Follicular metabolic alterations are associated with obesity in mares and can be mitigated by dietary supplementation

Obesity is a growing concern in human and equine populations, predisposing to metabolic pathologies and reproductive disturbances. Cellular lipid accumulation and mitochondrial dysfunction play an important role in the pathologic consequences of obesity, which may be mitigated by dietary interventions targeting these processes. We hypothesized that obesity in the mare promotes follicular lipid accumulation and altered mitochondrial function of oocytes and granulosa cells, potentially contributing to impaired fertility in this population. We also predicted that these effects could be mitigated by dietary supplementation with a combination of targeted nutrients to improve follicular cell metabolism. Twenty mares were grouped as: Normal Weight [NW, n = 6, body condition score (BCS) 5.7 ± 0.3], Obese (OB, n = 7, BCS 7.7 ± 0.2), and Obese Diet Supplemented (OBD, n = 7, BCS 7.7 ± 0.2), and fed specific feed regimens for ≥ 6 weeks before sampling. Granulosa cells, follicular fluid, and cumulus-oocyte complexes were collected from follicles ≥ 35 mm during estrus and after induction of maturation. Obesity promoted several mitochondrial metabolic disturbances in granulosa cells, reduced L-carnitine availability in the follicle, promoted lipid accumulation in cumulus cells and oocytes, and increased basal oocyte metabolism. Diet supplementation of a complex nutrient mixture mitigated most of the metabolic changes in the follicles of obese mares, resulting in parameters similar to NW mares. In conclusion, obesity disturbs the equine ovarian follicle by promoting lipid accumulation and altering mitochondrial function. These effects may be partially mitigated with targeted nutritional intervention, thereby potentially improving fertility outcomes in the obese female.

Maturation and culture affect the metabolomic profile of oocytes and follicular cells in young and old mares

Introduction: Oocytes and follicular somatic cells within the ovarian follicle are altered during maturation and after exposure to culture in vitro. In the present study, we used a nontargeted metabolomics approach to assess changes in oocytes, cumulus cells, and granulosa cells from dominant, follicular-phase follicles in young and old mares. Methods: Samples were collected at three stages associated with oocyte maturation: (1) GV, germinal vesicle stage, prior to the induction of follicle/oocyte maturation in vivo; (2) MI, metaphase I, maturing, collected 24 h after induction of maturation in vivo; and (3) MIIC, metaphase II, mature with collection 24 h after induction of maturation in vivo plus 18 h of culture in vitro. Samples were analyzed using gas and liquid chromatography coupled to mass spectrometry only when all three stages of a specific cell type were obtained from the same mare. Results and Discussion: Significant differences in metabolite abundance were most often associated with MIIC, with some of the differences appearing to be linked to the final stage of maturation and others to exposure to culture medium. While differences occurred for many metabolite groups, some of the most notable were detected for energy and lipid metabolism and amino acid abundance. The study demonstrated that metabolomics has potential to aid in optimizing culture methods and evaluating cell culture additives to support differences in COCs associated with maternal factors.

Use of confocal microscopy and intracytoplasmic sperm injection (ICSI) to assess viability of equine oocytes from young and old mares after vitrification

BACKGROUND

The impact of vitrification on oocyte developmental competence as a function of donor age remains an important issue in assisted reproductive technologies (ARTs).

METHODS

Equine germinal vesicle (GV) or metaphase II (M(II) oocytes were vitrified using the Cryotop® method. Spindle organization and chromosome alignment were evaluated from confocal imaging data sets of in vivo (IVO) or in vitro (IVM) matured oocytes subjected to vitrification or not. Intracytoplasmic sperm injection (ICSI) from the same groups was used to assess developmental potential.

RESULTS

An increase in chromosome misalignment was observed in spindles from older mares when compared to those of younger mares (P < 0.05). When MII oocytes subjected to vitrification were examined following warming, there was no difference in the percentage of oocytes displaying chromosome misalignment. Next, GV oocytes, collected from the ovaries of younger and older mares, were compared between fresh IVM and IVM following vitrification and warming. For nonvitrified samples, an age difference was again noted for spindle organization and chromosome alignment, with a higher (P < 0.05) percentage of normal bipolar meiotic spindles with aligned chromosomes observed in nonvitrified oocytes from young versus older mares. Vitrification led to a reduction of spindle length (P < 0.05) for oocytes from old mares, whether vitrified at GV or MII stages, whereas this effect was not observed in oocytes from young mares except those vitrified at GV and subjected to IVM. Oocyte developmental potential after vitrification was evaluated after ICSI of vitrified and warmed MII or GV oocytes from young mares. From 25 MII oocytes, 18 oocytes were injected with sperm, and six blastocysts were produced, which, upon transfer to mares' uteri, resulted in four pregnancies. Immature (GV) oocytes collected from live mares were also vitrified, warmed, and matured in vitro before ICSI. In this group, nonvitrified, control, and vitrified oocytes did not differ (P > 0.05) with respect to the incidence of maturation to MII, cleavage after ICSI, or blastocyst development.

