Continuous administration of low-dose GnRH in mares II. Pituitary and ovarian responses to uninterrupted treatment beginning near the autumnal equinox and continuing throughout the anovulatory season

We tested the hypothesis that continuous subcutaneous treatment with low-dose GnRH, administered to mares from late September/early October through March, would prevent the development of seasonal anovulation. Quarter Horse mares (n=20) were stratified by age and body condition score and assigned randomly to either a saline control (n=9) or a GnRH (n=11) treatment group. Gonadotropin-releasing hormone was delivered continuously via osmotic minipumps, with sham pumps placed in control mares. Initial pumps were inserted on Day 3 following ovulation or during the follicular phase if the next anticipated ovulation did not occur by 9 October. Delivery rate of GnRH was 2.5 microg/h (60 microg/day) for the first 60 days, followed by 5.0 microg/h (120 microg/day) thereafter. Pumps were replaced every 30 days. Eighty and 100% of all mares had become anovulatory by 1 November and 1 December, respectively, and remained anovulatory through the end of February. Neither serum concentrations of LH throughout the study nor total releasable pools of LH in March differed between groups. Although control mares that exhibited ovulatory cycles after study onset had greater (P<0.05) mean concentrations of LH during the follicular phase and metestrus compared to GnRH-treated mares, neither size of ovulatory follicles nor interovulatory intervals differed between groups. Serum concentrations of FSH were not affected by treatment, but were lowest (P<0.05) from November through January. Continuous infusion of low-dose GnRH, beginning soon after autumnal equinox and continuing until just after vernal equinox, failed to prevent the occurrence of or to hasten transition from seasonal anovulation.     

Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Continuous administration of low-dose GnRH in mares I. Control of persistent anovulation during the ovulatory season

Three experiments were conducted during the operational breeding season to confirm that continuous, subcutaneous infusion of low-dose GnRH would not disrupt established estrous cycles (Experiment 1), and test the hypotheses that a similar treatment would stimulate secretion of LH and induce development of ovulatory follicles in persistently anovulatory mares (Experiments 2 and 3). Treatment with GnRH (5 microg/h) increased (P<0.001) serum P4 during the luteal phase (7.7+/-0.5 versus 6.4+/-0.5 ng/mL), tended to increase serum LH (2.6+/-0.27 versus 1.9+/-0.25 ng/mL), and did not modify interovulatory intervals. In Experiment 2, GnRH treatment (2.5-5 microg/h) of persistently anovulatory mares increased (P<0.001) serum LH compared to controls (0.5+/-0.08 versus 0.1+/-0.03 ng/mL), with all GnRH-treated and no Control mares ovulating. Mares exhibiting Delayed Recrudescence (n=29) or Lactational Anovulation (n=18), were assigned randomly in Experiment 3 to receive either (1) GnRH/GnRH (n=23); 2.5 microg GnRH/h for 14 d (Period I) and 5 microg/h during the subsequent 28 d (Periods II and III); or (2) Control/GnRH (n=24); no treatment during Period I (control period) and GnRH treatments as in 1 during Periods II and III. Percentage of mares ovulating and pregnant during Period I was greater (P<0.05) for GnRH-treated than Control mares. Thereafter, cumulative ovulation frequency (85%), pregnancy (72%) and cycles/conception (1.3+/-0.2) were similar between groups; however, interval to conception was reduced (P<0.01) by 10.3 d in GnRH/GnRH compared to Control/GnRH.     

Factors affecting gestation length and estrus cycle characteristics in Spanish donkey breeds reared in southern Spain

