Consequences of increasing or decreasing plasma FSH concentrations during the preovulatory period in Romney ewes

Romney ewes were infused with ovine FSH (NIADDK-oFSH-16) for 48 h from the initiation of luteolysis with cloprostenol. Doses of 2.5 or 5 micrograms/h which partly or completely prevented the normal preovulatory decline in plasma FSH concentrations caused a significant increase in mean ovulation rates. Ovulation rates were not increased significantly if the FSH (5 micrograms/h) was infused for only 20 h starting from the initiation of luteolysis or 24 h later. Infusion of a less potent and relatively impure preparation of FSH (i.e. FSH-P) at 0.5 mg/h for 48 h after cloprostenol treatment also increased the mean ovulation rate significantly. However, if the FSH-P was given for only the first 24 h, or if the start of the infusion was delayed for more than 12 h, mean ovulation rates were not increased significantly. Infusion of LH (NIADDK-oLH-25, 5 micrograms/h) for 48 h from the initiation of luteolysis decreased the mean ovulation rate significantly. Administration of bovine follicular fluid to suppress plasma FSH concentrations below normal during the first 24 h after cloprostenol injection did not delay oestrus. However, oestrus was delayed by approximately 2 days if plasma FSH concentrations were reduced by bovine follicular fluid 24 h after the initiation of luteolysis. As ovulation rate increased, the mean weight of individual corpora lutea of each ewe decreased. In ewes with a single ovulation, most corpora lutea weighed greater than 600 mg, but as the ovulation rate increased the proportion of corpora lutea present weighing less than 400 mg rose steadily.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal relationship between the onset of oestrus, the preovulatory LH surge and ovulation in farmed fallow deer, Dama dama

A study was conducted to determine the timing of ovulation relative to the onset of oestrus and the preovulatory LH surge in fallow deer. Mature fallow does were randomly allocated to two treatments (N = 10 per treatment) designed to synchronize oestrus on or about 17 May. Does assigned to Group 1 (prostaglandin-induced oestrus) each initially received single intravaginal CIDR [Controlled Internal Drug Release] devices for 13 days followed by an i.m. injection of 750 mg cloprostenol on Day 12 (15 May) of the subsequent luteal cycle. Does assigned to Group 2 (progesterone-induced oestrus) each received CIDR devices for 13 days, with withdrawal occurring on 15 May. All does were run with crayon-harnessed bucks (10:1 ratio) from the start of synchronization (18:00 h 15 May). Ten does (5 per group) were blood sampled via indwelling jugular cannulae every 2 h for 72 h from cloprostenol injection or CIDR device withdrawal and the plasma was analysed for concentrations of progesterone and LH by radioimmunoassay. Does within each treatment were randomly allocated to an ovarian examination time of 12, 16, 20 or 24 h after the onset of oestrus. Laparoscopy was repeated at 12-h intervals until ovulation was recorded. The ovaries of does failing to exhibit oestrus were examined 72 and 86 h after cloprostenol injection or CIDR device withdrawal. A total of 17 does were observed to exhibit oestrus at a mean (+/- s.e.m.) interval from treatment of 44.6 +/- 3.6 h for Group 1 (N = 9) and 34.1 +/- 2.5 h for Group 2 (N = 8).(ABSTRACT TRUNCATED AT 250 WORDS)     

Duration of oestrus, ovulation rate, time of ovulation and plasma LH, total oestrogen and progesterone in Galway adult ewes and ewe lambs

The mean duration of oestrus, ovulation rate, duration of the preovulatory LH discharge, time interval between sponge removal and beginning of the LH discharge, total LH discharged, maximum LH value observed and the concentration of progesterone in the peripheral plasma during the luteal phase of the oestrous cycle was similar in Galway adult ewes and 8-month-old ewe lambs after treatment with intravaginal sponges containing 30 mg cronolone for 12 days and injection of 500 i.u. PMSG. The interval between sponge removal and the onset of oestrus was shorter for adults than for ewe lambs; the interval between the onset of oestrus and the beginning of the LH discharge was longer in adults. During the period 12-36 h after sponge removal the mean plasma total oestrogen concentration was significantly higher in lambs than in adults. In a separate study of the time of ovulation in Galway ewe lambs given the same progestagen-PMSG treatment, ovulation did not occur in any lamb before 17 h after the onset of oestrus and the majority ovulated close to the end of oestrus.     

