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.
Caballeros JE, Camacho C, Cazales N, Estradé MJ, Fiala-Rechsteiner S, Jobim MIM, Mattos RC.Rapid endometrial adaptations occur with the embryo entering the uterus to create a receptive uterine environment, which is essential for the conceptus' development. The aim of this study was to demonstrate ultrastructural and histological changes of the endometrium at day 5 after ovulation in cyclic and inseminated mares. Mares were daily examined by transrectal palpation and ultrasonographic examination of the reproductive tract until ovulation was detected. In the first cycle, endometrial biopsies from 10 cyclic mares (Cyclic group) were collected on day 5 post-ovulation. In the second cycl...
Gérard N, Robin E.Terminal follicular differentiation and ovulation are essential steps of reproduction. They are induced by the increase in circulating LH, and lead to the expulsion from the ovary of oocytes ready to be fertilized. This review summarizes our current understanding of cellular and molecular pathways that control ovulation using a broad mammalian literature, with a specific focus to the mare, which is unique in some aspects of ovarian function in some cases. Essential steps and key factors are approached. The first part of this review concerns LH, receptors and signaling, addressing the descripti...
Dutra GA, Ishak GM, Pechanova O, Pechan T, Peterson DG, Jacob JCF, Willard ST, Ryan PL, Gastal EL, Feugang JM.Proteomic studies of follicular fluid (FF) exist for several species, including the horse; however, the seasonal influence on FF proteome has not been explored in livestock. The application of high-throughput proteomics of FF in horse has the potential to identify seasonal variations of proteins involved in follicle and oocyte growth. Methods: This study (i) profiles the proteomes of equine FF collected from dominant growing follicles during the spring anovulatory season (SAN), and spring (SOV), summer (SUM), and fall (FOV) ovulatory seasons; and (ii) identifies season-dependent regulatory net...
Donnelly CG, Sones JL, Dockweiler JC, Norberg LA, Norberg LE, Cheong SH, Gilbert RO.OBJECTIVE To evaluate use of flunixin meglumine as a treatment to postpone ovulation in mares, mare fertility after flunixin meglumine treatment during estrous cycles, and effects of flunixin meglumine on function of the corpus luteum after ovulation. ANIMALS 13 healthy mares. PROCEDURES A single-blinded, placebo-controlled, crossover study was conducted. Flunixin meglumine (1.1 mg/kg, IV, q 24 h) or lactated Ringer solution (placebo treatment) was administered for 2 days to mares with a dominant follicle (≥ 35 mm in diameter) and behavioral signs of estrus. Mares then were bred by artificia...
Huber D, Amsler E, Vidondo B, Kaeser R, Wespi B, Sieme H, Burger D.There exist differences in the reproductive behavior of stallions and mares under free-running and domestic in-hand breeding conditions. Contrary to artificial insemination programs, a stallion mates a mare multiple times per estrus under natural conditions. The objective of this study was to determine if multiple periovulatory artificial inseminations (MI), four times in two different time intervals instead of two, would result in increased pregnancy outcome or higher incidences of breeding induced endometritis. Methods: Eighty-two estrous mares were allocated randomly to one of three experim...
Kouba JM, Burns TA, Webel SK.The effects of dietary marine-derived n-3 fatty acids (FA) on mare milk and mare and foal plasma FA, postpartum ovarian follicular growth and prostaglandin concentrations were evaluated. Sixty days prior to expected foaling dates, mares were assigned to one of three diets: corn oil (CORN, n = 6), docosahexaenoic acid (DHA) diet (D; 12.64 g/d, n = 7), or eicosapentaenoic acid (EPA) and DHA (ED; 8.84 g EPA, 10.43 g DHA/d, n = 7). Milk and plasma were collected for FA analysis. Follicular data were recorded through the first postpartum ovulation. Post-ovulation serial blood samp...
O'Neil MM, Korthanke CM, Scarpa JO, Welsh TH, Cardoso RC, Williams GL.We tested the hypotheses that in winter anovulatory mares (1) both chronic daily injections of estradiol-17β (E2) and subcutaneous E2 implants could enhance pituitary secretion of gonadotropins in response to continuous subcutaneous infusion of native gonadotropin-releasing hormone (GnRH); and (2) the secretory pattern of follicle-stimulating hormone (FSH) in response to continuous subcutaneous infusion of native GnRH is similar to that of luteinizing hormone (LH) but differs between mares that develop or fail to develop an estrogen-active, preovulatory follicle. In Experiment 1, 20 winter an...
