Gonadotropin-Releasing Hormone (GnRH) is a neuropeptide hormone produced in the hypothalamus of horses. It is involved in the regulation of reproductive processes by stimulating the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary gland. These hormones are key regulators of gonadal function, influencing processes such as estrus, ovulation, and spermatogenesis. The study of GnRH in horses includes understanding its physiological roles, mechanisms of action, and its application in managing reproductive health. This page compiles peer-reviewed research studies and scholarly articles that explore the function, regulation, and clinical applications of Gonadotropin-Releasing Hormone in equine reproduction.
Joonè CJ, Schulman ML, Fosgate GT, Claes ANJ, Gupta SK, Botha AE, Human A, Bertschinger HJ.Circulating anti-Müllerian hormone concentration (AMH) is positively correlated to the number of small growing follicles in the mare and may reflect ovarian function. Dynamics of AMH during immunocontraception have not previously been investigated. This study aimed to compare serum AMH in mares following treatment with native porcine zona pellucida (pZP), recombinant pZP3 and pZP4 (reZP) or gonadotrophin releasing hormone (GnRH) vaccines, and saline-treated controls. Stored sera collected during two previous studies examining ovarian activity in mares during zona pellucida (ZP) or GnRH immuno...
Bhardwaj A, Nayan V, Sharma P, Kumar S, Pal Y, Singh J.Equine pituitary gonadotropins (eLH, eFSH, eCG) are heterodimeric glycoprotein hormones with alpha (α) and beta (β) subunits. It is responsible for maintenance of pregnancy in mares during early gestation and fairly valuable for inducing superovulation in animals other than equines. The alpha subunit is common, while beta subunit is species-specific in all glycoprotein hormones. In the present investigation, molecular cloning and in silico characterization including homology modeling and molecular docking analysis of the equine chorionic gonadotropin (eCG) alpha subunit was carried out for g...
Bailly-Chouriberry L, Loup B, Popot MA, Dreau ML, Garcia P, Bruyas JF, Bonnaire Y.Since the availability on the European market of the vaccine Improvac® dedicated to male pig immunological castration, the risk of misuse of this product in horses is now considered as a threat for the horseracing industry. Immunological castration is not allowed by the racing codes (immune system, Article 6). Indeed, this vaccination against the hypothalamic hormone luteinizing hormone-releasing hormone or gonadotropin-releasing hormone (GnRH) will prevent the release from the anterior pituitary of luteinizing hormone and follicle stimulating hormone, which are required for the development a...
Miki W, Oniyama H, Takeda N, Kimura Y, Haneda S, Matsui M, Taya K, Nambo Y.We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus wer...
Brito LF, Baldrighi JM, Wolf CA, Ginther OJ.The objective of the present study was to investigate the effect of reproductive hormones (GnRH, hCG, LH and progesterone) on the regulation of corpus luteum (CL) and ovarian blood flow. Diestrous mares received a single treatment of saline, 100μg gonadorelin (GnRH), or 1500IU hCG 10days after ovulation. Plasma LH and progesterone concentrations, resistance index (RI) for ovarian artery blood-flow, and percentage of corpus luteum (CL) with color-Doppler signals of blood flow were determined immediately before treatment (hour 0) and at hours 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, and 6. In the GnRH gr...
Finan SA, Lamkin EL, McKinnon AO.To investigate the comparative efficacy of BioRelease Deslorelin® (BRD) and Ovuplant® for induction of ovulation in cyclic mares in Australia. Methods: Ovarian follicular activity of 60 mares for a total of 95 cycles was monitored by ultrasonography until they developed a follicle ≥30 mm and a uterine oedema pattern of 3. Mares were then randomly allocated to one of three treatment groups: (1) treatment with 1.25 mg BRD, (2) a single Ovuplant pellet or (3) 1 mL compound sodium lactate control. Follicular activity was monitored with ultrasonography every 12 h until ovulation was detec...
Davolli GM, Ball BA, Esteller-Vico A, Claes AN, Canisso IF, Fedorka CE, Woodward EM, Troedsson MH, Squires EL.The GnRH antagonist, acyline, has not yet been investigated in the stallion. Our study aimed to: (1) evaluate the downregulation of the stallion hypothalamic-pituitary-gonadal axis by acyline through assessment of seminal parameters, testicular volume, and sexual behavior; (2) assess hormonal response of acyline-treated stallions to GnRH stimulation; and (3) verify reversibility after treatment. Stallions were assessed pretreatment and subsequently treated (every five days) for 50 days: acyline (n = 4; 330 μg/kg acyline) or control (n = 4, vehicle). The stallions were then monitored for 62Â...
