Effects of a new injectable short-term release deslorelin in foal-heat mares

Mares treated with subcutaneous deslorelin implants on the first postpartum estrus early in the breeding season had significant reductions in the number of large follicles at early pregnancy examinations and delayed return to estrus (in mares that failed to become pregnant); these adverse effects were attributed to a prolonged release of the drug from the implant. In 2003, an injectable short-term release (<24 h) deslorelin product became available. The objective of this study was to determine if this product would hasten ovulation in early foaling first postpartum estrus mares without reducing the number of large follicles at early pregnancy examination (14-15 days postovulation). Beginning 5-6 days postpartum, first postpartum estrus (foal-heat) mares were teased daily and examined thrice weekly (Tuesday, Thursday and Saturday) by transrectal ultrasonography. Mares in estrus with a follicle > or = 34 mm diameter on Tuesdays or Thursdays were alternately assigned to: Treatment 1, n = 17; 1.5 mg injectable short-term release deslorelin, or Treatment 2, n = 16; Control (no treatment). The schedule allowed accurate determination of the number of mares ovulating within 2 days of treatment (i.e., ovulations detected on Thursday or Saturday). Mares were mated on the day of treatment and at 2-day intervals until either ovulation was confirmed or until behavioral estrus ceased. Transrectal ultrasonography was done 14-15 days after ovulation to assess ovarian follicles and pregnancy status. Fewer covers were required and more mares ovulated within 2 days of treatment in deslorelin-treated versus Control mares (P < 0.01). Pregnancy rates were normal (69%) in deslorelin-treated mares. The number of large follicles 14-15 days after ovulation did not differ between deslorelin-treated and Control mares (P > 0.10), suggesting follicular suppression did not occur with this formulation of deslorelin.     

Pulsatile administration of gonadotropin-releasing hormone advances ovulation in cycling mares

Cycling standardbred mares were infused with saline or 20 micrograms gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (one 5-sec pulse/h, 2 h or 4 h) beginning on Day 16 of the estrous cycle. Although serum concentrations of luteinizing hormone (LH) increased significantly earlier in all three GnRH-treated groups (within one day of the initiation of infusion) compared to saline-infused controls, there were no differences in peak periovulatory LH concentrations among treatments (overall mean +/- SEM, 8.98 +/- 0.55 ng/ml). The number of days from the start of treatment to ovulation was significantly less in mares infused with 20 micrograms GnRH/h (mean +/- SEM, 2.9 +/- 0.6 days after the initiation of treatment, or 18.9 days from the previous ovulation; N = 7) compared to mares treated with saline (5.9 +/- 0.3 days, or 21.9 days from previous ovulation; N = 7) or 20 micrograms GnRH per 4 h (5.4 +/- 0.9 days or 21.4 days from previous ovulation; N = 5). Although mares infused with 20 micrograms GnRH/2 h ovulated after 4.3 +/- 0.7 days of treatment (Day 20.3; N = 7), this was not significantly different from either the control or 20 micrograms GnRH/h treatment groups. Neither the duration of the resulting luteal phase nor the length of the estrous cycle was different between any of the treatment groups (combined means, 14.7 +/- 0.2 days and 21.3 +/- 0.4 days, respectively). We conclude that pulsatile infusion of GnRH is effective in advancing the time of ovulation in cycling mares, but that the frequency of pulse infusion is a critical variable.     

The use of deslorelin implants for the synchronization of estrous in diestrous bitches

A novel approach to estrous induction in diestrous bitches is described. Twelve spontaneously cycling anestrous bitches served as controls. Thirteen anestrous and 15 diestrous bitches were induced to come into synchronous estrous using prostaglandin (diestrous bitches only) and deslorelin implants (Ovuplant). Implants contained either 2.1 or 1.05 mg deslorelin and were administered beneath the vestibular submucosa. All treated bitches came into estrous, regardless of implant size. Whereas all anestrous bitches ovulated, one of six diestrous bitches treated with the larger implant and three of nine treated with the smaller implant failed to ovulate. Induced bitches generally produced fewer corpora lutea than controls. Sixty-seven percent of control bitches became pregnant, with 0.63 fetuses per corpus luteum, whereas the pregnancy rate and fetuses per corpus luteum were 67 and 70% and 0.42 and 0.55 in the anestrous bitches induced with 1.05 and 2.1 mg deslorelin implants, respectively (not different from controls). Only 2 of 15 induced diestrous bitches conceived a detectable pregnancy, one of which was resorbed. In conclusion, although ovulatory estrous can be induced in bitches that had their most recent ovulation 40-100 days ago, these bitches are very unlikely to become pregnant during the induced estrous. The reason for the poor fertility in these diestrous bitches requires further study.     

