Intra-ovarian regulation of follicular development and oocyte competence in farm animals

Effect of recombinant bovine somatotropin on the reproductive efficiency of beef cows subjected to differently timed-artificial insemination protocols

This study aimed to verify the reproductive efficiency of beef cows treated with recombinant bovine somatotropin (rbST). Study 1, Bos indicus cows were distributed (three groups). The control group (CG) was subjected: on day zero (d0), the animals received a CIDR and oestradiol benzoate (EB); on (d8, CIDR was removed, and PGF2α and oestradiol cypionate (EC) were administered; on d10, timed Artificial Insemination (TAI) was performed; on d45, pregnancy diagnosis was made. The rbST on d0 group (bST0G) was subjected to an identical protocol as CG, except for the addition of 250 mg rbST on d0. The rbST on d8 group (bST8G) was subjected to the same protocol as bST0G, except that the rbST was administered on d8 rather. In study 2, the animals followed the same design which was used in Bos taurus cows. The follicular growth rate (FGR) was calculated between d8 and d10. In study 1, pregnancy/artificial insemination (P/AI) did not differ among the treatments. FGR in bST8G was higher than in other groups. In study 2, bST0G showed higher Pregnancy/Artificial Insemination (P/AI) (p < .05) when compared with other groups. bST0G showed a different FGR (p < .0001) than the other groups. In conclusion, rbST (Bos indicus cows) did not increase P/AI, but it did promote follicular growth when administered on d8; the rbST administered on d0 improved P/AI (p < .05) and the FGR in Bos taurus cows.

Ovarian activation delays in peripubertal ewe lambs infected with Haemonchus contortus can be avoided by supplementing protein in their diets

BACKGROUND

The ewe lamb nutritional and physiological state interfere with the ovarian environment and fertility. The lack or excess of circulating nutrients reaching the ovary can change its gene expression. A protein deficiency in the blood caused by an Haemonchus contortus abomasal infection is detrimental to the organism's development during puberty. The peripubertal period is a time of intensive growth that requires a high level of nutrients. An essential feature controlling pubertal arousal and female reproductive potential is ovarian follicle growth activation. Protein supplementation improves the sheep's immune response to helminthic infections. We aimed to determine if supplementing protein in infected ewe lambs' diet would impact the ovarian environment leading to earlier ovarian follicle activation than in infected not supplemented animals.

METHODS

We fed 18 Santa Ines ewe lambs (Ovis aries) - bred by the same ram - with either 12% protein (Control groups) or 19% protein (Supplemented groups) in their diets. After 35 days of the diet, they were each artificially infected or not with 10,000 Haemonchus contortus L3 larvae. Following 77 days of the diet and 42 days of infection, we surgically collected their left ovaries and examined their genes expression through RNA sequencing.

RESULTS

We found that protein supplementation in infected animals led to an up-regulation of genes (FDR p-values < 0.05) and biological processes (p-value cut-off = 0.01) linked to meiotic activation in pre-ovulatory follicles and primordial follicle activation, among others. The supplemented not infected animals also up-regulated genes and processes linked to meiosis and others, such as circadian behaviour. The not supplemented animals had these same processes down-regulated while up-regulated processes related to tissue morphogenesis, inflammation and immune response.

CONCLUSION

Diet's protein supplementation of peripubertal infected animals allowed them to express genes related to a more mature ovarian follicle stage than their half-sisters that were not supplemented. These results could be modelling potential effects of the interaction between environmental factors, nutrition and infection on reproductive health. When ovarian activation is achieved in a timely fashion, the ewe may generate more lambs during its reproductive life, increasing sheep breeders' productivity.

Association between Anti-Müllerian Hormone Concentration and Inflammation Markers in Serum during the Peripartum Period in Dairy Cows

The relationships between changes in anti-Müllerian hormone (AMH) concentration and various traits, including milk somatic cell counts (SCC), were evaluated. Blood samples were collected from 43 Holstein cows 14 days before (D-14) and 10 (D10) and 28 days after (D28) parturition, and vaginal discharge score (VDS) and polymorphonuclear leukocyte (PMNL) percentages were assessed in endometrial samples at D28. Cows were separated into four quartiles (Q1-Q4) based on changes in AMH concentration during the peripartum period (AMH ratio: D28/D-14). Correlations between AMH ratio and each parameter were evaluated and classified into high-AMH (Q4, 1.83 ± 0.12, n = 11) and low-AMH (Q1, 0.83 ± 0.05, n = 11) groups. The AMH ratio was positively correlated with magnesium and non-esterified fatty acids levels, and the albumin/globulin ratio at D10 and D28, but negatively correlated with serum amyloid A (SAA) at D10. SAA and γ-globulin levels were significantly higher in the low-AMH group at D28. There was no significant difference in VDS, PMNL percentage, and milk SCC between the two groups. The decreasing AMH ratio from the prepartum to the postpartum period corresponds to high inflammation biomarker levels. Whether it subsequently affects the reproductive prognosis of postpartum cows needs further investigations.

