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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.
Estrogen metabolites in equine ovarian follicles: gas chromatographic-mass spectrometric determinations in relation to follicular ultrastructure and progestin content. Equine follicular fluid was aspirated at various developmental stages (viable, preovulatory and atretic) determined by ultrastructural study. Estrogens and progestins were analyzed by gas chromatography-mass spectrometry associated with stable isotope dilution. Progesterone and 17-hydroxyprogesterone were the principal progestins of the preovulatory and viable follicles. Among the catechol estrogens, 2-hydroxy-estradiol was particularly abundant in the preovulatory follicle and its definitive identification was made by the scan of a full mass spectrum.
The biosynthesis of 3 beta-hydroxy-5,7-androstadien-17-one by the horse fetal gonad. Horse fetal gonadal tissue was incubated with 3 beta-hydroxy-5,7-pregnadien-20-one and 5,7-cholestadien-3 beta-ol and it was shown that both substrates were converted to 3 beta-hydroxy-5,7-androstadien-17-one. These findings support the proposal that in this tissue there is a 5,7-diene pathway producing 3 beta-hydroxy-5,7-androstadien-17-one, the putative precursor of equilin in the placenta.
Induction of oestrus and ovulation by means of prostaglandin and gonadoliberin (GnRH) treatment in an old mare barren for two breeding seasons. A 17-year-old Nooitgedacht mare was presented in mid-summer after failing to conceive during the previous 2 breeding seasons. The mare conceived to service during a PG-induced oestrus when synthetic GnRH was used to induce ovulation.
Patterns of secretion of luteinizing hormone, follicle stimulating hormone and testosterone in stallions during the summer and winter. Samples of jugular blood were drawn from each of five stallions every 15 min for 12 h during the summer and winter to determine the short-term fluctuations in plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone. Concentrations of LH and FSH were generally not pulsatile, although one stallion exhibited three distinct pulses in these hormones during the winter. In general, patterns of secretion of all three hormones were similar in both seasons and the number of significant rises in hormonal concentrations did not differ between seasons. Concent...
Application of the peroxidase-antiperoxidase procedure to the localization of pituitary hormones and calcitonin in various domestic animals and human beings. Specific cell populations in the pituitary glands of the rat, cat, pig, and human being were positive for thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH). When reacted with prediluted rabbit anti-human TSH, LH, and FSH, antisera were not positive for the demonstration of these hormones in the horse, cow, or dog. Immunocytochemical staining was obtained in the horse, cow, and dog by the use of a primary antiserum against a specific beta-subunit of bovine TSH. The immunocytochemical staining of TSH, LH, FSH, adrenocorticotropic hormone, growth ...
Follicular dynamics in mares treated with an equine pituitary extract. The follicular dynamics of 112 mares treated with an equine pituitary extract were studied. Follicles >10 mm in diameter at day 15 post-ovulation appeared to represent the follicles which were induced with pituitary extract to grow and ovulate. This was shown by the greater number of >10 mm follicles in mares which subsequently had higher ovulation rates and by the subsequent decrease in number of small follicles (/=20 mm). The difference in diameter (mm) between the largest and second largest follicle on day 15 post-ovulation was greater (P0.1) from the expected ratio which was calculat...
Effects of phenylbutazone and anabolic steroids on adrenal and thyroid gland function tests in healthy horses. Adrenal and/or thyroid gland function tests were evaluated in horses at various times during short-term therapy with phenylbutazone, stanozolol, and boldenone undecylenate. There were no significant treatment or time effects on mean basal plasma cortisol concentrations in horses during treatment with the following: phenylbutazone, given twice daily (4 to 5 mg/kg, IV) for 5 days; stanozolol, given twice weekly (0.55 mg/kg, IM) for 12 days; boldenone undecylenate, given twice weekly (1.1 mg/kg, IM) for 12 days; or nothing. There was no significant effect of phenylbutazone treatment on the change...