CONCLUSION

These findings demonstrate an effect of maternal age in an equine model at the level of meiotic spindle integrity and chromosome positioning that is influenced by both the meiotic stage at which oocytes are vitrified and whether meiotic maturation occurred in vivo or in vitro.

Past, present and future of ICSI in livestock species

During the past 2 decades, intracytoplasmic sperm injection (ICSI) has become a routine technique for clinical applications in humans. The widespread use among domestic species, however, has been limited to horses. In horses, ICSI is used to reproduce elite individuals and, as well as in humans, to mitigate or even circumvent reproductive barriers. Failures in superovulation and conventional in vitro fertilization (IVF) have been the main reason for the use of this technology in horses. In pigs, ICSI has been successfully used to produce transgenic animals. A series of factors have resulted in implementation of ICSI in pigs: need to use zygotes for numerous technologies, complexity of collecting zygotes surgically, and problems of polyspermy when there is utilization of IVF procedures. Nevertheless, there have been very few additional reports confirming positive results with the use of ICSI in pigs. The ICSI procedure could be important for use in cattle of high genetic value by maximizing semen utilization, as well as for utilization of spermatozoa from prepubertal bulls, by providing the opportunity to shorten the generation interval. When attempting to utilize ICSI in ruminants, there are some biological limitations that need to be overcome if this procedure is going to be efficacious for making genetic improvements in livestock in the future. In this review article, there is an overview and projection of the methodologies and applications that are envisioned for ICSI utilization in these species in the future.

Maternal age affects equine day 8 embryo gene expression both in trophoblast and inner cell mass

BACKGROUND

Breeding a mare until she is not fertile or even until her death is common in equine industry but the fertility decreases as the mare age increases. Embryo loss due to reduced embryo quality is partly accountable for this observation. Here, the effect of mare's age on blastocysts' gene expression was explored. Day 8 post-ovulation embryos were collected from multiparous young (YM, 6-year-old, N = 5) and older (OM, > 10-year-old, N = 6) non-nursing Saddlebred mares, inseminated with the semen of one stallion. Pure or inner cell mass (ICM) enriched trophoblast, obtained by embryo bisection, were RNA sequenced. Deconvolution algorithm was used to discriminate gene expression in the ICM from that in the trophoblast. Differential expression was analyzed with embryo sex and diameter as cofactors. Functional annotation and classification of differentially expressed genes and gene set enrichment analysis were also performed.

RESULTS

Maternal aging did not affect embryo recovery rate, embryo diameter nor total RNA quantity. In both compartments, the expression of genes involved in mitochondria and protein metabolism were disturbed by maternal age, although more genes were affected in the ICM. Mitosis, signaling and adhesion pathways and embryo development were decreased in the ICM of embryos from old mares. In trophoblast, ion movement pathways were affected.

CONCLUSIONS

This is the first study showing that maternal age affects gene expression in the equine blastocyst, demonstrating significant effects as early as 10 years of age. These perturbations may affect further embryo development and contribute to decreased fertility due to aging.

Female age and parity in horses: how and why does it matter?

Although puberty can occur as early as 14-15months of age, depending on breed and use, the reproductive career of mares may continue to advanced ages. Once mares are used as broodmares, they will usually produce foals once a year until they become unfertile, and their productivity can be enhanced and/or prolonged through embryo technologies. There is a general consensus that old mares are less fertile, but maternal age and parity are confounding factors because nulliparous mares are usually younger and older mares are multiparous in most studies. This review shows that age critically affects cyclicity, folliculogenesis, oocyte and embryo quality as well as presence of oviductal masses and uterine tract function. Maternal parity has a non-linear effect. Primiparity has a major influence on placental and foal development, with smaller foals at the first gestation that remain smaller postnatally. After the first gestation, endometrial quality and uterine clearance capacities decline progressively with increasing parity and age, whilst placental and foal birthweight and milk production increase. These combined effects should be carefully balanced when breeding mares, in particular when choosing and caring for recipients and their foals.