Association among lipopolysaccharide, the transforming growth factor-beta superfamily, follicular growth, and transcription factors in spontaneous bovine ovarian cysts

The aim of this study was to investigate some of the growth and transcriptional factors originating from oocytes and granulosa cells in follicular fluid and to identify the relationships between the basic blood metabolite-metabolic hormones and intrafollicular lipopolysaccharide (LPS) concentrations. Thirty cows included in the study were allocated into 2 groups comprising 15 cows with healthy preovulatory follicles (cyclic cows) and 15 cows with confirmed cystic follicles. The ovaries and uteri of all cows were assessed by transrectal ultrasonographic examination. Blood serum samples were collected at 15, 25, 35, 45, and 55 d after calving for analysis of nonesterified fatty acids, β-hydroxybutyrate, insulin, glucose, IGF-I, ACTH, and cortisol. Ovaries and uteri were examined using transrectal ultrasound. Vaginal discharge was evaluated on the same days. Follicular fluid was also aspirated on days 35-55 from the healthy preovulatory follicles and cystic follicles using a transvaginal ovum pickup method. The densitometric levels of inhibin-α, growth and differentiation factor (GDF-9), bone morphogenetic protein (BMP-6), and GATA-4 and GATA-6 proteins were analyzed by the Western blotting technique; the concentrations of antimullerian hormone (AMH), IGF-I, estradiol-17 beta (E2), and progesterone (P4) were determined by ELISA; and the concentrations of LPS in the follicular fluid were measured by the Limulus amebocyte lysate test. The serum insulin, ACTH, and cortisol concentrations were higher in cystic cows than cyclic cows, but serum IGF-I concentrations were lower in cystic cows. The IGF-I concentrations of cystic follicular fluids were lower, whereas AMH levels were significantly greater than those of healthy preovulatory follicular fluids. The cystic follicles had significantly lower expression levels of GDF-9, BMP-6, GATA-4, and GATA-6; in contrast, inhibin-α expression and LPS concentrations were significantly higher than in healthy preovulatory follicles. The proportion of pathologic vaginal discharge within 25 d postpartum in cystic cows were higher than in the cyclic group. In conclusion, it is suggested that intrafollicular dysregulation of the transforming growth factor-β superfamily, growth, and transcriptional factors is affected by high intrafollicular LPS concentrations and systemic metabolic changes and these disturbances may be responsible for the generation of ovarian cysts.

n-3 PUFA Sources (Precursor/Products): A Review of Current Knowledge on Rabbit

This review compares the effects of different n-3 polyunsaturated fatty acid (PUFA) sources on biological activity, physiological/reproductive endpoints, and health implications with a special emphasis on a rabbit case study. Linoleic acid (LA) and α-linolenic acid (ALA) are members of two classes of PUFAs, namely the n-6 and n-3 series, which are required for normal human health. Both are considered precursors of a cascade of molecules (eicosanoids), which take part in many biological processes (inflammation, vasoconstriction/vasodilation, thromboregulation, etc.). However, their biological functions are opposite and are mainly related to the form (precursor or long-chain products) in which they were administered and to the enzyme-substrate preference. ALA is widely present in common vegetable oils and foods, marine algae, and natural herbs, whereas its long-chain PUFA derivatives are available mainly in fish and animal product origins. Recent studies have shown that the accumulation of n-3 PUFAs seems mostly to be tissue-dependent and acts in a tissue-selective manner. Furthermore, dietary n-3 PUFAs widely affect the lipid oxidation susceptibility of all tissues. In conclusion, sustainable sources of n-3 PUFAs are limited and exert a different effect about (1) the form in which they are administered, precursor or derivatives; (2) their antioxidant protections; and (3) the purpose to be achieved (health improvement, physiological and reproductive traits, metabolic pathways, etc.).

Bone morphogenetic protein 6 expression in cumulus cells is negatively associated with oocyte maturation

Bone morphogenetic protein 6 (BMP6) is a regulatory peptide secreted by oocytes and granulosa cells that locally regulates folliculogenesis and follicular development. To determine BMP6 location, we studied BMP6 expression in human follicles using immunohistochemistry, real-time polymerase chain reaction (RT-PCR) and western blot analysis. RT-PCR was performed on 354 individual cumulus cell (CC) masses from 48 women to investigate the relationship between BMP6 mRNA expression in CCs and oocyte developmental potential. Results showed that BMP6 protein was mainly located in oocytes from preantral follicles and in granulosa cells from antral follicles. BMP6 mRNA expression was much higher in oocytes than in CCs and mural granulosa cells (mGCs) from preovulatory follicles (p < 0.01), and BMP6 protein level was higher in CCs than in mGCs (p < 0.05). BMP6 mRNA expression was higher in CCs from immature oocytes than in those from mature oocytes (p < 0.05). However, BMP6 mRNA expression in CCs was not associated with oocyte fertilization, embryo morphological grading, or implantation. In conclusion, BMP6 was mainly expressed in oocytes at all human follicular developmental stages and BMP6 mRNA expression in CCs may be negatively correlated with oocyte maturation. BMP6 expression could therefore be used as a biomarker of oocyte maturation.

