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.
Hemberg E, Lundeheim N, Einarsson S.To minimize the number of matings/inseminations, controlled ovulation has been practised since a long time ago. A potent short-term implant, releasing the GnRH analogue deslorelin (Ovuplant((R))) has been used in Australia and North America for several years for hastening the ovulation time in mares, but the product is not registered on the European market. This study was aimed to investigate: (1) ovulation time in mares implanted with Ovuplant when the largest follicle was 42 mm or more in size, (2) repeatability of ovulation time in successive oestruses when treated with Ovuplant, (3) pregna...
Ben-Menahem D, Grotjan HE.Chorionic gonadotropins (CG) are unique because they have a carboxyl terminal peptide (CTP) extension on their beta subunits that prolongs circulatory survival. CGbeta genes from the human being and horse have evolved from ancestral luteinizing hormone (LH) beta genes by different pathways that involve deletions that change the reading frames and yield a CTP. Here we further review our previous analysis, aimed at determining whether LHbeta genes in non-primate, non-equid species inherently possess DNA sequences that encode CTP-like domains. In multiple mammalian species, simple frame-shift mut...
Jablonka-Shariff A, Roser JF, Bousfield GR, Wolfe MW, Sibley LE, Colgin M, Boime I.To study structure-activity relationships and the role of equine gonadotropins in the normal and pathophysiology of equine reproduction, the availability of purified hormones is essential. Previous expression studies in transfected CHO cells showed inefficient assembly of the human and bovine alpha and beta subunits, resulting in low levels of recombinant LH. The ability to express a single chain bearing genetically linked alpha and beta subunits bypasses this rate-limiting assembly step. A chimera was constructed by overlap PCR in which the carboxy terminal end of the eLHbeta subunit was gene...
Logan NL, McCue PM, Alonso MA, Squires EL.Superovulation could potentially increase embryo recovery for immediate transfer or cryopreservation. The objectives were to evaluate the effect of pretreatment with progesterone and estradiol (P+E) on follicular response to eFSH and compare doses of eFSH and ovulatory agents on follicular development and ovulation in mares. In Experiment 1, 40 mares were assigned to one of four treatment groups. Group 1 consisted of untreated controls. Group 2 mares were administered eFSH without pretreatment with P+E. Group 3 mares were administered P+E for 10 days starting in mid-diestrus followed by eFSH t...
Buff PR, Messer NT, Cogswell AM, Johnson PJ, Keisler DH, Ganjam VK.The objective of this study was to determine if seasonal and/or pulsatile variations occur in plasma concentrations of thyrotropin (TSH) and leptin in mares while maintaining a constant energy balance. Blood samples were collected every 20 min during a 24h period in winter and again in summer from six Quarter Horse type mares. Plasma concentrations of TSH, leptin, and T(4) were determined by radioimmunoassay. No differences were observed in body weight between winter (388.1+/-12.5 kg) and summer (406.2+/-12.5 kg; P=0.11). Plasma concentrations of TSH were greater in the summer (2.80+/-0.07 ng/...
Buff PR, Spader BR, Morrison CD, Keisler DH.Leptin, a protein hormone secreted by adipocytes, plays an important role in energy homeostasis and regulation of body composition. We previously observed that acute feed restriction resulted in a rapid decline in concentrations of leptin in obese pony mares. This acute response prompted us to characterize the temporal changes in concentrations of leptin, GH, and insulin in obese pony mares during the transition between fed and feed-restricted conditions. Nine obese pony mares of mixed breed, previously maintained on fescue pasture, were randomly allotted to 2 groups. Treatments consisted of a...
Bilińska B, Wiszniewska B, Kosiniak-Kamysz K, Kotula-Balak M, Gancarczyk M, Hejmej A, Sadowska J, Marchlewicz M, Kolasa A, Wenda-Rózewicka L.The purpose of this article was to summarize our results on the role of androgens and estrogens in human, rodent and equine testes and epididymides, in both, physiological and patological conditions, obtained in the space of the Solicited Project (084/PO6/2002) financially supported by the State Committee for Scientific Research during the last three years. Testosterone produced by Leydig cells of the testes is clearly the major androgen in the circulation of men and adult males of most mammalian species. However, androgen metabolites make up a significant fraction of total circulating steroid...
