GnRH Analogue Deslorelin Research Articles

Effects of different semen extenders on sperm motility and pregnancy rates in donkeys

Semen quality is highly associated with the success of artificial insemination (AI). The characteristics of semen preserved at room temperature will be influenced by various factors. The semen extender provides sufficient energy for sperm, maintains pH and osmotic pressure stability, inhibits the reproduction of microorganisms and thus prolongs the survival time of sperm. We investigated effects of extender type on semen motility and pregnancy rates in donkeys. Five Yangyuan jacks and 1000 Yangyuan jennies were included in the study. Semen was collected by artificial vagina and filtered to remove impurities. The sperm motility (i.e., total and progressive) and concentration were determined by computer-assisted sperm analysis. Biggers, Whitter and Whittingham (BWW), Brackett and Oliphant medium (BO), Human Tubal Fluid (HTF) and Beltsville Thawing Solution (BTS), were semen extenders from other animal species, CAU-A and CAU-B were diluents independently developed by our laboratory. Firstly, the semen was diluted with CAU-B in a ratio of 1:2 (v/v, sperm: CAU-B). After mixing, the semen was centrifuged at 1500rpm for 10 min. The precipitation was retained and added to each tube. Then, the prewarmed extenders were slowly added along the tube wall and mixed by gentle shaking. After cooling to 17°C, diluted semen was placed in an incubator, mixed every 8h, and the sperm motility was analyzed. Meanwhile, we used transrectal palpation andB-mode ultrasound to determine ovarian activity of jennies. Upon detection of a 30-35 mm follicle, jennies were treated with the GnRH analogue deslorelin (GnRH-D) and inseminated with fresh semen diluted appropriately. The pregnancy rate of jennies was evaluated 20 days after ovulation. Statistical analysis was performed by ANOVA. Values are given as mean ± standard error. When diluted semen was stored at 17°C, the motility decreased with the increase of storage time extender. After 16h, sperm in BWW, BTS, BO and HTF extender were all dead. After 48h storage, the motility of sperm in CAU-A (mean 36.14 ± 6.12%) was lower (p < 0.05) than that in CAU-B (53.87 ± 16.25%). Pregnancy rates after insemination with semen diluted in CAU-A, CAU-B, BWW and BO were 30.53%, 34.77%, 29.37% and 30.96%, respectively, and there was no significant difference among groups (p>0.05). However, the pregnancy rate of semen diluted by CAU-B, which contains raffinose and fructose was slightly higher than that of the other groups. In conclusion, the results show that extension of donkey semen in CAU-B extender resulted in a slightly although not significantly improved pregnancy rate. This suggests that the semen extender is important for both, sperm viability and fertilization. This finding may be of significance for breeding and reproduction of donkeys and other equid species.

Transient suppression of ovulatory ovarian function in pony mares after treatment with slow-release deslorelin implants

Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF2α analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive tract and ovaries and observation of estrous behavior and collection of blood samples for analysis of progesterone and LH concentrations were performed every second day until day 10 and thereafter at 5-d intervals. Stimulation tests with the GnRH-agonist buserelin were performed on days 10 and 45. Until day 50, there were less spontaneous ovulations in group D1 (P < 0.01) and estrous behavior was reduced in groups D1 and D2 compared with group C (P < 0.05). The time until first ovulation (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d, P < 0.05) and the number of days with estrous behavior (P < 0.05) differed among groups. On day 10 after treatment, a GnRH stimulation test revealed interactions between group and time (P < 0.001) in plasma LH concentration that were no longer detectable on day 45 after treatment. In conclusion, long-acting deslorelin implants result in a transient downregulation of pituitary GnRH receptors that is associated with inhibition of ovulation and estrous behavior in Shetland mares.