Evaluation of high nutrient diets and additional dextrose on reproductive performance and litter performance of heat-stressed lactating sows

This study investigated the litter performance of lactating sows fed nutrient-dense diets with or without dextrose at farrowing to weaning, during the summer with an average room temperature of 28.4°C. A total of 60 (13 first parity, 13 second parity, 19 third parity, and 15 forth parity) cross-bred sows were assigned to three treatments. The three treatments were: standard diet (ST), high nutrient diet (HN; ST + 3% higher energy and 18.0% protein), and high nutrient diet plus dextrose (HND; 3% higher energy, 18.0% protein, and 5% dextrose). BW loss was reduced in the HND sows compared with the ST sows during lactation. The HN and HND sows had a higher piglet and litter weight at weaning. Also, the HND sows had the highest post-prandial insulin levels at weaning and the shortest weaning-to-service interval (WSI). Serum LH was higher in the HND sows than the ST sows. The milk fat level was higher in the HND sows compared with the ST sows, but similar to the HN sows. In conclusion, these results suggest that it is possible to increase the blood insulin response by supplementing dextrose to a high nutrient diet, thus, improving WSI interval and litter growth during heat stress.

Angiopoietin expression in ovine corpora lutea during the luteal phase: Effects of nutrition, arginine and follicle stimulating hormone

The aim of this study was to evaluate angiopoietin (ANGPT) 1 and 2, and tyrosine-protein kinase receptor 2 (TIE2) expression in the corpora lutea (CL) of FSH-treated, or non-treated sheep administered arginine (Arg) or vehicle (saline, Sal), and fed a control (C), excess (O) or restricted (U) diet. Ewes from each dietary group were treated with Arg or Sal (experiment 1), and with FSH (experiment 2). Luteal tissues were collected at the early-, mid- and/or late-luteal phases of the estrous cycle. Protein and mRNA expression was determined using immunohistochemistry followed by image analysis, and quantitative RT-PCR, respectively. The results demonstrated that ANGPT1 and TIE2 proteins were localized to luteal capillaries and endothelial cells of larger blood vessels, and ANGPT2 was localized to tunica media of larger blood vessels. TIE2 protein was also present in luteal cells. In experiment 1, ANGPT1 protein expression was greater in O than C during early- and mid-luteal phases, and was greatest during late-luteal phase, less at the mid- and least at the early-luteal phase; 2) TIE2 protein expression was greatest at the mid-, less at the early- and least at the late-luteal phase; 3) ANGPT1 and 2 mRNA expression was greater at the mid- and late- than the early-luteal phase, and TIE2 mRNA expression was greatest at the late-, less at the mid- and least at the early-luteal phase. The ANGPT1/2 ratio was less at the early- than mid- or late-luteal phases. In experiment 2, ANGPT1 protein expression was greater in O during the mid-luteal phase than in other groups, and was greater at the mid- than early-luteal phase. TIE2 protein expression was highest at the mid-, less at the early- and least during the late-luteal phase. ANGPT1 and 2, and TIE2 mRNA expression was higher at the mid- than the early-luteal phase. During mid-luteal phase, ANGPT1 mRNA expression was greater in C than O and U, ANGPT2 was greatest in C, less in O and least in U, and TIE2 mRNA expression was greater in C than O and U. The ANGPT1/2 ratio was higher in U than in any other group. Comparison of FSH vs. Sal treatment effects (experiment 2 vs. experiment 1) demonstrated that FSH affected ANGPT1 and/or -2, and TIE2 protein and mRNA expression depending on luteal phase and/or diet. Thus, expression of ANGPTs and TIE2 in the CL changes during the luteal lifespan, indicating their involvement in luteal vascular formation, stabilization and degradation. Moreover, this study has demonstrated that plane of nutrition and/or FSH treatment affect the ANGPT system, and may alter luteal vascularity and luteal function in sheep.

Luteal function during the estrous cycle in arginine-treated ewes fed different planes of nutrition

Functions of corpus luteum (CL) are influenced by numerous factors including hormones, growth and angiogenic factors, nutritional plane and dietary supplements such as arginine (Arg), a semi-essential amino acid and precursor for proteins, polyamines and nitric oxide (NO). The aim of this study was to determine if Arg supplementation to ewes fed different planes of nutrition influences: (1) progesterone (P4) concentrations in serum and luteal tissue, (2) luteal vascularity, cell proliferation, endothelial NO synthase (eNOS) and receptor (R) soluble guanylate cyclase β protein and mRNA expression and (3) luteal mRNA expression for selected angiogenic factors during the estrous cycle. Ewes (n = 111) were categorized by weight and randomly assigned to one of three nutritional planes: maintenance control (C), overfed (2× C) and underfed (0.6× C) beginning 60 days prior to onset of estrus. After estrus synchronization, ewes from each nutritional plane were assigned randomly to one of two treatments: Arg or saline. Serum and CL were collected at the early, mid and late luteal phases. The results demonstrated that: (1) nutritional plane affected ovulation rates, luteal vascularity, cell proliferation andNOS3,GUCY1B3, vascular endothelial growth factor (VEGF) andVEGFR2mRNA expression, (2) Arg affected luteal vascularity, cell proliferation andNOS3,GUCY1B3,VEGFandVEGFR2mRNA expression and (3) luteal vascularity, cell proliferation and the VEGF and NO systems depend on the stage of the estrous cycle. These data indicate that plane of nutrition and/or Arg supplementation can alter vascularization and expression of selected angiogenic factors in luteal tissue during the estrous cycle in sheep.

