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.
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 ...
Laseca N, Cánovas Á, Valera M, Id-Lahoucine S, Perdomo-González DI, Fonseca PAS, Demyda-Peyrás S, Molina A.The phenomenon in which the expected Mendelian inheritance is altered is known as transmission ratio distortion (TRD). The TRD analysis relies on the study of the transmission of one of the two alleles from a heterozygous parent to the offspring. These distortions are due to biological mechanisms affecting gametogenesis, embryo development and/or postnatal viability, among others. In this study, TRD phenomenon was characterized in horses using SNP-by-SNP model by TRDscan v.2.0 software. A total of 1,041 Pura Raza Español breed horses were genotyped with 554,634 SNPs. Among them, 277 horses ge...
Bertin FR, Frank N, Breuhaus BA, Schott HC, Kritchevsky JE.Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical pro...
Elder E, Wong D, Johnson K, Robertson H, Marner M, Dembek K.Bacterial sepsis is the leading cause of death in foals and is associated with hypothalamic-pituitary-adrenocortical axis (HPAA) dysfunction. HPAA function can be evaluated by an arginine-vasopressin (AVP) stimulation test. Objective: Administration of AVP will stimulate a dose-dependent rise in systemic adrenocorticotropin-releasing hormone (ACTH) and cortisol in neonatal foals. There will be no response seen in corticotropin-releasing hormone (CRH) and baseline AVP will be within reference interval. Methods: Twelve neonatal foals, <72 hours old. Methods: HPAA function was assessed in foals...
Bourebaba L, Zyzak M, Sikora M, Serwotka-Suszczak A, Mularczyk M, Al Naem M, Marycz K.Sex hormone binding globulin (SHBG) deteriorated expression has been recently strongly correlated to increased level of circulating pro-inflammatory cytokines and insulin resistance, which are typical manifestations of equine metabolic syndrome (EMS). Despite previous reports demonstrated the potential therapeutic application of SHBG for liver-related dysfunctions, whether SHBG might modulate equine adipose-derived stem/stromal cells (EqASCs) metabolic machinery remains unknown. Therefore, we evaluated for the first time the impact of SHBG protein on metabolic changes in ASCs isolated from hea...
Medill SA, Janz DM, McLoughlin PD.Steroid-hormone concentrations from non-invasively obtained biomarkers, like hair, can provide a representation of circulating hormones diffused over relatively long time periods (e.g., weeks or months). The hormone cortisol is often associated with physiological or even psychological stress, while testosterone is strongly associated with male development and reproductive success. Increasingly, studies are using hormone levels derived from hair to make inferences among both domestic animals and wildlife. For horses, all previous hair hormone analysis has been done on companion or working anima...
Medill SA, Janz DM, McLoughlin PD.Cortisol is a glucocorticoid hormone produced during activation of the hypothalamic-pituitary-adrenal axis (HPA) in response to psychological or physiological demands. High amounts of circulating cortisol can be found in individuals experiencing energetically demanding physiological events, such as pregnancy, lactation, injury, or starvation, but, also, in individuals who may have less obvious HPA activation from social situations. The feral horse population on Sable Island (Nova Scotia, Canada) provides an opportunity to look at hair cortisol concentration (HCC) as a proxy for circulating cor...
Huggins L, Norris J, Conley A, Dini P.Abnormal or undesired mare behaviours are often assumed to be associated with ovarian abnormalities. Objective: We aimed to determine the incidence of abnormal behaviours and their association with concentrations of one or more ovarian hormones associated with a granulosa cell tumour (GCT). Methods: Retrospective descriptive. Methods: A total of 2914 hormonal profile samples submitted with the words behave, behaviour, or behaving in the submission history were analysed. The association between reported abnormal behaviours and concentrations of testosterone, anti-Müllerian hormone (AMH), inhib...
