Stag exposure advances the LH surge and behavioral estrus in Eld's deer hinds after CIDR device synchronization of estrus

The impact of male presence or absence on the timing of the preovulatory LH surge and estrus was studied in 3 experimental groups (n = 6/group) of Eld's deer hinds pretreated with intravaginal progesterone-releasing devices (CIDR-type G) as follows: Group 1 = indirect male contact barn; Group 2 = direct male contact barn; and Group 3 = male isolation barn. For all hinds, the duration of the preovulatory LH surge averaged 2.5+/-0.5 h, whereas mean peak preovulatory and basal LH concentrations were 2.9+/-0.2 ng mL(-1) and 0.27+/-0.03 ng mL(-1), respectively. Nine of 12 male-exposed hinds exhibited a preovulatory LH surge within 24 to 32 h postCIDR device withdrawal, whereas 0 of 6 male-isolated hinds exhibited a preovulatory LH surge during the same time period. Onset of behavioral estrus (45.2+/-2.3, 52.7+/-5.7 and 66.3+/-1.8 h, respectively) was significantly advanced (P<0.05) after CIDR device withdrawal in male exposed hinds (Groups 1 and 2) compared with male isolated hinds (Group 3). These data suggest that stag exposure is important for modulating the timing of the preovulatory LH surge and behavioral estrus after synchronization of estrus with exogenous progestagens.     

Timing of ovulation in relation to onset of estrus and LH peak in yak (Poephagus grunniens L.)

The objective of the study was to determine the timing of ovulation in relation to onset of estrus and the preovulatory LH peak in yaks. For this purpose, a sensitive LH enzymeimmunoassay previously established in buffaloes was successfully validated for measuring the hormone in yak plasma. Plasma LH and progesterone were estimated from blood samples collected from eight non-lactating cycling yaks at 2 h intervals after estrus onset until 6 h after ovulation (ovulation was confirmed by palpation of ovaries per rectum). The mean+/-S.E.M. preovulatory plasma LH peak was 10.11+/-0.35 ng/ml with the values ranging from 8.75 to 11.51 ng/ml in individual yaks. The mean+/-S.E.M. duration of the LH surge was 7.25+/-0.55 h with a range of 6-10 h. Onset of LH surge (mean+/-S.E.M.) occurred 3.0+/-0.65 h after the onset of estrus. Mean plasma progesterone stayed low (<0.25 ng/ml) during the entire duration of sampling. Ovulation occurred 30.5+/-0.82 h (range, 28-34 h) after the onset of estrus and 20.25+/-1.03 h after the end of LH surge. The occurrence of the LH peaks within a narrow time frame of 4-8h post estrus onset in yaks could have contributed to the animals ovulating within a narrow time interval.     

Antiovulatory effect of a single injection of pure antiestrogen ZK 191703 at early stage of rat estrus cycle

The effects of ZK 191703 (ZK), a pure antiestrogen, on ovulation, follicle development and peripheral hormone levels were investigated in rats with 4-day estrus cycle and gonadotropin-primed immature rats in comparison to tamoxifen (TAM)-treatment. In adult rats, a single s.c. injection of ZK (5 mg/kg) or TAM (5 mg/kg) at an early stage of the estrus cycle (diestrus 9:00) inhibited ovulation, and was associated with suppression of the surge of preovulatory LH, FSH and progesterone. In rats treated with ZK or TAM at a late stage of the estrus cycle (proestrus 9:00), no inhibitory effects on ovulation, the gonadotropin and progesterone surge were detected. ZK treatment at diestrus 9:00, in contrast to TAM, increased the baseline LH level. When immature rats were treated with antiestrogens in the earlier stage of follicular development, 6 and 30 h but not 48 h or later after injection of gonadotropin (PMSG), ovulation was attenuated, associated with a lowered progesterone level. Unruptured preovulatory follicles were found in most of the ovaries from anovulatory animals treated with ZK or TAM. Antiestrogens, ZK and TAM administered at an early phase of the estrus cycle delay the follicular development functionally and inhibit ovulation in rats and suppression of the preovulatory progesterone surge.     

