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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.
Serum and uterine fluid extracellular vesicles and prostaglandin E metabolite concentrations during diestrus and early pregnancy in mares. Prostaglandins produced by endometrial and conceptus tissues have an established role in maintaining luteal function in early pregnancy and initiating luteolysis during diestrus in mares. The cellular mechanisms controlling the secretion and delivery of prostaglandins have not been fully elucidated. We hypothesized that nanosized lipid bilayer extracellular vesicles (EV) that carry a variety of biological molecules would be involved in these key regulatory processes. Serum and uterine fluid samples were collected from diestrus and pregnant mares on day (D) 10 and D14 post-ovulation, and concep...
Low-dose histrelin for ovulation induction in mares: a partially randomized crossover pilot study. This partially randomized crossover pilot study evaluated reduced doses of histrelin for ovulation induction in mares and compared intramuscular (IM) administration with pharmacopuncture at the Bai-hui and Yan-chi acupoints. Eleven mares were enrolled, of which nine completed all eight protocols and were included in the analyses. The protocols comprised 250 µg histrelin IM (standard dose), 75 µg IM, 25 µg IM, no intervention, saline at Bai-hui, saline at Yan-chi, 25 µg histrelin at Bai-hui, and 25 µg histrelin at Yan-chi. Ovulation was assessed by transrectal ultrasonography at sched...
Superior Post-Thaw Sperm Quality and Fertility of Epididymal Compared with Ejaculated Sperm in Subfertile Stallions. Despite the benefits of seminal plasma during breeding, its value is questionable when utilizing biotechnological approaches such as artificial insemination. In addition, deleterious effects of secretions from accessory glands on sperm viability and conception rate have been reported, especially in stallions with poor semen quality. Objective: The present study aimed to compare the kinetics, structural and functional viability, and fertility parameters of spermatozoa obtained from the ejaculate and from the cauda epididymis of subfertile stallions, as well as to evaluate the differences in the...
Effect of Different Equilibration Times in the Freezing Process on Post-Thaw Motility Parameters in Equine Spermatozoa. Cryopreservation of stallion semen remains suboptimal, with approximately one-third of stallions producing semen that is poorly tolerant to freezing. As optimization of pre-freezing procedures may improve post-thaw sperm quality, this study evaluated the effect of different equilibration times before freezing on the post-thaw quality of stallion semen. For this purpose, 21 ejaculates were initially collected from 5 stallions and 15 were included in the final analysis after predefined exclusions. These ejaculates were separated from the seminal plasma via centrifugation in INRA 96 medium. After...
Understanding Stallion Sperm Capacitation: Species-Specific Mechanisms, Cryocapacitation, and Implications for IVF. Until recently, no repeatable protocol for equine in vitro fertilization (IVF) had been established, despite decades of trying. Recent studies have demonstrated reproducible IVF outcomes under specific experimental conditions, bringing equine IVF into a new perspective. Prolonged incubation of stallion spermatozoa in a TALP based medium supplemented with penicillamine, hypotaurine and epinephrine (PHE) appears to be important factors of protocols that support sperm capacitation and markedly improved IVF outcomes. The sperm capacitation procedure has now been applied successfully using both fre...
Cumulus cell DNA fragmentation as non-invasive biomarker of equine oocyte quality in in vitro embryo production. The efficiency of in vitro embryo production in animal species is constrained by the absence of practical, non-invasive biomarkers to assess oocyte quality. Cumulus cell DNA fragmentation index (CC-DFI) has been proposed as a biomarker in humans, but data in animals remain limited. Objective: This study investigated the association of CC-DFI with in vitro maturation (IVM) and intracytoplasmic sperm injection (ICSI) outcomes in horses, and its relationship with mare-related factors, autumnal transition period, cumulus cell viability, and cumulus expansion. Methods: Cumulus-oocyte complexes (COC...
Influence of Follicle Number and Reproductive Cyclicity on Mesenchymal Stromal Cell Yield Isolated From Equine Ovarian Follicular Aspirates. Follicular aspirates have emerged as an alternative source of mesenchymal stromal cells (MSC) in mares; however, factors influencing successful MSC isolation remain unclear. This study evaluated whether reproductive cyclicity and follicle count affect MSC recovery from ovum pick-up (OPU)-derived follicular aspirates. Twenty-eight OPU procedures were performed on 13 mares, and cells were cultured until passage 3. Successful MSC cultures were obtained in 15/28 procedures (53.6%), while 13 procedures (46.4%) yielded non-MSC populations. Neither reproductive status (cycling vs. anestrous) nor foll...