Frank N, Andrews FM, Sommardahl CS, Eiler H, Rohrbach BW, Donnell RL.A combined dexamethasone (DEX) suppression/thyrotropin-releasing hormone (TRH) test (DEX/TRH test) has been developed to evaluate horses for presence of a pars intermedia pituitary adenoma (PIPA), but to the authors' knowledge, the accuracy of this test has not been previously determined. Objective: The sensitivity and specificity of the DEX/TRH test can be determined by comparing test results with histopathologic examination findings. Methods: Age of 42 horses of various breeds ranged from 2 to 33 years. Methods: Plasma cortisol concentration was measured before and 24 hours after IV administ...
Jackson BF, Dyson PK, Hattersley RD, Kelly HR, Pfeiffer DU, Price JS.To investigate the relationship between stage of estrous cycle and bone cell activity in Thoroughbreds. Methods: Blood samples collected from forty-seven 2-year-old Thoroughbred mares in training for racing. Methods: Blood samples were collected monthly (in April through September) from the mares. Stage of estrus was determined by assessing serum progesterone concentration. Bone cell activity was determined by measuring concentrations of 2 markers of bone formation (osteocalcin and the carboxy-terminal propeptide of type I collagen [PICP]) and a marker of bone resorption (the cross-linked carb...
Beg MA, Ginther OJ.The eminent event in follicle selection during a follicular wave in monovular species is diameter deviation, wherein one follicle continues to grow (developing dominant) and other follicles (subordinates) begin to regress. In cattle, the IGF system, oestradiol and LH receptors are involved in the intrafollicular events initiating deviation as indicated by the following: (1) concentrations of free IGF-I and oestradiol in the follicular fluid and number of LH receptors in the follicular wall increase more dramatically in the future dominant follicle than in the future subordinate follicles befor...
Purcell SH, Seidel GE, McCue PM, Squires EL.The aim of this study was to compare the efficacy of three approaches for recovering equine oocytes via transvaginal ultrasound-guided follicular aspiration. Fourteen mares were used as oocyte donors during the spring transition period and physiologic breeding season, and 11 mares were bred for use as oocyte donors during early gestation. In all mares, large (>20 mm) and small (10-20 mm) follicles were aspirated in eight rounds every 10-11 days. In each of the four rounds during the transition period, half the mares received 12.5 mg eFSH once daily for 4 days prior to aspiration. For each of t...
Ginther OJ, Utt MD, Beg MA.The temporal relationships between follicle deviation and systemic hormone concentrations were studied in mares. Blood samples were obtained at 01:00, 07:00, 13:00, and 19:00 h from nine mares throughout an interovulatory interval. Diurnal variation in progesterone occurred on Days 4-12 and in LH on Days 4 and 5; the lowest concentration for both hormones was at 13:00 h. Ultrasonically observed deviation in the ovulatory follicular wave began on Day 15.7+/-0.5 (ovulation=Day 0). An increase (P<0.002) in LH began on Day 14 before the beginning of deviation, and an increase (P<0.05) in est...
Vick MM, Sessions DR, Murphy BA, Kennedy EL, Reedy SE, Fitzgerald BP.In mares, obesity is associated with continuous reproductive activity during the non-breeding season. To investigate the effect of obesity and associated alterations in metabolic parameters on the oestrous cycle, two related studies were conducted. In Experiment 1, obese (body condition score > 7) mares were fed ad libitum or were moderately feed restricted during the late summer and autumn months. Feed restriction did not alter the proportion of mares entering seasonal anoestrus. However, obese mares exhibited a significantly longer duration of the oestrous cycle, significant increases in ...
Danek J.Four clinically normal stallions were infused intravenously with endotoxin (LPS) from Escherichia coli 055:B5 at a dose of 0.3 microg/kg b.w. and four stallions were treated with flunixin meglumine (FM) as a single intravenous injection at a dose of 1.1 mg/kg b.w., 5 min after the infusion of LPS. In response to endotoxin infusion, stallions' reaction was fever (increased rectal and scrotal skin temperature), increased heart rate (HR) and leucopenia. Administration of endotoxin also influenced the level of testosterone (decrease at 3-24 h and increase at 48-72 h after LPS administration) in th...
Steelman SM, Michael-Eller EM, Gibbs PG, Potter GD.Energy is an essential nutrient for all horses, and it is especially important in performance horses, pregnant and lactating mares, and young growing horses. A negative energy balance in horses such as these may result in unsatisfactory performance, decreased fertility, or slow growth. Therefore, ensuring adequate energy intake is an important aspect of the nutritional management of the equine. This study was undertaken to investigate the effects of feeding large, carbohydrate-rich, concentrate meals on the satiety-inducing hormone, leptin. Three groups of yearling horses were rotated through ...
