Changes in patterns of luteinizing hormone secretion before and after the first ovulation in the postpartum mare

To determine whether luteinizing hormone (LH) secretion during the first estrous cycle postpartum is characterized by pulsatile release, circulating LH concentrations were measured in 8 postpartum mares, 4 of which had been treated with 150 mg progesterone and 10 mg estradiol daily for 20 days after foaling to delay ovulation. Blood samples were collected every 15 min for 8 h on 4 occasions: 3 times during the follicular phase (Days 2-4, 5-7, and 8-11 after either foaling or end of steroid treatment), and once during the luteal phase (Days 5-8 after ovulation). Ovulation occurred in 4 mares 13.2 +/- 0.6 days postpartum and in 3 of 4 mares 12.0 +/- 1.1 days post-treatment. Before ovulation, low-amplitude LH pulses (approximately 1 ng/ml) were observed in 3 mares; such LH pulses occurred irregularly (1-2/8 h) and were unrelated to mean circulating LH levels, which gradually increased from less than 1 ng/ml at foaling or end of steroid treatment to maximum levels (12.3 ng/ml) within 48 h after ovulation. In contrast, 1-3 high-amplitude LH pulses (3.7 +/- 0.7 ng/ml) were observed in 6 of 7 mares during an 8-h period of the luteal phase. The results suggest that in postpartum mares LH release is pulsatile during the luteal phase of the estrous cycle, whereas before ovulation LH pulses cannot be readily identified.     

Progestagen,androgen and oestrogen levels in plasma and ovarian follicular fluid during the oestrous cycle of the mare

The pattern of steroid hormone concentrations in the blood plasma of five mares was determined throughout eight oestrous cycles by radioimmunoassay. In three other mares the steroid hormone concentrations in the follicular fluid of 16 isolated follicles (⪖ 1 cm diameter) from both ovaries were analyzed on the first and third day of behavioural oestrus.The plasma levels of pregnenolone and progesterone as well as their 17α-hydroxylated metabolites showed similar ranges of concentration throughout the oestrous cycle. Luteolysis occurred 6 days prior to ovulation and was accompanied by a drop of all progestagens. Throughout the oestrous period (5 days prior to and including the day of ovulation) mean plasma concentrations of progestagens were <0.5 ng/ml and increased significantly one day after ovulation. Maximum plateau values were reached on day 6 after ovulation. A distinct (but not statistically significant) rise of androstenedione and testosterone plasma levels occurred during oestrus whereas dehydroepiandrosterone values increased significantly 6 days prior to ovulation and reached a maximum mean value of 1.14 ng/ml one day before ovulation. Levels then declined significantly on the day of ovulation. Oestrone and oestradiol-17β plasma concentrations increased significantly 4 and 3 days prior to the day of ovulation, respectively, and both remained elevated until one day before ovulation.A significant positive correlation could be detected between increasing follicle diameters and androstenedione as well as oestradiol-17β concentrations in the follicular fluid, whereas pregnenolone values showed a negative correlation with follicular diameter. Oestradiol-17β could be determined in 9 of the 16 follicular fluid samples. In 8 of these 9, oestradiol-17β predominated over all other steroid hormones.In view of the low concentrations of dehydroepiandrosterone detected in the follicular fluid, it is suggested that the increase in peripheral plasma values during oestrus is caused by an extra-follicular source(s).     

FSH and LH concentrations in periparturient mares.

The influence of the ovaries and presence of a foal on periparturient concentrations of FSH and LH were studied in 19 Pony mares. In intact and ovariectomized mares, mean concentrations of FSH fluctuated between 1.1and 9.9 ng/ml on Days -14 to-1 before parturition (Day 0). A surge of FSH occurred in all mares in association with parturition. From Days 1 to 10, the high levels of FSH gradually decreased in the intact group to the minimal concentrations that occur during oestrus, but remained elevated in the ovariectomized mares. There were no significant pre-partum changes in LH in either type of mare. Post-partum changes in LH concentrations increased at a similar rate in ovariectomized and intact mares. The presence of a foal significantly lengthened the interval to first oestrus, depressed LH levels on Days 6--10 and decreased the FSH concentrations as averaged over the 10 days before the first ovulation after parturition.     

