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Topic:Oocyte
Oocytes in horses are the female gametes involved in reproduction, playing a fundamental role in equine fertility and breeding. These cells are essential for the development of embryos following fertilization and are a focus of study in reproductive biology and veterinary medicine. Research on equine oocytes includes their maturation, quality, and the factors influencing their developmental competence. Studies often explore techniques for in vitro maturation and fertilization, as well as the impact of various physiological and environmental factors on oocyte viability. This page compiles peer-reviewed research studies and scholarly articles that examine the characteristics, developmental processes, and technological advancements related to oocytes in horses.
Ethical monitoring of ovum pick-up procedures in domestic horses: A standardised self-assessment checklist for responsible veterinary practice. Assisted reproductive technologies (ARTs) have the potential to accelerate genetic improvement in selective equine breeding programmes while addressing specific reproductive challenges. One recent assisted reproductive technique in domestic horse breeding is Ovum Pick-Up combined with Intracytoplasmic Sperm Injection (OPU-ICSI). Despite their advantages, the implementation of these new procedures, like more established breeding methods, raises ethical concerns relating to aspects like animal welfare, staff safety, professional and veterinary practice integrity, which must be monitored and asse...
Efficiency of transvaginal oocyte aspiration (TVA), post-mortem ovary harvest (OH), and Intracytoplasmic Sperm Injection (ICSI) in a Quarter Horse mare population in North America. In a clinical setting, Intracytoplasmic Sperm Injection (ICSI)-derived equine blastocysts can be obtained either by transvaginal oocyte aspiration (TVA) or post-mortem ovary harvest (OH). Most peer-reviewed retrospective reports have described the suitability of these techniques for obtaining blastocysts, pregnancies, and live foals, particularly in Warmblood horse populations in Europe. In this study, retrospective data from Quarter Horse client-owned mares subjected to TVA-ICSI (n = 105; 151 cycles) or OH-ICSI (n = 42) at an academic institution in North America between 2023 and 2025...
Factors Influencing Equine Embryo Outcomes in OPU‑ICSI Systems: Insights from a Large‑Scale Program in Brazil. Equine OPU‑ICSI supports commercial IVEP, yet substantial variability persists. We retrospectively analyzed a large dataset generated in Brazil spanning Quarter Horses, Warmbloods, and Mangalarga to evaluate whether predictors previously identified in the literature show comparable patterns under distinct ecological and breeding conditions. Overall oocyte and embryo outcomes were aligned with broadly reported trends from previous studies. Oocytes retrieved from estrous mares bearing a dominant follicle exhibited higher maturation and blastocyst rates. Stallion effects segregated into distinc...
Genetic Diversity in Domestic Horses: Temporal Patterns, the Influence of Assisted Reproductive Technologies, and Implications for the American Quarter Horse. Genetic diversity is the heritable variation within and among populations and is essential for the long-term health and selection potential of domestic horses. Previous studies show diversity across breeds is shaped by effective population size, founder events, artificial selection, and levels of inbreeding. While some closed-studbook breeds retain moderate genetic diversity, others have experienced rapid losses due to popular-sire effects and recent and extensive inbreeding. Even so, mare lines continue to help maintain genetic diversity within these populations. Assisted Reproductive Technol...
Follicular growth and atresia at the time of oocyte aspiration differentially affect in vitro embryo production in mares. Ovum pick-up (OPU) followed by intracytoplasmic sperm injection (ICSI) is increasingly used in horses, yet embryo production rates remain variable, potentially reflecting differences in oocyte developmental competence at the time of aspiration. We investigated whether the stage of the follicular wave, growth phase (GP) versus atresia phase (AP), and associated endocrine profiles in mares, influence oocyte developmental competence. Mares underwent follicular ablation to synchronize follicular waves, and oocytes were aspirated during GP or AP for in vitro production of embryos. Serum concentrati...
