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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.
Placental adaptation to maternal environment in domestic animals. The developmental origins of health and disease (DOHaD) is based on the observation that environmental conditions during sensitive windows of development shape lifelong physiology and disease susceptibility. While fetal organs are often viewed as direct programming targets, the placenta is a crucial mechanistic hub because it senses maternal conditions and actively constructs the fetal environment through nutrient transport, endocrine signaling, and immune regulation. Placental plasticity spans morphology and how exchanges are favored by tissue topology, vascular development and perfusion, tra...
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...
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...
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...
Maternal age-related changes in renin-angiotensin-aldosterone system and electrolyte homeostasis during equine pregnancy. The renin-angiotensin-aldosterone system (RAAS) plays a key role in fluid and electrolyte homeostasis during pregnancy. In humans and laboratory animals, maternal age has been shown to modulate RAAS activity, potentially altering the secretion of renin (REN), angiotensin II (ANG-II), and aldosterone (ALD), thereby influencing sodium (Na⁺) and potassium (K⁺) regulation. Objective: To evaluate whether maternal age influences RAAS activity in pregnant mares. Methods: Forty-five Spanish Purebred mares were monitored monthly over 11 months of pregnancy and categorized into three age groups: You...
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...
Effect of Antioxidant Supplementation on Systemic Oxidative Status in Breeding Stallions During Intensive Semen Collection. Breeding stallions are subjected to increased metabolic and physiological demands during the reproductive season, which may lead to enhanced production of reactive oxygen species and disruption of redox balance. The present study evaluated the effects of dietary antioxidant supplementation on oxidative status, metabolic profile, and hindgut fermentation in stallions undergoing intensive semen collection activity. Ten adult breeding stallions were assigned either to a control group or to a treatment group receiving a commercial antioxidant supplement (Oxyliver) for 60 days, followed by a 60-day...
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...
Prevalence, genomic diversity and emerging antimicrobial resistance of Taylorella asinigenitalis in Grand Noir du Berry breeding donkeys. Taylorella asinigenitalis is a fastidious Gram-negative bacterium of the equine genital tract, found more commonly in donkeys than horses. Although considered non-pathogenic, it is closely related to Taylorella equigenitalis, the agent of contagious equine metritis, and has been linked to experimental and natural cases of endometritis. The SAFRAN project (French acronym for "Sauvegarde de la fertilité de l'âne", meaning "Preservation of donkey fertility"), launched in 2024 by the French National Research Institute for Agriculture, Food and Environment (INRAE) with support from the Centre-Val...
Estrous cycle-dependent changes in platelet indices in healthy mares. Platelets (PLTs) are key regulators of hemostasis, inflammation, and tissue remodeling, and their phenotype is known to fluctuate with sex steroid concentrations in several species. However, the influence of the estrous cycle on PLT characteristics in mares has not been investigated. We hypothesized that PLT indices vary between reproductive phases in association with changes in estradiol-17β (E2) and progesterone (P4). The aim of this study was to characterize PLT indices in estrus and diestrus and to determine how these hematological parameters relate to circulating E2 and P4 concentrations...
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 ...
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...
Vitrification of in vivo produced equine embryos: Size really does matter! Vitrification rather than slow-freezing has become the method of choice for the cryopreservation of in-vivo produced embryos. It is a simple technique that does not require a programmable freezing machine and relies chiefly on placing the embryo on a surface, rather than within a straw, in a small volume of vitrification solution to achieve extremely rapid cooling rates. However, in the field of equine embryo vitrification size truly does matter. Methodologies for both vitrification and warming prior to transfer are largely dictated by the size of the embryo. Since embryo size is directly rela...
