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.
Ginther OJ, Bergfelt DR, Beg MA, Meira C, Kot K.In cattle and mares, free insulin-like growth factor 1 (IGF-1) is higher in the future dominant follicle (F1) than in the future largest subordinate follicle (F2) before deviation in diameter or selection is manifested between the two follicles. The effect of IGF-1 on other follicular-fluid factors and on the destiny of F2 were studied in two experiments in each species, using a total of 40 heifers and 42 mares. An injection of IGF-1 was made into F2 at the expected beginning of deviation (heifers, F1 >or= 8.5 mm; mares, F1 >or= 20.0 mm; Hour 0). In heifers, follicular fluid was taken fr...
Camillo F, Vannozzi I, Rota A, Di Luzio B, Romagnoli S, Aria G, Allen WR.Mules, hybrids resulting from the mating of a horse mare (Equus caballus, 2n = 64) to a Jack donkey (E. asinus, 2n = 62), are generally infertile. Five horse embryos were transferred non-surgically to two cyclic and one acyclic recipient mules. In the mares and cycling mules, oestrus and ovulation were induced with, respectively, d-cloprostenol and human chorionic gonadotrophin (hCG). The acyclic mule, on the other hand, received oestradiol benzoate when the embryo donor was showing oestrus and progesterone after the donor had ovulated and until pregnancy diagnosis. Non-surgical embryo collect...
Guillaume D, Chavatte-Palmer P, Combarnous Y, Duchamp G, Martinat N, Nagy P, Daels PF.The aim of this study was to compare the effects of treatment with repeated injections of sulpiride (a dopamine D2 antagonist) on prolactin secretion and induced lactation in ovariectomized and intact adult mares and to verify if this induction was possible at the beginning and at the end of the birth season. Two experiments were carried out in September [experiment (expt) 1], and in March (expt 2), in France (48 degrees N). In expt 1, three groups of five mares were tested: intact-control, intact-treated and ovariectomized-treated mares. In expt 2, mares previously subjected to artificial pho...
Hoque S, Senba H, Tsunoda N, Derar RI, Watanabe G, Taya K, Osawa T, Miyake Y.To clarify the endocrinological characteristics of the mares with granulosa theca cell tumor (GTCT), peripheral plasma samples from the 6 mares affected with GTCT were collected before and after the surgical removal of the affected ovary. Concentrations of testosterone (T), follicle stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive-inhibin (ir-INH), progesterone (P) and estradiol-17beta (E(2)) in the plasma samples were measured by radioimmunoassay. Before removal of GTCT in all cases, the concentrations of T were significantly higher than those of normal mares at the breedin...
Dzikiti TB, Hellebrekers LJ, van Dijk P.Physiological parameters, metabolic parameters and stress-related hormones are evaluated in horses anaesthetized with isoflurane in oxygen combined with lidocaine intravenously. Two groups of horses anaesthetized with isoflurane (six horses in each group) were studied: a lidocaine group (IL), which received intravenous lidocaine and a control group (C), which received intravenous saline. Horses in both groups were premedicated with detomidine (i.v.), and anaesthesia was induced with midazolam-ketamine (i.v.). The lidocaine group received intravenous lidocaine as a loading dose of 2.5 mg kg(-1)...
Nie GJ, Johnson KE, Wenzel JG, Braden TD.Mares (n = 30) were treated in the post-ovulatory period with saline, oxytocin, or cloprostenol (Clo). Dose, administration frequency and treatment day (Day 0, 1 or 2 post-ovulation) were evaluated. Interovulatory interval of control cycles was 22.7 (+/-0.36) days with a range of 20.6 (+/-1.44) to 23.8 (+/-1.39) days among all treatment groups. Mares treated with two micro-doses of cloprostenol on Day 2 post-ovulation had the shortest interovulatory interval. This group also had the lowest mean circulating progesterone concentrations on Days 3-7 and 13, and was the slowest group to reach conce...
Nie GJ, Johnson KE, Wenzel JG, Braden TD.Mares (n = 37) were treated from 4h after breeding through 2 days post-ovulation with oxytocin or cloprostenol. Oxytocin (20 units i.m.) was administered every 6 h and cloprostenol (250 mcg i.m.) daily. Luteal function was impaired for several days following treatment, however, lower progesterone levels among cloprostenol treated mares in this study did not result in decreased pregnancies. Pregnancy outcome at 15 days post-ovulation was not different between the oxytocin (13/18) and cloprostenol (13/19) treatment groups, respectively (P = 0.80). The results of this study indicate cloprostenol ...
