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.
Moore HL, Klabnik JL, Boothe DM, Cruz-Espindola C, Mita N, Thungrat K, Babu RJ, Lyman CC.To investigate the IV pharmacokinetic parameters of clomiphene citrate (CC), a selective estrogen receptor modulator, in mares. Unassigned: This was an experimental study to assess the pharmacokinetic parameters of CC in the mare. Eight mares received a single 2,000-mg dose of IV CC to identify plasma concentrations over 336 hours. Following this, 6 mares received a multidose regimen of IV CC (2,000 mg, q 24 h) for 5 days to identify trough plasma concentration each day. Unassigned: CC was well tolerated, demonstrated a short elimination half-life of 4.95 ± 1.10 hours and a mean residence tim...
Thomé C, Márquez-Moya A, Sala-Ayala L, Carreras-Vico N, Cuervo-Arango J.Post-mortem oocyte collection serves to preserve the genetic material of valuable mares and to obtain recipient oocytes for cloning purposes. Therefore, the number of oocytes retrieved per ovary is a critical factor in increasing the likelihood of obtaining a viable embryo. This study evaluated the efficiency of two post-mortem oocyte retrieval techniques: follicular scraping (Scraping) and ultrasound-guided follicular aspiration (OPU). The comparison was based on several parameters, including the number of follicles aspirated per ovary, oocyte recovery rate (ORR), number of oocytes obtained p...
de Lara NSS, Weiss RR, Oba E, Kozicki LE, Souza FA, Bergstein-Galan TG, Muehlbauer E, Silvestri M, de Lima PHL, Vaz ES.In equine reproduction, determining foetal sex is of economic and strategic importance, but currently available methods are often invasive, costly, or require specialised expertise. This study aimed to assess whether plasma progesterone concentrations could serve as a predictive tool for foetal sex determination in Criollo mares between the 4th and 8th months of gestation and to determine whether these measurements could identify foetal sex. Blood samples were collected at 30-day intervals from 17 Crioula mares between 114 days and 240 days of gestation. Maternal plasma progesterone concen...
Khan Y, Gautier C, Aurich C, El-Shalofy A.Letrozole is a potent and highly selective third-generation aromatase inhibitor. In the present study, we aimed to investigate the effects of letrozole treatment of non-pregnant mares on estrous cycle characteristics. Cyclic, non-lactating mares (n = 9) were included. After estrus synchronization, mares were monitored to detect ovulation (d0:) of the treatment cycle. Each three mares were randomly assigned to one of three treatments: control, 0.5, and 1 mg/kg body weight letrozole in three consecutive cycles (d7 to d13 of the treatment cycle). Mares were inseminated in the estrus after trea...
Roxon CA, Deacon LJ, Abraham M, Stefanovski D, Sertich PL.Gestation length is not a reliable indicator of fetal maturity due to the variability of normal gestation length in the mare. A standard method to accurately predict equine fetal maturity is not being used clinically. The presence of continuous gastrointestinal peristalsis, as detected ultrasonographically, is an indicator that both human and canine fetuses are mature (can survive after elective cesarean section). To determine if continuous gastrointestinal peristalsis, which we termed Phase 5, was a valid indicator of fetal maturity in the horse, and whether this indicator varied in late-gest...
Najjar A, Dhaouadi A, Ezzar S, Benaoun B, Khaldi S.Stallion sexual behavior during semen collection can be influenced by multiple factors, yet the role of sexual arousal intensity remains underexplored. Understanding how arousal modulates behavioral and physiological reproductive traits is essential for improving artificial insemination (AI) efficiency and semen quality. This study aimed to evaluate the effects of sexual arousal intensity, age, origin, and semen collection method on stallion sexual behavior and the quality of fresh and frozen semen. Unassigned: Thirteen Arabian stallions (7 Tunisian, 6 foreign parentage) aged 6-20 years (total...
de Zutter BM, de Paula Freitas-Dell'Aqua C, Dell'Aqua-Junior JA, Monteiro GA, Troncarelli T, Papa FO.This study evaluated the effects of cholesterol, pentoxifylline and casein, with or without skim milk, added to extenders during pre-centrifugation on equine sperm cryosurvival. Seven ejaculates from four stallions (n = 28) were divided into four groups: SM (skim milk), SMP (SM + pentoxifylline), SMCho (SM + cholesterol) and ChoCa (cholesterol + casein). After centrifugation and freezing, sperm kinematics and plasma membrane integrity were assessed immediately and 30 min post-thaw. SMCho and ChoCa showed superior results compared with SM and SMP. These findings indicate that chol...
