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.
Ware VC.In an attempt to understand more fully processes that control the selection or recruitment of follicles for ovulation, the superovulation paradigm in combination with the androgen, 5 alpha-dihydrotestosterone, or the antiandrogens, cyproterone or cyproterone acetate, was used in the immature mouse to alter the developmental potential of follicles destined to ovulate or to become atretic. Quantitative analysis of the numbers of eggs ovulated after one or more rounds of stimulation by pregnant mare's serum gonadotrophin followed by human chorionic gonadotrophin (PMSG-hCG), revealed a dose-depend...
Turner JE, Irvine CH.Administration to mares of the anabolic steroid, methandriol, at the maximum recommended dose (300 mg every 3 weeks) for 1 1/2 years had no effect on reproductive characteristics except for suppression of GnRH-induced LH release and a tendency to suppress basal LH levels and the height of the ovulatory LH surge. A 4-fold increase in dosage caused marked suppression of basal LH, the LH surge, and GnRH-induced LH release. Other reproductive responses were minimally affected. There were no behavioural effects, and no changes in weight occurred when mares were compared with matched controls. Small...
Sharp DC, Grubaugh W, Berglund LA, McDowell KJ, Kilmer DM, Peck LS, Seamans KW, Chen CL.The pituitary stalk was transected in 10 Pony mares by a surgical approach that involved dorsal reflection of the brain and micro-dissection from the ventro-lateral aspect of the pituitary. Diabetes insipidus was the most immediate and marked result, requiring extensive electrolyte and antidiuretic therapy for approximately 48 h after operation. Fluid stasis then developed and no further supportive measures were necessary. Endocrine challenge tests with GnRH and TRH before and after stalk transection indicated a loss of responsiveness (GnRH) or suppressed responsiveness (TRH) after the operati...
Sarkar DK, Smith GC, Fink G.We have investigated the effect of manipulating central catecholamines on the timing of puberty (as assessed by vaginal opening) in female rats and the surge of luteinizing hormone (LH) and gonadotropin releasing hormone (GnRH) induced by pregnant mare serum gonadotropin (PMSG) in immature female rats. Manipulation of the catecholamines was carried out with either 6-hydroxydopamine (6-OHDA) administered with or without either desipramine (DMI) or pargyline, or alpha-methyl-p-tyrosine (alpha-MPT). The neonatal administration of 6-OHDA delayed puberty, an effect which was potentiated by pretreat...
Dees WL, Sorensen AM, Kemp WM, McArthur NH.Immunohistochemical localization of the decapeptide gonadotropin releasing hormone (GnRH) in neural structures in the pony brain and infundibulum (INF) was conducted at the light-microscopic level. This procedure utilized an antiserum generated against GnRH conjugated to bovine serum albumin. In the rostral INF, GnRH was distributed mainly in the external layer, with greatest concentrations adjacent to the long capillary loops of the hypophyseal portal system. The intermediate portion of the INF contained the hormone throughout the external layer, especially in the dorsolateral regions just ve...
Downey BR.Neuroendocrine and endocrine factors involved in the regulation of reproductive cycles in domestic animals are discussed. Although research data from many species are considered, emphasis is placed on their relevance for the cow, sow, ewe and, to a lesser extent, the mare. Literature cited is not designed to be complete, but rather to be representative of the large volume of material which has been written on the subject.Gonadotropin-releasing hormone is synthesized and secreted in response to various exteroceptive stimuli, but both its release and its effects on the anterior pituitary are mod...
Wesson JA, Miller KF, Ginther OJ.Plasma FSH and LH response to a synthetic GnRH analog was measured in adult ovariectomized pony mares (OVX) and in pony foals (<70 days of age) during late spring (May-June). FSH and LH responded in a similar fashion (200% increase) in the OVX mare, which is different from other reports for intact mares. There was a greater mean response to a comparable dose of GnRH in the prepubertal foal for both FSH (500%) and LH (900%) than in the OVX mare. There was a positive correlation between age and the maximum FSH response to GnRH in male and female foals. The LH response was positively correlate...
Booth LC, Oxender WD, Douglas RH, Woodley SL.A gonadotropin-releasing hormone (GnRH) was injected in mares given prostaglandin F2 alpha (PGF2 alpha) to induce luteolysis in an attempt to sunchronize ovulation. Pretreatment with estradiol-17 beta (E2-17 beta) was used to determine whether or not estradiol would enhance the release of luteinizing hormone (LH) after treatment with GnRH. Twelve mares were used in a balanced Latin square crossover design. Mares were injected with PGF2 alpha, treatment A; PGF2 alpha mgnRH, treatment B; or PGF2 alpha me2-17 beta mgnRH, treatment C. The interval +/- SEM from PGF2 alpha injection to estrus was 3....
