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, Rodriguez MB, Beg MA.The temporal relationship of several hormones to a metabolite of prostaglandin F2α (PGFM) was studied in mares and heifers from the beginning of the first PGFM pulse during luteolysis to the end of the second pulse. Mares (n=7) were selected with a 9-h interval between the peaks of the two pulses. In mares, estradiol-17β (estradiol) increased (P<0.05) within each PGFM pulse and plateaued for a mean of 6h between the pulses, resulting in a stepwise estradiol increase. Progesterone decreased linearly (P<0.0001) throughout the intra-pulse and inter-pulse intervals of PGFM. In heifers (n=6...
Mozzaquatro FD, Verstegen JP, Douglas RH, Troedsson MH, Delacorte FD, Silva CA, Rubin MI.Ultrasound-guided follicular aspiration was performed in 26 Criollo crossbred mares, followed by the evaluation of ultrasonographic images of the Corpus luteum (CL) that was formed after puncture of follicles of different diameters (Group 25-29 mm; Group 30-35 mm and Group >35 mm). Serum progesterone (P(4) ) concentrations were measured to determine CL function. The size of the CL was measured and the CL was classified based on the following echoscore: 1- anechoic tissue; 2- poorly defined luteal structure with low echogenicity; 3- echogenicity analogous to a luteal structure. The proport...
Ginther OJ, Pinaffi FL, Silva LA, Beg MA.Hourly blood samples were collected from 10 mares during 24 h of each of the preluteolytic, luteolytic, and postluteolytic periods. The autocorrelation function of the R program was used to detect pulse rhythmicity, and the intra-assay CV was used to locate and characterize pulses of prolactin (PRL) and a metabolite of prostaglandin F2α (PGFM). Rhythmicity of PRL and PGFM concentrations was detected in 67% and 89% of mares, respectively. Combined for the three periods (no difference among periods), the PRL pulses were 5.2±0.4 h (mean±SEM) at the base, 7.5±1.5 h between nadirs of adjacent p...
Copas VE, Durham AE.Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy, frequently diagnosed via plasma adrenocorticotropic hormone (ACTH) concentrations. Seasonal variation in plasma ACTH concentrations has been described in normal horses prompting caution in diagnosing PPID at certain times of the year. The aims of this study were to determine appropriate reference intervals for equine plasma ACTH throughout the year; and to examine the circannual variation of plasma ACTH concentrations in PPID cases. Objective: Plasma ACTH can be used as a test for PPID throughout the year with the use of ...
Evans MJ, Alexander SL, Irvine CH, Kitson NE, Taylor TB.The GnRH antagonist cetrorelix was given during the early (Days 1-5), mid (Days 6-10 or 5-12) or for the entire (Days 1-16) luteal phase of mares to inhibit the secretion of FSH and LH (Day 0=ovulation). Frequent blood sampling from Day 6 to Day 14 was used to determine the precise time-course of the suppression (cetrorelix given Days 6-10). Cetrorelix treatment caused a decrease in FSH and LH concentrations by 8 and 16 h, respectively, and an obliteration of the response to exogenous GnRH given 24h after treatment onset. Treatment never suppressed gonadotropin concentrations to undetectable l...
Satué K, Domingo R, Redondo JI.The coordinated interaction of the components of the renin angiotensin aldosterone system (RAAS) with reproductive hormones such as progesterone, oestrogens and cortisol during pregnancy has been widely reported to play a vital role in foetal and placental development in various species, significantly influencing the proper achievement of pregnancy and foetal viability at birth. These interactions have not yet been clarified in mares. Thus, the purpose of the present research was to analyse the relationship between cortisol (CORT), progesterone (P4) and oestrone sulphate (OESTRONE), and the co...
Crabtree J.This paper reviews the equine granulosa cell tumour (GCT) and describes the clinicopathological features, treatment and outcome in seven cases of GCT in mares. Mares were presented with unilateral ovarian enlargement during the 2007 to 2010 breeding seasons. The mean (sd) age of the mares was 11.7 (5.96) years. Three mares were multiparous barren, three were nulliparous and one was primigravida. Behaviour at presentation was 57 per cent anoestrus, 28 per cent with stallion-like behaviour and 14 per cent with persistent oestrus. All mares had unilateral ovarian enlargement. Six non-pregnant mar...