Sieme H, Schäfer T, Stout TA, Klug E, Waberski D.This study investigated the effects of different artificial insemination (AI) regimes on the pregnancy rate in mares inseminated with either cooled or frozen-thawed semen. In essence, the influence of three different factors on fertility was examined; namely the number of inseminations per oestrus, the time interval between inseminations within an oestrus, and the proximity of insemination to ovulation. In the first experiment, 401 warmblood mares were inseminated one to three times in an oestrus with either cooled (500 x 10(6) progressively motile spermatozoa, stored at +5 degrees C for 2-4 h...
Pinto CR, Paccamonti DL, Eilts BE, Venugopal CS, Short CR, Gentry LR, Thompson DL, Godke RA.In the present study, follicular fluids of estrous mares treated with saline solution (Control) or nitric oxide synthase (NOS) inhibitors were analyzed for nitric oxide (NO), estradiol-17beta (E2) and progesterone (P4) concentrations before and 36h after administration of human chorionic gonadotropin (hCG). Follicular fluids obtained before (0h) hCG administration from control mares had lower concentrations of NO than those obtained 36h after administration of hCG (58.3+/-17.8 micromol versus 340.4+/-57.7 micromol; P<0.05). A similar pattern was also noted for intrafollicular P4 in control ...
Saint-Dizier M, Chopineau M, Dupont J, Daels PF, Combarnous Y.Luteal steroids are necessary to maintain the first 70-90 days of pregnancy in the mare. At 35 days postovulation, the resurgence of the primary corpus luteum (CL) coincides with the secretion of the fetal hormone eCG. In order to study the responsiveness of the primary CL to eCG, we have examined levels of luteal equine LH/CG receptors (eLH/CG-R) mRNAs by Northern blot analysis and measured concentrations of eLH/CG binding sites on luteal membranes using 125I-eLH saturation binding assays at three stages of gestation: before the onset of eCG secretion (Days 14-31), from onset to maximum eCG s...
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...
Hoque S, Derar RI, Osawa T, Taya K, Watanabe G, Miyake Y.A 21 year old thoroughbred mare with granulosa theca cell tumor (GTCT) in the right side and atrophic contralateral ovary was investigated in this study. After arrival at our laboratory on 10th December 1999, the clinical diagnosis of GTCT was examined by rectal palpation and ultrasonographic image of ovaries. Plasma from peripheral blood was collected in the breeding and non-breeding seasons for hormonal analysis. The results showed that the contralateral ovary regained normal activity without any treatment of the GTCT affected ovary and contained follicles showing different sizes 19 months l...
Hoque S, Derar RI, Senba H, Osawa T, Kano K, Taya K, Miyake Y.To clarify the morphological and immunohistochemical characteristics in mares with granulosa theca cell tumor (GTCT), the localization of inhibin subunits (alpha, betaA, betaB) and aromatase in the granulosa cell layers and theca layers in the ovarian follicles were determined by immunohistochemical staining. The follicles were obtained from the ovaries of 6 mares with GTCT and 4 normal mares as controls. Immunohistochemically, inhibin alpha-subunit was localized in the granulosa cells of all follicles showing different sizes in all GTCT cases and betaA- subunit was localized in two GTCT cases...
Stecco R, Paccamonti D, Gutjahr S, Pinto CR, Eilts B.Oxytocin is released in response to teasing during both estrus and diestrus in mares, and at least during estrus, teasing results in an increase in electromyographic activity in the uterus. Exogenous oxytocin causes an increase in intrauterine pressure and prior studies have shown that this response is correlated to the day of the estrous cycle. To determine if teasing causes an increase in intrauterine pressure and if this response varies by day of the cycle, intrauterine pressure was measured while mares were teased with a stallion 2 days before ovulation, on the day ovulation was detected a...
Ginther OJ, Beg MA, Donadeu FX, Bergfelt DR.Diameter deviation is a distinctive change in growth rates among the follicles of a wave, heralding the formation of a dominant follicle and subordinate follicles. When the follicles are about 5mm in cattle and 13 mm in horses, the wave-stimulating FSH surge reaches peak concentrations. Follicle and FSH manipulation studies in both species have shown that the declining portion of the surge before the beginning of deviation is a function of multiple growing follicles that require the decreasing FSH. During this time, all follicles of the wave have the potential for future dominance. Deviation b...