Foster JP, Evans MJ, Irvine CH.Mares at different stages of the oestrous cycle were given a single intravenous injection of 0.5 mg synthetic Gn-RH. The mean area of the induced LH peak was significantly less at mid-cycle (Day 10-11) than at any other time. The mean height of the LH peak above preinjection concentration was greater at late oestrus and early cycle (Day 5-6) than at mid-cycle and early oestrus. There were no significant different in mean FSH responses. The LH:FSH ratio for both height and area of induced peaks was significantly less at mid-cycle than at other times of injection. These results suggest that one ...
Vivrette SL, Irvine CH.Acyclic mare given oestradiol for 3 days to simulate the preovulatory plasma oestradiol surge showed a non-significant 37% decrease in plasma LH during treatment. When GnRH analogue injections were given with oestradiol on Days 1--3, oestradiol had no effect on each GnRH-induced LH increase, but LH increases were more prolonged following subsequent GnRH injections on Days 4--7 when oestradiol was no longer being given. A much greater prolongation of LH release occurred when the course of GnRH injections was commenced after oestradiol treatment ceased; the LH response was almost identical to th...
Evans MJ, Irvine CH.Deeply acyclic (seasonally anovulatory) mares were treated with GnRH or a GnRH analogue to induce follicular development and ovulation. Courses of GnRH (3--4) were administered at approximately 10-day intervals to reproduce the gonadotrophin surges which precede ovulation in the normal cycle. Exogenous progesterone was administered in an attempt to reproduce the luteal phase pattern. Induced serum FSH concentrations were comparable to those causing follicular development in the normal cycle, but induced LH levels were lower and of shorter duration than those of the periovulatory surge. Three o...
Voss JL, Wallace RA, Squires EL, Pickett BW, Shideler RK.Fifty-four normally cycling, non-lactating mares were given 2 injections (i.m.) of PGF-2 alpha (10 mg) 14 days apart without regard to stage of the oestrous cycle. At 19 days after the first PGF-2 alpha treatment, a single i.m. injection of either hCG (3300 i.u.) or a GnRH-analogue (500 micrograms) was administered. Each mare was inseminated with 100 X 10(6) motile spermatozoa at one of the following frequencies: once only on Day 20; every other day during oestrus or at least on Days 19 and 21; or daily during oestrus or at least on Days 19, 20, 21 and 22. Eighteen control mares received salin...
Strauss SS, Chen CL, Kalra SP, Sharp DC.Fifteen Pony mares, ovariectomized during the previous summer, were randomly assigned to three seasonal treatment groups, winter, spring and summer (N = 5). At the designated season, the animals were killed and hypothalamic areas were collected and assayed by radioimmunoassay for gonadotrophin-releasing hormone (GnRH) activity. The hypothalamic areas were sectioned into 54 5-mm cubes to determine the sites of GnRH storage. Maximum immunoreactive GnRH activity was located in an oblique pattern extending from the arcuate nucleus-median eminence area to the anterior hypothalamic area dorsally and...
Pope AM, Campbell DL, Davidson JP.Foal heat was significantly delayed in 15 Thoroughbred and Quarter-horse mares by 200 mg progesterone in oil from Days 5--14 post partum. Nine of these mares subsequently received daily i.v. injections of 2 mg of a synthetic GnRH preparation (AY-24,031) from Day 2 of the progesterone-delayed oestrus but this treatment did not significantly shorten oestrus or hasten ovulation. Uterine biopsies taken on Day 15 post partum from all the mares showed a mixed endometrial morphology having both oestrous and dioestrous characteristics. There was an increased proliferation of endometrial glands in thes...
Freedman LJ, Garcia MC, Ginther OJ.A 16 h daily photoperiod hastened the onset of the ovulatory season (first ovulation); gonadotrophin and follicular changes prior to the onset were similar in intact light-treated and control mares. A preovulatory decline in FSH concentrations before the onset of the ovulatory season preceded the decrease in number of follicles (15--25 mm) and the rise in LH concentrations which was temporally associated with the growth of an ovulatory follicle. Seasonal changes of FSH and LH concentrations were found in ovariectomized mares and were influenced by photoperiod. During the anovulatory season, th...
