The estrous cycle in horses is a recurring reproductive cycle that mares undergo, typically during the breeding season. This cycle is characterized by a series of hormonal changes that prepare the mare for potential conception. The cycle is divided into two main phases: estrus and diestrus. During estrus, the mare is receptive to mating, and ovulation occurs. In contrast, the diestrus phase is a period when the mare is not receptive to a stallion. The regulation of the estrous cycle involves a complex interplay of hormones such as estrogen, progesterone, luteinizing hormone, and follicle-stimulating hormone. Understanding the estrous cycle is important for effective breeding management and reproductive health in horses. This page compiles peer-reviewed research studies and scholarly articles that explore the physiology, hormonal regulation, and implications of the estrous cycle in equine reproduction.
Gradil CM, Uricchio CK, Schwarz A.The present study evaluated a novel intrauterine device for its effect on estrus suppression. The self-assembling intrauterine device (Upod) consists of three 12 mm × 26 mm elliptically shaped units each with a magnetic core and coated with a polymer (total weight 22.5 g). Each magnetic unit is inserted independently from the other. Once inside the uterus, these magnetic elliptical units self-assemble and adapt the lower energy "ring" conformation. In mares, the devices can be inserted at any stage of the estrous cycle without the need for multiple exams. Shatter-proof grade material is u...
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...
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...
Manning HS, Runcan EE, Dias de Moraes CR, Coutinho da Silva MA.The objective of this study was to use estrous behavior alone to determine the appropriate time for beginning an oxytocin treatment protocol for estrus suppression. We hypothesized that administration of oxytocin beginning 8 days after the onset of estrus will prolong the luteal phase in mares. Twenty-three light breed mares (aged 4-20 years) were exposed to a stallion and observed for signs of sexual receptivity. Mares not displaying signs received 250 μg of cloprostenol intramuscularly (IM) and were teased again 3-4 days later. On the day that estrous behavior was observed (Day 0), mare...
Sarnecky BA, Vanderwall DK, Mason HM, Kirschner SM, Ambrose B, Parker TL.Prolonging function of the corpus luteum (CL) is a method of suppressing estrus that relies on continued secretion of endogenous progesterone to keep mares out of heat naturally. The use of oxytocin treatment to prolong CL function is gaining increasing use, and the most common treatment protocol involves administration of 60 units of oxytocin intramuscularly (IM) once daily on days 7-14 after ovulation (eight daily treatments). Although that protocol induces prolonged CL function in ≥70% of treated mares, the need for daily administration is a drawback to its use. Therefore, the objective o...
Maloney SE, Khan FA, Chenier TS, Diel de Amorim M, Anthony Hayes M, Scholtz EL.Proteomic analysis of mare uterine flush fluid provides a minimally invasive technique for studying protein changes associated with the oestrous cycle. The aim of this study was to identify differentially abundant proteins in the uterine flush fluid of mares in oestrus and dioestrus. In this study, uterine flush fluid samples were collected from eight reproductively healthy mares in either oestrus (n = 5) or dioestrus (n = 3). Proteomic analysis was performed using liquid chromatography-tandem mass spectrometry. Of 172 proteins identified, six proteins (immunoglobulin lambda-like polypepti...
Rebordão MR, Amaral A, Lukasik K, Szóstek-Mioduchowska A, Pinto-Bravo P, Galvão A, Skarzynski DJ, Ferreira-Dias G.Prostaglandin E (PGE) has contradictory effects in many organs. It may have proinflammatory, anti-inflammatory, or anti-fibrotic roles, depending on the type of receptors to which it binds. By signaling through its receptors EP2 and EP4, PGE mediates anti-inflammatory and anti-fibrotic actions. In spite of chronic endometrial fibrosis (endometrosis) being a major cause of mare infertility, its pathogenesis is not fully understood. We have shown that contact of mare endometrium in vitro with neutrophil extracellular traps (NETs) proteases favors endometrial collagen type I production. Therefor...
