Effect of dose of GnRH analog on ovulation in mares

GnRH analogs induce a LH peak and increase pregnancy per timed-AI in ewes

To date, there have been no studies testing the capacity of GnRH analogs and respective doses to induce a LH peak in sheep. In this sense, the present study aimed to evaluate the capacity of different synthetic forms and doses of GnRH in inducing LH release in sheep, and the effect of GnRH administration at timed artificial insemination (TAI) on pregnancy per timed-AI. In experiment 1, ewes (n = 40) received an intravaginal device (IVD) of medroxyprogesterone acetate (MPA; 60 mg) for 7 d and prostaglandin F2α analog on Day 5. On Day 7, the ewes were allocated randomly into one of eight groups (n = 5/group), which received a GnRH analog at a specific dose, as follows: lecirelin (12.5 or 25 μg), gonadorelin (50 or 100 μg), buserelin acetate (4.2 or 8.4 μg), or deslorelin (375 or 750 μg). Blood samples for LH determination were obtained at 0, 2, 4, and 6 h after GnRH and the IVDs were removed after the last blood collection. The maximal LH concentration induced by gonadorelin at doses of 50 μg and 100 μg (12.0 ± 2.4 ng/mL and 28.6 ± 7.1 ng/mL, respectively) was lower (P < 0.05) than serum LH induced by 8.4 μg of buserelin (78.9 ± 12.9 ng/mL), 375 μg and 750 μg of deslorelin (75.6 ± 7.4 ng/mL and 72.1 ± 10.6 ng/mL, respectively) and 12.5 μg and 25 μg of lecirelin (73.3 ± 17.8 ng/mL and 61.6 ± 5.9 ng/mL, respectively). However, the maximal LH concentration induced by 4.2 μg of buserelin (49.4 ± 5.9 ng/mL) was similar (P > 0.05) to the 100 μg of gonadorelin. The total release of LH (area under the curve - AUC) after treatment with 50 μg of gonadorelin (31.7 ± 5.9 ng h/mL) was lower (P < 0.05) than after other agonists. In a second experiment, 330 ewes were treated with IVD containing MPA for 7 d. Simultaneously with IVD removal, 250 μg of cloprostenol and 200 IU of eCG were administered. Then, ewes were assigned randomly to either no further treatment (control); or to receive 4.2 μg of buserelin acetate (GnRH group) at cervical TAI, which was performed with fresh semen 54 h after IVD withdrawal in all the animals. Higher pregnancy per timed-AI was observed for GnRH (50.3 %) compared to control (40.7 %). We conclude that buserelin acetate (8.4 μg), lecirelin (12.5 and 25 μg) and deslorelin (375 and 750 μg) induced a greater stimulatory effect on LH secretion than gonadorelin treatment. Furthermore, buserelin acetate treatment at TAI increased pregnancy per timed-AI in ewes previously treated with MPA and eCG.

Hormonal Management for the Induction of Luteolysis and Ovulation in Andalusian Jennies: Effect on Reproductive Performance, Embryo Quality and Recovery Rate

Two prostanglandins (luprostiol, LUP, and dinoprost, DIN) and two ovulation-inducing agents (human Chorionic Gonadotropin, hCG, and deslorelin, DES) were evaluated for luteolysis and estrus induction, and for ovulation induction, respectively, in embryo donor jennies. Twenty-six fertile Andalusian jennies were used. In Experiment 1, jennies (n = 112 cycles) were randomly treated with either LUP or DIN after embryo flushing. In Experiment 2, donors (n = 84 cycles) were randomly treated with either hCG or DES to induce ovulation. No differences were found between prostaglandins for all variables studied (prostaglandin–ovulation interval (POI), interovulatory interval (IOI), embryo recovery rate (ERR), positive flushing rate (PFR) and embryo grade (EG)). The ovulation rate was similar for hCG and DES (60.9% vs. 78.7%). However, the interval to ovulation (ITO) was affected (62.61 ± 7.20 vs. 48.79 ± 2.69 h). None of the other variables studied (ERR, PFR and EG) were affected (p > 0.05), except for embryo quality (p = 0.009). In short, both prostaglandins evaluated are adequate to induce luteolysis and estrus. Both ovulation-inducing agents hastened ovulation, but DES seems to be more effective than hCG. Follicular diameter affected the interval from treatment to ovulation, and high uterine edema was related to low embryo quality.

