Ovarian response to exogenous hormones in six-week-old lambs.

Crossbred lambs 5--6 weeks old were treated with human chorionic gonadotrophin (hCG) (500 or 1500 i.u.) alone, hCG plus pregnant mare serum gonadotrophin (PMSG) (1000 or 2000 i.u.), 1000 i.u. PMSG alone, or were untreated. PMSG alone and PMSG + hCG increased ovarian weight and uterine weight. PMSG alone stimulated growth and luteinization of follicles but PMSG + hCG induced ovulations and formation of corpora lutea. hCG alone did not change any of the characteristics which were measured. PMSG had a significant effect on the number of vesicular follicles but none of the treatments affected the number of growing follicles.     

Superovulation and embryo recovery in rabbits (Oryctolagus cuniculus) using different doses of pregnant mare serum gonadotrophin (PMSG)

Present investigation was conducted to study the ovarian response and embryo recovery using different PMSG dose levels. Six rabbits each were assigned randomly to treatment 1 (PMSG 50 IU + hCG 100 IU), treatment 2 (PMSG 75 IU + hCG 100 IU) and the control group (no hormone administered). PMSG injection (im) was followed 68 hr later by natural mating to a fertile rabbit buck and human chorionic gonadotrophin (hCG) injection iv post coitum. Embryos were recovered 96 hr post coitum by a modified surgical method. Mean number of ovulations in the control group differed significantly from treatment 1 and 2, but no significant difference was observed between treatments 1 and 2. Mean embryo recovery percentage was lowest in treatment 2 and highest in the control group. The higher dose PMSG (treatment 2) was observed to be more disturbing in terms of recovery of embryos as well as their morphology.     

Effects of monoclonal antibody against PMSG administered shortly after the preovulatory LH surge on time and number of ovulations in PMSG/PG-treated cows

Normally cyclic heifers received 2500 i.u. PMSG i.m. at Day 10 of the oestrous cycle and 15 mg prostaglandin (PG) i.m. 48 h later. From 30 h after PG the LH concentration in the peripheral blood was estimated every hour using a rapid RIA method which allowed the LH concentration to be known within 4 h. Monoclonal antibody against PMSG was injected in the jugular vein of 29 heifers at 4.8 h after the maximum of the preovulatory LH peak; 28 heifers were not treated with anti-PMSG (controls). Peripheral blood concentrations of PMSG, LH, progesterone and oestradiol were compared. Ovaries were collected by ovariectomy at fixed times, 22-30 h after the LH peak, and numbers were counted of small (2-10 mm), large (greater than 10 mm) and ovulated follicles, and of follicles with a stigma. In anti-PMSG-treated cows, the PMSG concentration fell sharply to non-detectable levels within 2 h of the treatment, indicating that PMSG was neutralized in these cows at the onset of final follicular maturation. In all cows, the concentration of oestradiol showed a significant decrease at about 8 h after the LH peak. After anti-PMSG treatment ovulations took place from 24 until 30 h after the LH peak, whereas in control cows follicles had already ovulated at or before 22 h and ovulations continued until 30 h. At 30 h 90% of the follicles had ovulated in anti-PMSG-treated cows vs 72% in the controls, resulting in 15 and 8 ovulations per cow respectively (P less than 0.05). Also, administration of monoclonal antibody against PMSG synchronized final follicular maturation and shortened the period of multiple ovulations. In conclusion, neutralization of PMSG shortly after the preovulatory LH peak suppresses adverse effects of PMSG on final follicular maturation, leading to an almost 2-fold increase of the ovulation rate.     

Action of PMSG on follicular populations in the heifer

The short-term action of PMSG on the population of growing follicles in cattle was studied using histological methods. On Day 7 of a synchronized oestrous cycle 10 Friesian heifers were unilaterally ovariectomized. The remaining ovary was immediately stimulated by an injection of PMSG (2000 i.u.) and was removed 48 h after the preovulatory discharge of LH. Control animals did not receive any injection of PMSG. In all ovaries, follicles greater than 70 micron diameter were counted, measured and checked for atresia. The mitotic index in granulosa cells of follicles of different sizes was estimated in both ovaries of all the PMSG-injected animals. Unilateral ovariectomy alone had no significant effect on follicular populations. In the interval between PMSG injection and removal of the second ovary (148 +/- 22.7 h), PMSG significantly increased the number of normal preantral follicles but did not change the number of normal antral follicles. The mitotic index doubled in preantral and early antral follicles but remained unchanged in large antral follicles. PMSG stimulated slightly the growth of the antrum in large antral follicles but did not stimulate its formation in preantral follicles. The incidence of atresia among antral follicles, particularly the largest ones (diam. greater than 1.7 mm), was significantly reduced after PMSG, suggesting some 'rescue' of follicles from atresia.     