Amaral A, Fernandes C, Lukasik K, Szóstek-Mioduchowska A, Baclawska A, Rebordão MR, Aguiar-Silva J, Pinto-Bravo P, Skarzynski DJ, Ferreira-Dias G.We have shown that bacteria induce neutrophil extracellular traps (NETs) in mare endometrium. Besides killing pathogens, NETs may contribute for endometrosis (chronic endometrium fibrosis). Since elastase (ELA) is a NETs component that regulates fibrosis and prostaglandin (PG) output, the aim was to evaluate if inhibition of ELA would affect collagen 1 (COL1) transcription and PGs secretion by endometrium explants, in different estrous cycle phases. Follicular-FP (n = 8) and mid luteal-MLP (n = 7) phases explants were cultured for 24-48 hr with medium alone (Control), ELA (0.5 μg/ml,1 ...
Młodawska W, Grzesiak M, Kochan J, Nowak A.Steroidogenic activity in the equine ovary from birth to puberty has been poorly investigated. This study aimed to examine the capability of the ovarian follicles of prepubertal and pubertal fillies to produce steroid hormones and to evaluate the expression and cellular localization of androgen receptor (AR) in their ovaries. The ovaries of 6-18 month-old fillies were divided into two groups: prepubertal (PrP) - without preovulatory follicle (pF) and corpus luteum (CL), and ovulating/postpubertal (Ov/pB) - with pF and/or CL in at least one of the gonads. Adult mares (Me) were used as a control...
Thompson RL, Gunn AJ, Stephen CP, Ip H, Brookes VJ.Uterine luminal pH has been demonstrated to be a valid indicator of uterine health in species such as cattle and sheep. However, research regarding uterine luminal pH in equines is lacking. The objectives of this study were to assess uterine luminal pH in mares during the estrous cycle, and evaluate the effect of dilute vinegar lavage on both uterine luminal pH and endometrial health. The study was conducted using a randomized block design in which eight mares (four Thoroughbred and four Standardbred) were aged matched then randomly assigned to two groups. Endometrial biopsies were taken from ...
Fischer CD, Wachoski-Dark GL, Grant DM, Bramer SA, Klein C.Interferon epsilon (IFNE) is type I interferon which stands out through its unusual expression profile and differing regulation compared to classic type I interferons such as interferon alpha and interferon beta. Unlike other type I interferons, the expression of IFNE is not stimulated through exposure to viral agents. Expression of IFNE is most abundant in mouse and human endometrium where it is constitutively expressed in luminal and glandular epithelial cells and expression levels are up-regulated with estrogen exposure. The aim of the current study was to determine whether a cycle or pregn...
Rink BE, Kuhl J, Esteves CL, French HM, Watson E, Aurich C, Donadeu FX.Mesenchymal stem or stromal cells (MSCs) play key roles in tissue homeostasis. In the cyclic equine endometrium, this may be regulated by changes in serum concentrations of sex steroid hormones. This study was designed to investigate the changes in endometrial expression of MSC markers during reproductive cycles in mares and the influence of sex steroid hormones on endometrial MSC proliferation in vitro. Endometrial biopsies were collected from pony mares at different reproductive stages (estrus; day 5 and 13 after ovulation; seasonal anestrus; 20 h and 7days post-partum; n = 5 per stag...
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 ...
Ginther OJ, Domingues RR, Dangudubiyyam SV, Araujo ER.Diameter deviation or follicle selection during a follicular wave begins with continuous growth rate of F1 (dominant or selected follicle; DF) and decreasing growth rate of F2 (largest subordinate). Intraovarian patterns based on presence or absence of the DF and CL are DF-CL, DF, CL, and devoid (neither DF nor CL). The DF and CL relationships in a pair of ovaries are ipsilateral (DF-CL pattern and devoid pattern) and contralateral (DF pattern and CL pattern). The effects of patterns and relationships on F1, F2, and FSH during deviation were determined in 21 mares. Diameters of F1 and F2 at ex...
