Hormones in horses are chemical messengers produced by various glands and tissues, regulating numerous physiological processes essential for maintaining homeostasis. These hormones influence a wide range of functions, including growth, metabolism, reproduction, and stress responses. Key hormones in equine physiology include cortisol, estrogen, testosterone, and insulin, among others. The levels and effects of these hormones can vary based on factors such as age, sex, and environmental conditions, impacting overall health and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the production, regulation, and physiological roles of hormones in equine biology.
Lindström H, Peer SM, Ing NH, Mannervik B.Glutathione transferases (GSTs) comprise a superfamily of enzymes prominently involved in detoxication by making toxic electrophiles more polar and therefore more easily excretable. However some GSTs have developed alternative functions. Thus, a member of the Alpha class GSTs in pig and human tissues is involved in steroid hormone biosynthesis, catalyzing the obligatory double-bond isomerization of Δ-androstene-3,17-dione to Δ-androstene-3,17-dione and of Δ-pregnene-3,20-dione to Δ-pregnene-3,20-dione on the biosynthetic pathways to testosterone and progesterone. The human GST A3-3 is the ...
Toishi Y, Tsunoda N, Nagata SI, Kirisawa R, Nagaoka K, Watanabe G, Yanagawa Y, Katagiri S, Taya K.Testosterone (T) concentration is a useful indicator of reproductive function in male animals. However, T concentration is not usually measured in veterinary clinics, partly due to the unavailability of reliable and rapid assays for animal samples. In this study, a rapid chemiluminescent enzyme immunoassay system (CLEIA system) that was developed for the measurement of T concentration in humans use was validated for stallion blood samples. First, serum T concentrations were measured using the CLEIA system and compared with those measured by a fluoroimmunoassay that has been validated for use i...
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 ...
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...
Wynn MAA, Esteller-Vico A, Legacki EL, Conley AJ, Loux SC, Stanley SD, Curry TE, Squires EL, Troedsson MH, Ball BA.During the latter half of gestation in mares, there is a complex milieu of pregnanes in peripheral blood. Progesterone concentrations are often assessed by immunoassay during late gestation as a measure of pregnancy well-being; however, interpretation of results is complicated by the numerous cross-reacting pregnanes present in high concentrations during late gestation. Further, many mares are supplemented with an exogenous progestin, altrenogest, which may also cross-react with existing assays and further confound interpretation. The objectives of this study were: 1) to compare differences in...
Joonè CJ, Schulman ML, Fosgate GT, Claes ANJ, Gupta SK, Botha AE, Human A, Bertschinger HJ.Circulating anti-Müllerian hormone concentration (AMH) is positively correlated to the number of small growing follicles in the mare and may reflect ovarian function. Dynamics of AMH during immunocontraception have not previously been investigated. This study aimed to compare serum AMH in mares following treatment with native porcine zona pellucida (pZP), recombinant pZP3 and pZP4 (reZP) or gonadotrophin releasing hormone (GnRH) vaccines, and saline-treated controls. Stored sera collected during two previous studies examining ovarian activity in mares during zona pellucida (ZP) or GnRH immuno...
Migdał A, Migdał Ł, Zagrajczuk A, Kochan J, Nowak A, Okólski A.The aim of this study was to determine the effect of increased levels of prolactin (PRL) on the concentration of immunoglobulins in the blood, colostrum and milk of mares. The study was conducted on 12 mares of the Polish Pony breed (6 in the control and 6 in the experimental group). To induce hyperprolactinaemia in mares of the experimental group, 750 mg sulpiride was administered orally once a day. The initial PRL concentration was 52.22 ± 11.21 ng/ml in the control group and 49.39 ± 10.12 ng/ml in the experimental group. In the subsequent days, the concentration of PRL dynamically changed...
Leisinger CA, Medina V, Markle ML, Paccamonti DL, Pinto CRF.A novel in vivo model utilizing serial administrations of PGF2α to induce aluteal cycles in the mare was used to evaluate the effects of progesterone-deprivation on the morphology of in vivo preimplantation embryos. We hypothesized that equine embryos produced during induced aluteal cycles (AL) would be developmentally affected, characterized by earlier embryo stage at collection, smaller embryo diameter, and lower quality grade, compared with those collected on the same day post-ovulation from control cycles during diestrus (high progesterone; > 4 ng/mL). Seven cyclic mares with a median ...
