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.
Cleaver BD, Grubaugh WR, Davis SD, Sheerin PC, Franklin KJ, Sharp DC.Melatonin is thought to play a role in relaying photic information to the central nervous system as part of the seasonal reproductive cycle of the mare. However, the mechanisms by which melatonin may act are unknown. Therefore, this study was designed to determine whether exposure to constant light would, by reducing circulating melatonin concentrations, have any effect on hypothalamic gonadotrophin-releasing hormone (GnRH) content and circulating levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Blood samples were collected for 12 h at 15-min intervals from 8 ovariect...
Tomanelli RN, Sertich PL, Watson ED.Receptors for progesterone and oestrogen were measured in cytosol extracted from the endometrium of mares. Samples of endometrium were obtained from mares during the oestrous cycle and during other physiological and pathological states, and from mares with persistent endometritis. The concentration of binding sites was high around oestrus and early in dioestrus and was low by mid- to late dioestrus. Numbers of receptors were low in mares sampled on Day 15 of pregnancy and in mares in prolonged dioestrus, whereas receptor concentrations in ovariectomized mares were high. In 2 mares with endomet...
Houghton E, Holtan D, Grainger L, Voller BE, Rossdale PD, Ousey JC.Radioimmunoassay (RIA) and gas chromatography-mass spectrometry (GC-MS) were used to determine plasma progestagen concentrations in the normal and premature foal. Radioimmunoassay provides a profile of plasma progestagens with respect to time but, due to the non-specific nature of the technique and without prior chromatographic purification, quantitative data based on RIA analysis must be interpreted with caution. In contrast, the greater specificity of GC-MS allows identification of specific plasma progestagens and measuring of multiple analytes in a single analysis. Both techniques demonstra...
Ball BA, Altschul M, McDowell KJ, Ignotz G, Currie WB.Research has indicated that trophoblastic vesicles (TV) formed from Day-14 equine conceptuses would prolong luteal maintenance in mares after surgical transfer to the uterus at Day 10 after ovulation. The current study assesses TV as a further model for maternal recognition of pregnancy in mares. The objectives of the study were to determine the ability of TV to prolong luteal maintenance in mares, their effect on endometrial production of prostaglandin F (PGF) in vitro, and their ability to secrete polypeptides in vitro. In contrast to our previous study (Ball et al., 1989b), transfer of TV f...
Varner DD, Forrest DW, Fuentes F, Taylor TS, Hooper RN, Brinsko SP, Blanchard TL.Eighteen fertile mares were used to determine the effects of the oestrous cycle and location in the reproductive tract on the amount and concentration of glycosaminoglycans in luminal fluids. Ovariohysterectomies were performed in 3 groups of 6 mares on Day 3 of behavioural oestrus, within 6 h after ovulation or on Day 8 of dioestrus. The lumina of the uterine horns and oviducts ipsilateral and contralateral to the active ovary were flushed and fluid was aspirated from the dominant follicle in the oestrous preovulation group. Glycosaminoglycans and protein concentrations were measured in these...
Rossdale PD, Ousey JC, Cottrill CM, Chavatte P, Allen WR, McGladdery AJ.Between 1985 and 1990, 25 Thoroughbred mares were classified as having an abnormal pregnancy on the basis of precocious signs of impending parturition. Throughout the remainder of their pregnancies, plasma progestagen and mammary secretion calcium concentrations were monitored. After parturition, evidence of placental pathology was recorded and their foals were assessed with regard to adrenocortical function and behaviour. Seven pony mares were used to establish a model of placental pathology and, following induced placental separation, were subjected to the same protocol. Control animals cons...
Hofferer S, Duchamp G, Palmer E.Twelve anoestrous mares were treated with an intravaginal sponge containing 0.5 g allyl trembolone (Regumate; Roussel UCLAF, Paris) and 50 mg oestradiol benzoate for 7 days, followed by daily intramuscular (i.m.) injections of 25 mg crude equine pituitary extract (CEG), with (n = 6) or without (n = 6) 0.25 mg porcine growth hormone (pGH). No difference in ovarian response to this superovulation treatment was observed between the 2 groups (2.2 +/- 0.4 vs 2.3 +/- 0.4 ovulations per mare, respectively). CEG treatment was then combined with allyl trembolone (40 mg per os per day) and prolonged in ...