Burger D, Meuwly C, Thomas S, Sieme H, Oberthür M, Wedekind C, Meinecke-Tillmann S.Although female preferences are well studied in many mammals, the possible effects of the oestrous cycle are not yet sufficiently understood. Here we investigate female preferences for visual and non-visual male traits relative to the periodically cycling of sexual proceptivity (oestrus) and inactivity (dioestrus), respectively, in the polygynous horse (Equus caballus). We individually exposed mares to stallions in four experimental situations: (i) mares in oestrus and visual contact to stallions allowed, (ii) mares in oestrus, with blinds (wooden partitions preventing visual contact but allow...
Rebordão MR, Amaral A, Lukasik K, Szóstek-Mioduchowska A, Pinto-Bravo P, Galvão A, Skarzynski DJ, Ferreira-Dias G.Neutrophil extracellular traps (NETs) are DNA complexes carrying nuclear and cytoplasmic proteins, such as elastase (ELA), cathepsin-G (CAT) and myeloperoxidase (MPO). Mare endometrosis is a chronic degenerative process characterized by excessive collagen in endometrium. While NETs fight bacteria that cause endometritis, they may trigger endometrial fibrogenesis. The aim was to evaluate the in vitro effect of some NETs components on mare endometrial fibrogenesis and determine its relationship with histopathology or estrous cycle. Endometrial explants were incubated with NETs components (ELA, ...
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...
Guillaume D, Moussu C, de Geoffroy F, Chesneau D, Keller M.Stallions show decreased sexual responses and activities during short days in winter. To evaluate the importance of sexual olfactory communication in horses, we tested whether sexual responses could be stimulated through various sexual olfactory stimulations in winter. To this end, we presented stallions with various olfactory stimulations (urine from mares at different stages of the reproductive cycle, urine from stallions or geldings, or chemically defined synthetic odorant) during the non-breeding season and measured their behavioral responses through (1) a test of olfactory investigation (...
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...
Fernandes CB, Loux SC, Scoggin KE, Squires EL, Troedsson MH, Esteller-Vico A, Ball BA.The cervix is a dynamic structure that undergoes dramatic changes during the estrous cycle, pregnancy and parturition. It is well established that hormonal changes, including estrogens, progestogens and prostaglandins, regulate the expression of key proteins involved in cervical function. The arachidonic acid cascade is important in the remodeling and relaxation of the cervix in the days preceding parturition. Despite the complexity of this mechanism, regulation of cervical function has received little study in the mare. Therefore, the objective of this study was to compare the expression of e...
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...
Campbell MLH, Hampshire D, Hamstead LE, Rose BV, Smith KC, de Mestre AM.Intrauterine infusion of peanut oil at Day 10 post-ovulation has been reported to prolong dioestrus in mares. However, the effects of peanut oil treatment on the endometrium and whether the technique is painful have not been assessed. The objectives of this study were, (i) to determine the effect of intrauterine infusion of peanut oil on endometrial health, (ii) to determine whether use of intrauterine peanut oil is painful and (iii) to confirm that peanut oil causes prolonged dioestrus. Six mares aged 3-12 years old were used in a cross-over design with each mare administered both 1 ml of in...
Tangyuenyong S, Nambo Y, Nagaoka K, Tanaka T, Watanabe G.Most thyroid hormone determinations in animals are based on immunoassays adapted from those used to test human samples, which may not reflect the actual values of thyroid hormone in horses because of the presence of binding proteins. The aims of the present study were i) to establish a novel radioimmunoassay (RIA) using a more simple and convenient method to separate binding proteins for the measurement of total thyroxine (T4) in horses and ii) to validate the assay by comparing total T4 concentrations in yearling horses raised in different climates. Blood samples were collected from trained y...