Gao Y, Yoshida S, Takeyama A, Tagami M, Rajabi-Toustani R, Tsogtgerel M, Nambo Y.Ultrasound examination during late gestation is one of the best methods for monitoring potential pregnancy risks. Enlarged bladder is a urological disorder rarely observed in equine fetuses. This clinical case report aimed to present a case illustrating the development of equine fetal enlarged bladder using transabdominal ultrasound examinations and maternal hormone evaluation during gestation. An 8-year-old Hokkaido native pony was impregnated by embryo transfer, and at 215 days of gestation, abnormalities of the fetal bladder were detected. The bladder volume increased with gestational age, ...
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...
Thompson RE, Meyers MA, Palmer J, Veeramachaneni DNR, Magee C, de Mestre AM, Antczak DF, Hollinshead FK.The equine chorionic girdle is comprised of specialized invasive trophoblast cells that begin formation approximately 25 days after ovulation (day 0) and invade the endometrium to become endometrial cups. These specialized trophoblast cells transition from uninucleate to differentiated binucleate trophoblast cells that secrete the glycoprotein hormone equine chorionic gonadotropin (eCG; formerly known as pregnant mare serum gonadotropin or PMSG). This eCG has LH-like activity in the horse but variable LH- and FSH-like activity in other species and has been utilized for these properties both in...
Satué K, Fazio E, La Fauci D, Bruschetta G, Medica P.The maintenance of iron (Fe) homeostasis is vital for the physiological function along life. In sexually mature humans and experimental animals, estrogens downregulate hepcidin (Hpc) expression, in order to improve the intestinal absorption and to mobilize Fe stores for maternal erythropoietic expansion and placental development. However, changes of these mechanisms related to regulation of Hpc on the availability of Fe during gestation with advancing age in mares, remain unknown. The objective of this study was to evaluate the interrelationships between serum Fe, Ferritin (Ferr) and Hpc with ...
Setoguchi LS, Siqueira LM, Lucca LK, Oquendo PS, Oquendo FMG, Nogueira GP, Silva ESM.Although the use of different estradiol esters has been extensively studied in hormonal protocols in cows, such information is lacking in mares. The present study aimed to assess the effects of treatment with the same doses and administration frequency of estradiol cypionate, estradiol benzoate and 17β estradiol on plasma estradiol (E2) concentrations of acyclic mares and correlate the E2 profile to the endometrial edema score. Sixteen treatments were performed in 14 mares randomly divided into three groups: EB (n = 5), EC (n = 5), and 17β (n = 6), receiving 10 mg on day 0 (D0), 6 mg o...
The present experiment aimed at determining whether the timing of the maternal recognition of pregnancy (MRP) was specific to individual mares by determining when luteostasis, a failure to return to oestrus, reliably occurred in individuals following embryo reduction. Singleton (n = 150) and synchronous twin pregnancies (n = 9) were reduced in 10 individuals (5-29 reductions/mare) at pre-determined time points within days 10 (n = 20), 11 (n = 65), 12 (n = 47), 13 (n = 12) or 14 (n = 15) of pregnancy. Prior to embryo reduction, the vesicle diameter was measured in 71% (106/150) of the singleton...
Epper P, Glüge S, Vidondo B, Wróbel A, Ott T, Sieme H, Kaeser R, Burger D.To successfully inseminate mares, precise detection of ovulation time is crucial, especially when using frozen-thawed semen. Monitoring body temperature, as has been described in women, could be a noninvasive way to detect ovulation. The objective of this study was to investigate the relationship between the time of ovulation and the variation of body temperature in mares based on automatic continuous measurements during estrus. The experimental group included 21 mares for 70 analyzed estrous cycles. When the mares showed estrous behavior, they were administered intramuscular deslorelin acet...
Bamford NJ, Stewart AJ, El-Hage CM, Bertin FR, Bailey SR.Plasma adrenocorticotropic hormone (ACTH) concentration is commonly measured to diagnose pituitary pars intermedia dysfunction (PPID). Several intrinsic and extrinsic factors affect ACTH concentrations, including breed. The objective of this study was to prospectively compare plasma ACTH concentrations among different breeds of mature horses and ponies. Three breed groups comprised Thoroughbred horses (n = 127), Shetland ponies (n = 131) and ponies of non-Shetland breeds (n = 141). Enrolled animals did not show any signs of illness, lameness or clinical signs consistent with PPID. Blood ...