Efficiency of Equilume Light Mask on the Resumption of Early Estrous Cyclicity and Ovulation in Thoroughbred Mares

Equilume light masks had no impact on hastening the resumption of estrous cyclicity in mares maintained in outdoor pastures on the mainland of Korea due to the cold weather conditions. Jeju Island is a major horse-breeding site in Korea and is warmer than the mainland during the winter season. Therefore, the primary objective of this study was to explore the efficiency of the Equilume light mask on the resumption of seasonal estrous cycles in Thoroughbred mares on Jeju Island. A total of 20 nonpregnant mares were randomly divided into the Equilume light mask (n = 9) and stable lighting (n =11) groups. The experiment was performed at seven different horse-breeding farms located on Jeju Island from November 15, 2020, to February 15, 2021. The mares were exposed to the respective lights from 16:00 to 23:00. Follicle size and uterine edema were measured by ultrasound scanning. Body condition scores (BCS) were also monitored during the experiment. Statistical analysis was conducted using the SAS and SPSS software, and p-values of < 0.05 were considered statistically significant. Two of the nine (22.2%) mares in the Equilume light mask group and three of the 11 (27.28%) mares in the stable lighting group were still cycling in December and January, which were considered as all-year-round cycling mares. On February 15, there was no difference between groups in the resumption of early seasonal estrus cycle, which was determined by follicles > 25 mm in addition to uterine edema. All mares in the Equilume light mask group and five of the eight mares (62.5%) in the stable lighting group had resumed cycling. Interestingly, six of the seven mares (87.5%) in the Equilume light mask and four of eight mares (50%) in the stable lighting group had already ovulated on February 15 (p > 0.05), as determined by the presence of a recent corpus luteum. No difference was observed in BCS and uterine edema between groups (p > 0.05). In conclusion, the Equilume light mask can be an effective approach to induce early seasonal estrus cycles of mares in Jeju Island, and it also enhances the efficiency of farm management by reducing labor.

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 PGF_2α 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.

Single injection of triptorelin or buserelin acetate in saline solution induces ovulation in mares the same as a single injection of hCG

The aim of this study was to assess the efficacy of different doses of buserelin acetate and another GnRH agonist, triptorelin acetate, in saline solution in a single subcutaneous injection, to induce ovulation of growing pre-ovulatory follicle in mare and compare it with the classical treatment of a single injection of hCG. The study is split into 3 experiments over different breeding seasons in the same stud with a random distribution of treatment. The first one was to compare the injection of 6 mg of buserelin with 1,500 IU of hCG; the second one consisted of comparing different doses of buserelin (6 mg and 3 mg); and the third one compared three different doses of buserelin (3, 2 and 1 mg), 0.1 mg of triptorelin with 1,500 IU of hCG as a control group. The results of all experiments showed the same efficacy between all treatments with mares ovulating between 24 and 48 hr after injection: experiment 1: hCG (78% n = 41) and buserelin 6 mg (90% n = 50); experiment 2: buserelin 6 mg (78,1% n = 192) and buserelin 3 mg (78% n = 341); and experiment 3: hCG (87% n = 106), buserelin 3 mg (84,7% n = 137), buserelin 2 mg (82,7% n = 104), buserelin 1 mg (87% n = 54) and triptorelin 0.1 mg (84,7% n = 72). In conclusion, this study contributes to erasing the dogma that has been established since 1975 that a single injection in solution without any long-acting excipient of a GnRH agonist cannot induce ovulation in the mare. This study also shows that a injection of 0.1 mg of triptorelin in solution is a good alternative for ovulation induction and is comparable to small doses of buserelin acetate in solution (1 mg) and 1,500 IU of the gold standard trigger hCG, mainly in countries where human formulation of buserelin is not available.

Efficacy of hCG and GnRH for inducing ovulation in the jenny

Knowledge about management of ovulation in the donkey is limited compared to that in the horse. This experiment was designed to evaluate the efficacy of injecting single doses of lecirelin (a GnRH-analogue) or of hCG to induce ovulation in the jenny and to determine whether effects are dependent upon follicular diameter at time of injection. Ovarian activity and follicular growth were monitored by rectal ultrasonography. Jennies were randomly allotted to the following groups: Group GnRH, treated with 100 microg lecirelin; Group hCG, treated with 2500 IU hCG; Group C, untreated and monitored for spontaneous ovulation. Animals were also categorized into subgroups depending upon follicular diameter: 30-35 mm (GnRH-1, hCG-1 and C-1) or 36-40 mm (GnRH-2, hCG-2 and C-2). Jennies in the two hormone treatment groups did not differ significantly for time from treatment to ovulation, but there was a significant reduction in time to ovulation as follicle size at treatment increased. Jennies treated with either lecirelin or hCG had significantly smaller follicle size at ovulation than jennies in the Control groups that underwent spontaneous ovulation. Treatment groups did not differ significantly in the proportion of jennies that ovulated within 48 h of injection or between 25 and 48 h following injection. These results highlight the usefulness of lecirelin for induction and synchronization of ovulation in the jenny, particularly since it would avoid the risk of reduced hCG response in reproductive management programs in which that hormone was repeatedly used.

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.

