Omneity® Pellets
All-In-One Vitamin & Mineral Pellet
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.
Developmental changes in blood pressure and the renin-angiotensin system in pony fetuses during the second half of gestation. Blood pressure, heart rate and the plasma concentrations of cortisol and components of the renin-angiotensin system were measured in chronically catheterized Pony mares (n=15) and their fetuses during the second half of gestation (day 153-336 of gestation; term is normally between day 320 and day 340 of gestation). Fetal blood pressure increased towards term with the prepartum surge in plasma cortisol concentration, and there was a correlation between fetal blood pressure and both gestational age (r = 0.88, P < 0.0005) and plasma cortisol concentration (r = 0.88, P < 0.0005). Plasma conc...
Response of newborn foals with thyroid musculoskeletal disease to adrenocorticotrophic hormone (ACTH). Fetal maturation and equine parturition are not understood fully, although the adrenal and thyroid glands are thought to have regulatory roles. Thyroidectomized equine fetuses undergo prolonged gestation, and spontaneous diseases such as thyroid musculoskeletal disease and gestational fescue endophyte exposure are also associated with delayed parturition. Thyroid musculoskeletal disease is characterized by: histologically hyperplastic thyroid glands, chondro-osseous dysplasia and dysgenesis, angular limb deformity, low resting thyroxine and triiodothyronine concentrations, and lack of response...
Functional disturbances in the endometrium of barren mares: a histological and immunohistological study. Different types of endometrial maldifferentiation were investigated by histopathological (haematoxylin-eosin (HE), periodic acid Schiff-alcian blue and picro-sirius red staining) and immunohistological (oestrogen and progesterone receptors, Ki-67 antigen, intermediate filaments and laminin) analysis of endometrial biopsy specimens from mares (n=34), most of which had been barren for at least 1 year. Two major features were observed: (i) unequal differentiation, in which two functional stages are visible within a single biopsy sample: areas which are differentiated in accordance with the stage ...
Oxytocin and PGF2alpha release in mares resistant and susceptible to persistent mating-induced endometritis. Mares resistant (n=7) and susceptible (n=9) to persistent mating-induced endometritis were artificially inseminated (AI) during oestrus with chilled extended semen. Blood samples were collected from 30 min before AI, for 2 h after AI and again between 16 and 18 h after AI. Samples were assayed for oxytocin and the PGF2alpha metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM). AI caused a significant increase in oxytocin concentrations in both the resistant and susceptible mares and there was no significant difference in oxytocin release between the two groups of mares. Mean PGFM concentrations w...
Effects of steroids on endometrial oxytocin mRNA production. In this study, the roles of oestrogen and progesterone in the regulation of oxytocin gene expression in equine endometrium were examined. Anoestrous mares (n=19) were assigned randomly to one of the following treatment groups: control (vehicle control for 1 day; n=3); progesterone (250 mg progesterone per day for 6 days; n=4); oestradiol (5 mg beta-oestradiol 17-valerate per day for 6 days; n=4); oestradiol plus short duration progesterone (5 mg beta-oestradiol 17-valerate per day for 6 days followed by 250 mg progesterone per day for 6 days; n=4); and oestradiol plus long duration progesteron...
Effects of follicular fluid or progesterone on in vitro maturation of equine oocytes before intracytoplasmic sperm injection with non-sorted and sex-sorted spermatozoa. In Expt 1, compact cumulus oocyte complexes (COCs) were matured in: (i) control medium (Hepes-buffered TCM-199 with 10% oestrous cow serum (OCS) + oestradiol, LH and FSH); (ii) Hepes-buffered TCM-199 with 20% follicular fluid; or (iii) control medium containing 250 ng progesterone ml(-1). Mature oocytes were collected by transvaginal aspiration as a positive control for the in vitro maturation (IVM) treatments. Oocytes were fertilized by ICSI and cultured in Menezo's B2 + 5% fetal calf serum (FCS). There were no significant differences among IVM treatments. In Expt 2, oocytes with expanded COC...
