Ovulation In Mares Research Articles

Ovarian and endocrine changes during oestrus and early pregnancy in Arabian mares

Faecal and plasma steroid evaluations are well established approaches for monitoring reproductive function in mares. The purpose of this study was to detect the ovarian and uterine changes by transrectal ultrasonographic scanning, beside the estimation of progesterone and estradiol-17β profiles in plasma and faecal samples of Arabian mares. Eight cyclic barren mares of different parities were used in the current work, and hormones were assayed using radioimmunoassay. The continuous significant increase in the follicular size starting from day–7 until reaching its largest size at 0-day of ovulation was accompanied by a continuous significant (P<0.05) decrease and increase in the profile of plasma progesterone (P4) and estradiol-17β (E1-17β), respectively. In addition, the minimum level of P4, and the maximum level of E1-17β were detected at 0-day of ovulation. Similarly, the faecal progesterone metabolites (20∝-hydroxy-progesterone; i.e. 20∝-G) content showed a significant (P<0.05) decrease in its value starting from day –7 reaching its minimum level at second day post ovulation, meanwhile, the faecal E1-17β content was reaching its maximum value on day 1 after ovulation. Following ovulation, the plasma P4 and E1-17β content showed a continuous significant (P<0.05) increase, and the faecal levels of both 20∝-G and E1-17β showed a continuous significant decrease. Meanwhile, the levels of P4 in plasma and 20∝-G in faecal samples increased starting from the 3rd day post ovulation, and E1-17β decreased starting from the 2nd day post ovulation. The levels of P4 in plasma and 20∝-G in faeces increased significantly (P<0.05) at days 14 up to 45 of gestation than those recorded during ovulation in non-pregnant mares. Moreover, the levels of E1-17β in plasma and faeces increased significantly (P<0.05) at days 21 up to 45 of gestation than those estimated during 14th day of gestation as well as in non-pregnant mares. In conclusion, both ultrasonography and analysis of P4 and E1-17β in plasma, and 20∝-G and E1-17β in faeces have a predictive value for assessment of the follicular sizes, ovulation time and early pregnancy in Arabian mares.

The efficacy of a single chain recombinant equine luteinizing hormone (reLH) in mares: Induction of ovulation, hormone profiles, and inter-ovulatory intervals

The objectives of this study were to determine the efficacy of recombinant equine luteinizing hormone (reLH) in shortening the time to ovulation in cycling mares and to determine the effects of treatment on endogenous hormones and inter-ovulatory intervals. In study 1, mares of light horse breeds (3–20 years) were treated with either a vehicle, various doses of reLH, or human chorionic gonadotropin (hCG). Cycling mares were examined by palpation and ultrasound per rectum daily or every 12 h from the time of treatment to ovulation. In studies 2 and 3, jugular blood samples were collected daily or every 12 h from the time of treatment to ovulation for analysis of LH, follicle stimulating hormone (FSH), estradiol-17β (E 2), and progesterone (P 4) by radioimmunoassays (RIA). Increasing doses of reLH (0.3, 0.6, 0.75, and 0.9 mg) showed increasing effectiveness at inducing ovulation within 48 h of treatment. Treatments with the 0.75 and 0.9 mg doses of reLH resulted in 90% and 80% ovulation rates, which were similar to hCG treatment (85.7%). Except for the early rise in LH after treatment with 0.5, 0.65, and 1.0 mg of reLH, hormone profiles appeared to be similar between control and treated cycles. Inter-ovulatory intervals were similar between control and treatment cycles. In conclusion, reLH is a reliable and effective ovulatory agent that does not significantly alter endogenous hormone profiles or affect inter-ovulatory intervals.

Utilizing Body Temperature to Evaluate Ovulation in Mares

Although reproductive technology has added many dimensions to the horse breeding industry, less invasive and more efficient methods of evaluating follicular development and ovulation would be beneficial to both the commercial breeder and private horse owner. Because of the highly variable estrous cycle of the mare, it is difficult for breeders to coordinate insemination with ovulation, and much time is invested in evaluation via palpation, ultrasound, and teasing. In both dairy cattle and women, a significant change in body temperature has been measured during the hours immediately prior to ovulation. Research exploring the relationship of body temperature and ovulation in horses has been limited to one study in which no relationship between temperature and ovulation was identified. The current study utilized 38 mature mares and was conducted during the physiologic breeding season. Each mare was implanted in the nuchal ligament with a microchip capable of reporting body temperature, and rectal temperatures were obtained using a digital thermometer. Once an ovulatory follicle was detected using ultrasonography and the mare was exhibiting signs of estrus, the follicle size and temperature were recorded approximately every 6 h until ovulation. No difference was found in rectal temperature in relation to the presence or absence of a follicle. Under specific circumstances, temperatures obtained using the microchip were higher (P < 0.05) prior to ovulation compared with those temperatures collected immediately following ovulation.