Ovarian function in Holstein cows immunized against pregnant mare serum gonadotrophin

Six Holstein-Friesian cows were immunized against pregnant mare serum gonadotrophin (PMSG) using Freunds' adjuvant during the mid-luteal phase of the estrous cycle. Antibody response was maintained by five booster immunizations at 2- to 3-wk intervals. Four cows were treated with a single intramuscular injection of PMSG (2350 I U) 107 d after primary immunization. Cloprostenol (500 ug) was administered at 56 h and 72 h after the treatment with PMSG; the cows were inseminated three times at 12-h intervals starting 56 h after cloprostenol treatment. Five days after insemination, the animals were slaughtered and their reproductive organs were recovered to quantify the population of corpora lutea and unovulated follicles (>10 mm dia). Antibody titres and progesterone concentrations were determined from blood samples collected either on alternate days or twice a week. Initially, progesterone concentrations were measured in milk samples. All cows produced antibodies, and titres were elevated within 6 to 9 d following each booster immunization. After each boost, however, the antibody titres declined rapidly. Progesterone concentrations declined to below 1 ng/ml after two weeks of initial immunization and remained low throughout the study, except in one cow that ovulated on Day 75. All animals were observed to have large follicular cysts during this period. Treatment with PMSG induced a single ovulation in one cow. Ovulations were neither induced by PMSG nor observed in any of the other animals. In PMSG-treated animals, the mean number of large follicles (5.0) was greater than in those which were not treated (2.0). The results of this study suggest that low titres of antibodies against PMSG are sufficient to disturb ovarian activity, result in follicular cysts and block multiple ovulations in response to exogenous PMSG.     

Evaluation of three equine FSH superovulation protocols in mares

Superovulation could potentially increase embryo recovery for immediate transfer or cryopreservation. The objectives were to evaluate the effect of pretreatment with progesterone and estradiol (P+E) on follicular response to eFSH and compare doses of eFSH and ovulatory agents on follicular development and ovulation in mares. In Experiment 1, 40 mares were assigned to one of four treatment groups. Group 1 consisted of untreated controls. Group 2 mares were administered eFSH without pretreatment with P+E. Group 3 mares were administered P+E for 10 days starting in mid-diestrus followed by eFSH therapy. Group 4 mares were administered P+E for 10 days followed by eFSH therapy. All treated mares were administered 12.5mg eFSH twice daily and prostaglandins were given on the second day of eFSH therapy. Mares were bred with fresh semen the day of hCG administration and with cooled semen the following day. The numbers of preovulatory follicles and ovulations were lower for mares treated with P+E prior to eFSH treatment. Pretreatment with P+E in estrus also resulted in a lower embryo recovery rate per ovulation compared to the other two eFSH treatment groups. In Experiment 2, two doses of eFSH (12.5 and 6.25mg) and two ovulation-inducing agents (hCG and deslorelin) were evaluated. The number of preovulatory follicles was greater for mares given 12.5mg of eFSH compared to mares given 6.25mg. Number of ovulations was greatest for mares given 12.5mg of eFSH twice daily followed by administration of hCG. Embryo recovery per flush was similar among treatment groups, but the percent of embryos per ovulation was higher for mares given the low dose of eFSH. In summary, there was no advantage to giving P+E prior to eFSH treatment. In addition, even though the lower dose of eFSH resulted in fewer ovulations, embryo recovery per flush and embryo recovery per ovulation were similar or better for those given the lower dose of eFSH.     

