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.
Aguilar J, Fraser HM, Wilson H, Clutton E, Shaw DJ, Watson ED.The temporal relationship between endothelial cell death, vascular regression and the death of hormone-producing cells in the mare has not been established. To determine the dynamics of cell proliferation and death throughout the luteal phase, corpora lutea were studied at the early, mid- and late luteal phase, and after treatment with cloprostenol in the mid-luteal phase to induce premature luteolysis. Changes in cell proliferation and apoptosis were investigated utilising specific markers (phosphorylated histone-3 and activated caspase-3 respectively). Histone-3 positive cells were most abun...
Bleul U, Theiss F, Rütten M, Kähn W.This case report describes a three-year-old Friesian stallion with hypospadias. Physical examination revealed a ventrocaudal deviation of the shaft of the penis and an incomplete glans penis. The urethral opening was 4 cm in length, slit-like and had a mucous membrane covering. A short fold ran from the ventral aspect of the anus and ended with a non-pigmented hairless area of skin. A human choriongonadotropin (hCG)-stimulation test resulted in an increase in the plasma levels of estrogen sulfate and testosterone, indistinguishable from that of a normal stallion. The karyogram had a normal num...
Gordon ME, McKeever KH.This study tested the hypothesis that grain and intravenous dextrose challenges would alter plasma concentrations of active ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in Standardbred mares. To deliver 0.5 g of glucose (dextrose solution for the intravenous test)/kg of BW, mares received intravenous dextrose (50% solution) or oral grain administration in 2 trials. In response to the oral grain challenge, plasma glucose and insulin concentrations increased (P < 0.001) by 56 and 802%, respectively. Plasma ghrelin concentration initially decreased (P < 0.001) by 40%, then s...
Imboden I, Janett F, Burger D, Crowe MA, Hässig M, Thun R.The aim of this study was to evaluate the effect of active immunization against GnRH on ovarian activity, plasma progesterone and estradiol concentrations and on estrous behavior in adult mares. Eighteen cyclic mares were randomly divided into a treatment and control group. Nine mares were immunized twice with 2 mL (400 microg GnRH-protein conjugate) of a GnRH-vaccine (Improvac, CSL Limited, Australia) administered intramuscularly, 4 weeks apart. Control mares received the same amount of saline solution. Ovaries and uterus of all mares were examined weekly by ultrasonography from 3 weeks befor...
Handler J, Hoffmann D, Weber F, Schams D, Aurich C.The aim of the present study was, to investigate the effects of oxytocin administration on Day 7 post-ovulation on progesterone secretion, pregnancy rate and embryonic growth in mares. Endogenous stimulation of oxytocin release was compared to the administration of native oxytocin or the long-acting oxytocin analogue carbetocin. At Day 7 after ovulation, mares had to undergo four treatments in a crossover design: (a) control, (b) oxytocin (10 IU i.v.), (c) carbetocin (280 microg i.m.) and (d) cervical dilation. On Day 13, all mares (8 of 8 mares) were pregnant on groups control, oxytocin and c...
Squires EL, McCue PM.Embryo recovery from single ovulating mares is approximately 50 per cent per estrous cycle. Superovulation could be used to increase embryo recovery and provide extra embryos for embryo freezing. This review addresses some historical approaches to superovulation, as well as examines factors that affect the response of mares to equine FSH. eCG, GnRH and inhibin vaccines have been of limited success in stimulating multiple ovulation. Numerous studies have shown that injection of equine pituitary extract (EPE) will result in three to four ovulations per estrous cycle and two embryos. A purified, ...
Bousquet-Mélou A, Formentini E, Picard-Hagen N, Delage L, Laroute V, Toutain PL.The present study aimed to characterize the adrenal response to ACTH. A model was developed that coupled the nonlinear disposition of cortisol with a physiologically based model for cortisol secretion by the adrenals. It was assumed that the response to ACTH resulted from two mechanisms: a stimulation of the cortisol secretion rate and control of the duration of the secretion. Seven dose levels of ACTH were tested in horses, a species similar to man as regards adrenal function. The main result was that the secretion rate of the adrenal gland can be modelized by a zero order process that is max...