Control of ovulation in cycling mares with ovarian steroids and prostaglandin

A combined progesterone-estradiol-17beta treatment was given in two experiments conducted to examine its effectiveness in controlling ovulation time in cycling mares. In the first experiment, the combined steroid (150 mg progesterone, 10 mg estradiol-17beta daily for 10 days) alone or combined with prostaglandin on the first and last days of steroid treatment resulted in ovulation in 15 of 16 mares 9-13 days after last injection, 13 of them on days 10-12. A CL present prior to treatment in one mare that received no prostaglandin persisted through and for 14 days after treatment. In the second experiment the combined steroid treatment started on the first or second day of estrus blocked ovulation in only 5 of 13 mares. Thus prostaglandin is necessary at least at the end of treatment. In both experiments a total of 20 mares with no luteal function at the end of steroid treatment ovulated on days 9-13 after last injection, 18 of these on days 10-12. These results indicate that the combined steroid-prostaglandin treatment can result in ovulations in a very restricted interval with apparently a normal distribution.     

Effects of hormone implants on estrus and ovulation in feral mares

Five groups of 30 captive feral mares each were implanted with silastic rods containing estradiol (E) and/or progesterone (P): E only with 8 g, P only with 24 g, P+HE with 8 g P + 8 g E, HP+E with 12 g P + 4 g E, HP+LE with 12 g P + 2 g E. Arbitrary group designations were differentiated by relative high (H) and low (L) amounts of steroid. Thirty mares received silastic rods containing no hormone (CI). Five mares from each group were bled every 2 wk for 4 mo and monthly for another 5 mo. All mares were tested for estrus by allowing them to stand in an alley between two pens of stallions and visually monitoring her response to the stallion. Serum P levels increased from 0.3 +/- 0.1 to 1.8 +/- 0.1 ng/ml in the P only group during the first 3 wk after implanting. Levels remained stable for the next 2 wk and then began a gradual decline. Serum P levels in the other groups were lower. Serum E levels were slightly increased in the groups receiving 8 g of E (E only and P+HE groups). Significantly fewer animals in the E only and P+HE groups exhibited estrus as compared with control animals (10 of 23 and 13 of 26 versus 22 of 25, respectively, P less than or equal to 0.003). However, animals receiving 24 g of P (P only) showed similar occurrences of estrus as controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of buserelin to induce ovulation in the cyclic mare

Inducing ovulation in a cyclic mare is often necessary. For this purpose, hCG has been used commonly, but the response can be reduced after successive administrations. The aims of this study were to test the effectiveness of buserelin in hastening ovulation in estrus mares, and its influence on fertility; and to investigate the effect of treatment on LH secretion. Five crossover trials were designed to compare the effect of two treatments: buserelin (40 microg in 4 doses i.v. at 12 h intervals) vs placebo (Experiments 1 and 2); buserelin 40 microg (in 4 doses i.v.) vs 20 microg (Experiment 3); buserelin (4 doses of 20 microg i.v.) vs hCG (1 dose of 2,500 IU i.v.) (Experiment 4); or buserelin (3 doses of 13.3 microg at 6 h interval) vs hCG (Experiment 5). In Experiment 2, blood samples were taken hourly until ovulation, for LH measurements. In Experiment 1, buserelin treatment significantly hastened ovulation. Reduction of the dose by half (Experiment 3) did not alter the effectiveness. In Experiments 4 and 5, buserelin was as effective as hCG in inducing ovulation between 24 and 48 h after initiation of treatment. Buserelin treatment induced a rise in LH concentration during the 48 h period of the experiment, and LH concentrations before ovulation were significantly higher in buserelin treated cycles than in placebo cycles. These experiments demonstrated the usefulness of two new protocols of administration of buserelin, as an alternative to hCG for induction of ovulation. One hypothesis explaining the mechanism of action is that the persistant rise in LH concentration could modify the ratio of biological/immunological LH, as it occurs physiologically, thereby hastening ovulation.     