Leisinger CA, Klein C, Markle ML, Premanandan C, Sones JL, Pinto CRF, Paccamonti DL.Aluteal cycles were induced in the mare to evaluate the effects of progesterone deprivation on the gene expression of embryos and endometrium collected eight days after ovulation. We hypothesized that the transcript expression would be altered during induced aluteal (AL) cycles (low progesterone <1 ng/mL) when compared with control cycles during diestrus (high progesterone; > 4 ng/mL) for 1) the embryonic expression of progesterone-mediated transcripts and those related to normal embryo growth and development and 2) the endometrial expression of progesterone-mediated transcripts and those ...
Ginther OJ.Heifers have two or three major follicular waves per interovulatory interval (IOI). In mares and women, the ovulatory wave is the only major wave in most (75%) IOI. The beginning of diameter deviation during follicle selection of the future dominant follicle (DF) is followed by continued growth of DF and decreasing growth of the future subordinate follicles. Diameter deviation in Bos taurus heifers, mares, and women begins when the future DF is a mean of 8.5, 22.5, and 10.5 mm, respectively. Selection of the ovulatory follicle occurs more frequently from right ovary (RO) in heifers and women...
Duguma A, Lemma A, Hibste A.Equine reproduction is unique by having long behavioral estrus and differences in time of breeding between breeds and individuals of mares. An experimental study was conducted at the Balderas Sport Horses and Recreational Center, Addis Ababa, Ethiopia, from January to June, 2018, to evaluate conception rate to frozen semen in local and exotic crossbreed mares. Mares were teased to characterize estrus behavior and examined by ultrasound in determining imminent ovulation. Inseminations were done post ovulation within an average of 6-9 h using frozen-thawed semen. The overall conception rate to ...
Ginther OJ, Dangudubiyyam SV.Effect of side (left ovary, LO; right ovary, RO) and intraovarian presence of the regressing corpus luteum (CL) on the preovulatory follicle (PF) and ovulation were studied using ultrasonic- records of complete interovulatory intervals (IOI) for 500 IOI in heifers and 485 IOI in mares. Only IOI with a recording of side of a single PF and a single CL at each end of the IOI were used. In heifers, ovulation at the end of the IOI occurred more frequently (P < 0.0001) from RO (n = 285, 57%) than LO (n = 215, 43%). In mares, frequency of ovulation did not differ between RO (n = 250. ...
Bogle OA, Carrasco RA, Ratto MH, Singh J, Adams GP.The objectives of the study were to compare the presence and localization of ovulation-inducing factor (OIF)/nerve growth factor (NGF) in male reproductive organs and determine the abundance in ejaculates of species representative of both spontaneous and induced ovulators. We hypothesized that the protein is a widely conserved component of semen among mammals, but is most abundant in camelids. Immunohistochemical analysis was performed on tissues from the male reproductive system of llamas, rats, cattle, bison, elk, and white-tailed deer (n = 2 males/species), and the abundance of OIF/NGF in...
Davis KA, Klohonatz KM, Mora DSO, Twenter HM, Graham PE, Pinedo P, Eckery DC, Bruemmer JE.Currently there is no contraceptive vaccine that can cause permanent sterility in mares. This study investigates the effect of vaccination against oocyte-specific growth factors, Bone Morphogenetic Protein 15 (BMP-15) and Growth Differentiation Factor 9 (GDF-9), on ovarian function of mares. It was hypothesized that immunization against these growth factors would prevent ovulation and/or accelerate depletion of the oocyte reserve. For this study, 30 mares were randomly assigned to three groups (n = 10/group) and vaccinated with BMP-15 or GDF-9 peptides conjugated to KLH and adjuvant, or a ...
Oberhaus EL, Thompson DL, Foster BA, Pinto CR.This experiment assessed the hormonal production, secretory aspects, and changes in luteinizing hormone (LH) receptor gene expression of early induced ovulatory-sized follicles relative to the first ovulatory-sized follicles occurring naturally in the spring. Anovulatory mares were treated on January 21 with (1) 50 mg of estradiol cypionate (ECP, n = 8) alone or (2) with ECP followed by two 3-g sulpiride injections (n = 8), 5 and 12 days later. Half of each group also received complete follicle ablation via transvaginal aspiration before ECP treatment. Ovaries were scanned regularly until ...
Kikuchi K, Kozai K, Hojo T, Sakatani M, Okuda K, Bai H, Kawahara M, Takahashi M.We investigated the electrical impedance of the reproductive tracts (vagina and uterine endometrial tissues) and the expression of mucus-related genes to identify the stage of the estrous cycle in mares. We first examined vaginal impedance in native Hokkaido mares during their estrous cycle and found no significant differences. However, impedance levels tended to decrease towards ovulation. Furthermore, we investigated the estrous cycle by measuring the electrical impedance of the uterine endometrial tissues obtained from carcasses of mares. We found that impedance levels in the endometrial ti...