Tratamento de éguas receptoras de embriões visando sua utilização no segundo dia pós-ovulação

Durante as estações de monta de 2001/2002 e 2002/2003, 43 éguas da raça Mangalarga Marchador receptoras de embriões foram tratadas aleatoriamente, via intramuscular, com 200 mg/dia de progesterona oleosa (P4) e 41 éguas da mesma raça receberam 0,044 mg/kg/dia de Altrenogest, aleatoriamente, via oral. Ambos os tratamentos foram efetuados entre D0 (dia da ovulação) e D5. As receptoras foram avaliadas no D2 e, se consideradas aptas, foram inovuladas. Dois grupos de 85 éguas da mesma raça foram utilizados aleatoriamente como controle e não receberam progestágeno, mas foram avaliados e inovulados em D2 ou D5, se considerados aptos. Os grupos D2 com P4 e D5 sem progestágeno tiveram maior número de éguas consideradas excelentes ou boas (aptas) no momento da avaliação, 55 (64,71%) e 25 (65,12%), respectivamente. O grupo D2 com Altrenogest apresentou número estatisticamente igual de receptoras aptas a inovulação e descartadas (20 e 21 éguas, respectivamente) no momento da avaliação. Nesta avaliação, no grupo D2 sem progestágeno, a quantidade de receptoras descartadas foi significativamente maior. A taxa de prenhez foi maior nos grupos D2 com P4 e D5 sem progestágeno (72,72 e 76,36%, respectivamente). No grupo D2 com Altrenogest, obteve-se taxa de prenhez de 52,38%, não-significativa, e, no grupo D2 sem progestágeno, a quantidade de éguas não-gestantes foi maior, embora não-significativa. O tratamento com P4 do D0 ao D5 possibilita antecipar a inovulação de receptoras para D2, com resultados semelhantes ao D5.

Effect of eFSH on Ovarian Cyclicity and Embryo Production of Mares in Spring Transitional Phase

The use of equine FSH (eFSH) for inducing follicular development and ovulation in transitional mares was evaluated. Twenty-seven mares, from 3 to 15 years of age, were examined during the months of August and September 2004, in Brazil. Ultrasound evaluations were performed during 2 weeks before the start of the experiment to confirm transitional characteristics (no follicles larger than 25 mm and no corpus luteum [CL] present). After this period, as the mares obtained a follicle of at least 25 mm, they were assigned to one of two groups: (1) control group, untreated; (2) treated with 12.5 mg eFSH, 2 times per day, until at least half of all follicles larger than 30 mm had reached 35 mm. Follicular activity of all mares was monitored. When most of the follicles from treated mares and a single follicle from control mares acquired a preovulatory size (≥35 mm), 2,500 IU human chorionic gonadotropin (hCG) was administered IV to induce ovulation. After hCG administration, the mares were inseminated with fresh semen every other day until ovulation. Ultrasound examinations continued until detection of the last ovulation, and embryo recovery was performed 7 to 8 days after ovulation. The mares of the treated group reached the first preovulatory follicle (4.1 ± 1.0 vs 14.9 ± 10.8 days) and ovulated before untreated mares (6.6 ± 1.2 vs 18.0 ± 11.1 days; P < .05). All mares were treated with prostaglandin F2α (PGF2α), on the day of embryo flushing. Three superovulated mares did not cycle immediately after PGF2α treatment, and consequently had a longer interovulatory interval (22.4 vs 10.9 days, P < 0.05). The mean period of treatment was 4.79 ± 1.07 days and 85.71% of mares had multiple ovulations. The number of ovulations (5.6 vs 1.0) and embryos (2.0 vs 0.7) per mare were higher (P < 0.05) for treated mares than control mares. In conclusion, treatment with eFSH was effective in hastening the onset of the breeding season, inducing multiple ovulations, and increasing embryo production in transitional mares. This is the first report showing the use of FSH treatment to recover embryos from the first cycle of the year.