Renaudin CD, Conley AJ.Methods to diagnose and monitor equine pregnancy continue to advance with improved instrumentation enabling the development of novel, non-invasive approaches to assess fetal well-being and viability using ultrasound and endocrine testing. From early embryonic loss to placentitis, that is typically encountered later in gestation, fetal viability and development as well as placental function can be evaluated using two fundamentally different, structural and functional, approaches. Ultrasound provides structural information on embryonic and fetal growth using such parameters as combined thickness...
Satué K, Fazio E, Cravana C, Medica P.During pregnancy, maternal erythropoietic expansion and fetal development require greater mobilization of available iron (Fe) stores. These adjustments in Fe metabolism in humans and rodents are largely mediated by the hormone hepcidin (Hepc), which controls the expression of ferroportin (Fpn), a transporter responsible for exporting Fe from stores to extracellular fluid and plasma. These mechanisms based on the regulation of Hepc on the availability of Fe during gestation in healthy mares remain unknown. The objective of this study was to determine the existence of interrelationships among co...
Bigler NA, Gross JJ, Baumrucker CR, Bruckmaier RM.This review discusses endocrine and functional changes during the transition from late gestation to lactation that are related to the production of colostrum in different mammalian species. Species covered in this article include ungulate species (cattle, sheep, goats, pigs, horses), rodents (rat, mouse), rabbits, and carnivores (cats, dogs), as well as humans. An immediate availability of high quality colostrum for the newborn after birth is crucial in species where a transfer of immunoglobulins (Ig) does not or only partially occur via the placenta during pregnancy. Declining activity of ges...
Kikuchi M, Nagata SI, Ishige T, Minamijima Y, Hirota KI, Tozaki T, Kakoi H, Kizaki K.Glucocorticoid preparations have anti-inflammatory effects, and are commonly used in the equine clinical setting; however, such treatments can cause a number of side effects. Adrenal insufficiency is an adverse effect induced by the suppression of adrenal function following drug administration. This study aimed to investigate the influence of two glucocorticoid preparations, dexamethasone and hydrocortisone, on adrenocortical function in horses. The usual doses of dexamethasone and hydrocortisone preparations in equine practice were administered intramuscularly to six horses, and peripheral bl...
Timms M, Botteon A, Manos C, Griffin J, Levina V, Steel R.Gonadotropin-releasing hormone (GnRH) and its synthetic analogues are considered banned substances by the racing industry. GnRH is used as a pharmaceutical to regulate the female oestrous cycle, but the hormone is also thought to increase the production of testosterone in male animals. Using liquid chromatography in conjunction with high-resolution mass spectrometry (LC-HRMS) and data-independent acquisition (DIA), a method is presented for the detection of intact and truncated peptides of GnRH and its analogues down to the low picogram level in equine urine. The study of the catabolism of GnR...
Peric T, Ellero L, Comin A, Pividori I, Prandi A.In humans, allopregnanolone plays important roles in a number of different neurodegenerative disorders, and it has been proposed for use in some therapies. Horses are commonly used as animal models for human neurodegenerative diseases, mental and behavioral disorders, and neuropsychiatric disorders, and there is interest in using hair as a biological sample to study hormones in these conditions. We validated the use of a commercial ELISA kit (DetectX allopregnanolone kit; Arbor Assays), which was designed for serum, plasma, feces, urine, and tissue samples, to assess allopregnanolone in hair s...
During husbandry, domestic animals are exposed to many factors that can influence their circadian physiology organization leading to an increase in animals' discomfort. Thermal homeostasis is at the basis of animal wellness, the aim of the present study was to investigate the daily fluctuation of serum concentrations of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) in association with the daily fluctuation of uncoupling protein 1 (UCP1) and clock gene Per2 in healthy horses housed in individual box, to improve the knowledge on this matter. Seven clinically healthy female Italian Saddle horse...