Bovine in vitro embryo production: the effects of fibroblast growth factor 10 (FGF10)

PURPOSE

In an attempt to improve in vitro embryo production, we investigated the effect of fibroblast growth factor 10 (FGF10) during in vitro maturation on the developmental capacity of bovine oocytes.

MATERIAL AND METHODS

Cumulus-oocyte complexes (COCs) were aspirated from follicles of 3-8 mm diameter. After selection, the COCs were matured in medium with or without 0.5 ng/mL of FGF10. The effect of FGF10 during in vitro maturation (IVM) on nuclear maturation kinetics and expansion of the cumulus cells was investigated. Oocyte competence was assessed by the production and development speed of embryos and the relative expression of genes associated with embryo quality.

RESULTS

FGF10 delayed the resumption of meiosis from 8 h onwards, but did not affect the percentage of oocytes reaching metaphase II, nor did it increase cumulus expansion at 22 h of maturation. We found no difference between treatments regarding embryo production, developmental speed, and gene expression.

CONCLUSION

In conclusion, the presence of FGF10 during IVM had no effect on embryo production, developmental speed, and gene expression.

Expression of genes involved in progesterone receptor paracrine signaling and their effect on litter size in pigs

Background

Embryonic mortality during the period of implantation strongly affects litter size in pigs. Progesterone receptor (PGR) paracrine signaling has been recognized to play a significant role in embryonic implantation. IHH, NR2F2, BMP2, FKBP4 and HAND2 were proved to involve in PGR paracrine signaling. The objective of this study was to evaluate the expression of IHH, NR2F2, BMP2, FKBP4 and HAND2 in endometrium of pregnant sows and to further investigate these genes’ effect on litter size in pigs. Real-time PCR, western blot and immunostaining were used to study target genes/proteins expression in endometrium in pigs. RFLP-PCR was used to detect single nucleotide polymorphisms (SNPs) of target genes.

Results

The results showed that the mRNA and protein expression levels of IHH, NR2F2 and BMP2 were up-regulated during implantation period (P < 0.05 or P < 0.01). All target proteins were mainly observed in luminal epithelium and glandular epithelium. Interestingly, the staining of NR2F2 and HAND2 was also strong in stroma. SNPs detection revealed that there was a -204C > A mutation in promoter region of NR2F2 gene. Three genotypes were found in Large White, Landrace and Duroc sows. A total of 1847 litter records from 625 sows genotyped at NR2F2 gene were used to analyze the total number born (TNB) and number born alive (NBA). The study of the effect on litter size suggested that sows with genotype CC tend to have higher litter size.

Conclusions

These results showed the expression patterns of genes/proteins involved in PGR paracrine signaling over implantation time. And the candidate gene for litter size was identified from genes involved in this signaling. This study could be a resource for further studies to identify the roles of these genes for embryonic implantation in pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-016-0090-z) contains supplementary material, which is available to authorized users.

Regimen of ovarian stimulation affects oocyte and therefore embryo quality

Without any doubt the regimen used to mature multiple capable oocytes for IVF impacts IVF outcomes. Studies have indicated that the inclusion of LH activity, adjuvant agents such as growth hormone (GH), and regimens providing for simultaneous action of both LH and FSH during final oocyte maturation may have beneficial effects on IVF outcomes. Because of the difficulty in improving IVF outcomes in poor responders, the studies on GH are of particular interest. As pointed out in this review, the apparent beneficial effects of GH on oocyte competence may also apply to older women or to normal responders with reduced embryo quality. A much more difficult question is whether and how much ovarian stimulation impacts on oocyte competence. Paradoxically it seems that there are not demonstrated differences between the stimulated and the natural unstimulated cycle, whereas studies in laboratory animals and IVF patients have shown deleterious effects of higher compared with lower doses of gonadotropins. Recent studies suggest that the use of high doses of gonadotropins as an independent factor correlates negatively with the probability of live birth, whereas a high ovarian response per se is associated with better cumulative pregnancy rates, owing to the availability of more euploid and good-quality embryos. Although adjunctive use of androgens has not been discussed here, it is briefly covered in the first review of this series.

Characterization of transforming growth factor beta superfamily, growth factors, transcriptional factors, and lipopolysaccharide in bovine cystic ovarian follicles