Oliveira Neto IV, Canisso IF, Segabinazzi LG, Dell'Aqua CPF, Alvarenga MA, Papa FO, Dell'Aqua JA.This study compared hormone treatments given to mares during anestrus, spring transition, and different stages of the estrous cycle, by assessing uterine features and pregnancy rates after embryo transfer (ET). Embryo recipient mares (n = 160) were equally arranged as follows: G1-spontaneous ovulation (control), G2-anestrus, G3-spring transition, G4-early estrus, G5-estrus, G6-diestrus, G7-early diestrus treated with a dose of dinoprost, and G8-early diestrus treated with two doses of dinoprost. At treatment initiation (Day-4), G2-7 were given dinoprost and estradiol-17β, thereafter, estr...
Ferreira JC, Filho LFN, Boakari YL, Canesin HS, Thompson DL, Lima FS, Meira C.The aim of the current project was to characterize the luteal vascularity and the plasma concentrations of progesterone (P4), prolactin (PRL) and 13,14-dihydro-15-keto-PGF (PGFM) in mares with luteal disturbances during early and mid-diestrus. In Experiment 1, twenty-one mares were treated with 2 mL of 0.9% NaCl, or 1 mg Dinoprost, or 10 mg Dinoprost on day two after ovulation (Control-D2, 1/10PGF-D2 and PGF-D2 groups, respectively; n = 7 mares/group). In Experiment 2, similar treatments were performed eight days post-ovulation using a different cohort of 21 mares (Control-D8, 1/10PGF-D8 ...
Ishak GM, Bashir ST, Gastal MO, Gastal EL.Color Doppler ultrasonography was used to study the temporal relationships between pre-ovulatory follicle (POF) and corpus luteum (CL) diameter and blood flow, with systemic progesterone (P4) concentration during two transitional ovulatory seasons in mares. Variables of POF and CL/P4 were evaluated for 6days before and 17days after ovulation, respectively. Evaluations were performed during two consecutive estrous cycles in spring and fall seasons, and during the last estrous cycle of the season. There were significant correlations among POF and CL variables, and P4 concentration that ranged fr...
Barua S, Macedo A, Kolb DS, Wynne-Edwards KE, Klein C.Milk-fat globule epidermal growth factor (EGF) 8 protein (MFGE8), also known as lactadherin, promotes cell adhesion in an Arg-Gly-Asp (RGD)-dependent modus via integrins. In the present study, the expression of MFGE8 was examined in equine endometrium during oestrus and at Days 12 and 16 after ovulation in pregnant and non-pregnant mares and in mares during the 5th month of gestation. Results demonstrated that MFGE8 is expressed at the embryo- and fetal-maternal interface in equine pregnancy. In non-pregnant endometrium its expression was upregulated by oestrogen, a finding that was confirmed ...
Sinclair CD, Webel SK, Douthit TL, Murray LW, Jager AL, Grieger DM, Kouba JM.The objective of these studies was to investigate the efficacy of an intravaginal triptorelin acetate (TA) gel as an ovulation-inducing agent in mares. In Exp. 1, 24 mares were blocked using a combination of parity and age and randomly assigned to 1 of 3 treatment groups: 5 mL TA gel (TA5), 10 mL TA gel (TA10), or 5 mL vehicle gel only (CON). Following the appearance of a follicle ≥ 25 mm, a blood sample was obtained for measurement of LH from each mare every 24 h until treatment administration. When a follicle ≥ 35 mm was observed, treatments were administered intravaginally. Following tr...
Garcia-Muñoz A, Valldecabres-Torres X, Newcombe JR, Cuervo-Arango J, Garcia-Rosello E.The objective of this study was to determine the effect of exogenous progesterone administration at ovulation and during the early development of the CL, on its future sensitivity to a single administration of PGF2a in mares and cows. Horse Retrospective reproductive data from an equine clinic in the UK during three breeding seasons were used. Mares were divided into: control group, cycles with single ovulations; double ovulation group cycles with asynchronous double ovulations; and PRID group: cycles with single ovulations and treatment with intravaginal progesterone device (CIDR) immediately...
Boakari YL, Ferreira JC, Canesin HS, Thompson DL, Lima FS, Pantoja JCF, Meira C.The objective of the current study was to evaluate the effects of deslorelin and hCG, two ovulation-inducing therapies, on LH surge and follicle vascularity in mares. Thirty mares were either treated with 1.5 mg IM of deslorelin, 2,500 IU IV of hCG or 2 mL IM of NaCl 0.9% (GnRH, hCG and Saline groups, respectively). Power-flow Doppler examination and blood collection were performed every hour during the first 12 hours after treatment (H0) and every six hours between hours 12 (H12) and 30 (H30) after treatment. Moreover, endpoints were evaluated every hour through the last six hours before ovul...