Uterine involution in mares treated with progesterone and estradiol-17 beta. Bacteriology, histology, and scanning electron microscopy were used to evaluate uterine involution in 27 mares treated with daily injections of 150 mg of progesterone and 10 mg of estradiol-17 beta, commencing within 18 hours of parturition. These findings were compared with those for 24 untreated mares at postpartum day 10 or 11. The treatment resulted in significantly (P less than 0.05) greater uterine gland proliferation. Gland density was significantly (P less than 0.05) greater in mares treated for 6 to 10 days than in those treated 2 to 5 days. The proportion of ciliated cells to secreto...
Activity of delta(5)3beta-hydroxysteroid dehydrogenase and steroid hormones content in early preimplantation horse embryos. The activity of delta (5)3 beta-hydroxysteroid dehydrogenase was examined histochemically in 6 to 10 days aged horse blastocysts. A positive reaction was noted in the blastomeres of all embryos incubated in medium with substrate. Measurable amounts of progesterone, androgens and estrogens were found in blastocysts on day 8th. The presence of enzyme and hormones suggests that steroid hormone production takes place in very early preimplantation horse embryos.
Effects of dietary energy supply on serum thyroxine, tri-iodothyronine and insulin concentrations in young horses. The effects of meal ingestion on the circulating concentrations of the growth-regulating hormones thyroxine (T4), tri-iodothyronine (T3) and insulin were examined in weanling Thoroughbreds fed 70% (diet A), 100% (diet B) or 130% (diet C) of their energy and protein requirements. Peak insulin concentrations occurred 1, 2 and 3 h after the ingestion of diets C, B and A respectively. Increases in plasma glucose concentrations preceded the increases in serum insulin concentrations. Serum T4 concentrations increased after the ingestion of diets A and B and decreased after diet C. In contrast, serum...
Radioimmunoassay of 19 nor testosterone. Evidence of its secretion by the testis of the stallion. Antiserum has been raised in rabbits treated with a 19 nor testosterone-hemisuccinate-bovine-serum-albumin conjugate and used for the development of a specific RIA of plasma 19 nor testosterone. Plasma samples are drawn from testicular and jugular veins of stallions during castration under general anesthesia. Results demonstrate a testicular secretion of 19 nor testosterone and a stress inhibition of this secretion correlatively with stress inhibition of testosterone secretion.
Physiological peripubertal activation of the ovary is not reproduced by pregnant mare serum gonadotropin (PMSG) administration. During the days preceding the first ovulation the ovary of the rat exhibits a remarkable increase in estradiol (E2) and progesterone (P) release in response to gonadotropins. No such increase is observed in the case of androgens (A, testosterone + dihydrotestosterone). The present experiments were undertaken to examine the possibility of reproducing these developmental events by stimulating the ovary with a gonadotropin that has substantial FSH-like activity. In vivo administration of pregnant mare serum gonadotropin (PMSG) to juvenile 29-day-old rats greatly increased the in vitro E2 and A re...
[Direct and indirect methods of the diagnosis of pregnancy in mares]. This review article deals with a critical comparison between the direct clinical diagnosis for the pregnancy of the mare (rectal and in some cases also vaginal exploration) and indirect methods. Both methods are discussed whether they can be seen as a mutual completion or are suitable for their own. The indirect methods for the pregnancy diagnosis include the hormone-analytic tests as progesterone concentration in serum or milk, the biological and immunological measurements for PMSG in the serum, finally the biological and chemical methods for estrogen contents in the urine of the mare. Furthe...
The effect of estradiol and progesterone on the sexual behavior of ovariectomized mares. Daily treatment (5 days) with estradiol resulted in increased levels (p less than 0.05) of proceptive behavior in ovariectomized as compared to control mares (N = 8 per treatment) within 4 hr of injection and for the 4 subsequent days. Ejaculations occurred more often (p less than 0.05) in estrogen-treated mares on days 2-5, but the number of precopulatory investigations by the stallions was not altered. Progesterone treatment resulted in an absence of sexual behavior except in one mare on Day 1. Control mares exhibited varying levels of sexual interest. The concurrent administration of estrad...
Serum testosterone levels in young normal horses. Serum testosterone levels were measured in normal young male horses (29 to 34 weeks old). No differences were found between gelded and intact males. The values for all the horses were low. On the basis of their testosterone levels, all the horses were prepubertal.