This paper investigated gestation length and estrus cycle characteristics in three different Spanish donkey breeds (Andalusian, Zamorano-Leones, and Catalonian) kept on farm conditions in southern Spain, using data for ten consecutive breeding seasons. Gestation length was measured in 58 pregnancies. Ovarian ultrasonography was used to detect the ovulation, in order to ascertain true gestation length (ovulation-parturition). Pregnancy was diagnosed approximately 14-18 d after ovulation and confirmed on approximately day 60. Average gestation length was 362 ±15.3 (SD) d, and no significant differences were observed between the three different breeds. Breeding season had a significant effect (P < 0.01), with longer gestation lengths when jennies were covered during the early period. Breed, age of jenny, year of birth, foal gender, month of breeding, and type of gestation had no significant effect on gestation length.After parturition, foal-heat was detected in 53.8% of the postpartum cycles studied (n = 78), and ovulation occurred on day 13.2 ± 2.7. The duration of foal-heat was 4.7 ±1.7 d, with a pregnancy rate of 40.5%.When subsequent estrus cycles were analyzed, the interovulatory interval (n = 68) and estrus duration (n = 258) were extended to a mean 23.8 ± 3.5 and 5.7 ± 2.2 d, respectively. Both variables were influenced by the year of study (P < 0.03 and P < 0.001), whereas month and season of ovulation (P < 0.005 and P < 0.009, respectively) affected only interovulatory intervals. Estrus duration was significantly longer than that observed at the foal-heat (P < 0.006), and the pregnancy rate was 65.8%.This study provides reference values for true gestation length and estrus cycle characteristics in Spanish jennies. Breeding season affected gestation length in farm conditions. Also, seasonal influence was observed on the length of the estrus cycle (i.e., interovulatory interval), although foal-heat was not affected by environmental factors.     

Seasonal variation in the estrous cycle of mares in the subtropics

Data on the estrous cycles and sexual receptivity scores of 7 maiden Australian Stock Horse mares were used to study seasonal variation from December until the following November. Mares were grazed in paddocks containing both native and improved tropical pasture species. The study was conducted in South-East Queensland (27 degrees 27' South latitude). There were no differences between either the sexual receptivity or the lengths of natural (Mean=7.5 days, SEM=0.4) and PGF-induced estruses (Mean=7.6 days, SEM=0.4). Plasma estrogens were not related to differences in sexual receptivity scores between mares. The lowest incidence of estrus occurred at the time of the winter solstice (June 22) in the Southern Hemisphere. Winter estruses (Mean=9.3 days, SEM=0.8) were longer than those of summer (Mean=6.6 days, SEM=0.5) and autumn (Mean=6.6 days, SEM=0.9). Approximately 30% of estruses were anovulatory. Most of these occurred in autumn and winter (P<0.05). There was considerable variation in the occurrence of anovulatory estrus between mares. There were no differences between the lengths of ovulatory and anovulatory estruses. Ovulatory estruses were significantly longer in spring than in summer (P<0.05). There were no seasonal differences between the lengths of anovulatory estruses. The length of diestrus (Mean=16.6 days, SEM=0.3) was not affected by mare or season. Only 3 of the 7 mares did not cycle during winter (anestrus), as confirmed by progesterone concentrations of less than 1 ng/ml. Finally, there was no evidence of mares having 2 breeding seasons per year in this study.     

Estrous cycle characteristics and response to estrus synchronization in mammoth asses (Equus asinus americanus)

Breeding records from a herd of mammoth asses (Equus asinus americanus) maintained on pasture in southeast Texas from 1990 to 1998 were reviewed. Jennies were pasture or hand mated, and estrus was either observed while the jennies were on pasture or when exposed to a jack after being penned. Eighty-one estrus periods and 43 diestrus intervals were recorded in 33 jennies over 4 seasons of the year (January-March, April-June, July-September, and October-December). Estrous cycle length and the duration of estrus were similar among seasons. Over all seasons, estrous cycle length was 23.3 +/- 2.6 d, duration of estrus was 5.9 +/- 2.1 d, and diestrus length was 17.4 +/- 2.6 d (mean +/- SD). During these same 9 yr, 58 injections of PGF2 alpha (5 mg, i.m.) were administered to 38 jennies without regard to stage of estrous cycle. Seventy-six percent (44/58) of the jennies showed signs of estrus after PGF2 alpha treatment, with an interval to estrus of 4.4 +/- 1.6 d and a duration of estrus of 5.6 +/- 1.7 d. Two estrus synchronization schemes were also assessed. Trial 1 was performed in October to November 1996, and Trial 2 was performed in February to March 1998. In Trial 1 (Group PE + PGF, n = 10), each jenny was injected intramuscularly once daily for 10 d with 150 mg progesterone and 10 mg estradiol-17 beta in sesame oil, and PGF2 alpha (10 mg) was injected intramuscularly on the last day of treatment. In Trial 2 (Group PGF-2X, n = 11), each jenny was injected intramuscularly twice, 16 d apart, with 10 mg PGF2 alpha. All Group PE + PGF jennies responded to treatment. One jenny in Group PGF-2X did not respond to either injection of PGF2 alpha, while 2 jennies responded to the first but not the second PGF2 alpha injection (8 of 11 jennies returned to estrus and ovulated after the second PGF2 alpha injection). Duration of estrus was 6.8 +/- 1.9 d for Group PE + PGF and 7.1 +/- 1.8 d for Group PGF-2X jennies. Interval to estrus and interval to ovulation following the last treatment were 9.0 +/- 0.9 d and 14.5 +/- 1.7 d, respectively, in Group PE + PGF jennies, and 4.5 +/- 0.9 d and 10.4 +/- 1.8 d, respectively, for Group PGF-2X jennies. In summary, estrous cycle characteristics of mammoth asses are similar to those reported for standard jennies, and estrus synchronization schemes used in horses are effective in mammoth asses.     