Effect of Mare Age on Transcript Abundance of Connexins-37 and -43, Zona Pellucida Proteins, and Sperm Binding

Zona pellucida (ZP) proteins are important for fertilization and sperm binding and are closely associated with cumulus cells. Communication between cumulus and oocytes is facilitated by intracellular membrane channels composed of connexins. The extent aging impacts potential differences in fertilization and reductions in fertility is not well understood. This study characterized age-related differences in transcript abundance of ZP proteins and connexins in cells from ovarian follicles. Additionally, differences in sperm binding to oocytes from old and young mares was evaluated. For experiment 1, oocytes, corona radiata, cumulus, and granulosa cells were collected from mares classified as young (4-12 years) or old (> 20 years). Transcript abundance was evaluated for connexins -37 (GJA4) and -43 (GJA1); zona pellucida glycoproteins 1, 2, 3, and 4 (ZP1, ZP2, ZP3, ZP4); Tubulin (TUBA1A), and equine chorionic gonadotropin β. For experiment 2, oocytes that failed to cleave following intracytoplasmic sperm injection (ICSI) were stored in salt solution for up to 4 years and used for sperm binding assays. Transcript abundance for GJA1 was decreased in oocytes, corona radiata, and granulosa cells while GJA4 was decreased in cumulus cells from old compared to young mares. Additionally, ZP1 tended to be decreased in corona radiata and cumulus cells from old mares. Oocytes from old mares tended to bind less spermatozoa compared young mares. Oocytes that failed to cleave following ICSI can be used for sperm binding studies for up to 2 years without losses in sperm binding. Our findings suggest that maternal age may contribute to changes in cellular communication and the ZP that could impact sperm binding.

Equine maternal aging affects oocyte lipid content, metabolic function and developmental potential

Advanced maternal age is associated with a decline in fertility and oocyte quality. We used novel metabolic microsensors to assess effects of mare age on single oocyte and embryo metabolic function, which has not yet been similarly investigated in mammalian species. We hypothesized that equine maternal aging affects the metabolic function of oocytes and in vitro-produced early embryos, oocyte mitochondrial DNA (mtDNA) copy number, and relative abundance of metabolites involved in energy metabolism in oocytes and cumulus cells. Samples were collected from preovulatory follicles from young (≤14 years) and old (≥20 years) mares. Relative abundance of metabolites in metaphase II oocytes (MII) and their respective cumulus cells, detected by liquid and gas chromatography coupled to mass spectrometry, revealed that free fatty acids were less abundant in oocytes and more abundant in cumulus cells from old vs young mares. Quantification of aerobic and anaerobic metabolism, respectively measured as oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in a microchamber containing oxygen and pH microsensors, demonstrated reduced metabolic function and capacity in oocytes and day-2 embryos originating from oocytes of old when compared to young mares. In mature oocytes, mtDNA was quantified by real-time PCR and was not different between the age groups and not indicative of mitochondrial function. Significantly more sperm-injected oocytes from young than old mares resulted in blastocysts. Our results demonstrate a decline in oocyte and embryo metabolic activity that potentially contributes to the impaired developmental competence and fertility in aged females.

Pregnancy obtained in a late gestational mare by in vitro embryo production

Recently, the demand for invitro embryo production in the horse has increased worldwide. Most clinical transvaginal ultrasound-guided ovum pick-up (OPU) procedures are performed in non-pregnant donor mares, and few experimental studies have described invitro embryo production from oocytes of pregnant donors 21-150 days in gestation. This report discusses OPU, follicular growth and invitro embryo production in a pregnant mare during late gestation.

