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.
Otzen H, Sieme H, Oldenhof H, Kassens A, Ertmer F, Rode K, Müller K, Klose K, Rohn K, Schoon HA, Meinecke B.The aim of this study was to evaluate the uterine blood supply and endometrial vessel architecture, during the equine estrous cycle. Narrow Band Imaging (NBI) hysteroscopy was used for evaluating changes in the endometrial vasculature during the estrous cycle [six mares, d 0 (representing the day of ovulation), d 6 and 11 in four locations]. In addition, endometrial biopsy samples were used for immunodetection of markers for angiogenesis (Vascular Endothelial Growth Factor A, its receptor 2, as well as angiopoietin-2 and its receptor-tyrosine-kinase Tie2) during the estrous cycle (three mares,...
Esteller-Vico A, Liu IK, Vaughan B, Steffey EP, Brosnan RJ.Uterine vascular elastosis in mares is characterized by degeneration of uterine vasculature through thickening of the elastin layers. Factors commonly associated with this degeneration include age, parity, and chronic uterine endometritis. Affected mares have also been shown to exhibit decreases in uterine blood flow and perfusion of the uterus. Due to the increased thickness of the elastin layers, we hypothesize that vasodilatation of the uterine vasculature is also impaired. To test the functionality of these vessels, we evaluated the vasodilatory effects of estradiol on the uterine vascular...
Geisert RD.Establishment and maintenance of pregnancy in a number of mammalian species depends upon a tightly regulated interaction between the semiallogeneic conceptus and the maternal uterine endometrium.The term "Maternal Recognition of Pregnancy" is attributed to Roger V. Short's paper titled "Implantation and the Maternal Recognition of Pregnancy" which was published in proceedings from the 1969 Symposium on Foetal Autonomy.Professor Short's landmark paper stimulated increased interest in elucidating how the conceptus signals its presence to assure maintenance of the corpus luteum beyond the normal ...
Lima AG, Costa LC, Alvarenga MA, Martins CB.The presence of anovulatory haemorrhagic follicles during the oestrous cycle of mares causes financial impacts, slowing conception and increasing the number of services per pregnancy. Non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam and phenylbutazone are used in the treatment of several disorders in mares, and these drugs can impair the formation of prostaglandins (PGs) and consequently interfere with reproductive activity. This study aimed to evaluate the effects of treatment with NSAIDs on the development of pre-ovulatory follicles in mares. In total, 11 mares were studied o...
Nelis H, Wojciechowicz B, Franczak A, Leemans B, D'Herde K, Goossens K, Cornillie P, Peelman L, Van Soom A, Smits K.The oviduct undergoes dramatic functional and morphological changes throughout the oestrous cycle of the mare. To unravel the effects of steroids on the morphology, functionality and gene expression of the equine oviduct, an in vitro oviduct explant culture system was stimulated with physiological concentrations of progesterone and 17β-oestradiol. Four conditions were compared: unsupplemented preovulatory explants, preovulatory explants that were stimulated with postovulatory hormone concentrations, unsupplemented postovulatory explants and postovulatory explants that were stimulated with pre...
Marth CD, Young ND, Glenton LY, Noden DM, Browning GF, Krekeler N.The physiological changes associated with the varying hormonal environment throughout the oestrous cycle are linked to the different functions the uterus needs to fulfil. The aim of the present study was to generate global gene expression profiles for the equine uterus during oestrus and Day 5 of dioestrus. To achieve this, samples were collected from five horses during oestrus (follicle >35 mm in diameter) and dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq). Differentially expressed genes between the two cycle stages were further inves...
Gajos K, Kozdrowski R, Nowak M, Siemieniuch MJ.Mares that fail to become pregnant after repeated breeding, without showing typical signs of clinical endometritis, should be suspected of subclinical endometritis (SE). Contact with infectious agents results in altered synthesis and secretion of inflammatory mediators, including cytokines and arachidonic acid metabolites, and disturbs endometrial functional balance. To address the hypothesis that SE affects the immune endocrine status of the equine endometrium, spontaneous secretion of prostaglandin E(2) (PGE(2)), prostaglandin F(2α) (PGF(2α)), 6-keto-PGF(1α )(a metabolite of prostacyclin ...