Ainsworth CG, Hyland JH.Continuous infusion of gonadotrophin releasing hormone (GnRH) has been shown to induce oestrus and ovulation in experimental mares in seasonal anoestrus. The present study sought to apply this form of treatment to anoestrous mares subjected to normal management procedures on 15 commercial Thoroughbred studfarms in Australia. The GnRH was delivered via subcutaneously implanted osmotic minipumps (OMP) at dose rates of 100 ng/kg/h and 200 ng/kg/h. The ovaries of treated mares were palpated on the day of OMP insertion (Day 0) and blood samples were collected twice weekly from a proportion of mares...
Davis SD, Sharp DC.This experiment investigated steroid production by ovarian tissues, in vitro, of pony mares during vernal transition from anoestrus to the breeding season. Follicular dynamics were monitored to detect the first, second, third or fourth transition follicle, greater than or equal to 30 mm diameter or the first large post luteal follicle of the breeding season. Twenty-four hours after a large follicle was detected, theca (T) and granulosa (G) tissues were harvested. Separate and co-incubations of these tissues were conducted to determine steroid production in early transition (ET), late transitio...
Turner JE, Irvine CH.Gonadotrophin-releasing hormone (GnRH) was used in several regimens in anoestrous mares in an attempt to investigate the effects of frequency and dose on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release, and consequently on ovulation and corpus luteum establishment. Thrice daily injections of GnRH induced development of pre-ovulatory follicles, but hourly injections or constant infusions were required to induce ovulation. Hourly injections induced a much higher LH:FSH ratio in the presence or absence of ovarian hormones. When anoestrous mares were given an implant that r...
Watson ED.Corpora lutea were recovered from mares either 4 to 5 days or 12 to 13 days after ovulation. Mixed populations of luteal cells were prepared by collagenase digestion and were incubated for 24 h in the presence or absence of prostaglandin (PG) F-2 alpha (250 ng/ml). PGF-2 alpha significantly (P = 0.03) reduced progesterone secretion by cells from late diestrous corpora lutea and tended (P = 0.06) to reduce secretion by early diestrous cells. PGF-2 alpha had no significant effect on leukotriene B-4 (LTB-4) production by cells from early diestrous corpora lutea, but significantly (P = 0.03) incre...
McCue PM, Troedsson MH, Liu IK, Stabenfeldt GH, Hughes JP, Lasley BL.Thirty-seven seasonally anoestrous mares were divided into treatment and control groups and given 10 micrograms of native GnRH (GnRH) per hour using a peristaltic pump, or 10 micrograms GnRH agonist (GnRHa) twice daily, beginning on either 13 January, 13 February or 14 March. Treatment with GnRH was equally effective in inducing ovulation in January (4/5), February (4/5) and March (3/4). GnRHa treatment was more effective in inducing ovulation in February (4/5) and March (4/4) than in January (2/8). Peak luteinizing hormone (LH) concentrations in mares induced to ovulate with GnRH (7.4 +/- 1.5...
Roser JF, Hughes JP.Hormonal effects of prolonged administration of gonadotrophin-releasing hormone (GnRH) were investigated in 7 fertile stallions in winter and summer. The stallions were divided into 4 groups so that 1 animal received 0.625 micrograms of GnRH and each of 2 animals received 1.25, 2.5 or 5.0 micrograms of GnRH subcutaneously every 30 min for 5 days. Daily blood samples were collected from 5 days before to 5 days after treatment for measurement of plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T) and oestrogen conjugates (EC). Five-minute blood...
Guillaume D, Palmer E.Two experiments tested the hypothesis that exogenous melatonin (12 mg) given 4 h before dusk (evening melatonin), or near dawn (morning melatonin), would mimic a prolongation of the night and suppress stimulation of the ovaries induced by long days. Experiment 1 consisted of a non-stimulated control group, a control group stimulated by 14.5 h of light, a treated group stimulated with 14.5 h of light plus evening melatonin, a control group given 17.5 h of light and a treatment group given 17.5 h of light plus morning melatonin. The mean (+/- s.e.m.) intervals from the start of treatment to the ...
Argo CM, Cox JE, Gray JL.This study tested the role of melatonin in the regulation of seasonal physiological change in the pony stallion. Four 3-year-old, Welsh Mountain pony stallions were housed initially under the prevailing short-day photoperiod in December (8 of light [L]:16 h of darkness [D]) before being transferred to long days (16L:8D) on 13 January for the remaining 22 weeks of the study. On Day 76 (11 weeks later) the stallions began an 11-week period of daily melatonin treatment (20 mg orally, 8 h after lights on). Marked changes in mean plasma testosterone, beta-endorphin and cortisol concentrations occur...
