycle. Serum high-density lipoprotein cholesterol (HDL), alkaline phosphatase (ALP) and progesterone (P4) concentrations were significantly higher in the luteal phase than in the follicular phase (P<0.05). Significant correlations were observed in the luteal phase between the total number of oocytes and cholesterol (Cho), HDL, sodium (Na), chloride (Cl); A-quality oocytes and Na, Cl, Mg; C-quality oocytes and Cho, HDL, and Mg in follicular fluid. These results offer new information concerning Anatolian water buffalo reproductive physiology, which may be useful for improving oocyte quality in buffalo. This is the first study to describe the number of ovarian follicles, oocyte yield and quality, and a variety of biochemical parameters in the serum and follicular fluid of Anatolian water buffalo during peak breeding season in Turkey.

The consequences of metabolic changes in high-yielding dairy cows on oocyte and embryo quality

Unsatisfactory reproductive performance in dairy cows, such as reduced conception rates, in addition to an increased incidence of early embryonic mortality, is reported worldwide and has been associated with a period of negative energy balance (NEB) early post partum. Typically, NEB is associated with biochemical changes such as high non-esterified fatty acid (NEFA), high β-hydroxybutyrate (β-OHB) and low glucose concentrations. The concentrations of these and other metabolites in the follicular fluid (FF) of high-yielding dairy cows during NEB were determined and extensively analyzed, and then were replicated in in vitro maturation models to investigate their effect on oocyte quality. The results showed that typical metabolic changes during NEB are well reflected in the FF of the dominant follicle. However, the oocyte seems to be relatively isolated from extremely elevated NEFA or very low glucose concentrations in the blood. Nevertheless, the in vitro maturation models revealed that NEB-associated high NEFA and low glucose levels in the FF are indeed toxic to the oocyte, resulting in deficient oocyte maturation and developmental competence. Induced apoptosis and necrosis in the cumulus cells was particularly obvious. Furthermore, maturation in saturated free fatty acid-rich media had a carry-over effect on embryo quality, leading to reduced cryotolerance of day 7 embryos. Only β-OHB showed an additive toxic effect in moderately hypoglycemic maturation conditions. These in vitro maturation models, based on in vivo observations, suggest that a period of NEB may hamper the fertility of high-yielding dairy cows through increased NEFA and decreased glucose concentrations in the FF directly affecting oocyte quality. In addition to oocyte quality, these results also demonstrate that embryo quality is reduced following an NEB episode. This important observation may be linked to the typical diet provided to stimulate milk yield, or to physiological adaptations sustaining the high milk production. Research into this phenomenon is ongoing.

Follicular fluid supplementation during in vitro maturation promotes sperm penetration in bovine oocytes by enhancing cumulus expansion and increasing mitochondrial activity in oocytes

The aim of this study was to examine the effects of bovine follicular fluid (bFF) on mitochondrial activity in in vitro-matured (IVM) oocytes and to assess its importance for fertilisation and embryo development. Bovine follicular oocytes were subjected to IVM in medium supplemented either with polyvinylpyrrolidone, bovine serum albumin, calf serum or bFF. Nuclear maturation, cumulus expansion, mitochondrial distribution and ATP content in oocytes were compared between groups along with subsequent in vitro fertilisation (IVF) and embryo development. Compared with other supplements, bFF generated significantly enhanced re-distribution of active mitochondria in oocytes and this effect was associated with elevated intracellular ATP content. Furthermore, bFF significantly improved cumulus expansion, which was associated with improved fertilisation rates when cumulus-enclosed oocytes were subjected to IVF; however, its promoting effect was neutralised when denuded oocytes were inseminated. Elevating ATP content in oocytes by bFF did not affect maturation or embryo development but promoted fertilisation when mitochondrial electron transport was blocked in oocytes before IVF by Rotenone. In conclusion, supplementation of IVM medium with bFF promotes sperm penetration both by the improvement of cumulus expansion and by enhancing ATP levels in oocytes, which maintains their ability to be fertilised after mitochondrial stress.