Cebulj-Kadunc N, Cestnik V, Kosec M.The onset of puberty and duration of seasonal cyclicity in Lipizzan fillies and young mares have been determined mostly by empirical data, but very little is known about the hormonal changes at puberty and during the seasonal cyclicity in this breed. Objective: To determine the onset of puberty and the course of the cyclicity in young Lipizzan mares from age 1-4 years. Methods: Blood samples were collected twice a month for 2 years from 46 Lipizzan fillies age 1-4 years. Progesterone concentrations, indicating ovarian activity, were measured using an EIA kit. Values above 6.4 nmol/l were taken...
Hedberg Y, Dalin AM, Santesson M, Kindahl H.Strong oestrous symptoms in the mare can cause problems with racing, training and handling. Since long-acting progesterone treatment is not permitted in mares at competition (e.g. according to FEI rules), there is a need for methods to suppress unwanted cyclicity. Spontaneous dioestrous ovulations in the late luteal phase may cause a prolongation of the luteal phase in mares. Methods: In this preliminary study, in an attempt to induce ovulation during the luteal phase, human chorionic gonadotropin (hCG) (3000 IU) was injected intramuscularly in four mares (experimental group) in the luteal pha...
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Hoffmann B, Ludwig C, Kindahl H.Ovariectomized mares and mares with inactive ovaries may show signs of estrus. The reason behind this phenomenon is not clear; however, steroid hormones of adrenal origin have been suggested. Moreover, aberrant adrenal hormone production has been implied as a reason why some intact mares may change behavior. In the present study, the effect of ACTH on plasma levels of cortisol, progesterone, androstenedione and testosterone was investigated in intact mares with normal estrous behavior ('controls', n=5) and intact mares that according to their owners showed deviant estrous behavior ('problem' m...
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Sandh G, Hoffmann B, Ludwig C, Kindahl H.The mare is the only non-primate species known to display estrous signs after ovariectomy and adrenal hormones have been implicated as a possible cause. Moreover, in several species, estradiol seems to have a stimulatory effect on the hypothalamic-pituitary-adrenal axis. The aim of the present study was to compare the effect of ACTH (tetracosactide) on pertinent hormones [cortisol, progesterone, androstenedione, testosterone (intact and ovariectomized mares) and estradiol (ovariectomized mares only)] in intact mares in estrus with the same mares after ovariectomy (n=5). Blood samples were coll...
Sayasith K, Bouchard N, Doré M, Sirois J.The progressive rise in gonadotropins prior to ovulation triggers a marked increase in intrafollicular levels of prostaglandin F(2alpha)(PGF(2alpha)), which is known to interact with PGF(2alpha) receptor (FP). Little is known about the regulation of FP during ovulation. This study was undertaken to characterize the equine FP and its gonadotropin-dependent regulation in preovulatory follicles prior to ovulation. The full-length equine FP encodes a 366-amino acid protein that is 82-93% homologous to other species. Using semi-quantitative RT-PCR/Southern blot, we showed that FP mRNA expression wa...
Aguilar J, Fraser HM, Wilson H, Clutton E, Shaw DJ, Watson ED.The temporal relationship between endothelial cell death, vascular regression and the death of hormone-producing cells in the mare has not been established. To determine the dynamics of cell proliferation and death throughout the luteal phase, corpora lutea were studied at the early, mid- and late luteal phase, and after treatment with cloprostenol in the mid-luteal phase to induce premature luteolysis. Changes in cell proliferation and apoptosis were investigated utilising specific markers (phosphorylated histone-3 and activated caspase-3 respectively). Histone-3 positive cells were most abun...
Bleul U, Theiss F, Rütten M, Kähn W.This case report describes a three-year-old Friesian stallion with hypospadias. Physical examination revealed a ventrocaudal deviation of the shaft of the penis and an incomplete glans penis. The urethral opening was 4 cm in length, slit-like and had a mucous membrane covering. A short fold ran from the ventral aspect of the anus and ended with a non-pigmented hairless area of skin. A human choriongonadotropin (hCG)-stimulation test resulted in an increase in the plasma levels of estrogen sulfate and testosterone, indistinguishable from that of a normal stallion. The karyogram had a normal num...
