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Topic:Reproduction
Reproduction in horses encompasses the biological processes and mechanisms involved in the breeding and development of equine offspring. This includes the study of reproductive anatomy, physiology, and endocrinology in both mares and stallions. Key areas of interest include the estrous cycle, ovulation, conception, gestation, and parturition. Researchers also examine factors influencing fertility, reproductive technologies such as artificial insemination and embryo transfer, and management practices that impact reproductive success. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological, genetic, and environmental aspects of equine reproduction.
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...
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...
Layer-Specific Quantitative Assessment of Collagen Distribution in Equine Uteri Using Masson’s Trichrome and Digital Image Analysis: A Comparative Study. Equine endometrial fibrosis is a chronic and progressive equine uterine condition characterized by fibrosis that affects mares' fertility, with a wide range of fertility outcomes being reported for these mares. Therefore, assessing layer-specific collagen (COL) distribution is essential for a comprehensive understanding of endometrial remodelling and its impact on equine reproductive potential. Full-thickness uterine samples, including stratum functionalis (SF), stratum basalis (SB) and myometrium, were collected post-mortem from healthy control mares (Category I; n = 10) and those with mo...
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. ...
Oxidative and Mitochondrial Status of Vitrified Equine In Vitro Matured Oocytes Using Temperature-Specific Equilibration Protocols. Cryopreservation of equine in vitro matured (IVM) oocytes remains a major challenge in assisted reproduction due to their high susceptibility to cryoinjury, including oxidative stress and mitochondrial dysfunction. The aim of this study was to evaluate the physiological status of vitrified/warmed equine IVM oocytes following vitrification using two temperature-specific equilibration protocols by assessing reactive oxygen species (ROS), intracellular glutathione (GSH) content and mitochondrial oxidative activity and distribution patterns. Oocytes were vitrified after 28 h of IVM either at 25...
Comparative Susceptibility of Donkey and Horse Sperm to Liquid-Storage Temperature. Preservation protocols for donkey sperm are based on those developed for horses, despite potential interspecific differences in cooling tolerance. This study compared horse and donkey sperm during long-term storage at 5°C and 17°C. Ejaculates from four stallions and four jacks (n = 16) were centrifuged, resuspended in skimmed milk-based extender, and stored at both temperatures. Sperm motility, plasma and acrosome membrane integrity, and morphology were evaluated after 1, 2 and 7 days. Fresh semen parameters showed no interspecific differences (p > 0.05). At 5°C, donkey sperm show...
Differential Gene Expression of Mesenchymal Stromal Cell and Granulosa Cell Markers in Equine Follicular Aspirates. Equine follicular aspirates obtained during ovum pick-up contain a heterogeneous mixture of mesenchymal stromal cells (MSC) and granulosa cells (GC). This study evaluates how selective isolation and expansion of MSC decrease GC populations. Follicular aspirates-derived cells were cultured up to passage four (P4) following a previously validated protocol. While freshly isolated follicular aspirates cells (FAC) displayed heterogeneous morphologies, early passages (P3-P4) showed a uniform, spindle-shaped phenotype compatible with MSC. Gene expression analysis by RT-qPCR revealed a marked upregula...
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 ...
Testicular Expression of Vitamin-D Receptor and Vitamin-D-Metabolizing Enzymes (CYP2R1, CYP27A1, and CYP27B1) in Normal and Cryptorchid Horses. Vitamin D (VD) is required for testis activity being a key regulator of calcium and testosterone, both essential for spermatogenesis and sperm maturation. VD is activated by a metabolizing machinery of enzymes (CYP2R1, CYP27A1, CYP27B1) and acts throughout its receptor (VDR). Cryptorchidism is a developmental defect caused by the failed scrotal descend of the testicle and can compromise fertility depending on whether one or both testes are retained. Here, we reported the expression and localization of VDR- and VD-activating enzymes in the testis of normal and unilateral cryptorchid equines obt...
Application of digital pathology to assess the effect of hormone treatment on placental histomorphometry in mares with induced ascending placentitis. This study aimed to evaluate the effects of hormonal treatments with altrenogest (ALT) and estradiol cypionate (ECP) on placental histomorphometry in mares with experimentally induced ascending placentitis, using digital pathology as a quantitative tool. Thirty pregnancies from 27 Criollo-type mares were assigned to six groups: healthy controls (n = 5); basic treatment (n = 5), treated with trimethoprim-sulfamethoxazole (TSM), and flunixin meglumine (FM); ALT group (n = 5) + basic treatment; ECP group (n = 5) + basic treatment; ALT + ECP group (n = 5) in addition to basic treat...
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...
Cryopreservation of Bovine, Equine, and Porcine Sperm. In livestock breeding, cryopreserved semen is routinely used for artificial insemination. Sperm cryopreservation enables long-term storage and transport of insemination doses, thereby securing genetic material for later use. Although specifics may vary, commonly used sperm cryopreservation protocols for domestic species feature similar processing steps as outlined in this chapter. We here describe common procedures for cryopreservation of bull, stallion and boar sperm. This includes preparation and use of the following diluents: TRIS egg yolk extenders (TEY) for bull sperm, ordinary and freezi...
