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Topic:Hormones
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.
Gene expression of ACTH, glucocorticoid receptors, 11βHSD enzymes, LH-, FSH-, GH receptors and aromatase in equine epididymal and testicular tissue. Glucocorticoids (GCs) are important mediators of the stress response and have been implicated in the function and regulation of testicular functions in different species. In many tissues, intracellular glucocorticoid activity is controlled by either or both of the two known isoforms of 11β-hydroxysteroid dehydrogenase (11βHSD) type 1 and 2, which interconvert active and inactive GCs. Little is known about the effects of stress on fertility in the equine species. The main objective of the present study was to investigate the expression of receptors for GCs and adrenocorticotropic hormone [ACT...
Secretion of luteinizing hormone into pituitary venous effluent of the follicular and luteal phase mare: novel acceleration of episodic release during constant infusion of gonadotropin-releasing hormone. We tested the hypothesis that continuous infusion of native GnRH into mares during the estrous cycle, at a dose of 100 μg/h, would elevate circulating concentrations of LH without disrupting the endogenous, episodic pattern of LH release. Ten cyclic mares were assigned to one of two groups (n = 5/group): (1) Control (saline) and (2) GnRH in saline (100 μg/h). On experimental day 0 (3 to 6 d after ovulation), osmotic pumps containing saline or GnRH were placed subcutaneously and connected to a jugular infusion catheter. Blood samples were collected from jugular catheters daily and at 5-min in...
Luteogenic and luteotropic effects of eCG during pregnancy in the mare. The role of eCG during pregnancy was evaluated through the study of the temporal relationships between changes in eCG and progesterone concentrations and the formation of supplementary corpora lutea (SCL) in mares impregnated with donkey semen (mule pregnancies) or with horse semen (equine pregnancies). Concentrations of eCG were higher (p<0.01) in equine than in mule pregnancies between weeks 6.5 and 13. Progesterone concentrations were higher in equine than in mule pregnancies between weeks 9 and 17. All animals developed at least one SCL, but more SCL accumulated during equine pregnancie...
Age- and gender-related variations in hematology, clinical biochemistry, and hormones in Spanish fillies and colts. In order to assess which laboratorial parameters need specific age- and/or gender-related reference values, hematological and biochemical profiles (including hormones) were performed in 205 Spanish foals of 5 groups: A (1-2 months; 20 fillies, 10 colts), B (2-3 months; 24 fillies, 18 colts), C (3-6 months; 25 fillies, 16 colts), D (6-9 months; 20 fillies, 23 colts) and E (9-12 months; 25 fillies, 15 colts). Additionally, 120 adult horses were sampled in order to establish baseline data for this breed in our laboratory. Group E had lower red blood cell number and mean cell volume than B, C and ...
The end of the tour de force of the corpus luteum in mares. Recent findings on the luteolytic process in mares are reviewed and differences from other farm species are noted. It is well known that the luteolysin, PGF2α (PGF), is secreted from the endometrium in the absence of pregnancy in farm animal species. But PGF is a potent chemical and safeguards have evolved so that only the corpus luteum (CL) is affected. The safeguards include a short PGF half-life and secretion in two or three pulses per day. In mares, endogenous PGF travels from the uterus to the CL through the systemic circulation, but the luteal-cell membranes are highly efficient in capt...
Cytokines tumor necrosis factor-α and interferon-γ participate in modulation of the equine corpus luteum as autocrine and paracrine factors. Knowledge on the regulation of corpus luteum (CL) function in the mare is scarce. In this study, the presence of cytokines tumor necrosis factor alpha (TNF) and interferon gamma (IFNG), and their receptors (TNFRI, TNFRII and IFNRI), was investigated in equine CL throughout the luteal phase. The effects of TNF and IFNG on secretory function and viability of luteal cells were defined in vitro. Cytokine ligands and receptors were present in steroidogenic and endothelial cells. Protein expression for TNF was greater in mid-phase and regressing CL, while TNFRI was increased in regressing CL and TNF...