The process of transformation of growing bovine follicles into cysts is still a mystery. Local expression of proteins or factors, including transforming growth factor β, growth factors, and transcription factors, plays a central role in mammals. Therefore, in abattoir-derived cystic ovarian follicles and follicular fluid, the role of some transforming growth factor β superfamily proteins, insulinlike growth factor-1 (IGF-1) and GATA-4 and GATA-6, were investigated. The relationship between intrafollicular lipopolysaccharide (LPS) and etiopathogenesis of ovarian cysts was also assessed. Data on the preovulatory follicle and the largest follicle (F1) were compared. The number of intrafollicular LPS-positive samples and LPS concentrations were higher in cysts. Immunohistochemical staining was mildly positive for IGF-1, inhibin alpha, and GATA-4 in thecal cells. Staining for anti-Müllerian hormone (AMH), growth differentiation factor-9, bone morphogenetic protein-6 (BMP-6), and GATA-6 was insufficient for their quantitation, and oocytes could not be stained for any of the proteins tested in the cystic follicles. Expression of BMP-6, inhibin alpha, and IGF-1 was moderately higher in granulosa cells of F1 follicles, and all the proteins were moderately expressed in granulosa cells in preovulatory follicles. However, loss of GATA-6 staining was significant in F1 follicles. Intrafollicular progesterone, IGF-1, and AMH concentrations in cysts and F1 follicles were significantly higher than those in preovulatory follicles. Western blot analyses revealed that follicular fluid inhibin-α was strongly expressed, whereas expression of growth differentiation factor-9, BMP-6, GATA-4 and GATA-6 was lower in cysts than in preovulatory follicles. Also, high intrafollicular AMH concentration and low BMP-6 expression were closely associated with cystic degeneration and atresia. In conclusion, immunohistochemical loss of BMP-6 and GATA-6 in the granulosa cells together with high intrafollicular LPS levels may play important roles in disruption of the ovulatory mechanism and steroidogenic reactions in type 2 cyst. Also, high intrafollicular AMH concentration along with low BMP-6 expression may be used as indicators of the bovine degenarative ovarian follicles.

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Follicular dynamics and gene expression in granulosa cells, corpora lutea and oocytes from gilts of breeds with low and high ovulation rates

Follicular dynamics and the expression of candidate genes using real-time polymerase chain reaction (PCR) were compared during the oestrous cycle of pig breeds with high (commercial line; n = 24) and low (local Brazilian Piau; n = 21) ovulation rates and prolificacy. Gilts were killed on Days 0, 4, 10 and 18 of the oestrous cycle and visible ovarian follicles were classified by follicular diameter. Recovered cumulus–oocyte complexes were classified as normal or atretic and frozen in liquid nitrogen until RNA extraction. Low ovulation rates and/or prolificacy in Piau gilts was associated with a different pattern of follicle development, with lower numbers of small follicles on Day 18, fewer large follicles on Days 0 and 18 (P ≤ 0.05) and a higher proportion of atretic follicles on Days 0 and 18 (P ≤ 0.05). Compared with commercial line gilts, less-prolific Piau gilts exhibited higher expression of apoptotic genes during luteolysis (CASP3 and FASL; P ≤ 0.05), decreased expression of TGFBR2 and BAX mRNA in the corpus luteum (P ≤ 0.05), higher expression of apoptotic genes (FAS, BCL2 and CASP8; P ≤ 0.05) in granulosa cells and a greater abundance (P ≤ 0.05) of genes controlling oocyte-secreted factors (GDF9, BMP15 and BMP6), suggesting underlying mechanisms controlling differences in follicular development, ovulation rate and inherent prolificacy in this pig breed.

Ontogeny of the ovary in polycystic ovary syndrome

Activation of primordial follicles into the growing pool, selection of the dominant follicle, and its eventual ovulation require complex endocrine and metabolic interactions as well as intraovarian paracrine signals to coordinate granulosa cell proliferation, theca cell differentiation, and oocyte maturation. Early preantral follicle development relies mostly upon mesenchymal-epithelial cell interactions, intraovarian paracrine signals, and oocyte-secreted factors, whereas development of the antral follicle depends on circulating gonadotropins as well as locally derived regulators. In women with polycystic ovary syndrome (PCOS), ovarian hyperandrogenism, hyperinsulinemia from insulin resistance, and altered intrafollicular paracrine signaling perturb the activation, survival, growth, and selection of follicles, causing accumulation of small antral follicles within the periphery of the ovary, giving it a polycystic morphology. Altered adipocyte-ovarian interactions further compound these adverse events on follicle development and also can harm the oocyte, particularly in the presence of increased adiposity. Finally, endocrine antecedents of PCOS occur in female infants born to mothers with PCOS, which suggests that interactions between genes and the maternal-fetal hormonal environment may program ovarian function after birth.

Nutritional influences on folliculogenesis

Folliculogenesis is an intricate process that involves the proliferation and differentiation of both somatic and germ cells. This process depends on complex interactions between systemic factors such as both pituitary gonadotrophins and metabolic hormones and/or local factors produced by the ovarian somatic and germ cells, such as the IGF system and TGF-β superfamily members. In domestic ruminants, follicular development begins during foetal life with formation of primordial follicles from the association of germ cells and pre-granulosa cells. After follicular formation, folliculogenesis begins with a primordial follicle progressing into more developed stages (i.e. primary, secondary, pre-antral and antral) in a continuous, progressive process to either ovulation or, as in most cases, to atresia. Even early stages of follicular formation and subsequent development are influenced by both internal (e.g. genotype) and/or external environmental (e.g. nutrition and season) factors. Among these external factors, nutrition is one of the most important affecting reproductive function, and this is the focus of this review, because other reviews in this issue discuss other environmental factors. A number of studies have now shown that nutrition can have both positive and negative effects on follicular growth, oestrous activity, oocyte quality, blastocyst development and pregnancy outcome. Therefore, understanding the intricate processes involved during folliculogenesis and the ways in which factors, such as nutrition, affect them is leading to new opportunities to improve pregnancy rates by influencing follicle development and oocyte quality. This review will focus on follicular development from foetal to adult stages and the influences that nutrition has during some of these developmental stages.

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.