The effect of marine algae in the ration of high-yielding dairy cows during transition on metabolic parameters in serum and follicular fluid around parturition

Sixteen Holstein cows were assigned to 2 groups to evaluate the caloric and metabolic effect of feeding marine algae (ALG) from 3 wk prepartum until 12 wk postpartum. Milk production characteristics and the profiles of hormones and metabolites in the serum were monitored from -7 to 46 d in milk (DIM) and in follicular fluid (FF) from 14 to 46 DIM. All cows received a corn- and grass silage-based partially mixed ration supplemented with concentrate and protein supplement. In the diet of the ALG group, 2 kg of the concentrate was replaced by a concentrate containing ALG (44 g/d of docosahexaenoic acid). Diets were isocaloric (net energy basis) and equal in intestinal digestible protein. The ALG diet increased milk yield (41.2 vs. 38.2 kg/d) and decreased milk fat yield (1.181 vs. 1.493 kg/d) and milk fat content (31.6 vs. 40.7 g/kg). Protein yield (1.336 vs. 1.301 kg/d) was not affected but a tendency toward decreased milk protein content (32.8 vs. 34.7 g/kg) was observed. Marine algae supplementation increased the β-hydroxybutyric acid (BHBA) concentration in FF of the ALG cows compared with that in the controls (0.992 vs. 0.718 mmol/L). The total protein concentration in FF was decreased in ALG (62.9 vs. 67.6 g/L). Plasma and serum metabolites did not significantly differ between treatments except for a tendency toward a lower concentration of urea in the serum of the control compared with ALG (4.69 vs. 5.13 mmol/L). Based on metabolizable energy calculations, a daily energy-sparing effect of 3.48 Mcal was obtained due to milk fat depression (MFD). The concomitant increase in milk yield suggests that at least part of this spared energy is used to stimulate milk production. Theoretically, 3.48 Mcal of ME could lead to an increase in milk yield of 7.43 kg/d, which is higher than the observed 3 kg/d. However, when evaluating nutrient requirements during MFD in early lactation, we calculated that increased milk production is caused by a propionate-saving effect of 2.71 mol in the udder when milk fat is depressed. Concurrent increased BHBA concentrations in FF in the ALG group cannot be attributed to a worsened energy status of the animals because all other indicators contradict any change in energy balance, indicating that BHBA might not be an appropriate metabolic parameter to estimate the energy balance in early lactating dairy cows during MFD.

Follicle growth and oocyte developmental competence in cows with liver damage

Follicle growth, oocyte quality or oocyte growing environment (follicular fluid) were evaluated in cows with severe liver damage (haemorrhage, telangiectasis, cholangitis and abscess) that were visually diagnosed at the slaughterhouse. Holstein cows aged 40-90 months with either a healthy liver (HL cow) or damaged liver (DL cow) were selected as donors. Follicle development kinetics was evaluated by counting the follicles at various developmental stages. In addition, the biochemical characteristics of the follicular fluids, developmental competence of preantral follicles cultured for 16 days in vitro and the ability of oocytes to develop to the blastocyst stage 8 days after fertilization were examined. DL cows had fewer secondary follicles than HL cows, and the correlation between the number of secondary follicles and the number of primary follicles differed among DL and HL cows. The follicular fluid of DL cows contained significantly lower levels of albumin and a higher total protein content than that of HL cows. Oocyte nuclear maturation assessed at 5, 16 and 21 h after beginning of culture was slower in DL cows than in HL cows, although the final maturation rates did not differ. The rate of polyspermic fertilization was significantly higher and the proportion of cleavage at 48 h after insemination and blastulation lower in DL cows compared with HL cows. When preantral follicles were cultured in vitro, the rate of follicles with normal morphology was lower in DL cows than in HL cows. These findings suggest that the kinetics of folliculogenesis differ among DL and HL cows and the developmental ability of preantral follicles and oocytes is lower in DL cows than in HL cows.

Classification of bovine follicles based on the concentrations of steroids, glucose and lactate in follicular fluid and the status of accompanying follicles