Use of bovine follicular fluid to increase ovulation rate or prevent ovulation in sheep

Romney ewes were injected intramuscularly once or twice daily for 3 days with 0, 0.1, 0.5, 1 or 5 ml of bovine follicular fluid (bFF) treated with dextran-coated charcoal, starting immediately after injection of cloprostenol to initiate luteolysis on Day 10 of the oestrous cycle. There was a dose-related suppression of plasma concentrations of FSH, but not LH, during the treatment period. On stopping the bFF treatment, plasma FSH concentrations 'rebounded' to levels up to 3-fold higher than pretreatment values. The mean time to the onset of oestrus was also increased in a dose-related manner by up to 11 days. The mean ovulation rates of ewes receiving 1.0 ml bFF twice daily (1.9 +/- 0.2 ovulations/ewe, mean +/- s.e.m. for N = 34) or 5.0 ml once daily (2.0 +/- 0.2 ovulations/ewe, N = 25) were significantly higher than that of control ewes (1.4 +/- 0.1 ovulations/ewe, N = 35). Comparison of the ovaries of ewes treated with bFF for 24 or 48 h with the ovaries of control ewes revealed no differences in the number or size distribution of antral follicles. However, the large follicles (greater than or equal to 5 mm diam.) of bFF-treated ewes had lower concentrations of oestradiol-17 beta in follicular fluid, contained fewer granulosa cells and the granulosa cells had a reduced capacity to aromatize testosterone to oestradiol-17 beta and produce cyclic AMP when challenged with FSH or LH. No significant effects of bFF treatment were observed in small (1-2.5 mm diam.) or medium (3-4.5 mm diam.) sized follicles. Ewes receiving 5 ml bFF once daily for 27 days, from the onset of luteolysis, were rendered infertile during this treatment period. Oestrus was not observed and ovulation did not occur. Median concentrations of plasma FSH fell to 20% of pretreatment values within 2 days. Thereafter they gradually rose over the next 8 days to reach 60% of pretreatment values where they remained for the rest of the 27-day treatment period. Median concentrations of plasma LH increased during the treatment period to levels up to 6-fold higher than pretreatment values. When bFF treatment was stopped, plasma concentrations of FSH and LH quickly returned to control levels, and oestrus was observed within 2 weeks. The ewes were mated at this first oestrus and each subsequently delivered a single lamb.     

Plasma prolactin concentrations and cyclic activity in pony mares during parturition and early lactation

Five pony mares were blood sampled during late pregnancy, foaling and early lactation. An homologous assay for horse prolactin was used to measure plasma prolactin concentrations in these samples. Regular estimates of cyclic activity were also made. Plasma prolactin concentrations rose markedly in the last week of pregnancy and remained high although variable in early lactation, before declining to basal levels by 1-2 months post partum. All mares showed a post-partum oestrus 7.0 +/- 0.9 days after parturition. One mare whose foal died shortly after birth showed a rapid decline in plasma prolactin values after death of the foal and an early oestrous period (4 days after parturition). The pattern of prolactin changes reported for the mare are in agreement with those reported for other mammalian species.     

Ovulation rate and distribution in the thoroughbred mare, as determined by ultrasonic scanning: the effect of age

Ovarian activity was monitored in 2181 oestrous cycles from 1136 thoroughbred brood mares to accurately determine overall ovulation rate, the relative distribution of ovulations between left and right ovary, whether mare age had an effect on these parameters and whether ovulation pattern in one cycle affected the pattern within the next. Ultrasonic scanning was used in preference to rectal palpation and slaughterhouse material due to its greater accuracy. Mare's ages ranged from 3 to 22 years. The results obtained indicated a similar incidence of ovulation occurring on the right (49.5% of all ovulations) or left ovary (50.5%). Multiple ovulations (MO) occurred in 22.4% of oestrous cycles. Significantly (P<0.01), more double ovulations (DO) were bilateral (57.2%) than unilateral (42.8%); 20.7% were unilateral right and 22.1% were unilateral left. There were 828 mares grouped into six age groups: A (3-5 years), B (6-8 years), C (9-11 years), D (12-14 years), E (15-18 years), F (18-22 years). The distribution of ovulation between the left and right ovary was not affected by age group, but significant association (P<0.01) was evident between age and MO. Group A had 15% of cycles resulting in MO compared to 19.4, 24.6, 25.8, 28.6 and 35.1% in groups B-F, respectively. A significant (P<0.01) association between MO in successive cycles was also demonstrated, with a greater chance (P<0.05) of successive single ovulations (SO) being on alternate ovaries. There was no significant repeatability of the classification of DO in one cycle compared to the next. We conclude that: (i) the mare is a symmetrical ovulator; (ii) 22.4% of cycles yield MO (ovulation rate 1.23); (iii) this MO incidence increased (P<0.01) with age; (iv) the exhibition of MO in one cycle was linked to an increased probability (P<0.01) of a MO occurring at the next one and (v) SO in one ovary was more likely (P<0.05) to be followed by a SO on the alternate ovary during the next cycle.     