Veronesi MC, Carluccio A, Kindahl H, Faustini M, Battocchio M, Cairoli F.The aim of the present study was to evaluate within 24 h post-ovulation oxytocin-induced PGF(2alpha) release in mares with and without post-breeding delayed uterine clearance (DUC). Twenty-one of 34 mares with a variable amount of intrauterine fluids accumulation were considered to be affected by delayed uterine clearance (DUC group), while the other 13 mares did not show any uterine fluid accumulation, and were considered as controls (WDUC group). Both DUC and WDUC mares were administered with 20 IU oxytocin i.m. 90 min after the ultrasound examination performed 24 h after breeding. Immediate...
Nogueira GP, Barnabe RC, Verreschi IT.We measured progesterone and estradiol levels from birth to the beginning of adult life in 10 Thoroughbred fillies from the Equilia Stud Farm in Avaré SP, Brasil. The animals were measured and weighed monthly for the determination of body development and of a possible correlation between the rate of weight and height gain and the onset of detectable sex hormone levels. Jugular blood was collected twice a week and stored at -20 degrees C until assay of progesterone by a solid phase RIA with a sensitivity of 0.32 nmol L and of estradiol by liquid phase RIA adapted to low levels (3.67 pmol L ). ...
Peltier MM, Peltier MR, Sharp DC, Ott EA.The objective of this study was to determine whether supplemental beta-carotene would influence reproductive function in mares maintained on spring and summer pastures and to characterize plasma carotene concentrations during the estrous cycle. Carotene concentrations in plasma did not vary with day of estrous cycle (P = 0.7455). Mares receiving every other day injections of beta-carotene (400 mg; n = 4) or saline (10 ml; n = 4) during proestrus/estrus did not differ in plasma estradiol (E(2)) concentrations (P = 0.6313), follicle development (P = 0.8068), or plasma progesterone (P(4)) concent...
Brown KA, Boerboom D, Bouchard N, Doré M, Lussier JG, Sirois J.Aldo-keto reductases (AKRs) are multifunctional enzymes capable of acting on a wide variety of substrates, including sex steroids. AKRs having 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity can reduce progesterone to 20alpha-hydroxy-4-pregnen-3-one (20alpha-DHP), a metabolite with lower affinity for the progesterone receptor. The objective of this study was to investigate the regulation of equine AKR1C23 during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine AKR1C23 cDNA was cloned and shown to encode a 322 amino acid protein that is conserved (71-81...
Ginther OJ, Gastal EL, Gastal MO, Utt MD, Beg MA.The temporal relationships between blood flow in the corpus luteum (CL) and circulating progesterone concentrations were studied in 20 mares. Retrospective inspection of plasma progesterone concentrations indicated that a precipitous decrease occurred during Days 15-17 (Day 0 = ovulation) and was defined as the luteolytic period. Mean percentage of CL with color-Doppler signals for blood flow was maximum on Day 10 (77.3%), and Days 10-14 (49.8%) were defined as the preluteolytic period. The cross-sectional area of the CL decreased progressively from Day 4 (9.0 cm2) to Day 19 (1.5 cm2). Progest...
McKinney AR, Suann CJ, Stenhouse AM.A method was developed for the analysis of the synthetic progestin 17alpha-hydroxyprogesterone caproate in equine plasma following its administration by intramuscular injection. The method employed a reversed-phase solid-phase extraction followed by enol-trimethylsilylation and analysis by gas chromatography/tandem mass spectrometry. The intact ester was detectable in the plasma for up to 2 weeks after a single therapeutic dose, and was found to be stable in equine whole blood for at least 2 months.
Frank N, Elliott SB, Brandt LE, Keisler DH.To compare obese horses with insulin resistance (IR) with nonobese horses and determine whether blood resting glucose, insulin, leptin, and lipid concentrations differed between groups and were correlated with combined glucose-insulin test (CGIT) results. Methods: 7 obese adult horses with IR (OB-IR group) and 5 nonobese mares. Methods: Physical measurements were taken, and blood samples were collected after horses had acclimated to the hospital for 3 days. Response to insulin was assessed by use of the CGIT, and maintenance of plasma glucose concentrations greater than the preinjection value ...