Johnson CA, Thompson DL, Cartmill JA.Three experiments were performed to test the following hypotheses: 1) stallions and/or progesterone-estradiol-treated geldings could serve as models for the effects of a single implant of the GnRH analog, deslorelin acetate, on LH and FSH secretion by mares; and 2) multiple implants of deslorelin acetate could be used as a means of inducing ovarian atrophy in mares for future study of the mechanisms involved in the atrophy observed in some mares after a single implant. In Exp. 1, nine light horse stallions received either a single deslorelin implant (n = 5) or a sham injection (n = 4) on d 0. ...
Marchal R, Caillaud M, Martoriati A, Gérard N, Mermillod P, Goudet G.The aim of this study was to investigate the role of growth hormone (GH) on in vitro cumulus expansion and oocyte maturation in equine and porcine cumulus-oocyte complexes (COCs), and to approach its way of action. Equine COCs were cultured in a control medium (TCM199, 5 mg/ml BSA, 1 microg/ml estradiol, and antibiotics) supplemented with either 0.5 microg/ml equine GH or 5 microg/ml equine LH. Porcine COCs were cultured in a basal medium (TCM199 with 570 microM cysteamine) supplemented with 0, 0.1, 0.5, or 1 microg/ml porcine GH or in a control medium (basal medium with 10 ng/ml epidermal gro...
Estepa JC, Garfia B, Gao PR, Cantor T, Rodriguez M, Aguilera-Tejero E.Parathyroid hormone (PTH) plays a critical role in the regulation of mineral metabolism in mammals. Until recently, the standard method for PTH measurement has been the 2nd generation intact-PTH (I-PTH) assay. Current evidence indicates that the I-PTH assay binds to the PTH molecule and to an inactive N-terminally truncated PTH fragment that tends to accumulate in the blood of uraemic patients. Therefore, a new 3rd generation PTH assay that detects only the whole PTH molecule (W-PTH; cyclase-activating PTH [CAP]) has been developed. Objective: To validate this more specific W-PTH assay for mea...
Johnson PJ, Messer NT, Ganjam VK, Thompson DL, Refsal KR, Loch WE, Ellersieck MR.There exists a need for better diagnostic tests to characterise thyroid disease in horses. Currently available diagnostic tests fail to differentiate between thyroid gland disorders and thyroid abnormalities resulting from pituitary or hypothalamic problems. Objective: To evaluate the effects of treatment with propylthiouracil (PTU) and bromocryptine (BROM) on serum concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3) and equine thyroid-stimulating hormone (e-TSH, thyrotrophin) in mature horses. Methods: Healthy mature horses were treated using either PTU or BROM for 28 da...
O'Donnell LJ, Sheerin BR, Hendry JM, Thatcher MJ, Thatcher WW, LeBlanc MM.The mare exhibits nocturnal uterine contractions in the last 6 days of gestation. It is hypothesized that estradiol 17beta (O17beta) may be associated with the nightly increase in uterine contractions. The 24-h secretion pattern of plasma O17beta was measured in 3 pony mares in late gestation to identify changes in release as the mare neared parturition. Blood was collected weekly at 08:00 hours beginning on day 240 and every third day from day 330 until delivery. Serial blood samples were collected from each mare every 30-min for 24-h beginning on gestation day 310 and every sixth day thereaf...
Martoriati A, Gérard N.A growing body of evidences suggests that the ovary is a site of inflammatory reactions, and thus, ovarian cells could represent sources and targets of the interleukin-1 (IL-1) system. The purpose of this study was to examine the IL-1 system gene expressions in equine granulosa cells, and to study the IL-1beta content in follicular fluid during the follicle maturation. For this purpose, granulosa cells and follicular fluids were collected from the largest follicle at the early dominance stage (diameter 24 +/- 3 mm) or during the preovulatory maturation phase, at T0 h, T6 h, T12 h, T24 h and T3...
Briant C, Ottogalli M, Morel M, Guillaume D.The GnRH antagonist antarelix (Teverelix) was administered to mares (0.01 mg/kg, i.v., twice a day) during the periovulatory period. In Experiment 1, 20 mares were divided into a treated (A3d-) and a control (Control-) group. A3d- mares received antarelix for 3 days from the day when the dominant follicle (F1) reached 32 mm (D0). In Experiment 2, 10 mares were divided into a treated (A6d+) and a control (Control+) group. A6d+ mares received antarelix for 6 days from D0 and hCG was injected in all animals (1600 IU, i.v.) on D1. Pregnancies were determined 13 days after ovulation. In both experi...