Ovarian follicular activity and hormonal profile during estrous cycle in cows: the development of 2 versus 3 waves

Most estrous cycles in cows consist of 2 or 3 waves of follicular activity. Waves of ovarian follicular development comprise the growth of dominant follicles some of which become ovulatory and the others are anovulatory. Ovarian follicular activity in cows during estrous cycle was studied with a special reference to follicular waves and the circulating concentrations of estradiol and progesterone. Transrectal ultrasound examination was carried out during 14 interovulatory intervals in 7 cows. Ovarian follicular activity was recorded together with assessment of serum estradiol and progesterone concentrations. Three-wave versus two-wave interovulatory intervals was observed in 71.4% of cows. The 3-wave interovulatory intervals differed from 2-wave intervals in: 1) earlier emergence of the dominant follicles, 2) longer in length, and 3) shorter interval from emergence to ovulation. There was a progressive increase in follicular size and estradiol production during growth phase of each wave. A drop in estradiol concentration was observed during the static phase of dominant anovulatory follicles. The size of the ovulatory follicle was always greater and produced higher estradiol compared with the anovulatory follicle. In conclusion, there was a predominance of 3-wave follicular activity that was associated with an increase in length of interovulatory intervals. A dominant anovulatory follicle during its static phase may initiate the emergence of a subsequent wave. Follicular size and estradiol concentration may have an important role in controlling follicular development and in determining whether an estrous cycle will have 2 or 3-waves.     

Persistence of the luteal phase following ovulation during altrenogest treatment in mares

Two experiments were conducted to test the efficacy of altrenogest treatment in mares. The response to 15-d altrenogest treatment (Experiment 1) was characterized in 20 mares that were given 22 mg daily of altrenogest in oil (n = 10) or in gel (n = 10) from Day 10 to 25 after ovulation. In 17 mares, luteolysis occurred during altrenogest treatment (Day 17.7 +/- 0.5), while 2 mares retained their corpus luteum (CL), and 1 mare had a diestrous ovulation on Day 16, resulting in a prolonged luteal phase. Ten of the 17 mares in which the CL had spontaneously regressed returned to estrus after the end of treatment, and ovulated 5.7 +/- 0.8 d after the end of altrenogest treatment. Two of these 17 mares ovulated 2 and 3 d after the end of altrenogest treatment but ovulation was not accompanied by estrous behavior, and 5 mares ovulated during altrenogest treatment resulting in an interovulatory interval of 22.4 +/- 1.1 d (range: 20 to 25d). Five mares which ovulated during altrenogest treatment and 2 mares which ovulated during silent estrus after the end of altrenogest treatment failed to regress the CL around 14 d post ovulation, and had a prolonged luteal phase. In Experiment 2, the effect of altrenogest administered from luteolysis to ovulation on duration of the subsequent luteal period was analyzed. In 6 mares altrenogest was begun on Day 14 post ovulation and continued until the hCG-induced ovulation. The interval from ovulation during altrenogest treatment to spontaneous luteolysis was 45.6 +/- 2.4 d (range: 40 to 54d) in altrenogest-treated mares and was significantly longer than in 10 untreated control mares (14.5 +/- 0.3 d, range: 13 to 16d). The results suggest that the oil and gel altrenogest preparations are equally effective in modulating estrous behavior and time to estrus and ovulation. Altrenogest treatment started late in diestrus appears to result in a high incidence of ovulation during treatment and when luteolysis and ovulation occur during treatment; the subsequent luteal phase is frequently prolonged due to failure of regression of the CL.     