Removal of deslorelin (Ovuplant) implant 48 h after administration results in normal interovulatory intervals in mares

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 subsequent ovulation. We considered interovulatory intervals to be prolonged if they were greater than the mean +/- 2 standard deviation (S.D.) of the control group in study 1 and the hCG group in study 2. In study 1, we retrospectively reviewed reproduction records for 278 mares. We either allowed the mare to ovulate spontaneously or induced ovulation using deslorelin acetate implants or hCG. We administered prostaglandin intramuscularly, 5-9 days after ovulation in selected mares in each group. A higher percentage of mares which were induced to ovulate with deslorelin and given prostaglandins had a prolonged interovulatory interval (23.5%; n = 16), as compared to deslorelin-treated mares that did not receive prostaglandins (11.1%; n = 5). In study 2, we induced ovulation in mares with hCG (n = 47), a subcutaneous deslorelin implant via an implanting device provided by the manufacturer (n = 28), or a deslorelin implant via an incision in the neck (n = 43) and we removed the implant 48 h after administration. We administered prostaglandin to all mares 5-9 days after ovulation. In study 2, mares from which the implant was removed had a normal ovulation rate and none had a prolonged interval to ovulation. Administration of prostaglandin after deslorelin treatment was associated with a longer interval from luteolysis to ovulation than that found in mares not treated with deslorelin. Prostaglandin administration during diestrus may have exacerbated the increased interval to ovulation in deslorelin-treated mares. We hypothesize that prolonged secretion of deslorelin from the implant was responsible for the extended interovulatory intervals.

Deslorelin acetate (Ovuplant) therapy in cycling mares: effect of implant removal on FSH secretion and ovarian function

Following induction of ovulation with deslorelin acetate (Ovuplant), gonadotrophin concentrations are reduced in the subsequent cycle, leading to increased interovulatory intervals in some mares. This study determined whether implant removal after 2 days prevented the decrease in gonadotrophin concentrations and follicular growth during the ensuing cycle. Twenty-four mares were randomised equally into 3 groups. Group 1 ovulated spontaneously, Groups 2 and 3 received the deslorelin implant to induce ovulation. Two days after treatment, the implant was removed from Group 3. On Day 10 postovulation, FSH was lower (P = 0.009) in Group 2, but not different between Groups 1 and 3. Follicular diameter on Day 14 was less (P<0.05) in Group 2 (19.0 +/- 2.1 mm) than in Groups 1 and 3 (36.6 +/- 2.5 and 30.5 +/- 2.0 mm, respectively). Interovulatory interval was longer (P<0.05) for Group 2 (25.8 +/- 2.9 days) compared to Groups 1 and 3 (18.5 +/- 0.7 and 19.4 +/- 0.3 days, respectively). Removal of the deslorelin implant eliminated the decreased FSH secretion and the increased interovulatory interval associated with implant administration. Therefore, it is recommended that the implant be removed after ovulation is detected to prevent the occurrence of a prolonged interovulatory interval.

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 with a dominant ovarian follicle more than 30 mm in diameter, were evaluated, using a placebo as a negative control. The oestrous cycle of each mare was followed by teasing, palpation per rectum and transrectal ultrasonography. Follicles were monitored every 24 hours by ultrasonography until ovulation occurred. The mares were either mated naturally or inseminated artificially. In trial 1, 174 mares were treated at six locations in Canada, and in trial 2, 98 mares were treated at three locations in the USA. In trial 1, the treatment with deslorelin reduced the mean (sd) time to ovulation from 84.2 (48.4) hours to 50.2 (19.6) hours (P < 0.001) and in trial 2 it reduced it from 88.8 (40.3) hours to 54.1 (26.5) hours (P < 0.001). In trial 1, the percentage of mares ovulating within 48 hours increased from 37.7 per cent in control mares to 86.1 per cent in treated mares (P < 0.001) and in trial 2 the percentage increased from 26.5 to 80.9 per cent (P < 0.001). In trial 2, the duration of oestrus in the deslorelin-treated mares was reduced from 6.1 days to 4.3 days and the number of matings or artificial inseminations was reduced from 2.5 to 1.7 (P < 0.001). In trial 1, days 12 to 20 pregnancy rates for matings at the treatment oestrus were not different for deslorelin-treated (75.6 per cent) and placebo-treated (66.1 per cent) mares. In trial 2, days 12 to 20 pregnancy rates from matings at the treatment oestrus were lower for deslorelin-treated (58.7 per cent) than for placebo-treated (83.3 per cent) mares (P < 0.05), although pregnancy rates were similar for deslorelin-treated (97.1 per cent) and placebo-treated (95.0 per cent) mares after mating at the second oestrus. In both trials, pregnancy losses due to early or late abortions were within the normally expected range and similar for deslorelin-treated (3.6 and 3.7 per cent, respectively) and placebo-treated (13.4 and 7.5 per cent) mares. The treatments did not cause systemic side effects and local reactions at the implantation sites were slight and of short duration.

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.