Efficacy of intermittent or continuous administration of GnRH in inducing ovulation in early and late seasonal anoestrus in the Père David's deer hind (Elaphurus davidianus)

Père David's deer hinds were treated with GnRH, administered as intermittent i.v. injections (2.0 micrograms/injection at 2-h intervals) for 4 days, or as a continuous s.c. infusion (1.0 micrograms/h) for 14 days. These treatments were given early (February-March) and late (May-June) in the period of seasonal anoestrus. The administration of repeated injections of GnRH increased mean LH concentrations from pretreatment values of 0.54 +/- 0.09 to 2.10 +/- 0.25 ng/ml over the first 8 h of treatment in early anoestrus, and from 0.62 +/- 0.11 to 2.73 +/- 0.49 ng/ml in late anoestrus. The mean amplitude of GnRH-induced LH episodes was greater (P less than 0.01) in late (4.03 +/- 0.28 ng/ml) than in early (3.12 +/- 0.26 ng/ml) anoestrus, but within each replicate (early or late anoestrus), neither mean LH episode amplitude nor mean plasma LH concentrations differed significantly between the four periods of intensive blood sampling. On the basis of their progesterone profiles, 6/12 hinds had ovulated in response to treatment with injections of GnRH (1/6 in early anoestrus and 5/6 in late anoestrus), and oestrus and a preovulatory LH surge were recorded in all of these animals. Oestrus and a preovulatory LH surge were also recorded in one other animal treated in early anoestrus in which progesterone concentrations remained low. The mean times of onset of oestrus (91.0 +/- 1.00 and 62.4 +/- 0.98 h) and of the preovulatory LH surge (85.8 +/- 3.76 and 59.4 +/- 0.25 h) both occurred significantly earlier (P less than 0.001) in animals treated in late anoestrus. Continuous infusion of GnRH to seasonally anoestrous hinds resulted in an increase in mean plasma LH concentrations, but this response did not differ significantly between early (2.15 +/- 0.28 ng/ml) and late (2.48 +/- 0.26 ng/ml) anoestrus. Ovulation, based on progesterone profiles, occurred in 2/7 hinds in early anoestrus and in 4/6 hinds in late anoestrus. Oestrus was detected in all except one of these hinds. The mean time of onset of oestrus occurred earlier in animals treated in late anoestrus (66.2 +/- 0.32 h and 46.7 +/- 0.67 h, P less than 0.01). The administration of GnRH, given either intermittently or continuously, will induce ovulation in a proportion of seasonally anoestrous Père David's deer. However, more animals ovulate in response to this treatment in late than in early anoestrus (75% compared with 23%).     

The variability in the interval between estrus and ovulation in cattle and its determinants

Fertility of Holstein cows has been decreasing for years and, to a lesser extent, the fertility of heifers too but more recently. A hypothesis to explain this phenomenon may be that the chronology of events leading to ovulation is different for those animals bred nowadays when compared to what was reported previously; this would result in an inappropriate time of insemination. Therefore, two experiments were designed to investigate the relationships among estrus behavior, follicular growth, hormonal events and time of ovulation in Holstein cows and heifers. In the first experiment, the onset of estrus, follicular growth, patterns of estradiol-17beta, progesterone and LH, and the time of ovulation were studied in 12 cyclic Holstein heifers that had their estrus synchronized using the Crestar method; this was done twice, 3 weeks apart. The intervals between estrus and ovulation, estrus and the LH peak, and between the LH peak and ovulation were, respectively, 38.5 h +/-3.0, 9.1 +/- 2.0 and 29.4 h +/-1.5 (mean+/- S.E.M). The variation in the interval between estrus and the LH peak explained 80.6% of the variation in the interval between estrus and ovulation. The intervals between estrus and the LH peak, and estrus and ovulation were correlated with estradiol-17beta peak value (r=-0.423, P <0.04 and r=-0.467, P<0.02, respectively). Positive correlation coefficients for the number of follicle larger than 5 mm, and negative correlation coefficients for the size of the preovulatory follicle with the intervals between estrus and LH peak, LH peak and ovulation, and estrus and ovulation suggest an ovarian control of these intervals. In respect to its role to explain the variation in the interval between estrus and ovulation, the variation in the interval between estrus and the LH peak was evaluated further in a second set of experiments utilizing 12 pubertal Holstein heifers and 35 Holstein cows. The duration of the interval between the beginning of estrus and the LH peak was longer in heifers than in cows (4.15 h versus -1.0 h; P <0.002); the variation for this interval was higher in cows than in heifers (S.E.M.= 1.2 h versus 0.8 h; P=0.01). According to the results of these studies it can be proposed that estradiol and other product(s) of ovarian origin regulate not only the duration of intervals between the onset of estrus and the LH surge but also between the LH surge and ovulation. From the results obtained in the first experiment, it may be postulated that differences observed between cows and heifers for the duration of the interval between onset of estrus and the LH surge as well as for the variation of this interval would be observed also for the interval between the onset of estrus and ovulation. Therefore, on a practical point of view, the long interval between the onset of estrus and ovulation and the high variation of this interval, especially in cows, may be a source of low fertility and should be considered when analysing reproductive disorders.     

