Ovarian follicular population changes with the advance of the breeding season in intact and unilaterally ovariectomized ewes

In ewes at the 1st, 2nd or 4th oestrous cycle after unilateral ovariectomy, the ovulation rate remained constant at 1.5 in the control (sham-operated) ewes, but increased from 1.3 to 2.0 in unilaterally ovariectomized ewes. In control ewes, the proportion of preantral follicles declined significantly (P less than 0.05) with each oestrous cycle while the antral follicles increased as the breeding season progressed (P less than 0.05). In contrast, after unilateral ovariectomy, the proportion of preantral and antral follicles remained constant throughout the cycles studied. The rate of atresia of antral follicles, especially those from small size classes, decreased significantly after one cycle of unilateral ovariectomy (P less than 0.05). Larger antral follicles had a different rate of atresia as the breeding season advanced. It is concluded that unilateral ovariectomy acutely decreased the rate of atresia and maintained the within-ovary equilibrium between preantral and antral follicles which otherwise would have decreased due to the depletion of preantral follicles with the advance of the breeding season.     

Ovarian follicular differentiation with prepubertal gonadotropin surges and gonadotropin priming in mice

Preantral follicles were mechanically isolated from the ovaries of 1.5 to 8 week old mice and cultured in vitro for 4 days in the presence or absence of either activin A or FSH. Plasma gonadotropin, estradiol and immunoreactive (IR) inhibin levels were measured. Cultured follicles showed stepwise changes in response to recombinant human (rh) FSH, with no response until 11 days, a gradual increase from 2 weeks, culminating in a strong response to rhFSH at 8 weeks. The response to activin A was vice versa. It enhanced the effect of rhFSH on preantral follicular growth of up to 4-week-old mice, but inhibited the effect of rhFSH in 8-week-old mice. The peak of the prepubertal gonadotropin surge was observed on day 11. Seven-day-old mice were treated with either luteinizing hormone releasing hormone (LHRH) or rhFSH or human chorionic gonadotropin (hCG) for 3 consecutive days from day 7, and follicles were collected on day 11. Those follicles showed enhanced response to rhFSH, no response to activin A, and an enhanced response to the combination of rhFSH and activin A, suggesting that the chronological changes in follicular response are a result of the prepubertal gonadotropin surge.     

Ovarian follicular cell hyperplasia in fetal mice treated transplacentally with ethinyl estradiol

The occurrence of follicular cell hyperplasia was studied by light and electron microscopy in fetal mouse ovaries exposed to ethinyl estradiol (EE) from day 11 through day 17 of pregnancy. Pregnant mice were given EE in olive oil (0.02, or 0.2 mg/kg of body weight) and were sacrificed on day 18. The female fetuses were examined for ovarian histogenesis. Follicular cell hyperplasia was detected in both of the experimental groups, but the incidence was statistically significant only in fetuses exposed to 0.2 mg/kg of EE. Light and electron microscopic observations of the ovaries showed that the hyperplasia was located in the medullary region, and the follicular cells showed pleomorphism. Accumulation of abundant lipid droplets, enlarged rough endoplasmic reticulum with granular material, dense bodies, and vague masses of fibrous structures were seen in the cytoplasm. These morphological observations indicate that hyperplasia of follicular cells in fetal mouse ovaries at term can be induced by prenatal treatment with EE.     

Ovarian and behavioral cyclicity of the laboratory maintained cat

This study examined the sexual behavior-ovarian activity relationship of the laboratory cat maintained under consistent environmental conditions. Mean (±SEM) lengths of estrus for nonovulating, mated ovulating, and human chorionic gonadotrophin (HCG)-induced ovulating queens were 5.8 ± 0.17, 6.5 ± 0.75, and 10.0 ± 0.65 days, respectively. The duration of estrus was significantly (P < 0.01) longer in HCG-treated queens in comparison to the nonovulating or mated ovulating groups. No differences were observed in the number of behavioral estrous periods detected monthly. Duration of estrus was affected by season with significantly shorter periods of estrus observed in June (P < 0.05), September (P < 0.05), October (P < 0.05), and November (P < 0.01) compared to the March, April, May, August, or December averages. Length of estrous cycle (from Day 1 of estrus to Day 1 of next estrus) was variable (range: 6–120 days); however, 49.8% of the estrous cycles were 12 to 21 days in length. Although the ovaries of queens displaying sexual receptivity always contained developing or mature foilicles, ovaries of cats showing no estrous behavior also showed patterns of follicular development and regression at 14- to 19-day intervals. These results suggest that the estrous cycle of the laboratory maintained cat varies from 2 to 3 weeks in duration and that reproductive behavioral patterns alone are not always an accurate indication of ovarian activity or duration of the reproductive cycle.     