Effects of long-term release GnRH agonist “deslorelin” on testicular HSP expression, accessory sex glands and testicular functions in adult male rats

The objective of the present was to determine the effect of long-term release GnRH agonists “deslorelin” on suppression and restoration of testicular and accessory sex glands functions, and expression of HSP in testes of adult male rats. A group of twenty-eight male rats and fifty-six female rats were kept for eleven months. The male rats were subdivided into treatment (n = 18; deslorelin, an analogue of GnRH, 4.7 mg, S.C; six months) and control (n = 10; untreated), and the adult female rats were introduced with either treatment or control male rats at the 2nd, 6th and 11th months post implant insertion. At 6th month of deslorelin implants insertion, six male rats from treatment and five rats from control group were sacrificed. The remaining (twelve treatment and five control) male rats were sacrificed at 11 months. The testicular dimension were measured monthly in both treatment and control rats. The blood samples were collected for testosterone and HSP70 antibody, whereas, the testes and accessory glands were isolated for histological examination at each sacrificial time. The results showed that testicular dimension were significantly lesser in treatment group until 9 months post treatment. HSP70 protein expression was negligible at 6 months in treatment group but its intensity increased in spermatids 11 months of treatment similar to control group. Significantly lower testosterone concentrations with poor semen quality, and smaller litter size were observed in treatment group. The histological picture of accessory sex glands and seminiferous tubules shown a variable integrity in treatment group than control at 6 months implant insertion. In conclusion, the subcutaneous application of 4.7 mg of the GnRH-analogue deslorelin represents a practicable, like in the female rats, method to suppress testicular, accessory sex glands functions, testicular HSP expression and fertility in male rats. Moreover, the suppressive effects of deslorelin, continued until 11th months after removal of the implant.

Effectivness of the GnRH analogue deslorelin as a reversible contraceptive in a neotropical primate, the Common Marmoset Callithrix Jacchus (Mammalia: Primates: Callitrichidae)

Deslorelin is a synthetic GnRH analogue, which is being used as a contraceptive in animals by acting as a gonadal suppressant. The product Suprelorin (Virbac, Australia) contains deslorelin as a biocompatible, slow release subcutaneous implant. The continuous release of deslorelin provokes a down-regulation of GnRH receptors, and subsequently, inhibition of the synthesis and release of the gonadotropins FSH and LH, necessary for gonadal activities. The intention of this study was to investigate the effectiveness of a subcutaneous deslorelin acetate implant (2,35mg) in suppressing ovarian cyclic activity and inhibiting ovulation in captive Common Marmoset Callithrix jacchus, and investigate the reversibility of the treatment. Two experimental groups were formed, group deslorelin (D) with three couples and control group (C) with two couples. To monitor the effect of the implants, hormones indicating ovarian cyclic activity were monitored non-invasively by enzyme immunoassay (fecal monoclonal antibody anti-progesterone CL 425). Fecal samples were collected three times a week from all females during three trial phases (phase I: month 1,2,3 and 4; phase II: month: 5,6 and 7 and phase III: month 8,9 and 10). In contrast to expectations the results of this trial indicated that there was no suppression of the ovarian cyclic activity, nor inhibition of the ovulation after the application of the implants. The outcome of our trial can possibly be explained by the fact that the dosage of 2.35mg of deslorelin is not effective in C. jacchus. We confirmed significant changes (p&lt;0.05) of P4 metabolites from phase I to phase II due to the treatment after the implantation of the GnRH analogue Deslorelin. The employed non-invasive fecal progesterone monitoring could be biologically validated and proved to be efficient in the detection of ovarian cyclic activity in this neotropical primate species, C. jacchus.

The use of the gonadotropin-releasing hormone analog deslorelin for short-term contraception in red pandas (Ailurus fulgens)

Red pandas (Ailurus fulgens) are threatened with extinction owing to habitat loss, exacerbated by their unique ecology and low fecundity. Regional breeding programs manage captive red panda populations. Recommendations not to breed may be made for various reasons, including genetic overrepresentation of certain individuals. No recommendations have been published on the use of contraception for red pandas. This article discusses the use of the GnRH analog deslorelin as a reversible method of contraception in both male and female pandas. The mean time from last contraception to conception was 3 years with a 4.6-mg deslorelin implant. The average dose of GnRH implant received was 1.09 mg/kg (range, 0.88–1.32). Males returned to breeding sooner than females. No reproductive side effects were noted with up to three consecutive annual GnRH implants.

