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.
Messer NT, Johnson PJ, Refsal KR, Nachreiner RF, Ganjam VK, Krause GF.Six healthy, adult horses, with normal (mean +/- SEM) baseline serum concentrations of total triiodothyronine (T3, 1.02 +/- 0.16 nmol/L), free T3 (FT3, 2.05 +/- 0.33 pmol/L), total thyroxine (T4, 19.87 +/- 1.74 nmol/L), free T4 (FT4, 11.55 +/- 0.70 pmol/L), total reverse T3 (rT3, 0.68 +/- 0.06 nmol/L), and cortisol (152.75 +/- 17.50 nmol/L), were judged to be euthyroid on the basis of response to a standardized thyroid-stimulating hormone response test. Serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol were determined immediately before and every 24 hours during a 4-day period of foo...
Messer NT, Ganjam VK, Nachreiner RF, Krause GF.The effect that 5 consecutive days of treatment with dexamethasone (0.04 mg/kg of body weight, IM, q 24 h) would have on baseline concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3), free T3 (FT3), and free T4 (FT4), and on response to thyroid-stimulating hormone (TSH) administration was determined in 12 clinically normal horses. Results of TSH response tests indicated that the horses could be placed into 2 groups: in 6 horses (group A), T4 concentration after administration of TSH was more than twice the baseline concentration; in the other 6 horses (group B), T4 concent...
Meyers SA, Overstreet JW, Liu IK, Drobnis EZ.Mammalian sperm that have completed capacitation are capable of undergoing the acrosome reaction in response to a number of biological and chemical stimuli. In the present report, we have investigated the ability of progesterone to stimulate acrosome reactions of stallion sperm capacitated in vitro. Motile sperm were selected by a two-layer Percoll gradient centrifugation and were incubated in TALP medium modified by the 1:1 (v/v) addition of TEST-yolk medium for 5 hours at 39 degrees C, under 5% CO2 in humidified air. Sperm incubated in vitro in TALP-TEST medium had a higher percentage of acr...
Ellis MJ, Livesey JH, Donald RA.Immunoreactive corticotrophin-releasing hormone (irCRH) was present in methanolic extracts of equine peripheral blood and showed no elevation in maternal peripheral serum in late gestation (0.54 +/- 0.25 pmol/l; mean +/- S.D.) compared with control horses (0.41 +/- 0.15 pmol/l). The irCRH of methanolic extracts of pituitary venous plasma had a similar elution position following reverse-phase HPLC to synthetic human CRH(1-41) and to irCRH released from horse stalk-median eminence tissue incubated in vitro. Gel chromatographic studies showed no evidence for a plasma CRH-binding protein (CRHBP) a...
de Brabander HF, van Hende J, Batjoens P, Hendriks L, Raus J, Smets F, Pottie G, van Ginkel L, Stephany RW.When residues of nortestosterone (NT) were found in the urine of cattle, racehorses or bodybuilders, exogenic administration was thought to be proven. In previous literature, no records were found of the endogenic presence of this molecule. In the horse-racing world, Houghton and Courthot found that NT is normally present in the urine of the stallion. Belgian and Dutch researchers found that NT is also present in the urine and edible parts of the intact boar. Vandenbroeck et al. (1991) suggested the endogenous presence of NT (in the beta form) in the pregnant cow. Meyer (1992) reported the pre...
Williams JK, Honoré EK, Washburn SA, Clarkson TB.We attempted to determine whether continuous and cyclic medroxyprogesterone acetate modulates the effects of estrogen on dilation of atherosclerotic coronary arteries in surgically postmenopausal female monkeys. Background: Estrogen replacement in postmenopausal women preserves normal dilator responses of atherosclerotic coronary arteries. The effects of progestins on coronary artery reactivity have not been determined. Methods: Repeated quantitative coronary angiography was used to study the effects after 1 month of 1) no hormone replacement (control) or oral administration of 2) continuous c...