Zelli R, Sylla L, Monaci M, Stradaioli G, Sibley LE, Roser JF, Munro C, Liu IK.Granulosa-theca cell tumors (GTCTs) are able to secrete variable amounts of sex steroids and immunoreactive inhibin (ir-INH). Although the pituitary appears to be affected by the presence of a GTCT, pituitary responsiveness to exogenous GnRH has not been examined. The aims of the present study were to: (i) assess the plasma hormone concentrations of ir-INH, gonadotropins and sex steroids in eight mares with GTCT and (ii) assess the responsiveness of pituitary gonadotroph cells to exogenous GnRH stimulus both before and after tumor removal. In seven mares, the contralateral ovary was firm, smal...
Ginther OJ, Gastal EL, Gastal MO, Beg MA.The effect of a single injection of prostaglandin F2alpha (PGF) during mid-diestrus on systemic concentrations of progesterone, LH, FSH, estradiol, and cortisol and on blood flow to the corpus luteum was studied in 10 controls and 10 PGF-treated mares. Blood flow was assessed by estimating the percentage of corpus luteum with color-Doppler signals of blood flow during real-time scanning of the entire structure and by the diameter of the vascular pedicle near its attachment to the ovary. Treatment was done 8 days after ovulation and 0 h was immediately before the treatment. Examinations and col...
Roberto da Costa RP, Ferreira-Dias G, Mateus L, Korzekwa A, Andronowska A, Platek R, Skarzynski DJ.Nitric oxide (NO) plays an important role in angiogenesis and in the regulation of the blood flow. This study was carried out to investigate (i) the effects of endogenous estrogens and progestins and exogenous progesterone (P(4)) (5 ng/ml or 1 microg/ml) or estradiol 17beta (E(2)beta) (50 pg/ml or 1 microg/ml) on in vitro endometrial NO synthesis; (ii) the presence of different isoforms of NO synthase; (iii) and their relationship to microvascular density in the equine endometrium during the estrous cycle. NOS expression was also evaluated in the myometrium. Expression of endothelial and induc...
Handler J, Schönlieb S, Hoppen HO, Aurich C.In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 a...
Becker F, Kurth J, Schneider F, Nürnberg G, Heinrich H, Kanitz W.The aim of this study was to prove if oxidation-reduction levels in the follicular fluid were new functional indices of follicular health and whether there was a high level of accordance with endocrinological parameters and with the growth stage as detected by ultrasound monitoring of individual follicles during the oestrous cycle in mares. Follicles were classified as growing and regressing follicles using ultrasonography. Altogether 48 follicles with a diameter from 20 to 56 mm were aspirated by transvaginal ultrasound guided follicular aspiration. Follicular concentration of oestradiol and ...
Buff PR, Johnson PJ, Wiedmeyer CE, Ganjam VK, Messer Iv NT, Keisler DH.Horses fed beyond their nutritional requirement and that are physically inactive will develop obesity, which is often accompanied by insulin resistance and heightened risk of laminitis. The use of pharmacologic agents in combination with nutritional restriction may promote weight loss in obese horses unable to exercise because of laminitic pain. This study shows that reducing feed intake of brome grass hay to 75% of ad libitum intake in obese pony mares reduces body weight without induced exercise. Additional supplementation of ractopamine hydrochloride for 6 weeks resulted in a tendency for i...
Gastal EL, Gastal MO, Ginther OJ.A duplex grey-scale and colour-Doppler ultrasound instrument was used to study the changes in the wall of the preovulatory follicle in mares. When the follicle reached > or =35 mm (hour 0), mares were randomized into control (n = 16) and human chorionic gonadotropin (hCG)-treated (n = 16) groups. The hCG treatment was given at hour 0. Scanning was done every 12 h until hour 36, every hour between hours 36 and 48, and every 12 h thereafter until ovulation. Blood was sampled every 12 h for oestradiol assay. During the period 0-24 h post-treatment, oestradiol concentrations decreased in the hC...
Soma LR, Uboh CE, Luo Y, Guan F, Moate PJ, Boston RC.To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses. Methods: 6 Thoroughbreds. Methods: In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry. Results: A 5-compartment pharmacokinetic-pharmacodynamic model was used to des...
