Superovulatory response in a bovine model of reproductive aging

Effect of maternal age on ATP content and distribution of mitochondria in bovine oocytes

Our objective was to understand how maternal age influences the mitochondrial population and ATP content of in vivo matured bovine oocytes. We hypothesized that in vivo matured oocytes from older cows would have altered mitochondrial number and distribution patterns and lower cytoplasmic ATP content compared to the oocytes obtained from younger cows. Follicles ≥5mm were ablated in old cows (13 to 22 yrs, Old Group, n = 7) and their younger daughters (4 to 10 years old, Young Group; n = 7) to induce the emergence of a new follicular wave. Cows were treated twice daily with eight doses of FSH starting 24 hr after ablation (Day 0, day of wave emergence). Prostaglandin F2alpha (PGF) was given on Days 3 and 3.5, LH on Day 4.5, and cumulus-oocyte-complexes were collected 18-20 hours post-LH by ultrasound-guided follicular aspiration. Oocytes were either processed for staining with MitoTracker Deep Red FM or for ATP assay. Stained oocytes were imaged with a Zeiss LSM 710 confocal microscope, and mitochondria were segmented in the oocyte volume sets using Imaris Pro 7.4. In vivo matured oocytes obtained from old cows were similar in morphological grades to those from young cows. However, the oocytes of COC from older cows had 23% less intracellular ATP (27.4±1.9 vs 35.7±2.2 pmol per oocyte, P = 0.01) than those of young cows. Furthermore, the average volume of individual mitochondria, indicated by the number of image voxels, was greater (P<0.05) in oocytes from older cows than in those from younger cows. Oocytes from older cows also tended to have a greater number of mitochondrial clusters (P = 0.06) and an increased number of clusters in the central region of the oocytes (P = 0.04) compared to those from younger cows. In conclusion, our study demonstrated that maternal age was associated with a decrease in the cytoplasmic ATP content of in vivo mature oocytes and an altered distribution of mitochondrial structures. These findings suggest that maternal age may negatively influence the developmental competence of oocytes from older cows.

The Implications of Insufficient Zinc on the Generation of Oxidative Stress Leading to Decreased Oocyte Quality

Zinc is a transition metal that displays wide physiological implications ranging from participation in hundreds of enzymes and proteins to normal growth and development. In the reproductive tract of both sexes, zinc maintains a functional role in spermatogenesis, ovulation, fertilization, normal pregnancy, fetal development, and parturition. In this work, we review evidence to date regarding the importance of zinc in oocyte maturation and development, with emphasis on the role of key zinc-binding proteins, as well as examine the effects of zinc and reactive oxygen species (ROS) on oocyte quality and female fertility. We summarize our current knowledge about the participation of zinc in the developing oocyte bound to zinc finger proteins as well as loosely bound zinc ion in the intracellular and extracellular environments. These include aspects related to (1) the impact of zinc deficiency and overwhelming production of ROS under inflammatory conditions on the offset of the physiological antioxidant machinery disturbing biomolecules, proteins, and cellular processes, and their role in contributing to further oxidative stress; (2) the role of ROS in modulating damage to proteins containing zinc, such as zinc finger proteins and nitric oxide synthases (NOS), and expelling the zinc resulting in loss of protein function; and (3) clarify the different role of oxidative stress and zinc deficiency in the pathophysiology of infertility diseases with special emphasis on endometriosis-associated infertility.

Current Animal Model Systems for Ovarian Aging Research

Ovarian aging leads to menopause, loss of fertility and other disorders in multiple organs, which brings great distress to women. For ethical reasons, it is impossible to use humans as direct study subjects for aging research. Therefore, biomedical researchers have employed different non-human organisms to study ovarian aging, including worms, fruit flies, fishes, amphibians, birds, mice, rats, cavies, rabbits, pigs, sheep, cows, horses, monkeys, and apes. Because each of these model organisms has its own features, multiple factors, such as size, anatomical structure, cost, ease of operation, fertility, generation time, lifespan, and gene heredity, should be carefully considered when selecting a model system to study ovarian aging. An appropriate model organism would help researchers explore the risk factors and elucidate molecular mechanisms underlying declined ovarian functions, which might be conducive to preventing or delaying the ovarian aging process. This article will offer an overview on several currently available and commonly used model organisms for ovarian aging research by comparing their pros and cons. In doing so, we hope to provide useful information for ovarian aging researchers.