Saint-Dizier M, Foulon-Gauze F, Lecompte F, Combarnous Y, Chopineau M.In order to investigate the role of the unique seventh N23-glycosylation site of the equine LH/CG receptor (eLHCGR) in the cAMP pathway activation, COS-7 cells were transiently transfected with either the wild-type or the mutant eLHCGR(N23Q) cDNA and challenged with porcine LH and eCG for cAMP production. We showed that the N23-glycosylation site of the eLHCGR is not required for the functional coupling of the receptor with the cAMP pathway and is not responsible for the limited potency of eCG relative to pLH to activate this receptor.
Almeida J, Ball BA, Conley AJ, Place NJ, Liu IK, Scholtz EL, Mathewson L, Stanley SD, Moeller BC.Anti-Müllerian hormone (AMH), a member of the transforming growth factor β superfamily of growth and differentiation factors, is expressed in granulosa cells of preantral and small antral ovarian follicles. In humans, AMH appeared to regulate recruitment and growth of small ovarian follicles. Furthermore, circulating AMH concentrations were elevated in women with granulosa-cell tumors (GCT). In the horse, GCTs are the most common tumor of the ovary, and a variety of endocrine assays have been used to diagnose presumptive GCTs. The objectives of the present study were to validate a heterologo...
Pereira GR, Lorenzo PL, Carneiro GF, Ball BA, Gonçalves PB, Pegoraro LM, Bilodeau-Goeseels S, Kastelic JP, Casey PJ, Liu IK.The objective of this study was to test the hypothesis that equine growth hormone (eGH), in combination with insulin growth factor-I (IGF-I), influences positively in vitro nuclear and cytoplasmic maturation of equine oocytes. Cumulus-oocyte complexes were recovered from follicles that were < 25 mm in diameter, characterized by morphology and were allocated randomly as follow: (a) control (no additives); (b) 400 ng/ml eGH; (c) 200 ng/ml IGF-I; (d) eGH + IGF-I; and (e) eGH + IGF-I + 400 ng/ml anti-IGF-I antibody. Oocytes were matured for 30 h at 38.5°C in air with 5% CO2 and then stained wi...
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...
Ginther OJ, Hannan MA, Beg MA.The changing concentrations and temporal relationships among a PGF2α metabolite (PGFM), progesterone (P(4)), LH, and estradiol-17β (E(2)) before, during, and after luteolysis were studied in 10 mares. Blood samples were collected every hour for ≥4 d beginning on day 12 after ovulation. The luteolytic period extended from a decrease in P(4) at a common transitional hour (Hour 0) at the end of preluteolysis and beginning of luteolysis to a defined ending when P(4) reached 1 ng/mL. The length of luteolysis was 22.9 ± 0.9 h, contrasting with 2 d in published P(4) profiles from sampling every ...
Dhakal P, Tsunoda N, Nakai R, Kitaura T, Harada T, Ito M, Nagaoka K, Toishi Y, Taniyama H, Gen W, Taya K.Changes in follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, immunoreactive(ir)-inhibin, testosterone, estradiol-17β, and insulin-like growth factor (IGF)-I in Thoroughbred stallions along with changes in prolactin secretion in geldings were studied. The correlations of day-length with changes in the concentrations of these hormones were also studied. Five stallions and thirteen geldings were employed to draw blood samples in monthly basis and radioimmunoassay was performed to measure these hormones. All hormones showed a seasonal pattern, the levels being highest durin...
McFarlane D, Paradis MR, Zimmel D, Sykes B, Brorsen BW, Sanchez A, Vainio K.Plasma α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropin (ACTH) concentrations in horses vary with season, confounding diagnostic testing for pituitary pars intermedia dysfunction (PPID). Objective: The goals of this study were to determine whether seasonal variation in plasma α-MSH and ACTH concentrations in horses is influenced by geographic location, breed, or PPID. Methods: Healthy light breed horses residing in Florida, Massachusetts, and Finland (n = 12 per group); healthy Morgan horses (n = 13); healthy ponies (n = 9) and horses with PPID (n = 8). Methods: Monthly plas...
Derar DR, Taya K, Watanabe G, Miyake YI.The aim of this study was to characterize ir-IGF-I pattern and its relation to other hormones during the oestrous cycle in mares. Nine non-pregnant non-lactating pluriparous thoroughbred mares were used. The studied mares were examined ultrasonically and bled daily to follow the ovarian changes and the hormonal milieu for a complete Interovulatory interval (IOI). Two (minor and major) follicular waves were characterized per IOI in thoroughbred mares. The largest follicle of the first follicular wave (DF1) was firstly detected at D - 1.75 ± 0.47 with a growth rate of 2.78 ± 0.14mm/day and max...