Feijo LS, Ledeck J, Wolfsdorf K, Ponthier J, Parry S, Felippe MJB.Associations between the immune and endocrine systems during equine pregnancy remain poorly understood. Based on the hypothesis that distinct phases of the equine healthy gestation are characterized by specific associations between circulating immunological and hormonal parameters, contributing to pregnancy maintenance, this investigation aimed to: (i) evaluate how circulating immunological and hormonal parameters change across different phases of pregnancy; (ii) investigate associations between changes in circulating immunological and hormonal parameters; and (iii) propose potential hormonal ...
Ali A, Derar DR, Alaeyeari AA, Alharbi YM.This study aimed to monitor intrauterine fetal growth, establish predictive equations for gestational age estimation, and determine the optimal period for fetal sexing in Arabian horses using ultrasonography. Unassigned: Seven Arabian mares were monitored from insemination to parturition using transrectal ultrasonography. The following fetal and embryonic parameters were measured: embryonic vesicle (EV), crown-rump length (CRL), biparietal diameter (BIP), stomach diameter (STD), chest depth (CHD), abdominal diameter (ABD), kidney length (KDL), eyeball diameter (EBD), and eye lens length (ELL)....
Solanki O, Talluri TR, Jhamb D, Kumar S, Pargi KK, Paul N, Kutty M, Dedar RK, Meena M, Gaur M, Bhattacharya TK.The current study evaluated the effect of L-Carnitine supplementation to the stallion semen extender on pre-freeze and post-thaw semen quality and oxidative parameters in Marwari breed stallions. Methods: For this purpose, thirty-six semen ejaculates (6 ejaculates from each stallion) were collected using an artificial vagina (AV) from six adult Marwari stallions. The gel free semen was extended with different concentrations of L-Carnitine (LC) i.e. 0 mM (control), 2.5 mM (T1), 5 mM (T2) and 10 mM (T3). Pre-freeze and post-thaw semen evaluations were conducted for various seminal attributes and...
Broothaers K, Jouneau A, Angel-Velez D, De Coster T, Festuccia N, Archilla C, Calderari S, Jouneau L, Van den Branden E, Peere S, Polfliet E....In vitro production of equine embryos has been performed using intracytoplasmic sperm injection (ICSI) for the last two decades. Since 2022, a repeatable protocol for conventional in vitro fertilization (IVF) provides a successful alternative. However, little is known about the influence of the fertilization method on embryo quality and the transcriptomic profile. In this study, we aimed to examine differentially expressed genes (DEGs) between ICSI and IVF embryos in the horse. Therefore, ten equine sibling blastocysts, produced in vitro by either ICSI or IVF from three different mares, were s...
Silva JA, Vasquetto A, Mouguelar H, Nader-Macías MEF, Pellegrino MS.Equine endometritis, a major cause of subfertility in mares, has a significant economic impact on horse breeding. In the face of rising antimicrobial resistance, the use of beneficial bacteria to prevent this disease is a non-antibiotic alternative which aligns with "One Health" principles. This study characterised vaginal autochthonous lactic acid bacteria (LAB) from healthy mares. Out of the 25 presumptive LAB isolates obtained from 15 clinically healthy thoroughbred mares, 24 were confirmed. Surface properties were assessed (autoaggregation, hydrophobicity, biofilm formation, exopolysacchar...
Sala-Ayala L, Cuervo-Arango J, Martínez Boví R.Endometrial edema is an ultrasonographic sign of estrus in mares and is positively associated with fertility. This study aimed to evaluate the influence of follicular size, systemic progesterone (P4), and exogenous estradiol benzoate (EB) on the onset and duration of endometrial edema. In Experiment 1, anestrus (n = 4) and diestrus mares (n = 4) received 4 mg of EB intramuscularly; edema scores and plasma P4 were monitored over four days. In a complementary group (n = 5), mares were monitored until ovulation, then administered 4 mg of EB and examined every 12 h for 48 h. In Experimen...
Martin-Pelaez S, Orsolini M, Verstraete M, de la Fuente A, Takahashi K, Meyers S, Dini P.Equine in vitro embryo production (IVP) offers a valuable opportunity to enhance the efficient utilization of genetically and economically valuable horses. In cases of subfertility, sudden death, emergency euthanasia, or limited sperm availability, IVP becomes the only viable option to produce offspring. Due to steadily improving success rates, IVP has become one of the most sought-after assisted reproductive techniques. The rising global demand has created a clear need for veterinarians and stallion owners to provide IVP-suitable sperm, where the selection of intact sperm for intracytoplasmic...
Tainturier D, Tainturier B, Michaud S, Briand-Amirat L, Topie E, Moreno D.A total of 147 mares of different breeds (110 were sport or race horses, often very valuable) have been monitored over 5 years from 2012 to 2016. When at or near term, the mares were monitored in order to induce foaling, by checking the mammary development by palpation, analysing the colour and consistency of the precolostrum, estimating the calcium and antibodies concentrations in the precolostrum and by measuring the plasmatic progestagens concentration every day at 6 p.m. At the end of gestation, it has been observed that the progestagens rate levelled off (the top concentration varies from...
