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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.
Antibiofilm action of ozonated sunflower oil against bacteria isolated from the uterus of mares susceptible to endometritis. This study aimed to characterize the antibiofilm action of ozone-enriched sunflower oil (O) against pathogens associated with endometritis in mares. Initially, samples from 41 mares with a history of subfertility were stored in BHI broth and 0.9% NaCl solution. The samples underwent microbial culture, identification, and sensitivity testing at LABRAPE-UFRPE, Brazil. Biofilm production was evaluated by the crystal violet method. Subsequently, biofilm-forming bacteria were subjected to the action of different concentrations of ozonated sunflower oil. Of the 21 isolates tested for biofilm produc...
Genome-Wide Characterization of the TGF-β Gene Family in Donkey (Equus asinus) Reveals Lineage-Specific Gene Duplications and Deleterious Mutations. The transforming growth factor-beta (TGF-β) superfamily regulates diverse biological processes, including proliferation, differentiation, apoptosis, tissue remodeling, and reproductive signaling across metazoans. Here, we performed a genome-wide characterization of the TGF-β gene family in donkey (, ASM1607732v2) using comparative genomics and bioinformatics analyses, with horse (, EquCab3.0) as a reference to investigate evolutionary conservation and functional divergence. Genome assemblies and proteomes were retrieved from NCBI, and TGF-β genes were identified using BLASTp and HMMER searc...
Genetic Diversity in Domestic Horses: Temporal Patterns, the Influence of Assisted Reproductive Technologies, and Implications for the American Quarter Horse. Genetic diversity is the heritable variation within and among populations and is essential for the long-term health and selection potential of domestic horses. Previous studies show diversity across breeds is shaped by effective population size, founder events, artificial selection, and levels of inbreeding. While some closed-studbook breeds retain moderate genetic diversity, others have experienced rapid losses due to popular-sire effects and recent and extensive inbreeding. Even so, mare lines continue to help maintain genetic diversity within these populations. Assisted Reproductive Technol...
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...
Exploring the role of epigenetics in the processes related to the development of endometrosis in the mare. Endometrosis is a chronic degenerative condition of the mare endometrium characterized by progressive fibrosis and glandular alterations that impair uterine function and fertility. Its pathogenesis involves persistent inflammation, the activation of myofibroblasts, and the accumulation of extracellular matrix (ECM), leading to disrupted glandular secretion and compromised maintenance of pregnancy. While histopathological studies of endometrosis are well described, the underlying molecular mechanisms remain incompletely understood. Emerging evidence highlights the crucial role of epigenetic reg...
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...
Ultrasonographic fetal sex determination in large domestic animals: a comparative, mechanistic, and field-oriented synthesis. Ultrasonographic fetal sex determination is commonly used in livestock production to aid genetic selection, reproductive planning, and economic optimization. Despite consistently high diagnostic accuracies under controlled conditions, its use in field settings is variable and frequently unpredictable. This disparity is due to the combined effects of embryological development, species-specific anatomy, fetal positioning, operator expertise, and technical limitations. Unassigned: This review aims to provide a comparative and integrative synthesis of ultrasonographic fetal sex determination acros...
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) ...
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...
Comparison of cost for conventional embryo transfer versus intracytoplasmic sperm injection. There are obvious practical advantages of both conventional ET and ICSI. One question that has not been addressed adequately, however, is the relative cost of each procedure and if there is a cost advantage of one over the other. Objective: The objective of the present study was to obtain additional cost data from clinics and breeding farms that perform both ET and ICSI. Methods: A request was sent to 10 clinics that performed either just OPU or OPU/ICSI. These facilities were representative of reproductive specialists located all across the United States. Six clinics provided information on a...