Efficacy of human chorionic gonadotropin to induce ovulation in the mare, when associated with a single dose of dexamethasone administered at breeding time. Human chorionic gonadotropin (hCG) and dexamethasone have a role in the reproductive management protocols of mares susceptible to persistent mating-induced endometritis (PMIE). However, it is possible that there is interference between these 2 drugs. Objective: The objective of this retrospective study was to determine the efficacy of hCG to induce ovulation in mares treated with dexamethasone at breeding time. Methods: Medical records from 152 mares and 223 cycles were analysed. In 113 cycles, mares susceptible to PMIE were treated with 1500 iu hCG and a single dose of 50 mg dexamethasone, 11...
How type of parturition and health status influence hormonal and metabolic profiles in newborn foals. Thyroid hormones, insulin growth factor I (IGF-I) and non-esterified fatty acids (NEFA) represent important hormonal and metabolic factors associated with perinatal growth and maturation. Their action could be influenced by the type of parturition and the health status of the foal and therefore the aim of this work is to evaluate their plasma concentrations in newborn foals during the first 2 wks of life. Three groups of subjects were enrolled: 15 healthy foals born by spontaneous parturition, 24 healthy foals born by induced parturition and 26 pathologic foals. From each of the healthy foals,...
The reproductive performance of Thoroughbred mares treated with intravaginal progesterone at the start of the breeding season. The objective of this study was to investigate the effects of intravaginal progesterone on the reproductive performance of transitional Thoroughbred mares on commercial stud farms. Two hundred twenty-seven (227) non-lactating transitional Thoroughbred mares aged between 4 and 18 y (mean 9.4 ± 3.2 y) located on three stud farms in the Waikato region of New Zealand were used in the study performed during four consecutive breeding seasons (2007-10). Mares were age-matched in pairs and either treated with an intravaginal progesterone releasing device (Cue-Mare, 1.72 g progesterone, 10% w/w) for u...
Variations of plasma leptin in show horses during a work season. Leptin is an adipocytokine mainly expressed by adipose tissue. Secretion of leptin in healthy animals is closely related to fat mass and metabolic activity. The aim of this study was to investigate plasma leptin variations, in relation to nutritional and exercise parameters in adult show horses during a work season. EDTA-blood samples were taken at rest from 37 Iberian horses. Body weight, body condition score and fat percentage determined by ultrasonic measurement of rump fat thickness were measured. Plasma leptin was determined with a multi-species RIA kit. Linear mixed effects model was use...
The mare: a 1000-pound guinea pig for study of the ovulatory follicular wave in women. The mare is a good comparative model for study of ovarian follicles in women, owing to striking similarities in follicular waves and the mechanism for selection of a dominant follicle. Commonality in follicle dynamics between mares and women include: (1) a ratio of 2.2:1 (mare:woman) in diameter of the largest follicle at wave emergence when the wave-stimulating FSH surge reaches maximum, in diameter increase of the two largest follicles between emergence and the beginning of deviation between the future dominant and subordinate follicles, in diameter of each of the two largest follicles at th...
Expression of anti-Müllerian hormone, cyclin-dependent kinase inhibitor (CDKN1B), androgen receptor, and connexin 43 in equine testes during puberty. Sertoli cells are essential in development of a functional testis. During puberty, Sertoli cell maturation can be characterized by a number of markers, including anti-Müllerian hormone (AMH) and its receptor (AMHR2), androgen receptor (AR), cyclin-dependent kinase inhibitor (CDKN1B), and connexin 43 (Cx43). In the present study, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) were used to characterize changes in expression of AMH, AMHR2, AR, CDKN1B, and Cx43 in prepubertal, postpubertal, and adult equine testes. During puberty, AMH expression decrease...
Immunohistochemical localisation of progesterone and oestrogen receptors at the placental interface in mares during early pregnancy. Previous reports documenting progesterone receptors (PR) and oestrogen receptors (ER) in the endometrium of early pregnant mares included specimens only up to Day 20 post ovulation. This study aimed to localise PR and ERα on equine feto-maternal tissues between Days 20 and 68 to encompass the period around fixation of the conceptus, development of the endometrial cups and attachment and initial interdigitation of the allantochorion. During early pregnancy mares had the same pattern of PR in the endometrium as that reported for other mammals; namely, a loss of PR from the endometrial epithelia...
