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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.
Changes in the hypothalamic-hypophyseal axis of mares in relation to the winter solstice. In mares, the amount of gonadotrophin-releasing hormone (GnRH) is low in the hypothalamus during seasonal anoestrus, but by early spring, concentrations of GnRH are high. The timing of this response was characterized more precisely by determining concentrations of GnRH in hypothalamic tissue collected immediately before and at various times after the winter solstice (22 December 1986). Ovaries, pituitary gland, hypothalamus and a blood sample were collected from six groups of mares (6-12 mares per group) at death, 1 week before day of the winter solstice and 1, 2, 3 and 12 weeks afterwards. No...
Increase in plasma progestagen concentrations in the mare after foetal injection with CRH, ACTH or betamethasone in late gestation. Maternal plasma progestagen concentrations increase about 20 days before parturition. The major contributors to the increase are reduced metabolites (ie 5 alpha-pregnanes). Precocious increases (ie less than 310 days of gestation) in these metabolites may occur in abnormal pregnancies. The effects of CRH, ACTH or betamethasone administered to the foetus at gestational ages ranging from about 250 to 320 days were examined. Sixteen healthy pony mares were used for foetal injection employing aseptic techniques. Water or normal saline were used as controls. Maternal plasma progestagen concentratio...
Clinical and biochemistry findings, and parathyroid hormone concentrations in three horses with secondary hyperparathyroidism. Three cases of horses with nutritional secondary hyperparathyroidism (NSH) are described. The horses showed typical thickening of the maxillae and mandibular bones with or without lameness. Laboratory findings included elevated concentrations of parathyroid hormone (carboxy-terminal and mid-molecule fractions), alkaline phosphatase and an increase in the fractional excretion rate of serum inorganic phosphorus.
Long-term cannulation of the ovarian vein in mares. A cannulation technique was developed to collect blood samples from the ovarian vein of mares over an extended period. Ovarian venous cannulae placed in 4 mares remained patent for a mean (+/- SEM) duration of 36.8 (+/- 6.2) days. During mid-diestrus, concentrations of progesterone in the ovarian vein ipsilateral to the corpus luteum (1,663.8 +/- 238.8 ng/ml) were significantly (P less than 0.001) higher than concentrations measured in paired samples from the jugular vein (6.1 +/- 0.3 ng/ml). Concentration of estradiol in the ovarian vein ranged from a mean of 1,053.2 +/- 303.1 pg/ml during di...
The development of gluconeogenic enzymes in the liver and kidney of fetal and newborn foals. The activities of glucose-6-phosphatase (G6P), fructose diphosphatase, phosphoenolpyruvate carboxykinase (PEPCK), aspartate and alanine transferases were measured in liver and kidney of fetal foals between 100-318 days of gestation (term approximately 335 days) and during the immediate postnatal period (0-48 h after birth). All 5 enzymes could be detected in the fetal liver and kidney at the youngest gestational age studied. Mean fetal activities were lower than those observed in their mothers and showed no change with gestational age for the majority of enzymes studied. However, renal PEPCK a...
Use of progesterone in microspheres for maintenance of pregnancy in mares. Administration of progesterone in poly(d-,l-lactide) microspheres was used to maintain pregnancy in mares after luteolysis was induced by treatment with prostaglandin F2 alpha at day 14 of pregnancy. Mares were given vehicle only (control, n = 6) or 0.75 g (n = 7), 1.5 g (n = 8), or 2.25 g (n = 5) of microencapsulated progesterone at days 12 and 22 of pregnancy. Serum progesterone concentrations were determined daily, and pregnancy was evaluated by transrectal ultrasonography on alternate days. Significantly (P less than 0.05) more mares given 1.5 or 2.25 g of progesterone (6 of 8 and 4 of 5 m...
Plasma renin activity and aldosterone and vasopressin concentrations during incremental treadmill exercise in horses. Six untrained mares were subjected to incremental treadmill exercise to examine exercise-induced changes in plasma renin activity (PRA) and plasma aldosterone (ALDO) and plasma arginine vasopressin (AVP) concentrations. Plasma renin activity, ALDO and AVP concentrations, and heart rate (HR) were measured at each step of an incremental maximal exercise test. Mares ran up a 6 degree slope on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s each minute until HR reached a plateau. Plasma obtained was stored at -80 C and later was thawed, extracted, and assayed for PRA and AL...