Waller CA, Thompson DL, Cartmill JA, Storer WA, Huff NK.Previous results from our laboratory indicated that a majority of mares with high body condition scores (BCS) displayed estrous cycles or had considerable follicular activity during the winter. Among these high BCS mares, about 35% of them exhibited a persistent hyperleptinemia and hyperinsulinemia. The current experiment was designed to compare the reproductive characteristics of high BCS mares with hyperleptinemia to those with normal (low) plasma concentrations of leptin during the winter and the first estrous cycle (or the first full cycle encountered for those already cycling). Light hors...
Kearns CF, McKeever KH, Malinowski K.Adipose tissue plays complex role(s) in metabolic and endocrine control. To date, little work has been done in the horse regarding adipocytokines. Objective: This study was conducted to determine whether therapeutic levels of chronic beta-agonist administration, exercise, or both could alter their concentrations. Methods: A total of 23 standard-bred mares were divided into four experimental groups: clenbuterol (2.4 microg.kg(-1) bw twice daily for 8 wk) plus exercise (8 wk, 20 min.d(-1) at 50% VO2max; CLENEX; N = 6), clenbuterol only (CLEN; N = 6), exercise only (EX; N = 5), and control (CON; ...
Parlevliet JM, Pearl CA, Hess MF, Famula TR, Roser JF.The presence of steroids and their receptors throughout development, specifically androgen receptor (AR), estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta), in the epididymis of a high estrogen producing species like the stallion has not been determined. Epididymal and testicular samples were collected for analysis of testosterone and estradiol-17beta (E(2)) concentrations and for immunolocalization of AR, ERalpha and ERbeta. The concentration of testosterone in the testis and epididymis were not different among age groups (P>0.05). AR was localized in the principal cell...
Romagnoli U, Macchi E, Romano G, Motta M, Accornero P, Baratta M.The aim of this work is to investigate on plasma profiles of leptin and estradiol 17beta during the interpartum period and leptin concentrations in the milk and in the colostrum during the period from parturition to the successive delivery in mare. Leptin plasma concentration varied from 5.1+/-2.3 ng/ml after the first parturition (week 0) to 3.0+/-0.7 at week 21 (p<0.05), then it increased to maximal level at week 49 (6.9+/-1.0 ng/ml, p<0.05). Leptin concentration in the colostrum and in the milk has been significantly (p<0.05) higher than that in plasma samples at week 1 (milk 8.8+/...
Gordon ME, McKeever KH, Betros CL, Manso Filho HC.Six Standardbred (STB) mares (11+/-2 years, 521+/-77 kg; means+/-SD) performed an exercise trial (EX) where they underwent an incremental exercise test (GXT) as well as a parallel control trial (CON) to test the hypothesis that short-term, high intensity exercise would alter plasma concentrations of glucose, leptin, adiponectin, ghrelin, insulin and cortisol. Plasma samples were taken before (0 min), during (last 10s at 6, 8m/s, and the velocity eliciting VO(2max)), and after exercise (2, 10, 30, 60 min; 12 and 24h post-GXT). A second set of blood samples was collected before and after an afte...
Utt MD, Acosta TJ, Wiltbank MC, Ginther OJ.The acute effects of prostaglandin F(2alpha) (PGF) on circulating oxytocin and progesterone concentrations were characterized in mares during the mid- or late-luteal phase. Pony mares were randomly assigned to the following experimental groups based on treatment with PGF (2.5mg) or saline on Day 8 or Day 13 (Day 0=ovulation): PGF-8, PGF-13, saline-8, or saline-13 (n=7/group). Mares were fitted with indwelling, jugular vein catheters and two blood samples (-5 and 0 min) were collected prior to treatment. Treatments were administered into the jugular vein (0 min) and blood collection continued t...
Kanitz W, Schneider F, Hoppen HO, Unger C, Nürnberg G, Becker F.The aim of the study was to investigate the effect of the GnRH agonist Buserelin given on day 10 after ovulation on pregnancy rate and concentrations of progesterone and LH. Altogether 191 warmblood mares were used for two trials. Fresh or frozen/thawed semen from 27 stallions was used for A.I. In trial A 171 mares received either Buserelin (Receptal, Hoechst, Germany, 40 microg/animal) or 10 ml 0.9% NaCl (placebo). On day 16 after A.I. pregnancy diagnosis was performed by ultrasound scanning of the uterus. For statistical analysis, data were analyzed by a mixed model, with four fixed factors ...