Santos VG, Bettencourt EM, Ginther OJ.Persistent CL (PCL; n = 10) in mares was studied daily from Day 20 (Day 0 = ovulation) to the ending ovulation. In addition, the 10 days before ovulation at the end of a PCL were compared with the end of an interovulatory interval (IOI; n = 28) during the same months. Concentration of P4, cross-sectional area of CL, and percentage of CL with Doppler signals of blood flow during PCLs remained constant from 64 to about 33 days before the end of luteolysis and then decreased linearly. Concentration of LH between Day 20 and beginning of the ovulatory LH surge increased linearly. A dominant follicl...
Scarlet D, Walter I, Hlavaty J, Aurich C.In mares, FSH and its receptor (FSHR) are essential for ovarian function. The objective of the present study was to analyse FSHR gene expression at the mRNA and protein levels in ovarian tissue from newborn and adult horses. Expression of mRNA was analysed by reverse transcription polymerase chain reaction, whereas FSHR protein was visualised by immunohistochemistry (IHC), immunofluorescence labelling (IF) and western blot. FSHR mRNA was detected in ovarian follicles and luteal tissue from adult mares, as well as in the ovaries of neonates. Follicular growth up to 4mm in diameter was already p...
Kozdrowski R, Sikora M, Buczkowska J, Nowak M, Raś A, Dzięcioł M.The aim of this study was to ascertain if (1) the stage of reproductive cycle influences cytological results, (2) cytology obtained from an endometrial biopsy is more accurate than cytology derived using the cytobrush, and (3) different methods used for evaluation of cytological samples produce similar diagnostic results. Material was collected from 46 mares in estrus, 48 in diestrus and from 33 mares in anestrus. Smears were evaluated using two criteria. In criterion I, a total of 300cells were counted and the percentage of polymorphonuclear cells was recorded. In criterion II, the number of ...
Cuervo-Arango J, Mateu-Sánchez S, Aguilar JJ, Nielsen JM, Etcharren V, Vettorazzi ML, Newcombe JR.The objective of this study was to determine the effect of the interval from induced luteolysis to ovulation on fertility of mares from two different farms. At farm 1, 215 mares were inseminated with frozen/thawed semen during 513 estrous cycles over seven consecutive breeding seasons. Estrus was induced with analogues of PGF2α in 179 cycles. At farm 2, 375 embryo flushings were performed in 65 donor mares inseminated with fresh semen; of which, 327 were performed following artificial insemination after PGF-induced luteolysis. In both farms, the intervals from PGF treatment to ovulation (ITO)...
Botelho JH, Pessoa GO, Rocha LG, Yeste M.The present research sought to determine whether the administration of estradiol benzoate and long-acting progesterone to anovulatory recipient mares could maintain the pregnancy after embryo transfer during the autumn transitional phase. Recipient mares (n = 40) received the hormonal supplementation (treated group) whereas the other 36 served as a control. The control group consisted of mares having typical estrous cycles with ovulations, development of a viable corpus luteum and received one transferred embryo 5 days after ovulation. Hormonal administrations in the treated group started 8 da...
Esteller-Vico A, Liu IK, Vaughan B, Steffey EP, Brosnan RJ.In the uterus of the mare, data obtained using transrectal Doppler ultrasonography indicate that uterine blood flow (UBF) is dynamic and changes throughout the estrous cycle. Degenerative lesions in the uterus are associated with subfertility and infertility. Among these lesions, vascular elastosis has been reported in aged, multiparous, and infertile mares. Angiosis of the uterine vasculature could potentially compromise UBF. The objectives of this experiment are to determine levels of UBF and perfusion of reproductively healthy mares and compare them to levels of subfertile/infertile mares a...