Ovarian features contributing to the variability of PMSG-induced ovulation rate in sheep

In Exp. 1, ovulation rate was measured in three groups of Romanov ewes given two injections of 600 i.u. PMSG 3 weeks apart with the ewes intact (Group I, N = 8), a similar treatment with the ewes intact at the first injection and unilaterally ovariectomized at the second (Group II, N = 8), or unstimulated ewes which were hemispayed at the same time as Group II ewes (Group III, N = 6). In Exp. 2, the follicular population of one ovary was correlated with the number of ovulations induced by 600 i.u. PMSG in the contralateral ovary (10 Romanov ewes). From 8.4 +/- 1.8 (Group I) and 8.2 +/- 3.3 (Group II) CL at the first injection, PMSG-induced ovulation rate at the second injection decreased to 3.9 +/- 1.8 and 3.7 +/- 1.2 in Groups I and II respectively, a value similar for ewes with 1 or 2 ovaries. Furthermore, despite no major changes in the number of antral follicles after the first injection, there was no correlation (r = -0.09) between the response to the two successive injections in intact ewes. Comparison of the ovarian status of the ovary removed before the PMSG injection (Group II ewes of Exp. 1, ewes of Exp. 2) to the number of CL found in the remaining ovary demonstrated that PMSG-induced ovulation rate was not correlated with the overall antral follicle population (r = 0.62 in Exp. 1, r = 0.49 in Exp. 2).(ABSTRACT TRUNCATED AT 250 WORDS)     

不同激素和注射方式对家猫超排效果的比较

比较了PMSG hCG和FSH hCG两种方案以及PMSG的不同剂量和注射方式对家猫的超排效果的影响。用 1 0 0IU的PMSG超排家猫所得到的排卵点数及平均每只猫获得的卵数显著低于 2 0 0IU处理组或 30 0IU处理组 (P <0 0 5 ) ,但 2 0 0IU处理组与 30 0IU处理组之间的超排效果也无显著差异 (P >0 0 5 ) ;用皮下注射 2 0 0IU的PMSG或用肌肉注射 2 0 0IU的PMSG对超排效果无差异 (P >0 0 5 ) ;用 2 0 0IUPMSG 2 0 0IUhCG和 1 5mgFSH 2 0 0IUhCG两种方案对家猫超排 ,发现不论是每只猫的排卵点数、卵子获得数 ,还是卵子的第一极体排放率都没有显著差异 (P >0 0 5 )。实验说明 ,PMSG的注射方式不影响对家猫的超排效果 ,用 2 0 0IU的PMSG超排家猫是较适合的剂量 ,FSH和PMSG都可用于家猫的超排 ,但PMSG使用更为方便。     

Inhibition of follicle-stimulating hormone-induced ovulation by indomethacin in the perfused rat ovary

In isolated, perfused ovaries of rats treated with pregnant mare's serum gonadotropin (PMSG), purified preparations of ovine follicle-stimulating hormone (FSH) (oFSH-211B) and rat FSH (rFSH-I-6), 100 ng/ml, were found to induce ovulations (4.8 +/- 0.9, n = 4, and 6.4 +/- 2.0, n = 5, ovulations per ovary, respectively). Indomethacin (5 micrograms/ml) added to the perfusate inhibited this ovulatory effect and exogenous prostaglandin F2 alpha (PGF2 alpha) (1 microgram/ml), or prostaglandin E2 (PGE2) (0.5 microgram/ml), reversed the blockade. Ovine FSH and rFSH had only a weak stimulatory effect on estradiol release, and only rFSH caused a significant increase in progesterone accumulation. Indomethacin reduced the stimulatory effect of rFSH on progesterone release, and this effect was reversed by PGE2 but not by PGF2 alpha. In a 6-h incubation experiment with preovulatory rat follicles, we tested the biological activity of gonadotropins used to induce oocyte maturation. The concentration of FSH used in the perfusion experiments induced oocyte maturation in more than 88% of the oocytes studied. The data confirm earlier findings that FSH can induce ovulations and show that prostaglandins are involved in this process. The data also indicate that prostaglandins might be involved in the FSH-induced increase of progesterone levels.     

Strategies to improve the ovarian response to equine pituitary extract in cyclic mares