Gordon ME, McKeever KH.This study tested the hypothesis that grain and intravenous dextrose challenges would alter plasma concentrations of active ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in Standardbred mares. To deliver 0.5 g of glucose (dextrose solution for the intravenous test)/kg of BW, mares received intravenous dextrose (50% solution) or oral grain administration in 2 trials. In response to the oral grain challenge, plasma glucose and insulin concentrations increased (P < 0.001) by 56 and 802%, respectively. Plasma ghrelin concentration initially decreased (P < 0.001) by 40%, then s...
Imboden I, Janett F, Burger D, Crowe MA, Hässig M, Thun R.The aim of this study was to evaluate the effect of active immunization against GnRH on ovarian activity, plasma progesterone and estradiol concentrations and on estrous behavior in adult mares. Eighteen cyclic mares were randomly divided into a treatment and control group. Nine mares were immunized twice with 2 mL (400 microg GnRH-protein conjugate) of a GnRH-vaccine (Improvac, CSL Limited, Australia) administered intramuscularly, 4 weeks apart. Control mares received the same amount of saline solution. Ovaries and uterus of all mares were examined weekly by ultrasonography from 3 weeks befor...
Handler J, Hoffmann D, Weber F, Schams D, Aurich C.The aim of the present study was, to investigate the effects of oxytocin administration on Day 7 post-ovulation on progesterone secretion, pregnancy rate and embryonic growth in mares. Endogenous stimulation of oxytocin release was compared to the administration of native oxytocin or the long-acting oxytocin analogue carbetocin. At Day 7 after ovulation, mares had to undergo four treatments in a crossover design: (a) control, (b) oxytocin (10 IU i.v.), (c) carbetocin (280 microg i.m.) and (d) cervical dilation. On Day 13, all mares (8 of 8 mares) were pregnant on groups control, oxytocin and c...
Squires EL, McCue PM.Embryo recovery from single ovulating mares is approximately 50 per cent per estrous cycle. Superovulation could be used to increase embryo recovery and provide extra embryos for embryo freezing. This review addresses some historical approaches to superovulation, as well as examines factors that affect the response of mares to equine FSH. eCG, GnRH and inhibin vaccines have been of limited success in stimulating multiple ovulation. Numerous studies have shown that injection of equine pituitary extract (EPE) will result in three to four ovulations per estrous cycle and two embryos. A purified, ...
Bousquet-Mélou A, Formentini E, Picard-Hagen N, Delage L, Laroute V, Toutain PL.The present study aimed to characterize the adrenal response to ACTH. A model was developed that coupled the nonlinear disposition of cortisol with a physiologically based model for cortisol secretion by the adrenals. It was assumed that the response to ACTH resulted from two mechanisms: a stimulation of the cortisol secretion rate and control of the duration of the secretion. Seven dose levels of ACTH were tested in horses, a species similar to man as regards adrenal function. The main result was that the secretion rate of the adrenal gland can be modelized by a zero order process that is max...
Veronesi MC, Carluccio A, Kindahl H, Faustini M, Battocchio M, Cairoli F.The aim of the present study was to evaluate within 24 h post-ovulation oxytocin-induced PGF(2alpha) release in mares with and without post-breeding delayed uterine clearance (DUC). Twenty-one of 34 mares with a variable amount of intrauterine fluids accumulation were considered to be affected by delayed uterine clearance (DUC group), while the other 13 mares did not show any uterine fluid accumulation, and were considered as controls (WDUC group). Both DUC and WDUC mares were administered with 20 IU oxytocin i.m. 90 min after the ultrasound examination performed 24 h after breeding. Immediate...
Nogueira GP, Barnabe RC, Verreschi IT.We measured progesterone and estradiol levels from birth to the beginning of adult life in 10 Thoroughbred fillies from the Equilia Stud Farm in Avaré SP, Brasil. The animals were measured and weighed monthly for the determination of body development and of a possible correlation between the rate of weight and height gain and the onset of detectable sex hormone levels. Jugular blood was collected twice a week and stored at -20 degrees C until assay of progesterone by a solid phase RIA with a sensitivity of 0.32 nmol L and of estradiol by liquid phase RIA adapted to low levels (3.67 pmol L ). ...
Peltier MM, Peltier MR, Sharp DC, Ott EA.The objective of this study was to determine whether supplemental beta-carotene would influence reproductive function in mares maintained on spring and summer pastures and to characterize plasma carotene concentrations during the estrous cycle. Carotene concentrations in plasma did not vary with day of estrous cycle (P = 0.7455). Mares receiving every other day injections of beta-carotene (400 mg; n = 4) or saline (10 ml; n = 4) during proestrus/estrus did not differ in plasma estradiol (E(2)) concentrations (P = 0.6313), follicle development (P = 0.8068), or plasma progesterone (P(4)) concent...