Matlina E.The investigation of catecholamine (CA) metabolism in animals subjected to various types of stress (different pain syndromes; cranial trauma; immobilization; cooling) and physical exercise shows considerable similarity among species in the sequence of changes, leading from the activation to the depletion of the sympathoadrenal system. The changes caused by physical exercise tend to be more pronounced in individuals with a genetic predisposition to greater stress responses. Stress adaption, induced by special training or by long-duration exposure to hypoxia, can substantially prevent the change...
Guillaume D, Rio N, Toutain PL.The aims of the present study were to determine basic kinetic parameters and the nycthemeral production rate of melatonin in the horse. Seven pony mares were used for the kinetic studies. Five other pony mares were used under long and short days for the production rate studies. Melatonin was administered by intravenous, oral, and intragastric routes at different dose levels. The plasma melatonin clearance was 1.02 +/- 0.31 l.kg-1.h-1, and the volume of distribution was 0.89 +/- 0.53 l/kg for the 0.4 microgram/kg melatonin dose. The systemic availability after oral and intragastric administrati...
Brito LF, Baldrighi JM, Wolf CA, Ginther OJ.The objective of the present study was to investigate the effect of reproductive hormones (GnRH, hCG, LH and progesterone) on the regulation of corpus luteum (CL) and ovarian blood flow. Diestrous mares received a single treatment of saline, 100μg gonadorelin (GnRH), or 1500IU hCG 10days after ovulation. Plasma LH and progesterone concentrations, resistance index (RI) for ovarian artery blood-flow, and percentage of corpus luteum (CL) with color-Doppler signals of blood flow were determined immediately before treatment (hour 0) and at hours 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, and 6. In the GnRH gr...
Jöchle W, Irvine CH, Alexander SL, Newby TJ.Nine mares received cannulae to collect blood from the pituitary venous outflow in the intercavernous sinus (ICS) and the jugular vein; in 4 mares, only jugular cannulae were used. Those 4 mares and 3 of the mares with cannulae in both positions received 7.5 mg luprostiol i.m. and 1 mare with both cannulae was treated with 3.75 mg uprostiol i.v. Blood samples were kept before and after treatment at 2-, 5- or 10-min intervals and concentrations of LH, FSH and GnRH were determined by RIA. Treatments resulted in an immediate sharp rise of LH and FSH in ICS and jugular blood samples within 2-10 mi...
Thompson DL, DePew CL.This experiment was designed to determine 1) the efficacy of daily s.c. injections of a dopamine antagonist, sulpiride, for increasing prolactin secretion in geldings in winter and 2) whether increasing prolactin concentrations would hasten the onset of hair shedding or enhance gonadotropin secretion. Five geldings each received vehicle (vegetable oil) or sulpiride (100 mg in vehicle) daily from February 8 through March 29. On February 8 and every 7 d thereafter through March 29, blood samples were drawn around treatment injections and hair samples were collected. On March 30, all geldings rec...
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 ...
Botelho JH, Pessoa GO, Rocha LG, Yeste M.The present research sought to determine whether the administration of estradiol benzoate and long-acting progesterone to anovulatory recipient mares could maintain the pregnancy after embryo transfer during the autumn transitional phase. Recipient mares (n = 40) received the hormonal supplementation (treated group) whereas the other 36 served as a control. The control group consisted of mares having typical estrous cycles with ovulations, development of a viable corpus luteum and received one transferred embryo 5 days after ovulation. Hormonal administrations in the treated group started 8 da...
Engle CC, Foley CW.Uterine tubal fluids were collected twice a day from mares for 5 consecutive estrous cycles between March 15 and September 1. Follicular fluids were aspirated from the follicles of exteriorized ovaries of 3 mares between days 2 and 5 of estrus. Uterine tubal fluid and follicular fluid were analyzed for osmolarity, dry matter, total lipids, total free fatty acids, glucose, fructose, and lactic acid. Blood samples were collected (jugular venipuncture) throughout the estrous cycle, and the same physical and biochemical analyses were made on blood plasma. A difference (P less than 0.01) was found ...