Aberrant blood flow area and plasma gonadotropin concentrations during the development of dominant-sized transitional anovulatory follicles in mares

Color Doppler transrectal ultrasound was used to evaluate blood flow area in the wall of dominant anovulatory follicles versus ovulatory follicles in mares during the transition between anovulatory and ovulatory seasons. Daily examinations were done in 11 control mares toward the end of the anovulatory season. In 13 separate mares, follicular fluid was collected from 30-mm follicles, and blood flow areas from control mares were used as a basis for designating the sampled follicle as either anovulatory or ovulatory. Blood flow area in the controls ranged from 0.18 to 0.35 cm(2) in six mares on the day of a 30-mm anovulatory follicle and from 0.25 to 0.86 cm(2) in 11 mares on the day of a 30-mm ovulatory follicle; the ranges did not overlap except for one follicle. In the controls, mean blood flow area was lower (P < 0.05) in the anovulatory group than in the ovulatory group for each day beginning with the first Doppler examination at 25 mm. For plasma LH in controls, an effect of follicle group (P < 0.0001) and an interaction (P < 0.0001) of group by day reflected lower (P < 0.05) concentrations in the anovulatory group on Days -6, -2, and 5-8 (Day 0 = 30-mm follicle). For plasma FSH, an interaction (P < 0.0001) reflected higher (P < 0.05) concentrations in the anovulatory group on Days -3 and 1-4. More (P < 0.05) statistically identified FSH surges occurred in the anovulatory group during Days -7 to 8. In the sampled mares, follicular-fluid concentrations of estradiol, free insulin-like growth factor-1, inhibin-A, and vascular endothelial growth factor were lower (P < 0.05) in 30-mm designated anovulatory follicles than in 30-mm designated ovulatory follicles. Results were interpreted as follows: 1) The future anovulatory dominant-sized follicle developed under an LH deficiency, 2) the LH deficiency led to reductions in blood flow area and in concentrations of follicular-fluid factors, and 3) the reduction in follicle production of FSH suppressors resulted in higher plasma FSH concentrations.     

Pharmacologic application of native GnRH in the winter anovulatory mare,I: Frequency of reversion to the anovulatory state following ovulation induction and cessation of treatment

The continuous, subcutaneous infusion of native GnRH into seasonally anovulatory mares stimulates the synthesis and secretion of LH without pituitary refractoriness, offering opportunities to markedly accelerate the timing of ovulation within the operational breeding season. Herein, we tested the hypothesis that ovarian cycles induced in winter anovulatory mares using continuous administration of native GnRH for 28 days, beginning in either early February or early March (North America) would not revert to an anovulatory state after treatment withdrawal. Anovulatory mares received sham pumps (control) or native GnRH (100 μg/h) for 28 days beginning from February 2 or 3 (GnRH-Feb) or March 2 or 3 (GnRH-Mar). Mean concentrations of LH were five- to seven-fold greater during February in the GnRH-Feb group compared with control and GnRH-Mar groups through February and ending on March 2 or 3. However, concentrations of LH returned to the winter baseline within 3 to 11 days after pump removal and all GnRH-Feb mares failed to remain cyclic after treatment withdrawal. Correspondingly, during March, concentrations of LH in the GnRH-Mar group were greater (P < 0.001) than in the control and GnRH-Feb groups during the 28-day treatment period. Follicular growth and frequency of ovulation (6/10 GnRH-Feb; 9/10 GnRH-Mar, 1/11 controls, respectively) were greater (P < 0.01) in GnRH-treated mares. Ovulatory cycles continued in five of nine GnRH-Mar mares that ovulated, with interovulatory intervals of 15 to 24 days; whereas, three of nine mares had extended (33–42 days) interovulatory intervals and one of nine mares had a persistent CL after cessation of treatment. In summary, continuous administration of native GnRH for 28 days, beginning in early February or March, elevated circulating LH adequately to stimulate follicular growth and ovulation up to 60 days earlier than in untreated controls. However, if continuous, subcutaneous infusion of GnRH is selected as the only pharmacologic or managerial intervention, and mares are not pregnant, treatment must be continued at least until the end of March. This will improve the likelihood of a normal interovulatory interval after treatment withdrawal.     