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.     

Luteinizing hormone, oestrogen and progesterone levels in peripheral serum of anoestrous and cyclic ewes as determined by radioimmunoassay.

Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean plus or minus S.E. value of 2-3 plus or minus 0-9 ng/ml. High LH values of 20-0, 41-2 and 137-5 ng/ml were observed in three ewes on Day - 24 of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0.11 plus or minus 0-01 ng/ml) before Day - 25 of anoestrus. A major rise occurred on Day - 12 of anoestrous and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4-40 plus or minus 0-1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5-2 plus or minus 0-3 pg/ml. A well-defined peak of 13-3 plus or minus 0-7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day - 25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.     

Reproduction in high body condition mares with high versus low leptin concentrations

Previous results from our laboratory indicated that a majority of mares with high body condition scores (BCS) displayed estrous cycles or had considerable follicular activity during the winter. Among these high BCS mares, about 35% of them exhibited a persistent hyperleptinemia and hyperinsulinemia. The current experiment was designed to compare the reproductive characteristics of high BCS mares with hyperleptinemia to those with normal (low) plasma concentrations of leptin during the winter and the first estrous cycle (or the first full cycle encountered for those already cycling). Light horse mares with high BCS (6-8.5) were assigned to groups based on leptin concentrations (8/group): low (<5 ng/mL) and high (>10 ng/mL). Beginning 7 January, mares were assessed every 3d for follicular activity and then daily once a follicle >25 mm was detected. Mares were subsequently monitored through their first and second ovulations. Leptin concentrations remained higher (P<0.001) in mares in the high leptin group over the duration of the experiment. Also, high leptin mares had greater (P<0.0001) insulin response to glucose infusion and a faster (P<0.05) rate of glucose clearance. One mare with high leptin and three mares with low leptin had progesterone concentrations indicative of the presence of a corpus luteum at the onset of the experiment. Plasma concentrations of LH, FSH, and progesterone did not differ between groups (P>0.1) during the first estrous cycle occurring after 7 January. Date of first ovulation after 7 January and interovulatory interval were similar (P>0.1) for the two groups, as were estimates of follicular numbers on the ovaries (small, medium, and large; P>0.1). It is concluded that the perturbations in leptin and insulin secretion observed in some high BCS mares are not associated with alterations in ovarian activity or the estrous cycle during winter and into the period of vernal transition.     

The effect of intrauterine and cervical manipulation on the equine oestrous cycle and hormone profiles.

Endometrial biopsy or endometrial biopsy and uterine culture taken on Day 4 after oestrus induced lysis of the corpus luteum (CL), resulting in a sharp decline in serum progesterone concentration and shortened the interoestrous interval in 8/12 and 32/33 oestrous cycles, respectively, during 2 experiments. Cervical dilatation 4 days after oestrus shortened the interoestrus interval in 5/10 and 0/5 oestrous cycles. Endometrial biopsy and culture on Days 1 and 3 after oestrus also induced CL lysis during 4 of 7 cycles. Total oestrogen (oestrone plus oestradiol) concentrations increased at the onset of the subsequent oestrus in mares biopsied on Day 4 of dioestrus or in control cycle oestrous periods. Endometrial biopsy also induced lysis of the CL in mares with persistent luteal function. It is postulated that intracervical or intrauterine manipulations during the luteal phase of the oestrous cycle may directly, or indirectly, stimulate the release of an endogenous luteolysin (prostaglandin) resulting in CL regression, followed by oestrus and ovulation in the mare.     