Meyers-Brown GA, Loud MC, Hyland JC, Roser JF.The most common equine breeding practice to decrease the time to the first ovulation of the year is to use artificial lights starting December 1 in the Northern Hemisphere. It can take 60-90 d for this lighting regimen to induce a fertile ovulation. The success rate for pharmaceutical compounds to carry out the same process has been variable. One compound that did induce an early ovulation was recombinant equine follicle stimulating hormone (reFSH), but neither pregnancy nor cyclicity was established in that study. Starting on December 1, 20 deep-anestrous mares of light horse breeds (4-15 y...
Silva ESM, Ignácio FS, Fritsch SC, Zanoni DS, Pantoja JCF, Oliveira-Filho JP, Meira C.To test the hypothesis that the administration of 2.5 mg of estradiol benzoate (EB) followed by 1500 mg of long acting progesterone (LA P4) causes similar uterine changes and molecular dynamics in anovulatory mares to those observed in cyclic ones, we evaluated the changes of estrogen (ERα and ERβ) and progesterone receptors (PR) in anestrous, transitional and cyclic mares by RT-qPCR and immunohistochemistry. In addition, we evaluated uterine edema, tonus and estrogens and progesterone plasma profile. Endometrial biopsies were taken from anestrous and transitional mares immediately before ...
Lemes KM, Silva LA, Alonso MA, Celeghini ECC, Pugliesi G, Carvalho HF, Affonso FJ, Silva DF, Leite TG, de Arruda RP.Follicular development and deviation processes during the postpartum period are not completely known in horses. Thus, we aimed to study the characteristics of follicular dynamics and ovarian vascular perfusion during the postpartum period in mares that demonstrated estrous behavior and had early ( 0.1) was detected between the groups when the data were normalized for the days preceding the first postpartum ovulation (from D-7 to D-1). However, when the data were normalized to days postpartum, the dominant follicle was larger (P 25 mm diameter was greater (P 0.1) was detected between grou...
Ginther OJ.Mares are superb models for study of follicle selection owing to similarities between mares and women in relative follicle diameters at specific events during the follicular wave and follicle accessibility for experimental sampling and manipulation. Usually, only 1 major follicular wave with a dominant follicle (DF) greater than 30 mm develops during the 22 to 24 d of the equine estrous cycle and is termed the primary or ovulatory wave. A major secondary wave occasionally (25%) develops early in the cycle. Follicles of the primary wave emerge at 6 mm on day 10 or 11 (day 0 = ovulation). The...
Miki W, Oniyama H, Takeda N, Kimura Y, Haneda S, Matsui M, Taya K, Nambo Y.We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus wer...
Piccinno M, Rizzo A, Cariello G, Sciorsci RL.In this study, the Authors investigated the modulatory effect of three single doses (10, 10, and 10 M) of neostigmine on the spontaneous contractility of equine pre-ovulatory follicles in an isolated organ bath, to establish the relationship between this acetylcholinesterase inhibitor and ovulation, in the mare. The results indicate that neostigmine increases pre-ovulatory contractility in equine follicles at each dose, but in a different manner. Indeed, the rise in contractility induced by neostigmine at 10 M and 10 M was phasic, while at 10 M it was tonic. The data obtained indicate poss...
Polasek TCM, Kozicki LE, Pedrosa VB, Weiss RR, Bertol MAF, Camargo CE, Talini R.This study aimed to correlate the inflammatory reaction (IR) caused by a progesterone-releasing intravaginal device (P4) with ovarian activity and pregnancy rate (PR) in embryo-recipient anestrus mares (to decrease the spring transitional period). 50 animals were assigned to three groups: GP4 (P4 group; n = 16), GP4OH (P4 + oxytetracycline hydrochloride and hydrocortisone sprayed onto the device; n = 14), and GNP4 (no intravaginal P4; n = 20). The administration protocol for GP4 was: Day 0, 750 mg P4 + ovarian examination by ultrasonography (US) + vaginal sample collection; Day 8, US;...
Finan SA, Lamkin EL, McKinnon AO.To investigate the comparative efficacy of BioRelease Deslorelin® (BRD) and Ovuplant® for induction of ovulation in cyclic mares in Australia. Methods: Ovarian follicular activity of 60 mares for a total of 95 cycles was monitored by ultrasonography until they developed a follicle ≥30 mm and a uterine oedema pattern of 3. Mares were then randomly allocated to one of three treatment groups: (1) treatment with 1.25 mg BRD, (2) a single Ovuplant pellet or (3) 1 mL compound sodium lactate control. Follicular activity was monitored with ultrasonography every 12 h until ovulation was detec...