McGrath BM, Scott CJ, Wynn PC, Loy J, Norman ST.Managing the return to regular cyclicity after the winter anestrous period in the mare has been a challenge for the equine breeding industry. Specifically, efforts have been made to shift or shorten the vernal transition period and to have it followed by a predictable first ovulation at the commencement of the breeding season. Intravenous administration of kisspeptin is known to stimulate an LH response in both reproductively active and inactive mares. This study examined the effects of a constant rate infusion (CRI) of kisspeptin on mares during vernal transition. Mares were given a 30Â hours...
Richards SL, Cawley AT, Cavicchioli R, Suann CJ, Pickford R, Raftery MJ.Over recent years threats to racing have expanded to include naturally occurring biological molecules, such as peptides and proteins, and their synthetic analogues. Traditionally, antibodies have been used to enable detection of these compounds as they allow purification and concentration of the analyte of interest. The rapid expansion of peptide-based therapeutics necessitates a similarly rapid development of suitable antibodies or other means of enrichment. Potential alternative enrichment strategies include the use of aptamers, which offer the significant advantage of chemical synthesis onc...
Ginther OJ, Baldrighi JM, Castro T, Wolf CA, Santos VG.In experiment 1, daily blood samples were available from Days 0 to 20 (Day 0 = ovulation) in mares with an interovulatory interval (IOI, n = 5) and in mares that developed idiopathic persistent corpus luteum (PCL, n = 5). The PCL was confirmed by maintenance of progesterone (P4) concentration until end of the experiment (Day 20). Significant interactions of group and day revealed the novel findings that luteinizing hormone (LH) was lower (P < 0.05) in the PCL group than that in the IOI group on Days 0 to 4, and prolactin was lower (P < 0.05) on Days 1, 4, 6, and 7. In experiment 2, treat...
Castro T, Oliveira FA, Siddiqui MA, Baldrighi JM, Wolf CA, Ginther OJ.A study was performed on the effect of a single dose per mare of 0 (n = 9), 100 (n = 8), or 300 (n = 9) of GnRH on Day 10 (Day 0 = ovulation) on concentrations of LH, FSH, and progesterone (P4) and blood flow to the CL ovary. Hormone concentration and blood flow measurements were performed at hours 0 (hour of treatment), 0.25, 0.5, 1, 2, 3, 4, and 6. Blood flow was assessed by spectral Doppler ultrasonography for resistance to blood flow in an ovarian artery before entry into the CL ovary. The percentage of the CL with color Doppler signals of blood flow was estimated from videotapes of real-t...
Köhne M, Kuhl J, Ille N, Erber R, Aurich C.For prevention of early conceptus loss in the horse, treatment with progestins has become common practice. In cattle, treatment with human chorionic gonadotrophin (hCG) during the early postovulatory phase stimulates endogenous progesterone synthesis, which is an important factor for maintenance of early pregnancy via stimulation of endometrial function and conceptus development. In the present study we have therefore investigated the influence of treatment with hCG either for induction of ovulation or during the early luteal phase on plasma progestin concentrations, size of the corpus luteum ...
Decourt C, Caraty A, Briant C, Guillaume D, Lomet D, Chesneau D, Lardic L, Duchamp G, Reigner F, Monget P, Dufourny L, Beltramo M, Dardente H.Kisspeptin has emerged as the most potent gonadotropin-releasing hormone (GnRH) secretagogue and appears to represent the penultimate step in the central control of reproduction. In the sheep, we showed that kisspeptin could be used to manipulate gonadotropin secretion and control ovulation. Prompted by these results, we decided to investigate whether kisspeptin could be used as an ovulation-inducing agent in another photoperiodic domestic mammal, the horse. Equine kisspeptin-10 (eKp10) was administered intravenously as bolus injections or short- to long-term perfusions to Welsh pony mares, ei...