Raeside JI.The role of steroids in human medicine is well recognized, but the major contributions made by the large domestic animals as a source of material in the discovery, isolation, and determination of the structure of the steroid hormones is less well appreciated. After a brief reminder of the early efforts to obtain a reliable source of steroids for clinical use, the narrative here is to outline one example where success was ultimately achieved for estrogen replacement therapy. Whereas knowledge of the high concentrations of estrogens in urine of pregnant women and mares dates from the late 1920s,...
Tangyuenyong S, Sato F, Nambo Y, Murase H, Endo Y, Tanaka T, Nagaoka K, Watanabe G.This study aimed to compare body growth, metabolic, and reproductive hormonal changes in trained Thoroughbred yearling horses under different climate conditions with and without light supplementation (LS). Thoroughbred yearlings raised at research centers of the Japan Racing Association in Hokkaido (north) or Miyazaki (south) were divided into control and LS groups. In the LS groups, 44 colts and 47 fillies from Hokkaido and 11 colts and 11 fillies from Miyazaki were exposed to LS with an extended photoperiod of 14.5 hr of daylight and 9.5 hr of darkness. One week before and once a month after...
Scheidegger MD, Gerber V, Bruckmaier RM, van der Kolk JH, Burger D, Ramseyer A.This study tested the hypothesis that adrenocortical function would be altered in horses with equine gastric ulcer syndrome (EGUS). Twenty-six sport horses competing at national or international levels in eventing (n=15) or endurance (n=11) were subjected to a gastroscopic examination and an adrenocorticotropic hormone (ACTH) stimulation test. Salivary cortisol concentrations were measured before (baseline) and after (30, 60, 90, 120 and 150min) IV ACTH injection (1μg/kg bodyweight). Within EGUS, two distinct diseases, equine squamous gastric disease (ESGD) and equine glandular gastric diseas...
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...
Legacki EL, Ball BA, Corbin CJ, Loux SC, Scoggin KE, Stanley SD, Conley AJ.Equine fetuses have substantial circulating pregnenolone concentrations and thus have been postulated to provide significant substrate for placental 5α-reduced pregnane production, but the fetal site of pregnenolone synthesis remains unclear. The current studies investigated steroid concentrations in blood, adrenal glands, gonads and placenta from fetuses (4, 6, 9 and 10 months of gestational age (GA)), as well as tissue steroidogenic enzyme transcript levels. Pregnenolone and dehydroepiandrosterone (DHEA) were the most abundant steroids in fetal blood, pregnenolone was consistently higher bu...
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...
Rota A, Sgorbini M, Panzani D, Bonelli F, Baragli P, Ille N, Gatta D, Sighieri C, Casini L, Maggiorelli MM, Aurich C, Camillo F.Reproductive management of male donkeys employed for artificial breeding has been poorly studied. The aim of this study was to evaluate the effect of housing system, with the animals grouped together in a paddock or kept in individual boxes, on sexual behaviour, cortisol and testosterone concentration and seminal characteristics of adult male donkeys. The study included four Amiata donkey jacks (stallions) from which ejaculates, saliva and blood were collected during two distinct 3 weeks periods, one in the group and one in the box housing system. Time needed for semen collection was shorter ...
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...
Akhtar RW, Shah SAH, Qureshi IZ.This study was conducted to determine the response of serum testosterone (T) in male equines (stallions, donkeys and mules) after administering intravenous doses of kisspeptin-10 (KP-10), human chorionic gonadotropin (hCG) and luteinizing hormone (LH) and saline as a control. The animals were divided into four groups of three each: Group I, 3 ml of 0.95% saline; Group II, 50 μg KP-10; Group III, 2500 IU hCG and group IV, 400 μg LH. The administration of KP-10 and hCG to stallions resulted in a significant increase in serum T concentration at 240 min; whereas it was significantly higher a...
Zutz C, Wagener K, Yankova D, Eder S, Möstl E, Drillich M, Rychli K, Wagner M, Strauss J.Estrogenic active compounds are present in a variety of sources and may alter biological functions in vertebrates. Therefore, it is crucial to develop innovative analytical systems that allow us to screen a broad spectrum of matrices and deliver fast and reliable results. We present the adaptation and validation of a fungal biosensor for the detection of estrogen activity in cow derived samples and tested the clinical applicability for pregnancy diagnosis in 140 mares and 120 cows. As biosensor we used a previously engineered genetically modified strain of the filamentous fungus Aspergillus ni...
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...
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...