Killisch R, Böttcher D, Theuß T, Edzards H, Martinsson G, Einspanier A, Gottschalk J, Schoon HA.The deep anoestrous phase in winter is part of the anovulatory season in mares and is bordered by the autumn and spring transitional periods (ATP/STP). To define an annual time span for effective prognostic biopsy sampling, the aim of this study was to provide a morphofunctional characterization of the endometrium during ATP and STP. To outline both transitional periods, endometrial specimens were taken in September, October and November (n = 76) as well as February, March and April (n = 184) with the requirement of a detailed clinical documentation. Tissue samples were examined histologic...
Pinto-Bravo P, Galvão A, Rebordão MR, Amaral A, Ramilo D, Silva E, Szóstek-Mioduchowska A, Alexandre-Pires G, Roberto da Costa R, Skarzynski DJ....The oviduct plays important roles in the early reproductive process. The aim of this study was to evaluate gene transcription and protein expression of progesterone receptor (PGR), estrogen receptors 1 (ESR1) and 2 (ESR2); oxytocin receptor (OXTR); prostaglandin F2α synthase (AKR1C3), and prostaglandin E2 synthase (Ptges) in mare oviduct in different estrous cycle stages. Estradiol (E), progesterone (P), oxytocin (OXT), and tumor necrosis factor α (TNF) effect on in vitro PGE and prostaglandin F2α (PGF) secretion by equine oviduct explants or by oviductal epithelial cells (OECs) were also ...
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 ...
Claes A, Ball BA, Scoggin KE, Roser JF, Woodward EM, Davolli GM, Squires EL, Troedsson MHT.Reproductive aging must be well understood to optimize the reproductive management of older mares and to predict their reproductive life-span. The objectives of this study were to: 1) examine age-related differences in follicular dynamics, endocrine profiles, and primordial follicle counts, 2) evaluate the influence of antral follicle count (AFC) on age-related changes in follicular parameters, and 3) determine the influence of diestrous ovulations on the estrous cycle. Young (3-8yr; n = 10), middle-aged (9-18 yr; n = 16), and old (>18 yr; n = 19) light horse mares were examined wit...
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...
Rudolf Vegas A, Podico G, Canisso IF, Bollwein H, Almiñana C, Bauersachs S.During the period of maternal recognition of pregnancy (MRP) in the mare, the embryo needs to signal its presence to the endometrium to prevent regression of the corpus luteum and prepare for establishment of pregnancy. This is achieved by mechanical stimuli and release of various signaling molecules by the equine embryo while migrating through the uterus. We hypothesized that embryo's signals induce changes in the endometrial gene expression in a highly cell type-specific manner. A spatiotemporal transcriptomics approach was applied combining laser capture microdissection and low-input-RNA se...
Cuervo-Arango J, Clark A.The mare is a seasonally polyestrus breeder. In early spring, the mare enters a "transition period" between the anovulatory season and the first ovulation of the year. This period is characterized by irregular estrus cycles and high incidence of regressing dominant follicles. There is a belief that pregnancy rates resulting from the first ovulation of the season is lower than in subsequent ovulations, however this has never been studied critically. Progestagens are often used as an aid to manage the transition period. The objective of this study was to compare pregnancy rates of mares from the...
Ball BA, Scoggin KE, Troedsson MH, Squires EL.Biological effects of prostaglandin E2 are mediated via one of four receptors designated EP1, EP2, EP3 and EP4 which are encoded by separate genes. In general, EP1 and EP3 induce smooth muscle contraction whereas EP2 and EP4 induce smooth muscle relaxation. The objective of the current study was to characterize the expression of the genes for PGE2 receptors (EP2 and EP4) in the horse oviduct based upon immunohistochemistry (IHC) and quantitative PCR (qPCR). Oviductal tissue was collected from mares at estrus (n=5), at 5 days post-ovulation (n=4), and from prepubertal mares (n=5). Isthmic and a...