Odeh AI, Dascanio JJ, Caceci T, Bowen J, Eng LA.Phospholipids are an essential component of all mammalian cells; platelet activating factor (PAF=1-O-alkyl-acetyl-sn-glycero-3-phosphocholine) is a signalling phospholipid that has many biological properties in addition to platelet activation. PAF receptors have been detected on stallion spermatozoa; therefore, the aim of this study was to evaluate the effect of synthetic PAF on the motility, capacitation and the acrosome reaction of stallion spermatozoa. Treatment of ten stallion semen samples with 10(-4)-10(-13) mol PAF l(-1) resulted in significant differences in motility and capacitation (...
Jimenez M, Hinchcliff KW, Farris JW.The responses of the plasma concentrations of catecholamines and cortisol in horses to varied relative intensities of exertion were examined. The plasma concentrations of cortisol, epinephrine and norepinephrine increased significantly (p < 0.05) with exertion. The plasma cortisol concentrations at relative work intensities of 48.3% +/- 1.4%, 82.3% +/- 2.0% and 99.6% +/- 0.4% of VO2max were 114%, 124%, and 126%, respectively, of those at rest, whereas the plasma epinephrine concentrations were 239%, 772% and 3483%, and the norepinephrine concentrations were 138%, 255%, and 1121% of the valu...
Parlevliet JM, Bevers MM, van de Broek J, Colenbrander B.Gonadotrophin-releasing hormone (GnRH) (a single intravenous injection with 0.042 mg busereline acetate) was administered to control stallions (n=5), aged stallions (n=5) and stallions with lack of libido (n=5). Jugular blood samples were taken at -10, 0, 10, 20, 40 and 80 minutes after treatment and measured for luteinizing hormone (LH) and testosterone concentrations. A single intravenous injection of hCG (3000 IE) was given 1 day later. Venous blood samples were taken at -60, 0, 15, 30, 60, 120, and 240 minutes after treatment and measured for the testosterone concentration. The experiment ...
Palmer E.The use of photoperiod, progestagen, prostaglandin and hCG treatments was investigated to obtain mating of mares at predetermined times. The objectives were: (1) synchronization of oestrus at an early time of the year, (2) simplification of treatment schedules by use of vaginal sponges, and (3) use of several controlled cycles by successive synchronization. The following conclusions were reached. First, after a 16 h photoperiod was applied beginning on 25 November, hormonal synchronization of oestrus and ovulation followed by cyclicity were obtained on 1 February; i.e. 2 months of light are es...
Silva ES, Roser JF, Gomes AR, Fritsch SC, Pantoja JC, Oliveira-Filho JP, Meira C.The present study evaluated the influence of different regimens of estradiol benzoate (EB) treatments followed by a single dose of long-acting progesterone (LA P4) on plasma estrogen and P4 concentrations in noncyclic mares prepared as embryo recipients. Twenty-one anestrous mares were distributed into three groups (n = 7 mares per group), according to the EB dose received (single dose of 2.5 mg, total of 5 mg in decreasing doses, and total of 10 mg in decreasing doses), which was followed by a single administration of 1500 mg of LA P4 in all groups. Mares were reevaluated during the ovula...
Shakeel M, Jung H, Yoon D, Yoon M.The economic impacts of infertility and subfertility of stallions greatly influence the horse breeding industry. Self-renewal and differentiation of spermatogonial stem cells are the initial processes to maintain an adequate sperm population. Thus, understanding these processes may provide useful information to reveal the causes and remedies of subfertile and infertile stallions. Stallions are seasonal breeders. About 50% of the sperm population is reduced during the non-breeding season (NBS) in stallions. The seasonal regulation of spermatogenesis renders stallions as ideal models to understa...
Porter RM, Akers RM, Howard RD, Forsten-Williams K.Alginate hydrogel culture has been shown to reestablish chondrocytic phenotype following monolayer expansion; however, previous studies have not adequately addressed how culture conditions affect the signaling systems responsible for chondrocyte metabolic activity. Here we investigate whether chondrocyte culture history influences the insulin-like growth factor-I (IGF-I) signaling system and its regulation by interleukin-1 (IL-1). Articular chondrocytes (ACs) from equine stifle joints were expanded by serial passage and were either encapsulated in alginate beads or maintained in monolayer cult...