A human-based assisted reproduction protocol for the menstruating spiny mouse, Acomys cahirinus

The Egyptian or Common spiny mouse (A. cahirinus) is the first rodent species to show human-like menstruation and spontaneous decidualisation. We consider from these, and its other, human-like characteristics that this species will be a more useful and appropriate small animal model for human reproductive studies. Based on this, there is a need to develop specific laboratory-based assisted reproduction protocols including superovulation, in-vitro fertilisation, embryo cryopreservation and transfer to expand and make this model more relevant. Because standard rodent superovulation has not been successful in the spiny mouse, we have selected to test a human protocol. Female spiny mice will receive a subcutaneous GnRH agonist implant and be allowed to recover. Menstrual cycle lengths will then be allowed to stabilize prior to ovarian stimulation. After recovery, females will be injected IP once a day for 4 days with a FSH analogue, to induce follicular growth, and on day 5 will be injected IP with a hCG analogue to trigger ovulation. Females will either be culled 36hrs after trigger to collect oocytes or immediately paired with a stud male and two cell embryos collected 48hrs later. Mature oocytes will be inseminated using fresh spiny mouse spermatozoa and all in-vitro grown and in-vivo collected two cell embryos will be cryopreserved using methods developed in a close spiny mouse relative, the Mongolian gerbil. For embryo transfer, vitrified embryos will be rapidly warmed and non-surgically transferred to surrogate mice. Surrogates will be monitored until pregnancy is apparent (roughly 30 days) and then left undisturbed until birth, 38-40 days after transfer. By successfully developing robust assisted reproduction protocols in A. cahirinus we will be able to use this rodent as a more effective model for human reproduction.

Factors affecting embryo production in superovulated Bos taurus cattle

Despite a long history of bovine superovulation research, significant commercial applications did not start until the early 1970s. For some 20 years thereafter, superovulation represented the primary tool for the production of cattle embryos. In the early 1990s, commercial invitro production (IVP) was initiated in cattle. Although ovum pick-up and IVP are now commercially practiced on a wide scale, superovulation and embryo recovery by flushing remain a widespread and very effective approach to the production of cattle embryos. This review covers both the history and the effects of multiple factors on superovulation in Bos taurus cattle. There are three general protocols for suitable pre-FSH programming of donors so that gonadotrophin-responsive follicles are available. Superovulation protocols vary widely based on the FSH source, the diluent used, the number and timing of FSH injections and the timing and utilisation of various prostaglandins, controlled internal progesterone releasing devices, gonadotrophin-releasing hormone, and other means of controlling follicular development and ovulation. The number of oocytes that can be stimulated to grow and ovulate within any given donor can be estimated by either ultrasound-guided sonography or by measuring concentrations of anti-Müllerian hormone in the blood. Animal-related factors that can influence the efficacy of superovulation include cattle breed, age, parity, genetics, lactational status and reproductive history. In addition, nutrition, stress, season, climate, weather and several semen factors are discussed.

Agricultural Animals as Biomedical Models: Occupational Health and Safety Considerations

The use of agricultural animals in biomedical research is increasing. Their overall size and metabolic rate, organ size, longer gestation period, and other physiological similarities make them good candidates for animal models of human disease. There are a number of special considerations for use of traditional farm animals for biomedical research. Differences in physical plant infrastructure, handling equipment, training of personnel, and potential zoonoses are some of the important considerations when traditional farm animals are used in biomedical research. This article provides an overview of some of the special considerations for using traditional agricultural animals in biomedical research. With the growing need for improved translational research, it is reasonable to predict significant growth in these animal models.

Influence of eCG and breed on the number of oocytes collected and the production of in vitro embryos of young goats during the reproductive season

The objective of this study was to determine the effect of breed and equine chorionic gonadotropin (eCG) on ovarian response and in vitro embryo production from young goats. Thirty-one (12 Alpine, 10 Nubian, and 9 Saanen) were randomly assigned into three treatments of eCG (T1, 0 IU; T2, 500 IU; and T3, 1000 IU). Alpine goats showed the highest amount and largest size of follicles (P = 0.003). The effect of eCG dose 24 h post application was significant (P < 0.05), and was superior in goats undergoing T2. The aspiration rate of cumulus-oocyte complexes (COC) was 34% (P > 0.05), except for percentage of denuded oocytes, which obtained the highest number (P = 0.003) in the Saanen goats. The same difference was found (P = 0.02) in oocytes grade III in T2 and T3, with 42.5 and 37.9% respectively. In vitro embryo production was 80.0% of IVF/cleavage in the Alpine goats (P = 0.003). Embryo production was the greatest for T2 (69.2%; P = 0.004). T3 goats had higher percentage of morula stage (66.6%; P = 0.030). It is concluded that the application of eCG has a significant effect on the ovarian status, and quality and quantity of embryos with a differential response depending on the breed.