Timing of the onset and duration of ovulation in superovulated beef heifers

Thirty-two beef heifers were induced to superovulate by the administration of follicle stimulating hormone-porcine (FSH-P). All heifers received 32 mg FSH-P (total dose) which was injected twice daily in decreasing amounts for 4 d commencing on Days 8 to 10 of the estrous cycle. Cloprostenol was administered at 60 and 72 h after the first injection of FSH-P. Heifers were observed for estrus every 6 h and were slaughtered at known times between 48 to 100 h after the first cloprostenol treatment. The populations of ovulated and nonovulated follicles in the ovaries were quantified immediately after slaughter. Blood samples were taken at 2-h intervals from six heifers from 24 h after cloprostenol treatment until slaughter and the plasma was assayed for luteinizing hormone (LH) concentrations. The interval from cloprostenol injection to the onset of estrus was 41.3 +/- 1.25 h (n = 20). The interval from cloprostenol injection to the preovulatory peak of LH was 43.3 +/- 1.69 h (n = 6). No ovulations were observed in animals slaughtered prior to 64.5 h after cloprostenol (n = 12). After 64.5 h, ovulation had commenced in all animals except in one animal slaughtered at 65.5 h. The ovulation rate varied from 4 to 50 ovulations. Approximately 80% of large follicles (> 10 mm diameter) had ovulated within 12 h of the onset of ovulation. Onset of ovulation was followed by a dramatic decrease in the number of large follicles (> 10 mm) and an increase in the number of small follicles (相似文献   

Effects of bromocriptine administration during the follicular phase of the oestrous cycle on prolactin and gonadotrophin secretion and follicular dynamics in merino monovular ewes

Two experiments using Spanish Merino ewes were conducted to investigate whether the secretion of prolactin during the follicular phase of the sheep oestrous cycle was involved in the patterns of growth and regression of follicle populations. In both experiments, oestrus was synchronized with two cloprostenol injections which were administered 10 days apart. Concurrent with the second injection (time 0), ewes (n = 6 per group) received one of the following treatments every 12 h from time 0 to 72 h: group 1: vehicle injection (control); group 2: 0.6 mg bromocriptine (0.03 mg per kg per day); and group 3: 1.2 mg bromocriptine (0.06 mg per kg per day). In Expt 1, blood samples were collected every 3 h from 0 to 72 h, and also every 20 min from 38 to 54 h to measure prolactin, LH and FSH concentrations. In Expt 2, transrectal ultrasonography was carried out every 12 h from time 0 until oestrus, and blood samples were collected every 4 h to measure prolactin, LH and FSH concentrations. Ovulation rates were determined by laparoscopy on day 4 after oestrus. Bromocriptine markedly decreased prolactin secretion, but did not affect FSH concentrations, the mean time of the LH preovulatory surge or LH concentrations in the preovulatory surge. Both doses of bromocriptine caused a similar decrease in LH pulse frequency before the preovulatory surge. The highest bromocriptine dose led to a reduction (P < 0.01) in the number of 2-3 mm follicles detected in the ovaries at each time point. However, bromocriptine did not modify the total number or the number of newly detected 4-5 mm follicles at each time point, the number of follicles > 5 mm or the ovulation rate. In conclusion, the effects of bromocriptine on gonadotrophin and prolactin secretion and on the follicular dynamics during the follicular phase of the sheep oestrous cycle indicate that prolactin may influence the viability of gonadotrophin-responsive follicles shortly after luteolysis.     

Oestrus, time of ovulation, ovulation rate and conception rate in progestagen-treated ewes given Gn-RH, Gn-TH analogues and gonadotrophins.