Cracks in the ice: biological challenges and incremental progress in equine oocyte vitrification. Equine oocyte vitrification could enhance the flexibility of in vitro embryo production, yet developmental competence remains reduced. Only vitrification of oocytes matured in vivo yields foaling rates comparable to fresh oocytes. Recent advances in vitrification at the germinal vesicle (GV) stage, supported by systematic comparisons of cryoprotective agents and exposure times, has enabled consistent blastocyst production and birth of several foals. Comparative studies of GV and metaphase II (MII) stages suggest biological advantages of vitrification after in vitro maturation (IVM), warranting...
Ovum pick-up in mares: Evidence review and best practice recommendations using a modified GRADE approach. Ovum pick-up (OPU) is a procedure that is now performed in mares worldwide to harvest oocytes for in vitro embryo production. There is a lack of consensus surrounding best practices for various procedural elements of the technique and recently there has been an increasing focus on the welfare aspects of the procedure. Our objective was to summarize current practice and to develop guidelines for OPU in the mare, using a modified GRADE approach to optimize efficiency and mare welfare. Published evidence on various aspects of the procedure was compiled, and to supplement the relative lack of publ...
Water and cryoprotectant permeability of mature equine oocytes: experimental measurements and in silico predictions. Vitrification of equine oocytes is an essential practice for advancing assisted reproductive technologies however, its efficiency remains limited due to the lack of stage and species-specific information on membrane permeability parameters. In this study, water (L) and CPA permeability (P) for dimethyl sulfoxide (Me₂SO) and ethylene glycol (EG) were measured in in vitro matured (MII) equine oocytes. Cumulus oocyte complexes were obtained from abattoir ovaries or by ovum pick-up and matured in vitro for 30 h at 6% CO. Oocytes followed ideal osmometer behavior principles, with an osmotically ...
Comparison of cost for conventional embryo transfer versus intracytoplasmic sperm injection. There are obvious practical advantages of both conventional ET and ICSI. One question that has not been addressed adequately, however, is the relative cost of each procedure and if there is a cost advantage of one over the other. Objective: The objective of the present study was to obtain additional cost data from clinics and breeding farms that perform both ET and ICSI. Methods: A request was sent to 10 clinics that performed either just OPU or OPU/ICSI. These facilities were representative of reproductive specialists located all across the United States. Six clinics provided information on a...
Conventional IVF in the horse past, present, and future: physiological and technical insights. For decades, conventional in vitro fertilization (IVF) in the horse was ineffective, leading to reliance on intracytoplasmic sperm injection (ICSI) for both research and clinical in vitro embryo production. However, the ability to achieve IVF is essential to the study of key reproductive processes, including sperm capacitation, fertilization, and early embryonic development. Recently we have established a repeatable and efficient IVF system for horses, using long-term (9-22 h) sperm pre-incubation. For clinical use, IVF has many features that may support higher embryo quality than does ICSI, a...
Hyperactivation and Tyrosine Phosphorylation of Cryopreserved Stallion Spermatozoa in Relation to Conventional In Vitro Fertilization Blastocyst Production. Challenges in establishing clinical conventional in vitro fertilization (IVF) in horses include variation in sperm and oocyte quality, which can be affected by mare age. Extended preincubation of stallion spermatozoa has resulted in successful IVF. However, there is limited research on the impact of preincubation on sperm characteristics and IVF success. Objective: Responses of frozen-thawed stallion spermatozoa over time under IVF preincubation conditions were evaluated, and samples based on specific responses were tested for their ability to fertilize oocytes, including those from older mare...
Equine Oocyte and Embryo Metabolism in the ART Setting: Current Knowledge and Clinical Significance. Equine in vitro embryo production has become very efficient and is used extensively worldwide for the clinical production of foals. What we know so far about offspring health and performance is promising; however, elements of the in vitro process remain unphysiological when compared to in vivo conditions. Studying the metabolism of oocytes and embryos can help inform the optimisation of culture systems and identify aberrations if they occur. Given the growing body of knowledge on the downstream effects of an inadequate peri-conception environment, both in vivo and in vitro, it is imperative th...