A mathematical model of the bovine oestrous cycle: simulating outcomes of dietary and pharmacological interventions

A mathematical model was constructed to simulate the bovine oestrous cycle by using nonlinear differential equations to describe the biological mechanisms which regulate the cycle. The model predicts circulating concentrations of gonadotrophin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, oestradiol, inhibin and progesterone. These hormones collectively provide control and feedback mechanisms between the hypothalamus, pituitary gland and ovaries, which regulate ovarian follicular dynamics, corpus luteum function and ovulation. When follicular growth parameters are altered, the model predicts that cows will exhibit either two or three follicular waves per cycle, as seen in practice. Changes in other parameters allow the model to simulate: effects of nutrition on follicle recruitment and size of the ovulatory follicle; effects of negative energy balance on postpartum anoestrus; and effects of pharmacological intervention on hormone profiles and timing of ovulation. It is concluded that this model provides a sound basis for exploring factors that influence the bovine oestrous cycle in order to test hypotheses about nutritional and hormonal influences which, with further validation, should help to design dietary or pharmacological strategies for improving reproductive performance in cattle.

Integration of physiological mechanisms that influence fertility in dairy cows

Fertility in dairy cows has been declining for the past three decades. Genetic selection for increased milk production has been associated with changes in key metabolic hormones (growth hormone, insulin, IGF and leptin) that regulate metabolism by homoeostasis and homeorhesis. These metabolic hormones, particularly insulin, provide signals to the reproductive system so that regulation of ovarian function is coordinated with changes in metabolic status. Studies have shown, for example, that increasing circulating insulin concentrations during the early post partum period can advance the resumption of oestrous cycles by enhancing follicular growth. However, high concentrations of insulin can be detrimental to the developmental competence of oocytes, which is also influenced by the supply of fatty acids at the systemic level and at the ovarian level. Insulin status is also associated with the incidence and characteristics of abnormal ovarian cycles. These changes can occur without significant variation in circulating gonadotrophin concentrations. This suggests that additional factors, such as peripheral metabolites, metabolic hormones and locally produced growth factors, may have a modulating role. Recent evidence has demonstrated that ovarian responses to metabolic signals and nutrient profile vary according to the stage of the reproductive cycle. Improved understanding of this multifactorial process enables nutrition to be matched to genotype and milk production, with a positive impact on pregnancy rate.

Feed restriction as a biostimulant of the production of oocyte, their quality and GDF-9 gene expression in rabbit oocytes

The use of short-term feed restriction (R) without or with subsequent refeeding (F) as biostimulant of rabbit fertility was examined in this study. A total of 40 mature, non-pregnant, non-lactating New Zealand white female rabbits were allocated to five treatments. The rabbits were individually caged and fed a complete pelleted diet (16.7% CP; 13.1 CF; 2490kcalDE/kg). Rabbits on the control (C) treatment received 150g/d of the diet. Two groups of 8 rabbits received 70% of the control daily feed intake (105g/d; moderate restriction; M) and the other two groups received 50% of the control feed intake (75g/d; severe restriction; S) for 21d. At the end of this period, one group each of M and S fed rabbits were slaughtered for oocyte recovery. Rabbits in the remaining three groups (C, MF and SF) were retained for a further 8d before slaughter and fed the control level of the diet during this period. The effects on body weight, oocyte number and quality, GDF-9 gene expression in oocytes, and changes in serum levels of leptin and IGF-1 were recorded. Initial mean body weights were not significantly different ranging from 2.50±0.33kg (S) to 2.58±0.24kg (C). After 3wk on treatment the C rabbits were significantly heavier (2.65±0.32kg; P<0.05) than rabbits on the M (2.26±0.33kg) or S (2.10±0.33kg) treatments. Following 8d of refeeding, the remaining group of S treated rabbits (SF) were still significantly lighter (2.40±0.21kg; P<0.05) than C (2.71±0.31kg) with MF rabbits having an intermediate weight (2.50±0.20kg). The number of mature grade A oocytes recovered per ovary was significantly lower for control (3.3±0.35) than the refed treatments (MF 4.0±0.30; SF 4.5±0.39; P<0.05). Semi-quantitative PCR analysis of GDF-9 expression showed that control mature grade A oocytes had significantly lower levels of expression (1.27±0.20; P<0.05) than those of refed rabbits (MF 1.60±0.10; SF 1.39±0.01). Leptin and IGF-1 values for refed rabbits were significantly higher (P<0.05) than at the end of feed restriction and the start point. It was concluded that this biostimulant method has the potential to improve the fertility of rabbits.

Follicular growth and atresia in mammalian ovaries: regulation by survival and death of granulosa cells

The mammalian ovary is an extremely dynamic organ in which a large majority of follicles are effectively eliminated throughout their reproductive life. Due to the numerous efforts of researchers, mechanisms regulating follicular growth and atresia in mammalian ovaries have been clarified, not only their systemic regulation by hormones (gonadotropins) but also their intraovarian regulation by gonadal steroids, growth factors, cytokines and intracellular proteins. Granulosa cells in particular have been demonstrated to play a major role in deciding the fate of follicles, serving molecules that are essential for follicular growth and maintenance as well as killing themselves by an apoptotic process that results in follicular atresia. In this review, we discuss the factors that govern follicular growth and atresia, with a special focus on their regulation by granulosa cells. First, ovarian folliculogenesis in adult life is outlined. Then, we explain about the regulation of follicular growth and atresia by granulosa cells, in which hormones, growth factors and cytokines, death ligand-receptor system and B cell lymphoma/leukemia 2 (BCL2) family members (mitochondria-mediated apoptosis) are further discussed.