[Double ovulation in mares. Clinical, hormone analytical and sonographic studies]. 108 mares with a total of 135 oestrous cycles were examined. 30% of the mares showed development of double follicles, found by palpation and ultrasonography. Eight cases of double ovulation, four of them synchronous and four asynchronous, were examined closely. These cases of double ovulation showed different growth and different development of the follicular wall. This occurred at the same time in cases of synchronous double ovulation whereas it differed in case of asynchronous double ovulation. The later ovulating follicle was still growing while the first one had already burst. With both fo...
Thermospray liquid chromatography-mass spectrometry of corticosteroids. A high-performance liquid chromatographic method was developed for thermospray mass spectrometric analysis of steroidal hormones. Using a Nova-Pak C18 reversed-phase column and isocratic elution with a solvent comprised of 25 mM ammonium formate in 30% acetonitrile, corticosteroids were separated within 10 min. This solvent also permitted ultraviolet absorbance detection down to 220 nm with low-nanogram sensitivity. The use of acetonitrile was favourable for thermospray mass spectrometric analysis because mass spectra were obtained with a pseudomolecular ion as the base peak. A combination of ...
Testicular feminization syndrome in a mare. Testicular feminization syndrome was diagnosed in a mare with aggressive, stallion like behavior and a history of infertility. She was found to have a high baseline testosterone concentration suggesting that testicular tissue was present, and ovarian-like structures examined by use of transrectal ultrasonography had the appearance typical of testicular tissue. Although her external female genitalia appeared normal, her vagina ended in a blind sac, and no cervix or uterus were identified. Surgery was performed, and structures removed from the abdominal cavity were determined to be hypoplastic t...
Short-term effect of aldosterone on Na-Cl transport across equine colon. In ponies fed concentrated (pelleted) meals, postprandial increases of plasma aldosterone have been temporally associated with a decrease in colonic fluid volume that parallels the conclusion of postfeeding fermentation. To determine the significance of short-term increases of plasma aldosterone on the rate of colonic Na absorption, in vitro transport studies were conducted on the mucosae of three morphologically distinct colonic segments (i.e., ventral, dorsal, and small colons) from ponies infused with a high physiological concentration of aldosterone for an 8-h period. In control ponies, ba...
A single gene encodes the beta-subunits of equine luteinizing hormone and chorionic gonadotropin. Equine (e) CG and LH beta-subunits have identical amino acid sequences, including an extended carboxyl-terminal peptide (CTP). This suggests that unlike the corresponding human genes, the beta-subunits of eCG and eLH may be encoded by a single gene and share a common proximal promotor region. To explore this, we isolated and characterized the eLH/CG beta gene(s). Data from Southern analyses suggest that the eCG beta and eLH beta subunits are products of the same single copy gene (eLH/CG beta). Overlapping fragments of the eLH/CG beta gene and cDNA were amplified from equine genomic DNA and pit...
Effects of fescue toxicosis on reproduction in livestock. Fescue toxicosis in livestock is due to ingestion of endophyte (Acremonium coenophialum) -infected tall fescue. Understanding mechanisms responsible for decreased calving and growth rates, delayed onset of puberty, and impaired function of corpora lutea in heifers at puberty consuming endophyte-infected fescue is an emerging field in reproductive toxicology. The condition decreases overall productivity through a reduction in reproductive efficiency, reduced weight gains, and lowered milk production. Reproduction in cattle may be further compromised by winter coat retention, increased susceptib...
Binding of estrogen-3-sulfates to stallion plasma and equine serum albumin. The binding of estrone-3-sulfate (E1-3-S) and estradiol-3-sulfate (E2-3-S) to adult stallion plasma was determined and compared with the binding to equine serum albumin (ESA). On the ESA molecule, two binding sites for E1-3-S with an association constant of 1.3 x 10(5) M-1 and several sites of weaker affinity were found; the data for E2-3-S showed the existence of four binding sites of moderate affinity (1 x 10(5) M-1) and several sites of weaker affinity. The removal of albumin from the stallion plasma resulted in the absence of binding of E1-3-S or E2-3-S, whereas the removal of glycoprotein...