Comparative analysis of mesenchymal stromal cells derived from ovarian follicular aspirates of young and aged mares. Mesenchymal stromal cells from equine ovarian follicular aspirates represent a promising source for cell-based therapies. However, the age of the donor mare may alter their biological properties and therapeutic potential. This study aimed to evaluate the effect of age on MSCs from ovarian follicular aspirates of young (< 10 years, n = 5) and aged (≥ 18 years, n = 5) mares. MSCs were isolated, expanded, cryopreserved at passage 3, and subsequently thawed to evaluate proliferation, immunophenotype, differentiation capacity, and gene expression profiles. Proliferation rates, total cel...
The Role of Omega-3 Fatty Acids in Horses’ Nutrition-A Review. This narrative review presents examples of omega-3 fatty acids supplementation in horse nutrition. Fats are essential in equine nutrition, serving not only as an energy source but also as functional components influencing health. Among them, omega-3 polyunsaturated fatty acids (PUFAs), particularly EPA and DHA, play a key role in modulating inflammatory and metabolic processes. This review summarizes their effects on respiratory health, equine metabolic syndrome (EMS), musculoskeletal function, reproduction, and early development. Omega-3 supplementation has been shown to support airway inflam...
Effect of N-acetyl cysteine treatment on uterine cytokine and chemokine profiles in mares with persistent breeding-induced endometritis. Persistent breeding-induced endometritis (PBIE) is a major cause of infertility in mares. Recent research has shown that PBIE-affected mares treated with intrauterine N-acetyl cysteine (NAC) 12 hours before breeding showed no improvement in clinical signs at 12- and 60-hours post-breeding. Objective: The present study was designed to examine the effects of NAC treatment on the uterine inflammatory cytokine and chemokine profiles in PBIE-affected mares. Methods: Using a randomized, blinded, cross-over design, mares susceptible to PBIE (n=9) were allocated to Control and Treatment cycles with at...
Near-Term Extrauterine Pregnancy Secondary To Uterine Rupture In A Mare. Uterine rupture is an uncommon but life-threatening complication of equine reproduction, typically associated with dystocia, uterine torsion, fetal manipulation, or hydrops. Tears may occur in either the uterine horns or body, although involvement of the ventral uterine body is rare. This case report describes an 11-year-old Arabian mare at 350 days of gestation that developed abdominal pregnancy secondary to uterine torsion and full-thickness ventral uterine rupture, resulting in fetal death and the free presence of the fetus within the peritoneal cavity. Surgical removal of the fetus and pri...
Ovarian follicle dynamics in the plains zebra (Equus quagga). Understanding follicular dynamics during the estrous cycle is essential for developing breeding programs and assisted reproductive technologies (ARTs) in any species. In this context, knowledge of follicular dynamics and related uterine changes in the plains zebra (Equus quagga) is essential to increase the declining population of this vital African species and to provide comparative insights into more endangered zebra species. Likely due to the difficulty of handling these wild species, no detailed reproductive study using ultrasonography has been performed in any zebra. Therefore, the presen...
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...
Insights from healthy mares reveal that mammalian uteri harbor a diverse virome. The Earth's estimated 10 virions, primarily phages, significantly impact microbial ecosystems. Despite their abundance, viromes remain relatively understudied-particularly in domestic animals. While recent studies have described a dynamic commensal microbiome in mammalian uteri, no research has yet characterized the commensal virome in a mammalian uterus. In this study, we report for the first time the presence of a sparse, but diverse native virome in the equine uterus. The resulting virome database consists of 513 non-redundant viral genomes (> 2 kb). Taxonomic annotations revealed the...
Molecular detection of pathogenic Leptospira spp. in mares with reproductive disorders enrolled in embryo transfer programs. Equine genital leptospirosis (EGL) is associated with reproductive disorders in mares. However, its occurrence in embryo transfer (ET) programs remains poorly characterized. Objective: Given the scarcity of data on the circulation of Leptospira spp. in mares enrolled in ET programs, this study aimed to investigate the serological and molecular occurrence of Leptospira spp. in mares with a history of reproductive disorders from 13 stud farms dedicated to embryo transfer in Brazil. Methods: Serum and endometrial cytobrush samples (ECS) were collected from 70 unvaccinated mares. Serological analy...