Thorson JF, Prezotto LD, Cardoso RC, Sharpton SM, Edwards JF, Welsh TH, Riggs PK, Caraty A, Amstalden M, Williams GL.RFamide-related peptide 3 (RFRP3), the mammalian homologue of avian gonadotropin-inhibitory hormone, has been shown to negatively regulate the secretion of LH and may contribute to reproductive seasonality in some species. Herein, we examined the presence and potential role of the RFRP3-signaling system in regulating LH secretion in the mare during the breeding and nonbreeding seasons. Hypothalamic NPVF mRNA (the precursor mRNA for RFRP3) was detected at the level of the dorsomedial nucleus and paraventricular nucleus, but expression did not change with season. A greater number of RFRP3-expres...
Thorson JF, Allen CC, Amstalden M, Williams GL.The continuous, subcutaneous infusion of native GnRH into seasonally anovulatory mares stimulates the synthesis and secretion of LH without pituitary refractoriness, offering opportunities to markedly accelerate the timing of ovulation within the operational breeding season. Herein, we tested the hypothesis that ovarian cycles induced in winter anovulatory mares using continuous administration of native GnRH for 28 days, beginning in either early February or early March (North America) would not revert to an anovulatory state after treatment withdrawal. Anovulatory mares received sham pumps (c...
Thorson JF, Prezotto LD, Cardoso RC, Allen CC, Alves BR, Amstalden M, Williams GL.Onset of the winter anovulatory period in mares is associated with a marked diminution in adenohypophyseal synthesis and release of LH. Native GnRH, unlike its synthetic agonists, stimulates the synthesis and secretion of LH in mares without pituitary refractoriness. Herein we tested the hypotheses that (1) the average Julian day of pregnancy can be accelerated by up to 2 months in winter anovulatory mares treated continuously with native GnRH beginning on February 1 and (2) mares will sustain luteal function and pregnancy after treatment withdrawal. Forty-two winter anovulatory mares were str...
Donovan CE, Hazzard T, Schmidt A, LeMieux J, Hathaway F, Kutzler MA.We investigated the effect of immunization against gonadotropin releasing hormone (GnRH) using a commercial canine GnRH vaccine on estrus suppression and unwanted estrous behavior in mares. In experiment 1, mares were immunized (n = 6) twice with vaccine (5 mL) given intramuscularly 4 weeks apart or received a control diluent (n = 5). Transrectal ultrasonographic examination of the reproductive tracts was performed three days a week for 40 weeks after initial vaccination. Blood samples were collected weekly for GnRH antibody titer and progesterone concentration determination. In experiment 2, ...
Abbara A, Ratnasabapathy R, Jayasena CN, Dhillo WS.The Kiss1 gene encodes a 145-amino acid pre-peptide, kisspeptin, which is cleaved into smaller peptides of 54, 14, 13, and 10 amino acids. This chapter reviews in detail the effects of kisspeptin on gonadotropin secretion in non-human mammals. Studies of kisspeptin's effects have included both acute and chronic administration regimens via a number of administration routes. Acute kisspeptin stimulates gonadotropin secretion in a wide range of species of non-human mammals, including rats, mice, hamsters, sheep, pigs, goats, cows, horses, and monkeys. In general, the stimulatory effect of kisspep...
Okamura H, Yamamura T, Wakabayashi Y.The hypothalamo-pituitary-gonadal (HPG) axis is the regulatory system for reproduction in mammals. Because secretion of gonadotropin-releasing hormone (GnRH) into the portal vessels is the final step at which the brain controls gonadal activities, the GnRH neuronal system had been thought to be central to the HPG axis. A newly discovered neural peptide, kisspeptin, has opened a new era in reproductive neuroendocrinology. As shown in a variety of mammals, kisspeptin is a potent endogenous secretagogue of GnRH, and the kisspeptin neuronal system governs both the pulsatile GnRH secretion that dri...
Schulman ML, Botha AE, Muenscher SB, Annandale CH, Guthrie AJ, Bertschinger HJ.Active immunisation against gonadotrophin-releasing hormone (GnRH) provides a reversible method for control of oestrous behaviour and fertility in mares. Previous reports failed to demonstrate the interval to resumption of cyclic ovarian activity after GnRH-vaccination. Objective: Administration of the GnRH-vaccine Improvac in a large group of mares of various ages will result in effective, reliably reversible suppression of ovarian activity within a 2 year period. Methods: The mares, subdivided into 3 age categories, were vaccinated twice (with a 35 day interval) using 400 µg Improvac and mo...