Ayala I, Martos NF, Silvan G, Gutierrez-Panizo C, Clavel JG, Illera JC.No detailed comparative data are available on the hormonal parameters of horses suffering from a number of diseases. The aim of our study was to measure concentrations of cortisol, adrenocorticotropic hormone (ACTH), serotonin, adrenaline and noradrenaline in horses with various diseases and following surgery, to assess the response of the HPA axis and adrenal medulla. Blood samples were obtained from six groups of horses comprising a total of 119 animals as follows: laminitis, acute abdominal syndrome (AAS), castration surgery, acute diseases, chronic diseases and healthy controls. Serum horm...
Ousey JC, Kölling M, Kindahl H, Allen WR.The foal requires an active hypothalamo-pituitary-adrenal (HPA) axis for organ maturation and post natal survival. Prenatal administration of synthetic glucocorticoids may provide an effective method for inducing fetal maturation safely in the mare. Objective: To determine whether dexamethasone administered to late pregnant mares: 1) will induce fetal maturation and precocious delivery; 2) is safe to use and 3) to identify endocrine responses in the mare and foal. Methods: Pregnant Thoroughbred mares received either 100 mg dexamethasone i.m. (treated n = 5) or 50 ml saline i.m. (control n = 5)...
Cravana C, Medica P, Prestopino M, Fazio E, Ferlazzo A.Limited knowledge exists about the differentiated effects of competitive and noncompetitive showjumping on thyroid function and relationships with hypothalamic-hypophysis-corticoadrenal hormones. Objective: To obtain preliminary data about differentiated effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol of horses. Methods: Five trained healthy jumper horses were studied during competitive and noncompetitive showjumping, performed in the same circuit design over 10 fences of 1.10 m. Hormone levels before, 5 and 30 min post ex...
Ferlazzo A, Medica P, Cravana C, Fazio E.Involvement of thyroid function on performance warrants further investigation as limited data exists on the effects of showjumping on the dynamics of total and free iodothyronines. Objective: To investigate the response of circulating total and free iodothyronines in horses to experimental showjumping sessions and compare with the effects normally induced by competition and determine if fence height has any effect. Methods: Using a randomised crossover study design 6 trained horses were studied during experimental showjumping sessions over 10 fences of different height: 1.00 m (Session 1), 1.1...
Finno CJ, McKenzie E, Valberg SJ, Pagan J.Recurrent exertional rhabdomyolysis (RER) occurs in fit, nervous Thoroughbreds fed high nonstructural carbohydrate (NSC) diets. Clinical signs are diminished by feeding low NSC, high fat diets; however, the mechanism is unclear. Objective: To determine if the glucose, insulin and cortisol response to isocaloric diets varying in fat and NSC availability differ in fit vs. unfit Thoroughbreds with RER. Methods: Four fit (10 weeks treadmill training) RER Thoroughbred mares were exercised and fed 3 isocaloric (121 MJ/day) diets in a 5 day/diet block design. Two high NSC concentrates, sweet feed (SF...
Leleu C, Haentjens F.The demands in the Standardbred trotters industry require young, still growing horses, to be trained well above light exercise level. During that period, the risk of occurrence of energy imbalance and maladaptation to training is high. In man, the lack of energy homeostasis is considered as the basic problem in the development of chronic fatigue. Objective: To find objective biomarkers of early maladaptation to training in young racehorses under field conditions. Methods: Sixty-five 2-year-old Standardbreds were followed during their first 3 months of training in 5 different training centres. ...
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...
Panzani S, Carluccio A, Probo M, Faustini M, Kindahl H, Veronesi MC.The aim of this study was to compare the plasma profiles of 15-ketodihydro-PGF(2α) (PGM) in healthy neonates of three different species from birth until the third week of life. Twenty-four horse foals, 12 donkey foals, and 9 calves were studied. Blood samples were collected at 10, 20 and 30 min after birth, at 3, 24 and 72 h after birth, and at 7, 10, 17 and 21 days of life. All mothers experienced normal gestation lengths and normal, spontaneous deliveries. All newborns were judged mature and viable. Hormone concentrations were higher (p < 0.05) in horse foals 20 and 30 min after birth compa...
