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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.
Induction of multiple ovulations during the ovulatory season in mares. The efficacy of an equine pituitary extract for induction of multiple ovulations during the ovulatory season was studied in 112 horse mares in four experiments. Combined for all experiments, 70% of the mares (78/112) had multiple ovulations for an average of 3.0 ovulations per mare. The interval between first and last ovulation was decreased (P<0.01) when human chorionic gonadotropin (hCG) was included in the treatment regimen (0.0+/-0.0 versus 1.6+/-0.4 days). Ovulation rate was lower (P<0.01) when extract treatment was initiated at day 19 (1.3+/-0.2) than when initiated at day 15 post-...
Equine anhidrosis: a review of pathophysiologic mechanisms. Anhidrosis is loss of the ability to sweat. The problem is seen in horses kept in a hot humid climate, and it may cause severe impairment of thermoregulation in the equine athlete. British Thoroughbreds imported to her tropical colonies are the earliest recorded cases, and since then the syndrome has come to be described as one of Thoroughbreds, usually performance athletes, undergoing acclimatization to heat and humidity. A recent epidemiologic study of cases in Florida has shown, however, that many different breeds, and long time inhabitants of a hot climate, may be affected. Equine sweat gl...
Luteal luteinizing hormone receptors during the postovulatory period in the mare. Changes in serum luteinizing hormone (LH) and progesterone concentrations, number of luteal unoccupied LH receptors, receptor affinity constants, luteal weights and luteal progesterone concentrations were determined during the postovulatory period in the mare. The number of unoccupied LH receptors and receptor affinity was less during the early (Days 1-4) and late [Day 15 through 3rd day after start of corpus luteum (CL) regression] luteal phases than during the mid-luteal (Days 9-14) phase of the postovulatory period (P less than 0.01). The number of LH receptors per CL increased 21-fold (P l...
The effect of altrenogest, an oral progestin, on hematologic and biochemical parameters in mares. Twenty mares were assigned to 1 of 4 groups: no altrenogest; altrenogest at 0.044 mg/kg BW; altrenogest at 0.132 mg/kg BW; or altrenogest at 0.220 mg/kg BW. Treatment was administered daily for 86 days. No signs of illness attributable to feeding altrenogest were observed during the trial. Treatment had no effect (P greater than .05) on the following parameters: WBC, differential WBC, platelet number, creatinine, LDH, CPK, total bilirubin, cholesterol, globulin, BSP, and erythrocyte sedimentation rate. When comparing values over time with pretreatment means or among treatment groups, there wer...
Radioimmunological measurement of beta-endorphin in equine plasma. Radioimmunoassay procedures were developed and validated for the quantification of beta-endorphin (beta-EP)-like immunoreactivity in equine plasma. beta-EP could be quantitatively extracted from plasma with silicic acid powder and subsequently assayed, however, valid estimates of this hormone could also be obtained on unextracted plasma. Although beta-lipotropin (beta-LPH) cross-reacted in the assay, it was not necessary to correct for beta-LPH activity when assaying unextracted plasma because chromatographic analyses showed that 92% of the immunoreactivity in plasma extracts was similar in mo...
Changes in oestrone sulphate concentrations in peripheral plasma of Pony mares associated with follicular growth, ovulation and early pregnancy. A simple and rapid (less than 2 h) immunoassay method has been developed based upon a novel separation technique called LIDIA (Ligand Differentiation Immunoassay), enabling direct estimation of the concentration of oestrone sulphate in ethanolic extracts of blood plasma. An antiserum raised against oestrone-3-glucuronyl-BSA was used which showed a higher cross-reaction with the sulphate than the glucuronide metabolite. The assay had a sensitivity of 5.2 pg/tube and acceptable inter-(less than 18%) and intra-(less than 8.5%) assay precision. Analysis of samples of peripheral venous plasma obtai...
Characteristics of receptors for prostaglandin F-2 alpha in bovine and equine corpora lutea. Prostaglandin F-2 alpha (PGF-2 alpha) receptors of bovine and equine corpora lutea (C.L.) were studied. From both the equilibrium binding data and the dissociation kinetics behaviour, two affinity classes of receptors are evident in the mare, with apparent dissociation constants (Kd) of 1,5 x 10(-9) M and 3.5 x 10(-8) M. Bovine PGF-2 alpha receptors present a homogeneous population of binding sites with Kd = 1 x 10(-8) M. Both bovine and equine C.L. receptors bind PGF-2 alpha in a specific manner; only 13, 14-dihydro-PGF-2 alpha considerably cross-reacts with these receptors. Since in the mare...
A review of twinning in horses and the possible therapeutic value of supplemental progesterone to prevent abortion of equine twin fetuses the latter half of the gestation period. Equine twinning, related abortion and progestogen plasma concentrations during the gestation period were reviewed. The supplemental administration of exogenous progesterone apparently prevented impending twin abortions in three mares after midgestation. A single viable twin and a mummified fetus were delivered at term by the mares.