Prepubertal Köpeklerde GnRH Analoğu Deslorelinin Kısa Dönem Klinik ve Endokrinolojik Etkileri: “Flare-up” Gözlenir mi?

Prepubertal Köpeklerde GnRH Analoğu Deslorelinin Kısa Dönem Klinik ve Endokrinolojik Etkileri: “Flare-up” Gözlenir mi?

Estrus induction in white rhinoceros (Ceratotherium simum)

The estrous cycle length in the white rhinoceros (Ceratotherium simum) is either 4 or 10 wk. The cause(s) for this variation as well as the poor fertility rate in captivity remains under debate in this species. Most captive adult white rhinoceros undergo long anovulatory periods without luteal activity which are considered a major reason for their low reproductive rate. In this study, the synthetic progestin chlormadinone acetate (CMA) was tested in combination with hCG or the GnRH analogue deslorelin for its efficiency to induce ovulation in fourteen females without luteal activity and in three, regular cycling females. HCG (N = 12), injectable GnRH analogue (N = 8) and GnRH analogue implants (N = 15) were given to induce ovulation after CMA treatment. Treatment success was determined using both transrectal ultrasonography and progesterone metabolite EIA analysis. A preovulatory sized follicle (3.5 ± 0.1 cm) or a corpus luteum (5.1 ± 0.7) was present on the ovary one day after induction in 93.1% of the treatments. Despite this high rate of ovarian response, ovulation rate differed between the study groups. The ovulation rate for hCG, injectable GnRH analogue and GnRH analogue implants was 66.7%, 62.5% and 93.3%, respectively. Ovulation rate in cyclic females treated with GnRH implants was 100% (6/6) compared with 89% (8/9) in females without luteal activity receiving the same treatment. The length of the estrous cycle when induced with hCG was 4 wk (85.7%). The estrous cycle when induced with GnRH analogue was predominantly 10 wk long. Two females without luteal activity treated with GnRH became pregnant. In conclusion, CMA in combination with GnRH analogue implants was highly effective to induce ovulation in white rhinoceroses and thus can contribute to efforts aimed at increasing natural mating and reproductive rates in the captive white rhinoceros population.

Effects of the GnRH analogue deslorelin implants on reproduction in female domestic cats

The aim of the present study was to investigate the safety and efficacy of deslorelin, a GnRH agonist, implants in suppressing estrus behavior and matings in a controlled ambient environment in feline queens in the presence of a tomcat. Local and utero-ovarian side effects of deslorelin implants were also investigated. The queens were housed in groups and assigned to one of three treatments: group 1 received 9.5 mg deslorelin implants (N = 14), group 2 received 5 mg megestrol acetate tablets and 9.5 mg deslorelin implants (N = 7), and group 3 were given placebo implants (N = 7). All implants were placed subcutaneously cranial to the interscapular region under xylazine hydrochloride sedation. Ovarian activity was monitored by fecal estradiol (E 2) analyses. The animals were observed daily and checked individually at three-day intervals for behavioral signs of estrus. After 18.5 mo of trial, queens were ovariohysterectomized, and ovaries and uteri were weighed and evaluated histologically. E 2 levels were significantly lower in group 1 and 2 than in group 3 with an average of 128.48 ± 19.97 ng/g, 90.44 ± 7.16 ng/g and 283.26 ± 39.21 ng/g, respectively, excepting the first week of treatment. After inserting implants an initial estrus-like increase in fecal E 2 concentrations occurred in all treated queens except one female in group 2. Ovarian and uterine weights were significantly different among the groups (P < 0.01), and were lowest in groups 1 and 2. Primordial and primary follicle numbers were significantly higher in groups 1 and 2 than in group 3 (P < 0.001). Endometrial gland, antral follicle, and corpus luteum (CL) numbers were highest in group 3 (P < 0.01, 0.001, and 0.001, respectively) compared with groups 1 and 2. Deslorelin implants successfully suppressed estrus behavior and E 2 secretion in queens for 18.5 mo of the study period. Further investigations are needed to demonstrate the effects of GnRH agonists on ovarian interstitial tissue.