Williams GL, Thorson JF, Prezotto LD, Velez IC, Cardoso RC, Amstalden M.Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular...
Caraty A, Decourt C, Briant C, Beltramo M.Kisspeptins (Kp) are a family of neuropeptides produced mainly by two hypothalamic neuronal cell populations. They have recently emerged as a major regulator of the gonadotropin axis and their action is located upstream of the gonadotropin-releasing hormone (GnRH) cell population. In less than 10 yr a growing body of literature has demonstrated the involvement of these peptides in most, if not all, aspects of reproductive axis maturation and function. In contrast to these abundant basic research studies, few experiments have evaluated the potential application of Kp as tools to manipulate repr...
Velez IC, Pack JD, Porter MB, Sharp DC, Amstalden M, Williams GL.We tested the hypothesis that continuous infusion of native GnRH into mares during the estrous cycle, at a dose of 100 μg/h, would elevate circulating concentrations of LH without disrupting the endogenous, episodic pattern of LH release. Ten cyclic mares were assigned to one of two groups (n = 5/group): (1) Control (saline) and (2) GnRH in saline (100 μg/h). On experimental day 0 (3 to 6 d after ovulation), osmotic pumps containing saline or GnRH were placed subcutaneously and connected to a jugular infusion catheter. Blood samples were collected from jugular catheters daily and at 5-min in...
Evans MJ, Alexander SL, Irvine CH, Kitson NE, Taylor TB.The GnRH antagonist cetrorelix was given during the early (Days 1-5), mid (Days 6-10 or 5-12) or for the entire (Days 1-16) luteal phase of mares to inhibit the secretion of FSH and LH (Day 0=ovulation). Frequent blood sampling from Day 6 to Day 14 was used to determine the precise time-course of the suppression (cetrorelix given Days 6-10). Cetrorelix treatment caused a decrease in FSH and LH concentrations by 8 and 16 h, respectively, and an obliteration of the response to exogenous GnRH given 24h after treatment onset. Treatment never suppressed gonadotropin concentrations to undetectable l...
Kirkpatrick JF, Lyda RO, Frank KM.Wildlife, free-ranging and captive, poses and causes serious population problems not unlike those encountered with human overpopulation. Traditional lethal control programs, however, are not always legal, wise, safe, or publicly acceptable; thus, alternative approaches are necessary. Immunocontraception of free-ranging wildlife has reached the management level, with success across a large variety of species. Thus far, the immunocontraceptive research and management applications emphasis have been centered on porcine zona pellucida and gonadotropin-releasing hormone vaccines. Contraceptive succ...
Pickles KJ, Berger J, Davies R, Roser J, Madigan JE.The aim of this study was to investigate the use of a gonadotrophin-releasing hormone (GnRH) vaccine in the treatment of headshaking in horses. Fifteen geldings received two doses of the GnRH vaccine four weeks apart. Serum was collected before and after vaccination to measure concentrations of luteinising hormone (LH) (10 horses) and follicle-stimulating hormone (FSH) (six horses). Owners recorded the frequency of seven common headshaking behaviours using a visual analogue scale (VAS) before vaccination and at two, four, eight, 12, 16 and 20 weeks after vaccination. Serum LH (P=0.008) and FSH...
Kuiper H, Blum N, Distl O.In a 1.5-year-old Oldenburg horse, a clitoris-like structure instead of a penis was identified in the prepuce. The external genital organs did not show any abnormalities at visual inspection except that exteriorization of the penis was not possible, not even under general anesthesia. The horse's owner observed a continuous dripping of urine and a tendency to mild colics beginning 2 weeks after birth. Testosterone concentration was 0.01 ng/ml and therefore under the threshold for geldings, and the horse did not respond to the application of gonadotropin-releasing hormone (GnRH). The inner genit...
Panzani D, Zicchino I, Taras A, Marmorini P, Crisci A, Rota A, Camillo F.Artificial photoperiod treatment is currently the best method to hasten the first ovulation of the breeding season in winter anoestrus mares. However, this is not easy to apply in large herds of mares and, to be effective, has to be planned in the northern hemisphere in December at the latest. Pharmacological treatments have been proposed as alternatives: GnRH agonists, progesterone or its synthetic agonist Altrenogest, and dopamino-antagonists, as pherphenazine, domperidone or sulpiride. Dopamino-antagonists protocols, beginning at a given day of the year, gave controversial results in terms ...