Beythien E, Wulf M, Ille N, Aurich J, Aurich C.In pregnant mares, peripheral insulin antagonism channels glucose preferentially to the foetus. On the other hand, horses reduce their metabolic activity in winter. Taking these aspects of equine pregnancy and metabolism together, we hypothesized that glucose clearance from blood and the insulin response to glucose do not only change throughout gestation but also with season. To test this hypothesis, the glucose and insulin response to an oral glucose test and relative insulin release were analysed in pregnant mares (n=12) and in geldings (n=10) as controls. Animals were tested in June, Septem...
Secombe CJ, Tan RHH, Perara DI, Byrne DP, Watts SP, Wearn JG.Longitudinal evaluation of plasma endogenous ACTH concentration in clinically normal horses has not been investigated in the Southern Hemisphere. Objective: To longitudinally determine monthly upper reference limits for plasma ACTH in 2 disparate Australian geographic locations and to examine whether location affected the circannual rhythm of endogenous ACTH in the 2 groups of horses over a 12-month period. Methods: Clinically normal horses <20 years of age from 4 properties (institutional herd and client owned animals) in Perth (n = 40) and Townsville (n = 41) were included in the study. M...
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...
Max MC, Silva CB, González SM, Lindquist AG, Búfalo I, Gomes RG, Morotti F, Costa CB, Barreiros T, Lisboa LA, Seneda MM.This study investigated the effects of different concentrations of FSH (10, 50, 100 and 200 ng/ml) in supplemented MEM+ on the development of equine pre-antral follicles that were cultured in vitro for 2 or 6 days. The ovaries (n = 5) from mares in seasonal anoestrus were collected from a local abattoir. Ten ovarian tissue fragments of approximately 3 × 3 × 1 mm were obtained from each animal. The fragments were cultured in situ for 2 days (D2) or 6 days (D6) in MEM+ or MEM+ supplemented with FSH at four different concentrations, establishing the following 11 groups: control (D0);...
Bailly-Chouriberry L, Loup B, Popot MA, Dreau ML, Garcia P, Bruyas JF, Bonnaire Y.Since the availability on the European market of the vaccine Improvac® dedicated to male pig immunological castration, the risk of misuse of this product in horses is now considered as a threat for the horseracing industry. Immunological castration is not allowed by the racing codes (immune system, Article 6). Indeed, this vaccination against the hypothalamic hormone luteinizing hormone-releasing hormone or gonadotropin-releasing hormone (GnRH) will prevent the release from the anterior pituitary of luteinizing hormone and follicle stimulating hormone, which are required for the development a...
Boegheim IJM, Leegwater PAJ, van Lith HA, Back W.Impairment of bone growth at a young age leads to dwarfism in adulthood. Dwarfism can be categorised as either proportionate, an overall size reduction without changes in body proportions, or disproportionate, a size reduction in one or more limbs, with changes in body proportions. Many forms of dwarfism are inherited and result from structural disruptions or disrupted signalling pathways. Hormonal disruptions are evident in Brooksville miniature Brahman cattle and Z-linked dwarfism in chickens, caused by mutations in GH1 and GHR. Furthermore, mutations in IHH are the underlying cause of creep...
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...
Aguiar FLN, Gastal GDA, Ishak GM, Gastal MO, Teixeira DIA, Feugang JM, Figueiredo JR, Gastal EL.The effect of FSH supplementation on an enriched cultured medium containing insulin (10 ng/mL) and EGF (50 ng/mL) was investigated on in vitro culture of equine ovarian biopsy tissue. Ovarian tissue fragments were collected from mares (n = 10) and distributed in the following treatments: noncultured control, cultured control, and cultured + FSH. Both treated groups were cultured for 7 or 15 days. The end points evaluated were: follicular morphology, estradiol levels in the culture medium, fluorescence intensity for TUNEL, EGFR and Ki-67 detection, and gene expression of GDF-9, BMP-15, a...
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 ...
Shikichi M, Iwata K, Ito K, Miyakoshi D, Murase H, Sato F, Korosue K, Nagata S, Nambo Y.Measurement of progestines and estrogens in maternal plasma has been advocated as an indicator of foeto-placental function. The goals of the present study were as follows: to determine progestin and estrogen concentrations in mares with normal and abnormal pregnancies during late gestation, evaluate the diagnostic value of hormone concentrations, and investigate the relationship between hormone concentrations after treatment and the survival of foals. Blood samples were collected monthly from 459 pregnant mares between Day 201 of gestation and foaling. Progestin and estrogen concentrations wer...