Follicle population, cumulus mucification, and oocyte chromatin configuration during the periovulatory period in the female dog

This study was designed to describe the follicular population present on the canine ovary (Canis familiaris) during the preovulatory period and essentially the changes in oocyte size, mucification, and chromatin configuration occurring from before the luteinizing hormone (LH) surge up to postovulation. In a first experiment, ovaries of beagle bitches were collected before (n = 21) or after LH surge but before ovulation (post-LH surge/preovulation stage, n = 24) as determined using hormone (LH, estradiol, progesterone) assays and ultrasonography. All large (>2 mm) follicles were measured and punctured. The numbers of oocytes collected per follicle and the degree of cumulus mucification were recorded. In a second experiment, ovaries were similarly collected before (n = 13) and after the LH surge but before ovulation (n = 11) as well as after ovulation as determined by ultrasonography (n = 9). Chromatin configuration of the oocytes was observed by DNA staining and confocal microscopy. In Experiment 1, before the LH peak, an average of 13.5 ± 0.7 follicles per bitch (total 284 follicles) were detected, and the maximal follicle diameter reached 6.5 mm. Large follicles were observed already in this period of the cycle and as early as when progesterone was still below 0.5 ng/mL. After the LH peak but before ovulation, 11.0 ± 0.7 follicles were present (total 264 follicles). Fully mucified cumulus cells were observed only in follicles larger than 4 mm. Multi-oocytic follicles represented 7% (before LH peak) and 4% (after LH peak) of the follicular population. In Experiment 2, all the oocytes were at the germinal vesicle (GV) stage, but three chromatin configurations could be distinguished: diffuse, partly grouped, and fully grouped chromatin. The proportion of oocytes with fully grouped chromatin increased with the follicular diameter and the time in estrus, the maximum being observed after the LH peak. These results suggest that (1) before LH peak, follicles are already of large diameter, similar to the ones at ovulation; (2) the ability for cumulus mucification is acquired during the late steps of follicular growth; (3) three GV patterns may be observed during the periovulatory period.     

Exposure to endotoxin during estrus alters the timing of ovulation and hormonal concentrations in cows

The effect of intramammary (IMM) or intravenous (IV) administration of E. coli endotoxin (LPS), at the onset of estrus, at the time of ovulation was examined. Steroid and gonadotropin concentrations around ovulation were also determined. Lactating Holstein cows (n=33) were assigned to saline-controls (n=12) and treated with LPS-IV (0.5mug/kg; n=13) or LPS-IMM (10mug; n=8). Synchronized cows were observed continuously for estrus. LPS (or saline) was injected within 30min from the onset of standing estrus, at peak estradiol concentrations. The typical rise of body temperature, somatic cell count, cortisol, and NAGase activity was noted. One-third of both LPS-IV- and LPS-IMM-treated cows were manifested by an extended estrus to ovulation (E-O) interval of around 75h or did not ovulate, compared with about 30h in the other 2/3 of LPS cows and all controls. Estradiol concentrations 24h before and after LPS did not differ between groups. However, LPS-IV cows with extended intervals exhibited another estrus and an additional rise of estradiol followed by delayed ovulation. LPS-treated cows with a delayed E-O interval had low or delayed LH surge; two LPS-treated cows did not exhibit LH surge and did not ovulate. All control cows exhibited normal hormone levels. Delayed ovulation was associated with a delayed rise of luteal progesterone. The results indicated that exposing cows to endotoxin during estrus induced a decreased and delayed LH surge in one-third of the cows. This was associated with delayed ovulation, which reduces the chances of successful fertilization.     