DNA methylation and mRNA expression of developmentally important genes in bovine oocytes collected from donors of different age categories

Epigenetic changes are critical for the acquisition of developmental potential by oocytes and embryos, yet these changes may be sensitive to maternal ageing. Here, we investigated the impact of maternal ageing on DNA methylation and mRNA expression in a panel of eight genes that are critically involved in oocyte and embryo development. Bovine oocytes were collected from donors of three different age categories-prepubertal (9-12 months old), mature (3-7 years old), and aged (8-11 years old)-and were analyzed for gene-specific DNA methylation (bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19, and bSNRPN) and mRNA expression (bTERF2, bBCL-XL, bPISD, and bBUB1). A total of 1,044 alleles with 88,740 CpGs were amplified and sequenced from 362 bovine oocytes. Most of the detected molecules were either fully methylated or completely unmethylated. Only 9 out of 1,044 alleles (<1%) were abnormally methylated (>50% of CpGs with an aberrant methylation status), and seven of the nine abnormally methylated alleles were within only two candidate genes (bDNMT3Lo and bH19). No significant differences were detected with regard to mRNA expression between oocytes from the three groups of donors. These results suggest that genes predominantly important for early embryo development (bH19 and bDNMT3Lo) are less resistant to abnormal methylation than genes critically involved in oocyte development (bTERF2, bBCL-XL, bPISD, bBUB1, and bSNRPN). Establishment of DNA methylation in bovine oocytes seems to be largely resistant to changes caused by maternal ageing, irrespective of whether the genes are critical to achieve developmental competence in oocytes or early embryos. Mol. Reprod. Dev. 83: 802-814, 2016 © 2016 Wiley Periodicals, Inc.

Mink aging is associated with a reduction in ovarian hormone release and the response to FSH and ghrelin

The endocrine mechanisms of mink ovarian hormones release and reproductive aging are poorly investigated. The aims of our study were to: (1) identify hormones produced by mink ovaries (the steroids progesterone [P] and estradiol [E], the peptide hormone oxytocin [OT], and the prostaglandin F [PGF] and prostaglandin E [PGE]); (2) examine the effect of FSH and ghrelin on the release of the hormones listed previously; and (3) understand whether these hormones can be involved in the control of mink reproductive aging, i.e., whether aging can be associated with changes (a) in the basal release of P, E, OT, PGF, or PGE and (b) their response to FSH and ghrelin. Fragments of ovaries of young (yearlings) and old (3-5 years of age) minks were cultured with and without FSH and ghrelin (0, 1, 10, or 100 ng/mL), and the release of hormones was analyzed by EIA/RIA. We found that isolated ovaries were able to release P, E, OT, PGF, and PGE, and the levels of P produced in the ovaries of old animals were lower than those produced in the ovaries of young animals, whereas the levels of other hormones did not differ. FSH was able to stimulate P and E and suppress OT and PGF and did not affect PGE release. Aging was associated with the inhibition of the effect of FSH on ovarian P and E, the appearance of the inhibitory action of FSH on OT, and the disappearance of this action on ovarian PGF. PGE was not affected by FSH, irrespective of animal age. Ghrelin was able to promote E (but not P) and suppress OT, PGF, and PGE output. Aging was associated with the appearance of an inhibitory influence of ghrelin on ovarian OT and PGE and with the disappearance of this influence on PGF output. Aging did not affect the action of ghrelin on ovarian P and E. Our observations (1) confirm the production of P and E and show that OT, PGF, and PGE are released from mink ovaries, (2) confirm the involvement of FSH and demonstrate the involvement of ghrelin in the control of mink ovarian hormone release, and (3) suggest that reproductive aging in minks is due to a reduction in basal P release and alterations in the response of E, OT, PGF (but not of PGE) to FSH and ghrelin.