The influence of Gn-RH, hCG and a PMSG-hCG mixture (PG600) on the time of ovulation, ovulation rate and on the occurrence of oestrus in ewes treated with progestagen-impregnated sponges for 12 days examined. The effects of Gn-RH analogues on plasma LH, oestrus, ovulation and conception rate were also investigated. Six separate experiments were carried out. When 50 micrograms Gn-RH were given 24 h after sponge removal ovulation occurred in 44--46% of ewes within 24 h and in all ewes by 34 h. Gn-RH was a more potent ovulation synchronizer than hCG. Both hCG and PG600 reduced the incidence of overt oestrus. Gn-RH also had this effect in ewes treated during February and May but not in August and September. Gn-RH analogues given 2 days before sponge removal significantly increased ovulation rate. The display of oestrus was not affected in ewes treated 2 days before sponge removal but was suppressed in 43-69% of ewes treated with an analogue at the time of sponge removal. Ovulation occurred in 50-62% of ewes within 30-35 h of injection of Gn-RH analogues, regardless of the time of their administration. The release of LH in response to one analogue was not influenced by the presence of the progestagen-impregnated sponge in the vagina. When given a Gn-RH analogue 2 days before sponge removal or at the time of sponge removal 63 and 62% of mated ewes became pregnant compared with 70% of control ewes.     

New estrus synchronization and artificial insemination protocol for goats based on male exposure, progesterone and cloprostenol during the non-breeding season

This study assesses the effectiveness of a method designed to induce and synchronize ovulation in goats during the non-breeding season, allowing for systematic timed artificial insemination (AI), without the need for prior estrus detection. This method (IMA.PRO2) induces ovulation through the "male effect" and a single 25 mg dose of progesterone given at the time of buck exposure, and early lysis of the induced corpus luteum by the administration of 75 microg of cloprostenol 9 days later. The method was tested in three separate experiments. In experiment 1, estrus was detected in 87.5% of the treated goats 37.0 +/- 1.4 h after cloprostenol administration, with the preovulatory LH surge occurring 40.5 +/- 1.6 h after the cloprostenol injection. In experiment 2, data from 503 does revealed no significant differences in fertility rates between two groups inseminated 48 h (65.5+/-4.0%) or 52 h (63+/-3.0%) after receiving cloprostenol. In experiment 3, 2184 does, comprising 37 replicate groups on 12 farms, were randomly assigned to two trial subgroups. Does in the first subgroup were treated with the IMA.PRO2 method and goats from the second group were given intravaginal progestagens for 11 days, plus 350 IU of eCG and 75 microg of cloprostenol on Day 9 of this treatment. Goats from both subgroups were cervically inseminated at the same time, 50 h after cloprostenol administration in the first group and 46 h after sponge removal in the second. The pregnancy rate achieved with the new method was 64.6%, significantly higher than the yield observed for the use of progestagens plus eCG (46.8%, P<0.01). The simple method proposed as an alternative to the use of progestagen-eCG treatment provides good pregnancy rates to AI undertaken at a fixed time point, and reduces the amount of hormone needed to synchronize estrus in the animals.     

Effects of dose and route of administration of cloprostenol on luteolysis,estrus and ovulation in beef heifers

