Embryonic loss in pony mares induced by intrauterine infusion of Candida parapsilosis

Pony mares which were detected pregnant by transrectal ultrasonography received a single intrauterine infusion of either sterile saline (control, n = 12 mares) or 10(6)Candida parapsilosis (treated, n = 12 mares) between Days 11 to 14 postovulation. Subsequent embryonic loss was studied by daily ultrasonography of the mare's uterus, by serum progesterone levels, by endometrial swabs for cytologic and microbiologic examination and by endometrial biopsies that were taken after embryonic loss was detected. Significantly fewer (P<0.01) embryonic losses occurred in control than in treated mares (4 12 vs 12 12 ). The mean interval from intrauterine infusion until embryonic loss was 5.8 +/- 2.8 d for control mares (n = 4) and 2.1 +/- 0.2 d for treated mares (n = 12). Prior to embryonic loss, moderate to marked edema of the endometrial folds in 12 of 12 treated mares and free fluid in the uterine lumen of 5 of 12 treated mares were detected by ultrasonography. After embryonic loss, Candida parapsilosis was cultured from the uteri of 8 of 12 treated mares, and E . coli was cultured from the uteri of 2 of 4 control mares. Postloss endometrial smears had cytologic evidence of inflammation in 10 of 12 treated mares and 3 of 4 control mares. Intrauterine inoculation of C. parapsilosis consistently induced embryonic loss and may provide a basis to further study the relationship between endometritis and embryonic loss in mares.     

Control of estrus in the lactating postpartum mare with fluprostenol (ICI-81,008)

During the 1976 breeding season 68 mares (56 Thoroughbred and 12 Quarter Horse) were allotted to 4 treatment groups. On day 7, 8 or 9 post-ovulation or day 6, 7 or 8 after foal heat each of 28 mares was injected intramuscularly with 250 μg of the prostaglandin analogue ICI-81,008 (generic name fluprostenol). In the second group, 32 mares were bred at foal heat. Group 3 consisted of 9 mares, which were passed at foal heat and bred at the second postpartum estrus. In group four, 12 of the mares which had failed to conceive at foal heat were bred at the second estrus. Twenty-four prostaglandin treated mares returned to estrus 4.2±.4 days post-injection. The interestrual interval was shorter (P<.05) for prostaglandin treated mares (11.4±.6 days) than for previously mated second heat control mares (19.2±2.3). Also, the interval between parturition and second estrus was decreased (P<.05) in treated mares (24.5±.8 days) compared to group three (32.8±2.5 days). Duration of the second postpartum estrus was similar for both treated and control mares. Plasma progesterone levels in prostaglandin treated mares as determined by RIA were 7.5±.5 and 6.9±.5 ng/ml before treatment and at l hour post-injection, then dropped precipitously to near undetectable levels at 48 hours after injection. Pregnancy rate at 45 days was significantly higher (P<.05) in prostaglandin treated mares (78%) as compared to foal heat mares (48%) and mares which were passed at foal heat and bred at the second postpartum estrus (44%).     

Embryo loss following GnRH-induced ovulation in anovulatory mares

Two experiments were conducted using a 21-day GnRH analogue treatment regimen to induce ovulation in seasonally anovulatory mares. In Experiment 1, nontreated (n=20) and treated (n=83) mares were defined as having inactive ovaries (largest follicle相似文献   

Plasma and endometrial progesterone content following exogenous progesterone administration in mares

Intact and ovariectomized pony mares were treated with either progesterone in-oil or repositol progesterone. Serum progesterone, endometrial progesterone and endometrial histology were examined. There were no differences in serum or tissue progesterone between intact and ovariectomized mares. Serum and tissue progesterone were greater for progesterone in-oil treated mares than for repositol treated mares. Both progesterone in-oil and repositol progesterone initiated endometrial gland proliferation with no difference in response observed between the two preparations.     