Grzędzicka J, Dąbrowska I, Malin K, Witkowska-Piłaszewicz O.Increased training loads in both human and equine athletes are generally implemented to improve their physical performance. These loads are tolerated only within appropriate training periodization with regard to recovery time. Otherwise, training overload causes failure in the systemic adaptation, which at first leads to overreaching, and progressively to overtraining syndrome (OTS). Exercise endocrinology, and anabolic/catabolic balance as an indicator of athlete performance status and OTS has continued to attract attention. In human medicine, changes in testosterone and cortisol levels, as w...
Joonè CJ, Cavalieri J.There is a need for a safe, effective and practical method of oestrus suppression in the mare. The aim of this study was to monitor ovarian activity in mares exposed to either 9.4 or 28.2 mg deslorelin acetate, a GnRH agonist, in the form of a sustained-release implant. Following oestrus synchronisation, mares were randomly assigned to one of three groups (n = 4 per group) and administered either one (Des1 group; 9.4 mg) or three (Des3 group; 28.2 mg) implants of deslorelin acetate (Suprelorin-12, Virbac Australia) or one blank implant (Control group; Virbac Australia). Mares underwe...
Moss A, Leise B, Hackett E.Laminitis is a complex and debilitating disease of horses. Numerous predisposing factors contribute to laminitis development, however the exact pathogenesis remains undetermined. Serum T4, cortisol, and histamine are components of the innate stress response and could play a causative or contributory role. Stress hormone concentrations in laminitis are largely unknown. Objective: To evaluate parameters associated with stress response in horses with laminitis, and compare these to healthy horses and horses with gastrointestinal (GI) disease. Methods: Thirty-eight adult horses presenting for non-...
Ginther OJ.Examples of research discoveries and first reports on mare reproduction by the O.J. Ginther team are (1) determined daily circulating concentrations of four hormones during the estrous cycle, (2) showed that mares can be induced to ovulate and superovulate by hormone treatment during both ovulatory and anovulatory seasons, (3) demonstrated that prostaglandin F2α was the luteolysin in mares, (4) described the mare's elaborate hormonal and biochemical mechanism for selecting the ovulatory follicle from a pool of like follicles, (5) developed the method for diagnosing fetal sex by Day 60 using l...
Hensel B, Jakop U, Schmicke M, Schröter F, Jung M, Schulze M.Artificial insemination (AI) is commonly used in the equine industry to enhance the genetic value in breeding programs and to effectively utilize ejaculates. Many stallions are used as breeding stallions as well as in high-level sports competitions to improve their market value. The goal of the present study was to investigate whether this dual use of stallions influences the animals´ stress levels and/or the quality of their ejaculates. For this purpose, 18 stallions were grouped into two categories: breeding stallions with (BSC = breeding stallion competition), and breeding stallions with...
Silva ESM, Newcombe JR, Cuervo-Arango J.Oestrogens treatment is often used to induce oestrus behaviour in anoestrous mares to aid in the collection of stallion semen and as recipient mares to receive embryos when combined with progesterone. However, there are no studies to describe the effect of dose and individual mare on the intensity and duration of the response, in both anoestrous and cyclic mares. In Experiment 1, 13 anoestrous mares were treated with one of five doses of oestradiol benzoate (OB) (1, 1.5, 2, 3 and 4 mg) per mare in five consecutive treatment periods (n = 65), to determine the response in terms of endometrial oe...
Gebremedhn S, Gad A, Ishak GM, Menjivar NG, Gastal MO, Feugang JM, Prochazka R, Tesfaye D, Gastal EL.Innumerable similarities in reproductive cyclicity and hormonal alterations highlight the considerable utility of the mare to study aspects of follicular dynamics and reproductive function in view of the largely constricted, human research subjects. The bi-directional communication between the growing oocyte and the surrounding somatic cells embodies the hallmark of mammalian follicular development, partially mediated by extracellular vesicles (EVs) encapsulated with microRNAs (miRNAs) and present in the follicular fluid (FF). Here, we aimed to decipher the dynamics of the miRNAs in EVs from e...