Four experiments were conducted (with crossbred beef heifers) to determine the effects of dose and route of administration of cloprostenol on luteolysis, estrus and ovulation. In Experiment 1, 19 heifers with a CL > or = 17 mm in diameter were randomly allocated to receive cloprostenol as follows: 100 microg s.c., 250 microg s.c., or 500 microg i.m. Heifers given 100 microg s.c. had a longer (P<0.03) interval (120.0 h+/-10.7 h; mean+/-S.E.M.) from treatment to ovulation than those given either 250 microg s.c. or 500 microg i.m. (92.0 h+/-7.4 h and 84.0 h+/-8.2 h, respectively). In Experiment 2, 28 heifers were given porcine LH (pLH), followed in 7 days by cloprostenol (same doses and routes as in Experiment 1), and a second dose of pLH 48 h after cloprostenol. Luteolysis occurred in all heifers, and no difference was detected among treatment groups in the interval from cloprostenol treatment to ovulation (mean, 101 h; P<0.9). In Experiment 3, 38 heifers at random stages of the estrous cycle (but with plasma progesterone concentrations > or =1.0 ng/ml) received 500 or 125 microg cloprostenol by either i.m. or s.c. injection (2/2 factorial design). There was no difference (P<0.4) among groups in the proportions of heifers that were detected in estrus or that ovulated. However, the interval from cloprostenol treatment to estrus was shorter (P<0.02) in the group that received 500 microg i.m. (58.5h) than in the other three groups (500 microg s.c., 75.0 h; 125 microg i.m., 78.0 h; and 125 microg s.c., 82.3h). In Experiment 4, 36 heifers were treated (as in Experiment 3) on Day 7 after ovulation. The proportions of heifers detected in estrus and ovulating after 125 microg s.c. (33 and 44%, respectively) or 125 microg i.m. (55 and 55%) were lower (P<0.05) than in those that received 500 microg s.c. (100 and 100%), but not different from those receiving 500 microg i.m. (78 and 89%, respectively). Overall, ovulation was detected in 9/18 heifers given 125 microg and 17/18 heifers given 500 microg of cloprostenol, on Day 7 (P<0.01) and was detected in 17/20 heifers given 125 microg and 18/18 heifers given 500 microg of cloprostenol, at random stages of the estrous cycle (P>0.05). Although there was no significant difference in luteolytic efficacy between i.m. and s.c. injections of the recommended dose (500 microg) of cloprostenol, variability in responsiveness to a reduced dose depended upon CL sensitivity, therefore, reduced doses cannot be recommended for routine use.     

Reduction of the developmental competence of sheep oocytes by inhibition of LH pulses during the follicular phase with a GnRH antagonist

A GnRH antagonist (Antarelix) treatment was used during the breeding season of Romanov ewes, to investigate whether LH pulses are required the day before the preovulatory surge for normal early embryo development in vivo (Expt 1) and in vitro (Expt 2). In Expt 1, at the onset of oestrus after removal of a fluorogestone acetate sponge, group A0.5 (n = 22) received a subcutaneous injection of 0.5 mg Antarelix, and ovulation was induced with an intravenous injection of 3 mg pig LH 24 h later. The control group (group C, n = 20) were untreated. All ewes were mated naturally at 36 and 48 h after oestrus and embryos were recovered 8 days after sponge removal. There were significant differences in the decrease in LH and in the increase in FSH concentration after Antarelix treatment between treated and control groups. The ovulation rate and embryo recovery rate were not significantly different between the two groups but the blastocyst rate was lower (P < 0.0001) in group A0.5 than in group C, with more unfertilized or degenerated oocytes in group A0.5 (69.2%). In Expt 2, 24 h after sponge removal, group A (n = 10) and group B (n = 10) received one subcutaneous injection of 0.5 mg Antarelix. The control group (group C, n = 10) was left untreated. LH pulsatility was re-established in group B with hourly intravenous injections of 5 micrograms ovine LH for 24 h. Oocytes were collected by flushing the oviducts 28 h after the LH surge, and were fertilized and cultured in vitro for 7 days. Ovulation and cleavage rates were not significantly different among the three groups but a higher rate of blastocysts (P < 0.01) was obtained after Antarelix treatment when LH pulsatility was re-established (group B). Oestradiol concentration was strongly depressed (P < 0.0003) after Antarelix treatment in group A, but was maintained after injection of LH pulses in group B, although at a lower value than before the preovulatory surge in the control group. In conclusion, inhibition of endogenous LH pulses 1 day before the preovulatory surge was not essential for ovulation and in vitro fertilization but was associated with a decrease in plasma oestradiol concentrations and inferior embryo development both in vivo and in vitro. When LH pulsatility was re-established, oestradiol concentrations increased and embryo development was restored.     