Comparison of Compounded Deslorelin and hCG for Induction of Ovulation in Mares

Abstract Ovulation-inducing agents are routinely used in broodmare practice. The objective of this study was to compare the efficacy of two compounded deslorelin products and human chorionic gonadotropin (hCG) in inducing ovulation in a clinical reproduction program. Breeding records of 203 mares administered an ovulation-inducing agent during the 2006 breeding season were reviewed. Estrous cycles were included for comparison if agents were administered when the largest follicle was 35 to 45 mm in diameter and endometrial edema was present. There was no significant difference ( P > .05) in interval to ovulation for mares receiving deslorelin (1.9 ± 0.7 days) or hCG (2.0 ± 0.7 days). The percentage of mares that ovulated within 48 hours after treatment was also not significantly different between the agents (90.1% and 88.3%, respectively). In summary, clinical efficacy at inducing a timed ovulation in estrual mares with follicles 35 to 45 mm was similar between compounded deslorelin and hCG.

CORELATIONS BETWEEN THE BODY TEMPERATURE FLUCTUATION AND THE PREDICTION OF OVULATION IN MARES

Due to the difficulties involved in the prediction of ovulation in mares, which ovulate before the end of estrus, a more efficient, less invasive method that could reduce the need for repeated teasing and ultrasonography is needed. It is possible that the conventional methods (palpation, ultrasonography, teasing) currently used are the most effective when predicting ovulation in the mare. The evaluation of the body temperature curve (temperature fluctuations) in the study of the prediction of ovulation is used successfully for humans and there are also some articles about it for dairy cattle and rats. The current study is presenting some observations about the fluctuation of body temperature around the moment of ovulation in mares. The current study utilized four mature cycling Romanian Sport Horse mares, and was conducted from July-August 2007. Observations were recorded from the first day mares exhibited signs of behavioral estrus through day three after the end of the estrus once daily. Beginning with the moment when an ovulatory follicle (>35mm) was detected using ultrasonography the mare's follicle size and temperature were recorded approximately every six hours until ovulation. All four mares were palpated every other day during estrus to determine the presence of an ovulatory follicle (>35mm). Ovulation was established through palpation by the presence of an ovulation depression or corpus hemorrhagicum on the ovary hosting the ovulatory follicle. The rectal temperatures were recorded using a veterinary digital thermometer four times daily . Differences in the fluctuation of the rectal temperature were found in relation to the presence of an ovulatory follicle of greater than 35mm compared with the absence of it (plus 0.1 OC -0.5 OC), but there were no changes 24 hr prior to ovulation that could be used to predict ovulation ( a mean of 37.7 OC pre-ovulation and post-ovulation).

Evaluation of three equine FSH superovulation protocols in mares

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 therapy. Group 4 mares were administered P + E for 10 days followed by eFSH therapy. All treated mares were administered 12.5 mg eFSH twice daily and prostaglandins were given on the second day of eFSH therapy. Mares were bred with fresh semen the day of hCG administration and with cooled semen the following day. The numbers of preovulatory follicles and ovulations were lower for mares treated with P + E prior to eFSH treatment. Pretreatment with P + E in estrus also resulted in a lower embryo recovery rate per ovulation compared to the other two eFSH treatment groups. In Experiment 2, two doses of eFSH (12.5 and 6.25 mg) and two ovulation-inducing agents (hCG and deslorelin) were evaluated. The number of preovulatory follicles was greater for mares given 12.5 mg of eFSH compared to mares given 6.25 mg. Number of ovulations was greatest for mares given 12.5 mg of eFSH twice daily followed by administration of hCG. Embryo recovery per flush was similar among treatment groups, but the percent of embryos per ovulation was higher for mares given the low dose of eFSH. In summary, there was no advantage to giving P + E prior to eFSH treatment. In addition, even though the lower dose of eFSH resulted in fewer ovulations, embryo recovery per flush and embryo recovery per ovulation were similar or better for those given the lower dose of eFSH.