LaPolt PS, Tilly JL, Aihara T, Nishimori K, Hsueh AJ.The actions of gonadotropins on ovarian differentiation are associated with dynamic changes in gonadotropin receptor content, presumably due to modulation of receptor gene expression. The present studies used a reverse transcription-polymerase chain reaction to obtain a rat FSH receptor cDNA fragment, followed by synthesis of a labeled cRNA probe to examine the regulation of FSH receptor mRNA levels during follicular maturation, ovulation, and luteinization. Northern blot analysis of ovarian RNA with the FSH receptor probe revealed two predominant hybridization signals of 7.0 and 2.5 kilobases...
Alexander SL, Irvine CH, Ellis MJ, Donald RA.We have used the technique which we have developed for collecting pituitary venous blood from conscious, undisturbed horses to study the effect of acute vigorous exercise on the secretion of CRF, arginine vasopressin (AVP) and ACTH. Pituitary venous (pit) blood was collected every 1-5 min from nine trained racehorses at rest in the stable. The horses then trotted quietly for 10 min, after which they galloped as fast as possible for 4-6 min, before returning to the stable where sampling continued. In Exp 1 (n = 5) no blood samples were taken during exercise, whereas in Exp 2 (n = 4), pit blood ...
Roser JF.It is well established in many mammalian species, including the horse that normal testicular function is dependent upon a functional hypothalamic-pituitary-testicular (HPT) axis, which involves classic feedback mechanisms. The major HPT hormones involved in the stallion are gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), estrogens (Es) and inhibin (INH). Although prolactin (PRL) fluctuates with season in the stallion and both PRL and thyroid hormone (TH) affect reproduction in other male species, their effects on stallion r...
Stout TA, Allen WR.A growing equine conceptus must suppress the cyclical release of PGF(2 alpha) from the endometrium to effect maternal recognition of its presence in the uterus. Paradoxically, the conceptus itself secretes PGF(2 alpha), together with other prostaglandins. In this study, the PGF(2 alpha) and PGE(2) content of, and production in vitro by, day 10-32 equine conceptuses were measured and the influence of pregnancy on the concentrations of these prostaglandins in the uterine lumen was examined. In vitro, the release of both prostaglandins per mg conceptus tissue was very high on day 10 after ovulati...
Manteca Vilanova X, De Briyne N, Beaver B, Turner PV.Collection of blood from pregnant mares for extraction of equine chorionic gonadotropin (eCG) is a critical but relatively unknown and poorly regulated practice in the countries in which it occurs. Equine chorionic gonadotropin is a hormone that is widely used to enhance reproductive performance and management of dairy and beef cattle, sheep, goats, and pigs kept under intensive housing systems. eCG is extracted from the blood of brood mares between days 40-120 of gestation. Although alternatives have been sought, there is currently no efficacious replacement, natural or synthetic, for eCG. Re...
Vick MM, Sessions DR, Murphy BA, Kennedy EL, Reedy SE, Fitzgerald BP.In mares, obesity is associated with continuous reproductive activity during the non-breeding season. To investigate the effect of obesity and associated alterations in metabolic parameters on the oestrous cycle, two related studies were conducted. In Experiment 1, obese (body condition score > 7) mares were fed ad libitum or were moderately feed restricted during the late summer and autumn months. Feed restriction did not alter the proportion of mares entering seasonal anoestrus. However, obese mares exhibited a significantly longer duration of the oestrous cycle, significant increases in ...
Fitzgerald DM, Anderson ST, Sillence MN, de Laat MA.Generalized obesity, regional adiposity, hyperinsulinemia and hypertriglyceridemia are all potential indicators of equine metabolic syndrome (EMS). This study aimed to assess the relationship between morphometric measurements of body condition and metabolic hormone concentrations in ponies, with and without a neck crest or generalised obesity. Twenty-six ponies were assigned a body condition score (BCS) and cresty neck score (CNS). Height, girth, and neck measurements were taken. An oral glucose test (OGT; 0.75g dextrose/kg BW) was performed and blood samples collected prior to and 2 hours pos...