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)     

Comparison of the effects of two GnRH antagonists on LH and FSH secretion,follicular growth and ovulation in the mare

The effects of two GnRH antagonists were tested in order to delay and/or synchronise ovulation in mares. Five mares received Antarelix (0.01 mg.kg(-1)), 5 mares received Cetrorelix (the same dose), 5 mares (control mares) received the vehicle intravenously, twice daily, for 8 days from the day the largest follicle reached 22 mm following prostaglandin administration. Ovulation was postponed in all mares injected with Antarelix (19.4 +/- 1.2 days after the beginning of the treatment) and in 2/5 mares injected with Cetrorelix (20 +/- 1 days) vs. 6.2 +/- 0.4 days in control mares. During the treatment, LH concentrations were strongly depressed in Antarelix and in Cetrorelix mares (1.6 +/- 0.1 and 3.8 +/- 0.5 ng.mL(-1) respectively vs. 21 +/- 2.5 ng.mL(-1) in control mares). In the 3 Cetrorelix mares which ovulated during the treatment. 2 initiated their LH surge at this moment. FSH concentrations were not affected in Antarelix or in Cetrorelix mares during the treatment (11.4 +/- 1.3 and 7.9 +/- 0.8 ng.mL(-1) respectively vs. 10.5 +/- 0.8 ng.mL(-1) in control mares). In conclusion, Antarelix seems more efficient than Cetrorelix for postponing ovulation in mares. The role of LH in antral follicular development before the preovulatory stage is confirmed.     

Evaluation of two treatments in superovulation of mares

The efficiency of superovulating mares with an enriched fraction of equine follicle-stimulating hormone (feFSH) and an equine pituitary extract (EPE) with similar FSH content but differing in the LH amount was compared. Mares were randomly assigned to an feFSH (n = 5) or EPE (n = 5) treatment. The experimental period was of 2 successive estrous cycles, with the first cycle as the control. At Days 6 and 7 of the estrous cycle, the mares received 250 micrograms i.m. cloprostenol. The treatments consisted of daily injections of 25 mg feFSH or EPE beginning on Day 6 post ovulation. Mares were inseminated every other day until the last ovulation was detected. When the mares in the control and treatment cycles developed at least 1 or 2 > or = 35-mm follicle, respectively, the treatment was interrupted, and a single injection of EPE (25 mg, i.v.) was administered to induce ovulation(s). Nonsurgical embryo recovery was performed 6 or 7 d after ovulation in both control and treatment cycles. The number of ovulations per mare was not significantly different (P > 0.05) between feFSH and EPE groups, but both were higher (P < 0.05) than that of the control cycle. The number of recovered embryos per ovulation was similar (P > 0.05) for control, feFSH and EPE groups. The high amount of LH presented in EPE did not affect the superovulatory response of the mares. Superovulatory treatments increased the ovulation rate of mares but did not affect the embryo recovery rate per ovulation.     

Temporal relationships among LH, estradiol, and follicle vascularization preceding the first compared with later ovulations during the year in mares

Diameter of the preovulatory follicle, plasma concentrations of LH and estradiol, and vascularization of the follicle wall, based on color-Doppler signals, were characterized in 40 pony mares for 6 days preceding ovulation (Days -6 to -1; preovulatory period). Comparisons between the preovulatory periods preceding the first compared with a later ovulation during the year were used to study the relationships between LH and estradiol and between vascularization and estradiol. Diameter of the preovulatory follicle was greater (P<0.02) and concentration of LH was less (P<0.02) during the first preovulatory period, whereas concentration of estradiol was not different between the first and second preovulatory periods. Vascularized area (cm(2)) of the follicle wall increased at a reduced rate during the first preovulatory period, as indicated by an interaction (P<0.03) between day and group. Vascularized area was similar between the preovulatory groups on Day -6, and a reduced rate of increase resulted in a lesser (P<0.001) area on Day -1 before the first ovulation (1.4+/-0.1cm(2)) than before a later ovulation (2.2+/-0.2 cm(2)). Results demonstrated that follicle vascularization and the LH surge were attenuated preceding the first ovulation of the year with no indication that estradiol was involved in the differences between the first and later ovulations.     