Factors influencing ovarian activity and sexual behavior of postpartum mares under farm conditions

Management of the postpartum period is one of the most important factors of stud farm medicine. In horses, owing to the long gestation period, the time from parturition to repeat conception needs be short to maintain an optimal yearly foaling interval. For this reason the features of postpartum ovarian activity and sexual behavior were studied under farm conditions. During 2 consecutive breeding seasons, 107 mares on 5 commercial horse farms were monitored after parturition by regular teasing, transrectal ultrasonography and blood sampling for progesterone. Foalings took place from January 1 to June 15. Body condition scoring was carried out within 5 d and at 60 to 65 d after parturition. The first ovulation occurred within 20 d after foaling in 84.1% (90/107) of the mares. The mean intervals from foaling to the first and second ovulations were 17.8 +/- 1.6 d (+/- SEM) and 40.9 +/- 2.7 d (+/- SEM), respectively. The mean intervals from parturition to the first and second ovulation (P < 0.001), the interovulatory interval (P < 0.01), the second follicular phase (P < 0.001), and the time until the first overt estrus (P < 0.01) were significantly longer in mares foaling before the vernal equinox. In the beginning of the breeding season the intervals from parturition to the first ovulation (P < 0.01), to the second ovulation (P < 0.01), and to the first overt estrus (P < 0.001) were significantly longer for primiparous mares than for multiparous animals. There was a tendency for an increased interovulatory interval and for a longer second follicular phase in mares with decreased body condition after parturition (P = 0.069, P = 0.089, respectively). Suckling and breed had no effect on postpartum ovarian activity. We concluded that under field conditions the resumption of cyclic ovarian activity and sexual behavior in mares after foaling are strongly affected by the season of parturition and parity. In some cases, body condition change and other factors may also play a role in influencing postpartum reproductive function.     

Effects of deslorelin or hCG administration on reproductive performance in first postpartum estrus mares

A tendency for deslorelin implants to suppress subsequent follicular growth and delay return to estrus following induced ovulation has been documented in nonlactating mares. To investigate this phenomenon in lactating mares, 22 broodmares in southeast Texas were administered either deslorelin or hCG to induce ovulation in the first postpartum estrus during February and March 2001. Mares were teased daily and examined twice weekly (Tuesdays and Thursdays) by transrectal ultrasonography. When a follicle >35 mm diameter was detected on Tuesday, mares were treated with either 2,500 U hCG administered intravenously or with one implant (2.1 mg) deslorelin administered subcutaneously. Mares were bred every other day until ovulation was detected or until they ceased behavioral estrus, and were examined 16 days after treatment to detect pregnancy. Follicular measurements were recorded for all mares during each examination, and interestrous intervals were recorded for mares not becoming pregnant. Treatment of mares with either hCG or deslorelin resulted in similar ovulatory responses and pregnancy rates. Deslorelin-treated mares had fewer ovarian follicles >20 mm in diameter 16 days after treatment than hCG-treated mares (P < 0.01). Interestrous intervals for mares failing to become pregnant on foal heat breeding were prolonged in deslorelin-treated compared to hCG-treated mares (P < 0.01). Date of treatment was negatively correlated with length of the interestrous interval in deslorelin-treated mares (P < 0.01), but was not correlated with length of interestrous interval in hCG-treated mares (P > 0.10). All mares failing to become pregnant from foal heat breedings became pregnant from later breedings, but the parturition to conception interval was prolonged in deslorelin-treated compared to hCG-treated mares that did not become pregnant on foal heat (P < 0.01).     

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 PGF2alpha 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.     