Effect of tyrosine modification on the biological and immunological properties of equine chorionic gonadotropin. The tyrosine residues of equine chorionic gonadotropin have been nitrated with tetranitromethane and the resulting effects on the biological and immunological activities of the hormone studied. All of the tyrosine residues in equine chorionic gonadotropin were found to react with tetranitromethane when a 100-fold molar excess of reagent was used or with an 8.6 molar excess in the presence of 5 M guanidine hydrochloride. Complete nitration abolished the biological activities and decreased the immunological activity of the hormone. The nitration of one tyrosine residue resulted in the loss of 70...
Hormonal responses to high and low planes of nutrition in weanling thoroughbreds. Growth-related skeletal diseases in young horses have been associated with high planes of nutrition, although the mechanisms underlying such an association have not been determined. It is likely that nutrition-induced effects on growth rate or growth quality involve the endocrine system. Hormonal and metabolic responses to the ingestion of meals containing either 80% (diet A) or 160% (diet B) of National Research Council energy and protein recommendations were examined in eight Thoroughbred weanling horses after 3 wk of dietary adaptation. After 24 h fasts, prefeeding serum concentrations of t...
Studies on equine prematurity 4: Effect of salt and water loss on the renin-angiotensin-aldosterone system in the newborn foal. Plasma renin substrate concentration was measured in 18, four-day-old pony foals after the administration of the natriuretic agent frusemide. Thirteen foals had been delivered spontaneously; labour had been induced in the remaining five mares. Plasma aldosterone concentration was measured in 12 of the spontaneously delivered foals. Renin substrate concentration had risen sharply within 15 mins (P less than 0.005) and peaked at 1 h. The response was consistently greater in the induced foals. Serum sodium concentration fell rapidly in the induced foals (P less than 0.002 by 60 mins) but was bett...
Hypothyroidism in the foal. Hypothyroidism in the foal occurs as two entities because of the separate actions of thyroid hormones in regulation of metabolic rate and in cell differentiation. The hypometabolic state which results in inadequate thermogenesis and lethargy, occurs concurrently with a period when thyroid hormone secretion is inadequate. Also the severity of the concurrent symptoms is related to the degree of hormone inadequacy as measured by plasma concentrations of free T4 and T3. By contrast, the developmental lesions caused by hypothyroidism are often observed during periods when plasma thyroid hormone con...
Concentrations of 15-keto-13, 14-dihydro-prostaglandin F2 alpha in the mare during spontaneous and oxytocin induced foaling. Changes in plasma 15-keto-13, 14-dihydro-prostaglandin F2 alpha were monitored at frequent intervals before, during and after spontaneous deliveries (three mares) and foalings induced by oxytocin (eight mares). No evidence of increased concentrations of the prostaglandin metabolite was observed in the final 10 days of gestation. In spontaneously delivering mares, there was a marked increase from 3 ng/ml at -125 mins to 18 ng/ml at -65 mins to the highest observed value of 182 ng/ml at 20 mins pre-partum. Following delivery, concentrations declined rapidly to around 0.2 ng/ml. Further release o...
Concentration increase of unbound testosterone in plasma of the mare throughout pregnancy. Blood testosterone levels were measured by RIA and gas chromatography-mass spectrometry in the pregnant mare. They were found to increase from the very beginning of pregnancy, reaching peak values 10 times higher than the basal values at the seventh month and then to return to basal values by the week after parturition. Testosterone binding by plasma proteins was investigated in nonpregnant and pregnant mares throughout gestation. Equilibrium dialysis and gel equilibration methods did not reveal any blood specific testosterone-binding activity at any gestational stage. Hence, blood testosteron...
Active immunization of prepubertal colts against estrogens: hormonal and testicular responses after puberty. Prepubertal Quarter horse colts were immunized at 6 mo of age with either estrone-17-oxime-bovine serum albumin (n = 4; treated) or with albumin only (n = 5; controls). All colts received booster injections of the appropriate antigen at 8, 10, 12, 16 and 20 mo of age. Blood samples were drawn every 20 d from 6 to 26 mo of age; body weights were determined monthly. Immunization against estrone-albumin resulted in increased binding of [3H]-estradiol in serum within 40 d that was maintained through 24 mo of age. Antisera from treated colts crossreacted equally well with estrone and estradiol and ...