Donadeu FX, Ginther OJ.Follicle growth and associated changes in circulating hormone concentrations were evaluated after follicle ablation in mares (n = 13) during four 13 day periods beginning at means of -98.5, -61.4, -26.0 and 10 days from the first ovulation and corresponding to mid-anovulatory, early-transitional, late-transitional and ovulatory periods, respectively. During each period, all follicles > 5 mm in diameter were ablated (day 0) followed by no subsequent ablations (all-follicle group) or the ablation of all follicles > 5 mm when a new follicle reached > 10 mm (0-follicle group). A follicula...
Illera JC, Silván G, Munro CJ, Lorenzo PL, Illera MJ, Liu IK, Illera M.An amplified enzymeimmunoassay (EIA) was validated for androstenedione in the serum of male horses. We will use the assay as a tool for the diagnosis of equine cryptorchidism. We will compare androstenedione EIA to the currently used methods (testosterone and estrone sulphate determinations). The study was conducted on 115 horses of pure Spanish and Arabian breeds, that included 30 geldings, 60 bilateral cryptorchids and 25 stallions. Androstenedione standard curve covered a range between 0 and 1 ng per well. Low detection limit was 1.54 pg/ml. Intra- and inter-assay coefficients of variation ...
Fitzgerald BP, Reedy SE, Sessions DR, Powell DM, McManus CJ.The seasonal nature of reproductive activity in mares is widely accepted and considerable attention has focused on the mechanisms that lead to the initiation of the breeding season. In contrast, considerably less information is available about the termination of the breeding season. It is interesting to note that each winter a sub-population of mares continues to undergo oestrous cyclicity during the non-breeding season. Continuation of reproductive activity during the winter occurs most frequently in mares that maintain a non-pregnant condition in successive years. The maintenance of a non-pr...
Ousey JC, Forhead AJ, Rossdale PD, Grainger L, Houghton E, Fowden AL.In pregnant mares during late gestation, little, if any, progesterone (P4) is found in the maternal circulation. Hence, quiescence of the equine uterus is believed to be maintained by metabolites of pregnenolone and P4 known as progestagens, which are produced by the uteroplacental tissues. However, little is known about the ontogeny, distribution, or actual rates of uteroplacental progestagen production in pregnant mares and their fetuses during the second half of pregnancy. Therefore, the present study measured the rates of uteroplacental uptake and output of eight specific progestagens in c...
Gutierrez CV, Riddle WT, Bramlage LR.To determine whether serum thyroxine (T4) concentration was associated with pregnancy rates 15 to 16 days after ovulation in mares and to determine whether thyroid hormone supplementation would enhance fertility in mares. Methods: Cohort study. Methods: 329 clinically normal broodmares. Methods: Mares were examined 15 to 16 days after ovulation to determine whether they were pregnant; blood samples for determination of serum T4 concentration were collected at the same time. Sixty mares were receiving thyroid hormone supplementation prior to the study because of low serum T4 concentration (< 16...
Aurich JE, Kranski S, Parvizi N, Aurich C.This study investigated the regulation of growth hormone (GH) release in stallions and tested the hypothesis that the somatotrophic axis influences testicular function. Basal plasma GH concentrations, effects of an experimental decrease of GH release on testicular function and an opioidergic regulation of GH release were investigated in Shetland stallions (n=6). No seasonal variations in plasma GH concentrations were found over a 12-month period. Treatment with the somatostatin analogue octreotid (100mg twice daily over 10 days) caused a decrease in semen motility from 38.7+/-8.4% progressivel...
O'Connor SJ, Fowden AL, Holdstock N, Giussani DA, Forhead AJ.Angiotensin-converting enzyme (ACE) has an active role in the control of blood pressure and body fluid homeostasis both before and after birth. This study investigated the ontogeny of pulmonary and renal ACE concentrations in fetal and neonatal horses. Fetal pulmonary ACE concentration increased from 250 days towards term (c. 335 days). Newborn foals showed significantly higher mean concentrations of pulmonary ACE (4.40 +/- 0.62 nmol min(-1) mg protein(-1)) than both fetuses during late gestation (1.23 +/- 0.51 nmol min(-1) mg protein(-1)) and animals aged 1 day to 2 weeks of postnatal age (0....