Relationship between dose of cloprostenol and age of corpus luteum on the luteolytic response of early dioestrous mares: a field study. The objective of this study was to establish and characterize the relationship between the dose of cloprostenol (37.5, 250, 500 and 750 μg) and the age of the early corpus luteum (CL) (80, 88, 96, 104 and 112 h) on the luteolytic response of mares. Behavioural oestrus and ultrasonographic signs of return to oestrus were considered as the occurrence of full luteolysis. A total of 298 mares were divided into groups according to dose of cloprostenol and CL age. There was an effect of dose of cloprostenol (p < 0.001) and age of the CL at the time of treatment (p 0.05); and that of 500 similar...
Circadian variation in ghrelin and certain stress hormones in crib-biting horses. Crib-biting is classified as an oral stereotypy, which may be initiated by stress susceptibility, management factors, genetic factors and gastrointestinal irritation. Ghrelin has been identified in the gastric mucosa and is involved in the control of food intake and reward, but its relationship to crib-biting is not yet known. The aim of this study was to examine the concentration and circadian variation of plasma ghrelin, cortisol, adrenocorticotropic hormone (ACTH) and β-endorphin in crib-biting horses and non-crib-biting controls. Plasma samples were collected every second hour for 24h in ...
Assessment of endogenous growth hormone pulsatility in gelded yearling horses using deconvolution analysis. Defining normal Growth Hormone (GH) secretory dynamics in the horse is necessary to understand altered GH dynamics related to issues like welfare and disease. Methods: Twelve healthy yearlings and two mature Standardbreds were used to quantify GH secretion. Endogenous GH half-life was determined after administration of 1.0 µg/kg BW GH releasing hormone (GHRH). Exogenous GH half-life was determined after administration of 20 µg/kg BW recombinant equine GH (reGH) with and without suppression of endogenous GH secretion by somatostatin infusion (50 µg/m(2)/h). Pulse detection algorithm (C...
Comparison of cortisol and ACTH responses after administration of thyrotropin releasing hormone in normal horses and those with pituitary pars intermedia dysfunction. Changes in both adrenocorticotropin (ACTH) and cortisol concentration in response to thyrotropin releasing hormone (TRH) administration have been used to diagnose equine pituitary pars intermedia dysfunction (PPID), but the use of the 2 hormones has not been compared. Objective: Measuring ACTH concentration is superior to measuring cortisol concentration after TRH administration in differentiating between normal horses and those with PPID, and the 2 hormone concentrations are disassociated in PPID horses. Methods: Eleven horses and 2 ponies with PPID and 19 normal horses. Methods: A study eval...
Hormone concentration changes temporally associated with the hour of transition from preluteolysis to luteolysis in mares. The temporal associations of cortisol, estradiol-17β, and oxytocin with pulses of PGFM at the common hour of transition between preluteolysis and luteolysis was studied in plasma from hourly blood samples in mares (n=8). The transitional hour was determined from progesterone concentrations and occurred between 2PM and 2AM in all mares. Pulses of PGFM were grouped into those occurring at the last pulse of preluteolysis (preluteolytic pulse), at the hour of transition (transitional), and during luteolysis (luteolytic). The preluteolytic PGFM pulse (45±16pg/ml at peak) and transitional pulse (4...
The effect of interval versus continuous exercise on plasma leptin and ghrelin concentration in young trotters. The effect of interval vs. continuous exercise on plasma leptin and ghrelin concentration in young Standardbred horses was studied. The experiment was conducted on 27 trotters, in the age between 2 and 3 years. They were divided into two groups according to the type of exercise. Blood samples were collected through jugular venipuncture in the following experimental conditions: at rest, immediately after exercise and 30 minutes after the end of the effort. Plasma leptin and ghrelin concentrations were determined using RIA tests. The continuous exercise induced an increase in plasma leptin conce...