Checura CM, Beg MA, Parrish JJ, Ginther OJ.The effects of FSH, LH or both on follicular growth and intrafollicular free insulin-like growth factor (IGF)-1 and oestradiol were investigated in mares after the beginning of deviation (largest follicle >/= 20 mm; Hour 0). A single treatment with a gonadotropin-releasing hormone antagonist (acyline) was given at Hour 3 to suppress the concentrations of FSH and LH. Five groups (n = 5 mares per group) were evaluated in the present study: (1) control; (2) acyline treated; (3) acyline + recombinant equine (re) FSH treated; (4) acyline + reLH treated; and (5) combined acyline + reFSH + reLH tr...
Wenzinger B, Kähn W, Bleul U.The aim of this study was to investigate the effect of a GnRH vaccine (Equity) on behavior and gonadal function in horses with unwanted behavior. The reason for the treatment was asked using a questionnaire and the findings of physical examination, rectal palpation as well as rectal ultrasonography, were recorded. The results of these examinations and the behavior of 21 mares and 10 stallions before the first and after the second administration of the GnRH vaccine were compared. In 84 % of all cases a decrease of the unwanted behavior could be observed. In the mares the ovaries were significan...
Tait AD, Hodge LC, Allen WR.The production of equilin and the other ring B-unsaturated estrogens by the pregnant mare is anomalous in that they are biosynthesised by a cholesterol-independent pathway. Fetal horse gonads were incubated with tritiated sodium acetate and radiochemically pure 3 beta-hydroxy-5,7-pregnadien-20-one and 3 beta-hydroxy-5,7-androstadien-17-one were isolated. A fetal gonad--placental system is proposed for equilin production, 3 beta-hydroxy-5,7-pregnadien-20-one being a precursor for 3 beta-hydroxy-5,7-androstadien-17-one in the fetal gonad and the latter being the precursor of equilin in the place...
Caraty A, Decourt C, Briant C, Beltramo M.Kisspeptins (Kp) are a family of neuropeptides produced mainly by two hypothalamic neuronal cell populations. They have recently emerged as a major regulator of the gonadotropin axis and their action is located upstream of the gonadotropin-releasing hormone (GnRH) cell population. In less than 10 yr a growing body of literature has demonstrated the involvement of these peptides in most, if not all, aspects of reproductive axis maturation and function. In contrast to these abundant basic research studies, few experiments have evaluated the potential application of Kp as tools to manipulate repr...
McCue PM, Farquhar VJ, Carnevale EM, Squires EL.Deslorelin implants, approved for use in inducing ovulation in mares, have been associated with prolonged interovulatory intervals in some mares. Administration of prostaglandins in the diestrous period, following a deslorelin-induced ovulation, has been reported to increase the incidence of delayed ovulations. The goals of the present study were: (1) to determine the percentage of mares given deslorelin that experience delayed ovulations with or without subsequent prostaglandin treatment, and (2) to determine if removal of the implant 48 h after administration would effect the interval to sub...
Decourt C, Caraty A, Briant C, Guillaume D, Lomet D, Chesneau D, Lardic L, Duchamp G, Reigner F, Monget P, Dufourny L, Beltramo M, Dardente H.Kisspeptin has emerged as the most potent gonadotropin-releasing hormone (GnRH) secretagogue and appears to represent the penultimate step in the central control of reproduction. In the sheep, we showed that kisspeptin could be used to manipulate gonadotropin secretion and control ovulation. Prompted by these results, we decided to investigate whether kisspeptin could be used as an ovulation-inducing agent in another photoperiodic domestic mammal, the horse. Equine kisspeptin-10 (eKp10) was administered intravenously as bolus injections or short- to long-term perfusions to Welsh pony mares, ei...
Hodson DJ, Townsend J, Gregory SJ, Walters C, Tortonese DJ.A combined suppressive effect of prolactin (PRL) and dopamine on the secretion of luteinising hormone (LH) at the level of the pituitary gland has been identified in sheep, a short-day breeder. However, little is known about the role of PRL in the intra-pituitary regulation of the gonadotrophic axis in long-day breeders. In the present study, we investigated the effects of PRL on LH and follicle-stimulating hormone (FSH) secretion during the equine annual reproductive cycle. Horse pituitaries were obtained during the breeding season (BS) and nonbreeding season (NBS). Cells were dispersed, plat...