McFarlane JR, Cabrera CM, Coulson SA, Papkoff H.The rhinoceros is an endangered species related to the horse family. Little is known of its reproductive endocrinology. The objectives of this study were to partially purify rhinoceros pituitary hormones, determine which assays could be used for their assessment, and to ascertain whether rhinoceros LH possesses the intrinsic FSH activity of equine LH. A single pituitary each from a White (1.3 g) and a Black (1.2 g) Rhinoceros was homogenized and extracted (pH 9.5), then subjected to pH and salt fractionation, and ion-exchange chromatography (DEAE and Sephadex SP-C50) to yield partially purifie...
Pantke P, Hyland J, Galloway DB, MacLean AA, Hoppen HO.Equine plasma luteinizing hormone (LH) possesses both biological (in vitro bioassay, B) and immunological (radioimmunoassay, I) activities and the ratio of B:I varies with stage of the oestrous cycle. To estimate the contribution made by pituitary secretion and peripheral metabolism to changes in the B:I ratio, pituitary venous effluent and circulating plasma from 5 dioestrous and 2 oestrous mares were analyzed using both an in vitro bioassay and a radioimmunoassay. During dioestrus, LH was released in a pulsatile fashion with a frequency of 1.4 pulses/24 h and a pulse duration of 20-40 min (c...
Lindner A, Will Y, Chrispeels J.Reference values for Cortisol, T4 and T-Uptake, determined with the Fluorescence-Polarization-Immunoassays (FPIAs) in blood-plasma of different horse groups were established. The highest Cortisol values were measured in blood samples from thoroughbred racehorses and riding horses taken between 7 and 8 a.m. (181 +/- 37 and 268 +/- 43 nmol/l), the lowest gained between 5 and 6 p.m. (69 +/- 45 and 85 +/- 32 nmol/l respectively). Peak values for T4 in riding horses were found in blood samples collected between 1 and 2 p.m. (28.2 +/- 5.7 nmol/l) followed by the samples taken at 5-6 p.m. and 7-8 a.m...
Evers P, Hoffmann B.This paper describes the use of hormone analysis in the diagnosis of adrenal cortex dysfunction in the dog, cat and horse. Analytical problems concerning the determination of corticosteroid levels are discussed and the pathology of adrenal dysfunction is briefly presented. The paper focuses on the problems in establishing physiological norms for adrenal function based on the established assays. Own experiences and other reported data are referred to.
Piquette GN, Kenney RM, Sertich PL, Yamoto M, Hsueh AJ.The association of equine granulosa-theca cell tumors with atrophied contralateral ovaries and abnormal estrous cycles suggests that these tumors produce hormones that affect pituitary gonadotropin production. Because inhibin, a heterodimer protein secreted by granulosa cells, decreases FSH production, we examined the presence of inhibin alpha- and beta A-subunits and their mRNAs in ovarian tumors obtained from three mares. These tumors contained neoplastic cords and nodules, multiple fluid-filled cysts, and a predominance of neoplastic granulosa cells. Reduced proteins from tumor-conditioned ...
Sirois J, Kimmich TL, Fortune JE.Ovulation in mares is preceded by a long and variable estrous period. The differentiation of equine preovulatory follicles with respect to steroidogenic capacity and responsiveness to equine gonadotropins was studied by culturing pieces of follicle wall (FW = theca + attached granulosa cells) from preovulatory follicles isolated during late diestrus (day 14 of cycle, n = 5 mares), early estrus (1st-2nd day of estrus, n = 6) or late estrus (4th or 5th day of estrus, n = 6). FW was cultured with or without equine LH, FSH, LH + FSH, or CG (10 or 100 ng/ml) and medium was collected and replaced at...
Hinrichs K, Watson ED, Kenney RM.A functional corpus luteum was found in the ovary contralateral to the ovary with a granulosa cell tumor in a 24-year-old Standardbred mare. The mare was ovariectomized because she was to be used as a jump mare for collection of semen from stallions. The blood concentration of progesterone was 2.2 ng/ml, and the luteal tissue progesterone concentration was 6.3 micrograms/mg. Atrophy of the contralateral ovary is one of the major signs used in diagnosis of granulosa cell tumor; however, our findings indicate that the ovary contralateral to a granulosa cell tumor is not invariably nonfunctional....
Fenstermaker RA, Farmerie TA, Clay CM, Hamernik DL, Nilson JH.Expression of the glycoprotein hormone alpha-subunit gene occurs in the pituitaries of all mammals and in the placentas of primates and horses. In humans, tandem cAMP response elements (CREs), located in the proximal promoter-regulatory region of the alpha-subunit gene, act together with an adjacent upstream regulatory element to confer placenta-specific expression. Here, we report that the alpha-subunit genes of Old World Monkeys contain a single functional CRE. This suggests that tandem CREs are unique to higher primates and humans and are not absolutely required for placenta-specific expres...