Luteal blood flow during the estrous cycle in mares

Transrectal color Doppler ultrasound was used for the noninvasive investigation of luteal blood flow during the estrous cycle in six mares. Color was displayed in Power-Mode, in which the number of color pixels on the ultrasound image is related to the number of moving blood cells. Three pictures with a maximum number of color pixels of the corpus luteum (CL) during an examination period of about 20 min were selected and digitized on a laptop equipped with an external frame grabber card. The intra-class correlation coefficient for the number of color pixels was 0.90. In all estrous cycles similar patterns of changes in (C), in the cross-sectional area of sectional planes of the CL (A), and in plasma progesterone levels (P) occurred. Variance component estimates for the effect of the mare on (C), (A) and (P) were 14, 23 and 4%, for the influence of day of estrous cycle they were 41, 5 and 58% and for the effect of estrous cycle they were 7, 5 and 5%, respectively. There were high positive correlations between cyclic changes in (C) and (P) (r = 0.58; P < 0.0001). The increase in (C) between Days 0 and 5 (Day 0: ovulation) remained at high levels until Day 7 and then decreased until Day 15. There were relationships between (C) and (A) (r = 0.37; P < 0.0001) and between (A) and (P) (r = 0.24; P < 0.05), but correlation coefficients were not as high as between (C) and (P). Differences in (C), (A) and (P) between estrous cycles within mares and between mares were not related to each other (P > 0.05). The results show that transrectal color Doppler sonography is a useful, noninvasive method for examining luteal blood flow in mares, and that there are cyclic changes and individual differences in the vascularization of the CL. The possible influence of luteal perfusion on fertility in mares needs to be investigated in further studies.     

Evidence for ovulation and fertilization in beef cows with short estrous cycles

Calves were weaned from 15 Polled hereford anestrous cows 25 to 42 days after calving. In eight cows the uterus was flushed on day 6 or 8 after the first postweaning estrus (day 0), and in seven cows the oviduct ipsilateral to the ovary containing an ovulation papilla was removed and flushed on day 3. One ovum (morula) was recovered from the eight uterine flushings, while six ova were recovered from six of the seven oviductal flushings. Of the six, three were fertilized (4 to 8 cells), two unfertilized and only the broken zona pellucida of one was recovered. An ovulation papilla was observed in all cows at the time of oviduct removal. Six of the 15 cows had cycles less than 12 days, and from four of those six fertilized ova were recovered. The data indicate that previously anestrous cows ovulate at their first postweaning estrus and the ova released are capable of being fertilized. Failure to maintain pregnancy appears to be due to early corpus luteum regression.     

Body weight of mares and foals, estrous cycles and plasma glucose concentration in lactating and non-lactating Lipizzaner mares

This study summarizes weight development, plasma glucose concentrations and reproductive parameters in lactating (n = 46) and non-lactating Lipizzaner mares (n = 11) throughout the breeding season. It was the aim of the study to analyse if an energy deficit with possible effects on reproductive functions occurs at any time during the first 4 months of gestation. Mean gestation length was 334.3 +/- 7.3 days. Gestation of foals born in May/June was shorter (P < 0.01) than for foals born in March/April. Out of the 46 lactating mares, 44 ovulated between Days 8 and 18 postpartum and two mares ovulated on days 30 and 145, respectively. Pregnant mares were significantly (P < 0.001) heavier (600.1 +/- 5.3 kg) than non-pregnant mares (521.8 +/- 10.0 kg) at the beginning of the study. Birth resulted in weight reduction of 64.8 +/- 2.4 kg. During the first 2 weeks postpartum mares lost on average 3.0 +/- 1.8 kg and in the following 2 weeks gained 3.6 +/- 1.4 kg of weight. Thereafter, weight increased slightly but continuously (P < 0.01). At no time after foaling, weight differed significantly between groups. Weight of the foals three days after birth varied between 29 and 67 kg (53.7 +/- 1.1 kg). Average daily weight gain of foals was relatively constant throughout the study period (1.15 +/- 0.17 kg). Although lactation at no time was associated with a major weight loss, it had clear effects on energy metabolism as shown by constantly lower plasma glucose concentrations in lactating mares. Glucose concentrations decreased after foaling and were significantly lower in lactating mares from Weeks 3 to 16 after foaling than at corresponding times in non-lactating mares (P < 0.01). However, glucose concentrations were still within the physiological range. Mares seem to be able to compensate energy losses during lactation mainly by increasing feed intake and not by mobilisation of body fat.     

p- and m-Cresols emitted from estrous urine are reliable volatile chemical markers of ovulation in mares