Equine pituitary extract (EPE) has been reported to induce heightened follicular development in mares, but the response is inconsistent and lower than results obtained in ruminants undergoing standard superovulatory protocols. Three separate experiments were conducted to improve the ovarian response to EPE by evaluating: (1) effect of increasing the frequency or dose of EPE treatment; (2) use of a potent gonadotropin-releasing hormone agonist (GnRH-a) prior to EPE stimulation; (3) administration of EPE twice daily in successively decreasing doses. In the first experiment, 50 mares were randomly assigned to one of four treatment groups. Mares received (1) 25 mg EPE once daily; (2) 50 mg EPE once daily; (3) 12.5 mg EPE twice daily; or (4) 25 mg EPE twice daily. All mares began EPE treatment 5 days after detection of ovulation and received a single dose of cloprostenol sodium 7 days postovulation. EPE was discontinued once half of a cohort of follicles reached a diameter of >35 mm and hCG was administered. Mares receiving 50 mg of EPE once daily developed a greater number (P = 0.008) of preovulatory follicles than the remaining groups of EPE-treated mares, and more (P = 0.06) ovulations were detected for mares receiving 25 mg EPE twice daily compared to those receiving either 25 mg EPE once daily and 12.5 mg EPE twice daily. Embryo recovery per mare was greater (P = 0.05) in the mares that received 12.5 mg EPE twice daily than those that received 25 mg EPE once daily. In Experiment 2, 20 randomly selected mares received either 25 mg EPE twice daily beginning 5 days after a spontaneous ovulation, or two doses of a GnRH-a agonist upon detection of a follicle >35 mm and 25 mg EPE twice daily beginning 5 days after ovulation. Twenty-four hours after administration of hCG, oocytes were recovered by transvaginal aspiration from all follicles >35 mm. No differences were observed between groups in the numbers of preovulatory follicles generated (P = 0.54) and oocytes recovered (P = 0.40) per mare. In Experiment 3, 18 mares were randomly assigned to one of two treatment groups. Then, 6-11 days after ovulation, mares were administered a dose of PGF2, and concomitantly began twice-daily treatments with EPE given in successively declining doses, or a dose of PGF2alpha, but no EPE treatment. Mares administered EPE developed a higher (P = 0.0004) number of follicles > or = 35 mm, experienced more (P = 0.02) ovulations, and yielded a greater (P = 0.0006) number of embryos than untreated mares. In summary, doubling the dose of EPE generated a greater ovarian response, while increasing the frequency of treatment, but not necessarily the dose, improved embryo collection. Additionally, pretreatment with a GnRH-a prior to ovarian stimulation did not enhance the response to EPE or oocyte recovery rates.     

Factors affecting superovulation in heifers treated with PMSG

In this study we determined 1) if the immunoneutralization of PMSG affected the ovulatory response, the number of large follicles and embryo yield compared with that of PMSG alone or pFSH, and 2) whether the stage of the estrous cycle at which PMSG was injected affected the ovulatory response and yield of embryos in superovulated heifers. Estrus was synchronized in 99 (Experiment 1) and 71 (Experiment 2) heifers using prostaglandin F2alpha (PG) analogue, cloprostenol, given 11 d apart in replicate experiments over 2 yr. In Experiments 1 and 2, heifers were randomly allocated to 1 of 3 treatments (initiated at mid-cycle): Treatment 1--24 mg of pFSH (Folltropin) given twice daily for 4 d; Treatment 2--a single injection of 2000 IU PMSG; Treatment 3--2000 IU PMSG followed by 2000 IU of Neutra-PMSG at the time of first insemination. In Experiment 3, 116 heifers were given 2000 IU PMSG on Day 2 (n = 28), Day 3 (n = 27), Day 10 (n = 41) or Day 16 (n = 20) of the estrous cycle. The PG was given at 48 h (500 microg cloprostenol) and 60 h (250 microg cloprostenol) after the first gonadotropin treatment. Heifers were inseminated twice during estrus, and embryos were recovered on Day 7, following slaughter and graded for quality. The numbers of ovulations and large follicles (> or =10 mm) were also counted. There was no effect of treatment on ovulation rate in Experiment 1, but in Experiment 2 it was greater (P < 0.002) in heifers given PMSG (14.7 +/- 1.5) than pFSH (7.5 +/- 1.4) or PMSG-neutra-PMSG (8.7 +/- 1.5). The number of large follicles was higher following PMSG than pFSH treatment in Experiment 1, and it was higher (P < 0.004) in heifers given PMSG (5.5 +/- 0.8) than pFSH (1.12 +/- 0.7) or PMSG-neutra-PMSG (2.7 +/- 0.8) in Experiment 2. The use of Neutra-PMSG did not affect the numbers of embryos recovered or numbers of Grade 1 or 2 embryos, but it did decrease the number of Grade 3 embryos in both experiments. In Experiment 3, the ovulation rate decreased (P < 0.004) when PMSG was given on Day 3 (5.7 +/- 1.46) of the cycle rather than on Day 2 (12.3 +/- 1.64), Day 10 (13.4 +/- 1.45) or Day 16 (12.5 +/- 1.87). There was no effect of day of treatment on the numbers of large follicles. The mean numbers of embryos recovered were lower (P < 0.01) in heifers treated on Day 3 (2.1 +/- 0.67) than on Day 2 (6.8 +/- 1.0), Day 10 (6.4 +/- 0.86) or Day 16 (7.8 +/- 1.87). It is concluded that Neutra-PMSG given to heifers treated with PMSG did not improve embryo yield or quality and that treatment with PMSG early in the cycle can result in acceptable embryo yields provided sufficient time elapses between treatment and luteolysis.     