Mazerbourg S, Zapf J, Bar RS, Brigstock DR, Monget P.We recently showed that insulin-like growth factor-binding protein-4 (IGFBP-4) proteolytic degradation in ovine preovulatory ovarian follicles is IGF-dependent and regulated by the heparin-binding domain (HBD) from IGFBP-3 and from connective tissue growth factor (CTGF), heparan/heparin-interacting protein (HIP), and vitronectin. The present study investigated regulation of IGFBP-4 proteolytic degradation in porcine, bovine, and equine ovarian preovulatory follicles. Follicular fluid from such preovulatory follicles contains proteolytic activity, degrading exogenous IGFBP-4. An excess of IGF-I...
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 ...
Miki W, Oniyama H, Takeda N, Kimura Y, Haneda S, Matsui M, Taya K, Nambo Y.We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus wer...
Martoriati A, Duchamp G, Gérard N.Paracrine factors have significant effects during folliculogenesis. Because of various morphological features, the mare is a convenient model to study in vivo the effects of factors involved in periovulatory events. In the present work, epidermal growth factor (EGF; experiment 1, n = 49 mares) and interleukin-1beta and interleukin-1RA (IL-1beta and IL-1RA, respectively; experiment 2, n = 80 mares) were injected intrafollicularly to evaluate the influence of these factors on in vivo maturation of equine preovulatory follicles. A transvaginal ultrasound-guided injection was performed when the di...
Stewart F, Allen WR.Gonadotrophin-receptor binding studies involving the use of 125I-labelled highly purified FSH and LH have shown that equine gonadal tissues possess similar numbers of specific FSH and LH receptors per cell as the gonadal tissues of other mammals. However, while rat, cow and pig gonadal tissues were shown to bind as much 125I-labelled PMSG as 125I-labelled LH on a molar basis, the equivalent equine tissues bound only less than or equal to 4% as much of the labelled PMSG as LH. Competitive binding studies involving the use of radioreceptor assay techniques have further demonstrated that the smal...
Vogelsang MM, Kreider JL, Bowen MJ, Potter GD, Forrest DW, Kraemer DC.A series of experiments was conducted to develop a procedure for consistent, repeatable collection of oocytes from the preovulatory follicle of the mare. In one experiment, in situ follicular aspiration with a needle and syringe was performed on 19 mares. From 37 aspirations, four oocytes were recovered (10% recovery rate). In a second experiment, ovaries were visualized via standing flank laparotomy during which two different aspiration techniques were used. Use of a needle and syringe as in the first experiment resulted in successful oocyte recovery in one of seven (14%) attempts. Aspiration...
Neuhauser S, Palm F, Ambuehl F, Möstl E, Schwendenwein I, Aurich C.Mares with compromised pregnancies are often treated with altrenogest to prevent abortion. However, there is only limited information about effects on the foal when altrenogest treatment is continued during final maturation of the fetus. Objective: To determine effects of altrenogest treatment during late gestation in mares on maturity, haematology changes, adrenocortical function and serum electrolytes in their newborn foals. Methods: Six mares were treated with altrenogest (0.088 mg/kg bwt) once daily from Day 280 of pregnancy until foaling and 7 mares served as controls. Results: Foals born...
Dolin A, Schweiger P, Waselau M, Egerbacher M, Walter I.Sex cord-stromal tumors (SCSTs), generally referred to as granulosa cell tumors (GCTs) or granulosa-theca cell tumors (GTCTs) in equids, show complex compositions and variable numbers of hormone-producing cells. These tumors can be difficult to diagnose, especially in early stages. Therefore, we tested a panel of antibodies for vimentin, smooth muscle actin, laminin, Ki-67, E-cadherin, calretinin, moesin, p-ezrin, AMH, and aromatase, markers used for tumor composition and classification, progression, and prognosis in human SCSTs, on an exemplary grapefruit-size equine GCT within the left ovary...
