Ovulation in horses is a physiological process involving the release of an ovum from the ovary, typically occurring during the mare's estrous cycle. This process is regulated by hormonal changes, primarily involving luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Ovulation is a key component of equine reproduction, influencing breeding management and fertility outcomes. The timing and detection of ovulation are critical for optimizing breeding strategies, often involving techniques such as ultrasound examination and hormone assays. This page compiles peer-reviewed research studies and scholarly articles that investigate the mechanisms, detection methods, and implications of ovulation in equine reproductive health.
In this study, 198 donor mares of different breeds, ages, and reproductive category were inseminated with fresh, cooled and frozen or frozen and cooled semen at the embryo transfer station or in private artificial insemination centers during 10 breeding seasons. The results of this activity were retrospectively analyzed by Pearson Chi-square test and logistic regression to evaluate factors affecting multiple ovulations, embryo recovery, embryo quality, and embryo diameter. Out of the 661 cycles, 937 ovulations were recorded (mean ovulations/cycle: 1.42 ± 0.58). Ovulation rate and incidence of...
Laufkötter S, Längerer L, Wehrend A.This study presents the individual course of estradiol-17ß and progesterone concentrations in blood during the reproductive cycle in mares in order to point out physiological differences between individual animals and to aid in the interpretation of hormone values. Methods: Concentrations of estradiol-17ß and progesterone were determined in seven mares over the course of their cycle. One mare was excluded from the study due to a physiologically deviating cycle. In addition, the mares' ovaries were examined via ultrasound on a daily basis in order to match the hormone values to morphological ...
Sala-Ayala L, Martínez-Boví R, Querol-Paajanen A, Cuervo-Arango J.The aims of this study were to determine the effect of the embryo flushing technique and the number of flushing attempts performed by operators of different experience on embryo recovery (ER). Ten non-lactating mares were inseminated with the same stallion in six cycles each (n = 60). Embryo flushing (EF) was performed 7-9 days after ovulation by three operators (OP; 20 EF cycles each): OP1 had performed >500 EF before the study, while OP2 and 3 had performed 0 EF. Each EF was performed with 2 flushing attempts (FA) using 1L of ringer's lactate "in-and-out" using two EF techniques: 1) ...
Sala-Ayala L, Pytel AT, Stychno K, Cuervo-Arango J.Ovum pick-up (OPU) by transvaginal ultrasound guided follicle aspiration in mares is a common assisted reproductive technique used for oocyte recovery and in vitro production of horse embryos. There has been relatively little research into the factors influencing oocyte recovery in OPU from live mares. The objective of this study was to compare oocyte recovery and morphology of ultrasound-guided follicle puncture and aspiration in live mares and in postmortem excised ovaries, in order to validate an experimental model for research purposes of the efficiency of OPU in mares. Data from OPU perfo...
Mahmood K, Hassan M, Channa AA, Ghafoor A, Riaz A.The present study aimed to evaluate and compare the overall and breed-specific seasonal breeding patterns, fertility rates, cyclicity, and follicular dynamics of Arab, Thoroughbred, and Percheron mares under the subtropical conditions of Pakistan. Methods: A retrospective analysis of climatic data and breeding records of eleven breeding studs spanning four years (2020-2023) was made to find out the overall seasonality in the breeding pattern of mares. Fifty mares of each breed (n = 150 in total) were scanned by ultrasonography for a calendar year to find the cyclicity pattern and follicular ...
Goudet G, Beauclercq S, Douet C, Reigner F, Deleuze S, Nadal-Desbarats L.Successful reproductive management of domestic mammals depends primarily upon timely identification of oestrous cycle stages. There is a need to develop an alternative non-invasive, welfare-friendly, accurate and reliable method to identify reproductive cycle stages. This is of particular interest for horse breeders, because horses are high-value farm animals that require careful management and individual monitoring. Saliva sampling is non-invasive, painless and welfare-friendly. Thus, we performed a metabolomic analysis of equine saliva during different reproductive stages to identify changes...
Flores JG, Bueno VC, Bastos HBA, Rechsteiner SMDEF.Reproductive biotechniques in the equine species have advanced in the last decade and horse breeders have started to question the possibilities of interfering in the determination of foal sex. The aim of the present study was to verify whether the variables mares and stallion's age, side of the ovary containing the preovulatory follicle, preovulatory follicle diameter, time between breeding and ovulation, and ovulation inducing hormones influence the sex of the foal. A total of 259 reproductive cycles of 160 mares and 22 Thoroughbred stallions were used. Statistical analysis was performed usin...
Funes J, Ismer A, Hoogewijs M, Wilsher S.Variations in temperature throughout the reproductive tract have been noted in many species. A recent study found the cervix-rectum temperature differential (CR-TD) in cattle was related to fertility. The present study aimed to assess the CR-TD in mares around the time of ovulation and relate it to embryo recover. Over 52 cycles, mares were inseminated with a fertile stallion and embryo recovery was undertaken on Day 7 post ovulation. Further 10 control mares were not inseminated. Rectal and cervical temperatures were measured using a precision thermometer on four or five occasions: the day of...