Malmgren L, Andresen O, Dalin AM.The aim of this study was to investigate the effect of gonadotrophin-releasing hormone (GnRH) immunisation on mature stallions that had been used for breeding. Four Standardbred stallions were used in the study: 3 experimental animals and 1 control animal. Semen was collected regularly, i.e. twice/week, during the 4 months prior to the experimental period. The stallions were immunised against GnRH with a GnRH-BSA conjugate. Equimune was used as the adjuvant. The stallions were immunised on 5 occasions, 4 at 2 week intervals, and the fifth 4 weeks after the fourth. Blood samples were taken once...
Williams GL, Thorson JF, Prezotto LD, Velez IC, Cardoso RC, Amstalden M.Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular...
Alexander SL, Irvine CH.We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae...
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...
Bailly-Chouriberry L, Loup B, Popot MA, Dreau ML, Garcia P, Bruyas JF, Bonnaire Y.Since the availability on the European market of the vaccine Improvac® dedicated to male pig immunological castration, the risk of misuse of this product in horses is now considered as a threat for the horseracing industry. Immunological castration is not allowed by the racing codes (immune system, Article 6). Indeed, this vaccination against the hypothalamic hormone luteinizing hormone-releasing hormone or gonadotropin-releasing hormone (GnRH) will prevent the release from the anterior pituitary of luteinizing hormone and follicle stimulating hormone, which are required for the development a...
Gautier C, Schmidt K, Aurich J, Aurich C.The hypothesis in this study was continuous treatment of stallions with the GnRH agonist deslorelin inhibits reproductive functions. A 2-week pre-experimental period was followed by an 11-week deslorelin implant treatment. Stallions received 4.7 (D1, n = 7), or 18.8 mg deslorelin (D2, n = 5) or remained untreated (C, n = 5). Libido, sperm motility, membrane integrity, DNA fragmentation, estrogen receptors, basal plasma testosterone and Anti Muellerian hormone (AMH) concentrations were evaluated once weekly during the treatment period. The testosterone response to the GnRH agonist buserelin a...
Garza F, Thompson DL, French DD, Wiest JJ, St George RL, Ashley KB, Jones LS, Mitchell PS, McNeill DR.Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) to determine the relative importance of this hypothalamic hormone in the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Five mares immunized against the conjugation protein served as controls. Mares were initially immunized in November and received secondary immunizations 4 wk later, and then at 6-wk intervals until ovariectomy in June. All mares immunized against GnRH exhibited an increase (p less than 0.01) in the binding of tritiated GnRH by plasma, an indication that a...
Dowsett KF, Pattie WA, Knott LM, Jackson AE, Hoskinson RM, Rigby RP, Moss BA.This study tested the effectiveness of a conjugated GnRH vaccine for stimulating antibody production, suppressing testosterone secretion and depressing testicular development in yearling colts. Two colts were allocated to each of three groups, (1) control, (2) subcutaneous and (3) intramuscular vaccinations. Two injections of the vaccine were given 11 weeks apart. Liveweight gain was not affected by vaccination but plasma testosterone concentrations in the treated colts were suppressed and their antibody titres to GnRH were greater than 1:1000. Testicular development in the treated colts also ...
Panzani D, Zicchino I, Taras A, Marmorini P, Crisci A, Rota A, Camillo F.Artificial photoperiod treatment is currently the best method to hasten the first ovulation of the breeding season in winter anoestrus mares. However, this is not easy to apply in large herds of mares and, to be effective, has to be planned in the northern hemisphere in December at the latest. Pharmacological treatments have been proposed as alternatives: GnRH agonists, progesterone or its synthetic agonist Altrenogest, and dopamino-antagonists, as pherphenazine, domperidone or sulpiride. Dopamino-antagonists protocols, beginning at a given day of the year, gave controversial results in terms ...