Seasonal variation in preovulatory events associated with synchronization of estrus in dwarf goats

This experiment was conducted to define the temporal relationships among estrus, the LH surge and ovulation after estrus synchronization in dwarf goats and to assess the effect of season on these parameters. In November (breeding season), March (transition period) and July (non-breeding season), estrus was synchronized in 12 dwarf goats by means of intravaginal sponges containing 60 mg medroxyprogesterone acetate (MAP) for 10 d, coupled with 125 microg cloprostenol i.m. 48 h before sponge removal and 300 IU eCG i.m. at sponge removal. A different group of animals was used during each time period. Onset of estrus was monitored using two males, and blood samples for the measurement of plasma LH were collected at 2-h intervals from 24 to 60 h after sponge removal. Ovulation was confirmed by laparoscopy at 54 and 72 h after sponge removal. A seasonal shift was detected in the intervals to onset of estrus, LH surge, and ovulation after sponge removal (P<0.05), with sponge removal to onset of estrus being shorter (P<0.05) in November (25.0 +/- 1.56 h) and July (28.9 +/- 2.43 h) than in March (40.9 +/- 3.27 h). The intervals between onset of estrus and the LH surge and between the LH surge and ovulation were found to be constant throughout the different seasons. An optimal time for breeding, artificial insemination, oocyte and embryo recovery, and embryo transfer may be predicted using information gained from these studies.     

Synchronization of estrus and ovulation and associated endocrine changes in Bos indicus cows

The effects of 4 estrus synchronization treatments on intervals to and synchrony of estrus and ovulation, on timing of the preovulatory LH surge and associated changes in plasma progesterone, LH, FSH, and 17beta-estradiol (E(2)) were investigated in 48 Bos indicus cows. Treatment 1 consisted of 2 injections of PGF(2alpha) 14 d apart (n = 12); Treatment 2 of a subcutaneous 3-mg norgestomet implant and an intramuscular injection of 3 mg of norgestomet and 5 mg estradiol valerate, with the implant removed 10 d later (n = 12; norgestomet-estradiol); Treatment 3 of norgestomet-estradiol, with a subcutaneous injection of PMSG given at time of implant removal (Day 10; n = 12); and Treatment 4 of norgestomet implant (as for Treatments 2 and 3) inserted for 10 d, with an intramuscular injection of PGF(2alpha) given at the time of implant removal (n = 12). The experiment was conducted in 2 replicates (24 cows/replicate, 6 cows/group). Estrus, ovulation and timing of the preovulatory surge of LH varied less in cows treated with norgestomet-estradiol and PMSG than in cows in Treatments 1 and 4 (P < 0.008). Treatment with PMSG reduced variation in ovulation times and timing of the LH surge in cows treated with norgestomet-estradiol (P < 0.02). Concentrations of E(2) were higher in cows in Treatments 2 and 3 on the final day of treatment and at about 6 h post ovulation compared with cows in Treatments 1 and 4 (P < 0.05). Different methods for synchronizing estrus did not alter sequential endocrine and behavioral changes in relation to the timing of the LH peak, and the results were consistent with current recommendations for insemination times in Bos taurus cattle.     

Progesterone blocks the estradiol-stimulated luteinizing hormone surge by disrupting activation in response to a stimulatory estradiol signal in the ewe

The preovulatory surges of GnRH and LH are activated by increased concentrations of circulating estradiol, but ovulation is blocked when progesterone concentrations are elevated. Although it is has been shown that this action of progesterone is due to a central inhibition of the GnRH surge, the mechanisms that underlie the blockade of the GnRH surge are poorly understood. In this study we investigated whether progesterone can block the estradiol-dependent activation stage of the GnRH surge induction process, and thus prevent expression of the LH surge. The results demonstrated that exposure to progesterone for half or the full duration of the activation stage can prevent the stimulation of LH surges by estradiol (experiment 1), whereas exposure to progesterone midway though a period of estradiol exposure, which in itself is sufficient to activate the surge, did not block the LH surge (experiment 2). These results suggest that progesterone 1) disrupts activation of the surge induction system in response to a stimulatory estradiol signal and 2) does not compromise the ability of animals to respond to a stimulatory estradiol signal applied immediately after progesterone exposure. Because the disruptive effects of activated progesterone in response to estradiol are rapid but transient, it may be that progesterone directly interferes with the activation of estradiol-responsive neural systems to block the GnRH/LH surge.     