Thompson DL, DePew CL, Ortiz A, Sticker LS, Rahmanian MS.Three experiments were conducted to determine 1) the relationship between prolactin and growth hormone (GH) secretion in mares and the response to GH-releasing hormone (GHRH), 2) whether plasma GH and prolactin concentrations differed among mares, stallions, and geldings, and 3) whether sexual differences existed after administration of GHRH and acute exercise. In Exp. 1, 10-min blood samples were collected from 12 mares for 8 h, and GHRH (0, 45, 90, or 180 micrograms) was administered at 6 h. In Exp. 2, 15-min blood samples were collected for 4 h from 10 mares, stallions, and geldings. In Exp...
Aurich C, Sieme H, Hoppe H, Schlote S.To investigate the involvement of endogenous opioids in the regulation of gonadotrophin release in male horses, effects of the opioid antagonist naloxone (0.5 mg kg-1 i.v.) on plasma LH and testosterone concentrations and the possible influence of season and of gonadal steroids were investigated. To determine quantitative as well as qualitative changes in gonadotrophin release, LH concentrations were measured by radioimmunoassay and by an in vitro bioassay. Experiments were performed in May, August and December. In stallions, basal LH secretion in May and August was significantly higher than i...
Younis AI, Sehgal PK, Biggers JD.A single s.c. injection of 1000 IU of pregnant mare's serum gonadotrophin (PMSG) stimulates the growth of multiple antral follicles in cynomolgus monkeys (Macaca fascicularis). The number of cumulus-enclosed oocytes (CEO) from six non-stimulated controls was 36 (mean = 6). In contrast, a total of 95 CEO (mean = 31.7) were recovered from three animals stimulated and ovariectomized 3 days later, while 385 CEO (mean = 128.3) were obtained from three animals stimulated and ovariectomized 4 days later. A comparison of the effects of highly purified human follicle-stimulating hormone (FSH), human lu...
Redina OE, Amstislavsky SYa , Maksimovsky LF.This study examined the developmental capacity of oocytes in DD mice after they had been injected with pregnant mares' serum gonadotrophin at different stages of the oestrous cycle. The superovulation of mature DD mice at pro-oestrus, oestrus and metoestrus resulted in a large yield of viable embryos. The proportion of abnormal embryos was highest after injection of pregnant mares' serum gonadotrophin at dioestrus. The pool of viable oocytes was most synchronized with normal development after the hormone was injected at oestrus. The results demonstrate that oocytes of different morphology coul...
Gobbetti A, Zerani M, Vannucci F, Marini R.To delineate endocrine mechanisms regulating equine luteal function and the possible functional differences between one month and three month corpora lutea of pregnancy (CL), the in vitro basal releases of prostaglandin F (PGF), prostaglandin E2 (PGE2), progesterone, and 17 beta-estradiol by one and three month CL of pregnant mares were evaluated. In addition, the in vitro effects of PGF2 alpha PGE2, progesterone and 17 beta-estradiol on synthesis of prostaglandins (PGs) and sex steroids were studied. PGF, PGE2, and 17 beta-estradiol secretion was higher in one month than in three month CL, wh...
Ellis MJ, Mulligan RS, Evans MJ, Donald RA.Antagonists are useful for probing hormone action and receptor characteristics. In this study we have investigated the inhibitory effects of analogues of arginine vasopressin (AVP) and corticotrophin-releasing hormone (CRH) on stimulated release of immunoreactive ACTH from perifused equine anterior pituitary cells in vitro. Our aims were to gain some insight into the characteristics of the CRH and AVP receptors of the horse pituitary and to establish whether the response induced by AVP and CRH together could be blocked by combining antagonists. Experimental design included 5-min pulses of AVP ...
Bedford SJ, Hinrichs K.It has recently been reported that large insemination volumes might affect fertility of mares. The results from these studies are confounded by other factors, however, such as inadequate number of spermatozoa in the inseminate. We conducted a study to test whether volume alone affects fertility when sufficient numbers of spermatozoa are present. Semen from one stallion was collected, extended at 50 x 10(6) spermatozoa/ml, and stored in a commercial semen cooling device for 18 to 30 h before insemination. Ten pony mares were assigned during estrus in random pairs to be bred every other day with...