Toribio RE, Kohn CW, Sams RA, Capen CC, Rosol TJ.Abnormalities in calcium (Ca(2+)) homeostasis are reported in horses with several pathological conditions; however, there is little information on Ca(2+) regulation in horses. The objectives of the present study were to determine the Ca(2+) set-point in healthy horses, to determine whether the Ca(2+)/parathyroid hormone (PTH) response curves were characterized by hysteresis, and to determine if the order of experimentally induced hypocalcemia or hypercalcemia had an effect on PTH secretion. The Ca(2+) set-point and hysteresis were determined in 12 healthy horses by infusing Na(2)EDTA and calci...
Goto A, Tagami M, Kato F, Suzuki T, Yamaga T, Murase H, Sato F, Tsogtgerel M, Niikura T, Moriyama T, Chiba A, Watanabe KI, Tsuzuki N, Nambo Y.We performed a standing hand-assisted laparoscopic ovariectomy in a draft mare that presented with high serum anti-Müllerian hormone (AMH) level and had an enlarged single cystic ovary. Histopathological examination revealed no tumor cell proliferation in the ovary, but the presence of a large ovarian cyst was confirmed. In the diagnosis of abnormal ovaries in mares, a comprehensive assessment should be performed, including the monitoring of ovarian morphology and biomarkers over time, to determine the disease prognosis and treatment plan. The case of this mare with a nonneoplastic abnormal o...
Li CH, Chung D.Isolation of prolactin from equine pituitary glands has been described. It has a potency of 42 IU/mg in the pigeon crop-sac test and consists of 199 amino acids. The hormone has only four half-cystine residues in contrast to other mammalian prolactins which have six residues. From NH2-terminal sequence analysis and amino acid composition of cyanogen bromide fragments, the NH2-terminal disulfide loop is missing in the equine prolactin molecule. Circular dichroism spectra indicate that the alpha-helical content of equine prolactin appears to be lower (50%) than that found in the ovine hormone (6...
Raeside JI, Liptrap RM.Urine collections (24 hr) were made at weekly intervals from four Pony mares from the 3rd or 4th month of pregnancy until parturition. Separation of oestrogens on Celite columns was followed by Kober measurements of oestrone and equilin. Individual differences were noted in peak amounts of total oestrogens excreted (200 to 800 mg/day), when oestrone constituted 80 to 95% at the 6th to 7th months. Although equilin increased in later gestation, oestrone remained the major product. Total oestrogen values decreased rapidly from the peak and then more gradually towards the end of pregnancy. During ...
van der Kolk JH, Kalsbeek HC, Wensing T, Breukink HJ.The urinary corticoid:creatinine (c:c) ratio was determined in eight horses with hyperadrenocorticism (HAC). The mean (+/- SD) urinary c:c ratio of the eight horses with HAC (29 +/- 14 x 10(-6)) was significantly (P < 0.05) greater than the ratio in seven control horses (11 +/- 4.3 x 10(-6)). The urinary concentration of corticoids in control horses (201 +/- 60.4 nmol litre-1) was significantly (P 0.05) between both groups. As both false negative and false positive cases were found, it is concluded that a measurement of the urinary c:c ratio in the horse should not be used as the sole test...
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...
Newcombe JR, Cuervo-Arango J.One hundred and fifty-four mares were inseminated with fresh semen either during the pre- or post-ovulatory periods at different intervals relative to ovulation: 36-24 h (n = 17) and 24-0 h (n = 30) before ovulation; 0-8 h (n = 21), 8-16 h (n = 24), 16-24 h (n = 48) and 24-32 h (n = 14) h after ovulation. All mares received the same routine post-mating treatment consisting of an intrauterine infusion with 1 litre of saline and antibiotics followed 8 h later by an intravenous administration of oxytocin. Artificial inseminations (AI) from 36 h before ovulation up to 16 h post-ovulation were perf...
Raekallio M, Vainio O, Scheinin M.Single doses of the alpha 2-adrenergic sedative-analgesic drug, detomidine (10 micrograms/kg, n = 7; 20 micrograms/kg, n = 9), were administered IV to adult horses. Plasma concentrations of adrenaline, noradrenaline, the catecholamine metabolites 3,4-dihydroxyphenylglycol (DHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC), and cortisol were determined before the medication and 30 minutes after it. The plasma concentrations of noradrenaline and the catecholamine metabolites decreased significantly after administration of both 10 micrograms/kg and 20 micrograms/kg of detomidine. Plasma adrenaline...