Urine samples from 14 mares, belonging to five breeds, were collected at estrus and diestrus to search for estrous specific volatile compounds which could be used to determine ovulation time. Around 150 volatiles were collected from urine head-space samples by solid phase micro extraction technique, and analyses were conducted by gas chromatography-mass spectrometry methods. Comparison of chromatographic profiles of volatile substances revealed that concentrations of m- and p-cresols were significantly greater during estrus while diethylphthalate was more abundant at diestrus. Monitoring of m- and p-cresols during the period of estrus and a few days before and after estrus revealed irregular changes in amounts of cresols until 3-4 days before ovulation when the concentration of the compounds began to increase with peaks 1 day before ovulation. On the day when ovulation occurred, amounts of the metabolites decreased sharply, almost to basal concentrations, and remained at these concentrations for 6 days - when sampling was finished. In four of the mares changes in the concentration of diethylphthalate were less pronounced and more temporally variable compared with those of cresols. Based on reproducible temporal changes in concentrations of m- and p-cresols, with respect to the time of ovulation, a noninvasive test to determine a precise insemination time could occur. This would save time, reduce costs and simplify the procedure.     

Reproductive hormone secretions in pony mares subsequent to ovulation control during late winter

Beginning in December, pony mares were placed under a schedule of increasing light. Starting in February, onset of estrus was checked by daily teasing with a stallion. Mares were randomly assigned to one of three treatments (6 mares per group) administered in March. Treatments were: Group I — 75 mg progesterone injected intramuscularly every day for 10 days in combination with a 1.25 mg injection of PGF₂α on day 7 of progesterone treatment and a 2,000 IU injection of HCG on day 2 of estrus; Group II — a norgestomet ear implant inserted for 10 days in combination with 1.25 mg PGF₂α given 7 days after insertion and 2,000 IU HCG administered on day 2 of estrus; and Group III — same as II except that 2 mg of GnRH rather than HCG were administered on day 2 of estrus. Blood plasma for radioimmunoassay of progesterone, LH and estradiol was collected from the first day of treatment until 14 days after the end of estrus. Also in March, 6 mares were bled daily from the first day of estrus until subsequent estrus or day 21 (control estrus). Although estrus was detected in all mares, 14 of 18 mares ovulated subsequent to treatments and four of the six control estrus mares ovulated. Only among HCG treated mares was the ovulation rate higher (P < .05) than it was in the control estrus group. The interval from last progesterone injection or norgestomet implant removal to estrus did not differ between treatment groups. Concentrations of estradiol and LH were increased for several days around the time of ovulation and tended to be positively correlated with each other. In the mares that did not ovulate, concentrations of LH and estradiol appeared to be lower than in mares that ovulated. In summary, progestins in combination with PGF₂α and increasing light will synchronize estrus in mares during late winter and HCG will hasten ovulation in some mares.     

Uterine and ovarian blood flow during the estrous cycle in mares

Uterine and ovarian blood flow was investigated in four mares during two consecutive estrous cycles using transrectal color Doppler sonography. The uterine and ovarian arteries of both sides were scanned to obtain waves of blood flow velocity. The pulsatility index (PI) reflected blood flow. There were significant time trends in PI values of all uterine and ovarian blood vessels during the estrous cycle (P < 0.05). PI values did not differ between the uterine arteries ipsi- and contralateral to the corpus luteum or the ovulatory follicle. PI values of the uterine arteries showed a wave shaped profile throughout the estrous cycle. The highest PI values occurred on Days 0 and 1 (Day 0 = ovulation) and around Day 11, and the lowest PI values were measured around Days 5 and -2 of the estrous cycle. During diestrus (Days 0-15) PI values of the ovarian artery ipsilateral to the corpus luteum were significantly lower than PI values of the contralateral ovarian artery (P < 0.0001). No differences (P > 0.05) in resistance to ovarian blood flow occurred between sides during estrus (Days -6 to -1). In this cycle stage PI values decreased in both ovarian vessels (P < 0.05). During diestrus, high PI values of the ovarian artery ipsilateral to the corpus luteum were measured between Days 0 and 2, followed by a decline until Day 6 (P < 0.05). From this time on, the resistance to blood flow increased continuously until Day 15 (P < 0.05). The cyclic blood flow pattern in the contralateral ovarian artery was similar to that in the uterine arteries (r = 0.68; P < 0.0001). No correlations occurred between the diameter of the corpus luteum and the PI values of the ipsilateral ovarian artery (P > 0.05) during diestrus. During estrus, there was a negative relationship between growth of the diameter of the ovulatory follicle and changes in PI values of the dominant ovarian artery (r = -0.41; P < 0.05). PI values of the uterine arteries and of the ovarian artery ipsilateral to the ovulatory follicle were negatively related to estrogen (E) levels in plasma during estrus (uterine arteries: r = -0.21; P < 0.05; dominant ovarian artery: r = -0.35; P < 0.05). In diestrus, PI values of the dominant ovarian artery were negatively related to plasma progesterone levels (r = -0.38; P < 0.0001), but not the PI values of the uterine arteries (P > 0.05). The findings of this study show that there are characteristic changes in blood supply of the uterus and the ovaries throughout the equine estrous cycle. There are negative correlations between resistance to blood flow in the uterine and ovarian arteries and the plasma estrogen levels during estrus. In diestrus, there is a negative relationship between the resistance to ovarian blood flow and the progesterone levels.     