A preliminary study on the induction of dioestrous ovulation in the mare – a possible method for inducing prolonged luteal phase

BackgroundStrong oestrous symptoms in the mare can cause problems with racing, training and handling. Since long-acting progesterone treatment is not permitted in mares at competition (e.g. according to FEI rules), there is a need for methods to suppress unwanted cyclicity. Spontaneous dioestrous ovulations in the late luteal phase may cause a prolongation of the luteal phase in mares.MethodsIn this preliminary study, in an attempt to induce ovulation during the luteal phase, human chorionic gonadotropin (hCG) (3000 IU) was injected intramuscularly in four mares (experimental group) in the luteal phase when a dioestrous follicle ≥ 30 mm was detected. A fifth mare included in this group was not treated due to no detectable dioestrous follicles ≥ 30 mm. Four control mares were similarly injected with saline. The mares were followed with ultrasound for 72 hours post injection or until ovulation. Blood samples for progesterone analysis were obtained twice weekly for one month and thereafter once weekly for another two to four months.ResultsThree of the hCG-treated mares ovulated within 72 hours after treatment and developed prolonged luteal phases of 58, 68 and 82 days respectively. One treated mare never ovulated after the hCG injection and progesterone levels fell below 3 nmol/l nine days post treatment. Progesterone levels in the control mares were below 3 nmol/l within nine days after saline injection, except for one mare, which developed a spontaneously prolonged luteal phase of 72 days.ConclusionHCG treatment may be a method to induce prolonged luteal phases in the mare provided there is a dioestrous follicle ≥ 30 mm that ovulates post-treatment. However, the method needs to be tested on a larger number of mares to be able to draw conclusions regarding its effectiveness.

Single-chain recombinant eLH: induction of ovulation in mares

Single-chain recombinant eLH: induction of ovulation in mares

Exogenous eFSH, follicle coasting, and hCG as a novel superovulation regimen in mares

The objective of this study was to evaluate various equine follicle-stimulating hormone (eFSH) treatment protocols and the effect of “follicle coasting” on ovulation and embryo recovery rates in mares. Cycling mares (n = 40) were randomly assigned to one of four groups 7 days after ovulation: (1) 12.5 mg eFSH twice daily until follicles were 35 mm or larger; (2) 12.5 mg eFSH twice daily until follicles were 32 mm or larger; (3) 12.5 mg eFSH twice daily for 3.5 days followed by 12.5 mg eFSH enriched with luteinizing hormone (LH) twice daily until follicles were 35 mm or larger; and (4) 25 mg eFSH once daily until follicles were 32 mm or larger. Mares in groups 1 and 3 were injected with human chorionic gonadotropin (hCG) (2500 IU intravenously) at the end of eFSH treatment, whereas mares in groups 2 and 4 were given hCG approximately 42 and 54 hours, respectively, after the last eFSH treatment (“follicle coasting”). Nonsurgical embryo collection was performed 6.5 to 7.5 days after ovulation. Each mare experienced a nontreated estrous cycle before being reassigned to a second treatment. Ovulation rates for mares in treatment groups 1 to 4 were 3.3 ± 0.4, 4.1 ± 0.4, 3.5 ± 0.4, and 2.8 ± 0.4 (mean ± SEM; P < .05), respectively. One or more embryos were recovered from more than 80% of mares in each treatment group, and embryo recovery rate per flush was similar among treatment groups (1.9 ± 0.3, 2.6 ± 0.3, 1.9 ± 0.3 and 1.9 ± 0.3, respectively; P > .05). The overall embryo recovery rate was 2.1 ± 1.5 embryos per flush. In summary, ovulation rate was higher for mares treated with eFSH (3.4 ± 0.4) compared with non-treated controls (1.1 ± 0.2). Ovulation rate in mares in which hCG was delayed (follicle coasting) was higher ( P < .05) when treatments were given twice per day versus once per day. Administration of equine luteinizing hormone (eLH) in conjunction with eFSH did not have an advantage over mares treated only with eFSH.