DePew CL, Thompson DL, Fernandez JM, Southern LL, Sticker LS, Ward TL.Concentrations of prolactin, glucose, insulin, urea N, and total amino acids in plasma of stallions after ingestion of pelleted feed were compared to those after direct gastric administration of water, NaCl, egg albumin, or corn starch (Exp. 1) or water, egg albumin, hydrolyzed casein (Amicase), or a mixture of indispensable amino acids (Exp. 2). Stallions were fed once daily (75% pellet and 25% hay) at 1500 for 30 d. On d 22, 24, 26, 28, and 30, blood samples were collected every 30 min from 1 h before through 4 h after treatment, which occurred at 1100. In Exp. 1, there was a positive secret...
Alexander SL, Irvine CH, Donald RA.To characterize the short-term ACTH secretion pattern and to investigate factors regulating it, pituitary venous (PV) blood was collected using our nonsurgical method from 8 unperturbed horses every 20 or 30 s for approximately 1 h. In all but 1 horse, sampling occurred during the broad circadian maximum in plasma cortisol concentrations. Concentrations of corticotropin-releasing hormone (CRH; n = 7 horses), arginine vasopressin (AVP), ACTH and cortisol were measured by radioimmunoassay. In all horses, CRH, AVP and ACTH secretion patterns appeared irregular in time and amplitude. The mean (+/-...
Silver M, Fowden AL.The present study was carried out on 19 chronically catheterized mares and fetuses in late gestation (term > 320 days). In six animals which were monitored up to the time of delivery of a live foal, plasma and amniotic fluid cortisol concentrations remained low until 4-5 days before parturition when there was a rapid, significant rise (P < 0.05) which was not accompanied by any corresponding changes in maternal plasma cortisol. Circulating fetal ACTH concentrations became more variable close to delivery and ANOVA revealed no significant increases during this critical period, although a n...
Thomas PG, Ball BA, Brinsko SP.Regulation of attachment of equine spermatozoa to homologous oviduct epithelium was investigated by co-culture of spermatozoa with oviductal epithelial cell explants. Stallion spermatozoa were incubated with explants derived from the isthmus and ampulla of follicular, postovulatory, and diestrous mares. Steroid treatments (estradiol, progesterone, or control) were applied across all explant groups. Estimates of motility and total numbers of attached spermatozoa were made 0.5, 24, and 48 h after initiation of co-culture. Equine spermatozoa attached by their rostral acrosomal region to both cili...
Eisenhauer KM, McCue PM, Nayden DK, Osawa Y, Roser JF.Stallion testes secrete large amounts of estrogens, but the cellular location of the enzyme that converts androgens to estrogens, cytochrome P450 aromatase, has not been determined. The goal of the present study was to immunocytochemically localize stallion testicular aromatase using a polyclonal antibody generated against human placental cytochrome P450 aromatase. Testes were obtained from 12 stallions from 2 to 23 years of age, during both the breeding and non-breeding seasons. Immunoreactivity was confined to the Leydig cells in all testes examined. No immunostaining was observed in the Ser...
Constant SB, Larsen RE, Asbury AC, Buoen LC, Mayo M.A bilateral cryptorchid stallion with mild development of mammary glands was identified as an XX male by karyotyping. Necropsy revealed underdeveloped accessory sex organs and hypoplastic, inguinally located testes that were deficient of spermatogonia. Evaluation of routine hormonal profiles (without karyotyping) would have failed to diagnose this syndrome.
Aurich C, Schlote S, Hoppen HO, Klug E, Hoppe H, Aurich JE.To investigate an involvement of endogenous opioids in the regulation of circannual changes in reproductive activity, effects of the opioid antagonist naloxone on the concentration of immunoreactive and bioactive luteinizing hormone (LH) in plasma were measured in mares during the anovulatory season. Naloxone (0.5 mg/kg i.v.) caused a significant increase (P < 0.05) in immunoreactive as well as bioactive LH concentration in plasma. The amplitude of the increase in LH concentrations measured with an in vitro bioassay was more pronounced than the amplitude of the increase in LH secretion dete...
