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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.
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...
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...
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...
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...
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...
Sequencing and Differential Analysis of miRNA in the Ovaries of Kazakh Horses During Estrus and Anestrus States. To reveal the regulatory role of miRNA in the estrous cycle transition of Kazakh horse ovaries and improve their reproductive efficiency, this study took the ovaries of Kazakh horses in the estrus period (DY group) and the quiescent period (DB group) as research objects. Small RNA sequencing and bioinformatics analysis were used to systematically analyze the expression characteristics and functional pathways of miRNA under the two physiological states. A total of 161 million high-quality miRNA tags were obtained through sequencing. Principal component analysis showed that the intra-group repea...
Isolation of high-quality stallion spermatozoa: a comparison of methods and their effects on sperm quality and yield, DNA damage, and functional competence by ICSI. Intracytoplasmic sperm injection (ICSI) is the primary method for equine in vitro embryo production, yet outcomes may be influenced by sperm selection techniques. Objective: This study compared four isolation methods: EquiPure™, Vetmotl™, Felix™, and Samson™, to assess effects on sperm quality and embryo development. Methods: Semen was collected from four fertile stallions, processed and evaluated for sperm motility, viability, DNA integrity, and yield of high-quality cells relative to input. Isolated samples were compared to non-isolated (centrifuged) samples. Spermatozoa were used fo...
Pre-ovulatory follicles and ipsilateral ovarian stroma are cooler than non-dominant antral follicles and stroma on the contralateral ovary of the mare. Reports in several species have demonstrated that pre-ovulatory follicles (POFs) are cooler than neighbouring ovarian tissue, with cooling important for fertility. This study measured the temperature of POFs and compared it with other regions of the ovary, cervix, and rectum to determine if POF cooling occurs in mares. Fourteen oestrous cycles in 11 mares were monitored, and when an ovarian follicle ≥38 mm was present, deslorelin was given. Thirty hours later, rectal and cervical temperature measurements were taken. Mares were sedated and ovarian temperature measurements taken using a ther...
Sperm Energy-restriction and Recovery (SER) enhances equine sperm function and embryo development after ICSI. Assisted reproductive technologies (ART) are extensively used in domestic animal reproduction; however, improving their efficiency and consistency remains a major challenge for achieving reliable reproductive outcomes. The equine industry faces unique challenges related to sperm capacitation, which limited the success of conventional in vitro fertilization (IVF) for many years. Consequently, intracytoplasmic sperm injection (ICSI) became the most widely used technique for commercial in vitro embryo production. Even though a successful IVF protocol was recently developed, substantial opportunit...
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...
Blood ammonia levels: A potential indicator of high-risk pregnancy in Thoroughbred broodmares. Exposure to high blood ammonia (hyperammonemia) interferes with gestation due to its detrimental effect on hormone levels, fetal development, the immune system, placental integrity, and fertility of broodmares. Increases in ammonia levels are dangerous and elusive, as damage may occur from earlier peaks, resulting in the trapping of ammonia in the amniotic fluid and then disappearing from the blood circulation before clinical symptoms are observed. Thus, it should be recognized early and treated immediately before complications arise. This study aimed to investigate if blood ammonia levels in ...
Advanced paternal age is associated with reduced reproductive success and offspring racing performance in Australian Thoroughbred racehorses. Reproductive ageing influences fertility and offspring fitness across mammals. In humans and model organisms, paternal age has been associated with changes in sperm quality and genomic integrity, including oxidative stress, DNA damage, and epigenetic alterations; however, these mechanisms have not been directly examined in large equine populations. Thoroughbred racehorses provide a system to investigate paternal age effects at scale using detailed breeding records. In this retrospective observational study, with data from 35 retired stallions and 33,546 progeny, we assessed associations betwee...
Matched embryo-endometrium RNA-seq reveals coordinated but asymmetric transcriptomic reprogramming at the onset of early equine pregnancy. Maternal recognition of pregnancy (MRP) in the mare requires coordinated adaptations of both the conceptus and the endometrium during the peri-recognition interval; however, integrated transcriptomic analyses of both compartments within the same biological window remain limited. Here, we analyzed conceptus RNA-seq data across embryonic age (Days 8 and 12 post ovulation) and endometrial RNA-seq data across pregnancy status (pregnant versus non-pregnant mares sampled between Days 8 and 12 post ovulation). In pregnant mares, conceptus recovery and endometrial biopsy collection were performed with...