Karasek M, Marek K, Kunert-Radek J.The influence of gonadotropic hormones on the ultrastructure of rat pinealocytesin short-term organ culture was studied. Human chorionic gonadotropin (HCG), as well as pregnant mare serum gonadotropin (PMSG), caused a marked activation of pinealocytes. An hypothesis is discussed implying the presence of a feedback mechanism between the pineal organ and the hypothalamo-hypophysial system.
Garcia MC, Ginther OJ.Three experiments were performed to study the luteinizing hormone (LH) and ovulatory responses to various doses and methods of administration of gonadotropin-releasing hormone (GnRH) in estrous pony mares and the influence of estradiol-17beta (E2-17beta) on LH response to GnRH treatment. In experiment 1, single injections of synthetic GnRH were subcutaneously given to 5 groups of estrous (day 2) mares (3 mares/group) on a body weight basis as follows: group A--isotonic saline solution; group B--GnRH, 0.14 mug/kg; group C--GnRH, 0.28 mug/kg; group D--KGnRH, 0.59 mug/kg; and group E--GnRH, 2.37 ...
Irvine DS, Downey BR, Parker WG, Sullivan JJ.Synthetic Gn-RH, administered during oestrus, stimulates the release of pituitary LH in the cyclic mare. Duration of oestrus was significantly reduced by 1 mg Gn-RH given on Day 2 of oestrus; the time of ovulation, measured in days from the onset of oestrus, also tended to be reduced. An injection of 2 mg Gn-RH had nor further effect, but daily injections from Day 2 until ovulation significantly shortened the duration of oestrus and the time to ovulation. The profiles of LH were found to be variable from mare to mare, but in all mares, treated and control, elevation of LH was detected close to...
Heinze H, Klug E.Clinical tests with synthetic gonadotrophin-releasing hormone (Hoechst) were made during the breeding seasons of 1973 and 1974, using 128 mares injected with 1-0 to 4-0 mg of the substance intramuscularly. The mares were placed in one of five groups based on ovarian condition determined by clinical evidence. Some success was obtained in the induction of ovulation in mares with inactive and sub-normally active ovaries and in a small group having cystic ovaries. A large proportion of mares having a mature follicle responded within 48 hr, but others with atretic follicles failed to respond. The u...
Gautier C, Aurich J, Kaps M, Okada CTC, Wagner LH, Melchert M, Aurich C.In stallions temporarily not intended for breeding, reversible suppression of testicular function by vaccination against GnRH can be of interest. In the present study, effects of GnRH agonist treatment on the resumption of testicular function after GnRH vaccination were investigated. Testis size, testosterone release, semen characteristics and behavior were evaluated. We hypothesized that GnRH agonist treatment would restore testicular function. Shetland stallions were assigned to an experimental and a control group (n = 6 each). Experimental stallions were GnRH-immunized twice, four weeks a...
Alexander SL, Irvine CH, Shand N, Turner J.Removal of opioid inhibition of GnRH neurones is thought to be a critical event in generating the ovulatory surge in some species. In the present study, a nonsurgical technique was used to collect pituitary venous blood samples from eight mares every 0.5-1.0 min for 1 h before and after administration of the opioid receptor antagonist naloxone (0.2 mg kg(-1), i.v.), to investigate whether opioid inhibition is also important in mares. Jugular blood samples were taken at 10-15 min intervals. Mares were studied 0, 1 or 2 days before ovulation. Naloxone administration increased mean rates of GnRH ...
Reville-Moroz SI, Thompson DL, Archbald LF, Olsen LM.The in vitro incorporation of [3H]leucine into immunoprecipitable follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was assessed for pituitaries from pony mares treated with testosterone propionate (TP) or oil (controls). Mares were treated every other day with TP (n = 4) at 350 micrograms/kg of body weight or with an equivalent volume of oil (n = 4). One day following the sixth injection of TP, each mare received an intravenous injection of gonadotropin releasing hormone (GnRH) at 1.0 micrograms/kg body weight and was bled frequently for 4 h. Treatment of mares with TP reduced F...