Morphology, developmental stages and quality parameters of in vitro-produced equine embryos

Intracytoplasmic sperm injection (ICSI) is used to produce equine embryos invitro. The speed of embryo development invitro is roughly equivalent to what has been described for embryos produced invivo. Morphological evaluations of ICSI-produced embryos are complicated by the presence of debris and the dark nature of equine embryo cytoplasm. Morulas and early blastocysts produced invitro appear similar to those produced invivo. However, with expansion of the blastocyst, distinct differences are observed compared with uterine embryos. In culture, embryos do not undergo full expansion and thinning of the zona pellucida (ZP) or capsule formation. Cells of the inner cell mass (ICM) are dispersed, in contrast with the differentiated trophoblast and ICM observed in embryos collected from uteri. As blastocysts expand invitro, embryo cells often escape the ZP as organised or disorganised extrusions of cells, probably through the hole incurred during ICSI. Quality assessment of invitro-produced early stage equine embryos is in its infancy, because limited information is available regarding the relationship between morphology and developmental competence. Early embryo development invivo is reviewed in this paper, with comparisons made to embryo development invitro and clinical assessments from a laboratory performing commercial ICSI for >15 years.

Perspectives on the development and incorporation of assisted reproduction in the equine industry

Marked changes in equine breeding technologies have occurred over the past 25 years. Although there have been numerous reviews on assisted reproduction techniques for horses, few publications include the acceptance and impact of these techniques on the horse industry. In this review, several techniques are discussed, with an emphasis on how they developed in the horse industry and altered equine reproductive medicine. Embryo transfer has become a widely used technology, allowing multiple foals to be produced per year. Embryos can be collected, cooled or frozen, and shipped to a distant facility for transfer into recipient mares. Failure to obtain embryos from some mares stimulated the development of oocyte collection and transfer. Oocyte technologies became more practical when intracytoplasmic sperm injection was developed in the early 2000s. There are now facilities across the world that routinely produce embryos invitro. Cryopreservation of oocytes has lagged because of limited success, but embryo cryopreservation is commonplace. Techniques such as sex-sorted semen, superovulation and genetic diagnosis of embryos are not widely used, and they will require more development before they are established in the horse industry in a cost-efficient manner.

Mare and stallion effects on blastocyst production in a commercial equine ovum pick-up-intracytoplasmic sperm injection program

This study retrospectively examined the degree to which success within a commercial ovum pick-up (OPU)-intracytoplasmic sperm injection (ICSI) program varied between individual mares and stallions. Over 2 years, 552 OPU sessions were performed on 323 privately owned warmblood mares. For mares that yielded at least one blastocyst during the first OPU-ICSI cycle, there was a 77% likelihood of success during subsequent attempts; conversely, when the first cycle yielded no blastocyst, the likelihood of failure (no embryo) in subsequent cycles was 62%. In mares subjected to four or more OPU sessions, the mean percentage of blastocysts per injected oocyte was 20.5% (range 1.4-46.7%), whereas the mean number of blastocysts per OPU-ICSI session was 1.67 (0.2-4.2). Age did not differ significantly between mares that yielded good or poor results. The number of recovered oocytes per OPU was positively associated with the likelihood of success (P<0.001). Although there were considerable between-stallion differences, most stallions (14/16) clustered between 15.6% and 26.8% blastocysts per injected oocyte, and the number of blastocysts per OPU (mean 1.4; range 0.2-2.2) was less variable than among mares. In conclusion, although both mare and stallion affect the success of OPU-ICSI, mare identity and the number of oocytes recovered appear to be the most reliable predictors of success.

Equine blastocyst production under different incubation temperatures and different CO2 concentrations during early cleavage

Some basic parameters for equine invitro embryo production have not yet been established, including the optimum temperature for maturation and embryo culture, and the optimum CO2 concentration and pH during early embryo development. To explore this, we first performed cultures in incubators set at 37.2°C, 37.7°C or 38.2°C. At these temperatures, the corresponding maturation rates were 33%, 38% and 42%; cleavage rates were 84%, 86% and 88%; and blastocyst rates were 35%, 44% and 44% per injected oocyte. These rates did not differ significantly (P>0.2). We then evaluated three different CO2 concentrations (6%, 6.5% or 7% CO2) in 5% O2 for culture over Days 0-5 after intracytoplasmic sperm injection, using a commercial human embryo medium with added serum, at 38.2°C. The pH values of these media were 7.36, 7.33 and 7.29 respectively. In the presence of 6%, 6.5% or 7% CO2, cleavage rates were 68%, 80% and 70% respectively, and blastocyst rates per injected oocyte were 42%, 54% and 27% respectively. The blastocyst rate for the 7% CO2 treatment was significantly lower than that for the 6.5% CO2 treatment (P<0.05). We conclude that equine invitro embryo production is equally effective within the range of 37.2-38.2°C, but that equine early cleavage stage development is sensitive to small changes in CO2 atmosphere and/or medium pH.