Hyland JH, Langsford DA.Foetal death was induced in 10 Standardbred mares at day 45 of gestation by injecting 20 to 45 ml of hypertonic (24% W/V) saline into the conceptus at surgery. Ten mares underwent sham treatment and acted as controls. Blood and urine samples were collected every other day between days 30 and 45 post ovulation and at 0, 3 and 6 h relative to the infusion of saline in the treated mares, or sham treatment in control mares. Blood and urine samples were then collected daily between days 46 and 55 post ovulation. Urine oestrone sulphate (E1S) concentrations, measured by radioimmunoassay, increased b...
Martinuk SD, Bristol F, Murphy BD.Breeding trials were designed to determine the influence of the mare on serum concentrations of equine chorionic gonadotropin (eCG) from Day 39 to Day 104 of gestation. Sires were ranked according to mean eCG concentrations found in the groups of randomly selected mares to which they were mated in 1983. Mares were ranked according to their mean eCG concentrations on Days 55, 71 and 85 of gestation (Day 0 = mating), in 1983 and 1985. In the 1986 breeding season, mares that had pregnancies characterized by high eCG levels were mated to sires previously associated with low eCG concentration pregn...
Rabb MH, Thompson DL, Barry BE, Colborn DR, Hehnke KE, Garza F.Six pony geldings were actively immunized against GnRH conjugated to bovine serum albumin (BSA) to study 1) the relative dependency of LH and FSH storage, secretion and response to GnRH analog on GnRH bioavailability and 2) the effects of reduced GnRH bioavailability on GnRH storage in the hypothalamus. Five geldings were immunized against BSA. Geldings were immunized in December and 4, 8, 14, 20, 26 and 32 wk later. Ponies immunized against GnRH had increased (P less than .01) GnRH binding in plasma within 6 wk. By June, plasma concentrations of LH and FSH in ponies immunized against GnRH had...
Meinecke B, Gips H.The aim of the present investigations was to characterize the endocrine changes in the peripheral plasma during the periparturient phase of mares with a known history of obstetrical disorders. Blood plasma samples from 9 mares (8 mares during parturition, 1 mare during abortion) were collected and the following steroid hormones were radioimmunologically determined: progesterone (P4), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), estrone (E1), estrone sulfate (E1-S), estradiol-17 beta (E2), estriol (E3), cortisol and transcortin. In general, with the exception of corti...
Ginther OJ.Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequ...
Taylor PM.Information on the equine stress response to anaesthesia and surgery is sparse but offers a promising approach to elucidating the high anaesthetic risk in this species. Previous work has shown that halothane anaesthesia induces substantial metabolic and endocrine changes. This paper reports the effects of barbiturate anaesthesia. Anaesthesia was induced with thiopentone in six ponies and no further agents were given. They stood within 30 mins. On another occasion, these animals, and three further ponies, were anaesthetised with pentobarbitone and anaesthesia was maintained for 2 h. No surgery ...
Robertson SA, Steele CJ, Chen CL.The effect of general anaesthesia and arthroscopic surgery on blood glucose and lactate, plasma non-esterified fatty acids, insulin, beta-endorphin and cortisol was investigated in seven horses. Animals were premedicated with xylazine and anaesthesia was induced with guaifenesin and sodium thiamylal and maintained with halothane vaporised in oxygen. Blood samples were collected in the pre-, intra- and post operative period. Induction of anaesthesia was associated with a transient hyperglycaemia and a significant rise in plasma insulin levels. Plasma insulin values fell during surgery but showe...
McDonnell SM, Diehl NK, Garcia MC, Kenney RM.Twelve pony geldings with (n = 6) and without (n = 6) testosterone replacement (200 micrograms/kg testosterone propionate in oil, SC every 48 hours) received either gonadotropin releasing hormone (GnRH; 25 micrograms SC every 3 hours) or control treatment. Sexual behavior was recorded during 4-minute exposure to an estrous mare, 3 times weekly for 2 weeks before treatment, 3 weeks during treatment, and 3 weeks after treatment had been discontinued. The group receiving testosterone and GnRH (n = 3) exhibited significantly greater flehmen response frequency and attention duration and significant...