Effects of selenium toxicity on oestrous cyclicity, ovarian follicles, ovulation and foetal survival in rats

Effects of intraperitoneal injections of sodium selenite (2.0 and 4.0 mg/kg body weight) to normally cycling female albino Wistar rats daily for 30 days, and of single injection either during proestrous or oestrous and at each stage of the 4-day oestrous cycle were determined on oestrous cyclicity, ovarian follicles, ovulation, implantation and pregnancy outcome on day 14 of gestation. Administration of selenite for 30 days had no effect on the duration of first two oestrous cycles but afterwards the rats remained at the dioestrus stage. Their ovaries developed cystic follicles. Selenite treatments during the oestrous cycle preceding mating affects the implantation and pregnancy outcome in a dose-related manner. Its single dose containing 2.0 mg/kg body weight administered either at proestrous or oestrous, though had no effect on different reproductive parameters investigated in this study but its daily dose during the 4 day oestrous cycle reduced the number of corpora lutea and implantations as compared to saline injected control female rats. Similar effects of a single dose of selenite (4.0 mg/kg body weight) when injected at proestrous were recorded. Higher dose of selenite at oestrous or throughout the cycle decreased the number of implantations, but in addition, also increased the resorption rate/litter on day 14 of gestation. The present studies clearly show that high selenium levels in the body during the oestrous cycle preceding mating affects the number of ovulations, implantations and live embryos depending upon its dose and stage of administration.     

Effect of a low dose of pregnant mare's serum gonadotropin on follicular recruitment and atresia in cycling rats

Atresia appears to play a central role in selecting the correct number of follicles for ovulation in the rat. A wave of atresia, apparent by noon on metestrus, reduces the number of large healthy follicles to the appropriate quota for ovulation. The purpose of this study was to test the hypothesis that falling levels of gonadotropin on the morning of estrus precipitate the wave of atresia of large follicles seen on metestrus. Endogenous concentrations of follicle-stimulating hormone (FSH) were augmented by a single injection of pregnant mare's serum gonadotropin (PMSG; 0.025 IU/gram body weight) administered at different times during the periovulatory period. Animals given PMSG at 0800 h on estrus (when the endogenous FSH surge was waning) had a supernormal number of large healthy follicles in their ovaries at 1200 h on metestrus. This increase in large healthy follicles was accompanied by a decrease in large atretic follicles in the ovaries. The same dose of PMSG, when administered at other times during the periovulatory period, did not affect any of the parameters measured. These observations suggest that the wave of atresia normally seen in large follicles on metestrus is triggered by the decline in the concentration of FSH during the morning of estrus and can be prevented by prolonging the surge of FSH with administration of PMSG.     

Effects of ovarian hyperstimulation and isolated preovulatory follicles on LH responses to GnRH in rats

Adult rats were pretreated with a 3-day regimen of human menopausal gonadotrophin (hMG), PMSG, human FSH or hCG and experiments were carried out on the day of pro-oestrus. Treatment with hMG and hFSH induced a significant increase in the number of preovulatory follicles on the day of pro-oestrus and this was correlated with increased circulating concentrations of oestradiol. There was a parallel increase in the self-priming effect of GnRH, as observed from the biphasic LH response to a continuous GnRH challenge. PMSG treatment did not stimulate increased numbers of maturing follicles and was less effective in raising circulating oestrogen concentrations compared with hMG and hFSH. However, pituitary responsiveness was much higher after PMSG treatment and the biphasic response to continuous perfusion with GnRH was absent; LH release was high from the initiation of the stimulus. hCG alone failed to stimulate follicular maturation but enhanced pituitary LH responses. Hemi-pituitary glands perfused in the presence of isolated preovulatory follicles also showed augmented biphasic LH responses to GnRH compared with control hemi-pituitary glands. The apparent dissociation which can occur between follicular maturation, circulating oestrogen concentrations and pituitary responsiveness to GnRH supports the idea of non-steroidal ovarian factors modulating LH release.     