Derar D, Ali A, Al-Sobayil F, Refaai W.Granulosa cell tumors (GCTs) represent the most common ovarian neoplasms in mares, yet data on their epidemiology, risk factors, and clinical outcomes in Arabian horses are limited. Understanding their prevalence and diagnostic features is crucial for improving fertility management in this breed. Unassigned: Clinical records from 807 Arabian mares housed on 35 stud farms in central Saudi Arabia were retrospectively reviewed to determine the prevalence of GCT and potential risk factors, including age, parity, and anabolic steroid use. Twenty-four confirmed cases were further investigated using ...
Fresa K, Catandi GD, Gonzalez-Castro R, Omar A, Whitcomb LA, Cheng MH, Chen TW, Carnevale EM, Chicco AJ.Advancing age is associated with a decline in fertility and functional capacity, which may result in part from suboptimal nutrition and impaired mitochondrial function. Dietary essential polyunsaturated fatty acids (PUFA) are broadly recommended to mitigate weight loss and reduce risk of chronic disease in aged populations, but their effects on mitochondrial function are less clear. The present study investigated the impacts of dietary supplementation with essential omega-3 PUFA (flaxseed oil; N3) or omega-6 PUFA (corn oil, N6) on blood, muscle and follicular cell fatty acid composition and mi...
Mendoza Cerna MN, Anderson H, Avni G, Kahila Bar-Gal G, Juras R, Raudsepp T.Robertsonian translocations (ROBs) or centric fusions of acrocentric chromosomes are the most common structural chromosomal rearrangements in mammals. ROBs are of medical and veterinary concern because of associated subfertility and congenital disorders but are also of interest as a mechanism of chromosome and karyotype evolution. While ROBs are well documented in humans, mice, and cattle/bovids, they are extremely rare in horses, despite the 18 acrocentric chromosomes in the horse karyotype. Methods: We characterize the case using conventional and molecular cytogenetic approaches and DNA anal...
Otero JC, Neild DM, Ferrante AA, Gambarotta MC, Caldevilla ML.Glycerol, a penetrating cryoprotectant, is most employed for deep freezing spermatozoa. However, it can induce toxic, chemical, and osmotic effects, altering the lipid structure of the sperm membrane. Rapid glycerol addition has been demonstrated to have fewer toxic effects than its removal. Objective: To minimize both the toxic and osmotic effects of glycerol on equine sperm through post-thaw dilution using two different extenders. Methods: Samples of equine semen frozen with 5% glycerol from nine stallions were thawed, re-diluted 1:2, and incubated for 30 minutes at 22°C in Tyrodes (Tyr) an...
Song D, Wang G, Baterin T, Weng Y, Dugarjaviin M, Li B.Normal spermatogenesis in Mongolian horses depends on the mitotic division of spermatogonia, two successive meiotic divisions, and the morphological transformation of spermatids into mature spermatozoa. The gene is involved in the meiosis cycle and is required for normal chromosome association during meiosis. Previous studies have shown that alternative splicing of may promote spermatogenesis in Mongolian horses. In this paper, the regulatory effects of different alternative splicing events on Mongolian horse spermatogenesis are investigated. Results: In this study, two overexpressed lentiv...
Risvanli A, Salykov R, Timurkaan N, Seker I, Ekinci E.This study was conducted to examine glandular histological changes in the uterus of Kyrgyz breed mares during the first 6 months of pregnancy. The study used 53 Kyrgyz breed mares; 43 of these were at different stages of pregnancy, while 10 were non-pregnant mares. Uterine samples obtained at the slaughterhouse were evaluated histomorphometrically; endometrial thickness, gland density, gland epithelial height and gland diameter were measured. In conclusion, it was concluded that in Kyrgyz mares, endometrial thickness, glandular epithelial height and diameter increased as pregnancy progressed...
Vilela VMT, Zutter BM, Gomes LLO, Silva DF, Diniz JHW, Sancler-Silva YFR, Ignácio FS, Papa FO, Monteiro GA.This study investigated the effects of cholesterol-loaded cyclodextrin (CLC) before cryopreservation and the use of FertTalp (FT) after thawing on the structural and functional quality of equine spermatozoa. Methods: Two ejaculates from twelve stallions were divided into four groups: G1 (0 mg CLC), G2 (1.0 mg), G3 (1.5 mg), and G4 (2.0 mg). Post-thaw semen quality was evaluated through computer-assisted sperm analysis and flow cytometry. Results: In Experiment I, supplementation with 1.5 mg (G3) significantly improved total motility (64.9 ± 10.1 %) and progressive motility (40.5 ± 8.8 %) com...