Jellyman JK, Allen VL, Forhead AJ, Holdstock NB, Fowden AL.The effects of overexposure to glucocorticoids during early life of the foal on the subsequent HPA programming of the hypothalamic-pituitary-adrenal axis are unknown. Objective: To test the hypotheses that excess glucocorticoid exposure in early life subsequently increases both basal plasma concentrations of cortisol and the adrenocortical responsiveness to exogenous adrenocorticotropic hormone (ACTH). Methods: Foals received either saline (0.9% NaCl, n = 9) or long-acting ACTH (0.125 mg i.m. b.i.d., n = 6) for 5 days from Day 1 to increase endogenous cortisol concentrations. Long-term indwell...
Ginther OJ, Siddiqui MA, Beg MA.Responses to intravenous treatment of mares with prostaglandin F2alpha (PGF) 8 d after ovulation were studied in three groups (n=4/group): control (no treatment), bolus (single treatment with 2.5 mg PGF), and infusion (0.1 mg PGF during 2 h). Infusion resulted in a 13,14-dihydro-15-keto-PGF2alpha (PGFM) concentration (559+/-44 pg/mL) that was not different from the mean concentration for the major portion of a natural PGFM pulse associated with luteolysis (569+/-45 pg/mL; n=5). Progesterone in the bolus group increased (P<0.03) between 0 (17.8+/-3.5 ng/mL) and 2 min (25.3+/-4.8 ng/mL), peak...
Kooistra LH, Ginther OJ.At day 24 of gestation, pregnant mares were allotted to 1 of 5 treatment groups (3 to 5 mares/group): group A--nontreated controls; group B--intraembryonic injection of 4 mg of colchicine on day 24; group C--removal of embryo on day 24; group D--subcutaneous injection of 1.25 mg of prostaglandin F2alpha (PGF2alpha) on day 32; and group E--removal of embryo on day 24 and subcutaneous injection of PGF2alpha on day 32. In all mares treated with colchicine (group B), the fetal bulge was absent within 2 days. The interval from injection of colchicine to onset of estrus was very short (mean, 4 days)...
Vischer CM, Foreman JH, Constable PD, Benson GJ, Kline KH, Freeman DE, Campbell KL, Grubb TL.To investigate hemodynamic effects of thyroidectomy in horses at rest. Methods: 6 healthy aged Quarter Horse mares. Methods: Horses were monitored for 5 months before and 4 weeks after thyroidectomy and for an additional 4 weeks after administration of thyroid hormone supplement (2.5 microg of thyroxine/kg of body weight, PO, q 12 h, and 0.6 microg of triiodothyronine/kg, PO, q 12 h). Responses to thyroid-stimulating hormone (TSH) were measured before and 4 weeks after thyroidectomy. Other variables monitored daily were resting rectal temperature (T), heart rate (HR), respiratory rate (RR), an...
Neely DP, Hughes JP, Stabenfeldt GH, Evans JW.Intrauterine saline infusion in the dioestrous mare shortened the ovulatory interval by inducing premature luteolysis. Plasma progestagen levels began to decrease approximately 1 day after the infusion and had declined to less than 1-0 ng/ml in 4 days. The CL, including others formed from ovulations during dioestrus, must be 4 to 5 days old before intrauterine saline will induce luteolysis. Of 10 mares infused on Day 4 or 5 after ovulation, only six had a shortened ovulatory interval. Of 10 mares infused on Day 6 or 7 after ovulation, seven had a shortened ovulatory interval and three failed t...
Porter MB, Cleaver BD, Peltier M, Robinson G, Sharp DC.Hourly pulses of gonadotropin-releasing hormone (GnRH) or bi-daily injections of estradiol (E2) can increase luteinizing hormone (LH) secretion in ovariectomized, anestrous pony mares. However, the site (pituitary versus hypothalamus) of positive feedback of estradiol on gonadotropin secretion has not been described in mares. Thus, one of our objectives involved investigating the feedback of estradiol on the pituitary. The second objective consisted of determining if hourly pulses of GnRH could re-establish physiological LH and FSH concentrations after pituitary stalk-section (PSS), and the th...
Figueras F, Castelo-Branco C, Pons F, Sanjuán A, Vanrell JA.The aim of the present study was to determine whether assignment to continuous estrogen-progestin therapy is more effective in protecting against bone loss than assignment to a sequential regimen. Methods: A total of 104 postmenopausal women were randomly assigned to one of two groups of treatment, Conjugated Equine Estrogens and Medroxyprogestin without interruption (continuous group) and Conjugated Equine Estrogens over 25 days with Medroxyprogestin beyond the 14th day (sequential group). Bone mineral density (BMD) was measured at inclusion, 12 and 24 months later by dual energy X-ray absorp...