LeBlanc M, Neuwirth L, Mauragis D, Klapstein E, Tran T.The effects of oxytocin on the percentage of technetium 99m albumin colloid (99mTc-microAA), cleared from the uterine lumen was measured in 13 mares. Scintigraphy was performed during 4 consecutive oestrous cycles, on Day 3 of oestrus during Cycles one and 3 and 48 h after ovulation during Cycles 2 and 4. Oxytocin (20 iu) was given i.v. after the initial scintigraphy image during Cycles 3 and 4. Seven multiparous mares (Group 1) were classified as 'susceptible' and 6 mares (2 nulliparous and 4 multiparous; Group 2) were classified as 'resistant' to endometritis. All mares cleared > 90% of 99mT...
DePew CL, Thompson DL, Fernandez JM, Sticker LS, Burleigh DW.Experiment 1 was conducted to characterize the concentrations of prolactin, growth hormone (GH), cortisol, insulin, glucagon, glucose, nonesterified fatty acids (NEFA), urea N, and 10 indispensable amino acids in the plasma of mares (n = 8) and stallions (n = 8) during the last 4 h of a 19-h period of feed deprivation and for 8 h after a noon meal. Experiment 2 was similar to Exp. 1 except that only stallions (n = 8) were used, and they were either fed (n = 4) or not fed (n = 4) at noon in a 2 x 2 Latin square design conducted over two sampling days 7 d apart. In Exp. 1, increases (P < .01)...
Frayne J, Stokes CR.The quantity and distribution of MHC Class II positive cells and T cells in the equine endometrium was investigated throughout the oestrous cycle. Significantly more MHC Class II positive cells were detected in the stratum compactum and stratum spongiosum of endometria from naturally cycling mares during the follicular than during the luteal phase of the oestrous cycle. Significantly more T cells were also detected in the stratum compactum, but not stratum spongiosum, of these mares during the follicular phase. Furthermore, there was a marked increase in the number of MHC Class II positive cel...
Vivrette S.The endocrinology of late gestation and parturition in the mare has been described, but unlike other domestic animal species, the factors that initiate parturition in the mare have not been elucidated. In contrast to ruminant species, maternal estrogen and progesterone concentrations do not change markedly, and a well-defined fetal cortisol surge is not observed just prior to parturition in the mare. Parturition is associated with large increases in prostaglandin and oxytocin concentrations, which induce uterine contractions and delivery of the foal. There are many methods of inducing parturit...
Holyoak GR, Little TV, Vernon M, McCollum WH, Timoney PJ.Correlation between serum testosterone concentration and morphometric findings from ultrasonography of the accessory sex glands in peripubertal colts was investigated during pubertal development. Nineteen colts of initial age ranging from 5 to 12 months were monitored over a 13-month period. Serum testosterone concentration was determined on a biweekly basis, and accessory sex gland development was ultrasonographically monitored once a month. Notwithstanding individual variation, there was significant correlation (r = 0.913; P < 0.01) between increasing serum testosterone concentration and ...
Vos PL, van der Schans A, de Wit AA, Bevers MM, Willemse AH, Dieleman SJ.Normally cyclic heifers (n = 34) received 2500 iu pregnant mares' serum gonadotrophin (PMSG) i.m. at day 10 of oestrus, and 15 mg prostaglandin (PG) i.m. at day 12. Thereafter, a monoclonal antibody against PMSG was administered i.v. before (n = 24), at (n = 6) or shortly after (n = 4) the preovulatory LH surge. Peripheral blood concentrations of LH and oestradiol were compared; follicular development was monitored by daily ultrasound scanning; and the numbers of preovulatory-sized follicles and ovulations were counted 96 h after injection of PG following death. Anti-PMSG treatment before the ...
Dybdal NO, Hargreaves KM, Madigan JE, Gribble DH, Kennedy PC, Stabenfeldt GH.Pituitary pars intermedia dysfunction is a slowly progressive disorder that afflicts most breeds of horses. Because it shares features with human Cushing disease, it has been referred to as equine Cushing disease. A variety of tests of pituitary-adrenocortical function were performed on horses with evidence of pituitary pars intermediate dysfunction, and results were compared with those in healthy control horses. Diurnal variations in plasma cortisol concentration were not statistically different between control horses and those with pituitary pars intermedia dysfunction. An ACTH stimulation (...