The effect of hormone treatments (hCG and cloprostenol) and season on the incidence of hemorrhagic anovulatory follicles in the mare: A field study

The association between use of hormone treatments to induce estrus and ovulation and the incidence of hemorrhagic anovulatory follicles (HAFs) was studied in a mixed population of mares (Equus caballus) during two breeding seasons in a commercial breeding clinic. Mares treated with cloprostenol (CLO) were more likely to develop HAFs than were mares with spontaneous cycles (P < 0.001) or those treated with human chorionic gonadotropin alone (P = 0.08). There was no significant effect of season on the incidence of HAFs. The mean (±SEM) interval from CLO treatment to beginning of HAF development was 6.1 ± 0.5 d. Age of mares with HAF cycles was not different (12 ± 1.3 yr; P > 0.05) from that of mares with ovulatory cycles (10.5 ± 1.5 yr).     

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.     

Postpartum reproductive performance in the multiparous mare fed to obesity

Twenty multiparous Quarter Horse mares were assigned to one of two treatment groups at 40 to 75 d of pregnancy. Group 1 was the control group and the mares were fed to maintain a moderate degree of body fat (condition score 5.5 to 7). Group 2 was the obese group and the mares were fed to achieve (prepartum) and then maintain (post partum) an extremely high degree of body fat (condition score 9). Estrous intensity was evaluated using subjective teasing scores ranging from 0 (rejection) to 4 (maximum receptivity). Mares were artificially inseminated beginning with the second postpartum ovulatory cycle; the study was terminated after 63 d of pregnancy. Duration of estrus, maximum teasing score and the number of mares exhibiting overt estrus (teasing score > 2) did not differ between treatment groups during the first and second postpartum ovulatory cycles. The intervals from foaling to first cycle ovulation, foaling to second cycle ovulation, and first to second cycle ovulation were also similar between treatment groups. All mares in both treatment groups conceived and maintained pregnancy. The first cycle conception rate and the number of cycles per conception did not differ between treatment groups. A high degree of body fat produced by overfeeding during gestation did not adversely affect postpartum reproductive performance in the multiparous mare.     

Ultrasonic characteristics of preovulatory follicle and ovulation in Caspian mares

The Caspian breed of horses is believed to be the direct descendant of the earliest equine animals. Some special characteristics of Caspian horse differentiate this breed of horses from other breeds. In the current study the ultrasonically observed characteristics of a preovulatory dominant follicle and the lengths of estrus, diestrus as well as some related parameters were studied during 42 interovulatory intervals in 11 healthy Caspian mares. The preovulatory dominant follicle deviated from subordinate follicles and became the largest follicle in the ovaries at Day −8.7±0.53 (Day 0=ovulation). Every mare was a single ovulator with ovulations more frequent from the left ovary than from the right (65% versus 35%). Mean length of estrus, diestrus, and interovulatory interval were 8.3±0.86, 13.8±0.59, and 22.1±0.40 days, respectively. The time interval from ovulation until the time in which the mares were no longer in estrus was 1.9±0.42 days.     

Route of prostaglandin F2alpha injection and luteolysis in mares (38519).

Nine groups of pony mares (3/group) were used in a 3 times 3 factorial experiment. The factors were dose of PGF-2 alpha (0, 0.25 of 1.25 mg and route of administration (im, iu or il). Mares were laparotomized and treated on day 7 postovulation. Jugular blood was collected for progesterone RIA at 0 (pretreatment) and 1,6,12,24,48, and 72 hr posttreatment. In mares given either 0.25 mg or 1.25 mg PGF-2alpha, progesterone concentrations were not significantly different among the three routes at any of the posttreatment times studied except at 6 hr posttreatment. In mares given 0.25 mg, progesterone concentrations at 6 hr was less (p less than 0.05) for mares injected im than for mares injected iu. Compared to pretreatment progesterone values, PGF2-alpha (0.25 mg and 1.25 mg groups combined) administration significantly decreased progesterone concentration by 12 hr posttreatment in mares injected im and 24 hr in mares injected iu or il. In the iu group, a significant increase in progesterone concentration occurred between 1 and 6 hr followed by a significant decrease at 12 hr posttreatment. There were no significant differences among the three routes for intervals from treatment to estrus or ovulation, length of posttreatment estrus or length of interovulatory interval. Injection of either 0.25 mg or 1.25 mg PGF-2alpha significantly shortened the interval from treatment to estrus. Although 0.25 mg tended to shorten the interval from treatment to ovulation and interovulatory interval, these two end points were significantly shortened only in mares given 1.25 mg PGF-2alpha. Results indicated that local administration (iu or il) did not improve the luteolytic efficacy of PGF-2alpha over systemic administration (im).     