Fertility control in a male rabbit using a deslorelin implant. A case report

Continuous low-dose release of the GnRH analogue deslorelin (Suprelorin, Peptech, Australia) causes a suppression of reproductive function in different species such as dogs, koalas, or kangaroos. No studies concerning the effi cacy and safety in male rabbits have yet been conducted. A male rabbit with hypospadia was introduced to the Clinic for Animal Reproduction. The owner intended to keep it together with a fertile female rabbit. To avoid reproduction, a 4.7 mg deslorelin implant was injected subcutaneously. No negative reaction to implant placement was diagnosed by daily examination of the injection site for one week. To test the effectiveness of the treatment, blood samples were taken and the testes size was measured regularly. After an initial rise in testosterone levels for 14 d, a down regulation for seven month with values lower than 0.1 ng/mL was observed. In the same period, the size of the testes declined to 50 % of the original dimensions. Afterwards, both testes regained their former shape and size. Since it was not a stud rabbit, semen parameters were not determined. During the suppression of the reproductive function, no sexual activity was observed by the owners. These fi ndings have yet to be proven by clinical trials with a suffi cient number of animals, but this case indicates the effi cacy of deslorelin implants in male rabbits.

Effects of long-term treatment with the GnrH agonist deslorelin (Suprelorin®) on sexual function in boars

Immunization against GnRH has been proven effective for boar taint removal, and long-term treatment with GnRH analogues has been shown to suppress GnRH dependent reproductive processes in several species. This study was conducted to treat boars (n = 5) with Suprelorin®, i.e., an implant that contains 4.7 mg of the long-acting GnRH analogue deslorelin, and to test the effects on sexual function. Insertion of the implant occurred at the age of 5 weeks and animals were observed until market age at 26–27 weeks. Surgically castrated (n = 4) and intact boars (n = 3) served as controls. Testes growth was markedly reduced and steroidogenesis (testosterone, estrone, estrone sulphate, estradiol 17β) as well as spermatogenesis suppressed in 4 of 5 GnRH treated boars, respectively. The remaining fifth boar resumed testes growth after week 17 of age and had high hormone concentrations when tested at weeks 26 and 27. Restoration of spermatogenesis was observed at 34 weeks of age. There were no effects of treatment on general health, nor were there local inflammatory reactions. Results indicate that suppression of sexual functions in boars due to long-term treatment with the GnRH agonist deslorelin through an implant such as Suprelorin® is possible and can last for several months up to market age; thus it has potential as an alternative to other methods used for boar taint removal. Because the maximum duration of suppression seems to vary between boars, further studies are necessary to refine the treatment.

Induction of estrus and ovulation: Why some mares respond and others do not

The two most common procedures for breeding management of mares involve induction of luteolysis and induction of ovulation. Although both of these events are usually achieved, physiologic conditions affect the timing of the response. In a diestrus mare treated with prostaglandin F(2alpha) (PGF), or a PGF analogue, it is well documented that, on average, the interval from treatment to the onset of estrus is 3-4 days, whereas ovulation occurs 8-10 days after treatment. However, the diameter of the ovulatory follicle, as well as its status at the time of PGF treatment, determines the intervals from treatment to onset of estrus and to ovulation; these intervals can range from 48h to 12 days. Ovulation is routinely induced with human chorionic gonadotropin (hCG), recombinant LH (rLH), or the GnRH analogue Deslorelin. On average, ovulation occurs approximately 36h after treatment, but the effectiveness of any of these treatments can be affected by the stage of the estrus cycle, follicle size and maturity.