Beech J, McFarlane D, Lindborg S, Sojka JE, Boston RC.To compare endogenous ACTH and α-melanocyte-stimulating hormone (α-MSH) concentrations after administration of thyrotropin-releasing hormone (TRH) and to compare ACTH concentrations after TRH administration with those following domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction (PPID). Methods: Prospective case series. Methods: 69 clinically normal horses and 47 horses with or suspected to have PPID. Methods: ACTH concentrations were measured during 108 TRH stimulation tests in 88 horses, and α-MSH concentrations were measured during 56 TRH st...
Murphy BA, Martin AM, Furney P, Elliott JA.In contrast to studies showing gradual adaptation of melatonin (MT) rhythms to an advanced photoperiod in humans and rodents, we previously demonstrated that equine MT rhythms complete a 6-h light/dark (LD) phase advance on the first post-shift day. This suggested the possibility that melatonin secretion in the horse may be more strongly light-driven as opposed to endogenously rhythmic and light entrained. The present study investigates whether equine melatonin is endogenously rhythmic in extended darkness (DD). Methods: Six healthy, young mares were maintained in a lightproof barn under an LD...
Dhakal P, Tsunoda N, Nakai R, Nagaoka K, Nambo Y, Sato F, Taniyama H, Taya K.The aim of present study was to clarify the post-natal profile of follicle-stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive (ir)-inhibin, progesterone, testosterone, and estradiol-17β, and their relationships in Thoroughbred colts. Six hundred and thirty-six colts were used for the study. Single plasma samples from each animal were harvested from the blood drawn through jugular venipuncture. The subjects were born with high amounts of progesterone, testosterone, and estradiol-17β, all of which dropped significantly and remained at lower levels till the end of 6 months. FSH...
Cuervo-Arango J.Prostaglandins (PGs) are essential to trigger the cascade of events that degrade the extracellular matrix of follicles leading to follicular rupture and ovulation. In mares, systemic administration of flunixin meglumine (FM), a PG synthetase inhibitor, blocks ovulation by inducing luteinized unruptured follicles (LUF). In the rat, the administration of PGF(2α) (PGF) and PGE restored ovulation in indomethacin treated animals. The mares were treated with FM 0, 12, 24 and 36 h after human chorionic gonadotrophin (hCG) administration to induce experimentally LUF (n = 15) or were left untreated (c...
Ginther OJ, Cuervo-Arango J, Beg MA.The role of passage of follicular fluid into the peritoneal cavity during ovulation in the transient disruption in the periovulatory FSH and LH surges was studied in ovulatory mares (n=7) and in mares with blockage of ovulation by treatment with an inhibitor of prostaglandin synthesis (n=8). Mares were pretreated with hCG when the largest follicle was ≥32 mm (Hour 0). Ultrasonic scanning was done at Hours 24 and 30 and every 2h thereafter until ovulation or ultrasonic signs of anovulation. Blood samples were collected at Hours 24, 30, 32, 34, 36, 38, 48, and 60. Ovulation in the ovulatory gr...
Kelley DE, Gibbons JR, Smith R, Vernon KL, Pratt-Phillip SE, Mortensen CJ.The objectives were to evaluate the effects of exercise on ovarian folliculogenesis and related hormones in mares. Mares (n = 11) were randomly assigned into a control (non-exercised) or treatment (exercised) group. Treatment mares (n = 5) were moderately exercised for 30 min, 6 d/wk. All mares underwent daily transrectal ultrasonographic examinations and ovarian follicles > 6 mm were measured. Blood samples were collected during the first (Cycle 1) and last (Cycle 4) cycle, and serum concentrations of cortisol, LH, and FSH were determined. Mean cortisol concentrations were elevated (P <...
Cuervo-Arango J, Beg MA, Ginther OJ.The objective was to determine differences in follicle and reproductive hormone characteristics in mares with ovulatory and flunixin meglumine (FM)-induced anovulatory cycles. Estrous mares were given 1500 IU hCG when the follicle was ≥ 32 mm (0 h). In Experiment 1, control mares (n = 7) were not treated further. The remaining mares (n = 11) were given 1.7 mg/kg FM i.v. twice daily, from 0 to 36 h after hCG treatment. Blood samples and ultrasonographic examinations were performed every 12 h. All control mares ovulated normally between 36 and 48 h. In contrast, eight of 11 FM mares did not ov...