Uterine contractile activity in mares during the estrous cycle and early pregnancy

Transrectal ultrasonography was used to quantitate uterine contractile activity during the estrous cycle and early pregnancy in pony mares (nonbred, n = 9; pregnant, n = 16). Continuous 1-min scans of longitudinal sections of the uterine body were videotaped, and uterine activity scores (1=minimal activity, 5=maximal activity) were assigned to each tape segment. There was a tendency (P<0.06) for a main effect of reproductive status (nonbred versus pregnant), a main effect of day (P<0.0001), and a reproductive status by day interaction (P<0.006). Uterine activity scores were higher (P<0.05) in pregnant mares on Days 1, 11, 12, and 17 (Day 0=day of ovulation) than in nonbred mares. Maximal activity in pregnant mares occurred on Days 11 to 14 during the reported period of maximal embryo mobility. Activity scores decreased (P<0.05) between the day prior to and the day of fixation (mean = Day 15) of the embryonic vesicle. Activity scores were maintained at an intermediate level for several days following fixation before declining to minimal levels by 7 d postfixation. A postovulatory decrease (P<0.04) in activity scores was observed in nonbred mares, but not in pregnant mares, between Days 0 and 1 followed by a progressive increase (P<0.03) between Days 2 and 4. Maximal activity in nonbred mares occurred during the late luteal phase (Days 13 to 14), corresponding temporally to the reported onset of luteolysis.     

Effects of prostaglandin on estrous cycles,behavior and blood progesterone levels of American Saddlebred mares

Twelve American Saddlebred mares ranging in weight from 365 to 450 kg were given intramuscular injections of 2.5, 5.0 and 7.5 mg of Prostaglandin (PGF_2α) on day 6 of diestrus a mean length of control estrus and diestrus were 6.5 ± .6, 16.9 ± 1.0 days, respectively. The 2.5, 5.0 and 7.5 mg PGF_2α doses significantly (P < .01) shortened the length of the treatment diestrus to 10.8 ± 1.8, 9.9 ± .7 and 9.9 ± .7, respectively. The 2.5 mg dose was 90% effective in shortening the duration of diestrus while doses of 5.0 and 7.5 mg were 100% effective. No effects were noted on the mean length of estrus or diestrus following treatment. Peripheral plasma progesterone concentrations were measured by radioimmunoassay to determine the luteolytic effect of PGF_2α. As compared to the non-treatment estrous cycles, all three treatments caused a significant (P < .01) decline in peripheral plasma progesterone concentrations 24 and 48 hr after treatment. The 2.5 mg PGF_2α dose caused a drop in progesterone from 7.7 ± .4 on day 6 to 2.6 ± 1.0 and 2.1 ± .9 ng/ml 24 and 48 hr later, respectively. Similarly, 5.0 mg lowered the progesterone level from 7.7 ± .3 to 1.6 ± .6 and 1.5 ± .5 ng/ml, and the 7.5 mg dose lowered the progesterone level 7.5 ± .3 to 1.2 ± .2 and 1.3 ± .3 PGF_2α. Abdominal cramps were noted in some mares after treatment. The incidence and severity of these reactions increased with the dose of PGF_2α.     

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.     

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.     