Age-associated events in bovine oocytes and possible countermeasures

Maternal aging profoundly affects oocyte quality. This has become common knowledge in industrialized countries and extensive studies addressing the causes and possible countermeasures against age-associated deterioration of oocytes suggest that mitochondrial dysfunction is a causal factor in infertility. However, almost all studies addressing age-associated events in oocytes have used mice as an animal model, and the reproductive life of mice is very short, making it difficult to study the gradual decline in fertility observed in humans. In the present review, age-associated changes in the quality and quantity of bovine oocytes and possible countermeasures related to mitochondrial quality control are introduced.

Proteome analysis of early lineage specification in bovine embryos

During mammalian embryo development, the zygote undergoes embryonic cleavage in the oviduct and reaches the uterus at the morula stage, when compaction and early lineage specification take place. To increase knowledge about the associated changes of the embryonic protein repertoire, we performed a comprehensive proteomic analysis of in vitro produced bovine morulae and blastocysts (six biological replicates), using an iTRAQ-based approach. A total of 560 proteins were identified of which 502 were quantified. The abundance of 140 proteins was significantly different between morulae and blastocysts, among them nucleophosmin (NPM1), eukaryotic translation initiation factor 5A-1 (EIF5A), receptor of activated protein kinase C 1 (GNB2L1/RACK1), and annexin A6 (ANXA6) with increased, and glutathione S-transferase mu 3 (GSTM3), peroxiredoxin 2 (PRDX2), and aldo-keto reductase family 1 member B1 (AKR1B1) with decreased abundance in blastocysts. Seventy-three percent of abundance altered proteins increased, reflecting an increase of translation activity in this period. This is further supported by an increase in the abundance of proteins involved in the translation machinery and the synthesis of ATP. Additionally, a complementary 2D saturation DIGE analysis led to the detection of protein isoforms, e.g. of GSTM3 and PRDX2, relevant for this period of mammalian development, and exemplarily verified the results of the iTRAQ approach. In summary, our systematic differential proteome analysis of bovine morulae and blastocysts revealed new molecular correlates of early lineage specification and differentiation events during bovine embryogenesis.

Granulosa cell function and oocyte competence: Super-follicles, super-moms and super-stimulation in cattle

The review presents an overview of studies that examined the effects of follicular aging and maternal aging in the bovine model. The first of three main sections is a discussion of the developmental competence of oocytes from (1) the ovulatory follicle of 2-wave and 3-wave estrous cycles, (2) dominant follicles that develop under high or low LH pulse frequency, and (3) natural versus FSH-stimulated ovulatory follicles. The second section highlights the effects of maternal aging. Maternal aging in cattle is associated with (1) elevated circulating FSH concentrations, (2) reduced response to superstimulatory treatment, and (3) markedly decreased early embryonic development in cows >12 year of age. The third and final section on superstimulation protocols addresses the effects of the duration of FSH stimulation and withdrawal (i.e., FSH "starvation" or "coasting") on oocyte competence. Ovarian superstimulation for 4 days altered the expression of genes related to angiogenesis, and activated oxidative stress-response genes. Extending the duration of FSH stimulation from 4 to 7 days resulted in a greater and more synchronous ovulatory response and optimal oocyte maturation. The highest rates of blastocyst development in vitro were obtained when FSH support was discontinued for 44 to 68h and granulosa cell SMAD7 mRNA was predictive of this period. Longer periods of FSH starvation resulted in a loss of oocyte competence or ovulatory capability. By extending the bovine model to the transcriptome level, new approaches and treatments may be devised to resolve subfertility in women and animals.

Age-associated changes in bovine oocytes and granulosa cell complexes collected from early antral follicles

PURPOSE

To assess the age-associated changes in oocytes and granulosa cells derived from early antral follicles (EAFs).

METHOD

Gene expression analysis of granulosa cells of the EAFs using a genome analyzer (Illumina) and in vitro culture of oocyte-granulosa cell complexes (OGCs) of EAFs (400-700 μm in diameter) collected from ovaries of aged (>120 months) and young (<50 months) cows.

RESULTS

Gene expression profiles in granulosa cells of EAFs of aged cows, which included changes in genes that encode chaperone proteins and antioxidants. In vivo development of EAFs, as determined by oocyte diameter of EAFs and AFs (3-6 mm in diameter), appeared to be impaired in aged cows and the OGCs of aged cows contained low GSH compared to younger counterparts. When the OGCs were cultured in a medium containing low estradiol (E2, 0.1 μg/mL), the ratio of antrum formation was higher for OGCs from aged animals than that from young animals, while higher abnormal fertilization rate and lower total cell number of the blastocysts were observed in the OGCs of aged cows compared with those of young cows. On the contrary, when the OGCs were cultured in a medium containing 10 μg/mL E2, the ratio of antrum formation and fertilization outcome was comparable between the two age groups, whereas the total cell number of the blastocysts was still low in the aged group.