Holding immature equine oocytes for up to 3 nights prior to ICSI under practical shipping conditions (10-22 °C) is compatible with blastocyst development. In vitro embryo production via intracytoplasmic sperm injection (ICSI) is widely used in equine reproductive management. Shipping of immature oocytes allows oocyte recovery for ICSI to be performed by referring veterinarians. However, delays in oocyte shipment are common, and their effect on outcomes is unclear. Shipping is typically done at about 22 °C, but previous studies have shown that holding at 15 °C maintains equine oocyte developmental competence. We hypothesized that lower temperatures may better support oocyte viability if the case that delays occur. Oocytes (n = 664) were rec...
Comparative Evaluation of Follicular Flushing Frequency and Scraping Time During Ovum Pick-Up in Mares: Effects on Oocyte Recovery Rate and Technical Considerations. Transvaginal ultrasound-guided follicular aspiration or ovum pick-up (OPU) has become the standard technique for oocyte collection in mares for intracytoplasmic sperm injection (ICSI). Although repeated follicular flushes and wall scraping are commonly used to improve oocyte recovery rate (ORR), the relative contribution of each remains unclear. This study aimed to compare the effects of multiple flushes versus controlled scraping time on ORR in mares. A controlled trial was conducted in two phases: (1) an ex vivo phase using slaughterhouse ovaries (n = 32), and (2) an in vivo phase in c...
Nicotinic acid treatment improves the developmental potential of equine oocytes for cloned embryo production. Nicotinic acid (NA) treatment during in vitro maturation (IVM) has been shown to elevate nicotinamide adenine dinucleotide (NAD) levels and improve oocyte developmental competence. Suboptimal equine oocyte IVM systems currently limit the efficiency of viable embryo in vitro production. This study evaluated NA supplementation during IVM for cloned equine embryo production, using oocytes from abattoir-sourced ovaries and live mares via ovum pick-up (OPU). Abattoir-derived oocytes (n = 694) were treated without or with 50 or 200 μM NA during the 18 h holding period (Pre-IVM). Next, OPU-deriv...
Impact of dietary essential fatty acids on phospholipid composition and mitochondrial function in aged mares. Advancing age is associated with a decline in fertility and functional capacity, which may result in part from suboptimal nutrition and impaired mitochondrial function. Dietary essential polyunsaturated fatty acids (PUFA) are broadly recommended to mitigate weight loss and reduce risk of chronic disease in aged populations, but their effects on mitochondrial function are less clear. The present study investigated the impacts of dietary supplementation with essential omega-3 PUFA (flaxseed oil; N3) or omega-6 PUFA (corn oil, N6) on blood, muscle and follicular cell fatty acid composition and mi...
Naloxone supplementation during vitrification of equine in vitro matured oocytes after overnight holding: insights from a comparative study with the bovine model. Cryopreservation of equine mature oocytes remains a major challenge in assisted reproduction, mainly due to the limited availability of material and logistical constraints requiring a holding phase. To address these issues, this study evaluated whether naloxone (NX), an opioid receptor antagonist with reported antioxidant properties, could improve vitrification outcomes and whether bovine oocytes could serve as a suitable preliminary and supportive model. Two experiments were conducted. In experiment 1, immature (bGV) and mature (bMII) bovine oocytes were vitrified without (VIT) or with NX (VI...
Comparison of Oocyte Collection Yield Between Conventional Follicle Scraping and Ultrasound-Guided Follicle Aspiration in Postmortem Excised Horse Ovaries. Post-mortem oocyte collection serves to preserve the genetic material of valuable mares and to obtain recipient oocytes for cloning purposes. Therefore, the number of oocytes retrieved per ovary is a critical factor in increasing the likelihood of obtaining a viable embryo. This study evaluated the efficiency of two post-mortem oocyte retrieval techniques: follicular scraping (Scraping) and ultrasound-guided follicular aspiration (OPU). The comparison was based on several parameters, including the number of follicles aspirated per ovary, oocyte recovery rate (ORR), number of oocytes obtained p...