Follicle and systemic hormone interrelationships during induction of luteinized unruptured follicles with a prostaglandin inhibitor in mares

The objective was to determine differences in follicle and reproductive hormone characteristics in mares with ovulatory and flunixin meglumine (FM)-induced anovulatory cycles. Estrous mares were given 1500 IU hCG when the follicle was ≥ 32 mm (0 h). In Experiment 1, control mares (n = 7) were not treated further. The remaining mares (n = 11) were given 1.7 mg/kg FM i.v. twice daily, from 0 to 36 h after hCG treatment. Blood samples and ultrasonographic examinations were performed every 12 h. All control mares ovulated normally between 36 and 48 h. In contrast, eight of 11 FM mares did not ovulate, but developed luteinized unruptured follicles (LUFs). Three FM-treated mares did not develop conventional LUFs. Plasma progesterone concentrations were lower (P < 0.05) in LUF mares at 96, 120, and 216 h than in controls, whereas plasma LH concentrations were higher (P < 0.05) between 108 and 120 h in LUF mares than in controls. Plasma concentrations of PGFM and estradiol did not differ significantly between groups. In Experiment 2, the three mares that did not develop LUFs were treated, during the consecutive cycle, with the same dose of FM but with increased frequency at zero, 12, 24, 30, 36, and 48 h after hCG. One mare formed a LUF, whereas the other two did not. These two mares had lower LH concentrations than LUF or control mares in the two consecutive cycles. In conclusion, systemic treatment with FM blocked ovulation in 73% of treated mares. Mares with LUFs had lower progesterone and higher LH concentrations than control mares.     

Use of leukocytes as treatment for endometritis in mares experimentally infected with Streptococcus equi subsp. zooepidemicus

This study compared four treatments for bacterial endometritis in mares experimentally infected with Streptococcus zooepidemicus. Twenty-five mares were used, 20 resistant and five susceptible to endometritis. Mares would be in estrus when infected. Twenty-four hours after inoculation, clinical, bacteriological and cytological examinations were performed and repeated until the first occurrence: negative cytology and no Streptococcus growth or the seventh day post-infection. All mares showed clinical signs of endometritis and were assigned to one of the following treatments: (1) intrauterine infusion of fresh leukocytes; (2) intrauterine infusion of frozen-thawed leukocytes; (3) intrauterine infusion of lysed leukocytes; (4) intrauterine infusion of recombinant human interleukin-8 (rhIL-8); (5) control. Mares were submitted to all treatments, with at least a 14-day interval between treatments in a Latin square design. Treatment did not affect (P=0.121) time needed for resistant mares to eliminate bacteria. Time needed for elimination of bacteria was similar in susceptible mares treated with fresh and frozen leukocytes (P=0.333). Susceptible mares treated with frozen leukocytes also did not differ from those treated with lysed leukocytes (P=0.227) for time to eliminate bacteria, but were significantly different (P>0.02) from those treated with rhIL-8 and control. In resistant mares, physical clearance ability was probably the responsible for bacterial elimination. Intrauterine infusions in susceptible mares with viable or lysed leukocytes associated or not to opsonizing factors, reduced the time to elimination of bacteria. Infusions with bactericidal effect (functional neutrophils and granules) was likely effective and responsible for the more rapid elimination of bacteria in susceptible mares.     

Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses

Despite a large body of safety data, concern exists that porcine zonae pellucidae (PZP) immunocontraception--used to manage wild horse populations--may cause out-of-season births with resulting foal mortality. Our study at Assateague, Maryland indicated the effects of immunocontraception on season of birth and foal survival between 1990 and 2002 on wild horses from Assateague Island. Among 91 mares never treated, 69 (75.8%) of foals were born in April, May, and June (in season). Among 77 treated mares, 50 (64.9%) were born in season. Of 29 mares foaling within 1 year after treatment (contraceptive failures), 20 (68.9%) were born in season. Of 48 mares treated for greater than 2 years then withdrawn from treatment, 30 (62.5%) of 48 foals were born in season. There were no significant differences (p <.05) between either treatment group or untreated mares. Survival did not differ significantly among foals born in or out of season or among foals born to treated or untreated mares. Data indicate a lack of effect of PZP contraception on season of birth or foal survival on barrier island habitats.     

Induction of follicular development and ovulation in seasonally acyclic mares using gonadotrophin-releasing hormones and progesterone.