Successful Timing of Ovulation Using Deslorelin (Ovuplant®) is Labour‐saving in Mares Aimed for Single AI with Frozen Semen

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) pregnancy rate after single insemination with frozen-thawed semen near ovulation. This study included 11 mares, and altogether 17 timed ovulations. Follicular growth and ovulation were determined by palpation per rectum and by ultrasonography in the morning (at 7:00 hours) every second day until observation of a follicle of at least 42 mm in diameter. Then the mares were re-examined in the afternoon (at 19:00 hours), and an Ovuplant was inserted in the mucosa of the vulva. For detection of ovulation, the mares were palpated and ultrasounded repeatedly from 36-42 h after the insert. The mares were inseminated with frozen-thawed semen once at ovulation. All mares ovulated at 36-48 h after treatment and 94% at 38-42 h after treatment. The six mares that were treated at two oestruses ovulated at 39.9 and 39.7 h, respectively. Five of 11 mares (45.4%), inseminated with frozen-thawed semen at the first oestrous cycle were pregnant day 14-16 after ovulation. Using this protocol, there is no need of palpation/ultrasonography during night hours, and examination at 36 and 41 h after implantation might be enough for estimation of ovulation time.

Repeated use of the GnRH analogue deslorelin to down-regulate reproduction in male cheetahs ( Acinonyx jubatus)

The GnRH analogue deslorelin, as a subcutaneous implant, was initially developed in Australia as an ovulation-inducing agent in mares. Its uses, for the suppression of reproduction in the domestic dog and cat and in other species, including humans, have been developed subsequently. Such implants have been used as a contraceptive modality in a variety of wild carnivores, both males and females. This paper describes the use of deslorelin implants as a contraceptive agent for cheetah males maintained in a semi-captive environment and housed in various camps together with females. Annually, male cheetahs were treated for 1 ( n = 2), 2 ( n = 7), 3 ( n = 9), 4 ( n = 3) or 5 ( n = 1) consecutive years with an implant containing 4.7, 5.0 or 6.0 mg of deslorelin. On the first day of treatment and then on an annual basis, blood testosterone concentrations were analysed, testicular measurements were taken, appearance of penile spikes was determined, and semen was collected and evaluated. Pregnancy rates of mated or inseminated females were determined. A dose of 6 mg of deslorelin suppressed reproduction for at least 1 year, whereas with 4.7 and 5 mg of deslorelin, 3 of 17 males had a few non-motile spermatozoa in their ejaculates. All testosterone concentrations were basal at 1 year post-implant and no side effects were observed. We concluded that deslorelin implantation, at a dose of 6 mg, was a safe and reliable method of annual contraception in male cheetahs.

Use of the GnRH analogue, deslorelin acetate, in a slow-release implant to accelerate ovulation in oestrous mares

In two separate controlled clinical trials, the efficacy and safety of 2.2 mg of the GnRH analogue deslorelin, administered subcutaneously as a short-term implant to normally cycling mares in oestrus...

Repeated use of a GnRH analogue deslorelin (Ovuplant) for hastening ovulation in the transitional mare.

Equine Veterinary JournalVolume 29, Issue 2 p. 153-155 Repeated use of a GnRH analogue deslorelin (Ovuplant) for hastening ovulation in the transitional mare A. O. McKINNON, A. O. McKINNON Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorJ. R. VASEY, J. R. VASEY Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorT. B. LESCUN, T. B. LESCUN Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorT. E. TRIGG, T. E. TRIGG Peptech Animal Health Pty Ltd, DeeWhy, New South Wales 2099, Australia.Search for more papers by this author A. O. McKINNON, A. O. McKINNON Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorJ. R. VASEY, J. R. VASEY Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorT. B. LESCUN, T. B. LESCUN Goulburn Valley Equine Hospital, PO Box 2020, Shepparton, Victoria 3630Search for more papers by this authorT. E. TRIGG, T. E. TRIGG Peptech Animal Health Pty Ltd, DeeWhy, New South Wales 2099, Australia.Search for more papers by this author First published: 23 April 2010 https://doi.org/10.1111/j.2042-3306.1997.tb01659.xCitations: 23AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume29, Issue2March 1997Pages 153-155 RelatedInformation

Acceleration and Timing of Fertile Ovulation in Cyclic Mares with a Deslorelin Implant