Biological significance of follicular fluid discharged into the peritoneal cavity at ovulation in mares

Biological significance of follicular fluid discharged into the peritoneal cavity at ovulation in mares

Influence of reproductive stage at PRID™ insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID™ insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID™) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus ( n = 6), estrus ( n = 11) and diestrus ( n = 11). Plasma concentrations of progesterone at insertion (Day 1) of PRID™ differed among treatment groups (anestrus: 0.2–0.6 ng mL −1, estrus: 0.2–0.5 and diestrus: 1.6–10.8 ng mL −1; P < 0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2 ± 3.1 ng mL −1 h −1) followed by estrus (25.1 ± 2.7) and anestrus (21.0 ± 0.4 ng mL −1 h −1; P < 0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations ( R = 0.5; P < 0.05), but it did not correlate with the interval from PRID™ removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6 ± 28.6 ng mL −1 h −1) when compared to estrous and diestrous mares (349.7 ± 53.3 and 370.5 ± 40.3 ng mL −1 h −1; P < 0.05). Follicular size at PRID™ insertion had no effects on the intervals from PRID™ removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID™ were significantly correlated with the interval from coil removal to estrus ( R = −0.55, P < 0.05) and ovulation ( R = −0.72, P < 0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID™ removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID™ seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.

Effect of different doses of hCG on diameter of the preovulatory follicle and interval to ovulation in mares

Effect of different doses of hCG on diameter of the preovulatory follicle and interval to ovulation in mares

Effects of a gonadotropin-releasing hormone antagonist and altrenogest on luteinizing hormone concentration and ovulation in the mare

The objective of Experiment 1 was to determine a dose and frequency of gonadotropin-releasing hormone (GnRH) antagonist administration to effectively suppress serum luteinizing hormone (LH) concentration and to delay ovulation when administered to mares. The objectives of Experiment 2 were 1) to determine the effects of subcutaneous or intravenous administration of a GnRH antagonist or oral altrenogest on serum LH concentration in the estrual mare; and 2) to determine the effectiveness of human chorionic gonadotropin (hCG) in inducing ovulation in mares with suppressed LH concentrations. In Experiment 1, mares ( N = 20) were randomly assigned and treated with either 5% mannitol (control, single subcutaneous injection, 1 mL, at time 0; n = 5); low-dose GnRH antagonist (single subcutaneous injection, 0.01 mg/kg, at time 0; n = 5); frequent low-dose GnRH antagonist (subcutaneous injections, 0.01 mg/kg, at 0, 6, 18, and 24 hours; n = 5); or high-dose GnRH antagonist (single subcutaneous injection, 0.04 mg/kg, at time 0; n = 5). Both the frequent low-dose and high-dose GnRH antagonist treatments resulted in significantly lower LH concentrations compared with controls at 90, 102, and 114 hours after treatment ( P < .05). In Experiment 2, mares (N = 38) were randomly assigned and treated with subcutaneous sterile saline (control), altrenogest (oral), subcutaneous GnRH antagonist, or intravenous GnRH antagonist. LH concentration for the altrenogest group was lower than the control group at 3, 4, 18, and 30 hours after treatment ( P < .05). LH concentration for both the subcutaneous and intravenous GnRH antagonist groups were lower compared with the control group at several time points ( P < .05). Based on these data, dose but not frequency of administration of a GnRH antagonist lowered LH concentration in the estrous mare but did not delay ovulation. In addition, serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG. This indicates that serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG.

Serrated granulosa and other discrete ultrasound indicators of impending ovulation in mares

The incidence of discrete structural changes in the preovulatory follicle as ovulation approaches was studied sequentially by ultrasonography. Examinations were done every 12 hours in 27 mares, beginning when the follicle was ≥35 mm. The following discrete end points were recorded as present or absent: 1) serration of granulosa, indicated by an irregular or notched appearance; 2) decreased turgidity, indicated during transducer pressure; 3) loss of spherical shape; 4) an apex, indicated by a reduced area at one end; and 5) echoic spots floating in the antrum. When the records were examined as though scanning had been done only every 24 hours beginning at 35 mm, distinct serration was detected at the examination before ovulation in 37% of mares but not earlier. When mares were examined every 12 hours, serration was detected at the last examination in 59%. Decreased turgidity at the last 12-hour examination was detected concomitantly with serration, but was detected alone in 9% to 12% of previous examinations. Mares with serration at the last examination at 12-hour intervals were examined every hour thereafter (n = 14). Serration and decreased turgidity were present at each examination until ovulation 4.9 ± 0.7 hours later. Loss of spherical shape initially occurred less frequently than decreased turgidity, but the incidence increased from 50% to 100% during 6 to 1 hours before ovulation. The incidence of an apical area reached 100%, and echoic spots increased to 50% during the few hours before ovulation. Results indicated that serrated granulosa and the other discrete indicators were useful for predicting impending ovulation; however, optimal efficiency would require examinations every few hours.