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...
The effect of macrophage secretome on equine endometrial fibroblast transcriptomic and functional characteristics. Endometrial fibrosis is a main hallmark of endometrosis, a degenerative condition of the equine endometrium. Fibrosis, is characterized by the excessive accumulation of extracellular matrix (ECM) components. Current research highlights the crucial role of MΦ in activating fibroblasts in the development of fibrotic processes. However, the specific actions of distinct MΦ subpopulations on equine endometrial fibroblasts remain to be elucidated. Thus, this study aimed to investigate the long-term effect of the secretome of equine in vitro-generated monocyte-derived (eqMD)-MΦ (pro-inflammatory M...
Transcriptome Sequencing and Differential Expression Analysis of Ovaries from Kazakh Mares During Seasonal Quiescence and Estrus Activation. Kazakh horses are typical seasonal breeders, and ovarian activity is markedly reduced during the non-breeding period. Hormonal stimulation can induce ovarian functional responses during seasonal anestrus; however, the early ovarian transcriptional changes associated with this response remain incompletely understood. In this study, ovarian transcriptome sequencing was performed in 12 Kazakh mares examined during the seasonal anestrous period. The mares were classified into a non-hormonally stimulated seasonal quiescent group (DB, = 6) and a hormone-induced ovarian activation group (DY, = 6) f...
The Polish Konik Horse: A Multidisciplinary Review of Its Origin, Genetics, Ecology, Health, Behaviour and Reproductive Biology. The Polish Konik horse (PKH) is one of Europe's best-known native conservation breeds. Traditionally associated with the extinct Eurasian tarpan and conservation grazing, the breed has recently become the subject of multidisciplinary research encompassing genetics, ecology, health, behaviour and reproduction. This narrative review summarises current knowledge on the biological characteristics and contemporary scientific significance of the PKH. Literature published between 2005 and 2026 was identified through searches of PubMed, Scopus, Web of Science and Google Scholar and narratively synthes...
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...
Veterinarian and breeder perspectives surrounding ovum pick-up and intracytoplasmic sperm injection in mares: A survey study. There is an ethical debate about the application of ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) in mares. Objective: To survey the opinions of equine veterinarians and breeders of sport horses on the ethics of using OPU-ICSI in mares. Methods: Cross-sectional descriptive study. Methods: Three surveys were distributed. The first targeted breeders ('Breeder Survey') who were actively involved in sport horse breeding. The second targeted veterinarians performing OPU ('OPU-Reprovets Survey'). The third targeted general equine practitioners ('Practitioner Survey'). There were six...
Histological differences in the placenta of three mares treated for ascending bacterial placentitis compared to physiological pregnancies. Ascending bacterial placentitis is a frequent cause of late pregnancy loss in mares. The histology of placentitis has been described but mainly with a focus on inflammatory changes. In this study, we assessed several aspects beyond inflammatory processes between mares foaling close to term during treatment for placentitis and physiological pregnancies. We included placental tissue from physiological term pregnancies (group PP; n = 8) and clinical cases with confirmed ascending bacterial placentitis (group PL; n = 3). Samples were collected from several locations of the allantochorion (cerv...
Serum physiology, fecal microbiota, and metabolome signatures associated with perinatal stage transitions in Mongolian mares. Lactation is a critical reproductive trait that influences offspring survival and livestock productivity in equine production. Characterizing physiological transitions during the perinatal period can improve our understanding of how mares adapt to late gestation, parturition, and early lactation. However, in horses-a typical monogastric herbivore with unique digestive characteristics-the associations between gut microbiota and perinatal physiological adaptation, as well as related stage-associated microbial and metabolic features, remain largely uncharacterized. Unassigned: In this study, para...
Evidence-based interpretation of uterine cultures in mares: Linking bacterial growth patterns to endometrial inflammation. We evaluated uterine bacterial growth patterns and their association with endometrial inflammation (EI) in equine samples collected using uterine swabs (US) or low-volume uterine lavage (UL). A database including 1,545 US and 2,066 UL with cytological and bacteriological results was retrospectively analysed. Endometrial inflammation was defined as ≥2 polymorphonuclear cells per high-power field, and bacterial culture was considered positive when aerobic growth occurred within 48 h, with the number of bacterial isolates per sample recorded (0, 1, 2, or ≥3). Data were analysed using generali...
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...
Extracellular matrix and microvascularization regulatory genes in the mare placenta. In the mare placenta, molecular mechanisms regulating extracellular matrix (ECM) collagen deposition and vascularization are not fully understood. This study evaluated: (i) gene transcription and expression of enzymes regulating collagen deposition (matrix metalloproteinases - MMP2, MMP9), and their inhibitors (TIMP1, TIMP2); (ii) gene transcription of vascular endothelial growth factor (VEGF-A) and its receptors VEGF receptor 1 and 2 (VEGFR1 and VEGFR2); and (iii) methylation pattern of these genes promoter regions (MMP2, TIMP1, TIMP2), in both placental horns (pregnant-PH and non-pregnant-NP...