CONCLUSION

Aging affects the gene expression profiles of the granulosa cells, and impairs in vitro developmental ability of OGCs collected from EAFs.

Effects in cattle of genetic variation within the IGF1R gene on the superovulation performance and pregnancy rates after embryo transfer

The insulin-like growth factor 1 receptor (IGF1R) is a membrane glycoprotein mediating most biological actions of IGF1 and IGF2, and has an important effect on ovulation, pre-implantation embryo development and pregnancy rate. The objectives of this study were to detect IGF1R gene polymorphisms of cattle and analyze the relationship with superovulation performance and pregnancy rates after embryo transfer (ET), as well as the hormone concentrations at the day of ET. One reported SNP of IGF1R G404T and a novel SNP of IGF1R G399A were analyzed in 170 Chinese Holstein donor cows and 118 Luxi recipients cattle. Statistical analysis revealed that the G404T mutation was associated (p=0.019) with increased ovulation rate and females with this mutation had enhanced performance in producing transferable embryos. For the polymorphic locus G399A, recipients with g.399 GG and g.399 GA genotypes had greater pregnancy rates after ET than that of g.399 AA genotype. Furthermore, the same tendency was observed that the genotype groups with greater pregnancy rates had greater progesterone and lesser estrogen concentrations, but these did not reach statistical significance. Results of the present study showed, for the first time, that the polymorphism in IGF1R is associated with superovulation traits, and indicated that the IGFIR gene can be used as a potential marker for donor selection.

Effect of aging on follicular function may be relieved by exogenous gonadotropin treatment in a sheep model

The current study investigated hormonal and ovarian changes during physiological reproductive aging in Sarda ewes. In a first experiment, follicular and corpus luteum dynamics were compared during an induced oestrus cycle in aged (12-14 years) and young adult ewes (4-5 years). Oestrus cycle characteristics did not differ between the two experimental groups. However, follicular function during the follicular phase showed significant alterations in aged ewes, as determined by a lack of dominance effect and by lower mean values of circulating oestradiol (E(2)) and inhibin levels, compared with young adult ewes. In a second experiment, differences in follicle growth, hormonal milieu and oocyte quality in response to exogenous FSH administration were assessed in aged and adult ewes. No differences were recorded in ovarian response to FSH treatment between young adult and aged ewes, as evaluated by ultrasonographic data and circulating concentrations of LH, E(2) and inhibin-A. Although the total number of recovered oocytes was similar in the two age groups, the number of good quality oocytes selected for IVM was significantly lower in aged ewes compared with adult ones. Thereafter, no differences were recorded in cleavage rates, total blastocyst output, embryo developmental kinetic and quality between aged and adult groups. In conclusion, this study demonstrated that reproductive aging in sheep is associated with impaired follicle functionality and an increase in the proportion of oocytes showing morphological abnormalities. However interestingly, oocyte developmental competence in vitro and embryo cryotolerance were not affected by the aging process, when only good quality oocytes were chosen.

Large animal models for the study of ovarian follicular dynamics in women

Initial studies of the ovaries were based on postmortem anatomic descriptions, followed by histologic and endocrine approaches. The introduction of high-resolution ultrasonography provided a long-awaited tool to image the reproductive tissues in situ in both animals and humans. Critical studies of the characteristics and control of ovarian follicular and luteal dynamics in nonhuman primates, rodents, and domestic farm animals have involved frequent (i.e., daily or multiple times a day) blood sampling and ultrasonography. Studies of this nature in women are difficult, and often unethical to conduct. Differences in antral folliculogenesis between humans and animals appear to be more in detail rather than in essence, and may reflect differences in intrinsic physiology or merely differences in our ability to detect changes in a given species. In women, the presence of endometrial shedding and symmetric luteal and follicular phases are different from that observed during the estrous cycles of domestic farm animals but despite these differences, general similarities in antral follicular dynamics exist. A continuous pattern of antral follicle development was originally proposed in domestic livestock species; however, the use of frequent serial ultrasonography and simultaneous endocrine profiling in these animal species has resulted in a broad understanding of follicular wave dynamics. Follicular waves have now been described in every species in which this approach has been used, including humans. The relatively large diameters of antral follicles in cows and mares, compared with monkeys, sheep, and rodents provide greater feasibility for characterizing antral follicular dynamics ultrasonographically. While the use of large animal models has increased our understanding of ovarian function and provides the hypothetical basis for studies in women, differences in vocabulary, culture, and research methodologies has hampered knowledge translation. These differences represent a systemic impediment to a broad understanding of ovarian function and limits progress and innovation in the development of safer and more efficacious treatments for infertility and contraception.