Artificial insemination following observational versus electronic methods of estrus detection in red deer hinds (Cervus elephus)

The objectives were to determine the efficacy of the HeatWatch (HW) electronic estrus detection system for monitoring behavioral estrus (including duration and intensity) in red deer hinds and to evaluate pregnancy rate to AI after detected estrus. Red deer hinds (Cervus elephus; n = 50) were allocated into two treatment groups: AI following synchronization (CIDR/PMSG) and observed estrus (induced estrus group: IE; n = 25) or AI following the detection of natural estrus (NE; n = 25) without hormonal treatment. Hinds were fitted with two HeatWatch (HW) electronic estrus detection transmitters, one above the tail (bottom) and one between the tuber coxae of the pelvic girdle (top), and visual observations for mounting activity began with the aid of young sterile red deer stags (18 months old) fitted with marking harnesses. Hinds in both groups were inseminated (10-12h after observed estrus) with frozen-thawed red deer semen using a transvaginal/cervical AI approach. Following a 26-day period of AI, hinds were placed with a mature fertile stag for an additional 30-day natural breeding period. Pregnancy diagnosis was performed 57 and 86 days after the start of AI. While the hinds were housed with the young stags, 82% were detected in estrus by visual appraisal of stag crayon marks, but only 32% of these were detected by HW. In contrast, in the hinds housed with the mature stag, 93% detected in estrus by crayon marks were also detected by HW. The top HW transmitter consistently recorded more mounts (P < 0.05) than the bottom transmitter. The pregnancy rate was numerically better in IE versus NE hinds (42% versus 29%, P > 0.10). In summary, there were no differences (P > 0.10) in the intensity (number) or duration of mounts (detected by HW) during estrus in IE versus NE hinds, and HW was most effective in detecting estrus in the presence of a heavier, mature stag versus a younger stag. When used in combination with transvaginal AI, an overall first-service pregnancy rate of 36.6% was achieved with AI of frozen-thawed semen in red deer hinds following detected estrus.     

Relationship between the onset of oestrus, the preovulatory surge in luteinizing hormone and ovulation following oestrous synchronization and superovulation of farmed red deer (Cervus elaphus).

The timing of ovulation relative to the onset of oestrus and the preovulatory surge in luteinizing hormone (LH) was studied in red deer following treatments to synchronize oestrus and induce either a monovulatory or superovulatory response. Mature hinds (n = 36) were allocated randomly to two mating groups (n = 16 + 20), with respective treatments staggered by 4 weeks during the 1990 rut (March-April). Each hind was treated with an intravaginal controlled internal drug releasing (CIDR)-type S device for 14 days. Treatments to induce a monovulatory response included CIDR device alone (treatment A; n = 4 + 8) and additional injection of 200 iu pregnant mares' serum gonadotrophin (PMSG) at device removal (treatment B; n = 4 + 4). Treatments to induce a superovulatory response included injections of 200 iu PMSG and 0.5 units ovine follicle-stimulating hormone (FSH) at about time of removal of CIDR devices (treatment C; n = 4 + 4) and further treatment with gonadotrophin-releasing hormone (GnRH) analogue 18 h after removal of CIDR devices (treatment D; n = 4 + 4). The hinds were run with crayon-harnessed stags from insertion of CIDR devices (12 March or 9 April) and blood samples were taken every second day to determine plasma progesterone. Further blood samples were collected for determination of plasma LH and progesterone via indwelling jugular cannulae every 2 h for 72 h from removal of CIDR devices. Hinds were allocated randomly to an initial ovarian examination by laparoscopy at either 16 or 20 h (A and B), or 12 or 16 h (C and D) after the onset of oestrus, with laparoscopy repeated at intervals of 8 h until either ovulation was recorded (A and B), or for four successive occasions (C and D). All hinds received cloprostenol injections 15 days after device removal. A total of 28 hinds (78%) exhibited oestrus and a preovulatory LH surge, with mean (+/- SEM) times to onset of oestrus of 44.6 +/- 1.0 h (A; n = 7), 37.4 +/- 2.0 h (B; n = 7), 16.3 +/- 1.7 h (C; n = 6) or 14.0 +/- 1.7 h (D; n = 8). Failure to exhibit oestrus or LH surge was most prevalent among hinds in treatment A early in the rut.(ABSTRACT TRUNCATED AT 400 WORDS)     

Patterns of circulating gonadotropins and ovarian steroids during the first periovulatory period in the developing sheep.