Silva ES, Scoggin KE, Canisso IF, Troedsson MH, Squires EL, Ball BA.The objective of this study was to compare expression of estrogen receptor alpha (ER-α), β (ER-β), progesterone receptor (PR), as well as prostaglandin E2 type 2 (EP2) and 4 (EP4) receptors in the equine myometrium and endometrium during estrus, diestrus and early pregnancy. Tissues were collected during estrus, diestrus, and early pregnancy. Transcripts for ER-α (ESR1), ER-β (ESR2), PR (PGR), EP2 (PTGER2) and EP4 (PTGER4) were quantified by qPCR. Immunohistochemistry was used to localize ER-α, ER-β, PR, EP2 and EP4. Differences in transcript in endometrium and myometrium were compared ...
McNaughten J, Pozor M, Macpherson M, Kelleman A, Woodward E, Troedsson M.Mares who have not delivered a foal early in life may experience limitations in cervical relaxation, primarily during oestrus. A closed cervix prevents intrauterine deposition of semen during natural breeding, may delay uterine clearance after insemination leading to intrauterine fluid accumulation in, and subsequent infertility. Therefore, a reliable pharmacological method of dilating the equine cervix would have practical application in veterinary medicine. The goal of this study was to investigate the effectiveness of topically applied, synthetic prostaglandin E1 analogue (PGE1 ) for stimul...
Claes A, Ball BA, Scoggin KE, Esteller-Vico A, Kalmar JJ, Conley AJ, Squires EL, Troedsson MH.Anti-Müllerian hormone (AMH) is a granulosa-cell-derived glycoprotein, which plays an important inhibitory role during folliculogenesis. Concentrations of AMH are highly correlated with antral follicle counts (AFCs) in other species, which in turn are related to follicular reserve. Relatively little is known about AMH and AFC in the mare. Objective: To determine plasma AMH concentrations and AFCs in mares of different ages, to measure the repeatability of AMH concentrations and AFCs within and across oestrous cycles and to assess the relationship between plasma AMH concentrations and AFCs wit...
Aguilar JJ, Cuervo-Arango J, Santa Juliana L.It is scientifically demonstrated that lunar cycles have important effects on several biological events. Controversy exists about the lunar influence on human and animal parturition. In addition, in the horse industry, especially in Polo Horse breeders of Argentina and around the world there is a higher demand for female offspring than for males. The objective of this study was to determine whether there is a significant association between the lunar phase at the time of mating and the sex ratio at birth in horses. The Argentinean Stud Book provided information related to all matings registere...
Coffman EA, Pinto CR, Snyder HK, Leisinger CA, Cole K, Whisnant CS.A single dose of PGF2α does not consistently induce luteolysis in the equine CL until at least 5 days after ovulation, leading to the erroneous assumption that the early CL is refractory to the luteolytic effects of PGF2α. We hypothesized that serial administration of PGF2α in early diestrus would induce a return to estrus similar to mares treated with a single injection in mid-diestrus, and fertility of the induced estrus would not differ. The objectives of the study were to evaluate the effects of the 2 approaches as reflected by: (1) concentrations of plasma progesterone; (2) interovulat...
Salazar-Ortiz J, Monget P, Guillaume D.Feed intake affects the GH-IGF system and may be a key factor in determining the ovarian follicular growth rate. In fat mares, the plasma IGF-1 concentration is high with low GH and a quick follicular growth rate, in contrast to values observed in thin mares. Nothing is known regarding the long-term effects of differential feed intake on the IGF system. The objective of this experiment was to quantify IGFs, IGFBPs, GH, glucose, insulin, gonadotropin and progesterone (P4) in blood and in preovulatory follicular fluid (FF) in relation to feeding levels in mares. Methods: Three years prior to the...