The uterus as a source of oxytocin in cyclic mares. In a recent study, continuous administration of oxytocin by subcutaneous minipump to mares from day 8 to 20 after ovulation prevented luteolysis in most of the treated but none of the control mares, indicating a role for oxytocin in cyclical luteolysis in mares. In the present study, measurement of oxytocin concentrations in uterine flushings recovered from nine mares during days 14-18 after ovulation gave values that were many times higher than those measured concurrently in peripheral plasma. Furthermore, intrauterine administration of oxytocin to four mares on day 14 after ovulation stimula...
Simultaneous recording of pituitary oxytocin secretion and myometrial activity in oestrous mares exposed to various breeding stimuli. The aim of this study was to investigate the effect of different breeding stimuli on uterine contractility and pituitary oxytocin release in five oestrous mares, in order to design better treatments for mares with defective physical uterine clearance mechanisms. Electrodes and strain gauges were implanted surgically on the uterine myometrium and myometrial activity was monitored with a Grass polygraph. A catheter was placed non-surgically in the intercavernous sinus of each oestrous mare to sample pituitary venous blood and a second catheter was placed in the jugular vein. Continuous sampling ...
A detailed study of hormonal profiles in mares at luteolysis. Jugular blood samples were collected at 4 h intervals from six mares during an oestrous cycle to study the hormonal events that occur around the time of luteolysis. Blood samples from day 10 (day 0 = ovulation) until day 3 of oestrus were assayed for prostaglandin metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM), oxytocin, prolactin, progesterone and oestrogen conjugates. PGF2alpha (0.5 or 1.5 mg) was administered to six mid-dioestrous mares and the oxytocin and prolactin responses were measured. One to five large (peak > or =2 x nadir) pulses of PGFM, oxytocin and prolactin were detected ...
Progesterone, oestrogen and glucocorticoid receptors in the uterus and mammary glands of mares from mid- to late gestation. Progesterone, oestrogen and glucocorticoid receptor concentrations in the uterus and mammary glands of pregnant mares during mid- to late gestation (from day 150 of gestation to term) were measured by binding assays to investigate the hormonal mechanisms involved in pregnancy maintenance and lactation. Uterine progesterone receptor concentrations did not increase significantly with increasing gestational age (from 67.8 +/- 13.7 to 126.1 +/- 48.7fmol mg(-1) protein), whereas oestrogen receptor concentrations were significantly higher in pregnant mares (271.7 +/- 28.9 fmol mg(-1) protein) than i...
Seasonal variation and opioidergic regulation of growth hormone release in cyclic, ovariectomized, and pregnant pony mares. Modulation of reproductive functions is one of the multiple effects of growth hormone (GH). To investigate effects of reproductive functions on GH release in the horse, plasma GH concentrations in ovary-intact (n = 7) and ovariectomized (n = 8) mares during the anovulatory and breeding seasons and in pregnant mares (n = 6) at various stages of gestation were determined. To analyze an opioidergic regulation of GH release, repeated blood samples were taken over 3 h, and mares were injected with the opioid antagonist naloxone (0.5 mg/kg i.v.) or saline. GH was determined by RIA with an antiserum ...
Role of luteinizing hormone in follicle deviation based on manipulating progesterone concentrations in mares. The effects of several doses of progesterone on FSH and LH concentrations were used to study the role of the gonadotropins on deviation in growth rates of the two largest follicles during the establishment of follicle dominance. Progesterone was given to pony mares at a daily dose rate of 0 mg (controls), 30 mg (low dose), 100 mg (intermediate dose), and 300 mg (high dose). All follicles > or = 6 mm were ablated at Day 10 (Day 0 = ovulation) to initiate a new follicular wave; prostaglandin F(2alpha) was given to induce luteolysis, and progesterone was given from Days 10 to 24. The low dose ...
Dimeric inhibin concentrations in mares with granulosa-theca cell tumors. To determine whether concentrations of dimeric inhibin (CaCA) are greater in plasma and tumor fluid from mares with granulosa-theca cell tumors (GTCT), compared with concentrations in plasma and equine follicular fluid (eFF) from control mares. Methods: 6 mares with GTCT and 12 clinically normal mares. Methods: The alphabetaA immunoradiometric assay used 2 antibodies, one against each subunit of inhibin (alpha and betaA subunits). Tumor tissue, tumor fluid, and a single blood sample were collected at the time of surgical removal of the GTCT. A single blood sample was collected from 7 control m...