Comparative study of the dynamics of follicular waves in mares and women

Deviation in growth rates of the follicles of the ovulatory wave begins at the end of a common growth phase and is characterized by continued growth of the developing dominant follicle (F1) and regression of the largest subordinate follicle (F2). Follicle diameters during an interovulatory interval were compared between 30 mares and 30 women, using similar methods for collecting and analyzing data. Follicles were tracked and measured daily by ultrasonography. Diameter at follicle emergence (mares, 13 mm; women, 6 mm) and the required minimal attained diameter for assessment of follicles (mares, 17 mm; women, 8 mm) were chosen to simulate the reported ratio between the two species in mean diameter of F1 at the beginning of deviation (mares, 22.5 mm; women, 10.5 mm). F1 emerged before F2 (P < 0.02) in each species, and the interval between emergence of the two follicles was similar (not significantly different) between species. Growth rate for F1 and F2 during the common growth phase was similar within species, and the percentage of diameter increase was similar between species. Proportionality between species in diameter of F1 at deviation (2.2 times larger for mares than for women) and at maximum preovulatory diameter (2.1 times larger) indicated that relative growth of F1 after deviation was similar between species. A predeviation follicle was identified in 33% of mares and 40% of women and was characterized by growth to a diameter similar to F1 at deviation but with regression beginning an average of 1 day before the beginning of deviation. The incidence of a major anovulatory wave preceding the ovulatory wave was not different between species (combined, 25%). Results indicated that mares and women have comparable follicle interrelationships during the ovulatory wave, including 1) emergence of F1 before F2, 2) similar length of intervals between sequential emergence of follicles within a wave, 3) similar percentage growth of follicles during the common growth phase, and 4) similar relative diameter of F1 from the beginning of deviation to ovulation. Similar follicle dynamics between mares and women indicate the mare may be a useful experimental model for study of folliculogenesis in women, with the advantage of larger follicle size.     

Follicular and FSH dynamics in ewes with a history of high and low ovulation rates

Daily transrectal ultrasound scanning and twice-daily blood sampling were used to monitor the temporal relationships between FSH concentrations and follicle development during complete interovulatory intervals for ewes in which the ovulation rate in each of the 2 previous years was high or low (> or = 3 and < or = 2 ovulations, respectively). Follicles that reached > or = 5 mm were used to define a follicular wave and were tracked retrospectively to 3 mm (emergence). The hypothesis that FSH surges (identified with a computer program) and follicular waves (retrospectively determined based on ultrasound scanning) are temporally associated was supported in both groups by the emergence of an anovulatory or ovulatory follicular wave near the peak of an FSH surge. Further support for the hypothesis was a significant increase in FSH concentrations before and a significant decrease after follicular-wave emergence in both groups independent of the identification of FSH surges. Ewes with a history of high ovulation rates had smaller follicles (anovulatory and ovulatory) and more ovulations, but the 2 groups were similar in the number of ovulatory follicular waves and associated FSH surges, number and characteristics of the FSH surges, and mean FSH concentrations per interovulatory interval. Surges of FSH were periodic (every 3 or 4 d) regardless of the ovulation-rate group or follicle response. In ewes with a low ovulation rate, the nonovulatory FSH surges were most frequently associated with emergence of detected anovulatory follicular waves. In ewes with a high ovulation rate, more FSH surges were not associated with a detected follicular wave, as defined, presumably because the largest follicle did not reach 5 mm. The results indicated that the factors resulting in a high ovulation rate were not exerted through circulatory patterns or concentrations of FSH but involved a shorter growth phase and smaller maximal diameter of follicles.