Moudgal NR, Papkoff H.The ability of equine luteinizing hormone (eLH) to promote follicular growth and maturation in hypophysectomized rats has been assessed. A single injection of equine LH has been shown to promote the growth of a large number of antral and preovulatory follicles. In addition, equine LH markedly increased serum estrogen levels and uterine weight. Furthermore, equine LH, like equine chorionic gonadotropin (eCG; PMSG) was able to significantly enhance the incorporation of [3H]thymidine into ovarian DNA, an activity shown to be specific to hormones having follicle-stimulating hormone (FSH) activity....
Walker D.Rectal examination is a reliable method of diagnosing pregnancy in the mare. Also, test kits are available for the simple quick detection of pregnant mare serum gonadotrophin. Nevertheless there is a considerable demand by practitioners for an independent laboratory service in equine pregnancy diagnosis, particularly during the gestational phase when placental gonadotrophin is concentrated in the blood. An initial attempt to provide a service by means of the agar gel diffusion test was disappointing and alternatives were sought. The primary requirements for an ideal alternative technique were ...
Poskus E, Peña C, Pérez AR, Vita N, Heinrich JJ, Paladini AC.The immunological behavior of sera from hypopituitary patients treated with human GH (hGH) has been studied by homologous and heterologous RIAs using 125I-labeled hormones. Along with antibodies against hGH, antibodies exhibiting antibovine and antiequine GH (anti-bGH and anti-eGH, respectively) activities were also found. Displacement experiments showed that hGH was an effective competitor of 125 I-labeled hGH, whereas bGH and eGH were quite inefficient. Conversely, when the tracer was 125I-labeled bGH, both bGH and eGH were good displacers, while the human hormone was poor. The values of the...
Urwin V.Heterologous double-antibody radioimmunoassay were developed for the measurement of FSH and LH concentrations in the serum of both horses and donkeys. The FSH assay employed a rabbit anti-ovine FSH serum which showed a complete lack of cross-reaction with equine chorionic gonadotrophin (eCG) and negligible cross-reaction with equine LH. The LH assay utilized an antiserum raised against highly purified eCG. This similarly showed negligible cross-reaction with equine FSH but its high cross-reactivity with eCG prevented the measurement of equine LH concentrations in serum when eCG was also presen...
Squires EL, Hillman RB, Pickett BW, Nett TM.Thirty-two light-horse mares were confirmed to be pregnant and assigned to one of four treatments: (1) injected with 250 micrograms of Equimate on day 70 and again on day 77 if abortion had not occurred; (2) injected with 250 micrograms of Equimate on day 70 and every 24 hr until abortion occurred (maximum four injections); (3) injected with 250 micrograms of Equimate on day 70 and every 12 hr until abortion (maximum eight injections); and (4) injected with 250 micrograms of Equimate once only on day 35 of gestation. Mares were observed four times daily for incidence of abortion or side effect...
Hofferer S, Duchamp G, Palmer E.Twelve anoestrous mares were treated with an intravaginal sponge containing 0.5 g allyl trembolone (Regumate; Roussel UCLAF, Paris) and 50 mg oestradiol benzoate for 7 days, followed by daily intramuscular (i.m.) injections of 25 mg crude equine pituitary extract (CEG), with (n = 6) or without (n = 6) 0.25 mg porcine growth hormone (pGH). No difference in ovarian response to this superovulation treatment was observed between the 2 groups (2.2 +/- 0.4 vs 2.3 +/- 0.4 ovulations per mare, respectively). CEG treatment was then combined with allyl trembolone (40 mg per os per day) and prolonged in ...
Cuervo-Arango J.Flunixin meglumine (FM), a prostaglandin synthetase inhibitor, causes ovulatory failure in the mare. However, the effect of the FM treatment relative to the time of hCG administration on the ovulation failure has not been determined nor has its effect on the luteal function of treated mares. Estrous mares with a follicle ≥32 mm (range of 32-38 mm) were treated with 1.7 mg/kg b.w. of FM iv at zero, 12, 24 and 36 h (n=6), at 24 and 36 h (n=6), at 28 and 36 h (n=6), at 24h (n=6) or at 30 h (n=6) after treatment with 1500 IU hCG. One group received no FM (control, n=6). Progesterone concentratio...