Aragunde Vieytes R, Viñoles Gil C, Gastal GDA, Cavestany D.In order to assess the effect of equine chorionic gonadotropin (eCG) administered on Day 5 or 7 of a fixed-time artificial insemination protocol (FTAI) in anestrous suckled beef cows, two experiments were performed to determine the following endpoints: Experiment 1 (n = 22), preovulatory follicle (POF) diameter, ovulation time, corpus luteum (CL) area, estradiol (E2) and progesterone (P4) concentrations; and Experiment 2 (n = 676), a field trial to evaluate conception rate using the same experimental design. In both experiments, a synchronization protocol using estradiol benzoate (EB) (Day...
Greaves HE, Kalariotes V, Cleaver BD, Porter MB, Sharp DC.The potential involvement of ovarian factors in regulating GnRH and LH postovulation was studied in ovarian intact (Group 1; n=3) and ovariectomized (OVX; Group 2; n=3) mares (OVX within 12 hr of ovulation). Blood samples were collected every 10 min for 6 hr from jugular vein (JV) and intercavernous sinus (ICS) during estrus and on Day 8 postovulation for LH and GnRH analysis. Additionally, JV samples were collected twice daily (12-hr intervals) for 30 days for LH and progesterone (P4) analysis. A significant treatment x day effect (P<0.0001) describes declining plasma LH concentrations in ...
Rabb MH, Thompson DL, Barry BE, Colborn DR, Hehnke KE, Garza F.Six pony geldings were actively immunized against GnRH conjugated to bovine serum albumin (BSA) to study 1) the relative dependency of LH and FSH storage, secretion and response to GnRH analog on GnRH bioavailability and 2) the effects of reduced GnRH bioavailability on GnRH storage in the hypothalamus. Five geldings were immunized against BSA. Geldings were immunized in December and 4, 8, 14, 20, 26 and 32 wk later. Ponies immunized against GnRH had increased (P less than .01) GnRH binding in plasma within 6 wk. By June, plasma concentrations of LH and FSH in ponies immunized against GnRH had...
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...
Johnson AL.Four seasonally anestrous mares (Standardbred), housed under a nonstimulatory photoperiod of 8 hours light:16 hours dark, were administered gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (50 or 250 micrograms of GnRH/hour) for 8 to 18 days during February and March 1985. Treatment with GnRH, irrespective of dose or month, induced an increase in serum luteinizing hormone from a mean pretreatment value typical of anestrus (0.58 +/- 0.02 ng/ml +/- SE) to 10.84 +/- 1.27 ng/ml on day 8 of GnRH treatment. Ovulation in the 4 mares occurred 8.8 +/- 0.7 days after the initiation of pulsat...
McCue PM, Troedsson MH, Liu IK, Stabenfeldt GH, Hughes JP, Lasley BL.Thirty-seven seasonally anoestrous mares were divided into treatment and control groups and given 10 micrograms of native GnRH (GnRH) per hour using a peristaltic pump, or 10 micrograms GnRH agonist (GnRHa) twice daily, beginning on either 13 January, 13 February or 14 March. Treatment with GnRH was equally effective in inducing ovulation in January (4/5), February (4/5) and March (3/4). GnRHa treatment was more effective in inducing ovulation in February (4/5) and March (4/4) than in January (2/8). Peak luteinizing hormone (LH) concentrations in mares induced to ovulate with GnRH (7.4 +/- 1.5...
Booth LC, Oxender WD, Douglas RH, Woodley SL.A gonadotropin-releasing hormone (GnRH) was injected in mares given prostaglandin F2 alpha (PGF2 alpha) to induce luteolysis in an attempt to sunchronize ovulation. Pretreatment with estradiol-17 beta (E2-17 beta) was used to determine whether or not estradiol would enhance the release of luteinizing hormone (LH) after treatment with GnRH. Twelve mares were used in a balanced Latin square crossover design. Mares were injected with PGF2 alpha, treatment A; PGF2 alpha mgnRH, treatment B; or PGF2 alpha me2-17 beta mgnRH, treatment C. The interval +/- SEM from PGF2 alpha injection to estrus was 3....
Briant C, Ottogalli M, Guillaume D.With the objective of controlling the day of ovulation, 40 mares were assigned to a control or three treated groups: A3d, A4d, and A5d. The treated groups received antarelix (Teverelix 0.01 mg/kg, i.v., twice a day) for 3, 4, or 5 days from the day the dominant follicle (F1) reached 28 mm (=D0), and one injection of hCG (1600 IU, i.v.) on D1, D2, or D3, respectively. Control mares received one injection of hCG when F1 reached 35 mm. Plasma LH, FSH, progesterone, and total estrogens were assayed. In the A3d, A4d, and A5d groups, 9 (90%), 6 (60%), and 5 (50%) out of 10 mares, respectively, ovula...