Association of equine oocyte and cleavage stage embryo morphology with maternal age and pregnancy after intracytoplasmic sperm injection

In this retrospective study the morphological characteristics of oocytes and cleavage stage embryos were associated with pregnancy results from clinical intracytoplasmic sperm injection (ICSI) in mares. Oocytes were collected from preovulatory follicles, and images (×200; n=401) were captured for measurements of ooplasm, the perivitelline space and zona pellucida. After ICSI and before transfer into recipients' oviducts, cleavage stage embryos were imaged (n=178). Oocyte donor ages (3-13, 14-19, 20-23, 24-27 years) were compared, as were mares aged 3-13 years without versus with recent histories of performance or injury stress. Cleavage rates did not differ with age. However, pregnancy rates declined and pregnancy loss rates (11-50 days gestation) increased with mare age. Young mares with performance or injury stress had significantly lower pregnancy rates than young mares under management typical for broodmares. No morphological oocyte characteristic was consistently associated with age or pregnancy outcome. Cleavage stage embryo morphology was not associated with pregnancy outcome; however, the rate of embryo development before oviductal embryo transfer was faster (P<0.05) for embryos that resulted in an early pregnancy (≤17 days) and tended (P ≤ 0.1) to be higher for embryos that produced a 50-day pregnancy. Embryonic vesicles that had a more rapid increase in diameter were more often (P<0.05) maintained until 50 days gestation.

Equine Aging and the Oocyte: A Potential Model for Reproductive Aging in Women

Numerous similarities in reproductive aging have been documented between the mare and woman. Aging is associated with a decline in fertility. In mares and women, oocyte transfer procedures were initially used to establish that oocyte donor age is associated with oocyte quality. Age-associated differences in oocytes include altered morphology, gene expression, and developmental potential. Reactive oxygen species and mitochondrial dysfunction are thought to be important contributors to loss of oocyte quality. In the woman, aneuploidy is a primary consideration with maternal aging. Although misalignment of chromosomes during meiosis has been observed in the mare, less is known in this area. Reproductive aging will be reviewed in the mare and compared with the woman with emphasis on factors that affect oocyte quality and developmental potential. Areas in which the mare could be used as a research model to study reproductive aging in women will be highlighted.

A retrospective comparison of the efficiency of different assisted reproductive techniques in the horse, emphasizing the impact of maternal age

Advancing maternal age is known to negatively affect fertility in the horse. This age-related decrease in fertility has been linked primarily to reduced oocyte quality rather than to impaired uterine function. In the past decade, the use of ovum pick-up (OPU) and ICSI to produce foals has rapidly gaining popularity amongst sport horse breeders. However, it is not yet known how maternal age influences the efficiency of a commercial OPU-ICSI program and whether the age effect is similar to that observed for other ART in the horse. To answer this question, reproductive records of 289 mares bred by natural mating (NM), 328 mares bred by AI, 205 embryo donor mares (AI-EF-ET), and 473 mares submitted for OPU-ICSI and ET were analyzed retrospectively using a regression model to investigate the effects of maternal age and breeding technique on the likelihood of producing a viable pregnancy. The reproductive efficiency (quantified as the proportion of mares that yielded at least one Day 45 pregnancy) of the different breeding techniques NM, AI, AI-EF-ET and OPU-ICSI-ET was 63.3, 43.9, 45.8 and 37.4%, respectively (P < 0.05). However, the frequent production of multiple embryos per ICSI session (up to 10 embryos in one attempt), makes OPU-ICSI-ET as effective as AI-EF-ET when measured in terms of the mean number of Day 45 pregnant recipients per donor mare. Increasing maternal age was associated with a reduction (P < 0.05) in the reproductive efficiency of all breeding techniques (NM, AI, AI-EF-ET) except OPU-ICSI-ET (P > 0.05). In the OPU-ICSI-ET group, increasing maternal age was associated with a lower number of follicles aspirated and oocytes recovered per mare. Nevertheless, the percentage of blastocysts per injected oocyte, and post-ET likelihoods of pregnancy and pregnancy loss were not influenced by the age of the oocyte donor mare (P > 0.05).