Gastal EL, Gastal MO, Beg MA, Ginther OJ.The changing diameter interrelationships among follicles during the interval from emergence to deviation (common-growth phase) were studied in 59 mares. All follicles of > or =6.0 mm were ablated 10 days after ovulation. The four largest follicles of the postablation wave were ranked D1, D2, D3 and D4 at the expected beginning of deviation (D1 > or = 20.0 mm), according to descending diameter. The four follicles were also ranked independently, according to order of emergence at 6.0-6.9 mm as E1 (first to emerge), E2, E3 and E4. The follicles emerged during 1.3 +/- 0.1 to 3.1 +/- 0.1 days...
Ainsworth CG, Hyland JH.Continuous infusion of gonadotrophin releasing hormone (GnRH) has been shown to induce oestrus and ovulation in experimental mares in seasonal anoestrus. The present study sought to apply this form of treatment to anoestrous mares subjected to normal management procedures on 15 commercial Thoroughbred studfarms in Australia. The GnRH was delivered via subcutaneously implanted osmotic minipumps (OMP) at dose rates of 100 ng/kg/h and 200 ng/kg/h. The ovaries of treated mares were palpated on the day of OMP insertion (Day 0) and blood samples were collected twice weekly from a proportion of mares...
Watson ED, Aubrey ES, Zanecosky HG, Sertich PL.Glandular epithelial and stromal cells were isolated from the endometrium of mares by collagenase digestion and were incubated on plastic for 7-9 days until the cells formed confluent monolayers. The cells differed in morphology: epithelial cells appeared polyhedral and stromal cells were spindle like. The monolayers were incubated in the presence and absence of oxytocin. Medium was removed from wells after 2, 8 and 24 h of incubation. Concentrations of prostaglandin F (PGF) in the medium increased significantly during this time. Glandular epithelial cells produced significantly more PGF than ...
Lauderdale JW.Puberty: For the gilt and filly, the first corpus luteum (CL) appears to have a normal lifespan. For both species, first CL usually is associated with estrus but can form in the absence of estrus. For the ewe and cow, a transient (1 to 4 d, ewe; 3 to 10 d, cow) rise and fall of ovarian derived progesterone (P4) is detected in peripheral blood (80% of ewes; 50% of heifers) prior to first "normal" CL. The first CL of apparent normal lifespan is not accompanied by estrus in the ewe. The first CL in the cow may or may not be accompanied by estrus; first estrus in the cow can be anovulatory. Data a...
Han X, Fowden AL, Silver M, Holdstock N, McGladdery AJ, Ousey JC, Allen WR, Rossdale PD, Challis JR.An increase in fetal adrenal cortisol output signals the onset of parturition in many animal species but, in the fetal horse, plasma concentrations of cortisol remain low for much of late pregnancy, with a rise occurring only very close to the time of birth (term 320-360 days). Immunohistochemistry was used to determine the localisation and changes in distribution of key steroidogenic enzymes for cortisol production; P450scc, P450C17 and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in adrenal tissue from fetal and newborn horses and these findings were correlated with the appearance of imm...
Ginther OJ, Bergfelt DR.The temporal associations between increases in FSH and growth of small follicles (2-20 mm) were studied during one oestrous cycle (ovulation to ovulation) in 15 horse mares. Follicular diameters were obtained ultrasonically. For each day, follicles were combined for both ovaries, grouped from largest to smallest (excluding dominant follicles), and divided into three to five tiers of six follicles for each mare (for example: tier 1, six largest follicles; tier 2, next six largest follicles). A significant increase in mean diameters followed by a significant decrease was used to define a follicu...
Evans JW, Hughes JP, Neely DP, Stabenfeldt GH, Winger CM.Jugular blood samples were obtained from 8 mares at 5- and/or 20-min intervals for 2 to 5 days during various phases of the oestrous cycle for plasma LH determination. An episodic release pattern was observed in 1 of 3 mares sampled during the ovulatory period. One mare had one secretory burst and the other mare had several periods of fluctuating plasma LH concentration. During dioestrus, episodic secretions were observed in 2 mares sampled 11 to 13 days before and, in 1 mare, 9 days after ovulation. During the 2 to 5-day period before ovulation, episodic secretion was not observed (3 mares) b...
Bergfelt DR, Ginther OJ.In two experiments, PGF(2alpha) was given to all mares on Day 10 (ovulation = Day 0). In experiment 1, mares received either whole follicular fluid or saline i.v. every 12 hours on Days 10 to 14. Experiment 2 was similar to experiment 1, except the follicular fluid was extracted with charcoal to remove steroids. Analysis of the FSH data for Days 10 to 21 indicated an effect of treatment (P<0.08) with whole follicular fluid, but not with charcoal-extracted follicular fluid. However, there was an effect of day (P<0.05) and an interaction (P<0.01) of treatment with day for both experimen...