Kwok KY, Choi TLS, Kwok WH, Lau MY, Leung EMK, Leung GNW, Wong JKY, Wan TSM, Adrian FF, Prabhu A, Ho ENM.The use of bioactive peptides as a doping agent in both human and animal sports has become increasingly popular in recent years. As such, methods to control the misuse of bioactive peptides in equine sports have received attention. This paper describes a sensitive accurate mass method for the detection of 40 bioactive peptides and two non-peptide growth hormone secretagogues (< 2 kDa) at low pg/mL levels in horse urine using ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC/HRMS). A simple mixed-mode cation exchange solid-phase extraction (SPE) cartridge was...
Santos-Jimenez Z, Martinez-Herrero C, Encinas T, Martinez-Ros P, Gonzalez-Bulnes A.The present study compared the occurrence of oestrus behaviour and ovulation in response to the insertion of CIDR devices plus a classical treatment with equine chorionic gonadotrophin (eCG; single dose at CIDR removal) or alternative treatments with gonadotrophin-releasing hormone (GnRH, either in a single dose at 56Â hr after CIDR removal, or in one dose at CIDR insertion and another dose at 56Â hr after CIDR removal). The appearance of oestrus behaviour during reproductive season ranged between 84% and 95% and all females showing oestrus signs had subsequent ovulations. The response, during...
Behrendt D, Burger D, Gremmes S, Szunyog K, Röthemeier S, Sieme H.Stallion-like or aggressive behaviour in mares affected by unilateral granulosa theca cell tumour (GTCT) is well-known, but use of a GnRH-vaccine as an alternative to surgical removal of the neoplastic ovary has not been investigated. Objective: To determine the effect of immunisation against GnRH on ovarian size, testosterone concentration, Anti-Müllerian hormone (AMH) concentration, and owner-reported behaviour in four mares affected by unilateral GTCT. Methods: Retrospective case report. Methods: A presumptive diagnosis of GTCT was made in four mares based on clinical signs, behavioural ch...
Donadeu FX, Thompson DL.Sixteen seasonally anovulatory mares were randomly allotted to two groups and injected daily with either sulpiride (1 mg/kg body weight) or vehicle from 14 January to 14 February. Sulpiride administration increased daily plasma prolactin concentrations (P < 0.05), although the prolactin response during the 6 h following sulpiride injections decreased markedly from the 1st to the 6th day of treatment (treatment by day, P < 0.0001). Plasma concentrations of LH and FSH were not affected by treatment (P > 0.1). Injection of GnRH and TRH on 15 February showed that the response of plasma prolactin t...
Sharp DC, Grubaugh WR.Push-pull perfusion was used to study GnRH secretory ability of the hypothalamus in anoestrous, transitional, dioestrous and oestrous Pony mares. The technique involved placement of a concentric (tube within a tube) cannula into the area of the medial basal hypothalamus and perfusing a carrier medium (artificial cerebrospinal fluid) through the inner tube whilst aspirating from the outer tube so that the flow rate within the hypothalamic tissue was essentially constant. The perfusion rate was 0.5 ml/10 min and samples were collected at 10-min intervals for 10-15 h. The carrier medium, which co...
Gentry LR, Thompson DL, Gentry GT, Davis KA, Godke RA.Mares that had previously been fed to attain body condition scores (BCS) of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) were used to determine the interaction of BCS with the responses to 1) administration of equine somatotropin (eST) daily for 14 d beginning January 20 followed by administration of GnRH analog (GnRHa) daily for 21 d and 2) 4-d treatment with dexamethasone later in the spring when mares in low BCS had begun to ovulate. The majority of mares with high BCS continued to cycle throughout the winter, as evidenced by larger ovaries (P < 0.002), more corpora lutea (P < 0.05), greater proge...
Behrens C, Aurich JE, Klug E, Naumann H, Hoppen HO.Effects of the opioid antagonist naloxone on concentrations of LH and FSH in plasma were measured in mares during different stages of the oestrous cycle. During the follicular phase of the cycle, naloxone (300 mg i.v.) had no discernible effects on basal concentrations of LH and FSH. A significant increase in plasma LH (P < 0.01) and FSH (P < 0.05) concentrations was observed after naloxone in mares during the luteal phase. This response was not different between suckled and non-suckled mares. The gonadotrophin-releasing hormone analogue buserelin (0.02 mg i.v.) caused a significant (P < 0.05)...