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.

Regulation of inducible nitric oxide synthase expression in bovine ovarian granulosa cells

Nitric oxide (NO) is a potential regulator of ovarian follicle growth, and ovarian granulosa cells reportedly generate NO in response to gonadotrophins, suggesting that the regulated form of nitric oxide synthase (iNOS) is present. The objectives of the present study were to gain insight into the expression and role of iNOS in the follicle. Messenger RNA encoding iNOS was detected in granulosa cells, and abundance was higher in growing dominant follicles compared to subordinate follicles (P<0.01). FSH (P<0.05) and IGF1 (P<0.01) stimulated oestradiol secretion and iNOS mRNA abundance in granulosa cells in vitro, whereas FGF2 (P<0.05) and EGF (P<0.01) decreased oestradiol secretion and iNOS expression. The addition of an anti-oestrogen prevented FSH-induced iNOS mRNA accumulation. Inhibition of endogenous NO production did not affect steroidogenesis in granulosa cells, but increased FasL mRNA abundance, caspase-3 activation and the incidence of apoptotic cell death (P<0.05). These results demonstrate that iNOS is expressed in ruminant granulosa cells and is regulated by gonadotrophins and oestradiol. Physiological levels of NO may contribute to the survival of granulosa cells.

In vitro effects of relaxin on gene expression in porcine cumulus-oocyte complexes and developing embryos

BACKGROUND

Relaxin hormone peptide is found in porcine follicular and utero-tubal fluids, but its possible actions during early embryo development are still undetermined. Here, we investigated the effects of porcine relaxin during oocyte maturation and embryo development, and gene expression in the pig.

METHODS

Immature cumulus-oocyte complexes (COCs) were obtained from ovarian follicles of sows. In experiment 1, COCs were matured in the presence of 0, 20, or 40 ng relaxin/ml, or 10% (v/v) porcine follicular fluid. In experiment 2, COCs were in vitro matured, fertilized and resulting embryos were cultured in the presence of 0, 20, or 40 ng relaxin/ml. In experiment 3, COCs were matured in the presence of 40 ng relaxin/ml, fertilized and zygotes were cultured as indicated in experiment 2. We evaluated the proportions of matured oocytes in experiment 1, cleaved and blastocysts on Day 2 and Day 7 post insemination in all experiments. The total cell number of blastocysts was also evaluated. In parallel, transcription levels of both relaxin and its receptors (RXFP1 and RXFP2), as well as a pro- (Bax) and anti- (Bcl2-like 1) apoptotic-related genes were determined. All data were analyzed by ANOVA and significant differences were fixed for P < 0.05.

RESULTS

In experiment 1, relaxin significantly increased the proportions of matured oocytes and cleaved embryos, as well as the expression level of RXFP2 mRNA compared to RXFP1 (P < 0.05). There was no effect on endogenous expression of relaxin and Bcl2-like1/Bax ratios. In all experiments, relaxin did not affect the proportions of blastocysts, but did significantly increase their total cell numbers (P < 0.05). Furthermore, no effect of relaxin was observed on Bcl2-like1/Bax expression ratios, which were similar between groups.

CONCLUSIONS

Exogenous relaxin influences its own receptors expression, improves oocyte nuclear maturation. Its beneficial effect on total cell number of blastocysts appears to be through a Bcl2-like1/Bax-independent mechanism.

Follicular somatic cell factors and follicle development

Considerable attention is currently paid to oocyte-derived secreted factors that act upon cumulus and granulosa cells. Also important for follicle development are somatic cell-derived secreted factors. This is illustrated by the ability of granulosa cell-derived Kit ligand (KITL) to promote primordial follicle activation, and the loss of follicle development that accompanies KITL gene disruption. This review summarises our current understanding of somatic cell factors during both preantral and antral follicle growth, involving not only signalling from granulosa cells to the oocyte, but also signalling between granulosa and theca cells. Principal granulosa cell-derived factors include activin, anti-Müllerian hormone (AMH), bone morphogenetic proteins (BMPs) and fibroblast growth factors (FGFs). Theca cells also secrete BMPs and FGFs. The interplay between these factors is equally important for follicle growth as the activity of oocyte-derived factors.