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 of 4 mares treated with GnRH appeared to ovulate, but did not establish CL. Nine of 10 mares given GnRH analogue also developed follicles during the final treatment course, as did mares treated with progesterone only, while only 1 of 5 untreated control mares showed any ovarian development. Failure to induce final follicular maturation and CL development by this treatment regimen may be due to an inadequate LH surge at the time of the expected ovulation associated with the low preovulatory oestradiol-17 beta surge, possibly caused by the preceding FSH stimulation being inadequate or inappropriate. Progesterone treatment increased baseline FSH concentrations in GnRH-treated mares, and also stimulated follicular development in mares not treated with GnRH, indicating a possible role for progesterone in folliculogenesis and, indirectly, ovulation.     

The effect of GnRH on induction of follicular development and ovulation in anovulatory and ovulatory mares

The effects of estradiol cypionate (ECP) and GnRH injections were tested on mares during January and February. Sixteen mares were blocked on their ovarian status and equally allotted to two groups. Group one received daily injections of 500 μg ECP (im) for 14 days followed by a 21 day period of twice daily injections of 200 μg GnRH (im). Group two received the carrier vehicle.Mean length of diestrus of ovulatory mares was 14.3 ± 1.6 days and 17.8 ± 3.5 days for treated and control groups respectively. Corresponding estrus lengths were 8.0 ± 1.4 days and 6.3 ± 2.1 days. Plasma LH levels, number of follicles < 20 mm, number of follicles > 20 mm and diameter of the largest follicle in ovulatory mares were not significantly affected by treatment with ECP or GnRH.Anovulatory mares treated with ECP and GnRH exhibited estrus more frequently (54% and 70% of the time) than sham injected controls (17% and 15% of the time). Plasma LH levels were significantly elevated (P<.05) in anovulatory mares treated with GnRH. Also more follicles < 20 mm (P<.09) were detected on the ovaries of GnRH treated mares than on those of control mares. Effects of the treatment were transient since LH levels and ovarian activity were similar in both mare groups after cessation of treatment.     

Uterine defense mechanisms in the mare: The use of intrauterine plasma in the management of endometritis

Twenty-nine mares with either active or subclinical endometritis were treated with intrauterine infusions of their own plasma in one of two treatment schemes. Twenty-six mares actively infected, with an average of 2.4 years barren, were treated with combinations of saline irrigations and plasma infusions. Twenty-four showed clinical improvement and were bred, resulting in 15 pregnancies. Three mares with subclinical endometritis were treated post-breeding with a single plasma infusion and all became pregnant. The response to plasma infusions supports in-vitro observations which implicate serum-derived opsonins, particularly complement, as enhancers of phagocytic function.     

The efficacy of different hCG dose rates and the effect of hCG treatment on ovarian activity: ovulation, multiple ovulation, pregnancy, multiple pregnancy, synchrony of multiple ovulation; in the mare

Despite the widespread use of hCG to advance ovulation in the mare there is little information on efficacy of dose rates and any contraindications of its use. This study aims to investigate the effect of dose of hCG on ovulation within 48h and the effect of hCG on: ovulation, multiple ovulation (MO), pregnancy, multiple pregnancy (MP) rates and synchrony of MO; additionally whether any seasonal effect is evident. Sequential ultrasonic scanning was used to monitor the occurrence of ovulation, within 48h of treatment, in 1291 Thoroughbred mares treated with either 750iu hCG or 1500iu hCG s.c. Ovulation rate, type (single ovulations (SO), MO, synchronous, asynchronous) and subsequent pregnancy were then monitored in 1239 Thoroughbred mares on a commercial stud over 3 years, 536 of which were treated with 750iu hCG at mating, all mares were also allocated into groups according to month of mating. No significant difference existed between the two dose levels of hCG and no significant difference existed between treated and untreated mares in overall ovulations (1.32 and 1.28 respectively), MO (31.7% and 27.7%), pregnancy (65.1% and 65.6%) or MP rates (10.8% and 11.8%). There was no significant association between month of year and pregnancy or MP rates for either treated or control mares, nor for MO for untreated mares. A significant (p<0.05) association was evident between month and MO in treated mares, MO being lowest in April (22.3%). 95.9% of treated mares multiple ovulated within 48h compared with 90.7% controls, a near significant difference. In conclusion this study demonstrates that: (i) hCG dose of 750iu s.c. is just as effective in inducing ovulation within 48h as 1500iu, (ii) 750iu hCG has no significant effect on ovulation, MO, pregnancy or MP rates; (iii) a significant (p<0.05) association exists between season and MO in hCG treated mares; (iv) a tighter synchrony (ovulation within 48h) of MO is evident in hCG treated compared with control mares (p=0.052).     

