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Topic:Pregnancy
Pregnancy in horses, or equine gestation, is a physiological process that involves the development of a foal within the mare over approximately 11 months. This period is characterized by distinct stages, including fertilization, embryonic development, and fetal growth. Throughout gestation, mares undergo various physiological and hormonal changes to support the developing fetus. Monitoring pregnancy in horses involves assessing fetal health and mare well-being through veterinary examinations and diagnostic tools such as ultrasound. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological processes, management practices, and health considerations associated with equine pregnancy.
Endocrine and uterine hemodynamic differences between intra- and interspecific equine pregnancies during early gestation. Interspecific equine pregnancies (mare x donkey) are associated with altered endocrine patterns and increased pregnancy loss; however, the relationship between hormonal dynamics, luteal activity, and uterine hemodynamics in relation to conceptus origin remains incompletely understood. This study aimed to evaluate the influence of conceptus origin on endocrine profiles, supplementary corpora lutea (SCL) formation, and uterine hemodynamics, and to investigate the relationships among these variables. Twenty mares were initially included; however, six were excluded due to pregnancy loss or incompl...
Differential Serum Cytokine Profiles in Aborting and Subclinically Infected Pregnant Mares with Equine Herpesvirus Type 1. Equine herpesvirus type 1 (EHV-1) is a major cause of reproductive loss in mares. This cross-sectional field study evaluated serum concentrations of interleukin-2 (IL-2), interleukin-10 (IL-10), interferon-alpha (IFN-α), and interferon-gamma (IFN-γ), together with the IL-10/IL-2 and IFN-γ/IL-10 ratios, in 26 vaccinated pregnant Thoroughbred mares. The analytical cohort comprised healthy, EHV-1 PCR-negative mares (HM, n = 10), EHV-1 PCR-positive mares sampled within 4 h after fetal expulsion at approximately the sixth month of gestation (AM, n = 9), and EHV-1 PCR-positive pregnant mares with...
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...
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...
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 ...
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...
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...
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...
Use of computer-assisted tomography for diagnosis and standing surgical reduction of progressive ethmoidal hematoma in a mare. Progressive ethmoidal hematoma (PEH) is a rare, nonneoplastic mass occurring in the sinonasal passages of horses. An 11-year-old, pregnant Thoroughbred mare was presented with a history of intermittent nasal discharge and stertorous respiration. On examination, radiography revealed increased opacity in the sinus and nasal cavities and endoscopy identified a mass emerging from the left ethmoidal turbinate. Computed tomography (CT) showed the range and origin of the mass, indicative of PEH. A standing frontonasal flap was made under sedation, following temporary tracheostomy to secure the airway...
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...
Embryo developmental kinetics and vitrification in relation to pregnancy outcome, foaling percentage and foal sex. While fast in vitro embryo development has been associated with improved outcomes, the relationships of slow in vitro embryo development and vitrified versus fresh in vitro produced (IVP) embryo transfer to foaling percentage and foal sex are less explored. Objective: To determine the relationships of (1) day of blastocyst formation (D7-11 after intracytoplasmic sperm injection (ICSI)) and (2) vitrification and warming method (one- and three-step) versus fresh transfer with pregnancy, early pregnancy loss (EPL), foaling percentage and foal sex. Methods: Retrospective clinical study. Methods: B...
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...
Vaginal host-microbe signatures linked to placental outcomes in mares. Ascending placentitis is a leading cause of late-term pregnancy loss in mares. Although pathogens are presumed to ascend from the caudal reproductive tract, the association between the vaginal microbiome and placentitis has not been systematically examined. Objective: To characterise microbial and host gene expression in the equine vagina during gestation and to identify taxa or transcripts that were associated with the presence of an abnormal placenta at birth. Methods: Prospective, paired observational study. Methods: Vaginal wall swabs were collected from 49 multiparous Thoroughbred mares a...
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 Effects of L-Citrulline on the Apparent Digestion and Metabolism of Nutrients, Blood Hormone Levels, Amino Acid Metabolism and the Diversity of Faecal Microbiota in Mares in the Later Stage of Pregnancy. This study aimed to investigate the impact of dietary L-citrulline supplementation on the health of mares during late gestation. Thirty-two healthy mares in late pregnancy were randomly assigned to four groups: a control group (CON, 0 g/d) and three treatment groups receiving 15, 30, and 45 g/d/head of L-citrulline, respectively. The trial spanned 72 days, including a 12-day adaptation phase and a 60-day formal feeding period. A fixed daily feeding amount of 11.2 kg/head was provided, ensuring complete consumption and consistent dry matter intake across all groups. Results demonstrated that su...