Effects of nutritional cues on the duration of the winter anovulatory phase and on associated hormone levels in adult female Welsh pony horses (Equus caballus). Mares have an annual reproductive rhythm, with a phase of inactivity in midwinter. The aim of this study was to determine the impact of food restriction on physiological and metabolic hallmarks of this rhythm. Methods: Over three successive years, 3 groups of 10 mares were kept under natural photoperiod. A 'well-fed' group was fed to maintain the mares in good body condition; a 'restricted' group received a diet calculated to keep the mares thin and a 'variable' group was fed during some periods like the 'restricted' group and during some other periods like the 'well-fed' group, with the aim o...
Distribution of mast cells in vaginal, cervical and uterine tissue of non-pregnant mares: investigations on correlations with ovarian steroids. Mast cells constitute part of the cellular immune system of the genital tract. They play a potential role in cervical remodelling during parturition and are subject to the influence of ovarian steroids. In this study, the influence of oestradiol-17β and progesterone on the distribution of mast cells in equine vaginal, cervical and uterine tissue was evaluated. Genital tracts were retrieved from healthy mares at a local slaughterhouse. The cervix was divided along the longitudinal axis into five equivalent regions from cranial to caudal (R1 to R5). Toluidine blue staining was used for the dete...
Treatment with recombinant equine follicle stimulating hormone (reFSH) followed by recombinant equine luteinizing hormone (reLH) increases embryo recovery in superovulated mares. The dynamics of ovarian follicular development depend on a timely interaction of gonadotropins and gonadal feedback in the mare. The development and efficacy of genetically cloned recombinant equine gonadotropins (reFSH and reLH) increase follicular activity and induce ovulation, respectively, but an optimum embryo recovery regimen in superovulated mares has not been established. The objective of this study was to determine if treatment with reFSH followed by reLH would increase the embryo per ovulation ratio and the number of embryos recovered after superovulation in mares. Sixteen estrous cy...
Experimental jetlag disrupts circadian clock genes but improves performance in racehorses after light-dependent rapid resetting of neuroendocrine systems and the rest-activity cycle. Abrupt alterations in the 24-h light : dark cycle, such as those resulting from transmeridian air travel, disrupt circadian biological rhythms in humans with detrimental consequences on cognitive and physical performance. In the present study, a jetlag-simulated phase shift in photoperiod temporally impaired circadian peaks of peripheral clock gene expression in racehorses but acutely enhanced athletic performance without causing stress. Indices of aerobic and anaerobic capacities were significantly increased by a phase-advance, enabling prolonged physical activity before fatigue occurred. Thi...
Validation of a low-dose ACTH stimulation test in healthy adult horses. To determine the lowest ACTH dose that would induce a maximum increase in serum cortisol concentration in healthy adult horses and identify the time to peak cortisol concentration. Methods: Evaluation study. Methods: 8 healthy adult horses. Methods: Saline (0.9% NaCl) solution or 1 of 4 doses (0.02, 0.1, 0.25, and 0.5 μg/kg [0.009, 0.045, 0.114, and 0.227 μg/lb]) of cosyntropin (synthetic ACTH) were administered IV (5 treatments/horse). Serum cortisol concentrations were measured before and 30, 60, 90, 120, 180, and 240 minutes after injection of cosyntropin or saline solution; CBCs were per...
Concentrations of circulating hormones during the interval between pulses of a PGF2α metabolite in mares and heifers. 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...
Progesterone production in mares and echographic evaluation of the corpora lutea formed after follicular aspiration. 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...
Temporal relationships of a pulse of prolactin (PRL) to a pulse of a metabolite of PGF2α in mares. 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...
Circannual variation in plasma adrenocorticotropic hormone concentrations in the UK in normal horses and ponies, and those with pituitary pars intermedia dysfunction. 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 ...
Administration of a gonadotropin-releasing hormone antagonist to mares at different times during the luteal phase of the estrous cycle. 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...