Superovulation of cattle with equine pituitary extract and porcine ESH. Superovulation has been practiced in cattle for more than 50 years but the results have been highly variable. Scientists at six locations compared a horse pituitary extract (HAP) with a single batch of porcine FSH (pFSH) to determine the efficacy of these hormones to induce superovulation and to test for variability in the superovulatory response. Acetone-dried equine pituitaries were suspended in 40% ethanol containing 6% ammonium acetate, and the supernatant was mixed with 2.5 volumes of cold ethanol. The resulting precipitate was washed with cold ether and dried. Total doses of 18 mg of HAP...
Tissue-specific gene expression in the pituitary: the glycoprotein hormone alpha-subunit gene is regulated by a gonadotrope-specific protein. The molecular mechanisms for the development of multiple distinct endocrine cell types in the anterior pituitary have been an area of intensive investigation. Though the homeodomain protein Pit-1/GHF-1 is known to be involved in differentiation of the somatotrope and lactotrope lineages, which produce growth hormone and prolactin, respectively, little is known of the transcriptional regulators important for the gonadotrope cell lineage, which produces the glycoprotein hormones luteinizing hormone and follicle-stimulating hormone. Using transgenic mice and transfection into a novel gonadotrope ...
Seasonal effects on seminal quality, plasma hormone concentrations, and GnRH-induced LH response in fertile and subfertile stallions. Seasonal effects on hormonal and seminal parameters in subfertile stallions have not been well documented and could provide information that is needed to understand the underlying endocrine mechanisms associated with testicular dysfunction. Such information may be useful in developing diagnostic tools to identify those stallions who are candidates for treatment. This investigation characterizes and compares the effects of season on endocrine function and seminal quality in fertile and subfertile stallions. Eight fertile and six subfertile stallions between the ages of 5 and 18 years were injec...
Isolation and culture of glandular epithelial and stromal cells from the endometrium of mares. Glandular epithelial and stromal cells were isolated from the endometrium of mares by collagenase digestion and were incubated on plastic for 7-9 days until the cells formed confluent monolayers. The cells differed in morphology: epithelial cells appeared polyhedral and stromal cells were spindle like. The monolayers were incubated in the presence and absence of oxytocin. Medium was removed from wells after 2, 8 and 24 h of incubation. Concentrations of prostaglandin F (PGF) in the medium increased significantly during this time. Glandular epithelial cells produced significantly more PGF than ...
Growth hormone in mares and stallions: pulsatile secretion, response to growth hormone-releasing hormone, and effects of exercise, sexual stimulation, and pharmacological agents. Short-term patterns of growth hormone (GH) secretion and factors affecting it were studied in mares and stallions. In Exp. 1, hourly blood samples were collected from three mares and three stallions in summer and winter. Although GH concentrations varied in a pulsatile manner in all horses, there was no effect of sex or season (P greater than .1) on plasma GH concentrations and no indication of a diurnal pattern of GH secretion. In Exp. 2, 10-min blood samples were drawn for 8 h from 12 mares; after 6 h, porcine GH-releasing hormone (GHRH) was administered i.v. at 0, 45, 90, or 180 micrograms/...
Mediators of maternal recognition of pregnancy in mammals. No abstract available
Effects of gonadotropin-releasing hormone infused in a pulsatile or continuous fashion on serum gonadotropin concentrations and ovulation in the mare. Studies were conducted to compare continuous vs pulsatile i.v. infusion of GnRH on serum gonadotropin concentrations and ovulation in seasonally anestrous mares and in cycling mares. Anestrous mares (Exp. 1) received no treatment (control; n = 3), 2, or 20 micrograms of GnRH/h continuous infusion (CI) (n = 4 and n = 6, respectively), or 20 micrograms of GnRH/h pulsatile infusion (PI) (n = 5). After initiation of GnRH infusion, serum LH levels increased earlier, and to a greater extent, in the PI group than in other groups (P less than .05). In contrast, serum FSH concentrations did not differ ...
Endocrine abnormalities and hormonal therapy. Routine measurement of estrogens, testosterone, T4, insulin, FSH, and LH at least four times per year (e.g., during each of the four seasons) may improve the efficiency of stallion management. Benefits may not be realized in the short term but will provide valuable historical data on individual stallions that, when added to other data, will improve ability of management personnel to initiate early treatment and delay or slow declining fertility. This ability will be greatly improved as more data and products become available. There appears to be a relationship between low total estrogen concen...