Kennedy SR, Thompson DL, Pruett HE, Burns PJ, Deghenghi R.A series of experiments was performed to determine the factor(s) responsible for an apparent inhibition of GH secretion in mares administered the GH secretagogue EP51389 in combination with GnRH, thyrotropin-releasing hormone (TRH), and sulpiride. Experiment 1 tested the repeatability of the original observation: 10 mares received EP51389 at 10 microg/kg BW; five received TRH (10 microg/kg BW), GnRH (1 microg/kg BW), and sulpiride (100 microg/kg BW) immediately before EP51389, and five received saline. The mixture of TRH, GnRH, and sulpiride reduced (P = 0.0034) the GH response to EP51389, con...
Thompson DL, Reville SI, Derrick DJ.Five mature Quarterhorse mares were bled every 30 min for 25 h on day 50 of pregnancy to determine the short-term mode of secretion of equine chorionic gonadotropin (eCG). Three other mares with persistent endometrial cups after abortion were administered gonadotropin releasing hormone (GnRH; 1.0 mug/kg of body weight) and were bled immediately prior to and at 15, 30, 45, 60, 90, 120, 180 and 240 min after GnRH. Concentrations of eCG in plasma of pregnant mares were constant over the 24-h period; the variation of each mare's individual values was no greater (P>.05) than the predicted random...
Wiest JJ, Thompson DL, McNeill-Weist DR, Garza F.Twenty ovariectomized pony mares were used to determine if dihydrotestosterone propionate (DHTP) administration, with or without estradiol benzoate (EB) pretreatment, would have the same effects on follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion as testosterone propionate (TP) administration. All mares were given an initial injection of gonadotropin releasing hormone (GnRH) to characterize their LH and FSH response, and then two groups of mares (n = 4/group) were administered EB (22 micrograms/kg of body weight), two groups were administered vehicle (safflower oil) an...
Mumford EL, Squires EL, Jasko DJ, Nett TM.A lack of pituitary LH stores has been implicated as the cause of seasonal anestrus and failure to ovulate during the spring transition period in mares. In this experiment, 40 mares were used to study the effects of GnRH, estrogen, and an estrogen-GnRH combination on increasing releasable pituitary LH. Mares were stratified based on their ability to secrete LH in response to a 950-micrograms challenge of GnRH (n = 10 per group) and then assigned to one of four treatment groups: 1) controls, given no treatment; 2) 1 mg of estradiol-17 beta in oil i.m. daily for 8 d; 3) 200 micrograms of GnRH an...
Dippert KD, Hofferer S, Palmer E, Jasko DJ, Squires EL.Cyclic mares were assigned to 1 of 3 treatments (n=15 per group): Group 1 received equine pituitary extract (EPE; 25 mg, i.m.) on Day 5 after ovulation; Group 2 received EPE on Day 12 after ovulation; while Group 3 received 3.3 mg of GnRH analogue (buserelin implant) on the day of ovulation and 25 mg, i.m. EPE on Day 12. Mares in each group were given 10 mg PGF2alpha on the first and second day of EPE treatment. The EPE treatment was continued daily until the first spontaneous ovulation, at which time 3,300 IU of human chorionic gonadotropin (hCG) were given to induce further ovulations. Mares...
Johnson AL.A study was conducted to evaluate the effectiveness of gonadotropin-releasing hormone (GnRH) pulse infusion to stimulate follicular development and induce ovulation in seasonally anestrous standardbred mares. Seventeen mares were selected for use in this experiment, on the basis of a previous normal reproductive history, and were housed under a photoperiod of 8L:16D beginning one week prior to the start of the experiment (second week in January). Mares were infused with 20 micrograms (n = 7) or 2 micrograms (n = 6) GnRH/h, or were subjected to photoperiod treatment only (controls, n = 4). Seru...
Harrison LA, Squires EL, Nett TM, McKinnon AO.We hypothesized that the LH response to GnRH would be greater as the interval from foaling increases, whereas the FSH response would decrease, and that corpus luteum function after the first ovulation would be similar to that after the second ovulation. At parturition, mares were assigned to receive GnRH (2 micrograms/kg) intravenously on 1) d 3 postpartum (n = 6); 2) d 6 postpartum (n = 6); 3) d 1 of first postpartum estrus (foal estrus) and again on d 1 of second postpartum estrus (n = 8). Blood was collected through an indwelling cannula at -2, -1 and 0 h relative to GnRH stimulation (basal...