Induced abortion with two prostaglandin F2 alpha analogues in mares: plasma progesterone changes. Three experiments were conducted to test the abortifacient effects of PGF2 alpha analogues on mares during midgestation (average gestation length 141.5 days). The progesterone concentration was measured by radioimmunoassay. In experiment 1. five mares received an injection of PGF2 alpha analogue (fluprostenol: 500 micrograms intramuscularly) and a second injection either at 24, 48, of 72 h. Although the progesterone concentration decreased (P less than 0.05) an average of 44 per cent in 24 h, none of the pregnancies were terminated. In experiment 2, beginning at least 10 days after experiment ...
Plasma cortisol and beta-endorphin in horses subjected to electro-acupuncture for cutaneous analgesia. Electro-acupuncture (EA) treatment of horses to induce cutaneous analgesia also increased plasma concentrations of beta-endorphin (beta-EP) and cortisol. The magnitude of these increases did not relate consistently to the degree of EA-induced analgesia. Respiration and heart rates were also markedly increased during EA treatment. Intact female horses had higher packed cell volume and plasma beta-EP as well as lower plasma total protein than castrated male horses. Plasma cortisol, heart rate, and respiration rate did not differ significantly between sexes. None of the parameters measured before...
Clinical and endocrine studies during normal and induced parturition in mares. Parturition was induced in 6 mares between Day 327 and 346 of pregnancy using oxytocin (Group I) and in 6 mares between Day 315 and 330 of pregnancy with fluprostenol in combination with oxytocin (Group II). A third group of 4 mares which served as controls were allowed to go to full term (322-340 days) and foal down normally. Parturition occurred within 24-102 min (mean = 61,4; SD = 31,6) in 5 of the Group I mares and within 160-185 min (mean = 173; SD = 10,86) in the mares of Group II. Expulsion of the afterbirth took place between 7 and 206 min (mean = 79; SD = 76,38) and between 7 and 73 m...
[The value of blood progesterone determination about 18 days post ovulation for pregnancy testing in mares]. The reliability of determination of the plasma progesterone level within approximately eighteen days after ovulation in the pregnancy diagnosis of mares is examined in the present study. Studies were done in seventy-five mares, a number of which were served or inseminated during several cycles so that a total number of eighty-seven blood samples were obtained. On the analogy of other authors, the progesterone level above which mares were believed to be pregnant and below which they were assumed to be non-pregnant, was set at 2 ng/ml. The twenty-five mares in which the level was below 2 ng/ml. ...
Synthesis and properties of equine beta-melanotropin analogs with substitution in residue position 1. Five analogs of equine β-melanotropin have been synthesized by the solid phase method. The NH2-terminal aspartic acid was substituted with amino acids (Gly, Trp, Ile, Lys and Nα-acetyl-Asp) differing widely in physicochemical properties. On the basis of their lipolytic potencies it was concluded that this position plays a negligible role in this activity.
Testosterone administration to mares during estrus: duration of estrus and diestrus and concentrations of LH and FSH in plasma. To study the possible role of ovarian androgens in regulation of follicle stimulating hormone (FSH) secretion in the cycling mare, five mature, intact mares were treated with testosterone (20 micrograms/kg of body weight) daily during estrus; five control mares received safflower oil on the same schedule. Mares were teased for estrus and samples of jugular blood were drawn daily through one full estrous cycle. Concentrations of FSH in plasma were measured by a newly developed radioimmunoassay based on anti-ovine FSH serum and radioiodinated equine FSH. Testosterone treatment during estrus had ...
Identification and measurement of testosterone in plasma and follicular fluid of the mare, using gas chromatography-mass spectrometry associated with isotope dilution. Testosterone has been identified by mass spectrometry in blood and follicular fluid aspirated from mature Graafian follicles of mares. Quantitative measurements made by gas chromatography-mass spectrometry have validated the determination of plasma testosterone made by radioimmunoassay. However, because of high levels of epitestosterone (17 alpha-hydroxyandrost-4-en-3-one) in the follicular fluid, radioimmunoassay overestimates the true concentrations of testosterone. The occurrence of testosterone in mare follicular fluid at a concentration which is two orders of magnitude higher than that in...
Plasma cortisol variations induced in the stallion by mating. Plasma cortisol variations have been determined by radioimmunoassay in 5 stallions during mating and in 2 teasers during oestrous female exposure. In all the animals, cortisol plasma levels consistently increase (71.1 ng/ml vs 44.0 and 63.0 ng/ml vs 35.1, in the stallions and in the teasers, respectively) 7-30 min after female exposure; 120 min after exposure, cortisol concentrations are again low.