Collins CW, Monfort SL, Vick MM, Wolfe BA, Weiss RB, Keefer CL, Songsasen N.To date, there has been limited research on manipulation of the estrous cycle in endangered equids. The objectives of this study were to assess the efficacy of using combinations of: (a) oral altrenogest and PGF2α, and (b) injectable altrenogest and PGF2α for manipulation of ovarian activity in Przewalski's mares. Reproductive cycles were monitored by assessing follicular changes with rectal ultrasound and changes in urinary steroid hormones. In Study 1, five cycling mares were treated with oral altrenogest (n=11 cycles) for 14 days. In Study 2, cycling mares were treated with oral altrenoge...
Iacono E, Merlo B, Rizzato G, Mislei B, Govoni N, Tamanini C, Mari G.The aim of the present study was to verify how repeated ovum pick-up (OPU), performed in anestrous and cyclic mares, affect ovarian activity, measured by progesterone (P4) and 17ß-estradiol (E2) plasma levels. Ovum pick-up of all visible follicles was performed every 9 to 12 days, and four sessions were carried out during anestrous (A) and breeding season (BS). The number of aspirated follicles per mare at each session was not significantly different between the two periods (BS: 6.1 ± 2.4; A: 7.5 ± 4.4; P > 0.05), but the mean follicular diameter was significantly higher during BS (16.0 ...
Wespi B, Sieme H, Wedekind C, Burger D.Horses (Equus caballus) belong to the group of seasonally polyestrous mammals. Estrous cycles typically start with increasing daylight length after winter, but mares can differ greatly in the timing of onset of regular estrus cycles. Here, we test whether spatial proximity to a stallion also plays a role. Twenty-two anestrous mares were either exposed to one of two stallions (without direct physical contact) or not exposed (controls) under experimental conditions during two consecutive springs (February to April). Ovarian activity was monitored via transrectal ultrasound and stallion's direct ...
de Ruijter-Villani M, van Tol HT, Stout TA.Endometrial oxytocin receptors (OXTR) and prostaglandin-endoperoxide synthase 2 (PTGS2) are central components of the luteolytic pathway in cyclic mares, and their suppression is thought to be critical to luteal maintenance during early pregnancy. We examined the effect of pregnancy on endometrial expression of potential regulators of prostaglandin (PG) F2α secretion in mares. Expression of the nuclear progesterone receptor and oestrogen receptor ERα was high during oestrus, and depressed when progesterone was elevated; the opposite applied to the membrane progesterone receptor. PTGS2 was up...
Szóstek AZ, Adamowski M, Galvão AM, Ferreira-Dias GM, Skarzynski DJ.Tumor necrosis factor-α (TNF) is a cytokine that plays important roles in functions of the endometrium. The aims of this study were to determine whether (i) ovarian steroids modulate TNF production by endometrial cells (Experiment 1); (ii) TNF effects on prostaglandin (PG) production in cultured equine endometrial cells and tissue (Experiment 2). Epithelial and stromal cells were isolated from equine endometrium (Days 2-5 of the estrous cycle; n=20) and treated after passage 1. In Experiment 1, epithelial and stromal cells were exposed to progesterone (P4; 10(-7)M), 17-β estradiol (E2; 10(-9...
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)â€...
Thorson JF, Prezotto LD, Cardoso RC, Sharpton SM, Edwards JF, Welsh TH, Riggs PK, Caraty A, Amstalden M, Williams GL.RFamide-related peptide 3 (RFRP3), the mammalian homologue of avian gonadotropin-inhibitory hormone, has been shown to negatively regulate the secretion of LH and may contribute to reproductive seasonality in some species. Herein, we examined the presence and potential role of the RFRP3-signaling system in regulating LH secretion in the mare during the breeding and nonbreeding seasons. Hypothalamic NPVF mRNA (the precursor mRNA for RFRP3) was detected at the level of the dorsomedial nucleus and paraventricular nucleus, but expression did not change with season. A greater number of RFRP3-expres...