Ginther OJ, Gastal EL, Gastal MO, Beg MA.During a follicular wave in mares, the two largest follicles (F1 and F2) begin to deviate in diameter when F1 is a mean of 22.5 mm. The intrafollicular effects of pregnancy-associated plasma protein-A (PAPP-A), IGF-I, activin-A and vascular endothelial growth factor (VEGF) on other follicular-fluid factors during deviation were studied. In four treated groups (n = 7/group), a single dose of one of the four factors was injected into F2 when F1 was > or = 20.0 mm (expected beginning of deviation). In a control group (n = 7), F2 was injected with vehicle. One day after treatment, a sample of f...
Penrod LV, Allen RE, Turner JL, Limesand SW, Arns MJ.Increased secretion of prostaglandin F(2)α (PGF(2)α) within the uterus because of uterine inflammation can cause luteolysis and result in early embryonic loss. Supplementation with polyunsaturated fatty acids (PUFAs) has been shown to influence PG production in many species, although the effects on the mare remain unknown. The present study aimed to determine fatty acid uptake in equine endometrial explants and evaluate their influence on PG secretion and expression of enzymes involved in PG synthesis in vitro. Equine endometrial explants were treated with 100 μM arachidonic acid, eicosapen...
Saint-Dizier M, Chopineau M, Dupont J, Daels PF, Combarnous Y.Luteal steroids are necessary to maintain the first 70-90 days of pregnancy in the mare. At 35 days postovulation, the resurgence of the primary corpus luteum (CL) coincides with the secretion of the fetal hormone eCG. In order to study the responsiveness of the primary CL to eCG, we have examined levels of luteal equine LH/CG receptors (eLH/CG-R) mRNAs by Northern blot analysis and measured concentrations of eLH/CG binding sites on luteal membranes using 125I-eLH saturation binding assays at three stages of gestation: before the onset of eCG secretion (Days 14-31), from onset to maximum eCG s...
Bézard J, Mekarska A, Goudet G, Duchamp G, Palmer E.The objects of this study were to monitor the development of the cumulus complex and nuclear maturation in oocytes recovered from preovulatory follicles following treatment to induce ovulation and to investigate the in vitro maturation competence of oocytes recovered from smaller nonpreovulatory follicles of varying size. All follicles > or =5 mm in pony mares were individually punctured at 0, 6, 12, 24 and 35 h after an injection of LH to induce ovulation. The recovery rates of oocytes were 64% from 55 preovulatory follicles, 22% from 32 subordinate follicles and 52% from 227 small follicl...
Sticker LS, Thompson DL, Bunting LD, Fernandez JM, DePew CL, Nadal MR.Twelve light horse mares were fed a control diet that provided 100% of their maintenance protein and energy requirements for 7 d and were then either continued on the control diet or totally deprived of feed (with access to water) for 3 d . Plasma samples were drawn twice daily throughout the experiment, at 15-min intervals for 9 h beginning 45 h after feed removal, and at 10-min intervals around an exercise bout beginning 73 h after feed removal. Feed deprivation increased (P < or = .06) whole blood beta-hydroxybutyrate and plasma NEFA, urea N, L-lactate, and glucagon concentrations, decrease...
Riley SC, Thomassen R, Bae SE, Leask R, Pedersen HG, Watson ED.Profound hormonally controlled tissue remodelling occurs in the equine ovary for follicle growth and development, and also for the alteration in follicle shape directed towards the ovulation fossa, the site where ovulation occurs. The aim of this study was to examine the spatial and temporal regulation of matrix metalloproteinases (MMP)-2 and MMP-9, important enzymes in tissue remodelling, during follicle growth, and ovulation. Using gelatin substrate zymography, we measured these MMPs in follicular fluid of large anovulatory follicles collected during spring transition, early dominant follicl...
Hinrichs K, Sertich PL, Palmer E, Kenney RM.Pregnancy was established and maintained after embryo transfer in 3 ovariectomized mares treated with progesterone only. Four ovariectomized mares were used as recipients, and 7 transfers were performed. Progesterone in oil, 300 mg i.m. daily, was given starting 5 days before transfer of a 7-day embryo. If the mare was pregnant at 20 days, progesterone treatment was continued to 100 days of gestation. The 3 pregnant mares carried to term and delivered live foals with normal parturition, lactation and maternal behaviour. No differences were seen between pregnant and non-pregnant ovariectomized ...