Effect of passive immunization against inhibin on FSH secretion, folliculogenesis and ovulation rate during the follicular phase of the estrous cycle in mares

Physiological roles of inhibin in mares were investigated by means of passive immunization using an antiserum to inhibin that had been raised in a castrated goat. Eight mares were given an intravenous injection of either 100 mL (n = 4) or 200 mL (n = 4) of inhibin antiserum 4 d after a single intramuscular injection of PGF2 alpha on Day 8 after ovulation, 4 control mares were treated with 100 mL castrated goat serum in the same manner. Jugular vein blood samples were collected after treatment with the serum until 192 h post treatment. Follicular growth and ovulations were monitored by ultrasound examination at 24-h intervals. The ability of the inhibin antiserum to neutralize the bioactivity of equine inhibin was examined in vitro using a rat pituitary cell culture system. Suppression of secretion of FSH from cultured rat pituitary cells by equine follicular fluid was reversed by the addition of increasing doses of the inhibin antiserum, thereby indicating its bioactivity. Plasma levels of FSH and estradiol-17 beta were higher in mares treated with the inhibin antiserum. The ovulation rate was significantly higher in mares treated with antiserum (100 mL = 3.75 +/- 0.63; 200 mL = 4.50 +/- 0.65) than in control mares (1.25 +/- 0.25). These results demonstrate that inhibin is important in regulating FSH secretion and folliculogenesis in mares. They also show that neutralization of the bioactivity of inhibin may become a new method for the control of folliculogenesis and ovulation rate in mares.     

Serum calcium and magnesium concentrations and the use of a calcium-magnesium-borogluconate solution in the treatment of Friesian mares with retained placenta

The purpose of the present study was to compare serum calcium and magnesium concentrations in mares with or without a retained placenta (RP) and to evaluate treatment of mares with RP with oxytocin versus oxytocin combined with Ca-Mg-borogluconate solution. Blood samples were obtained within 12 h of foaling from Friesian mares with and without an RP (n = 90 and 65, respectively). Serum Ca and Mg concentrations were analyzed by atomic absorption spectrophotometry. In total, we treated 112 cases of RP in 101 Friesian mares by infusion of either oxytocin dissolved in saline solution or oxytocin dissolved in Ca-Mg-borogluconate solution. We defined RP as the failure to expel all or a part of the fetal membranes up to 3 h after delivery of the foal. We defined a positive response to the treatment as the passage of the entire placenta within 2 h after the infusion. Mares with RP had significantly lower serum calcium levels within 12 h of foaling than mares without RP. Serum magnesium levels showed no difference. Sixty-four percent of the mares treated with oxytocin in Ca-Mg-borogluconate solution responded positively to the treatment, compared to 44% of the mares treated with oxytocin in saline solution (P < 0.05).     

Ovarian superstimulatory response and embryo production in mares treated with equine pituitary extract twice daily

Equine pituitary extract (EPE), has been reported to induce multiple ovulation in mares, however ovulation rates are poor in comparison to those obtained in other species. Attempts to improve the effectiveness of EPE for induction of superovulation in cyclic mares has focused on daily frequency of EPE treatment. Two experiments were performed to compare the ovarian response of cyclic mares given EPE once or twice-daily. Mares were assigned to one of two treatment groups 6 to 8 days after ovulation: prostaglandin was given once and EPE (25 mg) was given once daily (Group 1) or twice daily (Group 2). In Experiment 1, more (P < 0.05) follicles > or = 35 mm were detected in mares treated with EPE twice daily (6.1 +/- 3.1) than in mares treated once a daily (2.0 +/- 0.6). In a second experiment, the embryo recovery rates of mares given the two EPE protocols used in Experiment 1 were compared. The number of ovulations per mare was higher (P < 0.05) for mares treated twice-daily (7.1 +/- 5.1, range 3 to 18) than for mares treated once daily (2.4 +/- 1.8, range 1 to 6). The number of embryos produced per mare was higher (P < 0.05) in mares in Group 2 (3.5) than in Group 1 (1.6). Although it is not clear whether the increased ovulation rate is due specifically to dose or frequency, twice-daily administration of a high dose of EPE significantly improved follicular development, ovulation and embryo recovery over the standard treatment of once-daily injection.     