Testicular endocrine function, seasonality and semen quality of the stallion. To gain further information on gonadal function of the stallion, concentrations of testicular steroids in blood plasma (bpl) and seminal plasma (spl) and their distribution in the ejaculate were determined. Blood and semen samples from a total of 11 stallions were collected from November to July. Estrone (E1), estrone sulfate (E1S), estradiol-17beta (E2beta) and testosterone (T) were determined in bpl and spl, and in addition androstenedione (A), dehydroepiandrosterone (DHEA) and 5alpha-dihydrotestosterone (5alpha-DHT) were measured in spl. At certain points of time, aliquots of an ejaculate w...
A selective increase in circulating inhibin and inhibin pro-alphaC at the time of ovulation in the mare. The relationship between a selective increase in circulating immunoreactive (ir)-inhibin and the time of ovulation was investigated in mares. Concentrations of plasma ir-inhibin were measured every 4 h during the periovulatory period. Inhibin pro-alphaC, a precursor protein of the inhibin alpha-subunit, was also measured. The changes in ir-inhibin and inhibin pro-alphaC in circulation were parallel. Concentrations of both ir-inhibin and inhibin pro-alphaC in the plasma increased at the same time when ovulatory follicles ruptured, and the peak levels of circulating ir-inhibin and inhibin pro-al...
MR 20492 and MR 20494: two indolizinone derivatives that strongly inhibit human aromatase. 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...
Dual regulation of promoter II- and promoter 1f-derived cytochrome P450 aromatase transcripts in equine granulosa cells during human chorionic gonadotropin-induced ovulation: a novel model for the study of aromatase promoter switching. Estradiol biosynthesis is a key biochemical trait of developing follicles. To study its regulation in equine follicles, the objectives of this study were to clone and determine the structure of equine cytochrome P450 aromatase (P450AROM), and characterize the regulation of P450AROM and P450 17alpha-hydroxylase/C17-20 lyase (P45017alpha) messenger RNAs (mRNAs) in vivo in equine preovulatory follicles isolated during hCG-induced ovulation. Two distinct P450AROM complementary DNAs (cDNAs) were isolated from an equine preovulatory follicle cDNA library. One clone was 2682 bp in length and included...
Comparison of the merits of measuring equine chorionic gonadotrophin (eCG) and blood and faecal concentrations of oestrone sulphate for determining the pregnancy status of miniature horses. The relative merits of measuring blood concentrations of equine chorionic gonadotrophin (eCG, previously known as pregnant mare serum gonadotrophin (PMSG)), or oestrone sulphate (OS), or faecal OS concentrations for determining pregnancy status in miniature horses were investigated. Pregnant mares between 40 and 140 days after mating had serum eCG concentrations > 1 I.U. mL-1, with the highest concentrations occurring between days 50 and 120. However, eCG measurements were susceptible to returning a 'false positive' diagnosis of pregnancy. Plasma OS concentrations ranged from 0.1 to 3.6 ng ...
New approaches to detect cortisol administration in the horse. The cortisol threshold concentration of 1.0 microg/ml in horse urine adopted by the International Federation of the racing Authorities in 1994 is specific. However, an increase in the sensitivity for the detection of cortisol administration would be helpful. Previous studies have shown that 20beta-dihydrocortisol concentration in urine would be a good indicator of cortisol administration. The purpose of the present work was to estimate the population parameters and the critical values of 20beta-dihydrocortisol and 20beta-dihydrocortisone concentration in urine compared with that of cortisol. U...
PGFM response to exogenous oxytocin and determination of the half-life of oxytocin in nonpregnant mares. We investigated the half-life of oxytocin in reproductively normal mares and the prostaglandin response after oxytocin administrations. Mares were given oxytocin, 10 or 25 iu, i.v., on the day of, or 2 days after, ovulation, and frequent jugular blood samples were collected for analysis of oxytocin and Prostaglandin F metabolite (PGFM) by RIA. Neither dose of oxytocin nor day of treatment affected the half-life of the exogenous oxytocin, which was determined to be 6.8 min. A significant increase in PGFM was observed within 6 min of oxytocin administration and peak values were observed within 1...