This report provides evidence that an increment in serum gonadotropin levels occurs at puberty in the sheep and that this reflects the critical hormonal event culminating in first ovulation in this species. Blood samples were collected from 6 female lambs at 4-h intervals for a period of approximately 2 mo around the expected time of puberty (32 wk of age) until behavioral estrus was observed and ovulation was verified by assay of serum progesterone. Patterns of circulating LH, FSH, progesterone, and estradiol concentrations were characterized during the peripubertal period for each lamb. A rise in serum levels of both LH and FSH began approximately 7-10 days before the first preovulatory surge of gonadotropins. Although the increase in gonadotropin levels occurred gradually over several days, serum estradiol levels rose only during the final 40-60 h prior to the preovulatory surge of gonadotropin. Serum progesterone profiles revealed, however, that normal (14-16-day) luteal phases were induced in only 2 of 6 females as a result of the first surge. In four lambs, a short luteal phase of 2.5 days' duration occurred, which was followed by another estradiol rise and a preovulatory surge that then resulted in a full luteal phase of 14 days' duration. These data demonstrate clearly that the precipitating event at puberty in the female sheep is an increase in circulating gonadotropin levels and that the estradiol secreted from the newly stimulated follicle provides the signal for the first preovulatory surge.     

Estrus synchronization and artificial insemination of hair sheep ewes in the tropics

Hair sheep ewes (St. Croix White and Barbados Blackbelly) were used to evaluate 3 methods of estrus synchronization for use with transcervical artificial insemination (TAI). To synchronize estrus, ewes (n = 18) were treated with PGF2alpha (15 mg, im) 10 d apart, with controlled internal drug release (CIDR) devices containing 300 mg progesterone for 12 d (n = 18), or with intravaginal sponges containing 500 mg progesterone for 12 d (n = 18). On the day of the second PGF2alpha injection or at CIDR or sponge removal, sterile rams were placed with the ewes. Jugular blood samples were collected from the ewes at 6-h intervals until the time of ovulation, and daily for 16 d after estrus (Day 0). Plasma was harvested and stored at -20 degrees C until LH, and progesterone concentrations were determined by RIA. There was no difference (P>0.10) in time to estrus among the CIDR-, PGF2alpha- or sponge-treated ewes. All of the ewes in the CIDR group and 94.4% of the sponge treated ewes exhibited estrus by 36 h after ram introduction, while only 72.2% of PGF2alpha-treated ewes showed signs of estrus by this time (P<0.06). The time from ram introduction to ovulation was not different (P>0.10) among the CIDR-, PGF2alpha- or sponge-treated ewes. The time to the preovulatory LH surge was similar (P>0.10) among CIDR, PGF2alpha and sponge treated ewes. Progesterone levels through Day 16 after the synchronized estrus were not different (P>0.10) among treatment groups. Hair sheep ewes (n = 23) were synchronized using PGF2alpha and bred by TAI using frozen-thawed semen 48 h after the second injection. The conception rate to TAI was 2/23 (8.7%) and produced 3 ram lambs. In a subsequent trial, 17 ewes were synchronized with CIDR devices and bred by TAI using frozen-thawed semen 48 h after CIDR removal, resulting in a conception rate of 52.9% (9/17). It is possible to synchronize estrus in hair sheep using either CIDRs, sponges or PGF2alpha. Even though there were no significant differences in the timing of ovulation or the LH surge among the treatment groups, a higher conception rate was achieved in ewes synchronized with CIDR devices during the second trial. This may reflect an increase in the skill level of the TAI technician.     

LH surge in Nelore cows (Bos indicus), after induced estrus or after ovarian superestimulation

Considering that there is limited information about the preovulatory LH surge in Zebu cattle (Bos indicus), the purpose of the present work was to assess the LH surge in Nelore cows during the estrous cycle and after ovarian superestimulation of ovarian follicular development with FSH. This information is particularly important to improve superovulatory protocols associated with fixed-time artificial insemination. Nelore cows (n=12) had their estrus synchronized with an intravaginal device containing progesterone (CIDR-B) associated with estradiol benzoate administration (EB, 2.5 mg, i.m., Day 0). Eight days later all animals were treated with PGF2alpha (Day 8) in the morning (8:00 h) and at night, when CIDR devices were removed (20:00 h). Starting 38h after the first PGF2alpha injection, blood sampling and ovarian ultrasonography took place every 4h, during 37 consecutive hours. Frequent handling may have resulted in a stress-induced suppression of LH secretion resulting in only 3 of 12 cows having ovulations at 46.7+/-4.9 and 72.3+/-3.8 h, respectively, after removal of CIDR-B. Thirty days later, the same animals received the described hormonal treatment associated with FSH (Folltropin), total dose=200 mg) administered twice a day, during 4 consecutive days, starting on Day 5. Thirty-six hours after the first injection of PGF2alpha, to minimize stress, only seven blood samples were collected at 4h interval each, and ultrasonography was performed every 12 h until ovulation. In 11 of 12 cows (92%) the LH surge and ovulation were observed 34.6+/-1.6 and 59.5+/-1.9 h, respectively, after removal of progesterone source. The maximum values for LH in those animals were 19.0+/-2.6 ng/ml (mean+/-S.E.M.). It is concluded that, in Nelore cows submitted to a ovarian superstimulation protocol, the LH surge occurs approximately 35 h after removal of intravaginal device containing progesterone, and approximately 12h before the LH surge observed after an induced estrus without ovarian superstimulation.     