Reproductive anatomy and physiology of the stallion. Examination of the stallion's reproductive tract involves assessments of external and internal anatomy. External examinations are performed by visual inspection, palpation, or ultrasonography and include the scrotum, testes, epididymides, penis, and prepuce. Internal examinations may be performed by rectal palpation, transrectal ultrasonography, or endoscopy and include the accessory sex glands, pelvic urethra, and inguinal rings. A fertile stallion must produce, transport, store, and deliver viable spermatozoa to the mare. The physiologic processes involved include neuroendocrine control, spe...
Control of FSH, follicular development and estrus synchronization in the mare with steroid-free follicular fluid. Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatment...
Endocrine and testicular changes associated with season, artificial photoperiod, and the peri-pubertal period in stallions. The seasonal reproductive cycle of stallions is characterized by an annual regression and recrudescence in testicular function and concentrations of LH, FSH, and testosterone in serum. Maximum reproductive capacity occurs during the increasing day lengths of spring and summer. The annual cycle in LH secretion may reflect a seasonally associated and photosensitive reduction and replenishment in pituitary content of LH. Similar to other seasonal breeders, it appears that stallions may possess an endogenous circannual rhythm in reproductive function that is subject to manipulation by altering the...
Hormonal contraception of feral mares with Silastic rods. Homogeneous Silastic rods containing ethinylestradiol (EE) (1.5 or 4 g), estradiol-17 beta (E) (4 g) or progesterone (P) (6 g) were implanted into feral mares (Equus caballus) between 4- and 10-yr-old. Six treatment groups (greater than or equal to 10 mares/group) of non-pregnant mares received 36 g P and 12 g E (P+E), 36 g P and 8 g EE (P+HEE), 1.5 g EE (LEE), 3 g EE (MEE, 8 g EE (HEE) or control-implanted mares (CI). CI received implants containing no steroid. Two groups of pregnant mares received P+HEE or HEE. Stallions were placed with the mares 15 to 26 mo after implanting. Blood was coll...
Breed differences in circulating equine relaxin. Equine relaxin has been previously determined in a small number of pregnant Thoroughbred mares. To better define the normal pregnancy pattern of relaxin, the current study reports on a much larger number of mares. It also was designed to determine if all equids have the same gestational pattern of relaxin secretion. Plasma samples were collected weekly in 24 Standardbred mares, every 7-10 days in 10 pony mares, and daily in late pregnancy from 16 burros. Standardbreds had higher concentrations of relaxin than that reported for Thoroughbreds during most of gestation and did not exhibit the midp...
Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function in feral horses (Equus caballus). Ten feral mares free-roaming in Maryland, USA, were inoculated with porcine zonae pellucidae (PZP) protein before the breeding season for three consecutive years (1988-90). Ovarian function was monitored for 51 days during the peak of the breeding season after the third annual PZP inoculation, in seven of these mares and in four untreated control mares, by means of urinary oestrone conjugates and nonspecific progesterone metabolites. None of the ten inoculated mares became pregnant in 1990, compared with 55% of 20 control mares, which included two of the four monitored for ovarian function. Th...
Increased ovulation rates in mares after immunisation against recombinant bovine inhibin alpha-subunit. THE name inhibin was first used around 60 years ago for a water-soluble. non-steroidal, gonadal factor that would regulate follicle-stimulating hormone (FSH) secretion through negative feedback McUullagh 1930. Inhihin is now defined as a glycoprotein hormone, consisting of two dissimilar, disulphide-linked, subunits termed at and 13 1 Burger and Igarashi 1988). Effective methods for blocking inhibin production could provide useful means by which FSH secretion, and therefore ovarian function and fertility, could be improved in the female. Increased ovulation rates have been demonstrated in shee...
Identification and partial purification of serum growth hormone binding protein in domestic animal species. The chemical nature and variations in serum concentrations of growth hormone binding protein (GHBP) from humans, rabbits, and rodents have been reported. To date little is known about the GHBP of domestic animals. Therefore, we initiated these studies to determine whether a serum GHBP was present in domestic animals and to purify the binding protein (BP) from serum of selected species. Using a dextran-coated charcoal separation assay, specific growth hormone (GH) binding was demonstrated in ovine, bovine, chicken, human, goose, porcine, and equine serum (listed in sequence from lowest to highe...