Impact of Equine and Bovine Oocyte Maturation in Follicular Fluid From Young and Old Mares on Embryo Production in Vitro

Equine follicular fluid (FF) provides autocrine and paracrine factors from theca, granulosa, and cumulus cells, both reflecting and impacting oocyte and follicle maturation. We hypothesized that maturation of oocytes in FF from old versus young mares has a deleterious effect on oocyte maturation and their subsequent developmental potential. Follicular fluid was collected from the large, dominant follicle from young mares (4-13 years) or old mares (21-26 years) and classified as: (1) Noninduced follicular fluid (NFF), FF from noninduced follicle 33 ± 3 mm, or (2) Induced follicular fluid (IFF), FF collected ∼24 hours after administration of ovulation-inducing drugs when a follicle 33 ± 3 mm was observed. In experiment 1, immature equine oocytes were collected, matured in vitro for 30 ± 2 hours in 100% IFF, collected from young or old mares, with the addition of follicle stimulating hormone (5 mU/mL), then fertilized by intracytoplasmic sperm injection. In experiment 2, immature bovine oocytes were collected, matured in 100% IFF or NFF, collected from young mares or old mares, then fertilized via in vitro fertilization. In experiment 1, more blastocysts tended (P = .08) to be produced from equine oocytes that were matured in old versus young mare FF. In experiment 2, when IFF and NFF groups were combined, cleavage rates were higher (P = .001) when bovine oocytes were matured in FF from young than old mares. In contrast to our hypothesis, we observed no conclusive evidence that FF from old mares has a deleterious impact on oocytes and their early developmental potential.

Lower blastocyst quality after conventional vs. Piezo ICSI in the horse reflects delayed sperm component remodeling and oocyte activation

PURPOSE

The aim of this study was to evaluate the differential effects of conventional and Piezo-driven ICSI on blastocyst development, and on sperm component remodeling and oocyte activation, in an equine model.

METHODS

In vitro-matured equine oocytes underwent conventional (Conv) or Piezo ICSI, the latter utilizing fluorocarbon ballast. Blastocyst development was compared between treatments to validate the model. Then, oocytes were fixed at 0, 6, or 18 h after injection, and stained for the sperm tail, acrosome, oocyte cortical granules, and chromatin. These parameters were compared between injection techniques and between sham-injected and sperm-injected oocytes among time periods.

RESULTS

Blastocyst rates were 39 and 40%. The nucleus number was lower, and the nuclear fragmentation rate was higher, in blastocysts produced by Conv. Cortical granule loss started at 0H after both sperm and sham injection. The acrosome was present at 0H in both ICSI treatments, and persisted to 18H in significantly more Conv than Piezo oocytes (72 vs. 21%). Sperm head area was unchanged at 6H in Conv but significantly increased at this time in Piezo; correspondingly, at 6H significantly more Conv than Piezo oocytes remained at MII (80 vs. 9.5%). Sham injection did not induce significant meiotic resumption.

CONCLUSIONS

These data show that Piezo ICSI is associated with more rapid sperm component remodeling and oocyte meiotic resumption after sperm injection than is conventional ICSI, and with higher embryo quality at the blastocyst stage. This suggests that there is value in exploring the Piezo technique, utilized with a non-toxic fluorocarbon ballast, for use in clinical human ICSI.

Use of Confocal Microscopy to Evaluate Equine Zygote Development After Sperm Injection of Oocytes Matured In Vivo or In Vitro

Confocal microscopy was used to image stages of equine zygote development, at timed intervals, after intracytoplasmic sperm injection (ICSI) of oocytes that were matured in vivo or in vitro. After fixation for 4, 6, 8, 12, or 16 h after ICSI, zygotes were incubated with α/β tubulin antibodies and human anticentromere antibody (CREST/ACA), washed, incubated in secondary antibodies, conjugated to either Alexa 488 or Alexa 647, and incubated with 561-Phalloidin and Hoechst 33258. An Olympus IX81 spinning disk confocal microscope was used for imaging. Data were analyzed using χ 2 and Fisher's exact tests. Minor differences in developmental phases were observed for oocytes matured in vivo or in vitro. Oocytes formed pronuclei earlier when matured in vivo (67% at 6 h and 80% at 8 h) than in vitro (13% at 6 and 8 h); 80% of oocytes matured in vitro formed pronuclei by 12 h. More (p=0.04) zygotes had atypical phenotypes, indicative of a failure of normal zygote development, when oocyte maturation occurred in vitro versus in vivo (30 and 11%, respectively). Some potential zygotes from oocytes matured in vivo had normal phenotypes, although development appeared to be delayed or arrested. Confocal microscopy provided a feasible method to assess equine zygote development using limited samples.