Superovulation and embryo recovery in Red deer (Cervus elaphus ) hinds

In two experiments, Red deer hinds were synchronized with intravaginal progesterone and were given 4 d of treatment (3 d before progesterone withdrawal and 1 d after) with an ovine follicle stimulating hormone (FSH) preparation which had a claimed low level of luteinizing hormone (LH) contamination. In Experiment 1, 12 hinds received one of four FSH levels by osmotic minipump. Hinds were run with fertile stags, and laparotomy and embryo recovery were performed 9 d after progesterone withdrawal. The ovulation rates (mean of three hinds per dosage) were 1.0, 2.0, 4.3 and 15.3 (number of corpora lutea counted) for estimated daily dosages rates of 0.036, 0.071, 0.11 and 0.14 units FSH preparation/day; the response to the increasing dosage was exponential (P<0.01). The recovery rate of ova on flushing was 38% (24 63 ), with all recovered ova being fertilized and of transferable quality. In Experiment 2, performed later in the breeding season, eight hinds received 0.14 units FSH/day either by minipump or by intramuscular injection. The mean ovulation rates were 3.0 and 11.0 (a significant difference, P<0.01), respectively, with a recovery rate of 72% (34 47 ), and with only 18 34 ova considered to be of transferable quality. The recovery rate in Experiment 2 was significantly higher than that in Experiment 1 (P<0.001). Overall, the results were better than those previously recorded for red deer, perhaps a function of both the FSH preparation used and an improved progesterone profile in estrus synchronization.     

Corpus luteum development and function in cattle with episodic release of luteinizing hormone pulses inhibited in the follicular and early luteal phases of the estrous cycle.

The influence of episodic LH pulses before and subsequent to ovulation on size and function of the corpus luteum (CL) in cattle was examined. Treatments were 1) control; 2) LHRH antagonist starting 2 days before the preovulatory LH surge (Antagonist [Ant] -2); 3) LHRH antagonist at initiation of the preovulatory LH surge (Ant 0); and 4) LHRH antagonist starting 2 days after the preovulatory LH surge (Ant 2). Treatments with an LHRH antagonist were continued until 7 days after the preovulatory surge. Diameter of the CL and concentrations of progesterone were monitored during the luteal phase that ensued after treatment. Maximum average diameters of CL were 9.5, 17.5, 21.6, and 28.8 mm for females from the Ant -2, Ant 0, Ant 2, and control groups, respectively (P < 0. 01). Compared with those in control animals, concentrations of progesterone in plasma were less (P < 0.01) in animals in which release of LH pulses was inhibited by treatment with antagonist. Arbitrary units under the curve for concentrations of progesterone during the luteal phase of the estrous cycle for Ant -2, Ant 0, Ant 2, and control groups were 19.6, 41.6, 43.6, and 142.2, respectively. There was no difference in circulating concentrations of progesterone (P > 0.1) among antagonist-treated groups. In conclusion, episodic release of LH pulses before, during, and after the time of the preovulatory surge of LH may stimulate development and function of the CL in cattle.     

Effect of induced suprabasal progesterone levels around estrus on plasma concentrations of progesterone, estradiol-17beta and LH in heifers