Polak KL, Kammlade WG.Vaginal hydrogen ion concentration of Saddlebred mares was measured throughout the behavioral estrous period. The mean pH on the day of ovulation was significantly (P = <.01) lower than on all other tested days of estrus. Follicular development and vaginal pH values in pony mares at time of slaughter were highly correlated. A significant decrease in vaginal pH values, determined through a series of carefully monitored measurements during estrus, was found to be characteristic and indicative of ovulation.
Brooks J, Maeda T, Ringhofer M, Yamamoto S.The oxytocinergic system has been suggested to make up an important part of the endocrine basis of group cohesion. However, controlled studies in open-group settings have not been performed. We here investigated the impact of exogenous intranasal oxytocin on the group-level social organization of 5 groups of horses ( = 58; 12 mares and 46 geldings) through GPS tracking and social network analysis. We find oxytocin flattened social differentiation across levels. Most strikingly, oxytocin did not simply reinforce existing bonds but selectively shifted social preferences toward homogenization -...
Papkoff H, Farmer SW, Cole HH.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...
Evans MJ, Loy RG, Taylor TB, Barrows SP.Cyclic mares were given daily i.m. injections of 150 mg progesterone (Group P, N = 4), 150 mg progesterone and 10 mg oestradiol-17 beta (Group PE, N = 3), 10 mg oestradiol-17 beta (Group E, N = 3) or cottonseed oil vehicle (Group C, N = 4), from the day after ovulation (Day 1) to Day 28. Blood samples were collected daily, and the ovaries were palpated every 1-2 days. Serum FSH and LH concentrations were measured in all samples, and means determined for 7 consecutive 4-day periods throughout treatment. Comparisons within each steroid treatment group between time periods and comparisons between...
Kindahl H, Odensvik K, Hansen B, Daels PF.The aim of this study was to characterize changes in PGF2alpha secretion in mares with persistent corpora lutea that were induced by administering altrenogest during oestrus. In Expt 1, PGF2alpha secretion was compared among mares undergoing normal oestrous cycles (n=7) and mares undergoing prolonged luteal phases (n=6), using the mean 15-ketodihydro-PGF2alpha (PGFM) plasma concentrations, peak PGFM concentrations and number of PGFM surges each day, from day 12 to day 16 of the luteal phase. In Expt 2, oxytocin-induced PGF2alpha secretion was characterized on days 13 and 16 of the luteal phase...
Requena F, Campos MJAPM, Martínez Marín AL, Camacho R, Giráldez-Pérez RM, Agüera EI.In equine reproduction, accurate and timely detection of the moment of ovulation is of great importance. Power Doppler ultrasound technology is a non-invasive method that enables to assess the morpho-echogenic features and blood flow changes during the estral cycle in mares. The objective of the present study was to evaluate the influence of age on ultrasonographic parameters (follicular diameter, follicular blood flow-FBF, corpus luteum (CL) area and corpus luteum blood flow-CLBF) and blood plasma progesterone concentrations in cycling Spanish Purebred mares (15 less than 8 years old and 15 e...
Fitzgerald BP, Meyer SL, Affleck KJ, Silvia PJ.The potential of a gonadotropin-releasing hormone (GnRH) agonist (goserelin acetate), delivered constantly for 28 days via a subcutaneous depot, to induce ovulation in seasonally anestrous mares, was investigated. Two experiments were conducted, in which a range of doses (30 to 240 micrograms/mare/d) was examined. Mares were selected on the basis of lack of substantial follicular development (follicle diameter < 20 mm determined ultrasonically) and low serum concentrations of luteinizing hormone (LH) and progesterone. Constant administration of the GnRH agonist-induced ovulation in anestrou...
Valenzuela OA, Jellyman JK, Allen VL, Holdstock NB, Fowden AL.Synthetic glucocorticoids are used to treat inflammatory conditions in horses. In other pregnant animals, glucocorticoids are given to stimulate fetal maturation with long-term metabolic consequences for the offspring if given preterm. However, their metabolic effects during equine pregnancy remain unknown. Objective: Thus, this study investigated the metabolic effects of dexamethasone administration on pregnant pony mares and their foals after birth. Methods: Experimental study. Methods: A total of 3 doses of dexamethasone (200 μg/kg bwt i.m.) were given to 6 pony mares at 48 h intervals beg...