Evans MJ, Irvine CH.Heterologous radioimmunoassays were developed for equine FSH and LH. Serum concentrations were measured in twenty-three mares throughout the oestrous cycle and early pregnancy. FSH concentrations were raised fivefold by 'surges' rather than 'spiked', occurring at 10- to 11-day intervals during the oestrous cycle and early pregnancy. The late oestrous/early dioestrous surge of FSH appeared to initiate development of up to twenty follicles. The mid-dioestrous surge may be important for the further development of follicles destined to ovulate 10 to 13 days later. Levels of LH were increasing by t...
Bollwei H, Weber F, Kolberg B, Stolla R.Uterine and ovarian blood flow was investigated in four mares during two consecutive estrous cycles using transrectal color Doppler sonography. The uterine and ovarian arteries of both sides were scanned to obtain waves of blood flow velocity. The pulsatility index (PI) reflected blood flow. There were significant time trends in PI values of all uterine and ovarian blood vessels during the estrous cycle (P < 0.05). PI values did not differ between the uterine arteries ipsi- and contralateral to the corpus luteum or the ovulatory follicle. PI values of the uterine arteries showed a wave shap...
Fischer CD, Wachoski-Dark GL, Grant DM, Bramer SA, Klein C.Interferon epsilon (IFNE) is type I interferon which stands out through its unusual expression profile and differing regulation compared to classic type I interferons such as interferon alpha and interferon beta. Unlike other type I interferons, the expression of IFNE is not stimulated through exposure to viral agents. Expression of IFNE is most abundant in mouse and human endometrium where it is constitutively expressed in luminal and glandular epithelial cells and expression levels are up-regulated with estrogen exposure. The aim of the current study was to determine whether a cycle or pregn...
Gerstenberg C, Allen WR, Stewart F.Immunohistochemical detection of the proliferation marker Ki-67 antigen was used to monitor mitotic activity in the endometrium of mares. The monoclonal antibody MIB1 was validated for use on equine tissues by demonstrating its reaction with activated peripheral blood lymphocytes, and endometrial biopsies were recovered from 26 non-pregnant mares at selected stages during the reproductive cycle. The proportion of positively stained nuclei was counted in five random areas on each histological section to determine the percentage and type of proliferating cells. Multiplication rates in the types ...
Heidler B, Aurich JE, Pohl W, Aurich C.This study summarizes weight development, plasma glucose concentrations and reproductive parameters in lactating (n = 46) and non-lactating Lipizzaner mares (n = 11) throughout the breeding season. It was the aim of the study to analyse if an energy deficit with possible effects on reproductive functions occurs at any time during the first 4 months of gestation. Mean gestation length was 334.3 +/- 7.3 days. Gestation of foals born in May/June was shorter (P < 0.01) than for foals born in March/April. Out of the 46 lactating mares, 44 ovulated between Days 8 and 18 postpartum and two mares ovul...
Johnson AL.Studies were conducted to characterize circulating concentrations of prolactin, thyroxine (T4) and triiodothyronine (T3) relative to season and the estrous cycle, and to evaluate the ability of thyrotropin-releasing hormone (TRH) to induce prolactin secretion in the horse mare. The increase in serum prolactin following the iv injection of 0, 5, 50 and 500 micrograms TRH was dose-related, while all three doses of TRH induced a significant and comparable increase in serum T4. Seasonal variations in serum prolactin were directly correlated (P less than .001) with changes in photoperiod (r = .80) ...
Behrendt-Adam CY, Adams MH, Simpson KS, McDowell KJ.A positive-feedback loop between luteal oxytocin and uterine prostaglandin F2 alpha (PGF) is a major signal for luteolysis in ruminants. Likewise, uterine PGF causes luteolysis in mares, but the involvement of oxytocin in this process is unclear. We wanted: 1) to determine if the oxytocin-neurophysin I (OT-NP I) gene is transcribed into mRNA in the endometrium of mares; and, if so, 2) to analyze relative changes in abundance of endometrial OT-NP I mRNA throughout the estrous cycle and during early stages of pregnancy. Endometrial biopsies were obtained from nonbred mares during estrus, and 5, ...
