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.
The measurement of oestrone, equilin and dehydroepiandrosterone in the peripheral plasma of pregnant pony mares by radioimmunoassay. Oestrone, equilin and dehydroepiandrosterone were measured by radioimmunoassay in peripheral plasma from five pony mares; samples were taken from day 60 of pregnancy at approximately weekly intervals through to parturition. Of the three steroids measured, dehydroepiandrosterone showed the most consistent pattern of secretion. DHA concentrations remained low until day 105, increased rapidly from day 120 and attained maximum values between days 168–210; levels declined to day 300, but there was considerable variation between mares in DHA patterns prior to parturition. There was great variation...
Observations on thyroid hormones in the blood of thoroughbreds. During an investigation of a group of clinically well thoroughbreds housed in the same stable, it was noted that seven of the 14 had no detectable thyroxine in the plasma (less than 5 nmol/litre). An investigation of thoroughbreds in this stable over a five month period suggested that the thyroids were functioning normally and that the thyroxine was excreted in the urine. Thyroxine binding studies on the blood of these horses suggested that the major part of the circulating thyroxine was bound to albumin. The thyroxine had been displaced resulting in an apparent absence of plasma thyroxine sin...
Uterine luminal prostaglandin F in cycling mares. Prostaglandin F was measured by radioimmunoassay in uterine flushings of cycling mares on days 4, 8, 12, 14, 16, 18 and 20 post-ovulation. Prostaglandin F was significantly (P less than .05) affected by day of the estrous cycle and reached maximal levels on day 14. Least squares means for days 4, 8, 12, 14, 16, 18 and 20 were: .66, .81, 4.77, 14.31, 5.48, 3.68 and 2.97 ng/ml, respectively.
Amino acid sequence of the beta-subunit of the follicle-stimulating hormone from equine pituitary glands. A tentative amino acid sequence of the beta-subunit of equine follicle-stimulating hormone (FSH) was derived from the sequences of tryptic, thermolytic as well as peptic, subtilisin, and chymotryptic peptides. Equine FSH-beta is analogous to human FSH-beta except six amino acid substitutions at positions 12, 16, 21, 62, 108, and 114. The amino acid sequence suggests that the hormone-specific beta-subunits of FSH are similar at the interspecies level, whereas the amino acid sequences of the hormone nonspecific alpha-subunits show variations.
Isolation and amino acid sequence of the alpha-subunit of follicle-stimulating hormone from equine pituitary glands. Six hundred milligrams of follicle-stimulating hormone (FSH), containing 110 NIH-FSH-S1 units/mg, was isolated from 9 kg of equine pituitary glands. The equine FSH was dissociated into alpha- and beta-subunits. A tentative amino acid sequence of the alpha-subunit was determined. The alpha-subunit contained 82 amino acids. The equine FSH-alpha is shorter by 10 to 14 amino acids at the NH2 terminus and has several substitutions at several positions as compared with human FSH-alpha and bovine thyroid-stimulating hormone-alpha. At the intraspecies level, the alpha-subunits of human FSH, human lute...
Foetal and maternal plasma concentrations of 13, 14-dihydro-15-oxo-prostaglandin F in the mare during late pregnancy and at parturition. The concentrations of 13, 14-dihydro-15-oxo-prostaglandin F(PGFM), the stable metabolite of prostaglandin F, were measured in the plasma of catheterized mares and foetuses and non-catheterized thoroughbred mares and ponies during the last months of gestation. The plasma concentration of PGFM increased gradually towards term in all groups of animals. During the operation for insertion of catheters, maternal and foetal concentrations of PGFM were high, but the values fell to basal levels 24--48 h after the operation. It was found the preoperative starvation (24 h) led to a rise in the concentrat...
Effects of endometrial biopsy, uterine culture, and cervical dilatation on the equine estrous cycle. In 10 mares, lysis of the corpus luteum was induced by endometrial biopsy and culture on day 4 after estrus, as evidenced by a sharp decline in serum progesterone concentration and a shortened interestrous interval. Estrus following the manipulations was prolonged. Endometrial biopsy and culture on days 1 and 3 after estrus or manually dilating the cervix on day 4 after estrus also decreased the serum progesterone concentration (within 24--48 hr after manipulation), shortened diestrus, and prolonged the subsequent estrus. In a 2nd experiment, endometrial biopsy on day 4 after estrus shortened ...
Isolation of a gonadotropin (PMEG) from pregnant mare endometrial cups: comparison with PMSG. The gonadotropin (PMEG) in pregnant mare endometrial cups was purified and compared to pregnant mare serum gonadotropin (PMSG). Purification methodology applicable to PMSG was employed. In vivo and in vitro assays for FSH and LH were used to evaluate PMEG preparations. In all cases, lower activities (11-54%) were observed with PMEG compared to PMSG. Antiserum raised in rabbits against PMSG cross-reacts fully with PMEG in agar double diffusion tests. The amino acid composition of PMEG is similar to PMSG, but amino terminal group analyses show PMEG preparations to be more heterogeneous than PMSG...