Lipopolysaccharide reduces progesterone and cytokines in equine follicular fluid without affecting oocyte development in vitro. Lipopolysaccharide (LPS) in follicular fluid impairs steroid production and oocyte developmental competence in cows and mice. This study assessed LPS concentrations in equine follicular fluid and their association with steroid and some cytokine levels. Additionally, we evaluated whether LPS exposure during in vitro maturation (IVM) affects equine oocyte developmental competence. In experiment 1, follicular fluid from large follicles (>30 mm in diameter) was collected from 16 slaughterhouse mares, and concentrations of LPS, estradiol, progesterone, TNF-α, and IL-6 were measured. In experim...
Isolation and characterization of mesenchymal stromal cells derived from equine ovarian follicular aspirates. The use of mesenchymal stromal cells (MSCs) in equine reproduction is increasing its interest in the treatment of specific pathologies. MSCs have been isolated from follicular aspirates obtained during transvaginal oocyte aspiration in women, offering a novel source for autologous therapies in reproductive treatments. However, this approach has not been tested in mares despite the common use of transvaginal oocyte aspiration for oocyte collection to produce equine embryos in vitro. Our study aimed to investigate the feasibility of isolating MSCs from equine ovarian follicular aspirates obtaine...
Phenylbutazone treatment of mares does not reduce embryo production via intracytoplasmic sperm injection. Production of embryos via intracytoplasmic sperm injection (ICSI) is a common clinical procedure in equine practice. A recent study indicates that treatment of mares with phenylbutazone paste significantly lowers blastocyst production after ICSI of recovered oocytes. The current study was conducted to determine the effect of different methods of phenylbutazone administration on in vitro embryo production of recovered oocytes in mares. Unassigned: In study 1 (July 29 through September 18, 2024), 14 mares received either oral liquid phenylbutazone once daily for 10 days or no treatment. On the l...
Endocrine profile and OPU-ICSI outcomes in mares: a comparative study. Despite recent improvements in equine ovum pick-up (OPU) combined with intracytoplasmic sperm injection (ICSI), there is still significant inter-individual variability. In this study, serum concentrations of the oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), as well as the GDF9/BMP15 complex, anti-Müllerian hormone (AMH), progesterone (P4), and free and conjugated estradiol-17β (E2), were determined in 59 mares (3-24 years) at the time of OPU. Mares were classified retrospectively, based on the number of embryos obtained, into low or...
Effect of Pre-IVM Duration with cAMP Modulators on the Production of Cloned Equine Embryos and Foals. The asynchrony of cytoplasmic and nuclear maturation in cumulus-oocyte complexes (COCs) due to prematurely declining concentrations of cyclic adenosine monophosphate (cAMP) has been shown to result in reduced oocyte developmental competence. The objective of this study was to evaluate the effect of pre-IVM treatment with cAMP modulators for different durations on the developmental potential of equine oocytes used for cloned embryo production. Collected COCs were transferred to cryovials filled with transport medium at 20-22 °C. Within the cryovials, the COCs were either untreated (Control) fo...
Follicular fluid secretome enhances the meiotic competence of in vitro matured equine oocytes, but not the developmental competence of zygotes after intracytoplasmic sperm injection (ICSI). In vitro embryo production is widely used in equine clinical reproduction; however, its efficiency remains suboptimal due to the undermined developmental competence of in vitro-matured oocytes. In this work, we evaluated the effect of mare preovulatory follicular fluid (PFF) secretome supplementation during in vitro maturation (IVM) of equine oocytes recovered post-mortem. Secretome was isolated from PFF and was added to the IVM medium at concentrations of 20 µg/ml (S20) or 40 µg/ml (S40). The percentage of mature oocytes, as well as embryo cleavage, blastocyst development, and gene expr...