Donadeu FX, Watson ED.The annual reproductive cycle in the horse involves a reduction in ovarian activity during short days. The absence of ovulatory activity during winter has important consequences for an equine industry eager to breed mares early during the year. The anovulatory season results from a reduction in the secretion of pituitary gonadotropin that is in turn triggered by the inhibitory effects of short photoperiod on the hypothalamus-pituitary axis. Recent studies have provided evidence that the response of the ovaries to endocrine stimuli during the anovulatory season is affected not only by circulati...
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 ...
Szóstek AZ, Galvão AM, Hojo T, Okuda K, Skarzynski DJ.The aim of the present study was to investigate the interaction between ovarian steroids, interleukins and prostaglandins (PG) in equine epithelial and stromal cells in vitro. In Experiment 1, cells were exposed to IL-1α (10 ng/mL), IL-1β (10 ng/mL) or IL-6 (10 ng/mL) for 24 h and cell proliferation was determined using MTT. In Experiment 2, cells were exposed to progesterone (P4; 10(-7) M); 17-β estradiol (E2; 10(-9) M) or P4+E2 for 24 h and later medium was replaced with a fresh one treated with IL-1α, IL-1β or IL-6 (10 ng/mL, each) for 24 h. The oxytocin (OT; 10(-7)...
Mainguy-Seers S, Diaw M, Lavoie JP.While the prevalence of asthma is higher in boys than in girls during childhood, this tendency reverses at puberty, suggesting an effect of sex hormones on the disease pathophysiology. Fluctuations of asthma severity concurring with the estrus cycle are reported in women, but this phenomenon has never been investigated in mares to date. The objective of this exploratory study was to determine whether the estrus cycle modulates airway obstruction in severe equine asthma (SEA). Five mares with SEA during exacerbation of the disease were studied. The whole breath, expiratory and inspiratory resis...
Donadeu FX, Ginther OJ.The temporal relationships in the changes in concentrations of follicular fluid factors during follicle selection were characterized in mares. All follicles > or =5 mm were ablated 10 days after ovulation, followed by follicular fluid collection from the three largest follicles (F1, F2, and F3) when F1 of the new wave reached a diameter of 8.0-11.9, 12.0-15.9, 16.0-19.9, 20.0-23.9, 24.0-27.9, or 28.0-31.9 mm (n = 4-8 mares/range). Diameter deviation between F1 and F2 began during the 20.0- to 23.9-mm range, as indicated by a greater difference in diameter between the two follicles at the 24...
Collins A, Palmer E, Bézard J, Burke J, Duchamp G, Buckley T.Samples of blood and follicular fluid were recovered from 27 Welsh Pony mares at 4 distinct stages of follicular development. Eighteen biochemical parameters were measured in each sample, including sodium, potassium, chloride, glucose, urea, creatinine, calcium, inorganic phosphate, total bilirubin, total protein, albumin, magnesium, triglyceride, total cholesterol, nonesterified fatty acids, alkaline phosphatase, gamma-glutamyltransferase and aspartate aminotransferase. The concentrations of progesterone, 17beta oestradiol and testosterone, pH and osmolarity, were also measured in all the fol...
Jasiński T, Zdrojkowski Ł, Ferreira-Dias G, Kautz E, Juszczuk-Kubiak E, Domino M.Endometrosis is a frequently occurring disease decreasing mares' fertility. Thus, it is an important disease of the endometrium associated with epithelial and stromal cell alterations, endometrium gland degeneration and periglandular fibrosis. Multiple degenerative changes are found in uterine mucosa, the endometrium. However, their pathogenesis is not well known. It is thought that nuclear factor-κB (NF-κB), a cell metabolism regulator, and its activation pathways take part in it. The transcription of the profibrotic pathway genes of the NF-κB in fibrotic endometria differed between the fo...