Mc Gowan TW, Pinchbeck GP, Mc Gowan CM.The sensitivity and specificity of basal plasma α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotrophic hormone (ACTH) for the diagnosis of pituitary pars intermedia dysfunction (PPID) has not been evaluated in a population-based study. Objective: To evaluate basal plasma α-MSH and ACTH concentrations for the diagnosis of PPID in a population of horses aged ≥ 15 years. Methods: Owner-reported data were obtained using a postal questionnaire distributed to an equestrian group. A subgroup of surveyed owners was visited and veterinary examination performed on horses aged ≥ 15 year...
Weber JA, Freeman DA, Vanderwall DK, Woods GL.This study was conducted to identify embryonic products whose secretion was temporally associated with the oviductal transport period of the mare. Chemicals secreted by oviductal-transport-stage equine embryos were identified by incubating Day 6 or Day 7 early uterine embryos with 35S-methionine/cysteine, 3H-progesterone, or 3H-arachidonic acid for 24 h, and subsequently identifying radioactively labeled proteins (SDS-PAGE; n = 3 embryos), steroids (HPLC; n = 3 embryos), or prostaglandins (HPLC; n = 3 embryos) in the culture medium. Early uterine embryos secreted 116.1 +/- 45.5 pg of prostagla...
Gold JR, Divers TJ, Barton MH, Lamb SV, Place NJ, Mohammed HO, Bain FT.Little information exists on the hypothalamic-pituitary-adrenal axis in septic foals. Objective: The plasma concentrations of adrenocorticotropin (ACTH) and cortisol are expected to be higher in septic foals as compared to normal foals. The concentrations of hormones in septic foals also are expected to differ further depending upon survival. Methods: Twenty-eight control foals and 46 septic foals 11 or a positive blood culture. The control foals were age matched to the septic foals in the study. ACTH and cortisol concentrations were measured by a chemiluminescent immunoassay system. Results: ...
Williams JK, Honoré EK, Washburn SA, Clarkson TB.We attempted to determine whether continuous and cyclic medroxyprogesterone acetate modulates the effects of estrogen on dilation of atherosclerotic coronary arteries in surgically postmenopausal female monkeys. Background: Estrogen replacement in postmenopausal women preserves normal dilator responses of atherosclerotic coronary arteries. The effects of progestins on coronary artery reactivity have not been determined. Methods: Repeated quantitative coronary angiography was used to study the effects after 1 month of 1) no hormone replacement (control) or oral administration of 2) continuous c...
Johnson HD, Vanjonack WJ.Recent data on various environmental stressors and blood hormone patterns are presented for lactating cattle. Known stressor effects of such factors as environmental temperature, air pollution, and noise on the plasma thyroxine, growth hormone, cortisol, prolactin, progesterone, luteinzing hormone, epinephrine, and norepinephrine of lactating cattle are discussed. Information on stressor effects is lacking on glucagon, insulin, vasopressin, calcitonin, oxytocin, thyrotrophic hormone, follicle stimulating hormone, melatonin, parathyroid hormone, and estrogens in the lactating cow. The importanc...
de Laat MA, Pollitt CC, Kyaw-Tanner MT, McGowan CM, Sillence MN.The reason why a sustained high concentration of insulin induces laminitis in horses remains unclear. Cell proliferation occurs in the lamellae during insulin-induced laminitis and in other species high concentrations of insulin can activate receptors for the powerful cell mitogen, insulin-like growth factor (IGF)-1. The first aim of this study was to determine if IGF-1 receptors (IGF-1R) are activated in the hoof during insulin-induced laminitis. Gene expression for IGF-1R and the insulin receptor (InsR) was measured using qRT-PCR, in lamellar tissue from control horses and from horses underg...