Tomanelli RN, Sertich PL, Watson ED.Receptors for progesterone and oestrogen were measured in cytosol extracted from the endometrium of mares. Samples of endometrium were obtained from mares during the oestrous cycle and during other physiological and pathological states, and from mares with persistent endometritis. The concentration of binding sites was high around oestrus and early in dioestrus and was low by mid- to late dioestrus. Numbers of receptors were low in mares sampled on Day 15 of pregnancy and in mares in prolonged dioestrus, whereas receptor concentrations in ovariectomized mares were high. In 2 mares with endomet...
Harada T, Nambo Y, Ishimaru M, Sato F, Nagaoka K, Watanabe G, Taya K.The effects of an extended photoperiod (EP) treatment (14.5 hr light, 9.5 hr dark) on Thoroughbred colts and fillies from December 25 at 7-9 months old to the following May at 12-14 months old on coat condition and gonadal functions were investigated. Coat condition was evaluated in April. The colts and fillies in the EP treatment group changed from winter to summer coats (molting of winter coats), whereas those in the control group did not. To determine the day of first ovulation, the plasma concentrations of progesterone were measured once a month in fillies. The day of first ovulation was a...
Gutjahr S, Paccamonti DL, Pycock JF, Taverne MA, Dieleman SJ, van der Weijden GC.To determine the effect of dose and day of oxytocin treatment on intrauterine pressure, 6 normal mares were treated with 10 or 25 IU oxytocin 2 days before ovulation, on the day of ovulation and 2 days after ovulation. Intrauterine pressure (IUP) was measured using micro-tip-catheters (one placed intrauterine, a second and third serving as reference sensors in the vagina and external to the mare) and transmitted by telemetry for 30 min to establish a baseline before saline was administered, iv, and for an additional 30 min after saline administration. Oxytocin was then given, iv, and IUP was r...
Martínez R, Godoy A, Naretto E, White A.1. Packed cell volume (PCV) and plasma catecholamines, cortisol and glucose were determined in blood samples obtained from race horses, after competition. 2. All these parameters were higher than basals but catecholamines increased 6-7 times while cortisol was enhanced only by 25%. 3. The increase of glucose and PCV was related to the rise of catecholamines. 4. In samples withdrawn after overnight stress caused by change of horseshoes, it was not possible to find values from basal values significantly different. 5. Influence of nervous temperament was observed only in the higher hematocrit fou...
Manning AW, Rajkumar K, Bristol F, Flood PF, Murphy BD.The variation in the quantity of circulating chorionic gonadotrophin (CG) and its follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activity in rodent bioassay systems was investigated. A portion of the variability in total CG could be attributed to the stallion that sired the pregnancy and it was possible to select sires and mares to increase CG production. It was further demonstrated that FSH activity per unit of CG was greater at Days 71 and 104 of gestation than at Day 39. LH activity per unit of CG varied with the sire, but no effect of day of gestation could be shown. It wa...
Clay CM, Clay JN.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...
Choi Y, Yoon M.Androstenone influences the changing behaviors of animals. Previous studies discovered that an androstenone receptor was expressed in horses and treatment with androstenone induced horses to be more compliant. As changes in the level of neuroendocrine factors result in animal behavioral changes, the objective of the study was to monitor the changes in the concentrations of 5-HT, β-endorphin, and cortisol in response to androstenone. Eight thoroughbred horses (five mares and three geldings) were treated with androstenone diluted in jojoba oil (10 µg/mL) and only oil for a control cross-overly...
Snyder DA, Turner DD, Miller KF, Garcia MC, Ginther OJ.Observations of follicular and gonadotrophic changes were conducted on 14 Pony mares for 31-day periods beginning at the penultimate (second last) ovulation and at the last ovulation of the season. There were no main effects or interaction of day or period on the numbers of small follicles (less than 20 mm). Concentrations of FSH, numbers of large follicles (greater than 20 mm), and oestrous behaviour each showed an effect of day (P less than 0.01), but no effect of period. Concentrations of LH and diameter of the largest follicle each showed an interaction (P less than 0.01) between day and p...
Teixeira ACB, Valle GR, Riveros JAN, Diniz JHW, Wenceslau RR, Monteiro GA, Leme FOP, Oliveira LZ.The aim of this study was to evaluate the effect of equine chorionic gonadotropin (eCG) at the end of progesterone (P4) treatment on follicular and luteal characteristics during transition period (TP) and reproductive breeding season (RP). A total of 13 crossbred mares were distributed in two experimental groups in the spring and summer (n = 26). The animals received intravaginal P4 (1.9 g) releasing device from D0 to D10. On removal of P4 device, the mares received 400 IU of eCG (eCG group) or saline solution (control group). Human chorionic gonadotropin (hCG; 1.750 IU) was administered (Dh...
