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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.
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...
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...
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...
Extreme male reproductive skew limits effective population size in American Standardbred horses. Standardbred horses are widely used for harness racing in North America, Europe, Australia, and New Zealand. In the U.S., two gaits (Pacers and Trotters) are genetically differentiated at a level typical for different horse breeds. We used the complete pedigree for all registered American Standardbred foals born 1970-2014 (>200 K Trotters and > 500 K Pacers) to calculate annual and lifetime reproductive skew and its consequences for the effective number of breeders per year (Nb) and effective size per generation (Ne). With rare exceptions, females can only produce 0 or 1 foal per year, w...
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...
Testicular Disorders in Equids: A Case Series. Equine testicular disorders represent a diverse group of conditions that impact the longevity of a stallion's breeding career. Stud farm veterinarians should be familiar with the variety of clinical presentations and diagnostic options for these conditions. This retrospective case series reports 57 cases of testicular abnormalities in stallions and donkeys presented to the clinic for further diagnostics and treatment. These disorders included neoplasia (three unilateral and one bilateral seminoma; two Sertoli cell tumors; two Leydig cell tumors; and one malignant mixed sex cord-stromal tumor),...
Genome-Wide Identification and Characterization of the Wnt Gene Family in Donkey (Equus asinus): Phylogenetic Analysis and Expression Profiling. The gene family encodes highly conserved signaling molecules involved in vertebrate development, tissue homeostasis, and cell fate regulation. However, the evolutionary characteristics and potential biological functions of genes in the domestic donkey () remain poorly understood. In this study, we performed the first genome-wide identification and comprehensive characterization of the donkey gene family. A total of 19 genes were identified, consistent with the conserved repertoire reported in other mammalian species. Phylogenetic and synteny analyses revealed strong evolutionary conservat...
Implications of dominance deviations for reproductive and morphological traits in the genetic management of the Pura Raza Española horse. Dominance is a non-additive genetic effect involving allele interaction at the same locus. In animal breeding, it has often been ignored due to its complexity and the low accuracy of pedigree-based estimates. This study analysed dominance variance components for reproductive traits [age at first foaling (AFF), reproductive efficiency (RE), interval between first and second foaling (I12)] and morphological traits [scapulo-ischial length (SIL), dorsal sternal diameter (DSD), knee circumference (KC)] in Pura Raza Española (PRE) mares. The aim was to assess the magnitude of dominance effects acro...
Russell’s viper envenomation in a 9-month pregnant mare saved with high-dose antivenom: a first-in-world case report. Snakebite during pregnancy is an uncommon but potentially catastrophic event, with maternal and foetal outcomes closely related to the severity of envenomation. While snakebite in pregnant women has been sporadically reported and is known to be associated with significant obstetrical complications, envenomation in animals, particularly in pregnant horses, is exceedingly rare. Only a few isolated cases of snakebite in horses have been documented, and to the best of our knowledge, snakebite in a pregnant mare has not been previously reported in the medical or veterinary literature. Russell's vip...
Body Condition, Metabolic Parameters and Semen Traits in Purebred Spanish Horses. The growing relevance of the Purebred Spanish horse has driven the extensive use of assisted reproductive technologies to preserve elite stallion genetics. Optimal reproductive performance is intrinsically linked to systemic health and high semen quality. This study aimed to evaluate the impact of body condition on the stallion's metabolic and endocrine profiles and their seminal parameters. Semen and blood samples were collected from 26 stallions (February-May in 2024-2025) whose body condition score (BCS) was assessed using the Henneke scale. They were classified into two groups, low BCS wit...
Somatic cell nuclear transfer as a complementary tool for genetic conservation of the Peruvian Paso horse. The Peruvian Paso horse, a breed of national significance in Peru known for its unique gait, has been selectively bred for nearly 500 years and now faces potential risks due to reduced genetic diversity. To investigate the potential of somatic cell nuclear transfer to enhance genetic conservation strategies, a program was initiated to produce cloned Peruvian Paso foals. Skin biopsies from a highly awarded stallion with exceptional breed-defining traits were used as the source of donor somatic cells. Of the 15 cloned embryos reconstructed, seven blastocysts were produced, and five were transfer...
Species-Specific Mechanisms of Sperm Transport: Predominant Roles of Motility in Ewes and Uterine Contractility in Mares. The factors controlling sperm transport within the female genital tract vary among species. The aim of this study was to quantify the respective roles of sperm motility and uterine contractions in passage of sperm within the reproductive tract of the mare and ewe. Sperm imaging was performed in vivo within the female genital tract of mares and ewes using probe-based confocal laser endomicroscopy (pCLE) after intrauterine insemination during two stages of the cycle characterized by high (oestrus) or low (luteal phase) uterine contractility. Fluorescent microbeads (2 µm in diameter) were insemi...
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...
Preliminary Metabolomic Analysis: Serum Metabolomic Dynamics During Estrus Synchronization in Kazakh Mares. This study aimed to analyze the differences in serum metabolomes at different stages of estrus synchronization in Kazakh horses, to characterize dynamic changes in serum metabolites during estrus synchronization, and to screen potential metabolic markers and key regulatory pathways. Four sampling stages (M1: intravaginal device insertion; M3: device removal, labeled consistently with the pre-experiment timeline; P: 24 h post-PG injection; L: tertiary follicle emergence) were selected. The research results showed that 37 significantly different metabolites (DAMs) were identified in the M1-vs.-M...
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...
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...
Hair steroid hormones concentrations in jennies and their donkey foals from parturition to 6 months postpartum. The period after parturition/birth represents a delicate time for the dam and the offspring, during which several physiologic changes occur under finely tuned hormonal control, with the hypothalamic-pituitary- adrenal (HPA) axis playing a key role. This period, well studied in horses, received little attention in donkeys, despite the importance of species-specific knowledge for population preservation programs in many endangered donkey breeds. The present study aimed to investigate cortisol (C), DHEA(S), 17-β-estradiol (E2), progesterone (P4), testosterone (T), and allopregnanolone (AlloP) ha...
Platelet indices’ dynamic in broodmares: Effects of parity and lactation. Lactation and parity are physiological factors influencing platelet (PLT) indices, yet their combined effects in mares remain poorly characterized. As a dynamic process, lactation involves metabolic and endocrine changes that may influence thrombopoiesis; therefore, reproductive history and lactation stage may modulate PLT indices. Objective: To characterize longitudinal platelet (PLT) indices during early lactation in mares and evaluate the influence of parity on thrombopoietic responses. Methods: Fifty-five clinically healthy Spanish Purebred mares were included (20 primiparous and 25 multip...
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...
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...