Effects of luteinizing hormone, progesterone, testosterone, estradiol and corticosterone on ovulation and luteinizing hormone release in hens treated with aminoglutethimide

Aminoglutethimide (AG), an inhibitor of steroidogenesis, was administered s.c. to 5 groups of laying hens at a dose of 200 mg AG/kg body weight 9 h before expected midsequence ovulation. This dose has previously been demonstrated to consistently block ovulation. The injection of AG was followed by s.c. injections of: Group 1, 1.0 mg progesterone; Group 2, 0.1 mg estradiol-17 beta; Group 3, 1.5 mg corticosterone, all at 6 h prior to expected ovulation; Group 4, 1.0 mg testosterone at both 8 h and 5 h before expected ovulation; and Group 5, 25 micrograms of ovine luteinizing hormone (LH) at 8 and 50 micrograms ovine LH at 6 h before expected ovulation. For each group, 4 control hens were injected with AG and the appropriate vehicle. Blood samples were taken at 1- or 2-h intervals from the time of AG injection to the expected time of ovulation. The hens were killed 4 h after expected ovulation and examined for the occurrence of ovulation. In all hens injected with vehicle, ovulation and the preovulatory surges of progesterone, testosterone, estradiol-17 beta and LH were inhibited. The plasma concentration of corticosterone was not reduced following an injection of AG. Four of 6 hens ovulated in response to injection of ovine LH, although neither endogenous LH nor progesterone were released. Thus, LH appears to play a direct role in follicular rupture and extrusion of the ovum. The administration of progesterone induced a significant and prolonged rise in LH, restoring AG-blocked ovulation in all hens treated (n = 6). Injections of testosterone restored LH release in all hens and ovulation in 2 of 7 hens treated. Three of 7 hens ovulated in response to the corticosterone injection. A preovulatory rise in LH was not observed, indicating that corticosterone may exert its ovulation-inducing effect directly on the mature follicle. Estradiol-17 beta did not restore LH release or ovulation in any of the hens treated with AG.     

Effect of oxytocin infusion on secretion of progesterone and luteinizing hormone and the concentration of uterine oxytocin receptors during the periovulatory period in cloprostenol-treated ewes.

Oxytocin infusions were initiated on day 10 of the oestrous cycle in ewes, and luteal regression was induced by injection of 100 micrograms cloprostenol on day 12. Blood samples were collected at frequent intervals via an indwelling jugular vein cannula to measure concentrations of progesterone and luteinizing hormone (LH) during the luteal and follicular phases in saline (n = 6) and oxytocin (n = 5) infused animals. The oxytocin infusion maintained peripheral plasma concentrations of 53 +/- 3.2 pg oxytocin ml-1 (mean +/- SEM) compared with values of about 1 pg ml-1 during oestrus in control ewes. Oxytocin infusion had no effect on luteal phase progesterone concentrations, the timing of luteolysis, basal luteinizing hormone (LH) secretion, LH pulse frequency, or the timing or height of the LH surge. Treated ewes came into oestrus significantly earlier than controls (P < 0.05) but ovulated normally. Uterine samples collected 96 h after cloprostenol injection (approximately day 2 of the cycle) showed that oxytocin receptor concentrations were significantly higher in the endometrium in ewes that had been given a 5 day oxytocin infusion than in control animals (556 and 262 fmol mg-1 protein, respectively: geometric means from ANOVA, P < 0.001), whereas myometrial receptor concentrations were not affected (113 and 162 fmol mg-1 protein, respectively). We conclude that the previously reported delay in luteal development caused by oxytocin infusion (Wathes et al., 1991) is not due to the inhibition or delay of ovulation, but must instead occur via a direct influence on the developing corpus luteum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a progestagen on buck-induced short ovarian cycles in the creole meat goat

Two experiments were conducted to determine the effects of progestagens on the buck-induced ovarian cycle in anovular female Creole goats. In the first experiment, 25 anovular females served as a control group and 23 anovular females received a fluorogestone acetate (FGA)-impregnated sponge (45 mg) which was removed at the time males were introduced in the two groups. In the second experiment 10 anovular females served as the control group, and another 10 anovular females received an injection of FGA (5.2 mg) at the time males were introduced. Ovarian activity was traced by laparoscopy (Exp. 1) or progesterone levels (Exp. 2); oestrus and litter size were recorded, and fertility was calculated. In Exp. 2 blood samples were taken every 4 h to study the buck-induced preovulatory luteinizing hormone (LH) surge, and twice daily for progesterone plasma levels.FGA pretreatment did not modify the percentage of females ovulating in either experiment. The percentage of females showing oestrus at first ovulation in Exp. 1 was enhanced by treatment (55% vs 100%), and in both experiments FGA pretreatment restored the normal lifespan of corpora lutea compared to untreated females (96% vs 14%). FGA injection delayed the onset of oestrus and the preovulatory LH surge by 20 h, but did not modify either duration of oestrus or duration of the LH surge.Fertility of control females was low at first ovulation compared to FGA-treated females (10% vs 85%); but fertilization occurred at the subsequent ovulations in most of the control females.It is concluded that progestagen pretreatment is an efficient technique to control buck-induced short ovarian cycles. The exact role of the progestagen, through a delay of LH surge or a direct effect on follicles, remains unknown.     