Factors affecting the incidence of postpartum oestrus, ovarian activity and reproductive performance in Thoroughbred mares bred at foal heat under Indian subtropical conditions

Decreased reproductive performance due to summer stress is a well known phenomenon in farm livestock. Whether this occurs in the mare and specifically how this might affect postpartum reproductive activity and performance, especially at Foal Heat (FH), is unknown. This study, therefore, aims to investigate this and the factors that might affect postpartum reproductive activity. Reproductive records of 228 Thoroughbred mares (694 mare years) bred in subtropical north-western India were retrospectively analysed. Overt oestrous activity occurred within 21 d postpartum in 92.94% (645/694) of mares. Significantly (p < 0.001) more April foaling mares (97.37%, 185/190) expressed postpartum oestrous activity than those foaling in January (83.61%; 51/61) and February (88.49; 123/139). Similarly significantly (p < 0.01) fewer multiparous mares failed to demonstrate oestrous activity than primiparous mares (6.12% vs.15.07%; 38/621 vs. 11/73, respectively). 190 of these 694 mares were additionally monitored to confirm ovulation; in these mares onset of FH (oestrus plus confirmed ovulation) occurred 8.42 ± 0.17 d and first ovulation 13.64 ± 0.20 d postpartum. Month, stud farm, year, and parity did not affect interval from parturition to FH onset or to first ovulation; or FH onset to ovulation. In FH bred mares Day 16 pregnancy rate and overall foaling rate were 53.76% (100/186) and 46.24% (86/186) respectively and were similar to those of mares bred later postpartum. FH pregnancy rates were not affected by stud, season, month, year, number of matings, or day of ovulation but were significantly (p < 0.008) lowered by increasing mare age. Significantly (p < 0.01) lower Day 16 pregnancy rates were observed in uterine treated mares compared to untreated mares (31.09% vs. 57.96%; 9/29 vs. 91/157, respectively), this difference was not evident during the rest of pregnancy. In conclusion, postpartum reproductive and ovarian activity appears to be affected by environment, i.e., delayed in subtropical kept Thoroughbred mares compared to those kept in temperate climates. However, resulting reproductive performance at FH and the factors affecting postpartum reproductive activity are similar.     

Effects of oestradiol implants on the ovulation rate of the ewe

In a series of 5 experiments, ewes were treated with implants releasing oestradiol-17 beta and the effects on ovulation rate were observed. Large doses of oestradiol-17 beta (greater than 20 micrograms/day) produced anovulation while smaller amounts only reduced the proportion of twin ovulations. Amounts of exogenous oestradiol comparable to ovarian production rate in the luteal phase (less than 1 microgram/day) produced a significant (P less than 0.01) suppression in ovulation rate. Treatment during the follicular phase of the oestrous cycle was most effective, but treatment during the luteal phase alone also appeared to suppress ovulation rate. Furthermore, in 2 of 3 experiments ewes treated with low amounts of oestradiol during the first half of the luteal phase were less likely to have multiple ovulations at the subsequent oestrous period. The results support the hypothesis that oestrogen is involved in the physiological control of ovulation rate in the ewe, but this action is probably not restricted to the assertion of dominance by a maturing follicle during the follicular phase.     