Szóstek AZ, Galvão AM, Ferreira-Dias GM, Skarzynski DJ.This study aimed to evaluate the influence of ovarian steroids on equine endometrial epithelial and stromal cells, specifically i) prostaglandin (PG) production in a time-dependent manner, ii) specific PG synthases mRNA transcription and protein expression, and iii) cell proliferation. After passage I, cells were exposed to vehicle, oxytocin (OT, positive control, 10(-7) M), progesterone (P4, 10(-7) M), 17β estradiol (E2, 10(-9) M), or P4+E2 for 12, 24, 48, or 72 h. Following treatment, PG concentration was determined using the direct enzyme immunoassay (EIA) method. Alterations in PG synth...
Thorson JF, Prezotto LD, Cardoso RC, Allen CC, Alves BR, Amstalden M, Williams GL.Onset of the winter anovulatory period in mares is associated with a marked diminution in adenohypophyseal synthesis and release of LH. Native GnRH, unlike its synthetic agonists, stimulates the synthesis and secretion of LH in mares without pituitary refractoriness. Herein we tested the hypotheses that (1) the average Julian day of pregnancy can be accelerated by up to 2 months in winter anovulatory mares treated continuously with native GnRH beginning on February 1 and (2) mares will sustain luteal function and pregnancy after treatment withdrawal. Forty-two winter anovulatory mares were str...
Murphy BA, Walsh CM, Woodward EM, Prendergast RL, Ryle JP, Fallon LH, Troedsson MH.Artificial lighting is commonly used to advance the breeding season in horses. Light masks have been developed that direct light at a single eye to inhibit the production of melatonin, the decoder of photoperiod for seasonally breeding animals. Objective: To investigate whether low-intensity blue light from light masks was effective at advancing the breeding season in mares. Methods: Controlled experiment. Methods: Data on reproductive activity was collected from 3 groups of mares maintained on Kentucky horse farms under various lighting conditions between 20 November 2011 and 10 February 2012...
Szóstek AZ, Lukasik K, Galvão AM, Ferreira-Dias GM, Skarzynski DJ.The aim of the study was to characterize endometrial mRNA transcription, immunolocalization, and protein expression of interleukin (IL) 1alpha, IL1beta, IL6, and IL1RI, IL1RII, and IL6Ralpha/beta in the course of endometrosis during the estrous cycle. Additionally, the influence of IL1alpha, IL1beta, and IL6 on prostaglandin (PG) secretion and PG synthase mRNA transcription in endometrial tissue during endometrosis was investigated. The endometrial samples were obtained at the early (n = 12), mid- (n = 12), and late (n = 12) luteal phases and at the follicular (n = 12) phase of the estrous cyc...
Elhay M, Newbold A, Britton A, Turley P, Dowsett K, Walker J.To examine the immunogenicity of an equine immunocontraceptive vaccine and its efficacy in controlling hormone-related behaviour. Methods: A total of 24 mares at two sites in Australia were vaccinated with an immunocontraceptive vaccine comprising gonadotrophin releasing hormone (GnRH) conjugated to a carrier protein in immunostimulating complex as an adjuvant. Twelve animals at each site received a placebo of adjuvant alone and served as controls for seasonal oestrus, hormonal and behaviour patterns. Animals were observed for injection site reactions, ovarian and follicular activity, and seru...
Sessions DR, Reedy SE, Vick MM, Murphy BA, Fitzgerald BP.Peripheral insulin resistance is the failure of proper cellular glucose uptake in response to insulin. Insulin resistance and hyperinsulinemia are associated with several disease states in the horse and reproductive function disturbances in humans, including polycystic ovarian syndrome. To test the hypothesis that insulin resistance (IR) and hyperinsulinemia disrupt the estrous cycle in mares, two experiments were conducted to first develop a model to induce IR and to then examine the effect of this model on the duration of the estrous cycle. In Exp. 1, a hyperinsulinemic-euglycemic clamp (HEC...