Re G, Badino P, Novelli A, Di Renzo GF, Severino L, De Liguoro M, Ferone MR.The distribution of oestrogen and progesterone receptors in the equine genital tract was investigated by means of a modified dextran-coated charcoal method on samples collected from the vagina, the cervix and the uterus of 30 healthy adult Polish mares, divided into two groups on the basis of their serum progesterone levels. The concentrations of oestrogen and progesterone receptors were significantly (P < 0.05) lower in the vagina and the cervix than in the uterus, in agreement with data from human beings, cattle and pigs, which showed that the highest concentrations of oestrogen and proge...
Ralston JM, Stenhouse AM, Stenhouse NS, Buck GJ, Lucks SF, Reynoldson JA, Bolton JR.A survey of the concentrations of cortisol in blood and urine samples taken from thoroughbred and standardbred horses after racing is presented. Statistical analysis showed the only significant difference between thoroughbred and standardbred horses was a higher cortisol concentration in thoroughbred urine. Urine volume and pH had no significant influence on the urinary cortisol concentration, however 9.5% of the urinary cortisol variation could be explained due to the influence of plasma cortisol concentration. The results of cortisol and ACTH administrations are also shown and compared with ...
Betteridge KJ, Raeside JI, Waelchli RO, Christie HL, Hayes MA.Sixteen cases of spontaneous pregnancy loss (11 of singletons and five of pairs of twins) are described. The losses occurred between gestation Days 13 and 25 in 12 mares being monitored almost daily by transrectal ultrasonography (for measurement of conceptus growth) and blood sampling (for determination of maternal plasma progesterone concentrations as evidence of luteolysis) in experimental studies of early pregnancy. In 10 of the 16 cases the uterus was flushed and eight conceptuses were recovered for morphological assessment. Five of the 11 losses of singletons occurred before Day 16 and, ...
Melrose PA, Pickel C, Cheramie HS, Henk WG, Littlefield-Chabaud MA, French DD.Recent reports have indicated that analysis of changes in the staining characteristics of gonadotropin-releasing hormone (GnRH) neurons and characterization of morphological plasticity of the related structural framework may help to elucidate the physiological mechanisms involved in neuroendocrine control of mammalian reproduction. Whether comparative studies will facilitate this process or simply elucidate species-specific mechanisms is not yet clear. The present study was performed in order to begin analysis of GnRH neurons in a seasonally breeding species that exhibits an unusually long ovu...
Popot MA, Houghton E, Ginn A, Jones M, Teale P, Samuels T, Lassourd V, Dunnett N, Cowan DA, Bonnaire Y, Toutain PL.The purpose of the present report was to estimate the population parameters of cortisol concentrations in urine, an endogenous hormone used as a 'doping' agent and for which an international threshold (1.0 micrograms/ml) has been proposed. Two data bases (French and UK) corresponding to 112 and 142 samples, respectively were considered. Urine was collected under specific post competition conditions. Cortisol concentrations were obtained by validated methods (HPLC for the French samples, and GC-MS for UK samples). No difference was observed between the 2 data sets and statistical analyses were ...
Driancourt MA, Prunier A, Palmer E, Mariana JC.To define ovarian follicular kinetics in the equine ovary during anestrus and the breeding season, the follicular population of pony mares was investigated at mid-anestrus and at the beginning and end of the breeding season. There was a clear effect of season on the exit of reserve (primordial and initiated) follicles since at the beginning of the breeding season we noticed a higher mitotic index for the smaller preantral follicles, leading to an accumulation of small and medium antral follicles. In contrast, the ovaries sampled during anestrus or at the end of the breeding season were very si...
Thompson DL, Godke RA, Squires EL.Twelve mares fed altrenogest for 14 d were used to study the effects of a single injection of testosterone propionate on concentrations of follicle-stimulating hormone (FSH) during diestrus, and to relate the normal and perturbed patterns of FSH secretion to subsequent estrous characteristics and fertility. Seven of 12 mares received testosterone propionate at 200 micrograms/kg of body weight on d 5 of progestogen feeding. Mares were teased and blood samples were drawn daily; all mares were artificially inseminated at the first estrus after progestogen treatment. Testosterone propionate treatm...