A controlled study was carried out to investigate the effects of suprabasal plasma progesterone concentrations on blood plasma patterns of progesterone, LH and estradiol-17beta around estrus. Heifers were assigned to receive subcutaneous silicone implants containing 2.5 g (n=4), 5 g (n=4), 6 g (n=3), 7.5 g (n=3) or 10 g (n=4) of progesterone, or implants without hormone (controls, n=5). The implants were inserted on Day 8 of the cycle (Day 0=ovulation) and left in place for 17 d. The time of ovulation was determined by ultrasound scanning. Blood was collected daily from Days 0 to 14 and at 2 to 4-h intervals from Days 15 to 27. Control heifers had the lowest progesterone concentrations on Days 20.5 to 21 (0.5 +/- 0.1 nmol L(-1)); a similar pattern was observed in heifers treated with 2.5 and 5 g of progesterone. In the same period, mean progesterone concentrations in the heifers treated with 6, 7.5 and 10 g were larger (P < 0.05) than in the controls, remaining between 1 and 2.4 nmol L(-1) until implant removal. A preovulatory estradiol increase started on Days 16.4 to 18.4 in all the animals. In the controls and in heifers treated with 2.5 and 5 g of progesterone, estradiol peaked and was followed by the onset of an LH surge. In the remaining treatments, estradiol release was prolonged and increased (P < 0.05), while the LH peak was delayed (P < 0.05) until the end of the increase in estradiol concentration. The estrous cycle was consequently extended (P < 0.05). In all heifers, onset of the LH surge occurred when progesterone reached 0.4 to 1.2 nmol L(-1). The induction of suprabasal levels of progesterone after spontaneous luteolysis caused endocrine asynchronies similar to those observed in cases of repeat breeding. It is suggested that suprabasal concentrations of progesterone around estrus may be a cause of disturbances oestrus/ovulation.     

Influence of lameness on follicular growth, ovulation, reproductive hormone concentrations and estrus behavior in dairy cows

The objective of this study was to examine the effect of a chronic stressor, lameness, on reproductive parameters. Seventy cows 30-80 days post-partum were scored for lameness and follicular phases synchronized with GnRH followed seven days later by prostaglandin (PG). Fifteen Lame animals did not respond to GnRH ovarian stimulation. Milk progesterone for 5 days prior to PG was lower in the remaining Lame cows than Healthy herdmates. Fewer Lame cows ovulated (26/37 versus 17/18; P = 0.04) and the interval from PG to ovulation was shorter in Lame cows. In Subset 1 (20 animals), the LH pulse frequency was similar in ovulating animals (Lame and Healthy) but lower in Lame non-ovulators. An LH surge always preceded ovulation but lameness did not affect the interval from PG to LH surge onset or LH surge concentrations. Before the LH surge, estradiol was lower in non-ovulating cows compared to those that ovulated and estradiol concentrations were positively correlated with LH pulse frequency. In Subset 2 (45 cows), Lame ovulating cows had a less intense estrus than Healthy cows, although Lame cows began estrus and stood-to-be-mounted earlier than Healthy cows. In conclusion, we have identified several parameters to explain poor fertility in some chronically stressed animals. From 30 to 80 days post-partum, there was a graded effect that ranged from 29% Lame cows with absence of ovarian activity, whereas another 21% Lame cows failed to express estrus or ovulate a low estrogenic follicle; in 50% cows, many reproductive parameters were unaffected by lameness.     

Influence of GnRH administration on timing of the LH surge and ovulation in dwarf goats

This study was conducted to determine whether or not exogenous gonadotropin releasing hormone (GnRH) alters the timing or improves the synchrony of estrus, the LH surge, and ovulation following estrous synchronization in dwarf goats, and to assess the effects of season on these parameters. In January and June, estrus was synchronized in 12 Pygmy and Nigerian Dwarf goats with a 10-day progestagen sponge, 125 microg cloprostenol i.m. 48 h before sponge removal, and 300 IU equine chorionic gonadotrophin (eCG) i.m. at sponge removal. Six of the 12 goats were given 50 microg GnRH i.m. 24h after sponge removal. Onset of estrus was monitored using two males. Samples for plasma LH were collected at 2 h intervals beginning 22 h after sponge removal and ending at 48 h in January and at 58 h in June. Time of ovulation time was confirmed by laparoscopy at 36, 50, 60, and 74 h in January and at 50, 60, and 74 h in June. Administration of GnRH had no significant effect on the onset of estrus; however, it reduced the interval from sponge removal to the LH surge and improved the synchrony of the LH surge (P<0.05). Treatment with GnRH also reduced the interval from sponge removal to ovulation and improved the synchrony of ovulation (P<0.05). Season had a significant effect on the timing and the synchrony of estrus with and without GnRH treatment (P<0.05). A seasonal shift was also observed in the timing of the LH surge in the absence of GnRH treatment (P<0.05). Further research is required to determine the optimum time for GnRH administration and the minimum effective dose in dwarf goats.