Thompson DL, DePew CL, Ortiz A, Sticker LS, Rahmanian MS.Three experiments were conducted to determine 1) the relationship between prolactin and growth hormone (GH) secretion in mares and the response to GH-releasing hormone (GHRH), 2) whether plasma GH and prolactin concentrations differed among mares, stallions, and geldings, and 3) whether sexual differences existed after administration of GHRH and acute exercise. In Exp. 1, 10-min blood samples were collected from 12 mares for 8 h, and GHRH (0, 45, 90, or 180 micrograms) was administered at 6 h. In Exp. 2, 15-min blood samples were collected for 4 h from 10 mares, stallions, and geldings. In Exp...
Waddington B, Penitente-Filho JM, Neves J, Pinho RO, Chaya AY, Maitan PP, Silveira CO, Neves MG, Guimarães S, de Carvalho GR, Guimarães JD.This study was conducted to characterize the daily profile of testosterone secretion and its mean concentrations in the four seasons as well as to evaluate the semen characteristics and testicular biometry of Mangalarga Marchador stallions throughout the year in a tropical region. Three stallions were submitted to semen collections and evaluation of testicular biometry every 14 days along a year. Blood samples were collected once at the middle of each season, in a 20-min interval during 24 hr in order to evaluate the testosterone secretion profiles among seasons. Testosterone concentrations ...
Ishak GMA, Dutra GA, Gastal GDA, Gastal MO, Feugang JM, Gastal EL.The inability to obtain in vivo samples of antral follicle wall layers without removing the ovaries or sacrificing the animals has limited more in-depth studies on folliculogenesis. In this study, a novel ultrasound-guided follicle wall biopsy (FWB) technique was used to obtain in vivo follicle wall layers and follicular fluid samples of growing antral follicles. The expression of proliferative, hormonal, angiogenic, and pro-/antiapoptotic receptors and proteins in the follicular wall among three follicle classes were compared during the spring transitional anovulatory (SAN) and spring ovulato...
Ishii M, Kobayashi S, Acosta TJ, Miki W, Yamanoi T, Matsui M, Miyake Y, Miyamoto A.The aim of this study was to clarify the relationship between circulating oxytocin (OT) and PGF(2alpha) metabolite (PGFM) in mares at the third stage of labor and placental expulsion time in order to investigate a cause of retained placenta of which the incidence increase in a heavy draft mare. Blood was sampled every 5 min from foaling to expulsion of the placenta in 18 heavy draft mares to evaluate circulating OT and PGFM. The relationships between OT and PGFM concentration and recorded placental expulsion times were investigated. The results were as follows (1) The highest level of OT conce...
Kawasumi K, Yamamoto M, Koide M, Okada Y, Mori N, Yamamoto I, Arai T.Age effects on plasma metabolites, hormone concentrations, and enzyme activities related to energy metabolism were investigated in 20 riding horses. Animals were divided into two groups: Young (3-8 years) and aged (11-18 years). They were clinically healthy, and not obese. Plasma adiponectin (ADN) concentrations in aged horses were significantly lower than those in young horses (mean±SE, 6.5±1.3 µg mL(-1) vs, 10.9±1.7 µg mL(-1), Mann-Whitney U test, respectively; P=0.0233). Plasma non-esterified fatty acid levels and Insulin and malondialdehyde concentrations in aged group tended to incre...
Koskinen E.In a previous study, times from parturition to the first ovulation were followed in 55 Finnhorse mares on the basis of milk progesterone determinations. Ninety-six per cent of mares had ovulated by day 20 post-partum. If intervals of more than 19 days are excluded from the data, the time from parturition to 1st ovulation was 117 days. However, in cases of foaling before and after the beginning of June the times were 13.0 days and 8.8 days, respectively (p less than 0.001). Long intervals (over 16 days) occurred mainly before 1st May (in 6 out of 7 cases). In a 2nd study, 25 post-partum Finnhor...
de Kock SS, Rodgers JP, Swanepoel BC.Previous studies have shown that insulin-like growth factor 1 (IGF-1) is a promising marker for the detection of growth hormone (GH) abuse in the horse. The significant increases observed with GH administration in comparison to natural levels imply the possibility of setting a threshold level for IGF-1 that would be indicative of GH abuse. Although an immunoradiometric assay (IRMA) has been identified as a reliable screening method, a more specific IGF-1 quantification method needs to be developed for the prosecution of GH abuse by horseracing authorities. This study describes such an HPLC ele...