Müller V, Toribio RE, Dembek K, Moraes BSS, Mousquer MA, Curcio BR, Nogueira CEW.There are few publications on occurrence of nonthyroidal illness syndrome in foals and on the prognostic value of cortisol and thyroid hormone (TH) concentrations in newborn foals. Objective: To determine serum cortisol and TH concentrations (total and free thyroxine: T and T ; total and free triiodothyronine: T and T ) in foals born from mares with placentitis, to determine their association with survival, and their use as prognostic markers. Methods: A cohort of 29 newborn foals comprising 5 Control, 14 Low-risk, and 10 Sick foals were evaluated over the first week of life. Methods: In thi...
Ginther OJ, Gastal EL, Gastal MO, Beg MA.Reported data were reviewed and reexamined to evaluate the concept that most of the follicular fluid enters the peritoneal cavity at ovulation in mares and transiently alters the circulating concentrations of LH, FSH, estradiol, and inhibin. A transrectal ultrasonographic study supported the hypothesis that the large volume (40-50 ml) of evacuated follicular fluid passes through the infundibular fimbriae into the peritoneal cavity. A spike in circulating inhibin and a decrease in the rate of reduction in circulatory estradiol occurs at ovulation. Simultaneously, a disruption occurs in the incr...
Baieli MF, Urtasun N, Hirsch DB, Miranda MV, Cascone O, Wolman FJ.Equine chorionic gonadotrophin (eCG) is a hormone widely used in superovulation protocols because of its follicle-stimulating action, which increases reproductive efficiency in animals of productive interest. It contains 45% carbohydrate, 10% of which is N-acetylneuraminic acid (sialic acid). The eCG purification procedures from equine serum or plasma are mainly based on chromatographic methods. However, before these procedures, it is necessary to follow sample pre-conditioning steps, such as several precipitation stages and/or ultrafiltration/diafiltration processes. In this work, an efficien...
Woods GL, Ginther OJ.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-...
Gündüz MC, Kaşikci G, Ekiz B.In this study, the aim has been to characterize the profiles of progesterone, estradiol and follicular changes during postpartum period from parturition to first postpartum ovulation. Jugular venous blood was taken daily for progesterone and estradiol assay until first postpartum ovulation. The diameters of the follicles of the ovaries were recorded. The mean progesterone and estrogen concentrations markedly decreased (p<0.05) during the 48h after parturition. No correlation was observed between estradiol concentrations and the diameter of the largest follicle whereas a negative correlation wa...
Squires EL, Ginther OJ.Examination of the ovaries of mares at various stages of pregnancy and after hysterectomy, together with measurement of progesterone concentrations in the peripheral plasma of pregnant and hysterectomized mares and in uterine and ovarian venous plasma of pregnant mares, demonstrated that the primary CL of pregnancy remains functional until at least Day 160 of gestation. The results showed that primary and secondary CL, and the placenta or uterus, all contribute to the total progesterone pool in mares during pregnancy. Similarities and differences in ovarian function observed between pregnant a...
Collins SM, Zieba DA, Williams GL.We tested the hypothesis that continuous subcutaneous treatment with low-dose GnRH, administered to mares from late September/early October through March, would prevent the development of seasonal anovulation. Quarter Horse mares (n=20) were stratified by age and body condition score and assigned randomly to either a saline control (n=9) or a GnRH (n=11) treatment group. Gonadotropin-releasing hormone was delivered continuously via osmotic minipumps, with sham pumps placed in control mares. Initial pumps were inserted on Day 3 following ovulation or during the follicular phase if the next anti...