Dawod A, Miro J, Elbaz HT, Fahmy H, Abdoon AS.This study was designed to examine the effect of the intrauterine infusion of platelet-rich plasma (PRP) or equine lyophilized growth factor (L-GFequina) on the follicular growth, endometrial thickness, estrus cycle length, and pregnancy rate in purebred Arabian mares. A total of 73 purebred Arabian mares who experienced repeat breeding for three successive cycles were randomly divided into the following three groups: control group, without treatment; second Group (PRP group), in which mares were intrauterine infused with 20 mL of fresh PRP on the second day after the end of physic estrus phas...
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...
Bollwein H, Mayer R, Stolla R.Transrectal color Doppler sonography was used for the noninvasive investigation of uterine blood flow in five mares. Both the left and right uterine arteries were scanned to obtain blood flow velocity waveforms during two consecutive estrous cycles and two early pregnancies in each mare. Blood flow was expressed as the time-averaged maximum velocity (TAMV) and the resistance index (RI). In all pregnancies the embryonic vesicle could be detected for the first time on Day 11 (day of ovulation: Day 0). No differences in mean TAMV and RI values of both uterine arteries were observed in comparison ...
Ababneh MM, Troedsson MH.Real-time PCR was used to investigate the role of progesterone (P4) and oestradiol (E2) in regulation of endometrial cytosolic, secretory and calcium-independent phospholipase A2 (PLA2G4A, PLA2G2A and PLA2G6, respectively) gene expression. Ovariectomized mares underwent 6 days of E2 pre-treatment followed by 14 days of P4 supplementation. At the start of P4 treatment (Day 1), mares were assigned in a 2 × 2 factorial design to receive either E2 or vehicle starting on Day 11 and endometrial biopsy collection on either Day 14 when P4 concentrations remained high (>4 ng/ml) or Day 16 when P4 conc...
Młodawska W, Grzesiak M, Kochan J, Nowak A.Steroidogenic activity in the equine ovary from birth to puberty has been poorly investigated. This study aimed to examine the capability of the ovarian follicles of prepubertal and pubertal fillies to produce steroid hormones and to evaluate the expression and cellular localization of androgen receptor (AR) in their ovaries. The ovaries of 6-18 month-old fillies were divided into two groups: prepubertal (PrP) - without preovulatory follicle (pF) and corpus luteum (CL), and ovulating/postpubertal (Ov/pB) - with pF and/or CL in at least one of the gonads. Adult mares (Me) were used as a control...
Kozai K, Tokuyama S, Szóstek AZ, Toishi Y, Tsunoda N, Taya K, Sakatani M, Takahashi M, Nambo Y, Skarzynski DJ, Yamamoto Y, Kimura K, Okuda K.In mares, prostaglandin F2α (PGF2α) secreted from the endometrium is a major luteolysin. Some domestic animals have an auto-amplification system in which PGF2α can stimulate its own production. Here, we investigated whether this is also the case in mares. In an in vivo study, mares at the mid-luteal phase (days 6-8 of estrous cycle) were injected i.m. with cloprostenol (250 µg) and blood samples were collected at fixed intervals until 72 h after treatment. Progesterone (P4) concentrations started decreasing 45 min after the injection and continued to decrease up to 24 h (P < 0.05). In t...
Reilas T, Katila T, Mäkelä O, Huhtinen M, Koskinen E.Intrauterine fluid (IUF) was collected using a tampon from mid-oestrous mares (n = 57) with and without ultrasonically detectable accumulations of free intraluminal fluid. Bacteria were cultured and neutrophils counted from all samples (n = 57). Total protein concentration, trypsin-inhibitor capacity (TIC), and plasmin, beta-glucuronidase (B-Gase) and N-acetyl-beta-D-glucosaminidase (NAGase) activities were determined in 27 IUF samples. The motility of spermatozoa in the presence of IUF, IUF extended with Kenney's medium (1:1) and Kenney's medium alone was analysed in 9 samples using a Hamilto...