Controlled sheep breeding: update 1980-1985

This contribution to the Symposium concerns four topics which have been addressed in our laboratory over the past five years. First, the responses to a controlled light environment of Merino ewes and rams have been compared with those of two British breeds. The endocrinological patterns were similar in all breeds but cyclic ovarian activity and ram libido were different. While showing a degree of entrainment to photoperiod, the breeding patterns were much less rigidly controlled in the Merinos than in the others. Second, the effectiveness of establishment of a cervical reservoir of spermatozoa, in ewes in which oestrus and ovulation have been controlled, has been re-examined. This is highly dependent on the time of insemination relative to that of the release of LH. Maximum numbers are found when ewes are inseminated shortly after the LH peak, i.e. some 6-10 h after the onset of oestrus. Third, the quantitative and temporal endocrinological and behavioural events following standard, progestagen-PMSG treatment have been quantified. Contrary to earlier expressed beliefs, these events are remarkably predictable provided an intensive system of mating or detection of oestrus is used. The onset of oestrus in treated anoestrous crossbred ewes has a normal distribution, with a range of 24 h, centred around a mean of 33 h after withdrawal of a 30 mg Cronolone intravaginal sponge and injection of 500 i.u. PMSG. This period of time is dose-dependent. The LH peak occurs 4.5 +/- 0.7 h later and the times of onset of oestrus and of LH release are highly correlated (r = 0.93). Ovulation is some 24 h later again. Fourth, differences in the response of ewes to different batches of PMSG have been defined. While the three commercial preparations studied regularly induced ovulation in anoestrous ewes at doses of 250 i.u. and above, the quantitative responses varied greatly. One preparation would not induce multiple ovulation, even at high doses. There are differences in steroidogenesis and in pregnancy rates, associated with dose of PMSG and the consequent ovulation rate: the ideal would be for every ewe to shed two or three ova. A higher ovulation rate is acceptable, as early embryonic mortality generally reduces the litter size. This is particularly important in deep anoestrus. However, this does not solve the problem of breeding in early lactation.     

Effects of continuous elevated cortisol concentrations during oestrus on concentrations and patterns of progesterone, oestradiol and LH in the sow

This study investigated the effect of continuous elevated cortisol concentrations during standing oestrus on time of ovulation and patterns of progesterone, oestradiol and luteinising hormone (LH) in sows. The elevation of cortisol concentrations was achieved through repeated intravenous injections of synthetic adrenocorticotropic hormone (ACTH) every 2 h for approximately 48 h, from the onset of the second standing oestrus after weaning. Treatment was terminated when ovulation was detected (monitored by transrectal ultrasonography every 4h) or when the sow had received a maximum of 24 injections. The dose of ACTH (2.5 microg/kg) was chosen to mimic the cortisol concentrations seen during mixing of unfamiliar sows. The sows (n=14) were surgically fitted with jugular vein catheters and randomly divided into a control (C group where only NaCl solution were injected) or an ACTH group. Blood samples were collected every 2 h. In parallel with the blood sampling, saliva samples for cortisol analyses were taken from eight sows before onset of treatment and from four of the sows during treatment. There was no difference in time from onset of standing oestrus to ovulation between the two groups. The interval between the peaks of oestradiol and LH to ovulation was prolonged in the ACTH group compared to the C group (p<0.05), with a tendency towards an earlier decline of oestradiol in the ACTH group. Cortisol and progesterone concentrations were significantly elevated during treatment in the ACTH group (p<0.001), with cortisol peak concentrations occurring between 40 and 80 min after each ACTH injection. Cortisol concentrations in saliva and plasma were highly correlated (p<0.001). In conclusion, elevated cortisol concentrations from the onset of standing oestrus increase progesterone concentrations and prolong the interval between oestradiol and LH peaks to ovulation, the latter possible due to an early decline in oestradiol concentrations and a change of the LH peak outline. The effect these hormonal changes have on reproductive performance need to be further investigated. Saliva samples might be a useful and non-invasive method to assess cortisol concentrations in sows.     