A simple and clear means to identify the physiological status of follicles is essential for study of follicular biology. In the present study, we verified a novel classification procedure based on analysis of the follicular population and glucose concentration in follicular fluid (FF) as an alternative method to classify bovine follicles. Paired ovaries were collected from heifers, and the number of follicles and stage of the CL were recorded. Follicles were initially divided into the following 3 groups according to diameter and the ratio of E2 and P4 (E/P): E2 active (E-A: E/P>or=1), E2 inactive (E-I: E/P<1, >or=8.5 mm) and small follicles (E/P<1, <8.5 mm). E-A follicles were easily identified as E2-rich dominant follicles and were further classified according to diameter and stage of the CL as early dominant (EDF: <8.5 mm), dominant (DF: >or=8.5 mm, stages I-III) or preovulatory follicles (POF: >or=8.5 mm, stage IV). E-I follicles were classified as follows based on the status of the accompanying follicles: early atretic (EAF: without an E-A follicle), mid-atretic (MAF: with an EDF or DF) and late atretic follicles (LAF: with an EAF or POF). The follicular P4 concentrations of the MAF and LAF were significantly higher compared with that of the EAF, while follicular glucose concentration of the LAF was lower compared with those of EAF and MAF, indicating that this classification can be used to distinguish early atretic follicles from more advanced atretic follicles. Small follicles were classified as growing (GF: without E-A follicles) and suppressed small follicles (SSF: with E-A follicles). The SSF was easily identifiable by this procedure, but some GF populations likely contained SSF. To identify true GF, the ratio of E2 in the GF and accompanying EAF may be used. In conclusion, analysis of the follicular population in conjunction with biochemical indices such as steroid and glucose concentrations in FF provides a simple and accurate means of classifying bovine follicles.

Effects of plasma urea nitrogen levels on the bovine oocyte ability to develop after in vitro fertilization

The overall aim of the present study was to evaluate in vitro development ability of oocytes recovered from 56 Holstein Frisian heifers with low [group 1 (G1): <13 mg /dl], moderate [group 2 (G2): 13-16 mg /dl] and high [group 3 (G3): >16 mg /dl] plasma urea nitrogen (PUN) concentrations, to determine whether PUN concentrations affect the competence of oocytes to progress to blastocysts after in vitro fertilization. In vitro oocyte and embryo development was assessed by blastocyst rates, embryo total cell numbers and apoptosis. Blood samples for the determination of PUN were collected 24 h prior to collection of the ovaries at the slaughter. A total of 112 ovaries were collected at a local abattoir and oocytes (n = 697) were aspirated, in vitro matured and fertilized. On day 8, blastocysts were assigned to the terminal dUTP nick end labelling assay. Cleavage rates were significantly higher (p < 0.001) for groups 1 and 2 than for group 3 (i.e. 72.5% and 72.2% vs 61.7%, respectively). The proportion of fertilized oocytes that developed into blastocysts was higher (p < 0.05) for group 1 than for group 3 (34.0% vs 23.0%, respectively). Day 8 blastocysts showed higher total cell counts (p < 0.05) for group 1 than for group 3 (123.7 vs 76.3), and a higher (p < 0.05) total apoptotic cell rate was found in group 3 (25.9 and 19.0 vs 43.2 for G1, G2 and G3, respectively). In conclusion, the ability of oocytes from heifers with increased levels of PUN to develop to the blastocyst stage was significantly reduced when standard routines for in vitro maturation, fertilization and culture were followed. These detrimental effects can be mediated in part through direct effect of urea and/or by the metabolic products on the process of follicle-enclosed oocyte nuclear and cytoplasmic development.

Follicle size-dependent changes in follicular fluid components and oocyte diameter in Antarctic minke whales (Balaenoptera bonaerensis)

The concentrations of various components of follicular fluid were compared among three groups of follicles (small, <5 mm; medium: 5-10 mm; large, >10 mm) with a control that consisted of the components of umbilical serum using seven pregnant Antarctic minke whales. Follicular oocytes recovered from the follicles were also used for measurement of oocyte diameter after removing the cumulus cells. The mean diameter of the ooplasm in the oocytes from the large follicles (143.2 microm) was significantly greater than those from the small (127.1 microm) and medium (131.7 microm) follicles, although there were no significant differences in diameter of the whole oocyte and thickness of the zona pellucida among the three follicular sizes. The osmolarity of the follicular fluid from the small follicles (363.3 mOsmol) was significantly lower than that of the medium follicles (388.9 mOsmol) and tended to be lower than that of large (381.9 mOsmol) follicles, respectively, both of which were similar to that of the umbilical serum (379.5 mOsmol). There was no significant difference in the concentrations of all components of the follicular fluid between the medium and large follicles. As compared with the values of the umbilical serum, the total-protein, glucose, albumin and chlorine concentrations of the follicular fluid from the medium and large follicles were significantly higher, and the total cholesterol and calcium concentrations were significantly lower. The concentrations of lactic acid (85.3-136.0 mg/dl) of the follicular fluid from the three groups of follicles were significantly lower than that of the umbilical serum (360.0 mg/dl). Among the follicles, the follicular fluid from the small follicles (136.0 mg/dl) contained a significantly higher concentration of lactic acid than that from the large follicles (85.3 mg/dl). The progesterone concentrations were not significantly different among the fluid from the three group of follicles and the umbilical serum: however, the estradiol 17-beta concentrations of the follicular fluid increased with the size of the follicle (14.3 and 34.6 ng/ml for small and large follicles, respectively). These results offer new information concerning whale reproductive physiology, especially for improvement of in vitro oocyte maturation and related technologies in whales.