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Hoffmann B, Ludwig C, Kindahl H.Ovariectomized mares and mares with inactive ovaries may show signs of estrus. The reason behind this phenomenon is not clear; however, steroid hormones of adrenal origin have been suggested. Moreover, aberrant adrenal hormone production has been implied as a reason why some intact mares may change behavior. In the present study, the effect of ACTH on plasma levels of cortisol, progesterone, androstenedione and testosterone was investigated in intact mares with normal estrous behavior ('controls', n=5) and intact mares that according to their owners showed deviant estrous behavior ('problem' m...
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...
Bollwein H, Mayer R, Weber F, Stolla R.Transrectal color Doppler ultrasound was used for the noninvasive investigation of luteal blood flow during the estrous cycle in six mares. Color was displayed in Power-Mode, in which the number of color pixels on the ultrasound image is related to the number of moving blood cells. Three pictures with a maximum number of color pixels of the corpus luteum (CL) during an examination period of about 20 min were selected and digitized on a laptop equipped with an external frame grabber card. The intra-class correlation coefficient for the number of color pixels was 0.90. In all estrous cycles simi...
Kozdrowski R, Sikora M, Buczkowska J, Nowak M, Raś A, Dzięcioł M.The aim of this study was to ascertain if (1) the stage of reproductive cycle influences cytological results, (2) cytology obtained from an endometrial biopsy is more accurate than cytology derived using the cytobrush, and (3) different methods used for evaluation of cytological samples produce similar diagnostic results. Material was collected from 46 mares in estrus, 48 in diestrus and from 33 mares in anestrus. Smears were evaluated using two criteria. In criterion I, a total of 300cells were counted and the percentage of polymorphonuclear cells was recorded. In criterion II, the number of ...
Caraty A, Decourt C, Briant C, Beltramo M.Kisspeptins (Kp) are a family of neuropeptides produced mainly by two hypothalamic neuronal cell populations. They have recently emerged as a major regulator of the gonadotropin axis and their action is located upstream of the gonadotropin-releasing hormone (GnRH) cell population. In less than 10 yr a growing body of literature has demonstrated the involvement of these peptides in most, if not all, aspects of reproductive axis maturation and function. In contrast to these abundant basic research studies, few experiments have evaluated the potential application of Kp as tools to manipulate repr...
Zavy MT, Clark WR, Sharp DC, Roberts RM, Bazer FW.In Experiment 1, 40 gilts and 30 pony mares were used to characterize changes in glucose, fructose, ascorbic acid and glucosephosphate isomerase (GPI) enzymatic activity in uterine flushings collected either during the estrous cycle or early pregnancy. Total recoverable glucose was greater (P less than 0.01) in uterine flushings from pregnant gilts, but pregnancy status had no effect on total recoverable glucose in pony mare uterine flushings. Fructose was undetectable in uterine flushings from nonpregnant gilts and pony mares and pregnant gilts and pony mares prior to Day 14, but occurred in ...
Mortensen CJ, Choi YH, Hinrichs K, Ing NH, Kraemer DC, Vogelsang SG, Vogelsang MM.The effect of exercise on mare reproductive efficiency was evaluated by comparing rates of embryo recovery from mares assigned to either an exercise regimen or a non-exercise (control) regimen. Exercised mares were worked daily for 30 min under average ambient conditions of >30 degrees C and >50% humidity. Mares were inseminated during estrus and subjected to uterine flush for embryo recovery on d 7 after ovulation for two consecutive cycles. After this, mares were allocated to the opposite group and allowed an estrous cycle without reproductive manipulation; then insemination and uterin...
Asa CS, Robinson JA, Ginther OJ.Daily blood samples from four mares were assayed for cortisol through a total of eight ovulatory cycles. Mean cortisol concentrations on days -14, -13, -10, -9 and -8 before ovulation (dioestrus) were greater than on days -5 to -1 (oestrus). The highest mean (+/- S.E.M) value of cortisol occurred on day -10 (260 +/-28 nmol/l) and the lowest on day -2 (142 +/- 14 nmol/l). A single episode on a day in late dioestrus characterized the maximum cortisol value per cycle for five of eight cycles. Extraction of plasma samples with petroleum ether or chromatography before assay, to eliminate interferen...