Regression and resurgence of the CL following PGF 2α treatment 3 days after ovulation in mares

The present study was designed to characterize and compare the physiology and ultrasonographic morphology of the corpus luteum (CL) during regression and resurgence following a single dose of native prostaglandin F 2α (PGF) given 3 days after ovulation, with a more conventional treatment given 10 days after ovulation. On the day of pre-treatment ovulation (Day 0), horse mares were randomly assigned to receive PGF (Lutalyse ®; 10 mg/mare, i.m.) on Day 3 (17 mares) or Day 10 (17 mares). Beginning on either Days 3 or 10, follicle and CL data and blood samples were collected daily until post-treatment ovulation. Functional and structural regression of the CL in response to PGF treatment were similar in both the Day 3 and 10 groups, as indicated by an abrupt decrease in circulating concentrations of progesterone, decrease in luteal gland diameter and increase in luteal tissue echogenicity. As a result, the mean ± S.E.M. interovulatory interval was shorter ( P < 0.0001) in the Day 3 group (13.2 ± 0.9 days) than in the Day 10 group (19.2 ± 0.7 days). Within the Day 3 group, functional resurgence of the CL was detected in 75% of the mares (12 of 16) beginning 3 days after PGF treatment, as indicated by transient major (6 mares) and minor (6 mares) increases ( P < 0.05 and <0.1, respectively) in progesterone. Correspondingly, mean length of the interovulatory interval was longer ( P < 0.03) in mares with major resurgence (15.8 ± 1.6 days) than in mares with minor (11.2 ± 1.2 days) and no resurgences (13.5 ± 0.3 days) in progesterone. Structural resurgence of the CL in the Day 3 group and functional and structural resurgence in the Day 10 group were not detected. In conclusion, PGF treatment 3 days after ovulation resulted in structural and functional regression of the CL and hastened the interval to the next ovulation, despite post-treatment resurgences in progesterone.

Effects of recombinant human follicle stimulating hormone on follicle development and ovulation in the mare

The only gonadotrophin preparation shown to stimulate commercially useful multiple ovulation in mares is equine pituitary extract (EPE); even then, the low and inconsistent ovulatory response has been ascribed to the variable, but high, LH content. This study investigated the effects of an LH-free FSH preparation, recombinant human follicle stimulating hormone (rhFSH), on follicle development, ovulation and embryo production in mares. Five mares were treated twice-daily with 450 i.u. rhFSH starting on day 6 after ovulation, coincident with PGF 2α analogue administration; five control mares were treated similarly but with saline instead of rhFSH. The response was monitored by daily scanning of the mares’ ovaries and assay of systemic oestradiol-17β and progesterone concentrations. When the dominant follicle(s) exceeded 35 mm, ovulation was induced with human chorionic gonadotrophin; embryos were recovered on day 7 after ovulation. After an untreated oestrous cycle to ‘wash-out’ the rhFSH, the groups were crossed-over and treated twice-daily with 900 i.u. rhFSH, or saline. At the onset of treatment, the largest follicle was <25 mm in all mares, and mares destined for rhFSH treatment had at least as many 10–25 mm follicles as controls. However, neither dose of rhFSH altered the number of days before the dominant follicle(s) reached 35 mm, the number of follicles of any size class (10–25, 25–35, >35 mm) at ovulation induction, the pre- or post-ovulatory oestradiol-17β or progesterone concentrations, the number of ovulations or the embryo yield. It is concluded that rhFSH, at the doses used, is insufficient to stimulate multiple follicle development in mares.

Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device (PRID™) in mares

To investigate seasonal effects on the efficacy of estrus synchronization in mares, we administered a progesterone-releasing device (PRID™) intravaginally to eight Haflinger mares for 11 days. In January 3 of 8 mares responded to the treatment with estrus and ovulation, in March 7 with estrus and 6 of 7 mares with ovulation, in June 6 of 7 and in October 7 of 8 mares with estrus and ovulation. Follicle distribution patterns at PRID™ insertion were different between January/October, March/June and June/October ( P < 0.05). Number of follicles decreased during PRID™ treatment in January, March and June (difference of number of follicles at Day 12 minus number of follicles at Day 1: −4.2 ± 2.7, −0.9 ± 0.9 and −4.9 ± 1.5 follicles), while it increased in October (3.9 ± 1.2 follicles; P < 0.05). Mean progesterone concentrations were lowest in January (0.3 ± 0.1 ng mL −1) when compared with March (3.5 ± 1.8 ng mL −1; P = 0.063), June (4.4 ± 1.4 ng mL −1; P < 0.05) and October (2.2 ± 0.9 ng mL −1; P < 0.05). At Day 2 of PRID™ treatment, mean progesterone concentrations significantly increased in all mares. Except from January, mean LH concentrations decreased within one day after PRID™ insertion and remained at low levels during treatments in January and March. Total secretion of LH during PRID™-treatment was significantly lower in January and March when compared with June and October. In the 5 of 7 mares that ovulated during PRID™ treatment a distinct increase of plasma LH concentrations after ovulation was detected. Administration of the progesterone releasing intravaginal device PRID™ combined with the PGF2α analogue cloprostenol was able to induce estrus and ovulation in mares at different times of the year. However, efficacy of the treatment was not satisfactory concerning effectiveness in relation to season and synchrony of intervals from removal of PRID™ to ovulation in mares.

365 THE EFFECT OF ADMINISTERING PROGESTERONE AND ESTRADIOL PRIOR TO eFSH ON THE SUPEROVULATORY RESPONSE OF MARES

eFSH has been used to induce multiple ovulation in cycling mares. However, the response to eFSH is variable. Generally, eFSH is initiated 5 to 7 days after ovulation at a time when the follicular population on the ovaries may be variable. The objective of this study was to determine whether administration of progesterone and estradiol for 10 days prior to eFSH (Bioniche Animal Health, Athens, GA) would enhance the response to eFSH administration. Thirty normal cycling mares were assigned to 1 of 2 groups. Group 1: Control eFSH treatment - mares were examined daily with ultrasonography beginning 5 days after ovulation. Once the follicles in these mares reached 20 to 25 mm in size, eFSH treatment (12.5 mg, i.m.) was administered twice a day. Cloprostenol (Schering-Plough, Union, NJ, USA) treatment (250 �g) was administered on the second day of eFSH treatment. eFSH treatment continued until the majority of the cohort of follicles reached e35 mm. Treatment was stopped and after approximately 36 h hCG (2500 IU, i.v.; Chorulon; Intervet, Millsboro, MD, USA) was administered. Group 2: Injectable progesterone + estradiol (150 mg of progesterone and 10 mg of estradiol; P+E) treatment was initiated in diestrus (5 to 7 days post-ovulation) for 8 mares and in early estrus for 7 mares in this group. Injectable progesterone was continued for 10 days and Cloprostenol (250 �g) was administered on Day 10. Mares were then examined daily with ultrasonography and, once they had acquired 20- to 25-mm follicles, eFSH treatment was initiated. Twice-daily injections of eFSH (12.5 mg, i.m.) were continued until a majority of the cohort of follicles was e35 mm. hCG was administered approximately 36 h later. All mares were inseminated with 1 billion progressively motile spermatozoa from one of two stallions on the day of hCG administration and on the following day with cooled semen (1 billion progressively motile spermatozoa) from the same stallion. Data were analyzed by t-test and Fisher's Exact Test. The number of days of eFSH treatment was similar for the P+E (2) vs. the control (1) group (4.2 � 2.0 vs. 4.9 � 1.3 days, respectively). However, the number of ovulations induced in response to eFSH was greater for mares in the eFSH control (1) group (5.6 � 2.0) than for those in the P+E (2) group (3.0 � 1.9). Embryo recovery per flush was also greater for eFSH control (1) mares (2.7) vs. P+E (2) mares (1.1). Embryo quality was excellent or good for all embryos in both groups. Seventy-three percent of the mares (11 of 15) in both groups gave at least one embryo at each recovery attempt. However, more mares in the eFSH control (1) group gave two or more embryos (60%) compared to those in the P+E (2) group (20%). In summary, treatment of mares with P+E prior to eFSH treatment resulted in fewer ovulations, fewer embryos recovered, and fewer mares providing e2 embryos. Thus, there was no advantage in pretreating mares with P+E prior to eFSH treatment.