Evaluation of oocyte quality: morphological, cellular and molecular predictors

Mounting evidence that oocyte quality profoundly affects fertilisation an d subsequent embryo development drives the continued search for reliable predictors of oocyte developmental competence. In the present review, we provide an overall summary and analysis of potential criteria that can be used to evaluate oocyte quality. These criteria are specifically classified as morphological and cellular/molecular predictors. Traditional methods for the evaluation of oocyte quality are based on morphological classification of thefollicle, cumulus-oocytecomplex, polar body and/or meiotic spindle. Although the use of morphological characteristics as predictors of oocyte quality is controversial, such a grading system can provide valuable information for the preselection of oocytes with higher developmental competence and, therefore, may maximise embryo developmental outcome. Several intrinsic markers (such as mitochondrial status and glucose-6-phosphate dehydrogenase 1 activity) and extrinsic markers (such as apoptosis of follicular cells and levels of the transforming growth factor-beta superfamily in follicular fluid or serum) have also been reported as useful indicators of oocyte competence and embryo quality. Compared with the morphological parameters, these cellular and molecular predictors of oocyte quality may prove to be more precise and objective, although further studies and refinement of techniques are needed.

Biochemical composition of ovine follicular fluid in relation to follicle size

The aim of this study was to biochemically characterize ovine follicular fluid and to relate possible changes in composition to follicular size. Ovaries were collected from adult and cycling non-pregnant slaughtered sheep (Ovis aries) during breeding season. A total of 104 pairs of ovaries were investigated and these data were then compared. Follicular fluid was aspirated from small (< 2 mm), medium (2-4 mm) and large (> 4 mm) nonatretic ovarian follicles. The follicular fluid was centrifuged at 4 degrees C and 5000 g for 30 min to remove any cells and stored at -80 degrees C prior to assay. Follicular fluid samples were analyzed for glucose, total protein, cholesterol, triglycerides, lactate, urea, creatinine, sodium, potassium, chloride, calcium, phosphorus, magnesium, acid phosphatase, alkaline phosphatase, and lactate dehydrogenase. Data were analyzed by the linear regression model. As follicles became larger, the concentrations of glucose and cholesterol significantly (P < 0.05) increased while those of triglycerides, lactate, alkaline phosphatase and lactate dehydrogenase significantly (P < 0.05) decreased.

Effect of Modification of Ovary Preservation Solution by Adding Glucose on the Maturation and Development of Pig Oocytes after Prolonged Storage

Oocytes lose their developmental competence during prolonged storage of the ovary. In the present study, we supplemented the preservation solution for pig ovaries (phosphate buffered saline, PBS) with glucose and preserved the ovaries for 6 h at 25 C. Subsequently, we examined the glucose concentration of the follicular fluid (FF), pH of the FF, survival rate of the granulosa cells, and maturation and developmental competence of oocytes after storage. During storage, the glucose concentration of the FF (2.1 mM), pH of the FF (7.4), and survival rate of the granulosa cells (69.5%) rapidly decreased (glucose concentration: under 1.1 mM; pH: 6.8; and survival rate: 43%). On the other hand, when the preservation solution was supplemented with glucose (15 mM), the glucose concentration of the FF increased and the survival rate of the granulosa cells improved, although the pH of the FF decreased further (from 6.8 to 6.6). In addition, supplementation with glucose significantly improved the rates of oocytes at metaphase II (0 h: 65.0%; 6 h without glucose: 23.8%; and 6 h with glucose: 43.8%) and attenuated the decline in the rates of fertilization and development that resulted from prolonged storage, although there were no significant differences. In conclusion, modification of the preservation solution by the addition of glucose increased the glucose concentration of the FF and improved the rate of maturation of pig oocytes.