Testosterone effects on mares during synchronization with altrenogest: FSH, LH, estrous duration and pregnancy rate. Twelve mares fed altrenogest for 14 d were used to study the effects of a single injection of testosterone propionate on concentrations of follicle-stimulating hormone (FSH) during diestrus, and to relate the normal and perturbed patterns of FSH secretion to subsequent estrous characteristics and fertility. Seven of 12 mares received testosterone propionate at 200 micrograms/kg of body weight on d 5 of progestogen feeding. Mares were teased and blood samples were drawn daily; all mares were artificially inseminated at the first estrus after progestogen treatment. Testosterone propionate treatm...
Effects of melatonin and thyrotropin releasing hormone on mares during the nonbreeding season. Two hormonal treatments, chosen for their effectiveness in other seasonally breeding species, were tested in mares during the nonbreeding season to determine if they could induce ovarian activity and estrus during the winter. Of 15 functionally anestrous (anovulatory) mares, five received intravaginal, polyurethane sponges containing .75 g of melatonin on December 16; fresh sponges containing melatonin were inserted weekly until February 3. These mares also received daily injections of saline. Five other mares received daily im injections of 100 micrograms of thyrotropin-releasing hormone (TRH...
Thyroid-stimulating hormone: response test in healthy horses, and effect of phenylbutazone on equine thyroid hormones. Adult horses showed a mild diurnal variation in equine plasma thyroxine (T4) concentrations, but not triiodothyronine (T3). Plasma T4 concentrations tended to be higher between 5 PM and 8 PM than at 8 AM. Increases in plasma T4 and T3 were similar in adult healthy horses given 5, 10, or 20 IU of thyroid-stimulating hormone (TSH). The T4 peaked at approximately twice (2.0 +/- 0.4 times) as high as the base line at 6 to 12 hours after the TSH was given. The greatest change from base line T3 occurred at 1 to 3 hours after the TSH was given, but the magnitude of increase was widely variable (4.36 ...
Plasma and endometrial progesterone content following exogenous progesterone administration in mares. Intact and ovariectomized pony mares were treated with either progesterone in-oil or repositol progesterone. Serum progesterone, endometrial progesterone and endometrial histology were examined. There were no differences in serum or tissue progesterone between intact and ovariectomized mares. Serum and tissue progesterone were greater for progesterone in-oil treated mares than for repositol treated mares. Both progesterone in-oil and repositol progesterone initiated endometrial gland proliferation with no difference in response observed between the two preparations.
Cortisol (hydrocortisone) disappearance rate and pathophysiologic changes after bilateral adrenalectomy in equids. Six ponies and 1 horse were bilaterally adrenalectomized (BADX). The survival time of 2 of the 7 animals after BADX was 24 and 72 hours without supplemental corticosteroids. The cause of death was not related to the surgical technique. The biological half-life of cortisol (hydrocortisone) was estimated to be 2.1 +/- 0.6 hours. The disappearance of cortisol in the horse was found to be biphasic, composed of redistribution and elimination phases. Pathophysiologic changes (ie, increased serum sodium and chloride, increased PCV, and decreased serum potassium) similar to those seen in other species...
Difference in sizes of human compared to murine alpha-subunits of the glycoprotein hormones arises by four-codon gene deletion or insertion. The sizes of the human and subhuman alpha-subunits of the glycoprotein hormones differ by four amino acids (hCG alpha, 92 amino acids; murine, equine, bovine, and ovine alpha, 96 amino acids). The shortening of the human alpha-subunit has been attributed to posttranslational proteolysis. We have recently determined the nucleotide sequences of the mRNAs encoding the precursors of the alpha-subunit of mouse TSH and rat gonadotropins using recombinant DNA techniques. In this report, we have compared these nucleotide sequences and their deduced amino acid sequences with those of the pre- alpha-sub...
[Dynamics of the functional, biochemical and hormonal indices of racehorses]. Parallel physiologic, biochemical, and hormonal investigations of racehorses were carried out within the time period of a training cycle. The changes found in the physiologic and biochemical indices were said to be in a general relationship with the amount of physical training of the animals, at the same time reflecting some seasonal variations. The changes in the level of T-4 and cortisol were found to be in direct relationship with the continuation of training.
Studies on prolactin 48: isolation and properties of the hormone from horse pituitary glands. Isolation of prolactin from equine pituitary glands has been described. It has a potency of 42 IU/mg in the pigeon crop-sac test and consists of 199 amino acids. The hormone has only four half-cystine residues in contrast to other mammalian prolactins which have six residues. From NH2-terminal sequence analysis and amino acid composition of cyanogen bromide fragments, the NH2-terminal disulfide loop is missing in the equine prolactin molecule. Circular dichroism spectra indicate that the alpha-helical content of equine prolactin appears to be lower (50%) than that found in the ovine hormone (6...