Induction of ovulation during the postpartum period in the thoroughbred mare with a prostaglandin analogue,Synchrocept™

Breeding of mares at the foal heat is desirable, but the low pregnancy rate and the not infrequent occurrence of subsequent anestrus are a deterrent. A PGF_2a analogue, Synchrocept^? (prostalene), as a single 2 mg subcutaneous injection was used to induce ovulation, either during the corpus luteum phase subsequent to a foal heat (test group 1) or at a fixed interval of 20 days from parturition (test group 2) in mares that also had a foal heat. Mares with no signs of a foal heat were treated 20 days postpartum (test group 3). A total of 80, mostly Thoroughbred, mares were treated in more than 15 breeding centers in Northern Germany between mid-January and mid-May 1975. At the same locations and over the same time periods, 60 control mares (control group 1) were bred at the foal heat and 40 additional control mares (control group 2) were bred later than 25 days postpartum.In groups 1 and 2, treatment induced estrus in 95% of the mares and in group 3 estrus was induced in 68% of the mares. Of these animals, 92% were bred and 81% conceived on the average 28 days after parturition. The number of services per conception in mares treated was 25% lower (2.5) than in controls (3.2). Synchrocept acted as a luteolysin, but seems also to have induced heat and estrus in animals with plasma progesterone levels below 1 ng/ml, as has been reported previously. Neither mares nor foals showed detectable clinical signs of drug intolerance.     

The effect of transcervical uterine manipulations on establishment of uterine infection in mares under the influence of progesterone

Four pony mares were used in a cross-over study to investigate the effect of different treatments on experimentally-induced endometritis. The mares were treated with progesterone to facilitate establishment of uterine infections. They received an intrauterine infusion of Streptococcus zooepidemicus 5 days after the start of progesterone therapy. Five days later, they were treated by intrauterine infusions of 2 g ampicillin in 50 ml sterile water or by sterile water without antibiotic for 3 consecutive days. Prior to infusion of Strep. zooepidemicus , no bacteria were cultured from the uteri of the mares. However, 5 days after infusion of Strep. zooepidemicus and prior to antibiotic therapy, mixed bacterial growths were cultured from endometrial swabbings. After antibiotic therapy, ampicillin-resistant organisms were cultured from endometrial swabbings. Two other progesterone-treated mares received an intrauterine infusion of sterile phosphate buffered saline instead of bacteria. Mixed bacterial cultures were recovered 5 days later from the endometrial swabbings of these mares. It was concluded that the high circulating concentrations of progesterone were probably responsible for the treatment failure and that in clinical situations, therapy involving transcervical manipulations should not be administered when mares are in diestrus.     

Influence of exogenous progesterone on early embryonic development in the mare

The influence of exogenous progesterone on the development of equine oviductal embryos was determined based upon the recovery of Day-7 uterine blastocysts from treated mares (n=13) that were given 450 mg progesterone daily between Days 0 and 6 and from untreated control mares (n=13). Daily administration of 450 mg progesterone in oil significantly (P<0.02) increased serum progesterone concentrations in the treated mares. There was no significant difference in the recovery rate of Day-7 embryos between treated and control mares (8/13 versus 6/13, respectively). Embryonic development, assessed by morphologic evaluation, embryo diameter, and number of cell nuclei was not significantly different for embryos from treated and from control mares. The results of this study indicate that administration of progesterone beginning on the day of ovulation does not affect the embryo recovery rate or embryonic development, based on evaluation of uterine blastocysts recovered at Day 7 after ovulation.     