Cytoskeletal alterations associated with donor age and culture interval for equine oocytes and potential zygotes that failed to cleave after intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) is an established method to fertilise equine oocytes, but not all oocytes cleave after ICSI. The aims of the present study were to examine cytoskeleton patterns in oocytes after aging in vitro for 0, 24 or 48h (Experiment 1) and in potential zygotes that failed to cleave after ICSI of oocytes from donors of different ages (Experiment 2). Cytoplasmic multiasters were observed after oocyte aging for 48h (P<0.01). A similar increase in multiasters was observed with an increased interval after ICSI for young mares (9-13 years) but not old (20-25 years) mares. Actin vesicles were observed more frequently in sperm-injected oocytes from old than young mares. In the present study, multiasters appeared to be associated with cell aging, whereas actin vesicles were associated with aging of the oocyte donor.

Maternal control of early embryogenesis in mammals

Oocyte quality is a critical factor limiting the efficiency of assisted reproductive technologies (ART) and pregnancy success in farm animals and humans. ART success is diminished with increased maternal age, suggesting a close link between poor oocyte quality and ovarian aging. However, the regulation of oocyte quality remains poorly understood. Oocyte quality is functionally linked to ART success because the maternal-to-embryonic transition (MET) is dependent on stored maternal factors, which are accumulated in oocytes during oocyte development and growth. The MET consists of critical developmental processes, including maternal RNA depletion and embryonic genome activation. In recent years, key maternal proteins encoded by maternal-effect genes have been determined, primarily using genetically modified mouse models. These proteins are implicated in various aspects of early embryonic development, including maternal mRNA degradation, epigenetic reprogramming, signal transduction, protein translation and initiation of embryonic genome activation. Species differences exist in the number of cell divisions encompassing the MET and maternal-effect genes controlling this developmental window. Perturbations of maternal control, some of which are associated with ovarian aging, result in decreased oocyte quality.

Effects of aging on gene expression and mitochondrial DNA in the equine oocyte and follicle cells

We hypothesised that advanced mare age is associated with follicle and oocyte gene alterations. The aims of the study were to examine quantitative and temporal differences in mRNA for LH receptor (LHR), amphiregulin (AREG) and epiregulin (EREG) in granulosa cells, phosphodiesterase (PDE) 4D in cumulus cells and PDE3A, G-protein-coupled receptor 3 (GPR3), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and mitochondrial (mt) DNA in oocytes. Samples were collected from dominant follicles of Young (3-12 years) and Old (≥20 years) mares at 0, 6, 9 and 12h after administration of equine recombinant LH. LHR mRNA declined after 0h in Young mares, with no time effect in Old mares. For both ages, gene expression of AREG was elevated at 6 and 9h and EREG was expression was elevated at 9h, with higher expression in Old than Young mares. Cumulus cell PDE4D expression increased by 6h (Old) and 12h (Young). Oocyte GPR3 expression peaked at 9 and 12h in Young and Old mares, respectively. Expression of PDE3A increased at 6h, with the increase greater in oocytes from Old than Young mares at 6 and 9h. Mean GDF9 and BMP15 transcripts were higher in Young than Old, with a peak at 6h. Copy numbers of mtDNA did not vary over time in oocytes from Young mares, but a temporal decrease was observed in oocytes from Old mares. The results support an age-associated asynchrony in the expression of genes that are essential for follicular and oocyte maturation before ovulation.

Influence of transvaginal ultrasound-guided follicular punctures in the mare on heart rate, respiratory rate, facial expression changes, and salivary cortisol as pain scoring

Transvaginal ultrasound-guided follicular punctures are widely used in the mare for diagnosis, research, and commercial applications. The objective of our study was to determine their influence on pain, stress, and well-being in the mare, by evaluating heart rate, breath rate, facial expression changes, and salivary cortisol before, during, and after puncture. For this experiment, 21 pony mares were used. Transvaginal ultrasound-guided aspirations were performed on 11 mares. After injections for sedation, analgesia, and antispasmodia, the follicles from both ovaries were aspirated with a needle introduced through the vagina wall into the ovary. In the control group, 10 mares underwent similar treatments and injections, but no follicular aspiration. Along the session, heart rate and breath rate were evaluated by a trained veterinarian, ears position, eyelid closure, and contraction of facial muscles were evaluated, and salivary samples were taken for evaluation of cortisol concentration. A significant relaxation was observed after sedative injection in the punctured and control mares, according to ear position, eyelid closure, and contraction of facial muscles, but no difference between punctured and control animals was recorded. No significant modification of salivary cortisol concentration during puncture and no difference between punctured and control mares at any time were observed. No significant modification of the breath rate was observed along the procedure for the punctured and the control mares. Heart rate increased significantly but transiently when the needle was introduced in the ovary and was significantly higher at that time for the punctured mares than that for control mares. None of the other investigated parameters were affected at that time, suggesting discomfort is minimal and transient. Improving analgesia, e.g., through a multimodal approach, during that possibly more sensitive step could be recommended. The evaluation of facial expression changes and heart rate is easy-to-use and accurate tools to evaluate pain and well-being of the mare.

