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Topic:Fertility
Fertility in horses encompasses the physiological processes and factors influencing reproductive success in equine species. It involves the study of reproductive anatomy, endocrinology, and behavior, as well as the management practices that affect breeding outcomes. Key aspects include the estrous cycle, conception rates, and factors impacting stallion and mare fertility. Reproductive technologies such as artificial insemination, embryo transfer, and hormonal therapies are also explored to enhance breeding efficiency. This page compiles peer-reviewed research studies and scholarly articles that examine the biological mechanisms, management strategies, and technological advancements related to equine fertility.
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...
Membrane and mitochondrial antioxidants improve post-thaw functional quality of stallion spermatozoa. Cryopreservation of stallion semen induces oxidative stress that compromises sperm motility, membrane integrity, and mitochondrial function. Given the high mitochondrial reliance of equine spermatozoa and their susceptibility to oxidative damage, compartment-specific antioxidant strategies may improve post-thaw functional resilience. This study evaluated the effects of astaxanthin, a membrane-active carotenoid, and MitoTEMPO, a mitochondria-targeted superoxide scavenger, on the functional and oxidative status of frozen-thawed stallion spermatozoa. Ejaculates from nine stallions were cryopreser...
Age, embryo donor status, and insemination with chilled semen all predispose to persistent breeding-induced endometritis in warmblood mares. Persistent breeding-induced endometritis (PBIE) is a common reason for mares failing to establish pregnancy. Objective: To examine the hypothesis that advancing mare age and embryo donor status predispose to PBIE and compromise fertility. Methods: Retrospective analysis of the impact of mare age, breeding system (embryo donor versus broodmare), and semen type (chilled versus frozen-thawed) on the likelihood of PBIE and subsequent pregnancy/embryo recovery. Methods: Warmblood mares (n = 769) inseminated during 1745 oestrous cycles were divided into three age categories (≤6, 7-13 and ≥14...
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...
Relationship between the estrus duration in cyclic mares and the endometrial gene expression on day 7 post-ovulation. This study investigated the effect of estrus duration on endometrial gene expression in cyclic mares on Day 7 post-ovulation, focusing on transcripts relevant to early pregnancy: uterocalin (P19), insulin-like growth factor 1 (IGF1), fibroblast growth factor 2 (FGF2), progesterone receptor (PGR), and estrogen receptor alpha (ESR1). Twelve mares were classified according to the estrus duration in long estrus (LE, ≥ 3 days of endometrial edema; n = 7) or short estrus (SE, 0.1). ESR1 expression was undetectable in all samples. These findings suggest that prolonged estrus enhances P19 e...
Fungal endometritis in broodmares: clinical presentation, prevalence in Ireland and diagnostic performance of cytology. Fungal endometritis is an uncommon uterine condition associated with poor fertility. Objective: This study aimed to 1) provide a descriptive summary of 11 cases of fungal endometritis, 2) assess prevalence trends of fungal endometritis over time, 3) assess fungal species distribution in diagnostic samples, and 4) evaluate the diagnostic accuracy of cytology. Methods: Study 1 reviewed records of 11 mares diagnosed with fungal endometritis for history, presentation, treatment, and outcome. Study 2 analysed 6,727 uterine samples (swabs and lavages; 2019-2024) for factors influencing fungal cultur...
Endometrial Evaluation Using Video-Assisted Hysteroscopy After Uterine Prolapse Management in a Mare. This case report describes the successful application of video-assisted hysteroscopy to evaluate endometrial recovery in a 6-year-old mare following treatment for complete uterine prolapse secondary to dystocia. Upon presentation, the uterus was manually reduced and supported with a Buhner's suture. A multimodal medical protocol, including broad-spectrum antibiotics, anti-inflammatory drugs and uterine lavage, was initiated. Five days after reduction, an endoscopic evaluation was performed using a dedicated videovaginoscope without uterine insufflation. The procedure provided high-resolution i...
Comparative analysis of uterine inflammation in jennies and mares after insemination with cryopreserved donkey semen. The limited fertility of jennies inseminated with frozen donkey semen remains a major challenge for donkey reproduction and conservation, contrasting with the more favorable outcomes observed in mares. Species-specific differences in post-breeding uterine inflammation have been proposed as a key factor underlying this disparity. This study compared the uterine inflammatory response and pregnancy outcomes of jennies and mares inseminated with frozen donkey semen. Twelve jennies and eleven mares were monitored over 48 and 44 estrous cycles, respectively. Artificial insemination (AI) was performe...