Hoffman LS, Adams TE, Evans JW.Blood samples were obtained from 5 mixed-breed, long-term castrated geldings during five 24-h periods between May 1984 and April 1985. Blood samples were collected, beginning at 09:00 h, at 15-min intervals for 8 h and hourly for the remaining 16 h. Plasma concentrations of LH and FSH were determined by RIA. Seasonal changes in hormone concentrations and frequency and amplitude of secretory pulses were evaluated. No diurnal variation in either LH or FSH secretion was observed: however, marked circhoral fluctuations in LH and FSH secretion were noted. Mean LH and FSH concentrations in these lon...
Chang M, Overk CR, Kastrati I, Peng KW, Yao P, Qin ZH, Petukhov P, Bolton JL, Thatcher GR.Oxidative metabolism of estrogens has been associated with genotoxicity. O-methylation of catechol estrogens is considered as a protective mechanism. 4-Methoxyequilenin (4-MeOEN) is the O-methylated product of 4-hydroxyequilenin (4-OHEN). 4-OHEN, the major catechol metabolite of the equine estrogens present in the most widely prescribed hormone replacement therapeutics, causes DNA damage via quinone formation. In this study, estrogen receptor (ERa) binding of 4-MeOEN was compared with estradiol (E2) and equilenin derivatives including 4-BrEN using computer modeling, estrogen response element (...
Kask K, Odensvik K, Kindahl H.The pattern of the main metabolite of prostaglandin (PG) F2alpha was recorded following a nonsurgical embryo transfer technique in 9 mares under field conditions in Estonia. Three patterns were observed. Two of them were characterised by PG release, thereas the third was not. A tendency towards a shortened cycle was seen in 3 mares. Observations were made regarding the manipulation of the uterus as being normal or difficult to perform. In general, mares where the procedure was considered difficult were also found to have a PG release.
Tan JH, Sasaki F.To determine the effect of age on immunocytochemical staining characteristics of adenohypophyseal cells of Mongolian pony mares and stallions. Methods: 35 Mongolian ponies. Methods: Pituitary glands from 1- to 22-year-old horses of both sexes were collected at a commercial slaughterhouse in China and allocated into 7 groups according to age and sex: prepubertal stallions (n = 5; 1 to 2 years old), young stallions (6; 3 to 7 years old), middle-aged stallions (4; 10 to 12 years old), old stallions (5; 15 to 22 years old), young mares (3; 3 to 7 years old), middle-aged mares (5; 10 to 12 years ol...
KIVALO E, TALANTI S.A good deal of hypothetical evidence has been presented for the view that the antidiuretic and oxytocic hormones are not produced in the posterior lobe of the hypophysis. These hormones appear to originate from a neurosecretory process in the neurosecretory nerve cells of the supraoptic and paraventricular nuclei in the hypothalamus and to migrate within the nerve fibers of the supraoptico-hypophysial tract and into the neurohypophysis (Hild, 1951, 1954 a, b and Hild & Zetler, 1951, 1952, 1953 a, b). Here they are stored and if necessary released. Neurosecretory neurons are described in many s...
Cuervo-Arango J, Newcombe JR.The association between use of hormone treatments to induce estrus and ovulation and the incidence of hemorrhagic anovulatory follicles (HAFs) was studied in a mixed population of mares (Equus caballus) during two breeding seasons in a commercial breeding clinic. Mares treated with cloprostenol (CLO) were more likely to develop HAFs than were mares with spontaneous cycles (P0.05) from that of mares with ovulatory cycles (10.5+/-1.5 yr).
Briant C, Toutain PL, Ottogalli M, Magallon T, Guillaume D.The appropriate dosage regimen for equine FSH (eFSH) (dose, dosing interval) administration in a superovulation treatment in pony mares was determined by a kinetic approach using production rates and kinetic parameters of elimination of the hormone. Two dosage regimens were then tested in superovulation protocols. The eFSH production rates were determined by sampling four ovariectomized pony mares every 10 min for 8 h during the breeding season. Kinetic parameters were determined by administering four dose levels of a preparation of eFSH (4.4, 8.8, 17.6 and 35.2 micro g/kg) by the i.v. route t...