McGowan CM, Neiger R.Trilostane, a competitive 3-beta hydroxysteroid dehydrogenase inhibitor, has been used successfully to control clinical signs and cortisol excess in canine pituitary dependent hyperadrenocorticism. Objective: Trilostane was evaluated for its efficacy in resolving clinical and clinicopathological abnormalities of equine Cushing's syndrome (ECS) and to assess its safety. Methods: Twenty horses (mean age 21 years) diagnosed with ECS were followed for 1 or 2 years. Affected horses received 0.4-1 mg/kg (mean 0.5 mg/kg) trilostane once daily. Results: Clinical signs assessed over 1 or 2 years, showe...
Stull CL, Rodiek AV.Two experiments were conducted to determine the response of blood glucose, insulin and cortisol levels to four common equine diets. Experiment 1 was designed to determine the diurnal variation of glucose and two glucoregulatory hormones, insulin and cortisol, in four fasting geldings. No diurnal variation was observed in either glucose or insulin levels during the 24-h sampling period. However, cortisol levels did exhibit a circadian rhythm, with elevated values observed in the morning and low values in the evening. Experiment 2 investigated the response of glucose, insulin, cortisol and selec...
Donadeu FX, Pedersen HG.The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or t...
Gordon ME, McKeever KH, Betros CL, Manso Filho HC.Concentrations of hormones related to energy homeostasis may differ between populations with varied body compositions, acting as signals to increase or decrease energy intake and/or expenditure. How these parameters correlate with body composition in horses and how they vary in fit (F) versus unfit (UF) Standardbred racehorses is unclear. The purpose of this study was to test the hypothesis that plasma concentrations of glucose (GLU), insulin (INS), cortisol (CORT), ghrelin (GHRL), adiponectin (ADIP) and leptin (LEP) would be correlated with body composition and differ in fit (F) versus unfit ...
Burger D, Dolivo G, Marti E, Sieme H, Wedekind C.Odours of vertebrates often contain information about the major histocompatibility complex (MHC), and are used in kin recognition, mate choice or female investment in pregnancy. It is, however, still unclear whether MHC-linked signals can also affect male reproductive strategies. We used horses (Equus caballus) to study this question under experimental conditions. Twelve stallions were individually exposed either to an unfamiliar MHC-similar mare and then to an unfamiliar MHC-dissimilar mare, or vice versa. Each exposure lasted over a period of four weeks. Peripheral blood testosterone levels ...
Ginther OJ.Prolonged luteal activity is one of the most formidable terminology challenges in mare reproductive biology. Prolonged luteal activity can be a result of persistence of an individual corpus luteum or the sequential development of luteal glands, each of which may have a normal life span. Luteal tissue can originate from an unovulated follicle or from an ovulation occurring during either follicular or luteal dominance. These complexities, together with ambiguous and inconsistent terminology, have resulted in confusion regarding those conditions which can be grouped broadly under the term prolong...
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...
Rasch K, Schoon HA, Sieme H, Klug E.The aim of this field study was to examine the influence of the uterotonic substance oxytocin in 2 different therapeutic dosages of 15 and 25 i.u., respectively on the uterine drainage of oestrous mares and on their fertility. In addition endometrial biopsies of mares with and without intrauterine fluid accumulations around the time of ovulation were evaluated histomorphologically regarding the aetiology of susceptibility to uterine infection. A population of 59 Hanoverian Warmblood mares was used in this study. The mares were divided into Group A (mares with intrauterine fluid accumulations [...
Scholtz EL, Krishnan S, Ball BA, Corbin CJ, Moeller BC, Stanley SD, McDowell KJ, Hughes AL, McDonnell DP, Conley AJ.One of the most widely accepted axioms of mammalian reproductive biology is that pregnancy requires the (sole) support of progesterone, acting in large measure through nuclear progesterone receptors (PRs) in uterine and cervical tissues, without which pregnancy cannot be established or maintained. However, mares lack detectable progesterone in the latter half of pregnancy. Instead of progesterone, several (mainly 5α-reduced) pregnanes are elevated and have long been speculated to provide progestational support in lieu of progesterone itself. To the authors' knowledge, evidence for the bioacti...
Cudd TA, LeBlanc M, Silver M, Norman W, Madison J, Keller-Wood M, Wood CE.Fetal maturation and the timing of parturition in both sheep and primates are thought to be controlled by the hypothalamic-pituitary-adrenal axis but little is known about the endocrinology of the equine fetus. We investigated the ontogeny of plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol and corticosteroid binding capacity in the late-gestation fetal horse. We also wished to determine whether there is ultradian rhythmic release of ACTH and cortisol in fetal horses and we compared fetuses to maternal and non-pregnant adult horses. Six fetuses, 278-304 days gestation (ter...