Effect of cycloheximide [correction of cyclohexamide] injected at proestrus on ovarian protein synthesis, peptide and steroid hormone levels, and ovulation in the hamster

Injecting 2 or 4 mg of cycloheximide (cyclo) at the onset of the proestrous release of gonadotropins prolongs the estrogen (E2) surge, diminishes progesterone (P4) secretion, and prevents ovulation by 0900 h of the next morning (Saidapur and Greenwald, 1981). The present study was designed to determine the effects of 0, 2, 4, or 8 mg cyclo injected at 1400 h proestrus (Day 4) on ovarian protein synthesis and other parameters. Ovulation was delayed until 1400 h estrus by 2 mg cyclo or prevented by 8 mg, and the latter treatment resulted in the death of all animals by 48 h. After 4 mg cyclo, ovulation was delayed in some animals, but the most characteristic feature was the development of large cystic follicles that ultimately transformed into corpora hemorrhagica. All animals lived after the injection of 4 mg cyclo. Ovaries collected 2, 8, 16, or 24 h after treatment were incubated with [3H]leucine for 1 h to assess the effects of cyclo on protein synthesis. Injection of phenobarbital at 1300 h proestrus, which blocks follicle-stimulating hormone (FSH) and luteinizing hormone (LH) surges, reduced ovarian protein synthesis at 1600 h to 61% of the control value. The incorporation of [3H]leucine was reduced to 75%, 37%, and 35% of the 1600-h control value by 2, 4, and 8 mg cyclo, respectively, but without affecting surge levels of FSH and LH. However, by 0600 h estrus, protein synthesis was increased significantly in all the cyclo-treated groups, which provides insight into the half-life of the compound (approximately equal to 8 h for 2-4 mg cyclo). At 1600 and 2200 h proestrus cyclo resulted in serum FSH and LH levels similar to controls, but increased serum prolactin and prolonged E2 levels at Day 4 of 2200 h and decreased serum P4 at both times. The second surge in FSH, which is in progress by 0600 h estrus, was abolished by 4 or 8 mg cyclo but not by the 2-mg dose. This is the first time for any species that ovarian protein synthesis has been measured in the proestrous normal or cyclo-treated animal. We conclude for the hamster that 4 mg cyclo is the optimal dose for blocking ovarian protein synthesis and ovulation and inducing formation of cystic follicles.     

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)     

Continuous infusion of oxytocin prevents induction of uterine oxytocin receptor and blocks luteal regression in cyclic ewes

Continuous intravenous infusion of oxytocin (3 micrograms/h) between Days 13 and 21 after oestrus delayed return to oestrus by 7 days (length of cycle 23.3 +/- 0.6 days compared to 16.6 +/- 0.2 days in control ewes). At a lower infusion rate (0.3 micrograms/h) oxytocin delayed luteolysis in only 2 of 5 ewes. Treatment from Day 14, when luteolysis had already begun, was ineffective. Delay of luteal regression by oxytocin had no effect on the length of subsequent cycles. Measurement of circulating progesterone concentrations and luteal weight showed that prolongation of the oestrous cycle was due to prevention of luteal regression. Luteal regression and behavioural oestrus were induced during continuous oxytocin administration begun on Day 13 when cloprostenol was given on Day 15 (mean cycle length, 17.3 +/- 0.21 days). Continuous oxytocin infusion from Day 13 blocked the rise in uterine oxytocin receptor concentrations which normally precedes oestrus. Mean receptor concentrations in caruncular and intercaruncular endometrium and in myometrium were 76, 36 and 9 fmol/mg protein on Day 17 in ewes receiving continuous oxytocin (3 micrograms/h); in control ewes these values were 675, 638 and 130 fmol/mg protein respectively at oestrus. Receptor concentrations on the day of oestrus in ewes receiving oxytocin and cloprostenol were not significantly different from those in control ewes (649, 852, and 109 fmol/mg protein respectively). Since cloprostenol, a PGF-2 alpha analogue, overcame the antiluteolytic action of oxytocin, it is suggested that continuous oxytocin treatment may inhibit uterine production of PGF-2 alpha, possibly by down regulating the uterine oxytocin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of an LHRH antagonist on the time of occurrence and amplitude of the preovulatory LH surge, progesterone and estradiol secretion, and ovulation in superovulated Holstein heifers