Effect of daily clenbuterol and exogenous melatonin treatment on body fat,serum leptin and the expression of seasonal anestrus in the mare

A small percentage of mature mares continue to exhibit estrous cyclicity during the non-breeding season which is of interest because of the importance of timing of the breeding season to the equine breeding industry. Previously, it was demonstrated that the continuation of estrous cycles was more likely to occur in mature than young mares. Additionally, an apparent association exists between elevated body fat and increased circulating concentrations of leptin, and the occurrence of estrous cycles during the non-breeding season. Two experiments were conducted to test the hypothesis that pharmacological manipulation of body fat and leptin by administration of the beta(2)-adrenergic receptor agonist clenbuterol, with and without continuous treatment with melatonin, would increase the proportion of mares entering anestrus or advance its timing. In Experiment 1, eight mature mares were administered clenbuterol (3.2 microg/kg) daily from October through January and six mares were untreated. In Experiment 2, eight mares were administered clenbuterol daily from June through December, eight mares were treated with continuous release melatonin implants, and seven mares were treated with both clenbuterol and melatonin. Melatonin treatment was included to confirm previous results that constant treatment with melatonin did not advance the timing of anestrus. In both studies, leptin concentrations (P<0.01, both experiments) and body fat percentage (P<0.01, Experiment 1; P<0.05, Experiment 2) declined in response to daily clenbuterol treatment. Unexpectedly, however, this decrease was attenuated in mares also treated with melatonin (P<0.05). Although treatment with clenbuterol was associated with a decline in body fat and circulating concentrations of leptin, the timing or proportion of mares exhibiting anestrus was not modified (P>0.05). The results demonstrate the manipulation of body condition via pharmacological intervention does not modify the mechanisms controlling seasonal anestrus in the mare.     

Systemic treatment with high dose of flunixin-meglumine is able to block ovulation in mares by inducing hemorrhage and luteinisation of follicles

Prostaglandins play an obligatory role during the process of ovulation in mammals. Ovulation can be blocked by intrafollicular administration of non-steroidal anti-inflammatory drugs (NSAIDs) in several domestic species including the mare as well as by systemic administration of these drugs in women. In the mare, the effect of systemic NSAIDs treatment on ovulation has not been critically studied. The objectives of this study were: a) to determine whether high dose of flunixin-meglumine (FM) administered systemically to mares during the periovulatory period was able to block ovulation; and b) to study the follicular ultrasound characteristics of FM treated mares. Six mares were used in the study during two consecutive estrous cycles. Each mare received 2 mg FM/kg i.v. twice a day starting at the time of treatment with hCG when the follicle reached a diameter of ≥ 32 mm and continuing until ovulation. During the consecutive control cycle (CON) the mares received the same dose of hCG but were not administered FM. During the FM cycles five of six mares failed to ovulate and collapse the preovulatory follicle; but echoic specks were observed within the follicles, which continued to grow until a mean diameter of 55 mm. Eventually, the follicular contents were organised and luteinised. All CON mares ovulated normally. In conclusion, when mares were treated with FM, they had a higher incidence of ovulatory failure and development of luteinised unruptured follicles (83%, P = 0.015) compared with untreated mares.     

Effect of GnRH treatment during the anovulatory season on multiple ovulation rate and on follicular development during the ensuing pregnancy in mares

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 was begun on 15 January and mares were categorized according to the largest follicle at start of treatment. The proportion of mares ovulating within 21 days increased significantly according to initial diameter of largest follicle (less than or equal to 15 mm, 9/25 mares ovulated; 15-19 mm, 13/21; 20-24 mm, 20/24; greater than 25 mm, 3/3). The multiple ovulation rate was greater (P less than 0.01) for treated mares (27/86 mares had multiple ovulations) than for control mares (2/35). Treated mares in which the largest follicle at start of treatment was greater than or equal to 25 mm had a higher (P less than 0.01) multiple ovulation rate (9/14) than did mares in which the largest follicle was less than 25 mm (18/72). The pregnancy rate for single ovulators was not different between control mares (26/30 pregnant mares) and treated mares (43/54).(ABSTRACT TRUNCATED AT 250 WORDS)