Prepubic Tendon Rupture and Uterine Herniation in a Late-Term Kurdish Mare: A Case Report. Prepubic tendon rupture (PPTR) is a rare but life-threatening complication in late-term pregnant mares. It results in abdominal wall failure, ventral oedema and a poor prognosis for both the mare and foetus. A 14-year-old multiparous Kurdish mare at approximately 310 days of gestation presented with acute ventral distension, reluctance to walk and cranial displacement of the udder. Clinical evaluation revealed tachycardia, pallor and Grade 3/4 ventral oedema. Haematology indicated leucocytosis and haemoconcentration. Transabdominal ultrasonography showed a viable foetus and severe thinning of ...
Age, embryo donor status, and insemination with chilled semen all predispose to persistent breeding-induced endometritis in warmblood mares. Persistent breeding-induced endometritis (PBIE) is a common reason for mares failing to establish pregnancy. Objective: To examine the hypothesis that advancing mare age and embryo donor status predispose to PBIE and compromise fertility. Methods: Retrospective analysis of the impact of mare age, breeding system (embryo donor versus broodmare), and semen type (chilled versus frozen-thawed) on the likelihood of PBIE and subsequent pregnancy/embryo recovery. Methods: Warmblood mares (n = 769) inseminated during 1745 oestrous cycles were divided into three age categories (≤6, 7-13 and ≥14...
Physiological and nutritional adaptation of broodmares during the transition from late pregnancy to early lactation: Digestibility changes and the role of uNDF as an internal marker. Nutritional management of broodmares during late pregnancy and early lactation is essential for maternal health and foal well-being. This study evaluated a targeted dietary adaptation during the transition from late gestation to early lactation, monitored nutrient digestibility, and applied undigested neutral detergent fiber (uNDF) as an intrinsic digestibility marker. A prospective nutritional study was conducted on 11 clinically healthy Trotter broodmares (3 primiparous, 8 multiparous) monitored under standardized conditions. Mares received a forage-based diet with controlled starch intake a...
Comparative analysis of the transcriptome and methylome in distinct trophoblast populations at the time of embryo implantation in mares. BACKGROUND: During equine implantation, two distinct trophoblast subpopulations are identified: the invasive chorionic girdle (CG) and the non-invasive allantochorion. The invasive CG trophoblast is believed to modulate the maternal immune response and facilitates embryo attachment to the endometrium, while the allantochorion contributes to placental development without breaching the endometrium. However, the mechanisms underlying differential adhesion and immune modulation by these two lineages remain poorly understood. This study aimed to investigate the regulation of biological processes un...
Longitudinal assessment of hemostatic adaptations in pregnant mares: Evidence of a physiological hypercoagulable state. Pregnancy triggers intricate hemostatic adjustments that support placental maturation and prepare the maternal organism for delivery. We hypothesized that pregnant mares would progressively shift toward a procoagulant state throughout gestation, reflected in changes to coagulation and fibrinolytic markers. To test this hypothesis, 15 clinically healthy Spanish Purebred pregnant mares were monitored monthly from conception to term, alongside 15 non-pregnant controls of similar age and breed. A comprehensive hemostatic profile-including platelet (PLT) count, prothrombin time (PT), activated part...
Saliva and plasma metabolome analysis during the five days before foaling in the mare. Saliva is a relevant biofluid for real-time welfare-friendly monitoring of systemic events in animals, because some bioanalytes have a systemic origin and its collection is painless, stress-free and non-invasive. Our aim was to analyze the metabolome of equine saliva during the five days before foaling, with a focus on identifying metabolites whose level significantly changed before parturition, that could be potential salivary biomarkers of the onset of parturition. We compared the saliva and plasma metabolomes to investigate their relationship. Saliva and blood samples were collected from tw...
Comparative analysis of uterine inflammation in jennies and mares after insemination with cryopreserved donkey semen. The limited fertility of jennies inseminated with frozen donkey semen remains a major challenge for donkey reproduction and conservation, contrasting with the more favorable outcomes observed in mares. Species-specific differences in post-breeding uterine inflammation have been proposed as a key factor underlying this disparity. This study compared the uterine inflammatory response and pregnancy outcomes of jennies and mares inseminated with frozen donkey semen. Twelve jennies and eleven mares were monitored over 48 and 44 estrous cycles, respectively. Artificial insemination (AI) was performe...