Relationships between FSH surges and follicular waves during the estrous cycle in mares

Individual follicles >/=15 mm were monitored daily by ultrasonography in 12 mares during the estrous cycle. Follicular waves were designated as major waves (primary and secondary) and minor waves based on maximum diameter of the largest follicle of a wave (major waves, 34 to 47 mm; minor waves, 18 to 25 mm). Dominance of the largest follicle of major waves was indicated by a wide difference (mean, 18 mm) in maximum diameter relative to the second largest follicle. Dominant follicles of primary waves (n=12) emerged (attained 15 mm) at a mean of Day 12 and resulted in the ovulations associated with estrus (ovulation=Day 0). The dominant follicle of a secondary wave (n=1) emerged on Day 2 and subsequently ovulated in synchrony with the dominant follicle of the primary wave, which emerged on Day 9. The largest follicles of minor waves (n=4) emerged at a mean of Day 5, reached a mean maximum diameter 3 days later, and subsequently regressed. There was a significant increase in mean daily FSH concentrations either 6 days (primary wave) or 4 days (minor waves) before the emergence of a wave. Mean concentrations of FSH decreased significantly 2 days after emergence of the primary wave. Divergence between diameter of the dominant and largest subordinate follicle of the primary wave was indicated by a significantly greater mean diameter of the dominant follicle than of the largest subordinate follicle 3 days after wave emergence and by the cessation of growth of the largest subordinate follicle beginning 4 days after the emergence of a wave. Surges of FSH were identified in individual mares by a cycle-detection program; surges occurred every 3 to 7 days. Elevated mean FSH concentrations over the 6 days prior to emergence of the primary wave was attributable to a significantly greater frequency of individual FSH surges before wave emergence than after emergence and to an increase in magnitude of peak concentrations of FSH associated with individual surges.     

Ovulation synchronization following commercial application of ultrasound-guided follicle ablation during the estrous cycle in mares

A regimen of progesterone plus estradiol (P&E) was used as a standard for ovarian synchronization to test the efficacy and evaluate the commercial application of ultrasound-guided follicle ablation as a non-steroidal alternative for ovulation synchronization in mares. Recipient mares at a private embryo transfer facility were at unknown stages of the estrous cycle at the start of the experiment on Day 1 when they were randomly assigned to an ablation group (n=18-21 mares) or to a P&E group (n=20-21 mares). In the ablation group, mares were lightly sedated and all follicles > or = 10 mm were removed by transvaginal ultrasound-guided follicle aspiration. In the P&E group, a combination of progesterone (150 mg) plus estradiol (10mg) prepared in safflower oil was given daily (im) for 10 d. Two doses of prostaglandin F(2alpha) (PGF, 10mg/dose, im) were given 12 h apart on Day 5 in the ablation group, or a single dose on Day 10 in the P&E group. Human chorionic gonadotropin (hCG, 2500 IU/mare, im) was given at a fixed time, 6 and 10 d after PGF treatment in the ablation and P&E groups, respectively, with the expectation of a follicle > or = 30 mm at the time of treatment. In both the ablation and P&E groups, transrectal ultrasonography was done at the start of the study (Day 1) and again on the day of hCG treatment and daily thereafter to determine the presence of a CL, measure diameter of the largest follicle and detect ovulation. The mean interval from the start of the study and from PGF treatment to ovulation was shorter (P<0.0001) in the ablation group (13.7 and 9.7 d, respectively) compared to the P&E group (22.3 and 13.2 d, respectively). Following fixed-day treatment with hCG after PGF treatment, the degree of ovulation synchronization was not different (P>0.05) between the ablation and P&E groups within a 2-d (56 and 70%) or 4-d (83% and 90%) period. Although ultrasound-guided follicle ablation may not be practical in all circumstances, it excluded the conventional 10-d regimen of progesterone and estradiol and was considered an efficacious and feasible, non-steroidal alternative for ovulation synchronization in mares during the estrous cycle.     

Disruption of estrous cycles in exercise-trained rats

The female Sprague-Dawley rat was evaluated as an animal model for the menstrual irregularities that are common in women athletes. Daily vaginal smears revealed that estrous cycles were markedly disrupted in rats during a 10-week exercise training program, while cycles remained normal in sedentary rats. Compared to 9 sedentary rats, the 10 exercise-trained rats had longer mean cycle lengths and fewer estrus smears. Six of the exercise-trained rats, but none of the sedentary rats, had an "anestrus period" with more than twice the normal interval between estrus smears; one exercise-trained rat became essentially acyclic. Weight gain during the 10-week training program was lower in exercise-trained rats than in sedentary rats. Colonic temperatures, monitored at rest and during 30 min of exercise, were slightly lower in exercise-trained rats with irregular estrous cycles than in exercise-trained rats with regular cycles, indicating that unusually elevated body temperatures during exercise are not responsible for exercise-related reproductive acyclicity. It is concluded that the female Sprague-Dawley rat may be a useful animal model for the study of menstrual irregularities associated with exercise training.