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...
Virgin J, Hendrickson D, Wallis T, Rao S.To compare the presence or absence of pain, pain-related behavioral responses, and hormonal responses to noxious stimuli during standing laparoscopic ovariectomy in mares sedated with continuous intravenous (IV) detomidine infusion and caudal epidural detomidine. Methods: A double blind prospective study. Methods: Mares (n=12) Methods: Mares were divided into 2 treatment groups; 6 were sedated using continuous IV detomidine infusion and 6 were sedated with caudal epidural detomidine. All mares received IV xylazine (0.33 mg/kg) and butorphanol tartrate (5 mg) premedication before detomidine adm...
Fitzgerald BP, Davison LA, McManus CJ.In seasonally breeding species photoperiodic information is thought to be conveyed to the reproductive and prolactin axis via changes in circulating concentrations of melatonin. For some species, a constant melatonin stimulus is perceived as a short day, whereas in others no photoperiodic information is provided. In the mare, a preliminary study demonstrated that constant administration of melatonin did not modify prolactin secretion, suggesting that this treatment regimen failed to provide photoperiodic information. To further investigate this proposal and to investigate an alternative explan...
Song Y, Massart C, Chico-Galdo V, Jin L, De Maertelaer V, Decoster C, Dumont JE, Van Sande J.In the literature, data obtained in signal transduction from various species thyroids and cells lines are often integrated in a common model. We investigate qualitatively and systematically, using the same protocol, the control by TSH of the two main functions of the thyrocytes, the synthesis and the secretion of thyroid hormones. In all species investigated, the TSH receptor activates both. In some species, including humans, rats and mice, the TSH receptor activates both the cAMP and phospholipase C-PIP2 cascades, in others (e.g. dog) it only stimulates the first. The cAMP pathway activates t...
Battut I, Colchen S, Fieni F, Tainturier D, Bruyas JF.The purpose of this study was to evaluate the exact age when the equine embryo reaches the uterus. The time of ovulation was determined by hourly ultrasound examinations starting 32 h after an injection of crude equine pituitary gonadotrophin or human chorionic gonadotrophin, or after the first of 4 injections of buserelin. Nonsurgical uterine flushings were carried out 144 h (Day 6), 156 h (Day 6.5) or 168 h (Day 7) after ovulation. Induction of ovulation was attempted in 101 oestrous cycles and 61 of 101 mares (60.4%) ovulated 32-44 h post injection. Sixty embryo collections were performed w...
Szóstek-Mioduchowska AZ, Shiotani H, Yamamoto Y, Sadowska A, Wójtowicz A, Kozai K, Hojo T, Kimura K, Skarzynski DJ, Okuda K.Glucocorticoids (GCs) are known to play an important role in maintaining basal and stress-related homeostasis by interacting with endocrine mediators and prostaglandins (PGs). Although a growing body of evidence shows that GCs exert their regulatory action at a multitude of sites in the reproductive axis through corticosteroid receptors, little is known about the direct role of cortisol, an active form of GCs, in the equine endometrium. Thus, the study aimed to determine the effect of cortisol on PGF synthesis in the endometrial tissue and cells in vitro. In Exp.1, the immunolocalization and ...
Pashen RL, Allen WR.The effects of fetal gonadectomy on steroid production and the maintenance of pregnancy in the mare were studied. Removal of the fetal gonads resulted in an immediate fall in maternal plasma concentrations of conjugated and unconjugated oestrogens whereas progestagen levels remained unchanged. Hormone profiles in mares carrying sham-operated fetuses remained similar to those in unoperated control mares. Plasma levels of 13,14-dihydro-15-oxo-PGF-2 alpha (PGFM) were much lower, and uterine contractions weaker, during labour in mares carrying gonadectomized foals than in control mares. Pregnancy ...
Shikichi M, Iwata K, Ito K, Miyakoshi D, Murase H, Sato F, Korosue K, Nagata S, Nambo Y.Measurement of progestines and estrogens in maternal plasma has been advocated as an indicator of foeto-placental function. The goals of the present study were as follows: to determine progestin and estrogen concentrations in mares with normal and abnormal pregnancies during late gestation, evaluate the diagnostic value of hormone concentrations, and investigate the relationship between hormone concentrations after treatment and the survival of foals. Blood samples were collected monthly from 459 pregnant mares between Day 201 of gestation and foaling. Progestin and estrogen concentrations wer...