McCue PM, Farquhar VJ, Carnevale EM, Squires EL.Deslorelin implants, approved for use in inducing ovulation in mares, have been associated with prolonged interovulatory intervals in some mares. Administration of prostaglandins in the diestrous period, following a deslorelin-induced ovulation, has been reported to increase the incidence of delayed ovulations. The goals of the present study were: (1) to determine the percentage of mares given deslorelin that experience delayed ovulations with or without subsequent prostaglandin treatment, and (2) to determine if removal of the implant 48 h after administration would effect the interval to sub...
Frauenfelder HC, Rossdale PD, Ricketts SW, Allen WR.Blood samples were collected twice weekly over a nine month period from 24 Thoroughbred racehorses in training at Newmarket to study the effects of daily training schedules and stage of oestrous cycle on serum enzyme levels and clinical signs of equine exertional myopathy. The sampling period extended from November to July and was performed between 16:00 h and 18:00 h so as to be at least 6 h after exercise. Serum creatine kinase, aspartate aminotransferase and plasma progestogen concentrations were measured. All horses were subjected to a similar traditional training programme. The study demo...
Szóstek-Mioduchowska A, Leciejewska N, Zelmańska B, Staszkiewicz-Chodor J, Ferreira-Dias G, Skarzynski D.Equine endometrosis is a chronic degenerative condition, described as endometrial fibrosis that forms in the stroma, under the basement membrane and around the endometrial glands. The role of lysophosphatidic acid (LPA) in the development of tissue fibrosis varies depending on the organ, and its profibrotic role in mare endometrosis remains unclear. The study aimed to establish the endometrial presence of LPA and its receptors (LPAR1-4), together with its effects on connective tissue growth factor (CTGF) and prostaglandins (PG) secretion from equine endometrium under physiological (estrous cyc...
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 ...
Ginther OJ, Utt MD, Beg MA.The temporal relationships between follicle deviation and systemic hormone concentrations were studied in mares. Blood samples were obtained at 01:00, 07:00, 13:00, and 19:00 h from nine mares throughout an interovulatory interval. Diurnal variation in progesterone occurred on Days 4-12 and in LH on Days 4 and 5; the lowest concentration for both hormones was at 13:00 h. Ultrasonically observed deviation in the ovulatory follicular wave began on Day 15.7+/-0.5 (ovulation=Day 0). An increase (P<0.002) in LH began on Day 14 before the beginning of deviation, and an increase (P<0.05) in est...
Jennings MW, Boime I, Daphna-Iken D, Jablonka-Shariff A, Conley AJ, Colgin M, Bidstrup LA, Meyers-Brown GA, Famula TR, Roser JF.The efficacy of a recently engineered single chain recombinant equine follicle stimulating hormone (reFSH) was investigated in estrous cycling mares whose gonadotropins and follicular activity had been suppressed by concurrent treatment with progesterone and estradiol (P&E). Time of estrus was synchronized in 15 estrous cycling mares during the breeding season with prostaglandins F(2alpha) (PGF(2alpha)). The day after ovulation, mares were treated once daily with P&E for 14 days. Mares received a second injection of PGF(2alpha) on day 6 of the synchronized estrous cycle to induce luteolysis. O...
Monfort SL, Arthur NP, Wildt DE.Immunoreactive urinary oestrogen conjugates were assessed in daily urine samples (approximately 5 samples/week) collected from 8 Przewalski's mares maintained under semi-free-ranging pasture conditions. The relative percentage contributions of immunoreactive urinary oestrogens during different reproductive stages (oestrus, luteal phase, early, mid- and late gestation) were determined using high-pressure liquid chromatography. In general, conjugated forms of oestrone (oestrone sulphate and oestrone glucuronide) were the major excreted immunoreactive oestrogens in nonpregnant and pregnant Przewa...