Alkhadrawy JMH, Aboelmaaty AM, Abou-Ahmed MM, Ghallab AM.Commercial embryo flushing of horses has required hormonal management of both the donor and recipient mares throughout the breeding season. Unassigned: This study aimed to find out the effect of using human chorionic gonadotropin (hCG) and prostaglandin F2α (PG) on the ovarian and uterine dynamics and hemodynamics, estradiol (E2), progesterone, oxidants-antioxidants, and blood biochemicals in embryo donor mares during the hottest months of the year in a subtropical climate. Unassigned: Three Control estrous cycles of native mares (10-20 years; = 10) followed by two treated cycles with hCG an...
Feugang JM, Gad A, Menjivar NG, Ishak GM, Gebremedhn S, Gastal MO, Dlamini NH, Prochazka R, Gastal EL, Tesfaye D.Ovarian follicular fluid (FF) is a dynamic environment that changes with the seasons, affecting follicle development, ovulation, and oocyte quality. Cells in the follicles release tiny particles called extracellular vesicles (EVs) containing vital regulatory molecules, such as microRNAs (miRNAs). These miRNAs are pivotal in facilitating communication within the follicles through diverse signaling and information transfer forms. EV-coupled miRNA signaling is implicated to be associated with ovarian function, follicle and oocyte growth and response to various environmental insults. Herein, we in...
Rodrigues LT, Segabinazzi L, Frasson M, Dell'Aqua C, Carmo MT, Takahira RK, Alvarenga M, Papa F.Although protocols for superovulation have been described in horses, this technique has been discouraged due to the low embryo recovery rates in superovulated mares. The reason for these poor results is poorly understood, but the formation of a blood clot in the ovulation fossa following ovulations has been hypothesized. Therefore, this study aimed to assess the safety and effect of periovulatory anticoagulant therapy on embryo recovery of superovulated mares. In experiment 1, five mares were assigned to receive five anticoagulant treatments in a crossover design: intravenous injections of 150...
Cuervo-Arango J, Necchi D, Clutton-Brock A, Profaska M, Crabtree J, Claes A.This retrospective clinical study describes different techniques for transvaginal follicle aspiration in mares and compares results from 5 different commercial ovum pick-up (OPU) clinics in which the same operator aspirated mares using different systems and equipment: Clinic 1 (n = 42 mares, two-operator OPU technique, double-lumen-echogenic-tip needle, and manual syringe-assisted flushing of follicles), Clinic 2 (n = 28 mares, single-operator-OPU-technique, double-lumen-echogenic-tip needle, infusion pump controlled by foot-pedal for follicle flushing), Clinic 3 (n = 18 mares, sin...
Hannan MA, Watanabe H, Takeyama A, Yoshida S, Wudamu D, Lkhagvasuren N, Claes A, Stout TAE, Cheong SH, Haneda S, Nambo Y.This study evaluated the viability of in vitro embryo production using ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) as breeding techniques for pure and crossbred Hokkaido native ponies (n = 9). Oocytes were collected using transvaginal ultrasound-guided follicle aspiration. ICSI was performed on in vitro matured oocytes using frozen semen. Embryonic cultures were monitored using time-lapse cinematography. Blastocysts were cryopreserved and, after thawing, were transferred non-surgically into recipient mares. Over nine OPU sessions, the mean number of aspirated follicles was 2...
Cui B, Liu Y, Wu X, Li X.The objective of this study was to evaluate the effects of exogenous GnRH administration at the beginning of estrus synchronisation in mares during the spring transitional period. Estrus was synchronised using a progesterone releasing intravaginal device (PRID). The PRID was left in the vagina for 10 days, followed by an injection of 0.4 mg of cloprostenol at PRID removal. The GnRH group (n = 32) was subjected to intramuscular administration of 100 μg of the GnRH agonist triptorelin at PRID insertion, while the control group (n = 32) received 1 mL of sterile physiological sali...
Gaber JTH, Cuervo-Arango J, Plaza-Dávila M, Martínez-Boví R.This experiment was performed to evaluate whether intrafollicular treatment of PGE2 or PGF2α administered in early estrus would induce normal ovulation, progesterone production (Experiment 1) and pregnancy (Experiment 2). In Experiment 1, mares in estrus after 2 days of endometrial edema were injected in all largest dominant follicles (28-35 mm in diameter) with 0.5 mL of sterile water containing 500 μg PGE2 (n = 6), 125 μg PGF2α (n = 6) or placebo (n = 7) (Hour 0). Ultrasound examinations were performed daily, until ovulation or anovulation was detected, and daily blood samples ...
Cuervo-Arango J.The objective of this study was to compare the fertility of diestrous mares with a follicle ≥ 30 mm in diameter treated with prostaglandin F2α (PGF) (PGF group) or left untreated for 7 days (SP group). Standardbred mares (n = 46) were assigned randomly to the SP (n = 23) and PGF groups (n = 23) when they were identified with a corpus luteum (CL) of unknown age and a follicle ≥ 30 mm in diameter (Day 0). The most frequent outcome in the PGF group was estrus and ovulation of the dominant follicle (74 %), while the outcomes of the SP mares 7 days after Day 0 were more variable: estrus and fo...