Janett F, Stump R, Burger D, Thun R.The aim of this study was to evaluate the effects of an anti-GnRH vaccine on testosterone concentration, antibody titer, scrotal width, semen quality and sexual behavior in the stallion. Adverse reactions to the vaccine were also determined. Eight clinically healthy sexually experienced stallions aged between 6 and 15 years from the National Stud in Avenches (Switzerland) were used. Five stallions were immunized 3 times at an interval of 4 and 8 weeks, respectively, with 200 microg of a GnRH-protein conjugate (Equity, CSL Limited, Australia) intramuscularly in the neck and 3 control animals re...
Yoon MJ, Berger T, Roser JF.The insulin-like growth factor-I (IGF-I) is a key regulator of reproductive functions. IGF-I actions are primarily mediated by IGF-IR. The main objective of this research was to evaluate the presence of IGF-I and IGF-I Receptor (IGF-IR) in stallion testicular tissue. The hypotheses of this study were (i) IGF-I and IGF-IR are present in stallion testicular cells including Leydig, Sertoli, and developing germ cells, and (ii) the immunolabelling of IGF-I and IGF-IR varies with age. Testicular tissues from groups of 4 stallions in different developmental ages were used. Rabbit anti-human polyclona...
Hart KA, Slovis NM, Barton MH.Transient hypothalamic-pituitary-adrenal (HPA) axis dysfunction occurs frequently in critically ill humans and impacts survival. The prevalence and impact of HPA axis dysfunction in critically ill neonatal foals are not well characterized. Objective: (1) HPA axis dysfunction occurs in hospitalized neonatal foals, and is characterized by inappropriately low basal serum cortisol concentration or inadequate cortisol response to exogenous adrenocorticotropic hormone (ACTH); (2) hospitalized foals with HPA axis dysfunction have more severe disease and are less likely to survive than hospitalized fo...
Dzikiti TB, Hellebrekers LJ, van Dijk P.Physiological parameters, metabolic parameters and stress-related hormones are evaluated in horses anaesthetized with isoflurane in oxygen combined with lidocaine intravenously. Two groups of horses anaesthetized with isoflurane (six horses in each group) were studied: a lidocaine group (IL), which received intravenous lidocaine and a control group (C), which received intravenous saline. Horses in both groups were premedicated with detomidine (i.v.), and anaesthesia was induced with midazolam-ketamine (i.v.). The lidocaine group received intravenous lidocaine as a loading dose of 2.5 mg kg(-1)...
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...
Beech J, Boston RC, McFarlane D, Lindborg S.To measure plasma ACTH, alpha-melanocyte-stimulating hormone (aloha-MSH), and insulin concentrations during various photoperiods between February and October in horses and ponies with and without pituitary pars intermedia dysfunction (PPID). Methods: Cohort study. Methods: 13 clinically normal (control) ponies, 14 clinically normal (control) horses, 7 ponies with PPID, and 8 horses with PPID. Methods: Blood samples were collected from February through October during 8 photoperiods: 1, February 13 through March 2; 2, April 4 through 6; 3, June 19 through 22; 4, August 6 through 7; 5, August 14 ...
McGowan CM, Frost R, Pfeiffer DU, Neiger R.Serum insulin concentration and its use as a prognostic indicator in horses with equine Cushing's syndrome (ECS) have been poorly documented. Objective: To examine daily insulin variations in horses with ECS and the effect of treatment using trilostane, a competitive inhibitor of 3beta-hydroxysteroid dehydrogenase. Further, we aimed to examine the relationship between baseline serum insulin concentration and survival in horses with ECS. Methods: Basal serum insulin concentrations were measured in 20 confirmed ECS cases by taking blood at regular 4 h intervals for 24 h (1200, 1600, 2000, 2400, ...