Redefining stallion sperm bioenergetics: lessons from a decade of change in mammalian sperm metabolism. In brief: Sperm bioenergetics is now understood as an integrated system in which ATP production, redox homeostasis, substrate availability, and cellular heterogeneity jointly determine sperm function. This review uses the stallion as an oxidative-biased model to synthesize advances from 2016 to 2026 and proposes a metabolically plastic framework with direct implications for semen preservation and fertility assessment. Abstract: Over the last decade, mammalian sperm metabolism has moved from a binary view centered on glycolysis versus oxidative phosphorylation to an integrated model in which AT...
Achieving Success in Conventional Equine Embryo Transfer: A Practical Review. Equine embryo transfer is a well-established procedure in horse breeding programs and it's used to increase the number of offspring from valuable mares, obtain embryos from mares in competition and produce foals from mares unable to carry a pregnancy to term. The success of embryo recovery depends mainly on the day of flushing, management of insemination, and the fertility of donor mare and stallion. Other relevant factors include donor age and reproductive status, number of ovulations, operator experience, and flushing technique. Pregnancy rates after transfer are influenced by donor-recipien...
Chromosomal chaos: understanding aneuploidy associated with assisted reproductive technologies. Pregnancy loss remains a significant challenge for the equine breeding industry, with substantial economic and management consequences. Chromosomal abnormalities have emerged as a central driver of pregnancy loss, particularly during early gestation, highlighting the need to better understand the etiology of this inherent genetic instability. Concurrently, the rapid expansion of assisted reproductive technologies (ART) offers promise for improving equine reproductive efficiency alongside the traditional practice of natural cover. However, the increasing use of in vitro embryo production (IVP) ...
Effect of Spirulina platensis extract (C-phycocyanin) supplementation to the semen extender on kinematic and oxidative parameters of Marwari stallions during freezing. The current research aimed at examining the impact of different quantities of Spirulina platensis extract (C-phycocyanin) supplemented to the semen extender on the post-thaw quality of Marwari stallion spermatozoa. Semen samples were obtained via an artificial vagina from six fertile stallions and diluted with an extender containing Spirulina platensis extract (C-phycocyanin) at concentrations of 10, 20, and 50 µg/mL, or without Spirulina as a control. Aliquots of diluted semen were subjected to cooling (4 °C, 120 min) and then frozen (-196 °C, 1 day), after which the kinematic paramet...
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...
Cytogenetic, genomic, and reproductive characterization of four pura Raza Española mares carrying a 64, X, del(X),t(X; Y) complex karyotype. Chromosomal abnormalities involving the sex chromosomes constitute critical genetic factors influencing fertility in horses. Nevertheless, a substantial proportion of individuals carrying sex chromosomal abnormalities exhibit normal reproductive phenotypes, which complicates their identification until adulthood. Here, we present four mares carrying a complex deletion/translocation rearrangement with the karyotype formula 64, X, del(X)(p∼25),t(X; Y)(p∼25; q∼15). The cases analyzed belong to three unrelated families of Pura Raza Española (PRE), all presenting the same chromosomal abnormal...
Novel technique for correcting urovagina via urethral transposition in the horse. Vesicovaginal reflux is a common cause of infertility in mares. Surgical correction is commonly recommended and involves caudal relocation of the urethral orifice which forces the urine to be expelled caudally. There have been several previously described techniques. Complications associated with caudal urethral extension occur in 11-33.3% of cases. Objective: To identify a novel technique for performing caudal urethral translocation that effectively corrects vesicovaginal reflux with minimal associated complications. Methods: In vivo experiment and clinical case series. Methods: The experimen...
Annual Variation in Stallion Testicular Measurements and Its Association With Hormonal Profiles and Semen Quality. In a stallion breeding-soundness examination, testicular volume may be estimated either from total scrotal width or by measuring the height, width and length of both testes. This study aimed to determine whether testicular morphometric parameters obtained by ultrasonography fluctuate throughout the year, and whether these variations affect semen quality and hormone production in stallions located at low latitudes in the Southern Hemisphere. Eight healthy light-breed stallions were evaluated every 15 days for 1 year, encompassing the breeding (October-April) and non-breeding(May-September) ...
Application of Anti-Müllerian Hormone in Regulation of Ovarian Function and Its Practical Relevance for Fertility and Embryo Production in Cows and Mares. In the female organism, Anti-Müllerian hormone (AMH) is produced exclusively by granulosa cells, particularly in secondary and early tertiary follicles. The amount of AMH released into the blood is proportional to the total number of follicles present in the ovaries and is therefore used to estimate the ovarian functional reserve. In both cattle and mares, a strong and highly repeatable association has also been demonstrated between AMH concentrations and antral follicle count. Therefore, AMH may serve as a biomarker with broad diagnostic utility in reproductive medicine in these species, as ...