Effect of dietary restriction on estrous cyclicity and follicular reserves in aging C57BL/6J mice

Restricting the food intake of female mice by alternating days of feeding and fasting delayed the age-related loss of estrous cycling potential and retarded the rate of follicular depletion, as determined after reinstatement of ad libitum (AL) feeding. During the period of food restriction (FR; 3.5-10.5 mo), food intake and body weight were about 80% of AL values. Mice were acyclic and predominantly in a state of diestrus during FR, but after reinstatement of an AL diet at 10.5 mo all FR mice resumed cycling regularly. By contrast, 80% of AL controls had become acyclic by this age, and the cycles of the remaining mice were significantly longer than those of the reinstated FR mice. Follicular reserves of 12.5-mo-old FR mice were twice those of age-matched AL controls. Cycling performance of reinstated FR mice, measured by cycle length and the proportion of mice still cycling, was equivalent to that of AL mice when the latter were 2-5 mo younger. Ovarian age, measured by the size of the follicular reserve, was similarly retarded in FR mice. Based on these data and previous evidence that follicular depletion plays a major role in the cessation of cyclicity in this strain, we hypothesize that the delayed loss of estrous cyclicity in aging FR mice is mediated at least in part by the retarding effect of dietary restriction on the rate of follicular depletion.     

Can reduced consumption of gonadotrophins account for ovarian compensation in unilaterally ovariectomized, immature mice injected with gonadotrophins?

The effect of unilateral ovariectomy on ovulation rates in immature mice was studied. Ovulations were induced by injecting PMSG and hCG and their number was determined by counting tubal oocytes. A 2--3-fold increase in number of ovulations per ovary was observed after unilateral ovariectomy, and daily injections of progesterone abolished this ovulatory compensation. No significant increase in serum concentrations of immunoreactive FSH and LH was observed at 4, 8, 32 and 51 h after unilateral ovariectomy. Progesterone treatment lowered FSH levels at all times, while LH was unaffected. In intact mice, ovarian sensitivity to PMSG and hCG was not substantially affected by progesterone. Ovulatory compensation in immature gonadotrophin-injected mice appears to arise through a negative feedback mechanism and transiently increased secretion of pituitary gonadotrophin rather than through a greater utilization of a fixed amount of gonadotrophin.     

The fate of embryos transferred to the oviducts of entire, unilaterally ovariectomized and bilaterally ovariectomized ewes

Embryos collected from donor ewes 2 days after oestrus were transferred to the oviducts of entire cyclic (Group EC), unilaterally ovariectomized and cyclic (Group UO), entire anoestrous (Group EA), and bilaterally ovariectomized (Group BO) ewes, and 4 h, 1, 3 or 5 days after transfer the oviducts and uteri were flushed to recover embryos. Ewes in Group BO were untreated or treated with regimens of progesterone and oestradiol designed to simulate ovarian secretion before, around the time of, and after oestrus in entire ewes. There were no differences in the proportions of transferred embryos that were recovered, or in their location (oviduct or uterus), between the two sides of Group UO ewes and they were similar to recovery rates and locations of embryos in Group EC ewes. At 3 days after transfer, 62% and 50%, respectively, of embryos recovered from ewes in Groups EC and UO were in the uterus and by 5 days the percentages had risen to 89% and 75%, respectively. With all treatment regimens fewer of the transferred embryos were recovered from Group BO ewes than from Group EC ewes and few were located in the uterus. In Group BO ewes low recovery rates, and failure of embryos to enter the uterus, appeared to be due to deficiencies in the treatment regimens rather than to effects of ovariectomy. Most embryos recovered from treated ewes in Group BO and those in Groups EC and UO showed apparently normal development (86% and 79%, respectively), while 65% and 75%, respectively, recovered from untreated Group BO and Group EA ewes had developed normally. Only 9 of 163 embryos recovered from the untreated Group BO and EA ewes were located in the uterus and 8 of the 9 had failed to develop normally. Clearly, the steroid hormone requirements for development in the oviducts are not critical, but this is not so for the uterus.     