Vanderwall DK, Woods GL, Weber JA, Lichtenwalner AB.The objective of this study was to test the hypothesis that intrauterine administration of prostaglandin E(2) (PGE(2)) or estradiol-17beta (E-17beta) would prolong CL function in nonpregnant mares. Nonpregnant mares were continuously infused with 240 mug/d of PGE(2), 6 mug/d of E-17beta, or vehicle (sham-treated) on Days 10 to 16 post ovulation (ovulation = Day 0), using osmotic minipumps surgically placed into the uterine lumen on Day 10 (n = 11 per group). Nonpregnant and pregnant mares served as negative and positive controls, respectively (n = 11 per group). Mares were defined as having pr...
Brown KA, Boerboom D, Bouchard N, Doré M, Lussier JG, Sirois J.Aldo-keto reductases (AKRs) are multifunctional enzymes capable of acting on a wide variety of substrates, including sex steroids. AKRs having 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity can reduce progesterone to 20alpha-hydroxy-4-pregnen-3-one (20alpha-DHP), a metabolite with lower affinity for the progesterone receptor. The objective of this study was to investigate the regulation of equine AKR1C23 during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine AKR1C23 cDNA was cloned and shown to encode a 322 amino acid protein that is conserved (71-81...
Samper JC.The two most common procedures for breeding management of mares involve induction of luteolysis and induction of ovulation. Although both of these events are usually achieved, physiologic conditions affect the timing of the response. In a diestrus mare treated with prostaglandin F(2alpha) (PGF), or a PGF analogue, it is well documented that, on average, the interval from treatment to the onset of estrus is 3-4 days, whereas ovulation occurs 8-10 days after treatment. However, the diameter of the ovulatory follicle, as well as its status at the time of PGF treatment, determines the intervals fr...
Downey BR.Neuroendocrine and endocrine factors involved in the regulation of reproductive cycles in domestic animals are discussed. Although research data from many species are considered, emphasis is placed on their relevance for the cow, sow, ewe and, to a lesser extent, the mare. Literature cited is not designed to be complete, but rather to be representative of the large volume of material which has been written on the subject.Gonadotropin-releasing hormone is synthesized and secreted in response to various exteroceptive stimuli, but both its release and its effects on the anterior pituitary are mod...
Vandeplassche GM, Wesson JA, Ginther OJ.Sexual behavior, follicular development and ovulation, and concentrations of circulating gonadotropins during the estrous cycle were studied during the summer in 7 jennies. Mean behavioral estrous length was 6.4 +/- 0.6 days (mean +/- SEM, n=19; 5.6 +/- 0.5 days preovulatory and 0.8 +/- 0.2 days post-ovulatory). Mean diestrous length was 19.3 +/- 0.6 days (n=14). Females in estrus typically showed posturing, mouth clapping, clitoral winking, urinating and tail raising. Mouth clapping began approximately one day sooner and lasted approximately one day longer than winking and tail raising, so th...
Kooistra LH, Ginther OJ.The effects of photoperiod on reproductive activity and hair changes in pony mares were studied in 2 experiments. In experiment I, the effect of a fixed daily photoperiod on the onset of the breeding season was studied in 36 mares from Nov 13, 1973, to June 13, 1974. The 4 treatment groups were as follows: daily photoperiod equivalent to the normal day length (control group); constant light 24 hours a day with no dark (L24:D0 group); 16-hour daily photoperiod with 8 hours of dark (L16:D8 group); and 9-hour daily photoperiod with 15 hours of dark (L9:D15 group). The intervals from beginning of ...
Nambo Y, Nagaoka K, Tanaka Y, Nagamine N, Shinbo H, Nagata S, Yoshihara T, Watanabe G, Groome NP, Taya K.In female mammals, inhibin is secreted by the granulosa cells and selectively inhibits secretion of FSH. Although circulating immunoreactive (ir)-inhibin levels decrease after ovulation as a result of the disappearance of its main source, they abruptly increase at the time of ovulation in mares. To investigate the mechanisms responsible for this increase, 50 ml of equine follicular fluid (eFF) was administered into the abdominal cavity of mares during the luteal phase (eFF, n = 4). One hour after treatment, plasma levels of ir-inhibin and inhibin pro-alphaC (but not estradiol-17beta) were sign...