Irvine CH, Alexander SL.We used our unique nonsurgical technique for collecting pituitary venous (pit) blood to study GnRH, FSH, and LH secretion patterns in midluteal phase mares. This method does not perturb endocrine function and allows continuous monitoring of GnRH and gonadotropin (Gn) secretion, determination of the amount of GnRH perfusing gonadotropes, and direct measurements of the amounts of Gn secreted. In a total of 80 h of 5-min sampling in four mares, eight Gn peaks occurred; however, more frequent sampling was needed to define secretory events precisely. Therefore, pit blood was collected continuously ...
Ponthier J, Rigaux G, Parrilla-Hernandez S, Egyptien S, Gatez C, Carrasco Leroy C, Deleuze S.This report describes an option to modulate the testicular function of wild horses and field methods to assess it. Non-surgical castration of a captive wild Przewalski's stallion with anti-gonadotropin-releasing hormone (GnRH) immunization was performed by sub-cutaneous injection of two doses of 450 μg (3 ml) of GnRH conjugated to diphtheria toxin, further repeated every 6 months. Semen quality was assessed after collection by electro-ejaculation under general anesthesia. Endocrine and behavioral consequences were studied during a 2-year follow-up period. The procedure of electro-ejaculation ...
Blanchar TL, Brinsko SP, Rigby SL.A tendency for deslorelin implants to suppress subsequent follicular growth and delay return to estrus following induced ovulation has been documented in nonlactating mares. To investigate this phenomenon in lactating mares, 22 broodmares in southeast Texas were administered either deslorelin or hCG to induce ovulation in the first postpartum estrus during February and March 2001. Mares were teased daily and examined twice weekly (Tuesdays and Thursdays) by transrectal ultrasonography. When a follicle >35 mm diameter was detected on Tuesday, mares were treated with either 2,500 U hCG admini...
Fanelli D, Beltramo M, Conte G, Cerretini B, Lomet D, Rota A, Aucagne V, Camillo F, Panzani D.Kisspeptins (KPs) are the most potent stimulating neurotransmitters of GnRH release, and consequently KP administration triggers LH and/or FSH release. In small ruminants, KP or its analogs induced an LH surge followed by ovulation in both cyclic and acyclic animals, while in the mare KP only increased LH plasma levels but failed to induce ovulation. This study in jennies compares the endocrinological effects, ovulatory and pregnancy rates of the KP analog C6 and the GnRH analog buserelin acetate. The ovarian activity of nine Amiata jennies was monitored daily by transrectal ultrasound for thr...
Birrell JR, Schulman ML, Botha AE, Ganswindt A, Fosgate GT, Bertschinger HJ.Surgical castration is one of the most frequently performed surgeries in horses and is associated with various post-surgical complications ranging in severity. Objective: We investigated the effects of administering an anti-GnRH vaccine to colts for reduction of testis size on the incidence of complications associated with their subsequent surgical castration. Methods: Randomised open controlled trial. Methods: Nineteen colts were randomly assigned to one of the three groups. Treatment Groups V1-57 and V2-100 received two treatments of Improvac (Zoetis, South Africa) before their castration in...
Ball BA, Davolli GM, Esteller-Vico A, Fleming BO, Wynn MAA, Conley AJ.The biological function of inhibin is mediated by two heterodimers, inhibin-A and inhibin-B. The relative importance of inhibin-A and -B in male reproductive function varies considerably across species with inhibin-B predominating in many species, whereas inhibin-A appears relatively more important in rams. Research reported to date in stallions has examined total or immunoreactive (ir) inhibin which does not distinguish the two heterodimers. Therefore, the objective of this study was to characterize changes in inhibin-A and inhibin-B concentrations in stallions: 1) across season for a period ...
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 ...
Brito LF, Baldrighi JM, Wolf CA, Ginther OJ.The objective of the present study was to investigate the effect of reproductive hormones (GnRH, hCG, LH and progesterone) on the regulation of corpus luteum (CL) and ovarian blood flow. Diestrous mares received a single treatment of saline, 100μg gonadorelin (GnRH), or 1500IU hCG 10days after ovulation. Plasma LH and progesterone concentrations, resistance index (RI) for ovarian artery blood-flow, and percentage of corpus luteum (CL) with color-Doppler signals of blood flow were determined immediately before treatment (hour 0) and at hours 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, and 6. In the GnRH gr...