Jones CJP, Aplin JD, Wilsher S.There is little information on non-ciliated secretory cell numbers in the equine oviduct isthmus over the course of the estrous cycle and the effect, if any, of insemination. Lectin histochemistry was used on a series of 13 oviducts taken at different stages of the estrous cycle, with and without insemination, to monitor glycosylation changes and the distribution of secretory cells characterised by a prominent cytoplasmic accumulation of glycoconjugates. There appeared to be an increase in secretory cells expressing a wide range of glycans in all specimens at estrus. One day after ovulation, o...
Bueno VLC, Bastos HBA, Centeno LAM, Schmitt F, Larentis G, Mattos RC, Fiala-Rechsteiner S.The seminal plasma (SP), a fluid originating from the testes, epididymis, and accessory sex glands, represents 98 % of the volume of stallion ejaculate. Metabolomic analysis enables the identification of final products of metabolic pathways, providing insights into reproductive physiology. Objective: This study aimed to investigate the metabolomic profile of stallion seminal plasma and to investigate metabolic differences between stallions with high and low pregnancy rates, in order to identify potential biomarkers associated with fertility. Methods: Twenty-four Criollo stallions, were sampled...
Ramsaran LN, Byron M, Parry S, Lection J, Back B, Grenier J, Cheong SH, Diel de Amorim M.Real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) is a technique that allows for the semi-quantification of mRNA transcripts present within a tissue of interest. Differences in the relative abundance of mRNA between samples detected by RT-qPCR require normalization with a reference gene or genes whose transcript abundance is stable within the tissue of interest independent of experimental conditions. In the field of equine reproductive studies, ACTB, GAPDH and B2M genes are the most widely used as reference genes for the normalization of RT-qPCR results. However,...
Rychtarova J, Fulka H, Loi P, Fulka J.In the mouse, spermatozoa are highly resistant to DNA damage, even when frozen without cryoprotectants, and can produce offspring when subsequently used for ICSI (intracytoplasmic sperm injection). It is not known whether the same applies to other mammals as well. For example, in the horse, even conventional sperm freezing is still very problematic and frequently leads to sperm immobility. It has, however, never been tested whether sperm immobility also mirrors sperm head DNA damage, and if so, to what extent. In our study, we evaluated the damage to DNA in horse frozen and thawed motile and i...
Rodrigues MF, Neves AP, Ferreira R, Pessoa GA, Araujo DN, de Souza GV.Melatonin has demonstrated beneficial effects in regulating inflammatory processes in various tissues, but its role in mare uterine physiology remains unclear. Objective: To investigate the effects of melatonin on the gene expression of cytokines (IL-1β, IL-6, IL-8, IL-10, and TNF-α) in equine uterine explants cultured for 6, 12, or 24 hours. Methods: The study was divided into two experiments. Part 1 aimed to evaluate the cytotoxicity of melatonin at concentrations of 0, 0.5, 1, 2, 4, and 8 mM on endometrial cells. Part 2 aimed to determine the expression of inflammatory cytokines in uterin...
Moroni R, Fanelli D, Maltinti S, Orefice M, Rota A, Camillo F, Melanie P, Cantile C, Miragliotta V, Pirone A, Lazzarini G, Passamonti F, Marmorini P....Equine persistent breeding-induced endometritis can lead to chronic uterine inflammation and fibrosis, reducing fertility. Intrauterine ozone (O₃) has recently been proposed as a potential treatment for mares unresponsive to conventional therapies. This case series describes O₃ treatment in eleven mares barren for at least one year despite multiple inseminations attempts. During the first oestrous cycle, low-volume uterine lavage and endometrial biopsy were performed, followed by 3 consecutive days of intrauterine O₂-O₃ gas insufflation. In the subsequent cycle, both procedures were re...
Latorre N, Gómez-Cuétara C, Cañizares E, Crespo F, Pérez-Aguilera V, Cuerda MI, Laborda-Gomariz JA, Soler AJ, Roldan ERS, Sanchez-Rodriguez A.Evaluating semen quality in Purebred Spanish Horses is essential to determine reproductive potential and optimize assisted reproductive techniques. Objective: This study compared several sperm analysis methods in Purebred Spanish Horses to standardize protocols suitable for both laboratory and field conditions. Methods: Fifteen stallions were evaluated through three ejaculates, analyzing sperm parameters using different techniques. Sperm kinematics was assessed by Sperm Computer Analyzer (SCA-CASA) or iSperm mCASA. Viability was analyzed by eosin-nigrosin-Giemsa (ENG) staining or Hoechst 33258...
Ryder E, Given J, Hamilton N.Prohibited gene editing in horses (either in embryos or via cell culture and cloning) can result in both desired and undesired outcomes. If left undetected, changes can proliferate within the population in subsequent generations, posing a major threat to welfare and breed integrity.