Real-time qRT-PCR analysis of EGF receptor in cumulus-oocyte complexes recovered by laparoscopy in hormonally treated goats

Ovarian stimulation with exogenous follicle stimulating hormone (FSH) has been used to increase the number of viable oocytes for laparoscopic oocyte recovery (LOR) in goats. The aim of this study was to evaluate the effect of two FSH protocols for ovarian stimulation in goats on the expression pattern of epidermal growth factor (EGF) receptor (EGFR) in cumulus–oocyte complexes (COCs) recovered by LOR. After real-time qRT-PCR analysis, expression profiles of morphologically graded COCs were compared prior to and after in vitro maturation (IVM) on a FSH protocol basis. The use of a protocol with higher number of FSH injections at a shorter interval resulted in GI/GII COCs with a higher level of EGFR expression in cumulus cells, but not in the oocyte, which was correlated with an elevated meiotic competence following IVM. Based on the maturation profile and EGFR expression patterns observed between groups, the morphological selection of COCs prior to IVM was not a good predictor of oocyte meiotic competence. Therefore, EGFR may be a good candidate marker for indirect prediction of goat oocyte quality. The IVM process of goat COCs increased the EGFR expression in oocytes and cumulus cells, which seemed to be strongly associated with the resumption of meiosis. In summary, differential EGFR expression in goat cumulus cells was associated with the in vivo prematuration process, and in turn, the upregulation in the entire COC was associated with IVM. Cause-and-effect relationships between such increased expression levels, particularly in the oocyte, and oocyte competence itself still need to be further investigated.

Prematuration of bovine oocytes with butyrolactone I reversibly arrests meiosis without increasing meiotic abnormalities after in vitro maturation

OBJECTIVES

Asynchrony between nuclear and cytoplasmic maturation, and possibly damage to the oocyte meiotic spindle, limits the application of in vitro maturation (IVM) in assisted reproduction. Several studies have suggested that Prematuration with meiosis blockers may improve oocyte quality after IVM, favoring early embryogenesis. Thus, we investigated the effect of Prematuration with the nuclear maturation inhibitor butyrolactone I (BLI) on the meiotic spindle and chromosomal configuration of bovine oocytes.

STUDY DESIGN

Immature oocytes obtained from cows slaughtered in a slaughterhouse (n=840) were divided into the following groups: (1) control (n=325), submitted only to IVM in TCM199 for 24h; (2) BLI 18h (n=208) submitted to meiotic blockage with 100 microM BLI for 24h (Prematuration) and then induction of IVM in TCM199 for 18h; and (3) BLI 24h (n=307), pre-matured with 100 microM BLI for 24h followed by 24h of IVM in TCM199. The oocytes were then fixed, stained by immunofluorescence for morphological visualization of both microtubules and chromatin, and evaluated.

RESULTS

Meiotic arrest occurred in 90.2% of the oocytes cultured with BLI. Maturation rates were similar for all groups (80.3%, 73.6% and 82.7% for the control, BLI 18h and BLI 24h groups, respectively). We observed 81.3% normal oocytes in metaphase II in the control group, and 80.0% and 81.2% in the BLI 18h and BLI 24h groups, respectively. The incidence of meiotic anomalies did not differ between groups (18.7%, 20.0% and 18.8% for the control, BLI 18h and BLI 24h, respectively).

CONCLUSION

Prematuration with butyrolactone I reversibly arrests meiosis without damaging the meiotic spindle or the chromosome distribution of bovine oocytes after in vitro maturation.

The effects of different concentrations of sodium selenite on the in vitro maturation of preantral follicles in serum-free and serum supplemented media

PURPOSE

This study was to investigate the effect of sodium selenite (SS) on in vitro maturation of mouse preantral follicles.

METHODS

The isolated preantral follicles were cultured in TCM 199 medium supplemented with different concentrations (0, 5, 10, 15 ng/ml) of SS and 3 mg/ml bovine serum albumin (BSA) or 5% Fetal Bovine Serum (FBS). The ovulation was induced by addition of 1.5 IU/ml human chorionic gonadotropin. The size and development of follicles and oocytes were assessed by calibrated eyepiece.

RESULTS

The survival rates of follicles in FBS supplemented groups containing 5 and 10 ng/ml SS (88.23%, 90.83%) were higher than other groups (P < 0.05 and P < 0.001 respectively). The mean diameter of follicles (199.84 +/- 15.58 microm) and the percentage of MII oocyte (33.08%) were higher in FBS supplemented group containing 10 ng/ml SS (P < 0.001).

CONCLUSION

The sodium selenite and FBS improve the in vitro growth and maturation of mouse preantral follicles.

Polycystic ovary syndrome and oocyte developmental competence

Folliculogenesis is a complex process, in which multiple endocrine and intraovarian paracrine interactions create a changing intrafollicular microenvironment for appropriate oocyte development. Within this microenvironment, bidirectional cumulus cell-oocyte signaling governs the gradual acquisition of developmental competence by the oocyte, defined as the ability of the oocyte to complete meiosis and undergo fertilization, embryogenesis, and term development. These regulatory mechanisms of follicle growth, controlled in part by the oocyte itself, are susceptible to derangement in polycystic ovary syndrome (PCOS), a heterogeneous syndrome characterized by ovarian hyperandrogenism, insulin resistance, and paracrine dysregulation of follicle development. Consequently, only a subset of PCOS patients experience reduced pregnancy outcome after ovarian stimulation for in vitro fertilization. Recent data implicate functional associations between endocrine/paracrine abnormalities, metabolic dysfunction, and altered oocyte gene expression with impaired oocyte developmental competence in women with PCOS. Therefore, an understanding of how developmentally relevant endocrine/paracrine factors interact to promote optimal oocyte developmental is crucial to identify those PCOS patients who might benefit from long-term correction of follicle growth to improve fertility, optimize follicular responsiveness to gonadotropin therapy, and enhance pregnancy outcome by in vitro fertilization.