McCann JS, Caudle AB, Thompson FN, Stuedemann JA, Heusner GL, Thompson DL.Thirty mares in late gestation were used in a 3-yr study to assess effects of the tall fescue endophyte Acremonium coenophialum on serum prolactin (PRL) and progesterone. Two paddocks of each treatment, 0 or 100% infected 'Kentucky 31' tall fescue, were grazed by the mares for 21 d. Blood was collected three times per week until parturition. At 7-d intervals, mares were challenged with thyrotropin-releasing hormone (TRH) while grazing and blood was collected postinjection. Mares grazing 100% infected tall fescue (E+) had decreased serum PRL compared with mares grazing the 0% infected tall fesc...
Johnson L, Varner DD, Thompson DL.To determine the age at which adult values for hormonal and testicular characteristics are established, testes and blood from 123 slaughtered horses, aged 1-5 years, were compared. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T) and intratesticular testosterone (ITT) were determined by radio-immunoassay. Specimens were obtained in the non-breeding (n = 46) or breeding (n = 43) season in Experiment 1 (Exp. 1) and in the breeding (n = 34) season in Experiment 2 (Exp. 2). Testicular parenchyma was fixed in glutaraldehyde and homogenized to...
Koskinen E, Katila T.The long-term effect of anabolic steroid was investigated in 3 experiments. In experiment I, 500 mg of 19-norandrostenololylaurate was given to 5 colts and a dose of 100 mg to another 5 colts every 3rd week. Six colts served as untreated controls. The animals were 12-16 months old at the start, and 24 months at the end of treatment. In experiment II, a dose of 1 mg/kg was given every 3rd week to 4 colts and 0.3 mg/kg every week to another 4 colts. Six colts served as controls. The colts were treated from 7 months to 12 months of age. In experiment III, 1 mg/kg of steroid was given every 3rd we...
Marth CD, Young ND, Glenton LY, Noden DM, Browning GF, Krekeler N.The physiological changes associated with the varying hormonal environment throughout the oestrous cycle are linked to the different functions the uterus needs to fulfil. The aim of the present study was to generate global gene expression profiles for the equine uterus during oestrus and Day 5 of dioestrus. To achieve this, samples were collected from five horses during oestrus (follicle >35 mm in diameter) and dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq). Differentially expressed genes between the two cycle stages were further inves...
Fazio E, Medica P, Trifiletti C, Ferlazzo A.The objective of this study was to compare in detail the total and free iodothyronines' pattern of mares from the first ovulation of the year over an extended period of 12 weeks. A total of 20 mares were used in the study. The mares were classified into two groups: mares mated at the ovulation (n = 10) used as observational group and mares unmated at the ovulation (n = 10) used as control group. Serum total and free triiodothyronine (T3, fT3) and thyroxine (T4, fT4) levels were measured in baseline conditions at the first ovulation of year and once a week until 12 weeks later. For the experi...
Sharp DC, Vernon MW, Zavy MT.Oestrous behaviour, ovarian follicular development, ovulation and changes in hair coat were observed in Pony mares which were unoperated, sham-ganglionectomized control or bilaterally superior cervical ganglionectomized. Surgery was performed during the winter anoestrus (1975--1976). Reproductive patterns in all groups were similar during the first breeding season (1976) after operation but in ganglionectomized mares the onset of the next breeding season (date of first ovulation in 1977), the pattern of follicular development, date of first oestrus and pattern of hair coat changes were all sig...
Bailly-Chouriberry L, Loup B, Popot MA, Dreau ML, Garcia P, Bruyas JF, Bonnaire Y.Since the availability on the European market of the vaccine Improvac® dedicated to male pig immunological castration, the risk of misuse of this product in horses is now considered as a threat for the horseracing industry. Immunological castration is not allowed by the racing codes (immune system, Article 6). Indeed, this vaccination against the hypothalamic hormone luteinizing hormone-releasing hormone or gonadotropin-releasing hormone (GnRH) will prevent the release from the anterior pituitary of luteinizing hormone and follicle stimulating hormone, which are required for the development a...
O'Connor SJ, Gardner DS, Ousey JC, Holdstock N, Rossdale P, Edwards CM, Fowden AL, Giussani DA.The aims of this study were to compare and contrast the development of the cardiac baroreflex and endocrine responses to acute hypotensive stress in healthy newborn pony foals and lambs during the first two weeks of postnatal life. Methods: Under general anaesthesia, seven Welsh pony foals and six Welsh Mountain lambs were catheterised with hind limb artery and vein catheters. Following post-surgical recovery, at 1 week and 2 weeks of age, blood pressures of the animals were raised and lowered acutely by intravenous infusion of phenylephrine and sodium nitroprusside, respectively. During hypot...