The effects of exercise and adrenaline infusion upon the blood levels of propranolol and antipyrine in the horse. There are now several examples showing that experimentally induced changes in hepatic blood flow can have a marked effect upon the elimination of certain high clearance drugs. Changes in hepatic blood flow produced by exercise might therefore be expected to influence the clearance of these drugs. There was an increase of up to 100%, compound to control values, in the plasma levels of propranolol in horses given either d- or dl-propranolol, 0.2 mg/kg b.wt., and then subjected to sustained exercise for 30 minutes. There was, however, no similar increase with exercise in the plasma levels of anti...
Pregnant mare’s serum gonadotropin. IV. Induction of premature labor by pregnant mare’s serum gonadotropin and its prevention by using clomiphene or indomethacin. The administration of pregnant mare's serum gonadotropin (PMSG), 30 IU on day 18 of pregnancy, resulted in premature labor in rats. However, this abortifacient efficacy of PMSG was not demonstrable when a simultaneous injection of progesterone, clomiphene, or indomethacin was scheduled, thus suggesting that the action of PMSG is medicated by the estrogen-stimulated release of prostaglandin. The termination of pseudopregnancy in bilaterally hysterectomized rats by PMSG and its reversal by indomethacin revealed that the inhibition of luteal function by PMSG does not require the presence of a ute...
Pregnant mare’s serum gonadotropin: V. Indomethacin or cortisone and the reversal of antifertility efficacy of pregnant mare’s serum gonadotropin. Pregnant mare's serum gonadotropin (PMSG) of 10 IU on day 5 of pregnancy induced luteal demise and consequently an absolute resorption of fetuses and placentae resulted on day 16 of pregnancy. Simultaneous regimen of PMSG and indomethacin or cortisone was found to be consistently effective in preventing the luteolytic effect of PMSG. The growth of the fetuses, placentae as well as corpora lutea was found to be parallel to controls. Similarly, shortening of the duration of pseudopregnancy to 10--12 days in the bilaterally hysterectomized rat by PMSG and its retaining the normal duration of 18--...
Monitoring of plasma and milk progesterone for evaluation of postpartum estrous cycles and early pregnancy in mares. Plasma and milk progesterone concentrations in 13 mares were determined 3 times a week for 5 months, beginning at parturition. The estrous cycle was divided into 2 phases. Estrus was considered to occur when the plasma progesterone concentration was less than 1 ng/ml, with diestrus occurring when plasma progesterone content was greater than or equal to 1 ng/ml. Based on this classification, the period of estrus averaged 8.9 days, diestrus averaged 13.9 days, and the estrous cycle averaged 22.8 days. During estrus, the progesterone concentration in plasma averaged 0.4 ng/ml and in milk averaged...
Testosterone and progesterone in peripheral plasma during the oestrous cycle of the mare. Measurements every day or every other day showed that testosterone levels ranging from 15 to 70 pg/ml were higher at oestrus in 4 of the 6 mares studied. In these 4 mares, another testosterone peak occurred 11--13 days before the next oestrus either before (3 mares) or after the fall in progesterone levels.
Cyclic and pathologic changes of the mare endometrium as detected by biopsy, with a note on early embryonic death. Normal histologic changes that occurred in concert with the ovarian cycle were evaluated. When combined with behavioral and physical findings, this evaluation enabled determination when there was synchrony between ovarian steroids (estrogen and progesterone) and their target tissues of endometrium. A system for classification as well as definitions of patterns types and degrees of severity of inflammatory and fibrotic changes was developed to facilitate a uniform system for description and communication. An attempt was made to relate the pathologic changes to their effect on fertility when fer...
Evaluation of a pregnant mares’ serum and human chorionic gonadotrophin mixture for alleviating summer infertility in sows. A controlled on-farm trial was conducted to evaluate the effectiveness of a commercial gonadotrophin hormone mixture at overcoming a seasonal decrease in fertility in pigs in a sub-tropical environment (summer infertility). The average weaning to oestrus interval of the untreated sows was more than double that of the treated sows and this difference was highly significant. However, fewer of the treated sows farrowed and they produced smaller litters. The improvement in fertility in the treated group achieved by reducing the weaning to oestrus interval was more than cancelled out by an overall ...
Somatostatin-containing cells in the rat and horse pancreatic islets. Somatostatin-, glucagon- and insulin-containing cells in the rat and horse pancreatic islets were investigated by an indirect immunofluorescent technique using antibodies to insulin, glucagon and somatostatin. In the rat pancreatic islets, insulin-containing cells were located centrally, and glucagon and somatostatin or somatostatin-like substance (SLS)-containing cells were peripherally disposed and glucagon-containing cells were situated more peripherally as compared with distribution of somatostatin-containing cells. On the other hand, in the horse pancreatic islets, insulin-containing cell...
Fertility, ovulation and maturation of eggs in mares injected with HCG. Pony mares were observed from January to August for incidence of oestrus, duration of oestrus, length of the oestrous cycle and for ovulation and fertility after injection of HCG. From January to 15 May most mares showed oestrus but the duration of oestrus was quite variable and few mares ovulated in response to HCG. From 15 May to 17 August oestrous cycles were more regular and ovulation was induced within 40-50 h by an intramuscular injection of 1500-5000 i.u. HCG. Pregnancy was established by one mating at a fixed time after HCG in 20 of 69 mares. Degenerate eggs were recovered from the ovi...