Impact of donor mare and stallion identity on the likelihood of pregnancy after transfer of in vitro produced embryos. The success of in vitro embryo production (IVEP) is influenced by donor mare and stallion. Objective: To determine whether donor mare and stallion influence the pregnancy rate after transfer of in vitro produced (IVP) blastocysts and to identify factors influencing the likelihood of obtaining one or more pregnancies from a single IVEP session. Methods: Retrospective clinical study. Methods: The influence of the following variables on pregnancy outcome was assessed in 2292 transfers of IVP blastocysts: speed of in vitro embryo development, embryo grade after thawing, age of the donor mare, blas...
Clinical pregnancy outcomes after transfer of fresh and vitrified-warmed conventional IVF equine embryos. In vitro fertilization (IVF) in horses has emerged as a valuable assisted reproductive technology, yet the impact of embryo cryopreservation on pregnancy outcomes when utilizing this technique remains unclear. This study reports pregnancy outcomes following transfer of conventional equine IVF embryos, with both fresh and vitrified-warmed embryos. Conventional IVF (cIVF) was used to produce 40 embryos, which were transferred to recipient mares, pregnancy diagnosis was performed at 6 days post-transfer followed by embryonic heartbeat detection between day 25 and 30 of gestation. Observed pregnan...
Comparative Evaluation of Sperm Quality Assessment Methods in Purebred Spanish Horses. Evaluating semen quality in Purebred Spanish Horses is essential to determine reproductive potential and optimize assisted reproductive techniques. Objective: This study compared several sperm analysis methods in Purebred Spanish Horses to standardize protocols suitable for both laboratory and field conditions. Methods: Fifteen stallions were evaluated through three ejaculates, analyzing sperm parameters using different techniques. Sperm kinematics was assessed by Sperm Computer Analyzer (SCA-CASA) or iSperm mCASA. Viability was analyzed by eosin-nigrosin-Giemsa (ENG) staining or Hoechst 33258...
Changes in the Mare Oviduct Across Different Seasons Throughout the Year. At present, oviductal pathologies and their influence on mare fertility have not been clearly determined. Checking changes throughout the year in the oviductal structure may be relevant to understand the influence on the appearance of problems in oviductal functionality and, thus, the impact on fertility, which is the objective of this work. The oviducts of 56 mares were examined. Their anatomy, permeability, oviductal cellularity and the presence of pathologies were assessed to establish the correlations between the time of the year and each of these parameters. We cannot conclude whether the...
Are antioxidants hindering stallion sperm capacitation? A perspective on hidden barriers to equine IVF success. Heavy use of antioxidants in equine in vitro fertilisation (IVF) media may suppress the reactive oxygen species (ROS) signals stallion sperm need for capacitation, which depends on high mitochondrial activity and a well-maintained endogenous redox homeostasis. A species-specific approach balancing oxidative protection with controlled ROS signalling could improve fertilisation efficiency and reduce prolonged incubation times.
Functional Characterization of Long Non-Coding RNAs Associated with Reproductive Fitness in Pura Raza Española Mares. Long non-coding RNAs (lncRNAs) are transcripts constituted of more than 200 nucleotides that have been associated with the regulation of different biological processes by modulating the expression of key genes. In horses, evidence suggests that lncRNAs play a role in female reproductive fitness, yet their functional implications remain poorly characterized. The objective of this study was to investigate potential DNA:RNA triplex interactions between the promoter regions of fertility-related genes and lncRNAs transcribed from non-coding loci located within ±50 kb of these genes. By doing so, w...
Deficiency in homozygous haplotypes reveals recessive lethal variants affecting fertility and viability in the Friesian horse. BACKGROUND: Recessive lethal alleles causing pre- or postnatal death in homozygous mutant animals, could lead to reduced fertility success. The Friesian horse breed has signs of reduced fertility and has faced high inbreeding rates in the past (∆F > 1%). Consequently, by genetic drift lethal alleles may have reached moderate to high frequencies in the population. Our aim was to identify lethal recessive alleles that — when homozygous — may cause pre- or postnatal death in the Friesian horse. RESULTS: We analyzed genotypes (70 K SNP) of over 8,000 Friesian horses, looking for hapl...