Effect of Uncoated Magnetic Nanoparticles on Stallion Sperm Parameters: Influence of Semen Quality. The aim of this study was to evaluate the effect of uncoated, non-functionalised magnetic nanoparticles (MNPs) on stallion sperm and to determine whether these effects depend on initial semen quality. Ten cooled ejaculates from 3 stallions were exposed to different MNP concentrations ([MNPs] = 0, 5, 25, and 50 mg/mL), agitated, and exposed to an external magnet to recover the unbound sperm fraction. Ejaculates were classified as high- or low-quality groups according to initial evaluation sperm quality index (HSQi and LSQi), and the effect of [MNPs] was evaluated within groups using GLM. ...
Recent Advances and Emerging Applications in Embryo Vitrification for Livestock. Vitrification has progressively supplanted conventional slow freezing as the method of choice for embryo cryopreservation in both human medicine and animal production, particularly for in vitro-produced embryos and for species or developmental stages highly sensitive to conventional freezing. By combining very high cooling and warming rates with concentrated cryoprotectant solutions and minimal sample volumes, it largely prevents intracellular ice formation and, in experienced hands, consistently yields post-warming survival and developmental rates that exceed those obtained with traditional ...
Redox homeostasis modulation promotes capacitation-associated events in equine sperm. Sperm capacitation, a crucial process for successful fertilization, is modulated by reactive oxygen species (ROS) and involves molecular changes including increased membrane fluidity, cholesterol depletion, and protein tyrosine phosphorylation. Although an effective equine in vitro fertilization protocol has recently been described, its requirement for prolonged capacitation limits applicability to high-quality ejaculates. Because stallion spermatozoa possess endogenous antioxidant systems that may mitigate ROS accumulation and delay ROS-mediated capacitation, this study investigated whether i...
Effect of conditioned medium from equine Wharton’s jelly mesenchymal stem/stromal cells on cool-stored stallion semen. Artificial insemination in horses largely relies on cooled transported semen, but stallion spermatozoa are highly sensitive to cold stress, limiting storage duration. Mesenchymal stem/stromal cell-derived conditioned medium (CM) has shown protective effects on sperm in other species, yet its impact on equine semen remains unexplored. This study investigated the effects of equine Wharton's jelly-derived MSC-CM (eWJ-MSC-CM), on the quality of cooled stallion semen. Semen from five stallions of proven fertility was extended in INRA96 supplemented with 0, 5, or 15% eWJ-MSC-CM at 5 °C for 0, 24 a...
Mare endometrosis induces endometrial proteome changes. Endometrosis, characterized by excessive endometrial fibrosis, is a major reproductive disorder that impairs fertility and remains a significant challenge in equine breeding. The molecular mechanisms underlying equine endometrosis are not fully understood. This study investigated endometrial proteomic changes induced by endometrosis to identify the biological processes (BP) and pathways involved. Cyclic mares' endometrial biopsies were categorized as category IIA (n = 5) or category IIB (n = 5), according to Kenney and Doig's classification. LC-MS/MS assessed the endometrial proteome, ...
Endocrine Disorders and Their Effect on Equine Reproduction. Continuing the reproductive potential of aged horses is a request many equine practitioners may receive. Reproductive performance may be impacted by a host of age-related comorbidities such as the endocrinopathies, pituitary pars intermedia dysfunction, and equine metabolic syndrome. While limited information is known, reproductive effects described may include irregular estrous cycles, development of anovulatory follicles, increased incidence of uterine infection, or generalized infertility. Accurate diagnosis, management strategies, and monitoring remain critical for improving quality of lif...
Oocyte and Embryo Vitrification in Horses. Vitrification has emerged as a decisive technique in assisted reproductive technology, offering superior cryopreservation outcomes for both oocytes and embryos compared with traditional slow freezing. This chapter provides a comprehensive overview of the vitrification of equine oocytes and embryos, emphasizing the influence of technical factors, including cryoprotectant selection, exposure time, temperature control, and device volume, on vitrification outcomes. Biological factors such as the oocyte maturation stage, the presence of cumulus cells, and embryo size are also explored, highlighting...
Comparison of donkey and stallion semen preservation: effects of egg yolk plasma, seminal plasma and extenders on sperm motility, MALDI profiles and fertility. The conservation of donkey breeds at risk of extinction requires the development and optimisation of semen preservation and artificial insemination strategies aimed at improving reproductive efficiency, increasing genetic diversity and supporting sustainable population management. The effects of commercial extenders (INRA96, BotuSemen Gold, Beyond), seminal plasma (SP) removal and egg yolk plasma (EYP; 0-10%) supplementation on jack semen stored at 4°C for 24-48 h were evaluated, using stallion semen as a reference. Sperm motility was assessed by computer-assisted sperm analysis (CASA), where...