Adams GP, Ratto MH.Ovulation in mammals involves pulsatile release of GnRH from the hypothalamus into the hypophyseal portal system with subsequent release of LH from the anterior pituitary into systemic circulation. Elevated circulating concentrations of LH induce a cascade of events within the mature follicle, culminating in follicle rupture and evacuation. The broad classification of species as either spontaneous or induced ovulators is based on the type of stimulus responsible for eliciting GnRH release from the hypothalamus. In spontaneously ovulating species (e.g., human, sheep, cattle, horse, pigs), relea...
Donadeu FX, Schauer SN.Relatively little is known about the physiological roles of microRNAs (miRNAs) during follicular development. Previous evidence from in vitro studies suggests specific roles for a subset of miRNAs, including miR-21, miR-23a, miR-145, miR-503, miR-224, miR-383, miR-378, miR-132, and miR-212, in regulating ovarian follicle development. The objective of this study was to gain insight on the involvement of these miRNAs during follicle maturation. Follicular fluid was aspirated from dominant follicles (>32 mm) during the ovulatory season (July to October) and the anovulatory season (January to M...
Novensa L, Selent J, Pastor M, Sandberg K, Heras M, Dantas AP.Conjugated equine estrogen therapy is the most common hormone replacement strategy used to treat postmenopausal women. However, the ability of an individual conjugated equine estrogen to modulate NO production and, therefore, to induce cardiovascular protection is largely unknown. The effects of equine and naturally occurring estrogens on NO generation were evaluated in human aortic endothelial cells by measuring in vivo NO production, as well as NO synthase (eNOS) activity and expression. The transcriptional activity on the eNOS gene was determined by the ability of estrogen receptors (alpha ...
Gérard N, Loiseau S, Duchamp G, Seguin F.Follicular development and ovulatory processes in mammals involve local biochemical changes as a result of substantial modifications in cellular metabolism, the most well known of which is steroid variation. In the present study, the intrafollicular variation of several other components was studied using proton nuclear magnetic resonance ((1)H NMR). This approach made it possible to demonstrate that the intrafollicular biochemical content changes during follicular growth and maturation. Follicular fluid was aspirated by ovarian puncture of the dominant follicle at various physiological stages ...
Okamura H, Yamamura T, Wakabayashi Y.The hypothalamo-pituitary-gonadal (HPG) axis is the regulatory system for reproduction in mammals. Because secretion of gonadotropin-releasing hormone (GnRH) into the portal vessels is the final step at which the brain controls gonadal activities, the GnRH neuronal system had been thought to be central to the HPG axis. A newly discovered neural peptide, kisspeptin, has opened a new era in reproductive neuroendocrinology. As shown in a variety of mammals, kisspeptin is a potent endogenous secretagogue of GnRH, and the kisspeptin neuronal system governs both the pulsatile GnRH secretion that dri...
Gentry LR, Thompson DL, Gentry GT, Davis KA, Godke RA, Cartmill JA.An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS...
Secombe CJ, Tan RHH, Perara DI, Byrne DP, Watts SP, Wearn JG.Longitudinal evaluation of plasma endogenous ACTH concentration in clinically normal horses has not been investigated in the Southern Hemisphere. Objective: To longitudinally determine monthly upper reference limits for plasma ACTH in 2 disparate Australian geographic locations and to examine whether location affected the circannual rhythm of endogenous ACTH in the 2 groups of horses over a 12-month period. Methods: Clinically normal horses <20 years of age from 4 properties (institutional herd and client owned animals) in Perth (n = 40) and Townsville (n = 41) were included in the study. M...
Ferlazzo A, Cravana C, Fazio E, Medica P.The review discusses the hormonal changes during exercise stress. The exercise generally produces a rise of adrenaline (A), noradrenaline (NA), adrenocorticotropic hormone (ACTH), cortisol, glucagon, growth hormone, arginine vasopressine, etc., and a drop of insulin. The hormonal events during reestablishment of homeostasis due to exercise stress can be divided into a catabolic phase, with decreased tolerance of effort, and reversible biochemical, hormonal and immunological changes, and an anabolic phase, with a higher adaptive capacity, and enhanced performance. The two main hormonal axes act...