Effect of ovarian stimulation on oocyte gene expression in cattle

The objective was to analyze the impact of follicle stimulating hormone (FSH, ovarian stimulation) on the transcriptome of in vivo bovine oocytes three times around the luteinizing hormone (LH) surge. In vivo bovine oocytes were collected 2 h pre-LH surge, 6 h post-LH surge, and 22 h post-LH surge in both naturally ovulating and superovulated animals. To assess potential changes in gene levels, samples were hybridized using a custom bovine microarray. Two series of hybridizations were performed: the first comparing natural vs. stimulated cycles, the second according to time of collection. Among the potential candidates, 13 genes were selected according to their degree of differential expression and their potential link to oocyte competence. Measurements of their relative mRNA levels was made using QPCR. Gene candidates BTG4 (P = 0.0006), PTTG1 (P = 0.0027), PAPOLA (P = 0.0245), and LEO1 (P = 0.0393) had higher mRNA levels in oocytes treated with FSH for all collection times when compared to oocytes produced through the natural cycle. Among our selected candidates, only one gene, GDF9 (P = 0.0261), was present at a higher level in oocytes collected at -2 h and 6 h than 22 h post-LH for all treatments, regardless of the presence of FSH. Although the number of genes influenced by ovarian stimulation seemed low, the observed differences occurred at a time of minimal transcriptional activity and supported the potential impact on the future embryo. These impacts could have been epigenetic in nature, as embryo quality was not reported to be different from stimulated animals.

Effect of bovine age on the proliferative activity, global DNA methylation, relative telomere length and telomerase activity of granulosa cells

Granulosa cells influence the growth and acquisition of the developmental competence of oocytes. We investigated the effects of ageing on the proliferative activity, global genomic DNA methylation, relative telomere length and telomerase activity of bovine granulosa cells. The proliferative activity of cells was examined by bromodeoxyuridine (BrdU) assay, genomic DNA methylation was examined by enzyme-linked immunosorbent assay (ELISA), and relative telomere length and telomerase activity were examined by real-time polymerase chain reaction. We first compared the proliferative activity of the granulosa cells of the medium follicles between in dominant phase ovaries and growth phase ovaries. We observed that the proliferative activity of the granulosa cells of dominant phase ovaries was significantly lower than those of growth phase ovaries. In addition, the proliferative activity of granulosa cells was inversely associated with follicular size. Based on the results, we used granulosa cells harvested from the medium follicles (3-5 mm in diameter) on the surfaces of the dominant phase ovaries collected from cows at a slaughterhouse. The proliferative activity of the granulosa cells harvested from the ovaries of old cows (N = 8; average age 165.1 months) was lower than that of the cells from young cows (N = 8; average age 30.9 months). Global loss of cytosine methylation was detected in the granulosa cells of old cows (N = 12; average age 141.0 months) compared with young cows (N = 15; average age 27.4 months). Although the relative telomere lengths of cumulus cells were similar in the two age groups, the relative telomere lengths and telomerase activity of the granulosa cells from old cows (N = 17 and 9; average age, 164.6 and 151.3 months, respectively) tended to be shorter than those of the cells from young cows (N = 17 and 10; average age 30.6 and 28.1 months, respectively); however, this difference was not significant p = 0.09 and 0.053, respectively). In conclusion, the proliferative activity and genomic global DNA methylation significantly decreased, and the relative telomere lengths and telomerase activity of granulosa cells tended to be shorter with the age of donor cows.