Use of Sildenafil Citrate for the Treatment of Erectile Dysfunction in Stallions: First Case Reports. Pharmacological aids can be useful alternatives to enhance penile erection and/or improve ejaculatory function, thereby prolonging the reproductive life of stallions with ejaculatory disorders. This study aimed to evaluate the effects of sildenafil citrate in the treatment of erectile dysfunction and on semen quality in two aged stallions, a Quarter Horse (18 years) and a Mangalarga Marchador (25 years), presented to the Veterinary Hospital of FMVZ-UNESP, Botucatu, SP, Brazil. The treatment consisted of oral administration of sildenafil citrate at 0.2 mg/kg. Thirty minutes after administ...
hCG promotes secondary ovulation and supplementary corpus luteum formation during early pregnancy in mares. This study evaluated whether the administration of human chorionic gonadotropin (hCG) during early pregnancy accelerates ovulatory dynamics and alters serum progesterone concentrations in mares with dominant follicles. Thirty pregnant embryo-recipient mares with follicles ≥35 mm during early gestation were randomly assigned to receive either 1500 IU hCG IV (hCG group; n = 17) or saline solution IV (control group; n = 13). Mares were monitored by serial ultrasonography to determine the ovulatory response and the interval to secondary ovulation. Serum progesterone concentrations were...
Sixty-day oral antioxidant supplementation enhances sperm morphology and seminal plasma antioxidant capacity in stallions. While dietary supplementation with antioxidants has been identified as an effective strategy for mitigating oxidative stress (OS) damage in stallion sperm, specific protocols and the duration of its efficacy remain poorly defined. This study aimed to evaluate the effects of a 60-d dietary supplementation with a commercial antioxidant combination on semen quality and OS biomarkers in stallions. Stallions were divided into two groups: the control group (n = 5; CTRL) received 30 g/500 kg of placebo while the treated group (n = 5; OXY) received 30 g/500 kg of Oxyliver daily for 60...
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...
Questionnaire-Based Investigation into Stallion Management Practices in 28 Countries. Modern stud farm practices may limit stallion social contact, with potential welfare and safety implications. Objective: To describe housing, management and safety outcomes for stallions kept at horse breeding operations throughout the world and to assess regional differences. Methods: An online questionnaire was distributed via mailing lists and WhatsApp; 116 complete responses from breeding operations were collected and analysed. The focus was on management of the breeding facility, and stallion welfare indicated by management, handling and housing. Results: Respondents were from Europe (40....
Effects of the Freezing Diluent Tonicity and Prefreezing Cooling Rates on Post-Thaw Sperm Quality Markers in the Pure-Bred Arabian Stallion. Stallion semen cryopreservation remains limited by inconsistent post-thaw sperm quality and fertility. This study evaluated the effects of freezing extender effective tonicity and prefreezing cooling rate on post-thaw sperm characteristics in pure-bred Arabian stallions. In a two-phase design, ejaculates ( = 40) from 10 stallions were processed using extenders with different osmotic conditions (330, 390, and 450 mOsm/kg) and subjected to cooling durations of 45 min, 1.5 h, or 3 h. Sperm quality was assessed using CASA, functional assays, flow cytometry, transcriptomic analysis, and...
The Effect of Different Extenders and Testicular Anaesthesia During Orchiectomy on Post-Thawed Spermatological Parameters of Stallion Epididymal Spermatozoa. Cryopreservation of epididymal stallion spermatozoa is a valuable tool for fertility preservation, particularly after orchiectomy. However, the potential interactions between local anaesthesia and extender composition on post-thaw spermatozoal quality remain poorly understood. This study investigated the effects of intratesticular lidocaine injection and the efficacy of various extender (egg yolk [EY] vs. lecithin [LC]) and cryoprotectant (glycerol [GLY] vs. dimethyl sulfoxide [DMSO]) combinations on stallion epididymal spermatological parameters. Using a paired factorial design, epididymal s...