In a blinded trial, the effectiveness and safety of 2.2 mg of the GnRH analog deslorelin acetate, administered in a short-term implant (STI) to normally cycling mares in estrus with a dominant ovarian follicle of 30 mm in diameter or larger, were evaluated, using a placebo implant as a negative control. A total of 39 mares received treatments at admittance with pre-randomized implants containing either 2.2 mg or 0 mg deslorelin. Mares were teased daily and examined rectally with ultrasound at 24 h intervals to determine time to ovulation and duration of estrus. The number of breedings and the pregnancy rate at 18 (+/- 3) and 38 (+/- 3) days were recorded, as were systemic side effects and local reactions at the implantation sites. Pregnancies resulting from breedings during the treatment estrus and/or from breedings during the next estrus were followed and the early and late pregnancy loss rate, the number of pregnancies going to term and of live-born foals was recorded. Mean follicle diameter at treatment was not significantly different between the deslorelin and placebo treatment group with 41.6 mm and 40.8 mm, respectively. Treatment with deslorelin STI reduced the time interval to ovulation significantly from 69.5 +/- 25.48 h to 42.7 +/- 12.35 h (p < 0.001). The percentage of mares having ovulated within 48 h rose from 26.3% to 95.0%, respectively, for placebo and deslorelin STI (p < 0.001). As a consequence, the duration of estrus in days and the percent of animals requiring more than 1 breeding were significantly reduced in deslorelin treated animals from 5.4 days to 4.6 days, and from 55.6% to 5.0%, respectively (p = 0.009 and = 0.001). The percent of mares pregnant from breedings at the treatment estrus (65.0% versus 44.4%) or the next estrus (83.3% versus 92.3%) was satisfactory and similar for deslorelin and placebo treated mares (p > 0.005), and in 70.0% and 66.7% of these once or twice bred mares did pregnancies go to term and live foals were born.

Control of Ovulation in the Mare With Ovuplant™. A Short-Term Release Implant (STI) Containing The GNRH Analogue Deslorelin Acetate: Studies from 1990 to 1994. (A Review)

Control of Ovulation in the Mare With Ovuplant™. A Short-Term Release Implant (STI) Containing The GNRH Analogue Deslorelin Acetate: Studies from 1990 to 1994. (A Review)

Predictable ovulation in mares treated with an implant of the GnRH analogue deslorelin

Predictable ovulation in mares treated with an implant of the GnRH analogue deslorelin

Advancing the time of ovulation in the mare with a short‐term implant releasing the GnRH analogue deslorelin

A small, biocompatible and short-term implant releasing 1.5 mg or 2.25 mg of the GnRH analogue deslorelin was evaluated in 140 Hanoverian (warm blooded) mares during the 1990 breeding season (Study I). Mares in oestrus and with a follicle 40 +/- 2 mm in diameter were assigned alternately to treatment (70) or remained as untreated controls. Implants were administered subcutaneously, and intervals to ovulation determined by rectal examination and ultrasound at 12-h intervals. Since results with both doses of deslorelin were similar, data were pooled. Deslorelin implantation resulted in ovulations in 65 of 70 mares within 48 h (93%), while only 5 of 70 control mares ovulated within the same time period (7%) (P < 0.01). Most induced ovulations (63%) occurred 36-48 h after implantation. In Study II, 4 groups of 12 Hanoverian mares each were treated with 3,000 or 5,000 iu hCG, or a 2.25 mg deslorelin implant, or received placebo. All treatments resulted in 100% ovulations within 48 h, versus 25% ovulations in controls (P < 0.01), and 63%, 75% and 86% of these ovulations occurred 36-48 h after treatment with 3,000 and 5,000 iu hCG and deslorelin respectively. Hormonal response to deslorelin in treated mares, sampled every 12 h, consisted of elevations of FSH and LH concentrations of > 200% and > 300% baseline values at 12 h (P < 0.001), of 67% and 79% at 24 h (P < 0.01) and of 35% and 49% at 48 h (P < 0.05), respectively. No local reactions at the implantation site were observed.