Beginning on Day 10 or 11 of the estrous cycle, mature Holstein heifers were given a superovulatory regimen of twice-daily injections of porcine FSH, together with injections of PG with the fifth and sixth FSH injections. Every 12 h from 24 to 60 h after PG administration, the animals received im injections of different doses of the LH releasing hormone antagonist [N-Ac-D-Nal(2)(1), D-pCl-Phe(2), D-Trp(3), D-Arg(6), D-Ala(10)]-LHRH or vehicle. Follicular development was monitored by transrectal ultrasonography every 12 h from 24 to 120 h after PG administration. All animals were given hCG at 72 h after PG injection, and were artificially inseminated. At Day 7 of gestation, the corpora lutea were counted by ultrasonography, and embryos were collected by nonsurgical flushing of the uterus. Treatment with the antagonist resulted in a dose-dependent decrease in the amplitude of the LH surge and in delays in the time of occurrence of the LH surge, ovulation and the shift from estradiol to progesterone production. These results indicate that LHRH antagonists can be used to delay the LH surge and ovulation in superovulated heifers. This finding may be beneficial to studies in the superovulation of cattle.     

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.     

Relationships between LH, FSH and prolactin secretion and reproductive activity in the weaned sow

Blood samples were collected from primiparous sows via indwelling jugular cannulae at 15-min intervals for 12 h before and for 24 h (2 sows) or 48 h (10 sows) after weaning and then every 4 h until behavioural oestrus. Weaning to oestrus intervals ranged from 3 to 10 days and 2 sows showed no signs of oestrus and had not ovulated by Days 11 and 16 after weaning. Prolactin concentrations in plasma decreased significantly (P less than 0.001) and reached basal levels 1-2 h after weaning in all sows whilst plasma progesterone concentrations remained basal until approximately 30 h after the preovulatory LH surge in sows that ovulated. Elevated concentrations of prolactin or progesterone during the post-weaning period were, therefore, not responsible for delayed restoration of cyclicity. Overall, mean LH concentrations rose significantly (P less than 0.001) from 0.22 +/- 0.02 during the 12-h period before weaning to 0.38 +/- 0.03 ng/ml during the 12-h post-weaning period. After weaning, pulsatile and basal LH secretions were markedly increased for sows that showed an early return to oestrus (less than or equal to 4 days) compared with sows showing a longer weaning to oestrus interval but a correlation did not exist between either of these LH characteristics and the time taken to resume cyclicity. Mean LH concentrations before weaning were, however, inversely related (r = -0.649; P less than 0.05) to the weaning to oestrus interval. Overall, mean FSH concentrations rose significantly (P less than 0.001) from 151.1 +/- 6.2 (s.e.m.) ng/ml in the 12-h period immediately before weaning to 187.7 +/- 9.7 ng/ml in the subsequent 12-h period but there was no correlation between FSH concentrations, before or after weaning, and the interval from weaning to oestrus. However, a significant correlation was apparent between ovulation rate and peak concentrations of the rise in FSH after weaning (r = 0.746; P less than 0.05) and overall mean FSH values (r = 0.645; P less than 0.05). It is concluded that both LH and FSH concentrations in peripheral blood rose in response to removal of the suckling stimulus at weanling. The increase in LH pulse frequency associated with weaning was not directly related to the weaning to oestrus interval although a specific pattern of LH secretion was observed in sows showing an early return to oestrus (less than or equal to 4 days).(ABSTRACT TRUNCATED AT 400 WORDS)