The relationship between post-thaw sperm quality parameters and blastocyst production following Intracytoplasmic Sperm Injection (ICSI) of in vitro-matured equine oocytes. In vitro production of equine embryos by Intracytoplasmic Sperm Injection (ICSI) is commonly utilized to maximize the availability of stallion sperm, particularly from stallions with limited semen supply. The relationship between standard measures of sperm quality in frozen/thawed semen (i.e., sperm motility, normal morphology, DNA quality) and embryo production after ICSI of in vitro-matured equine oocytes has not been thoroughly studied. In this study, frozen/thawed semen from 47 stallions utilized in a commercial ICSI program was analyzed for post-thaw sperm total and progressive motility (...
In vitro embryo production via ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) in pure and crossbred Japanese Hokkaido native ponies. This study evaluated the viability of in vitro embryo production using ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) as breeding techniques for pure and crossbred Hokkaido native ponies (n = 9). Oocytes were collected using transvaginal ultrasound-guided follicle aspiration. ICSI was performed on in vitro matured oocytes using frozen semen. Embryonic cultures were monitored using time-lapse cinematography. Blastocysts were cryopreserved and, after thawing, were transferred non-surgically into recipient mares. Over nine OPU sessions, the mean number of aspirated follicles was 2...
Evidence of glycan mosaicism in the equine oviduct. We report a lectin histochemical study of oviductal ampulla and isthmus of thirteen mares euthanised at anestrus (1), estrus (5), 1-day post-ovulation (5) or diestrus (2). Staining with a panel of 5 lectins recognizing N-Acetylgalactosamine (GalNAc) residues revealed mosaicism in glycan expression in some specimens of ampulla and isthmus, peaking at estrus and 1-day post-ovulation (ov+1). In the ampulla, this presented as positively stained areas of both ciliated and non-ciliated cells in otherwise negatively-stained ampullae, ranging from small foci (diestrus) to areas up to 200 microns in le...
Role of anti-Müllerian hormone in different reproductive aspects of female mammals: women, cow and mare. Anti-Müllerian hormone (AMH) is a dimeric glycoprotein belonging to the superfamily of the transforming growth factor-β. Due to the discovery of AMH functions, relative to the ovarian function, it is being postulated as being a highly important marker in studies on mammalian reproduction. Therefore, the objective of this review was to describe the role of this hormone in different reproductive aspects of female mammals, taking women, cows, and mares as reference species. The relationship between ovarian reserve and AMH was analysed, and it has been verified that there is a relationship betwe...
The Influence of Aspiration Pressure, Follicle Flushing Method and Needle Rotation During Single-Operator OPU Technique on Oocyte Recovery and Embryo Production in the Mare. The objective of this study was to determine the effect of two aspiration pressures (75 vs. 150 mmHg), the follicle flushing method (injection pump controlled by a foot pedal vs. a plastic syringe) and the twisting of the OPU needle on oocyte recovery and in vitro embryo production. OPU data from a total of 104 warmblood sport mares belonging to a commercial OPU-ICSI program were collected as part of a prospective study split into three experiments. Each mare was used only once for OPU. In Experiment 1, the mares' follicles were aspirated using either a high aspiration pressure (flow rate of 1...
Equine in vitro fertilization with frozen-thawed semen is associated with shortened pre-incubation time and modified capacitation-related changes. We recently reported successful equine IVF using fresh semen pre-incubated for a prolonged period (22 h) before co-culture with oocytes. In this study, we evaluated the feasibility of equine IVF with frozen-thawed sperm and evaluated capacitation-related changes in these sperm over the pre-incubation period. Sperm selected via a commercial sperm separation device (SSD) yielded significantly higher fertilization than did sperm selected by swim-up or by colloid centrifugation. Using the SSD method, fertilization rates with sperm pre-incubated for 15 min, 3 h, 6 h, and 9 h were 7.1, 22.2, 38...