Enders AC, Liu IK, Bowers J, Lantz KC, Schlafke S, Suarez S.Fertilization and early development in the horse were studied by recovering oviductal ova at various times after postovulatory mating. Ova collected between 7 and 22 h post coitum (pc) were examined for evidence of fertilizing sperm, cellular changes accompanying fertilization, and pronuclear development. Five ova collected between 7 and 9 h pc contained a marginal metaphase plate, but had no indication of sperm components; three of these, however, showed reduced numbers of cortical granules. Two activated ova (10 and 14 h pc) were in telophase of the second meiotic division, following incorpo...
Grubaugh W, Sharp DC, Berglund LA, McDowell KJ, Kilmer DM, Peck LS, Seamans KW.When mares were pinealectomized in summer or in winter there was no difference in the annual ovulation date of these animals and of pineal-intact controls during the first post-operative breeding season but in the second season the ovulation date of the winter pinealectomized mares was significantly delayed, suggesting a long-term but clear pineal involvement in seasonal reproductive patterns. Exposure of pinealectomized mares to a stimulatory photoperiod failed to advance the average date of first annual ovulation and was similar to that of intact mares receiving no stimulatory lighting. The ...
Ginther OJ, Gastal MO, Gastal EL, Jacob JC, Beg MA.A follicular wave and luteolysis were induced in mares by ablation of follicles > or =6 mm and treatment with prostaglandin F(2alpha) (PGF) on Day 10 (where ovulation = Day 0). The incidence of haemorrhagic anovulatory follicles (HAFs) in the induced waves (20%) was greater (P < 0.007) than in preceding spontaneous waves (2%). Hormone and follicle dynamics were compared between induced follicular waves that ended in ovulations (ovulating group; n = 36) v. HAFs (HAF group; n = 9). The day of the first ovulation or the beginning of HAF formation at the end of an induced wave was designated as po...
Vanderwall DK, Silvia WJ, Fitzgerald BP.The reproductive tracts of nine thoroughbred mares were examined by ultrasound to determine the day of ovulation (day 0). Mares were fitted with intercavernous sinus cannulae on the day before the start of sample collection of pituitary venous effluent rich in oxytocin. Intercavernous sinus blood samples were collected for at least 36 h at 5 min intervals beginning at noon on day 13 (n = 2), day 15 (n = 5) or day 16 (n = 2) after ovulation. Concentrations of oxytocin and 13,14-dihydro-15-keto prostaglandin F2 alpha (PGFM) in plasma were determined by radioimmunoassay. Three high-magnitude surg...
Segabinazzi LGTM, Oba E, Alvarenga MA.Equine practitioners often prescribe the combined use of hCG and GnRH to hasten ovulation due to presumed synergistic effects. Therefore, this study aimed to test whether the combination of hCG and deslorelin acetate to hasten ovulation in mares would show any effect in inducing ovulation more efficiently than when either drug is used by itself, and to verify whether this association would affect progesterone concentrations; corpus luteum (CL) diameter and blood flow; and pregnancy outcome in recipient mares after embryo transfer (ET). Seventeen mares had the ovulation hastened (≥35 mm folli...
Troedsson MH, Ababneh MM, Ohlgren AF, Madill S, Vetscher N, Gregas M.The objective of this study was to determine whether periovulatory treatments with PGF2alpha affects the development of the CL, and whether the treatment was detrimental to the establishment of pregnancy. Reproductively sound mares were assigned randomly to one of the following treatment groups during consecutive estrus cycles: 1. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol (PGF2alpha analogue) on Days 0, 1, and 2 after ovulation (n=8), 2. 2 mL sterile water injection within 24 hours before artificial insemination and 500 microg cloprostenol on Days ...
Irvine CH, Alexander SL.Conflicting views exist on the mode of gonadotrophin-releasing hormone (GnRH) secretion during the ovulatory LH surge and the relative importance of changes in pituitary responsiveness to GnRH in generating the LH surge. This disagreement may stem from species differences and/or methodological problems. To provide data on the exact relationship between GnRH and gonadotrophin secretion during the spontaneous LH surge, we collected pituitary venous (PV) blood every 30 s for 3-4 h from eight mares and then assayed GnRH (in six of the mares), FSH and LH. Jugular blood was also collected from twelv...
Dalin AM, Andresen O, Malmgren L.The aim of the present study was to investigate the effect of active immunization against GnRH in mature Standardbred mares (three experimental and one control mare) on antibody titres, ovarian function, hormonal levels and oestrous behaviour. The mares were individually teased with a stallion once each day. During the first part of the experiment (period I: late April until November), blood was sampled every third day during the first 3 months, thereafter once per week. In the second part of the experiment (period II: December until August), sampling was carried out every second week. Progest...