Koskinen E, Kuntsi H, Lindeberg H, Katila T.Follicular growth and hormone determinations were used to predict ovulation in the mare. Thirty Finnhorse mares were used for the investigation and 38 oestrous cycles were studied. The mares were examined by rectal palpation and ultrasonography every 6 hours during late oestrus. Daily blood samples were obtained for progesterone and oestrone sulphate determination. The preovulatory follicle grew 3 mm a day up to 2 days before ovulation. The size then remained constant, before diminishing by 2-3 mm during the last 12 hours. The maximal diameter of the follicle was 43 +/- 4 mm. In 89% of the fol...
Hirsbrunner G, Reist M, Couto SS, Steiner A, Snyder J, Vanleeuwen E, Liu I.Uterine smooth muscle specimens were collected from euthanatized mares in estrus and diestrus. Longitudinal and circular specimens were mounted in organ baths and the signals transcribed to a Grass polygraph. After equilibration time and 2 g preload, their physiologic isometric contractility was recorded for a continuous 2.0 h. Area under the curve, frequency and time occupied by contractions were studied. Differences between cycle phases, between muscle layers, and over the recorded time periods were statistically evaluated using linear mixed-effect models. In the mare, physiologic contractil...
Mattos MC, Bastos MR, Guardieiro MM, Carvalho JO, Franco MM, Mourão GB, Barros CM, Sartori R.The aim of this study was to evaluate the superovulatory (SOV) response of Sindhi (Bos indicus) donors submitted to an ovarian follicular superstimulatory protocol replacing the last two doses of pFSH by eCG. Forty-eight SOV treatments were performed in a crossover design in 19 nulliparous and primiparous females that were randomly divided into two groups: FSH (n=24), which consisted of eight pFSH injections, or FSH/eCG (n=24), which consisted of six pFSH injections followed by two eCG injections. Each female underwent two or three SOV treatments that consisted of an i.m. injection of 2mg estr...
Williams GL, Thorson JF, Prezotto LD, Velez IC, Cardoso RC, Amstalden M.Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular...
Alexander SL, Irvine CH.We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae...
Ishak GMA, Dutra GA, Gastal GDA, Gastal MO, Feugang JM, Gastal EL.The inability to obtain in vivo samples of antral follicle wall layers without removing the ovaries or sacrificing the animals has limited more in-depth studies on folliculogenesis. In this study, a novel ultrasound-guided follicle wall biopsy (FWB) technique was used to obtain in vivo follicle wall layers and follicular fluid samples of growing antral follicles. The expression of proliferative, hormonal, angiogenic, and pro-/antiapoptotic receptors and proteins in the follicular wall among three follicle classes were compared during the spring transitional anovulatory (SAN) and spring ovulato...
Marth CD, Young ND, Glenton LY, Noden DM, Browning GF, Krekeler N.The physiological changes associated with the varying hormonal environment throughout the oestrous cycle are linked to the different functions the uterus needs to fulfil. The aim of the present study was to generate global gene expression profiles for the equine uterus during oestrus and Day 5 of dioestrus. To achieve this, samples were collected from five horses during oestrus (follicle >35 mm in diameter) and dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq). Differentially expressed genes between the two cycle stages were further inves...
Khan FA, Chenier TS, Murrant CL, Foster RA, Hewson J, Scholtz EL.Nitric oxide (NO) may have a role in persistent breeding-induced endometritis in mares through an inhibitory effect on uterine contractility. The objectives of this study were to test the effect of NO on spontaneous uterine contractility in-vitro and to evaluate whether this effect varied between the longitudinal and circular muscle layers of the uterus. Reproductive tracts were collected from eight euthanized non-pregnant mares (age 4-19 years; body weight 405-530Â kg). Transrectal examination of the reproductive tract was performed before euthanasia to evaluate stage of the estrous cycle and...