Schmidt O, Deegen E, Fuhrmann H, Dühlmeier R, Sallmann HP.The aim of this study was to investigate the influence of a fat-supplemented diet compared with a carbohydrate diet on the lipid metabolism and the enteroinsular axis of Shetland ponies. The 'crossover' experiment was divided into two parts: in the first 10 weeks the diets comprised the correct number of calories according to requirements and in the following 10 weeks they were hypercaloric, in order to check the effect of a different energy content of the diets. Feeding the fat-enriched diet, independently of its energy content, led to a significant decrease in plasma triglycerides, associate...
Smyth GB, Young DW, Hammond LS.Gastrin is the only hormone known to stimulate secretion of hydrochloric acid. It also has trophic effects on specific parts of the mucosa of the gastrointestinal tract. Using radioimmunoassay techniques, postprandial serum gastrin and insulin concentrations were measured in six adult horses to establish effects of different diets on gastrin concentrations. Insulin concentrations were measured to provide support to the patterns of gastrin secretion because patterns of insulin secretion were already known. The horses were fed coastal bermuda hay, or twice daily 5 kg of a complete pelleted ratio...
Panzani S, Villani M, McGladdery A, Magri M, Kindahl H, Galeati G, Martino PA, Veronesi MC.Information regarding the plasma hormone profiles of prostaglandins (PGs), cortisol (C), and progesterone (P4) during pathologic processes in newborn foals is scarce. The aim of this study was to determine the plasma concentrations of these hormones in diseased foals (n=40) and healthy at-term foals (n=24) (Equus caballus) during the first 2 weeks of life. Blood samples were collected daily, before any treatment with nonsteroidal drugs in diseased foals, and plasma was analyzed by radioimmunoassay. 15-Ketodihydro-PGF(2alpha) (PGM) was consistently higher in diseased foals than in healthy foals...
Watson ED, Thomassen R, Steele M, Heald M, Leask R, Groome NP, Riley SC.Dominant and subordinate follicles were collected from mares on the day after the dominant follicle reached 30 mm in diameter, to investigate regulation of folliculogenesis during spring transition and the breeding season. Concentrations of oestradiol-17beta, progesterone and inhibin A, but not inhibin isoforms with pro- and alpha C-immunoreactivity, were significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. Steroidogenic activity was regained gradually in the dominant follicles of successive anovulatory waves through spring transition. The dominan...
Messer NT, Johnson PJ, Refsal KR, Nachreiner RF, Ganjam VK, Krause GF.Six healthy, adult horses, with normal (mean +/- SEM) baseline serum concentrations of total triiodothyronine (T3, 1.02 +/- 0.16 nmol/L), free T3 (FT3, 2.05 +/- 0.33 pmol/L), total thyroxine (T4, 19.87 +/- 1.74 nmol/L), free T4 (FT4, 11.55 +/- 0.70 pmol/L), total reverse T3 (rT3, 0.68 +/- 0.06 nmol/L), and cortisol (152.75 +/- 17.50 nmol/L), were judged to be euthyroid on the basis of response to a standardized thyroid-stimulating hormone response test. Serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol were determined immediately before and every 24 hours during a 4-day period of foo...
Nathanielsz PW, Rossdale PD, Silver M, Comline RS.Fetal plasma cortisol concentrations (mean +/- S.E.M.) in ten animals with indwelling umbilical catheters ranged from 13-9 +/- 1-5 ng/ml (227 to 244 days) to 18-1 +/- 2-2 ng/ml (290 to 310 days). Maternal values did not change over this period (15-9 +/- 1-7 ng/ml). Fetal cortisol production rates in two fetuses were 3-6 and 3-8 mg/kg/day at 291 days; there was little placental transfer of cortisol. In three fetuses (319 to 321 days) plasma cortisol values 1 to 10 days before birth were higher (30 to 50 ng/ml) than in any other group, and at birth the values were comparable with those found in ...
Douglas RH, Ginther OJ.In experiment 1, seven groups of pony mares (2 or 3/group) were given either no injections (controls), or 5 (5X) or 10 (10X) daily subcutaneous (SC) injections of 1.25 mg PGF2alpha beginning on days 1, 7 or 13 post-ovulation. Compared to controls (24.5 days), the interovulatory interval was longer (P less than ..05) for day 7, 10X (33.5 days) and day 13, 10X mares (49.0 days) but was not different for the remaining groups. In experiment 2, nine groups of pony mares (4/group) were given either no injections (controls) or 1 (1X) or 10 (10X) daily SC injections of 1.25 mg PGF2alpha beginning on d...