The fertility of a sub-population of stallions is negatively affected by ambient climatic conditions, mediated through DNA damage. Exposure to systemic heat stress in male mammals adversely affects sperm production, fertility, and DNA integrity. To date, few studies have investigated this phenomenon in horses, particularly in industry-relevant environments. Therefore, this study examined the relationship between ambient climatic conditions and fertility within a population of commercially fertile stallions. Post-coital semen samples ( = 804) were collected weekly from 46 Thoroughbred stallions during two successive breeding seasons (NSW, Australia; 22 weeks total). Semen samples were processed via single-layer colloid...
Relationship between the duration of endometrial edema and reproductive parameters of estrus, diestrus, and fertility in mares: a field study. The duration of endometrial edema has been positively correlated with uterine receptivity and likelihood of pregnancy. Therefore, this study aimed to evaluate whether there is a relationship between the duration of endometrial edema (DEdema) and other key parameters of the estrous cycle: maximum edema (MEdema), largest follicle diameter (LPF), corpus luteum and uterine tone on day 5 post ovulation (CLD5 and TD5), progesterone concentration (P4) and fertility. A total of 88 cycles from 36 mares were evaluated and divided into Short Estrus (SE), Long Estrus (LE), Inseminated (AI) and Non-insemin...
Temporal characterization of conditions that promote functional capacitation of stallion sperm. Equine in vitro fertilization (IVF) has historically been challenged due to lack of conditions that promote functional capacitation of stallion sperm. Capacitation success is often attributed to prolonged sperm incubation requirements. Advances to equine IVF are hindered by incomplete characterization of conditions that promote the functional capacitation of stallion sperm over time. Herein, we describe conditions that promote the functional capacitation of fresh, cooled, and frozen-thawed stallion sperm isolated by Percoll, Swim-Up, or Microfluidics (VetMotl). Fresh (diluted sperm) and previo...
Isolation and characterization of seminal extracellular vesicles subsets and their impact on sperm freezability in stallions. The ability of spermatozoa to withstand cryopreservation differs between stallions. While the underlying mechanisms of these differences are not fully understood, seminal plasma (SP) may play a crucial role in modulating sperm cryotolerance. Seminal plasma contains a heterogeneous population of extracellular vesicles (sEVs), nanometer-sized membrane particles that can transfer biomolecules to sperm modulating their function. This study aimed to isolate and characterize two sized-sEV subsets-small (S-) and large (L-)-from stallion SP, and to evaluate their involvement in sperm freezability. Sem...
Paternal determinants of Offspring Sex Ratio in horses: A retrospective analysis of stallion breed, age, and breeding method. Offspring Sex Ratio (OSR) at birth in mammals is generally assumed to follow a 1:1 male-to-female distribution, yet deviations in OSR have been observed and may be influenced by maternal and paternal factors. In this study we have focused on the effect of paternal factors (stallion age and breed) and breeding methods on the OSR. Using a retrospective dataset of 251,783 foal births recorded in France between 2015 and 2024, we applied generalized linear mixed models to evaluate the effects of these variables on the likelihood of producing a female foal. Stallion identity was included as a random...
Metabolomics reveals early predictors of blastocyst formation in equine ICSI-derived embryos. Equine in vitro embryo production (IVP) via ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) has gained prominence in sport-horse breeding due to high success rates, efficient semen utilization, and year-round embryo production, including from mares with fertility challenges or postmortem. However, assessing viability of early-stage ICSI-produced equine embryos remains challenging due to subjective morphological evaluations and limited visibility of developmental features. Non-invasive metabolomic analysis of culture media offers a promising alternative to enhance embryo selectio...
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...
Amniotic Mesenchymal Stromal/Stem Cell-Derived Extracellular Vesicles for Equine Chronic Degenerative Endometritis Treatment. Equine chronic degenerative endometritis (CDE) is a progressive process characterized by endometrial fibrosis that could be responsible for alterations of uterine environment and foetal-maternal communication. Objective: The aim of this study was to try to restore this communication by intrauterine administrations of amniotic cell-derived extracellular vesicles (AMC-EVs) in a case series. Methods: Twelve mares were selected on the basis of their reproductive history of early embryonic loss or abortion and clinical suspicion of CDE subsequently verified with histopathological examination of end...