Betteridge KJ, Eaglesome MD, Flood PF.Two experiments were conducted using 14 mares. In Exp. 1, mares were inseminated with semen treated with TEPA, which, in other species, has been shown to lead to an arrest in ovum cleavage at 2--4 cells. The oviducts and/or uterus were then flushed 7--10 days after ovulation in 6 mares (Group A) or 2--6 days after ovulation in 5 mares (Group B). Fresh eggs were found in the oviduct flushes of 5 Group A and 5 Group B mares: 9 of the 10 eggs appeared to have cleaved, but none had developed beyond 16-cells. Seven eggs contained spermatozoa and 3 of 4 eggs from each group showed evidence of fertil...
Camillo F, Vannozzi I, Rota A, Di Luzio B, Romagnoli S, Aria G, Allen WR.Mules, hybrids resulting from the mating of a horse mare (Equus caballus, 2n = 64) to a Jack donkey (E. asinus, 2n = 62), are generally infertile. Five horse embryos were transferred non-surgically to two cyclic and one acyclic recipient mules. In the mares and cycling mules, oestrus and ovulation were induced with, respectively, d-cloprostenol and human chorionic gonadotrophin (hCG). The acyclic mule, on the other hand, received oestradiol benzoate when the embryo donor was showing oestrus and progesterone after the donor had ovulated and until pregnancy diagnosis. Non-surgical embryo collect...
Meyers-Brown GA, McCue PM, Troedsson MH, Klein C, Zent W, Ferris RA, Lindholm AR, Scofield DB, Claes AN, Morganti M, Colgin MA, Wetzel RL, Peters AR....Traditionally, mares are put under artificial lights to advance the first ovulation of the year. The aim of the present study was to determine the efficacy of recombinant equine FSH (reFSH) in stimulating follicular development and advancing the first ovulation of the year in seasonally anestrous mares compared with anestrous mares given a placebo. Both groups of mares were housed under ambient light conditions. Sixty deep anestrous mares of light horse breeds (follicular diameters ≤ 20 mm in diameter and progesterone <1 ng/mL) were maintained under a natural photoperiod at three differen...
Mateu-Sánchez S, Newcombe JR, Garcés-Narro C, Cuervo-Arango J.The interval from both spontaneous and prostaglandin (PGF)-induced luteolysis to ovulation is greatly variable in mares. Several reports have shown a positive association between the length of the interval from PGF treatment to ovulation (ITO) and the subsequent pregnancy rate (PR). However, it is not known whether this association also occurs in estrous cycles with spontaneous luteolysis. The main objective of this study was to determine the effect of the duration of estrus-like echotexture of the uterus during the follicular phase on the subsequent PR in both spontaneous and PGF-induced cycl...
Cuervo-Arango J, Claes AN, Stout TAE.In recent years, the number of equine invitro-produced embryos (IVP) has increased markedly; as yet, there are few reports on what constitutes an 'ideal' recipient for an IVP embryo. This study retrospectively investigated the effects of recipient mare oestrous cycle characteristics on the likelihood of pregnancy after transfer of IVP (n=264) and invivo-derived embryos (n=262). IVP embryos tolerated only a narrow window of recipient mare 'synchrony', with transfer on Day 4 after ovulation resulting in a higher likelihood of ongoing pregnancy (69%) than transfer on Days 3, 5 or 6 (53.2%, 41.3% ...
Bergfelt DR, Pierson RA, Ginther OJ.The present study was designed to characterize and compare the physiology and ultrasonographic morphology of the corpus luteum (CL) during regression and resurgence following a single dose of native prostaglandin F2alpha (PGF) given 3 days after ovulation, with a more conventional treatment given 10 days after ovulation. On the day of pre-treatment ovulation (Day 0), horse mares were randomly assigned to receive PGF (Lutalyse; 10 mg/mare, i.m.) on Day 3 (17 mares) or Day 10 (17 mares). Beginning on either Days 3 or 10, follicle and CL data and blood samples were collected daily until post-trea...
Hayes KE, Pierson RA, Scraba ST, Ginther OJ.The morphological changes in ultrasound images of the uterus at various times of the year were characterized in nonbred mares, using a linear-array scanner. The uterus was recorded as having an ultrasonic morphology characteristic of diestrus (uterine score 1, endometrial folds not visible), estrus (score 3, distinct endometrial folds), or an intermediate stage (score 2). In Experiment I, uterine scores for the first ovulatory period of the year were compared to scores for the second period in 23 pony mares. More mares (P<0.05) showed endometrial folding prior to the second ovulation of the...