Effect of equine chorionic gonadotropin on weaning-to-first service interval and litter size of female swine

We evaluated the effect of PMSG on the weaning-to-first service interval, total litter size and born alive litter size in swine. Four doses of PMSG (0, 500, 750 and 1,000 IU) were administered intramuscularly after weaning to sows at 3 different farms, grouped by parities (1, 2 and 3 or higher) and 2 distinct time periods. The associations among main effects and response variables were assessed by analysis of variance. Polynomial orthogonal terms were used to adjust the estimates of weaning-to-first service interval, total litter size and born alive litter size for the interaction effect of parity and PMSG treatment. The weaning-to-first service interval did not differ across periods and farms (P>0.05), although the interval was shorter (P<0.05) for Parity 3+ sows (4.97 d) than for Parity 1 sows (5.29 d), with no other differences in intervals observed across parities (P>0.05). Time period did not influence litter size (P>0.05), but there were differences in litter size across farms (P<0.05). Both litter size traits were lower for Parity 1 sows than for higher parity sows (P<0.05), but there were no differences in litter size between Parity 2 and 3+ sows (P>0.05). Litter size increased with PMSG dose in both Parities 1 and 2 (P<0.05), but not in Parity 3+ (P>0.05). A significant quadratic effect (P<0.05) of PMSG treatment in weaning-to-first service interval was observed for both Parity 1 and 2 sows, with the shortest intervals occurring with the 750 IU dose for Parity 1 sows. Administration of PMSG after weaning was associated with a shortened weaning-to-first service interval in Parity 1 sows and increased litter size in Parity 1 and 2 sows.     

Superovulation in cattle: Effect of goat anti-PMSG serum

Sixteen heifers were superovulated using 5 000 i.u. PMSG on days 9 to 11 of the oestrous cycle (day 1 of the experiment) followed by two injections of 500 mug Estrumate 48 and 54 hours later. Eight of them were injected with goat anti-PMSG serum 5 hours after the first signs of oestrus were observed. Compared with the control group, the treatment with anti-PMSG serum resulted in a shorter heat period (25.8 vs. 51.3 hours), a higher mean number of ovulations (22.1 vs. 18.0) and a lower number of follicles over 10 mm in diameter (4.1 vs. 22.3). The mean numbers of eggs recovered in the experimental and control groups were 17.8 and 6.9, of which 70.2 and 42.0 per cent, respectively, were viable embryos. The concentrations of progesterone and 17-beta oestradiol in the blood plasma showed no significant differences between the experimental and control animals. A higher oestradiol in the control group on day 9 of the experiment was in keeping with the histological picture of the target organs and with a significantly higher number of follicles at slaughter on days 12 to 14 of the experiment.     

Sequential changes associated with the degeneration of preovulatory rat follicles.

In 26-day-old rats, follicles capable of ovulation were present 48 h after PMSG injection and they degenerated if not exposed to an ovulating dose of HCG. In such follicles 125I-labelled LH bound to the thecal and granulosa cells. By 60 h after PMSG, LH binding to the granulosa cells was reduced by 46% although these follicles retained their ability to ovulate. LH binding to the granulosa cells was lost in most follicles by 72 h and ovulation could not be induced. The thecal cells still possessed LH binding sites at 72 h after PMSG. HCG stimulation of these follicles resulted in disruption of the granulosa and the invasion of blood cells into the antrum.     

Recovery and fertilization of bovine follicular oocytes

Infertility in many valuable cows could be overcome by transferring ovarian oocytes to host animals for fertilization. Oocytes were recovered from 134 cows stimulated with gonadotropin. Ovulations occurred as early as 12 hr after first observance of estrus and by 24 hr ovulations were present in 73% of the donors. With 2000 IU PMSG donors averaged 19.4 visible follicles from which oocytes were recovered 60% of the time. Large doses of gonadotropin produced more visible follicles (mean of 52.9) but a low recovery rate of oocytes (32%) and a lower incidence of maturation within the oocytes (20%). Fertilization depended on the condition of the oocytes and the ease of transfer to the oviducts of hosts. Using this technique to obtain large numbers of embryos necessitates treatments either to render immature oocytes fertile or to obtain large numbers of mature follicular oocytes.     