Wesson JA, Miller KF, Ginther OJ.Plasma FSH and LH response to a synthetic GnRH analog was measured in adult ovariectomized pony mares (OVX) and in pony foals (<70 days of age) during late spring (May-June). FSH and LH responded in a similar fashion (200% increase) in the OVX mare, which is different from other reports for intact mares. There was a greater mean response to a comparable dose of GnRH in the prepubertal foal for both FSH (500%) and LH (900%) than in the OVX mare. There was a positive correlation between age and the maximum FSH response to GnRH in male and female foals. The LH response was positively correlate...
Nie GJ, Johnson KE, Wenzel JG, Braden TD.Mares (n = 37) were treated from 4h after breeding through 2 days post-ovulation with oxytocin or cloprostenol. Oxytocin (20 units i.m.) was administered every 6 h and cloprostenol (250 mcg i.m.) daily. Luteal function was impaired for several days following treatment, however, lower progesterone levels among cloprostenol treated mares in this study did not result in decreased pregnancies. Pregnancy outcome at 15 days post-ovulation was not different between the oxytocin (13/18) and cloprostenol (13/19) treatment groups, respectively (P = 0.80). The results of this study indicate cloprostenol ...
Wesson JA, Orr EL, Quay WB, Ginther OJ.Pony pineal glands and female reproductive tracts were collected monthly for 1 year from
a local slaughterhouse. Pineal gland weights did not change significantly throughout the year.
Pineal gland tissue homogenates were assayed for hydroxyindole-O-methyltransferase
(HIOMT) activity with N-acetylserotonin as the primary substrate. The greatest HIOMT
activity was obtained with N-acetylserotonin as substrate. but three other related S-OH
indole substrates (5-hydroxytryptophol, serotonin. and 5-hydroxy-2-methylindole) were also
methylated. HIOMT activity with all substrates was highest duri...
Becker SE, Johnson AL.Studies were conducted to compare continuous vs pulsatile i.v. infusion of GnRH on serum gonadotropin concentrations and ovulation in seasonally anestrous mares and in cycling mares. Anestrous mares (Exp. 1) received no treatment (control; n = 3), 2, or 20 micrograms of GnRH/h continuous infusion (CI) (n = 4 and n = 6, respectively), or 20 micrograms of GnRH/h pulsatile infusion (PI) (n = 5). After initiation of GnRH infusion, serum LH levels increased earlier, and to a greater extent, in the PI group than in other groups (P less than .05). In contrast, serum FSH concentrations did not differ ...
Kask K, Malmgren L, Odensvik K.Hormonal, chemical, and mechanical stimuli can activate the arachidonic acid cascade and result in formation of prostaglandins and related substances. These compounds can have a profound role in the initiation of the inflammatory process (Higgins & Lees 1984). Prostaglandin (PG) F2α is the key hormone in reproductive physiology with well-known effects on reproductive performance e.g. luteolysis and abortion. An activation of the arachidonic acid cascade, caused by mechanical manipulation during an embryo transfer procedure, might be one explanation for early embryonic loss.
Lefranc AC, Allen WR.The maintenance of luteal function is essential for the
establishment of pregnancy in all mammals. While the lifespan of
the corpus luteum (CL) is independent of the presence of a
conceptus in carnivores (Lawson and Findlay 1977), prolongation
of luteal function in polyoestrous animals requires the presence of
the conceptus to defuse and suppress the cyclical luteolytic
mechanism in the nonpregnant state (Short 1969). In the horse, the
conceptus remains spherical and unattached (Van Niekerk and
Allen 1975) after it enters the uterus between 144 and 168 h after
ovulation (Battut et al....
Squires EL, McKinnon AO.Because the reproductive performance of mares is lower than that of any other domesticated species, hormone therapy is important in ensuring fertility and proper management of pregnancy. Current techniques of hormone therapy are discussed.
Santos VG, Bettencourt EM, Ginther OJ.Mares with persistent CL (PCL) with no known etiology (idiopathic) were matched with mares with an interovulatory interval (IOI) of apparent physiological length, so that ovulation at the beginning of each PCL and IOI occurred during the same month (n = 6/group). Blood samples were collected daily from Days 12 to 22 (Day 0 = ovulation). Mean progesterone (P4) decreased in both groups on Days 14 and 15 and then diverged with a continued decrease in the IOI group and the beginning of constant and greater (P < 0.05) P4 concentration on each day in the PCL group. Before P4 divergence betw...
Papkoff H.The objectives of this paper are to review the chemical and biological properties of equine chorionic gonadotropin (eCG, PMSG) isolated from the serum. Comparisons are made with eCG isolated from endometrial cups, trophoblast cell culture medium, and low titer serum. The results show that eCG can vary, depending on the source, in both chemical and biological (LH and FSH activity) properties.