Diagnosis of Equine Genital Leptospirosis (EGL) in mares with poor reproductive performance. Leptospirosis is a zoonotic disease caused by spirochetes of the genus Leptospira. Equine genital leptospirosis (EGL) has been described as a chronic and silent syndrome, presenting reproductive alterations such as abortion, stillbirth, placentitis, embryonic loss, repeat breeding syndrome, and subfertility. This study aimed to investigate the genital Leptospira infection in naturally infected mares with poor reproductive performance, as well as to genetically characterize the agents. A total of 41 mares with a history of poor reproductive performance were selected. Sera were collected for ser...
Effective methods of horse reproduction in the production of mare’s milk. The research aims to study the dynamics of reproductive system pathologies in mares of Kazakh and Mugalzhar horse breeds and their impact on the reproductive traits of the breeding stock. The object of the research was horses of the Kazakh and Mugalzhar breeds. The formation of experimental groups was carried out using the pair-analog method. It was found that the frequency of detection of infertile mares is 13.8-25.0%. Subinvolution of the uterus from the total number of infertile mares is 8.3-10.7%, endometritis - 16.6-23.3%, atony and hypotonia of the uterus - 8.3-13.3%, ovarian diseases - ...
GnRH Administration Increases Synchronisation of Ovulation in Mares. The objective of this study was to evaluate the effects of exogenous GnRH administration at the beginning of estrus synchronisation in mares during the spring transitional period. Estrus was synchronised using a progesterone releasing intravaginal device (PRID). The PRID was left in the vagina for 10 days, followed by an injection of 0.4 mg of cloprostenol at PRID removal. The GnRH group (n = 32) was subjected to intramuscular administration of 100 μg of the GnRH agonist triptorelin at PRID insertion, while the control group (n = 32) received 1 mL of sterile physiological sali...
Cryoprotective Efficacy of Omega-3 Nano-Emulsion on Kinematic Parameters, Acrosome Status, Subcellular Ultrastructure, and Oxidative/Antioxidant Markers in Cryopreserved Stallion Semen. This study aims to investigate the cryoprotective effect of Omega-3 nano-emulsion (Omega-3 NE) on stallion sperm quality, kinematic parameters, acrosome status, subcellular ultrastructure, oxidative/antioxidant markers, and semen microbiota. Forty ejaculates were collected, extended, and cryopreserved from 5 fertile Pure Egyptian stallions (Equus caballus). The ejaculates were divided into five groups: a control group (without additive) and four groups supplemented with 25, 50, 100, and 200 μg of Omega-3 NE/mL. The Omega-3 NE exhibited an average particle size of 51-146 nm, a PDI of 0.58,...
Assessing the Sperm Head DNA Damage in Frozen/Thawed Horse Spermatozoa via Xenogeneic ICSI. In the mouse, spermatozoa are highly resistant to DNA damage, even when frozen without cryoprotectants, and can produce offspring when subsequently used for ICSI (intracytoplasmic sperm injection). It is not known whether the same applies to other mammals as well. For example, in the horse, even conventional sperm freezing is still very problematic and frequently leads to sperm immobility. It has, however, never been tested whether sperm immobility also mirrors sperm head DNA damage, and if so, to what extent. In our study, we evaluated the damage to DNA in horse frozen and thawed motile and i...
Effects of intrauterine ozone insufflation in eleven subfertile mares: a case series. Equine persistent breeding-induced endometritis can lead to chronic uterine inflammation and fibrosis, reducing fertility. Intrauterine ozone (O₃) has recently been proposed as a potential treatment for mares unresponsive to conventional therapies. This case series describes O₃ treatment in eleven mares barren for at least one year despite multiple inseminations attempts. During the first oestrous cycle, low-volume uterine lavage and endometrial biopsy were performed, followed by 3 consecutive days of intrauterine O₂-O₃ gas insufflation. In the subsequent cycle, both procedures were re...
Metabolomics of stallion seminal plasma: Identification of potential fertility biomarkers based on differences between high and low pregnancy stallions. The seminal plasma (SP), a fluid originating from the testes, epididymis, and accessory sex glands, represents 98 % of the volume of stallion ejaculate. Metabolomic analysis enables the identification of final products of metabolic pathways, providing insights into reproductive physiology. Objective: This study aimed to investigate the metabolomic profile of stallion seminal plasma and to investigate metabolic differences between stallions with high and low pregnancy rates, in order to identify potential biomarkers associated with fertility. Methods: Twenty-four Criollo stallions, were sampled...