Sharp DC, Grubaugh W, Berglund LA, McDowell KJ, Kilmer DM, Peck LS, Seamans KW, Chen CL.The pituitary stalk was transected in 10 Pony mares by a surgical approach that involved dorsal reflection of the brain and micro-dissection from the ventro-lateral aspect of the pituitary. Diabetes insipidus was the most immediate and marked result, requiring extensive electrolyte and antidiuretic therapy for approximately 48 h after operation. Fluid stasis then developed and no further supportive measures were necessary. Endocrine challenge tests with GnRH and TRH before and after stalk transection indicated a loss of responsiveness (GnRH) or suppressed responsiveness (TRH) after the operati...
Pantke P, Hyland J, Galloway DB, MacLean AA, Hoppen HO.Equine plasma luteinizing hormone (LH) possesses both biological (in vitro bioassay, B) and immunological (radioimmunoassay, I) activities and the ratio of B:I varies with stage of the oestrous cycle. To estimate the contribution made by pituitary secretion and peripheral metabolism to changes in the B:I ratio, pituitary venous effluent and circulating plasma from 5 dioestrous and 2 oestrous mares were analyzed using both an in vitro bioassay and a radioimmunoassay. During dioestrus, LH was released in a pulsatile fashion with a frequency of 1.4 pulses/24 h and a pulse duration of 20-40 min (c...
Joonè CJ, Cavalieri J.There is a need for a safe, effective and practical method of oestrus suppression in the mare. The aim of this study was to monitor ovarian activity in mares exposed to either 9.4 or 28.2 mg deslorelin acetate, a GnRH agonist, in the form of a sustained-release implant. Following oestrus synchronisation, mares were randomly assigned to one of three groups (n = 4 per group) and administered either one (Des1 group; 9.4 mg) or three (Des3 group; 28.2 mg) implants of deslorelin acetate (Suprelorin-12, Virbac Australia) or one blank implant (Control group; Virbac Australia). Mares underwe...
Ginther OJ, Bergfelt DR.Seasonally anovulatory mares were injected, i.m., twice daily with a GnRH analogue (GnRH-A), and hCG was given when the largest follicle reached 35 mm in diameter. In Exp. 1, treatment was initiated on 23 December when the largest follicle per mare was less than or equal to 17 mm. An ovulatory response (ovulation within 21 days) occurred in 17 of 30 (57%) GnRH-A-treated mares on a mean of 15.8 days. The shortest interval to ovulation in control mares (N = 10) was 57 days. The diameter of the largest follicle first increased significantly 6 days after start of treatment. In Exp. 2, treatment wa...
Nequin LG, King SS, Matt KS, Jurak RC.The transition from anoestrus to oestrus in mares is controlled by photoperiod. The present study examined whether additional daylength would accelerate the mares' response to gonadotrophin-releasing-hormone (GnRH). Nine anoestrous mares were placed under ambient or artificial long lighting on 7th January. The four month experimental period was divided into a three-day sequence which was repeated at 21 day intervals. Ovaries were palpated rectally on Day 1; saline was injected (1 ml intravenously [iv]) on Day 2; GnRH was administered (0.59 microgram/kg bodyweight iv) on Day 3. Blood was taken ...
Cui B, Liu Y, Wu X, Li X.The objective of this study was to evaluate the effects of exogenous GnRH administration at the beginning of estrus synchronisation in mares during the spring transitional period. Estrus was synchronised using a progesterone releasing intravaginal device (PRID). The PRID was left in the vagina for 10 days, followed by an injection of 0.4 mg of cloprostenol at PRID removal. The GnRH group (n = 32) was subjected to intramuscular administration of 100 μg of the GnRH agonist triptorelin at PRID insertion, while the control group (n = 32) received 1 mL of sterile physiological sali...
Muñoz-Jurado A, Requena F, Agüera EI, Escribano BM.Anti-Müllerian hormone (AMH) is a dimeric glycoprotein belonging to the superfamily of the transforming growth factor-β. Due to the discovery of AMH functions, relative to the ovarian function, it is being postulated as being a highly important marker in studies on mammalian reproduction. Therefore, the objective of this review was to describe the role of this hormone in different reproductive aspects of female mammals, taking women, cows, and mares as reference species. The relationship between ovarian reserve and AMH was analysed, and it has been verified that there is a relationship betwe...