Impact of donor mare and stallion identity on the likelihood of pregnancy after transfer of in vitro produced embryos. The success of in vitro embryo production (IVEP) is influenced by donor mare and stallion. Objective: To determine whether donor mare and stallion influence the pregnancy rate after transfer of in vitro produced (IVP) blastocysts and to identify factors influencing the likelihood of obtaining one or more pregnancies from a single IVEP session. Methods: Retrospective clinical study. Methods: The influence of the following variables on pregnancy outcome was assessed in 2292 transfers of IVP blastocysts: speed of in vitro embryo development, embryo grade after thawing, age of the donor mare, blas...
Clinical pregnancy outcomes after transfer of fresh and vitrified-warmed conventional IVF equine embryos. In vitro fertilization (IVF) in horses has emerged as a valuable assisted reproductive technology, yet the impact of embryo cryopreservation on pregnancy outcomes when utilizing this technique remains unclear. This study reports pregnancy outcomes following transfer of conventional equine IVF embryos, with both fresh and vitrified-warmed embryos. Conventional IVF (cIVF) was used to produce 40 embryos, which were transferred to recipient mares, pregnancy diagnosis was performed at 6 days post-transfer followed by embryonic heartbeat detection between day 25 and 30 of gestation. Observed pregnan...
Embryonic vesicle diameter at first pregnancy diagnosis in in vivo- and in vitro-derived pregnancies and its relationship with pregnancy loss in the mare. This retrospective study compared the relationship between embryonic vesicle diameter at first pregnancy diagnosis and early embryonic loss (EEL) across three pregnancy types: artificially inseminated broodmares (AI; n = 263), recipients carrying in vivo-derived flushed embryos (IVD-F; n = 312), and recipients carrying in vitro-produced embryos by intracytoplasmic sperm injection (IVP-ICSI; n = 161). Vesicle diameter was recorded at Day 12 post-ovulation in AI, Day 4 post-embryo transfer (ET) for IVD-F, and Day 7 post-ET for IVP-ICSI pregnancies. Mean (±SD) vesicle diameters and E...
Relationship between the duration of endometrial edema and reproductive parameters of estrus, diestrus, and fertility in mares: a field study. The duration of endometrial edema has been positively correlated with uterine receptivity and likelihood of pregnancy. Therefore, this study aimed to evaluate whether there is a relationship between the duration of endometrial edema (DEdema) and other key parameters of the estrous cycle: maximum edema (MEdema), largest follicle diameter (LPF), corpus luteum and uterine tone on day 5 post ovulation (CLD5 and TD5), progesterone concentration (P4) and fertility. A total of 88 cycles from 36 mares were evaluated and divided into Short Estrus (SE), Long Estrus (LE), Inseminated (AI) and Non-insemin...
Cryptophthalmia, microphthalmia, oronasal malformation, and hydrocephalus in an aborted equine fetus with umbilical torsion in the state of Mato Grosso, Brazil. Facial abnormalities and brain defects in aborted equine fetuses are rarely reported, and the causes that predispose the occurrence of this condition are difficult to identify. This work reports the morphological and tomographic findings of a case of cryptophthalmia, microphthalmia, oronasal malformation, and hydrocephalus in an aborted equine fetus with umbilical cord torsion in the state of Mato Grosso, Brazil, from a primiparous Quarter Horse female, with 7 months of gestational age. The occurrence of miscarriage was associated with compromised maternal-fetal blood flow due to umbilical cor...
Effects of rectal examination on intraocular pressure and behavioral responses in pregnant and non-pregnant mares. Rectal examination is routine in equine reproduction but may trigger acute stress affecting welfare and safety. Intraocular pressure (IOP) responds rapidly to autonomic changes and may capture short-lived stress responses. Objective: To evaluate whether rectal examination acutely affects IOP and behavioral responses in mares, and whether reactions differ by reproductive status. Methods: Twenty Rahvan mares (10 pregnant, 30-40 days' gestation; 10 non-pregnant; 4-7 years) underwent transrectal examination without sedation. IOP was measured bilaterally at six time points: 2 min pre-exam (T1), dur...