Bashir ST, Ishak GM, Gastal MO, Roser JF, Gastal EL.Changes in intrafollicular growth factors and hormones were evaluated in vivo in postdeviation and impending ovulation follicles. Mares (n = 30) were randomly assigned to five experimental groups based on target diameters of 25, 30, 35, 40 mm, and impending signs of ovulation. Furthermore, data belonging to two or more proximal diameter groups that were not different were combined and regrouped for each factor separately. Follicular fluid-free insulin-like growth factor 1 was highest (P 0.05) among groups. Additionally, follicular fluid activin A tended (P < 0.06) to be higher in i...
Morel MC, Newcombe JR, Hayward K.The importance of elucidating factors affecting reproductive performance and efficiency is of paramount concern to the equine industry. Oocyte viability is known to be one of the determinants of reproductive success and evidence suggests that it may be linked to follicle size. The aims of this study were, therefore, to ascertain: i) the average diameter and range of pre-ovulatory follicles in Thoroughbred mares; ii) whether this is affected by either mare age, time within the breeding season, or the presence of multiple pre-ovulatory follicles (MO). One thousand, four hundred and ninety two Th...
Veronesi MC, Battocchio M, Faustini M, Gandini M, Cairoli F.The aim of this study was to evaluate the possible relationship of pharmacological induction of estrous and/or ovulation with the occurrence of twin pregnancies in Thoroughbred mares. Out of 680 mares, 356 received one of the following treatments during the estrous cycle in which they became pregnant: injection of 0.5mg of cloprostenol at the ultrasonographic detection of a CL (n=86); injection of 5000 IU human chorionic gonadotropin (hCG) immediately before mating (n=221); injection of 0.5mg of cloprostenol at the ultrasonographic detection of a CL plus injection of 5000 IU hCG immediately be...
Friso AM, Segabinazzi LGTM, Cyrino M, Correal SB, Freitas-Dell'Aqua CP, Teoro do Carmo M, Dell'Aqua JA, Miró J, Papa FO, Alvarenga MA.Non-steroidal anti-inflammatory drugs (NSAIDs) are a therapeutic option for the treatment of inflammation. However, negative effects of non-selective NSAIDs for treatment of mares with endometritis have been described, including delayed uterine clearance and impairment of ovulations. Firocoxib is a specific cyclooxygenase-2 (COX-2) inhibitor and has the ability to act in the uterus of mares. We investigated the effects of firocoxib on ovulation rate, numbers of polymorphonuclear neutrophils (PMNs), and COX-2 protein levels in the endometrial tissue of susceptible mares after insemination. Two ...
Thompson DL, Hoffman R, DePew CL.Eight pony mares received 4 mg of recombinant porcine prolactin (rpPRL) daily for 45 d beginning on January 15; eight control mares received vehicle. Reproductive end points and various indicators of metabolism, hair shedding, and thyroid activity were monitored. Prolactin concentrations peaked in mares treated with rpPRL at 94 +/- 19 ng/mL 2 h after injection and were 5.1 +/- 1.7 ng/mL 24 h after injection. Treatment with rpPRL increased (P < .01) hair shedding within 14 d, which peaked at 28 d and then dropped precipitously. Binding of 125I-equine prolactin confirmed that antibodies were ...
Redina OE, Amstislavsky SYa , Maksimovsky LF.This study examined the developmental capacity of oocytes in DD mice after they had been injected with pregnant mares' serum gonadotrophin at different stages of the oestrous cycle. The superovulation of mature DD mice at pro-oestrus, oestrus and metoestrus resulted in a large yield of viable embryos. The proportion of abnormal embryos was highest after injection of pregnant mares' serum gonadotrophin at dioestrus. The pool of viable oocytes was most synchronized with normal development after the hormone was injected at oestrus. The results demonstrate that oocytes of different morphology coul...
Wesson JA, Ginther OJ.Reproductive tracts were collected monthly over a 3-year period from 1,003 nonpregnant ponies at a slaughtering plant in Wisconsin. Ages of the animals were estimated from tooth replacement and wear. Ovaries were examined for follicular and luteal activity. There were no differences between left and right ovaries in size or occurrence of ovulation. The frequency of multiple ovulations, 10%, was higher than previously reported for ponies. The follicular changes during the ovulatory cycle did not support a two-wave theory of follicular growth. Ovarian activity changed seasonally, a finding simil...
Kerban A, Doré M, Sirois J.In contrast to other species, the histology of the equine follicle during ovulation has not been described. Preovulatory follicles were isolated during oestrus at 0, 12, 24, 30, 33, 36 and 39 h (n = 5-6 follicles per time point) after an ovulatory dose of hCG to characterize the cellular and vascular changes associated with ovulation in mares. Pieces of follicle wall were formalin-fixed and processed for light microscopy to evaluate the general follicular morphology and quantify selected parameters. Marked changes were observed in the histology of equine follicles in the hours before ovulation...