Ing NH, Brinsko SP, Curley KO, Forrest DW, Love CC, Hinrichs K, Vogelsang MM, Varner DD, Welsh TH.Testicular steroidogenesis and spermatogenesis are negatively impacted by stress-related hormones such as glucocorticoids. The effects of two injections of a therapeutic dose of dexamethasone (a synthetic glucocorticoid, 0.1mg/kg; i.v.) given 24h apart to each of three stallions were investigated and compared to three saline-injected control stallions. Dexamethasone decreased circulating concentrations of cortisol by 50% at 24h after the initial injection. Serum testosterone decreased by a maximum of 94% from 4 to 20h after the initial injection of dexamethasone. Semen parameters of the dexame...
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...
Korosue K, Murase H, Sato F, Ishimaru M, Harada T, Watanabe G, Taya K, Nambo Y.The purpose of this study was to demonstrate that a barren parous Thoroughbred mare with lactation induced by hormonal treatment can be introduced to an orphan foal at the same farm and that the mare can become pregnant after the end of the hormonal treatment. An additional purpose was to investigate the changes in the plasma concentrations of prolactin, estradiol-17β, progesterone, follicle-stimulating hormone, and luteinizing hormone before, during, and after hormonal treatment. The difference in body weight between the adopted foal and the control foals, which were at the same farm and rai...
Castro T, Oliveira FA, Siddiqui MA, Baldrighi JM, Wolf CA, Ginther OJ.A study was performed on the effect of a single dose per mare of 0 (n = 9), 100 (n = 8), or 300 (n = 9) of GnRH on Day 10 (Day 0 = ovulation) on concentrations of LH, FSH, and progesterone (P4) and blood flow to the CL ovary. Hormone concentration and blood flow measurements were performed at hours 0 (hour of treatment), 0.25, 0.5, 1, 2, 3, 4, and 6. Blood flow was assessed by spectral Doppler ultrasonography for resistance to blood flow in an ovarian artery before entry into the CL ovary. The percentage of the CL with color Doppler signals of blood flow was estimated from videotapes of real-t...
Messer NT, Ganjam VK, Nachreiner RF, Krause GF.The effect that 5 consecutive days of treatment with dexamethasone (0.04 mg/kg of body weight, IM, q 24 h) would have on baseline concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3), free T3 (FT3), and free T4 (FT4), and on response to thyroid-stimulating hormone (TSH) administration was determined in 12 clinically normal horses. Results of TSH response tests indicated that the horses could be placed into 2 groups: in 6 horses (group A), T4 concentration after administration of TSH was more than twice the baseline concentration; in the other 6 horses (group B), T4 concent...
Yoon MJ, Roser JF.Localization of IGF-I and IGF-IR were observed in Leydig cells of horses using immunohistochemistry (IHC), suggesting IGF-I may play a role in equine Leydig cell steroidogenesis. Previous studies in other species have indicated that IGF-I increases basal and/or LH/hCG-induced testosterone production. The objectives of this study were to (1) test the synergistic effect of IGF-I on eLH-induced testosterone production in cultured equine Leydig cells and (2) determine if this effect is reproductive stage-dependent. Testes were collected from five pubertal (1.1±0.1 year; 1-1.5 year) and eight post...
Cartmill JA, Thompson DL, Storer WA, Crowley JC, Huff NK, Waller CA.Three experiments tested the hypotheses that daily cortisol rhythm, feeding time, and/or insulin infusion affect(s) leptin secretion in stallions. Ten mature stallions received ad libitum hay and water and were fed a grain concentrate once daily at 0700. In Exp. 1, stallions received either a single injection of dexamethasone (125 microg/kg BW i.m.; n = 5) or vehicle (controls; n = 5) at 0700 on d -1. Starting 24 h later, blood samples were collected every 2 h for 36 h via jugular venipuncture. Cortisol in control stallions varied (P < 0.01) with time, with a morning peak and evening nadir;...