The effects of clomiphene citrate on reproductive parameters in the mare. Clomiphene citrate (CC) is a longstanding human fertility drug that has yet to be investigated in horses. The objective was to evaluate effects of CC on mare reproduction. After follicle ablation on Day 0, treatment mares (n=5) received 2 grams of CC intravenously on Days 1-5 while control mares (n=4) received no treatment. Transrectal ultrasonography was performed on Days 1-5 and 8, and transvaginal oocyte aspiration occurred on Day 8. Hormones were analyzed on Days 0-5, 8, 11, and 15. Mares receiving CC exhibited higher uterine edema grades compared to control mares (P=0.009). Antral follicl...
Supplementation of IVM media with equine follicular fluid of large follicles increases blastocyst yield in equine ICSI programs. Despite advances in the use of intracytoplasmic sperm injection (ICSI) for the in vitro production of equine embryos, oocyte maturation and competence to sustain pre-implantation embryo development remain significant challenges. This study evaluated the supplementation of the in vitro maturation (IVM) medium with equine follicular fluid (eFF), obtained from young mares (2-15 years old) with oocyte-to-blastocyst conversion rates >22%, as a strategy to improve oocyte developmental competence. In the first experiment, IVM medium was supplemented with 10% eFF collected from ovarian follicles of di...
Combined effects of pre-freeze cholesterol-loaded cyclodextrin and post-thaw pentoxifylline on the functional longevity of cryopreserved stallion sperm. Cryopreservation causes structural and metabolic damage to stallion spermatozoa, impairing post-thaw functional competence. Objective: This study evaluated whether cholesterol-loaded cyclodextrin (CLC) supplementation before freezing, combined with pentoxifylline (PTX) after thawing, improves the functional quality, oxidative status, mitochondrial activity, and preliminary fertility outcomes of cryopreserved stallion semen. Methods: Semen from twelve stallions was assigned to four CLC concentrations (0, 1, 1.5, and 2 mg), frozen, thawed, and divided into subgroups with or without PTX supplemen...
Effects of a dimethylformamide-glycerol combination on freezing behavior, post-thaw sperm quality, and sperm-oocyte interaction in Arabian stallions. Although glycerol (GLY) and dimethylformamide (DMF) are widely used cryoprotectant agents (CPAs) for freezing equine semen, their combined use remains less characterized. Objective: To evaluate the effects of DMF, GLY, and their combination (DMF+GLY) on freezing behavior, sperm kinematics, membrane integrity, and IVF-related functional endpoints in Arabian stallion sperm. Methods: Twenty-four ejaculates from four stallions (six/male) were diluted in BotuSemen-Gold® extender supplemented with 5% DMF, 5% GLY, or 3% DMF+ 3% GLY, packed into 0.5-ml straws, and frozen. Sperm-oocyte binding and pro...
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...
Effects of equine sperm incubation under capacitation-supporting conditions on homologous and heterologous ICSI outcomes. Intracytoplasmic sperm injection (ICSI) in horses has become sufficiently efficient to be considered for clinical and commercial application; however, several factors influencing its efficiency remain poorly understood. This study evaluated whether incubating equine sperm under capacitating conditions induces capacitation-associated changes and affects embryo development following homologous equine ICSI, as well as oocyte activation, early cleavage, and 5-methylcytosine (5 mC) and 5-hydroxymethylcytosine (5hmC) levels following heterologous ICSI using bovine oocytes. Equine spermatozoa were ...
The effect of fenugreek (Trigonella foenum-graecum) on stallion spermatozoa motility and vitality in vitro. This study evaluated the effects of Trigonella foenum-graecum L. (fenugreek) seed extract on stallion spermatozoa quality in vitro, focusing on motility, vitality, and functional competence. In vitro spermatozoa analyses showed that fenugreek seed extract did not demonstrate overt cytotoxicity under the tested conditions: S1 = 1562 µg/mL; S2 = 781 µg/mL; S3 = 390.5 µg/mL; S4 = 195.25 µg/mL; S5 = 97.62 µg/mL; S6 = 48.81 µg/mL; S7 = 24.40 µg/mL. Computer-assisted semen analysis (CASA) revealed a concentration- and time-dependent Treatment × Time interac...
Seminal plasma exposure modulates peripheral T cell-associated transcription during early pregnancy in the mare. Successful establishment of pregnancy requires maternal immune tolerance to paternal antigens introduced by insemination. Regulatory T cell (Treg)-associated responses are thought to play a central role in this process, whereas pro-inflammatory T helper 1 (Th1) responses may disrupt pregnancy success. In other species, seminal plasma (SP) has been shown to modulate maternal immune adaptation; however, this relationship remains poorly defined in mares, where SP is frequently reduced during routine breeding practices. The objectives of this study were to (1) characterize temporal changes in syst...