Polymorphisms of the bovine luteinizing hormone/choriogonadotropin receptor (LHCGR) gene and its association with superovulation traits

The major limitation to the development of embryo transfer technique in cattle is the highly variable between individuals in ovulatory response to FSH-induced superovulation. The objective of this study was to identify a predictor to forecast superovulation response on the basis of associations between superovulation performance and gene polymorphism, variation in the bovine luteinizing hormone/choriogonadotropin receptor (LHCGR) gene was investigated using PCR-single-strand conformational (PCR-SSCP) and DNA sequencing. Four single nucleotide polymorphisms (SNPs) of G51656T, A51703G, A51726G and G51737A were identified at the intron 9 of the LHCGR gene in 171 Chinese Holstein cows treated for superovulation, and evaluated its associations with superovulatory response. Association analysis showed that these four SNPs had significant effects on the total number of ova (TNO) (P < 0.05). Moreover, the A51703G and A51726G polymorphisms significantly associated with the number of transferable embryos (NTE) (P < 0.05). In addition, significant additive effect on TNO was detected in polymorphisms of G51656T (P < 0.05) and A51703G (P < 0.01), and the A51703G polymorphism also had significant additive effects on NTE (P < 0.01). These results indicate that LHCGR gene is a potential marker for superovulation response and can be used to predict the most appropriate dose of FSH for superovulation in Chinese Holstein cows.

Association analysis between variants in bovine progesterone receptor gene and superovulation traits in Chinese Holstein cows

The objective of this study was to identify a predictor to forecast superovulation response on the basis of associations between superovulation performance and gene polymorphism. The PCR-RFLP method was applied to detect two reported single nucleotide polymorphisms (SNPs) of G59752C and T81637C (rs41614030) located in introns 3 and 4 of the bovine progesterone receptor (PGR) gene in 171 Chinese Holstein cows treated for superovulation and evaluate its associations with superovulation traits. In polymorphic locus 81637, all cows without superovulation response were g.81637TC and g.81637TT genotypes. Association analysis showed that these two SNPs had significant effects on the total number of ova (TNO) (p<0.05), and the T81637C polymorphism was significantly associated with the number of transferable embryos (p<0.05). In addition, significant additive effects (p<0.05) on TNO were detected in the polymorphisms of G59752C and T81637C. These results showed for the first time that the G59752C and T81637C polymorphisms in PGR gene were associated with superovulation traits and indicated that PGR gene can be used as a predictor for superovulation in Chinese Holstein cows.

An MspI polymorphism in the inhibin alpha gene and its associations with superovulation traits in Chinese Holstein cows

To identify a predictor to forecast superovulation response on the basis of associations between superovulation performance and gene polymorphism, the PCR-RFLP method was applied to detect an A>G transition determining an MspI polymorphism at position 192 in the exon I of the bovine inhibin alpha (INHA) gene and evaluate its associations with superovulatory response in 118 Chinese Holstein cows treated for superovulation. Association analysis showed that cows with the GG genotype resulted in a significant increase in the number of ova (TNO) than AG and AA genotypes in the first (P=0.023), second (P=0.004) and third (P=0.002) superovulation treatments and produced more transferable embryos (NTE) than that of AG and AA genotypes in the third (P=0.045) superovulation treatment. Moreover, individuals with GG genotype produced more transferable embryos than AA (P<0.05) genotype in the second superovulation treatment and all cows without superovulation response were mutations with genotypes of AA and AG. These results indicate that INHA gene can be used as a predictor for superovulation in Chinese Holstein cows, and imply that cows with AA genotype should be excluded for superovulation practices.

Polymorphisms in the 5' upstream region of the FSH receptor gene, and their association with superovulation traits in Chinese Holstein cows

To identify a predictor to forecast superovulation response on the basis of associations between superovulation performance and gene polymorphism, variation in the bovine follicle stimulating hormone receptor (FSHR) gene was investigated using PCR-single-strand conformational (PCR-SSCP) and DNA sequencing. One single nucleotide polymorphism (SNP) of G-278A located in the 5' upstream region of bovine FSHR gene was found in 118 Chinese Holstein cows treated for superovulation. Two SNPs of G-278A (GU253337) and A-320T (rs43676359) were analyzed. In polymorphic locus -278, all cows without superovulation response were mutations with genotypes of CD and DD. Cows with CC genotype had a significant increase in the total number of ova (TNO) (P<0.01), and produced more transferable embryos (NTE) than those of the CD and DD genotypes (P<0.01). At this locus, the additive effects seemed to be highly significant (P<0.01) and allele C was associated with an increase in the TNO and NTE. These results indicated that the FSHR is a potential marker for superovulation response and can be used as a predictor for superovulation in Chinese Holstein cows.