Gautier C, Schmidt K, Aurich J, Aurich C.The hypothesis in this study was continuous treatment of stallions with the GnRH agonist deslorelin inhibits reproductive functions. A 2-week pre-experimental period was followed by an 11-week deslorelin implant treatment. Stallions received 4.7 (D1, n = 7), or 18.8 mg deslorelin (D2, n = 5) or remained untreated (C, n = 5). Libido, sperm motility, membrane integrity, DNA fragmentation, estrogen receptors, basal plasma testosterone and Anti Muellerian hormone (AMH) concentrations were evaluated once weekly during the treatment period. The testosterone response to the GnRH agonist buserelin a...
Ginther OJ, Rodrigues BL, Ferreira JC, Araujo RR, Beg MA.Blood collections for characterising 13,14-dihydro-15-keto-PGF2alpha (PGFM) pulses in mares and colour-Doppler examinations for estimating percentage of corpus luteum with blood-flow signals were done hourly for a 24-h session on Day 15 (ovulation = Day 0; n = 13 mares) or during 12-h sessions from Days 12 to 16 (n= 10 mares). Luteolysis was defined as extending from the beginning of a precipitous decrease in progesterone until progesterone was <2 ng mL(-1). Comparisons were made among preluteolysis, luteolysis, and postluteolysis. Greater prostaglandin F2alpha activity (mean PGFM concentra...
Hannan MA, Murase H, Sato F, Tsogtgerel M, Kawate N, Nambo Y.The peripheral blood concentrations of insulin-like peptide 3 (INSL3) have been detected in many mammalian species, but the level of INSL3 in horse remains unknown. The objectives were to develop a time-resolved fluorescence immunoassay (TRFIA) to detect INSL3 concentrations from horse blood as well as to determine the age-related and seasonal changes of plasma concentrations of INSL3 and testosterone from birth to early-puberty in Thoroughbred male horse (n = 11). Monthly blood sample and measurement of body weight, height, chest and cannon bone size were done from birth until 16 mo. Th...
Kalpokas I, Mattos RC, Cavestany D, Martínez MN, Perdigón F, Meikle A.The effect of side of corpus luteum on uterine gene expression and protein localization of estrogen receptor α (ERα) and progesterone receptor (PR) in healthy cyclic and pregnant mares 13 days after ovulation (day 0) was investigated. Transcervical biopsies were performed to collect endometrium ipsilateral and contralateral regarding the side of corpus luteum on day 13 post-ovulation in cyclic (n = 6) and pregnant (n = 6) mares. Blood samples were collected daily from day 0 until the day of biopsy for 17β-estradiol (E2) and progesterone (P4) determinations. Receptor expression was d...
Rourke KM, Kohn CW, Levine AL, Rosol TJ, Toribio RE.Calcium has important physiological functions, and disorders of calcium homeostasis are frequent in horses. We have made important progress understanding equine calcium homeostasis; however, limited information on equine calcitonin (CT) is available, in part because of the lack of validated CT assays. To determine the CT response to high ionized calcium (Ca(2+)) concentrations in healthy horses, we induced hypercalcemia in 10 healthy horses using a calcium gluconate 23% solution (5mg/kg; 120 mL/500 kg horse) infused over 4 min. Four horses were infused with 120 mL of 0.9% NaCl and used as cont...
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...
Aleman M, McCue PM, Chigerwe M, Madigan JE.Transient hypothalamic-pituitary-adrenal axis dysfunction occurs in critically ill foals with sepsis and neonatal maladjustment syndrome (NMS). Cortisol is the most commonly measured steroid. However, a complex interaction of various steroid compounds might play a role in pathophysiology of this disorder. Objective: To identify steroid compounds present at high concentrations at birth that rapidly and steadily decrease within the first 7 days of life in healthy foals and that might be supportive diagnosis of NMS and other neonatal disorders. Methods: Ten healthy neonatal Quarter Horse foals ...
Hinrichsen SL, Yuen KY, Dryburgh EL, Bertin FR, Stewart AJ.Pituitary pars intermedia dysfunction (PPID) is diagnosed by increased basal or post thyrotropin-releasing hormone (TRH) stimulation ACTH concentrations. ACTH is known to be unstable; however, the effect of different temperatures and TRH stimulation on equine ACTH stability is poorly described. In total, 15 horses, including 8 PPID positive (ACTH > 35 pg/mL at baseline or >65 pg/mL 30 min after TRH stimulation), were divided into 2 groups: 9, including 5 PPID positive, with basal ACTH concentrations and 6, including 3 PPID positive, with post TRH stimulation ACTH concentrations. Whole bl...