Max MC, Silva CB, González SM, Lindquist AG, Búfalo I, Gomes RG, Morotti F, Costa CB, Barreiros T, Lisboa LA, Seneda MM.This study investigated the effects of different concentrations of FSH (10, 50, 100 and 200 ng/ml) in supplemented MEM+ on the development of equine pre-antral follicles that were cultured in vitro for 2 or 6 days. The ovaries (n = 5) from mares in seasonal anoestrus were collected from a local abattoir. Ten ovarian tissue fragments of approximately 3 × 3 × 1 mm were obtained from each animal. The fragments were cultured in situ for 2 days (D2) or 6 days (D6) in MEM+ or MEM+ supplemented with FSH at four different concentrations, establishing the following 11 groups: control (D0);...
Tischner M.In the first experiment the response of 93 adult stallions to stimulated and natural sexual stimuli was observed just before and 2 weeks after the breeding season (December and July respectively). About 72% of the stallions reacted the same before and after the breeding season (P less than 0.01) while 9% behaved similarly and 19% differently. Also, 72% of the stallions reacted with sexual arousal (mounting) to one of 3 successive simulated sexual stimuli; 25% to a dummy, an additional 44% to a gentle stallion and another 3% to a dummy smeared with mucus and urine from a mare in oestrus. In ano...
Işık R, Özdil F.Leptin receptor is a fundamental regulator in physiological functions of the regulation of food intake, energy homeostasis, immune function, and reproduction as well as on ovarian follicular cells on the placenta and lactating mammary glands. The aim of this study was to investigate the LEPR gene polymorphism in 60 donkeys reared in Thrace region of Turkey. A 585 bp long partial intron 6, exon 7, intron 7, and exon 8 regions of LEPR gene were amplified, and polymerase chain reaction products analyzed via DNA sequencing. A novel single-nucleotide polymorphism (SNP) was identified as g.713668A>...
Doyle LK, Hogg CO, Watson ED, Donadeu FX.The response of follicles to IGF1 was compared between the transition into the ovulatory season (transitional period) and the ovulatory season (ovulatory period) in eight mares using a cross-over experimental design within periods. Granulosa cells were collected from follicles 15-24 or 25-34 mm and expression of IGF1R, IGF2R, FSHR, LHCGR and PAPPA was determined by qPCR. In addition, 10 mg IGF1 or vehicle were injected into the largest follicle (transitional period) or the second largest follicle (ovulatory period) of a follicular wave before the beginning of diameter deviation between the two...
Becsek A, Tzanidakis N, Blanco M, Schmicke M, Bollwein H.The aim of this study was to investigate the effects of maternal, hormonal, and fetal factors on early fetal volume (FV) measurements in mares obtained by three-dimensional (3D) ultrasound. Furthermore, postpartum parameters were explored in regard to their association with early FV. For this purpose, 149 German warmblood mares that were artificially inseminated and confirmed to be pregnant between days 14-16 of gestation, were examined transrectally at day 45 ± 1 of gestation with the portable 3D ultrasound device Voluson® i (GE, Zipf, Austria). FV was calculated by using the extension so...
Stewart DR.Equine relaxin (eRlx) immunoactivity has previously been measured in the mare during pregnancy using the porcine relaxin (pRlx) RIA (pRlx-RIA). This was not the optimal system for measurement of eRlx because the dose-response curve obtained with equine plasma was not parallel to the pRlx standard curve. A homologous eRlx-RIA has been developed and used to measure relaxin immunoactivity during pregnancy and parturition in the mare. Highly purified eRlx was used for the generation of antiserum in rabbits, preparation of tracer, and as assay standards. A double antibody eRlx RIA (eRlx-RIA) was de...
Silberzahn P, Zwain I, Martin B.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...
Ginther OJ.Twenty-one pregnant pony mares were assigned to one of the following groups: 1) controls, 2) ovariectomy at Day 12, 3) ovariectomy at Day 12 plus daily progesterone treatment on Days 12 to 40, 4) PGF(2alpha) on Day 12, 5) PGF(2alpha) on Day 21, and 6) PGF(2alpha) on Day 30. Based on daily examinations by ultrasound, the embryonic vesicle was maintained to Day 40 in all control mares and in mares that were ovariectomized on Day 12 and given progesterone. The embryonic vesicle was lost in all mares of the other four groups. Administration of progesterone prevented the embryonic loss associated w...