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus. Ovarian progesterone was significantly increased on the days of metestrus, on diestrus 1, second proestrus and second estrus, but no differences were seen in ovarian androgen contents. After ULO there was an indication of an augmented FSH surge at the first and the second ovulation. Follicle counts revealed that the total number of healthy as well as of atretic antral follicles on the day of second estrus was significantly increased after ULO, due to increased numbers of the smallest antral follicles. At second metestrus the number of larger antral follicles (350-500 micron 3) and the total number of healthy antral follicles was higher after ULO. It is concluded that the compensatory process after ULO involved increased recruitment of small antral follicles. Activities in the remaining ovary were not simply doubled but a new hormonal balance was established.     

Ovarian follicular dynamics in the llama

Ovarian follicular dynamics were determined in adult llamas by ultrasonography and palpation per rectum and hormone analysis (estradiol-17 beta and estrogen conjugates) of plasma and urine. The relationship of gonadotropin secretion to follicular development was determined by the analysis of plasma FSH and LH concentrations. Progesterone analysis of plasma was used to verify or deny the presence of CL. Final follicular development (from 3 mm) averaged 4.8 days, while the duration of the mature follicle (8-12 mm) averaged 5.0 days; regression of the follicle occurred over about 4 days. The development of a subsequent dominant follicle usually began within 2-3 days after onset of regression of the dominant follicle. While several follicles were present at the time of the demise of the dominant follicle, only one follicle continued to develop. The interval between ovarian follicle waves averaged 11.1 days. Dominant follicle activity alternated between ovaries in 81% of the cycles. The occurrence of dominant follicles was evenly distributed between ovaries. While plasma estradiol and estrogen conjugate concentrations were positively associated (p less than 0.05) with follicular activity, urinary estrogen conjugate concentrations best reflected ovarian follicular dynamics (p less than 0.001). Daily FSH concentrations in plasma were not correlated with follicular activity. LH concentrations in plasma were low in all animals throughout the study, indicating estrogen from developing ovarian follicles does not induce the release of LH. Progesterone values were low during the study, indicating that the llama does not spontaneously ovulate, at least under the conditions of this study. In summary, llamas have overlapping ovarian follicle waves that occur at about 11-day intervals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicular wave characteristics in alpacas

The objectives were to describe in detail ovarian follicular growth characteristics and to establish the interval between successive large follicles in unmated alpacas. The ovarian follicular status of 16 non-pregnant, non-lactating mature alpacas was recorded using ultrasound every second day for between 46 and 100 days. An inverse relationship was observed between the diameter of the largest follicle and the total number of follicles indicating that follicular growth in alpacas occurs in waves. There were 15/38 (39%) inter-wave intervals of 12 days and 12/38 (32%) intervals of 16 days. The maximum follicular diameter in each follicular wave was 8.8±0.3 mm (n=38). Inter-wave intervals of longer duration were associated with a larger maximum follicle diameter (P<0.001). However, the growth rate of dominant follicles was consistent over the first 10 days after emergence. They reached a diameter capable of ovulation by this time, regardless of subsequent inter-wave interval. The latter observation suggested that the optimal time of mating might be predicted in alpacas, provided that the emergence of ovarian follicular waves was controlled.     

Ipsilateral vagotomy to unilaterally ovariectomized pre-pubertal rats modifies compensatory ovarian responses