Hydrocortisone levels in the urine and blood of horses treated with ACTH. An investigation was undertaken to demonstrate whether therapeutic treatment with ACTH raises hydrocortisone (cortisol) levels in horse urine above the limit (1000 ng/ml) established by the International Conference of Racing Authorities with the aim of controlling the abuse of cortisol and ACTH in equine sports. ACTH (200 iu) was administered i.m. to 3 Thoroughbred horses; urine and blood samples were collected at intervals afterwards and analysed by an immunoenzymatic system (ELISA) and HPLC-MS. To ascertain post exercise cortisol levels in untreated horses, 101 urine and 103 serum samples we...
Experimental assumption of dominance by a smaller follicle and associated hormonal changes in mares. A two-follicle model was used to study the nature of selection of the dominant follicle in mares by ablating neither or one of the two follicles on the day the larger follicle reached >/= 20 mm (Day 0). The larger follicle became the dominant follicle in all mares in which both follicles (n = 8) or only the larger follicle (n = 10) was retained. When only the smaller follicle (n = 9) was retained, it became dominant and ovulated in six mares and became atretic in three mares; the difference in diameter between the two follicles on Day 0 was less (p < 0.01) in mares in which the retained ...
Equine castration: review of anatomy, approaches, techniques and complications in normal, cryptorchid and monorchid horses. Complications associated with equine castration are the most common cause of malpractice claims against equine practitioners in North America. An understanding of the embryological development and surgical anatomy is essential to differentiate abnormal from normal structures and to minimise complications. Castration of the normal horse can be performed using sedation and regional anaesthesia while the horse is standing, or under general anaesthesia when it is recumbent. Castration of cryptorchid horses is best performed under general anaesthesia at a surgical facility. Techniques for castratio...
Nortestosterone: endogenous in urine of goats, sheep and mares? For a number of species it is known that nortestosterone, either the alpha- or beta-epimer, can be of endogenous origin. For goats and mares similar results have not yet been published. As a follow-up on the experiments with cattle, a large number of urine samples per animal were collected from pregnant goats, sheep and mares. These samples were analysed for the presence of alpha- and beta-nortestosterone and alpha-estradiol using GC-MS. The results show that in the goats and mares studied alpha-nortestosterone is present during pregnancy. In this study no alpha-nortestosterone could be demons...
Effects of anabolic steroid (19-nortestosterone) on the secretion of testicular hormones in the stallion. The aim of this study was to clarify the effect of anabolic steroids on the testicular endocrine function of mature stallions. Mature thoroughbred stallions were treated with 800 mg nandrolone decanoate every 3 weeks for 3 months. After the first treatment, plasma concentrations of LH, immunoreactive inhibin and testosterone decreased rapidly to the nadir. These hormones were maintained at significantly lower concentrations compared with concentrations in intact stallions. Histology of the testicular tissue indicated the arrest of advanced spermatogenesis in the seminiferous tubules and a seve...
[Diagnosis, therapy and endocrinologic parameters of persistent follicles in mares in comparison with preovulatory follicles]. During the 1997 breeding season persistent follicles were diagnosed in 17 mares. In 16 of these mares a total of 17 follicles were transabdominally punctured and the steroids oestradiol, progesterone and testosterone were measured in the follicular fluid and in blood serum. In ten mares serving as a control group preovulatory follicles were punctured. The follicular fluid of the persistent follicles revealed a very high variability of the steroid concentrations. Depending on the steroid ratio within the follicles, eight follicles were rated as being intact, three follicles were undergoing atre...
Follicle deviation and intrafollicular and systemic estradiol concentrations in mares. By definition, follicle deviation begins on the day the two largest follicles of a wave begin to differ in growth rates. The relationships between follicle deviation and intrafollicular and systemic estradiol concentrations were studied in ponies, using a two-follicle model in which all but the two largest follicles were ablated. A 20-microliter sample of follicular fluid was obtained from each of the two follicles by transvaginal ultrasonography. In experiment 1, the two follicles were sampled when the larger follicle reached 15 mm. No differences (p > 0.05) in post-sampling follicle chara...