Golland LC, Evans DL, Stone GM, Tyler-McGowan CM, Hodgson DR, Rose RJ.Basal concentrations of cortisol (CORT), beta-endorphin (beta EP), growth hormone (GH) and testosterone (T) and their disruption during 32 h of recovery after treadmill exercise were investigated in 4 geldings. Blood samples were collected from resting horses every 20 min between 0600-1000 and 1500-1900 h, and hourly between 1000-1500 h on 3 consecutive days. Treadmill exercise tests comprising 2 min intervals at 30, 50, and 70% VO2max then to fatigue at 100% VO2max were conducted between 1020-1130 h on Day 2. Blood was collected before, during and 15, 30, 60 and 90 min after exercise. Mean (C...
Auvray P, Sourdaine P, Moslemi S, Séralini GE, Sonnet P, Enguehard C, Guillon J, Dallemagne P, Bureau R, Rault S.In this study, we describe the synthesis of a new family of indolizinone derivatives designed to fit an extrahydrophobic pocket within the active site of aromatase and to strongly inhibit human aromatase. This could help improve the specificity of the inhibitors. Equine aromatase, very well characterized biochemically, is used as a comparative model. Indeed, in a previous comparison between both human and equine aromatases, we described the importance of the interaction between the inhibitor and this pocket for the indane derivative MR 20814. MR 20492 and MR 20494 are more potent inhibitors of...
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...
Hughes JP, Stabenfeldt GH, Evans JW.In eleven non-pregnant mares examined for 2 years, oestrous cycle length was 20-6 days (range 13 to 34) excluding any anoestrous periods. The duration of oestrus was 5-7 days (range 1 to 24); from February to May it was 7-6 days (range 2 to 24) and from May to November 4-8 days (range 1 to 10). The majority of ovulations occurred between 16.00 and 08.00 hours and 78% of the mares ovulated within 48 hr of the end of oestrus. Mean follicular diameter was 45 mm on the day of ovulation and there was a 25-5% incidence of multiple ovulations. It was uncommon for oestrus to occur without ovulation, w...
Rabb MH, Thompson DL, Barry BE, Colborn DR, Garza F, Hehnke KE.Six lighthorse stallions with previous sexual experience were used to determine the short-term effects of sexual stimulation (SS; 5 min exposure to an estrous mare), SS plus ejaculation (SSE), and no stimulation (control) on serum concentrations of LH, FSH, testosterone, cortisol and prolactin. Stallions received one treatment per day on d 1, 4 and 7. Treatments were assigned such that each stallion 1) received each treatment once and 2) experienced a unique sequence of treatments. Neither SS nor SSE had any consistent effects on LH or FSH concentrations. Testosterone concentrations during con...
Daels PF, DeMoraes JJ, Stabenfeldt GH, Hughes JP, Lasley BL.Thirty pregnant mares were assigned to 3 groups: Group 1 (n = 10) mares served as controls; Group 2 (n = 10) mares were treated with altrenogest (44 mg/day) from Day 16 to 80 and Group 3 (n = 10) mares were treated with a luteolytic dose of PGF2 alpha on Day 16 followed by altrenogest (44 mg/day) until Day 80. Concentrations of progesterone and chorionic gonadotrophin (CG) in plasma and oestrogen conjugate (OC) in urine were determined between Days 16 and 80 of gestation. In Group 3, complete luteolysis occurred in all 10 mares following administration of PGF2 alpha. Six of the 10 mares did no...
Cullen S, Donohoe A, McGoldrick A, McCaffrey N, Davenport C, Byrne B, Donaghy C, Tormey W, Smith D, Warrington G.The long-term implications of making-weight daily on musculoskeletal health and functioning of the kidney and liver remain unknown. This study aimed to investigate musculoskeletal health and kidney and liver function in a group of retired jockeys. 28 retired male jockeys (age 50-70 years) provided fasting blood samples for markers of bone metabolism and kidney and liver function. A dual-energy x-ray absorptiometry (DXA) scan was performed for the assessment of bone mineral density (BMD). Established reference ranges were used for interpretation of results. Comparisons were made between retired...