Lange-Consiglio A, Arrighi S, Fiandanese N, Pocar P, Aralla M, Bosi G, Borromeo V, Berrini A, Meucci A, Dell'Aquila ME, Cremonesi F.There is no published information about follicular-fluid leptin concentrations or the presence of leptin and leptin receptor in the equine ovary or oocyte. Three groups of mares - adult draft mares, draft fillies and adult Standardbred mares - were included in the study. Leptin and leptin receptor were detected in all immature oocytes by immunofluorescence with higher intensity in oocytes from draft mares compared with draft fillies and Standardbred mares. After in vitro maturation a higher proportion of oocytes reached metaphase II in draft mares than in draft fillies and Standardbred mares, ...
Lassourd V, Gayrard V, Laroute V, Alvinerie M, Benard P, Courtot D, Toutain PL.The influence of a 56-km endurance exercise on cortisol kinetics and production rate was evaluated in six horses administered [3H]cortisol. Exercise resulted in an immediate two- to threefold increase in plasma cortisol, with values returning very rapidly to preexercise levels. During exercise, clearance and steady-state volume of distribution of total cortisol were greatly increased (338 +/- 95 vs. 137 +/- 34 ml.kg-1.h-1 for clearance and 359 +/- 82 vs. 229 +/- 18 ml/kg for volume of distribution), whereas the terminal half-life decreased significantly (0.97 +/- 0.16 vs. 1.55 +/- 0.33 h). The...
Kuhl J, Nagel C, Ille N, Aurich JE, Aurich C.In the present study we have evaluated a possible stress reaction in response to two different PGF2α analogs-luprostiol and D-cloprostenol--and their effects on estrous cycle characteristics. In a cross-over-design eight mares received in alternating order either luprostiol (Treatment LUP; 3.75 mg im), D-cloprostenol (Treatment CLO; 22.5μg im) or saline (Treatment CON; NaCl 0.9% 0.5ml im) on day 8 after ovulation. Injection of either LUP or CLO, but not of CON resulted in a significant decline of progesterone concentration in plasma to baseline concentrations within two days (time: p<0.00...
Alexander SL, Irvine CH, Livesey JH, Donald RA.The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P < 0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P < 0.02). Three mares became mildly agitated during treatment. Mean PV concentratio...
Murase H, Saito S, Amaya T, Sato F, Ball BA, Nambo Y.Anti-Müllerian hormone (AMH), a glycoprotein secreted from the fetal testis, is responsible for regression of the Müllerian duct in the male fetus. The aim of this study was to evaluate the usefulness of serum AMH as a biomarker for diagnosis of cryptorchidism in horses. Serum AMH concentrations were measured in intact stallions, hemi-castrated unilateral cryptorchid stallions, and geldings. In addition, expression of AMH was characterized in cryptorchid testes by immunohistochemistry. Serum AMH was detected in intact stallions (n=11, 13.3 ± 1.8 ng/ml) and in hemi-castrated cryptorchid stal...
Huszenicza G, Nagy P, Juhász J, Kóródi P, Kulcsár M, Reiczigel J, Guillaume D, Rudas P, Solti L.The relationship between thyroid function and seasonal reproductive activity in mares was investigated by comparing plasma triiodothyronine and thyroxine concentrations in anoestrous mares and in mares with cyclic ovarian activity during the anovulatory season. In study 1, the diurnal changes in plasma triiodothyronine and thyroxine concentrations on a single day were compared in anoestrous and cyclic mares. The mean thyroxine concentrations were significantly higher (P < 0.001) in the cyclic mares than in the anoestrous mares, whereas mean triiodothyronine concentrations were similar in bo...
Matlina E.The investigation of catecholamine (CA) metabolism in animals subjected to various types of stress (different pain syndromes; cranial trauma; immobilization; cooling) and physical exercise shows considerable similarity among species in the sequence of changes, leading from the activation to the depletion of the sympathoadrenal system. The changes caused by physical exercise tend to be more pronounced in individuals with a genetic predisposition to greater stress responses. Stress adaption, induced by special training or by long-duration exposure to hypoxia, can substantially prevent the change...