FGF2, LIF, and IGF1 supplementation during in vitro maturation or culture improves equine ICSI embryo development in an age-dependent manner. Ovum pickup (OPU) combined with intracytoplasmic sperm injection (ICSI) has reshaped equine assisted reproduction, enabling embryo production from mares and stallions with constrained breeding opportunities; however, limited efficiency of in vitro maturation (IVM) and in vitro culture (IVC) continues to hinder embryo production. Growth factor supplementation with fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and insulin-like growth factor 1 (IGF1) in combination (FLI) has been shown to enhance oocyte and embryo developmental competence in several species. Objective: This...
Factors influencing gestation length in Mares in the Tiaret region, Algeria. Gestation length is a key parameter in equine reproductive management, yet its variability remains poorly documented in Barb and Arabian mares under Algerian conditions. Objective: This study aims to determine gestation length in mares and to assess the influence of various factors, including breed, year of mating, mating month, mare age, parity, reproductive status, stallion and the foal's sex on gestation duration. Methods: A total of 133 mares from the National Stud Farm of Tiaret (Algeria) were monitored over the period 2021-2024. Results: The mean gestation length was 332.5 days (range: 3...
The Equine Reproductive Microbiota: Composition, Dynamics, Dysbiosis, and Implications for Fertility in Mares and Stallions. The equine reproductive microbiota has emerged as an important factor influencing reproductive health and fertility in both mares and stallions. Traditionally, the equine uterus was considered sterile, and microbial presence was interpreted primarily in the context of infection. However, sequencing-based studies have demonstrated that the reproductive tract, including the uterus and semen, contains detectable microbial communities or microbial DNA signatures, challenging this traditional paradigm. In mares, the vaginal microbiota is consistently dominated by , , , and , whereas the uterine env...
Nano-Encapsulated Vitamin E Enhances Cryo-Resistance of Stallion Spermatozoa: A Comprehensive Evaluation of Sperm Quality, Kinematic Parameters, Antioxidant Capacity, Microbiota and Ultrastructure. This experiment explores the comparative ability of vitamin E (VE) and its nano-emulsion (VEN) in enhancing cryo-resistance of stallion spermatozoa by examining semen quality, kinematic variables, acrosome integrity, apoptosis, antioxidant capacity, ultra-structural alterations and microbiota of cryopreserved stallion sperm. Semen from five stallions (8-10 years) was cryopreserved with 0.1 or 1 mM of VE or VEN; and a non-additive group served as the control. The VEN particles ranged in size from 72 to 172 nm, with a mean diameter of 287 nm. Supplementation with VE (1 mM) or VEN (0.1 ...
miRNA Sequencing and Differential Analysis of Testis in 1-Year-Old and 2-Year-Old Kazakh Horses. The represents a significant genetic resource within China's population, characterized by notable resilience and an ability to thrive on coarse forage. Nevertheless, a decline in its numbers has been observed recently, making the improvement of its reproductive performance crucial for the preservation of this breed and the advancement of the related industry. In this study, testicular tissues from 1-year-old (pre-pubertal) and 2-year-old (post-pubertal) were analyzed. miRNA sequencing was conducted on tissues from these age groups, followed by bioinformatics analyses to elucidate the functi...
Comparative analysis of mRNA and circRNA expression profiles and interaction networks in testicular tissues of Mongolian horses before and after sexual maturity. Mongolian horses, celebrated for their resilience and adaptability, undergo marked physiological transformations during sexual maturation. This study employed whole-transcriptome sequencing to conduct a comparative analysis of mRNA and circular RNA (circRNA) expression profiles, along with their interactive regulatory networks, in testicular tissues of Mongolian horses pre- and post-sexual maturity. Histological examinations using hematoxylin-eosin (H.E.) and 4’,6-diamidino-2-phenylindole (DAPI) staining revealed distinct morphological differences between sexually immature and mature testicu...