Effects of hyperstimulation with gonadotrophins and age of females on oocytes and their metaphase II status in rats

The present study was undertaken to evaluate the effects of hyperstimulation and aging on the number and proportion of oocytes in the metaphase II stage in female Wistar rats. It explored the validity of the hypothesis that a combination of hyperstimulation with pregnant mare serum gonadotrophins (PMSG) and age could compromise, to a greater extent, the oocyte quality as indicated by the proportion of ovulated oocytes in the metaphase II stage. Female Wistar rats were stimulated with varying doses of PMSG and human chorionic gonadotrophins (hCG) and the number and proportion of ovulated oocytes in the metaphase II stage were examined and compared between different groups of young adult (8-10 weeks old) and aging (30-32 weeks old) female rats. While spontaneous ovulation occurred in all young adult rats, only 50% of the aging rats did. The ovulation rate in aging rats was increased from 50 to 93% when non-PMSG-stimulated rats were given a dose of 10 IU of hCG at proestrus. The lower number of ovulated oocytes noted, even in those hyperstimulated with high doses of PMSG/hCG, also indicated a reduction in fertility in aging rats. Under the influence of high doses of PMSG, all aging rats ovulated, but as with the young adult rats, a higher dose of hCG was needed to achieve the maximum number of ovulated oocytes from the PMSG-induced expanded pool of preovulatory follicles. However, the average number of ovulated oocytes in aging rats was, nevertheless, still significantly lower than in young adult rats even when approximation of weight was considered. No consistent significant difference in proportion of normal oocytes was noted within groups and between young adult and aging rats. A lower proportion of ovulated oocytes was arrested at the metaphase II stages when rats, whether they were young adult or aging, were hyperstimulated with 40 IU of PMSG. However, this proportion was restored to normal (about 100%) when a higher dose of hCG, which is a signal responsible for initiating oocyte maturation, was used. Results of the present study showed that there appears to be an age-related reduction of sensitivity of the preovulatory follicles to the ovulation induction signal of hCG and thus higher doses of hCG were needed to ovulate the PMSG-induced expanded pool of dominant follicles. In older rats, apart from the obvious depletion of the pool of follicles, the evidence from the present study suggests that some of these older rats do have follicles, but that these were unable to develop to preovulatory follicles, probably because of the absence of sufficiently high levels of gonadotrophins essential for the initiation of folliculogenesis. PMSG-hyperstimulation can affect nuclear maturation; the proportion of ovulated oocytes not arrested at the metaphase II stage was higher. However, the proportion of ovulated oocytes at the metaphase II was restored to normal by increasing the dose of hCG use. Hence, meiotic aberration in rats is not age-dependent but rather dependent on the amplitude of the luteinizing hormone (LH)/hCG surge present. The results from this study nullified the hypothesis that hyperstimulation in combination with aging would lead to a higher proportion of abnormality in ovulated oocytes with respect to their being at inappropriate meiotic stages.     

Spontaneous multiple ovulation in the mare and its effect on the incidence of twin embryo collections

Records from 183 nonlactating mares that experienced spontaneous multiple ovulation were examined to determine if: 1) double ovulations are as likely to be unilateral as bilateral; 2) the interval between two ovulations is shorter when the ovulations are unilateral than when they are bilateral; 3) the mean diameter of the two follicles on the day prior to ovulation is less when the ovulations are synchronous and unilateral; 4) for both unilateral and bilateral ovulation, twin embryos are more likely to be detected when double ovulations are asynchronous; and 5) for both synchronous and asynchronous ovulations, twin embryos are more likely to be detected when the ovulations are bilateral. Mares were teased daily with a stallion and follicular development was assessed daily during estrus by ultrasonography. Mares were inseminated daily during estrus and embryo recovery attempts were performed 6 to 7 d post ovulation. Double ovulations occurred as frequently from the same, as from opposite ovaries. The interval between the double ovulations was not shorter (P > 0.05) in unilateral versus bilateral ovulations. In addition, size of the largest and second largest preovulatory follicles was not altered (P > 0.05) by type of ovulation (bilateral vs unilateral) or synchrony of ovulation. Synchrony of ovulations had no affect (P > 0.05) on the incidence of twin embryos recovered. However, more (P < 0.05) twin embryos were recovered from bilateral ovulators compared to unilateral ovulators.