Morelli KG, Lourenço GG, Marangon VR, Feltrin IR, Imura Oshiro TS, Rodrigues da Silva IV, Pugliesi G.We aimed to evaluate the impact of corpus luteum (CL) and uterine characteristics accessed by B-mode and Color-Doppler ultrasonography in recipient mares at the time of embryo transfer (ET) on pregnancy outcomes. Recipient mares (n = 110), between days 3-9 after spontaneous ovulation, received a fresh embryo. Immediately before ET, the reproductive system was assessed by transrectal palpation for the following parameters: uterine tone (0-3), CL echogenicity (0-6), CL type (homogeneous, trabecular or anechoic center), luteal area (cm2), uterine echogenicity (0-3), uterine edema (0-3), luteal ...
Lauteri E, Mariella J, Beccati F, Roelfsema E, Castagnetti C, Pepe M, Peric T, Barbato O, Montillo M, Rouge S, Freccero F.Adrenal hormones, ACTH plasma concentrations and the ultrasonographic evaluation of the adrenal glands are considered complementary in clinical evaluations of the hypothalamic-pituitary-adrenal (HPA) axis function in several species. In dogs, age, size and weight have a significant effect on the ultrasonographic size of the adrenal glands. In neonatal foals, ultrasonographic evaluation and measurements of the adrenal glands have been demonstrated to be reliable; however, the effect of individual variables on ultrasonographic features has not been investigated, and the clinical usefulness of ad...
Huff NK, Thompson DL, Mitcham PB, Storer WA.Mares and geldings in good body condition selected for hyperleptinemia vs. normal leptin concentrations were studied to determine whether the hyperleptinemic condition affected various characteristics of the hematologic and hormonal systems after a challenge with lipopolysaccharide endotoxin. Four mares and 4 geldings that were determined to be hyperleptinemic (mean plasma leptin concentrations of 10.0 to 15.5 ng/mL) and 4 mares and 4 geldings with mean plasma leptin concentrations between 2.4 and 5.5 ng/mL were administered Escherichia coli O55:B5 endotoxin (35 ng/kg of BW in 500 mL of saline...
Linden A, Art T, Amory H, Desmecht D, Lekeux P.Seven sport horses were investigated to compare physiological and pharmacological stresses on the plasma glucocorticosteroid levels. Venous blood was sampled and analysed for cortisol concentrations before and after each type of stress. The physiological stress was induced by the completion of a cross-country and the pharmacological one, by an intravenous ACTH administration (200 micrograms) in the same horses, one week after the course. Both exercise and ACTH injection induced a highly significant cortisol increase of 79 +/- 0.10% and 160 +/- 0.18%, respectively. The relative plasma cortisol ...
Valenzuela OA, Jellyman JK, Allen VL, Niu Y, Holdstock NB, Forhead AJ, Giussani DA, Fowden AL, Herrera EA.Prenatal glucocorticoid overexposure has been shown to programme adult cardiovascular function in a range of species, but much less is known about the long-term effects of neonatal glucocorticoid overexposure. In horses, prenatal maturation of the hypothalamus-pituitary-adrenal axis and the normal prepartum surge in fetal cortisol occur late in gestation compared to other precocious species. Cortisol levels continue to rise in the hours after birth of full-term foals and increase further in the subsequent days in premature, dysmature and maladapted foals. Thus, this study examined the adult ca...
Goudet G, Bézard J, Belin F, Duchamp G, Palmer E, Gérard N.The in vitro maturation rate of equine oocytes remains low, regardless of culture conditions. Our objective was to determine the reasons for failure of equine oocytes to resume meiosis during in vitro maturation and to ascertain the influence of the estrous cycle stage on meiotic competence. In 10 cyclic mares, 7 ultrasound-guided follicular punctures were performed alternately during the follicular phase (group DF; n = 3 punctures), at the end of the follicular phase (group EF; n = 2), and during the luteal phase (group DL; n = 2). We evaluated the competence of the oocytes for in vitro matur...
Card CE, Manning ST.Fetal maturation and equine parturition are not understood fully, although the adrenal and thyroid glands are thought to have regulatory roles. Thyroidectomized equine fetuses undergo prolonged gestation, and spontaneous diseases such as thyroid musculoskeletal disease and gestational fescue endophyte exposure are also associated with delayed parturition. Thyroid musculoskeletal disease is characterized by: histologically hyperplastic thyroid glands, chondro-osseous dysplasia and dysgenesis, angular limb deformity, low resting thyroxine and triiodothyronine concentrations, and lack of response...