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...
Petrucci L, Maranesi M, Verini Supplizi A, Dall'Aglio C, Mandara MT, Quassinti L, Bramucci M, Miano A, Gobbetti A, Catone G, Boiti C, Zerani M.The objectives of this study were to evaluate in horse testes the expression of kisspeptin (KiSS) and GnRH1 neuropeptides and their cognate receptors, KiSS1R and GnRH1R, as well as their action on testosterone, GnRH1, prostaglandin F2α (PGF2α), and PGE2 synthesis and cyclooxygenase 1 (COX1) and COX2 activity by Leydig cells in vitro. Testes were obtained from 9 sexually mature horses by surgical castration. Immunohistochemistry, evidenced the presence of KiSS, KiSS1R, GnRH, and GnRH1R in Leydig cells, whereas germinal and Sertoli cells were positive only for GnRH1. Transcripts for both neur...
Ginther OJ, Gastal EL, Gastal MO, Beg MA.The functional and temporal relationships between circulating gonadotropins and ovarian hormones in mares during Days 7-27 (ovulation = Day 0) was studied using control, follicle ablation, and ovariectomy groups (n = 6 mares/group). In the follicle-ablation group, all follicles > or = 6 mm were ablated on Day 7, and every 2 days thereafter, newly emerging follicles were also ablated. Estradiol concentrations decreased (P < 0.01) similarly in the controls and the follicle-ablation group between Days 7 and 11 and by Day 15 began to increase in the controls and continued to decrease in the ...
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...
Christensen RA, Malinowski K, Massenzio AM, Hafs HD, Scanes CG.Two studies were performed with Standardbred geldings 7 to 21 yr of age to determine the sequence of changes in blood plasma concentrations of some hormones and metabolites during feed deprivation for 48 h and for 12 h after refeeding. Plasma hormone and metabolite concentrations were determined with methods validated for horse plasma. Insulin-like growth factor binding proteins (IGFBP) were determined with radioligand analysis following SDS-PAGE electrophoresis. In both experiments, plasma concentrations of triiodothyronine and thyroxine decreased (P < .01) during feed deprivation and incr...
Rendle DI, Duz M, Beech J, Parkin T, Durham AE.Paired measurement of ACTH concentration may be more reliable than a single measurement. Objective: To determine whether the mean of 2 measurements of ACTH concentration is more reliable in assessing pituitary pars intermedia dysfunction (PPID) than a single measurement. Methods: Paired ACTH measurements were performed on (1) 148 occasions from 124 horses being investigated for PPID, (2) 90 occasions from 76 horses with PPID that were receiving treatment with pergolide, and (3) 63 occasions from 50 horses in which there was no clinical suspicion of PPID. Histologic examination of the pars inte...
Eisenhauer KM, McCue PM, Nayden DK, Osawa Y, Roser JF.Stallion testes secrete large amounts of estrogens, but the cellular location of the enzyme that converts androgens to estrogens, cytochrome P450 aromatase, has not been determined. The goal of the present study was to immunocytochemically localize stallion testicular aromatase using a polyclonal antibody generated against human placental cytochrome P450 aromatase. Testes were obtained from 12 stallions from 2 to 23 years of age, during both the breeding and non-breeding seasons. Immunoreactivity was confined to the Leydig cells in all testes examined. No immunostaining was observed in the Ser...
Allen WR, Gower S, Wilsher S.Implantation and placentation in the mare does not commence until as late as day 40 after ovulation. The reasons for this and the growth factors and/or hormones which drive placentation when it does finally occur are of considerable academic and practical interest. Placental interface tissues recovered from 11 accurately aged and perfused-fixed horse uteri between 20 and 68 days of gestation were stained immunocytochemically for Epidermal Growth Factor (EGF), its specific receptor (EGF-R) and for the steroid hormone enzyme, aromatase. EGF was present in endometrial gland and lumenal epithelia ...
Sime A, McKellar Q, Nolan A.A serum-free cell culture method was developed for equine tracheal epithelial cells which allowed the growth and characterisation of the phenotypical properties of this cell type. Several variables influenced the efficacy of the attachment and growth of the isolated cells. Serum and a collagen matrix were essential components for efficient cell attachment. Once attachment had occurred, cell growth was enhanced by a serum-free medium containing bovine pituitary extract, retinoic acid, insulin, hydrocortisone, transferrin, epidermal growth factor, adrenaline and triiodothyronine. The mean time t...