Hodgson D, Howe S, Jeffcott L, Reid S, Mellor D, Higgins A.Oral administration of altrenogest for oestrus suppression in competition horses is believed to be widespread in some equestrian disciplines, and can be administered continuously for several months during a competition season. To examine whether altrenogest has any anabolic or other potential performance enhancing properties that may give a horse an unfair advantage, we examined the effect of oral altrenogest (0.044 mg/kg), given daily for a period of eight weeks, on social hierarchy, activity budget, body-mass and body condition score of 12 sedentary mares. It was concluded that prolonged ora...
Stewart F, Allen WR, Moor RM.Rat testicular radioreceptor assays specific for FSH and LH were used to determine the FSH:LH ratio of PMSG produced by horse, donkey, mule and hinny conceptuses. Measurements of FSH and LH activities in PMSG produced both in vivo and in vitro by the four types of conceptuses showed that the genotype of the foetus markedly influences the FSH:LH ratio of PMSG. The FSH:LH ratio of PMSG produced by the horse conceptus was around unity whereas the ratio of PMSG produced by the donkey conceptus was as low as 0-2. Furthermore, the hybrid mule and hinny conceptuses both produced PMSG with an FSH:LH r...
Pastorello M, Gastal MO, Godoi DB, Gastal EL.Among female livestock, the mare has the shortest interval from parturition to first ovulation. Due to the scarcity of research on postpartum mares, little progress has been made on the characterization of the resumption of ovarian cyclicity after parturition. This study compared follicular and gonadotropin dynamics during follicle emergence and deviation in postpartum lactating (PP Lactating) versus non-postpartum cycling (N-PP Cycling) mares. On the day of parturition, every PP Lactating mare was paired with a N-PP Cycling mare. Comparisons were made by considering the partum-ovulation inter...
Alexander SL, Irvine CH.We used our nonsurgical method for collecting equine pituitary venous blood to study the role of endogenous opioids in the basal regulation of the hypothalamo-pituitary-adrenal axis. We gave mares the opioid antagonist, naloxone (NAL), at either a high (0.5 mg/kg i.v. bolus, followed by infusion of 0.25 mg/kg.h; n = 4) or low (0.2 mg/kg i.v. bolus; n = 6) dose rate. Pituitary venous blood was collected continuously, divided into 0.5- or 1-min segments for 15-30 min before and 1 h after the NAL bolus, and assayed for CRH, arginine vasopressin (AVP), and ACTH. The mares tolerated NAL administrat...
Wilson CA, ter Haar MB, Bonney RC, Buckingham J, Dixson AF, Yeo T.We have shown previously that pregnant mare serum gonadotrophin (PMSG) induces ovulation only in rats weighing over 60 g on the day of injection. The under-60 g rats do not ovulate although they secrete a preovulatory surge of a pleiomorphic form of LH. Presumably this pleiomorph is inactive. Comparisons were made of plasma hormone concentrations in rats treated with PMSG that weighed over and under 60 g. The measurements were made on samples taken between 13.00 and 22.00 h on the day of the expected preovulatory LH surge. Prolactin and corticosterone levels were lower in the lighter group com...
Watson ED, Buckingham J, Björkstén TS.Oxytocin has been identified in the ovaries of many species
including ruminants (Wathes and Swann 1982; Rodgers et al.
1983), pigs (Jarry etal. 1990), sub-human primates (Khan-Dawood
1998), rats (Ho and Lee 1992) and women (Schaeffer et al. 1984).
In these species ovarian oxytocin has several roles, including
control of luteal regression (Fht and Sheldrick 1983) and possibly
luteinisation (Aladin Chandrase.kher and Fortune 1990; Eispanier et
al. 1997), and involvement in ovulation (viggiano et al. 1989).
In the mare, circulating oxytocin is reported to be high in
oestrus and early dio...
Song L, Porter DG, Coomber BL.Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) play very important roles in extracellular matrix (ECM) remodeling in ovarian follicle growth and ovulation. Equine follicles are embedded in cortex that is at the center of the ovary, and they must expand/emigrate to the fossa, the only site in the ovary for ovulation. Therefore, equine ovarian stromal cells (EOSC) are probably involved in ECM remodeling during follicle growth. This study examined whether cultured EOSC synthesize gelatinases and TIMPs, molecules essential for ECM remodeling in other systems. Results showed...