Advances in Collection, Transport and Maturation of Equine Oocytes for Assisted Reproductive Techniques

Assisted reproductive techniques that are based on oocyte manipulations have gained acceptance in the equine industry. Methods to collect and handle immature or maturing oocytes have been developed, and systems to ship oocytes now allow for collection in one location and intracytoplasmic sperm injection (ICSI) in another. Subsequently, ICSI-produced embryos can be transferred onsite, shipped to another location, or cryopreserved. Methods for the collection, identification, culture, maturation, and shipment of equine oocytes are reviewed, with an emphasis on procedures from laboratories providing clinical services with documented success.

Cloned foal derived from in vivo matured horse oocytes aspirated by the short disposable needle system

Transvaginal ultrasound-guided follicle aspiration is one method of obtaining recipient oocytes for equine somatic cell nuclear transfer (SCNT). This study was conducted: (1) to evaluate the possibility of oocyte aspiration from pre-ovulatory follicles using a short disposable needle system (14-G) by comparing the oocyte recovery rate with that of a long double lumen needle (12-G); (2) to investigate the developmental competence of recovered oocytes after SCNT and embryo transfer. The recovery rates with the short disposable needle vs. the long needle were not significantly different (47.5% and 35.0%, respectively). Twenty-six SCNT embryos were transferred to 13 mares, and one mare delivered a live offspring at Day 342. There was a perfect identity match between the cloned foal and the cell donor after analysis of microsatellite DNA, and the mitochondrial DNA of the cloned foal was identical with that of the oocyte donor. These results demonstrated that the short disposable needle system can be used to recover oocytes to use as cytoplasts for SCNT, in the production of cloned foals and for other applications in equine embryology.

Presumed monozygotic twins develop following transfer of an in vitro-produced equine embryo

An equine embryo produced by intracytoplasmic sperm injection (ICSI) was trans-cervically transferred to a recipient mare and pregnancy was confirmed via ultrasound examination on days 11, 12 and 15. On days 20 and 22, a single embryonic proper with a heartbeat was observed. On day 29, two embryos proper appeared during ultrasound examination, each possessing a heartbeat. Subsequent examinations on days 35 and 39 revealed continued viability and development of both embryos proper. On day 49, demise of both fetuses was present. Although no DNA analysis or post-partum examinations were performed, it is presumed that the fetuses were monozygotic twins based on membrane classification by ultrasound imaging as well as development occurring after the transfer of a single in vitro-produced embryo.

Ovum pick up, intracytoplasmic sperm injection and somatic cell nuclear transfer in cattle, buffalo and horses: from the research laboratory to clinical practice

Assisted reproductive techniques developed for cattle in the last 25 years, like ovum pick up (OPU), intracytoplasmic sperm injection (ICSI), and somatic cell nuclear transfer, have been transferred and adapted to buffalo and horses. The successful clinical applications of these techniques require both the clinical skills specific to each animal species and an experienced laboratory team to support the in vitro phase of the work. In cattle, OPU can be considered a consolidated technology that is rapidly outpacing conventional superovulation for embryo transfer. In buffalo, OPU represents the only possibility for embryo production to advance the implementation of embryo-based biotechnologies in that industry, although it is still mainly in the developmental phase. In the horse, OPU is now an established procedure for breeding from infertile and sporting mares throughout the year. It requires ICSI that in the horse, contrary to what happens in cattle and buffalo, is very efficient and the only option because conventional IVF does not work. Somatic cell nuclear transfer is destined to fill a very small niche for generating animals of extremely high commercial value. The efficiency is low, but because normal animals can be generated it is likely that advancing our knowledge in that field might improve the technology and reduce its cost.