Resumption of follicular activity in the early post-partum period of dairy cows

Lactating Friesian dairy cows (2nd-4th parity) which calved in spring (N = 7) or autumn (N = 15) were used. Their ovaries were examined by ultrasound scanning and blood samples were obtained daily for progesterone and oestradiol concentrations from the 5th day after calving until the first post-partum ovulation occurred. Five autumn-calving cows selected at random were bled every 15 min over a 6-h period on 1 day each week for 4 weeks after calving to assess the patterns of LH secretion. Follicular development during the post-partum anoestrous period was characterized by the growth and regression of small (less than or equal to 4 mm) and medium-sized (5-9 mm) follicles, until a dominant follicle (greater than 10 mm) was detected. The first detected dominant follicle ovulated in 14 cows, became cystic in 4 cows (all in autumn), and failed to ovulate in 1 cow. It was not possible to detect a dominant follicle in 3 cows due to scanning difficulties. The post-partum interval to detection of the first dominant follicle (mean +/- s.d.) was shorter (P less than 0.05) in autumn (6.8 +/- 1.8 days) than in spring (20 +/- 10.1 days). However, there was no significant difference between the respective intervals to first ovulation (autumn 27.4 +/- 25.9 and spring 27.3 +/- 18.9 days). Autumn-calved cows which had cysts had longer (P less than 0.001) intervals to first ovulation (58.2 +/- 23.5 days) than did normal cows (12.0 +/- 2.5 days). All cows with cysts had twin ovulations at their first post-partum ovulation. A pulsatile pattern of LH secretion was detected in the first week post-partum and LH pulse frequency was 2-3 per 6-h period in Weeks 1 and 2 post partum and increased to 5-7 pulses per 6-h period in the presence of a dominant or cystic follicle. Concentrations of progesterone in plasma during post-partum anoestrus were usually low (less than 0.2 ng/ml); oestradiol concentrations were also low (less than 5 pg/ml), but higher values (5-110 pg/ml) were observed in cows that had a dominant or a cystic follicle.     

Urinary steroid evaluations to monitor ovarian function in exotic ungulates: VII. Urinary progesterone metabolites in the Equidae assessed by immunoassay

A direct enzyme immunoassay (EIA) for non-specific urinary progesterone (Po) metabolites, utilizing a non-specific monoclonal antibody against pregnanediol-3-glucuronide, was evaluated for the purpose of assessing luteal function in equids. Urinary pregnanediol-3-glucuronide (PdG) and immunoreactive PdG-like conjugate (iPdG) concentrations, indexed by creatinine, were compared to plasma Po concentrations in non-conceptive ovarian cycles through two ovulations in four mares. High-performance liquid chromatography (HPLC) of urine from lutealphase mares and a pregnant zebra revealed an absence of significant concentrations of PdG and the presence of at least three immunoreactive compounds, all of which were more polar than PdG. The concentration of iPdG in the mare ranged from a nadir of approximately 3 ng/mg Cr at the time of ovulation to nearly 400 ng/mg Cr at the mid-luteal-phase peak and paralleled plasma Po concentrations. This non-radiometric assay for iPdG permits the assessment of ovulation, luteal formation and function, and luteolysis in unprocessed urine samples from domestic mares. Data from a single zebra indicate this approach also will permit simplified and non-invasive longitudinal studies of ovarian function among a wide range of Equidae.     

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.     

Ovarian and endocrine responses in the cat after coitus

LH release leading to ovulation was induced in 17 of 29 oestrous periods. The time of ovulation after coitus was determined by histological examination or by observation at laparotomy of ovaries in situ. Histological methods revealed that ovulation was complete in most follicles (9 of 13) at 32 h post coitum and in all follicles that were involved in the ovulatory process by 36 h. When laparotomy was used, no signs of preovulatory change were noted at the first observation time, 22 h post coitum, but in 4 cycles in which the entire process of ovulation was observed, the ovulatory process occurred between 23 and 28 h (3 follicles), 23 and 27 h (2 follicles), 25 and 28 h (3 follicles), and 25 and 29 h (3 follicles) post coitum. The first ovulatory process noted was complete at 25 h post coitum. In cats, LH release continued over a 16-h period before returning to baseline (long surge), values being 616 +/- 180 ng/ml at 1/2 h and 941 +/- 154 ng/ml at 2 h post coitum. In 6 cats the LH release pattern was limited to a 4-h period (short surge), values being 537 +/- 218 ng/ml at 1/2 h and 353 +/- 245 ng/ml plasma at 2 h and basal (49 +/- 18 ng/ml) by 4 h post coitum. Decreased secretion of oestrogen by follicles in animals undergoing ovulation was first observed at 16 h post coitum. It is concluded that coitus induces LH release within minutes in the cat and that ovulation begins about 24 h later and finishes by about 32 h post coitum. Only one coital input can cause LH release for as long as 16-20 h although shorter periods of LH release (4 h or less) can result in ovulation.