The present study evaluates the participation of the vagus nerve in pre-pubertal rats with unilateral ovariectomy on puberty onset, and on progesterone, testosterone and estradiol serum levels, and the compensatory responses of the ovary. Unilateral vagotomy did not modify the onset of puberty in unilaterally ovariectomized rats. Ovulation rates of animals with the left vagus nerve sectioned and the left ovary in-situ was lower than in rats with only unilateral ovariectomy. Sectioning the left vagus to 32-day old rats with the left ovary in-situ resulted in lower compensatory ovarian hypertrophy than in rats with right unilateral ovariectomy. Twenty-eight or 32-day old animals with sectioning of the right vagus nerve and the right ovary in situ showed higher compensatory ovulation. Twenty-eight -day old rats with the right ovary in situ had higher progesterone and testosterone levels than animals of the same age with the left ovary in-situ. Compared to animals with the right ovary in situ, animals treated at 32-days of age, sectioning the ipsi-lateral vagus nerve resulted in higher progesterone levels. Higher progesterone levels were observed in 28- and 32 days old rats with the left ovary in situ and left vagus nerve sectioned. Thirty-two day old animals with the right ovary in situ and right vagus nerve sectioned had higher progesterone levels than rats of the same age with the left ovary in situ and left vagus nerve sectioned. Left vagotomy to 28-day old rats with the left ovary in situ resulted in higher testosterone levels, a reverse response to that observed in animals with sectioning of the right vagus and the right ovary in situ. Thirty-two day old rats with the left ovary in situ and left vagus nerve sectioned showed lower testosterone levels than animals without vagotomy and with the left ovary in situ.     

Ovarian follicular wave synchronization and superstimulation in prepubertal calves

Two experiments were designed to artificially alter the follicular wave pattern in calves to determine if the mechanisms controlling the well-ordered pattern of follicular growth in adults are extant in prepubertal animals as well. Experiment 1 was designed to test the hypothesis that follicle ablation in a random group of calves will induce synchronous emergence of a new follicular wave which is not different from a spontaneous wave. Experiment 2 was designed to test the hypothesis that ovarian superstimulatory response in calves is enhanced when treatment is initiated before rather than after the time of selection of the dominant follicle. In Experiment 1, 6-month-old calves were assigned randomly to an ablation group (n = 10) and a control group (no ablation, n = 10). Follicle ablation was accomplished by transvaginal ultrasound-guided needle aspiration of all follicles > or = 4 mm in diameter. Blood samples were taken and ovarian changes were monitored daily. A rise (P < 0.01) in mean plasma FSH concentration was detected 24 h after follicle ablation (1.51 ng/ml in the ablation group and 0.93 ng/ml in the control group). Wave emergence was detected earlier (P < 0.01) and with less variation (P < 0.0001) in the ablation group than the control group (1.2 +/- 0.1 vs 4.0 +/- 0.7 d). Characteristics of the induced wave were not different from those of the spontaneous wave. In Experiment 2, 7-month-old calves were assigned randomly to a pre-selection group in which superstimulation treatment was initiated at the time of wave emergence (1 d after follicle ablation, n = 11), or to a post-selection group in which superstimulation treatment was initiated after selection of a dominant follicle (4 d after follicle ablation, n = 11). Superstimulation treatment consisted of 30 mg of FSH im twice daily for 3 d. Ultrasound-guided transvaginal follicle ablation was used to synchronize follicle wave emergence at the outset of the experiment. The mean diameter of the largest follicle at the start of superstimulation treatment was 3.2 versus 8.5 mm in the pre- and post-selection groups, respectively (P < 0.001). The day after the last treatment, the number of follicles > or = 3 mm in diameter was greater (P < 0.002) in the pre-selection group than in the post-selection group (19.3 +/- 1.7 versus 11.3 +/- 1.3). In summary, ultrasound-guided follicle ablation resulted in synchronous wave emergence in a random group of calves, and superstimulation treatment initiated at the time of wave emergence (pre-selection group) resulted in the growth of more follicles than treatment initiated later (post-selection group). Mechanisms involved in the control of follicle recruitment, selection, and suppression are extant in calves, similar to those found in adults.     

Follicular dynamics, repeatability and predictability of follicular recruitment in cows undergoing repeated follicular puncture

The aim of our study was to characterize follicular recruitment and growth in response to the repeated removal of follicles. All tertiary follicles (> 2 mm of diameter) in the ovaries of 10 non-lactating Holstein Friesian cows were punctured at midcycle (Day 0) by means of an ultrasound-guided needle. Puncture sessions were scheduled twice weekly at 3- or 4-d intervals over 3 mo. In the middle of the experiment, i.e., Week 7, the effects of 2- and 5-d intervals between follicular punctures were tested and compared with the previous 3- and 4-d intervals. After this period, 6 animals were slaughtered to study the effect of puncturing on gross ovarian morphology. The protocol of puncturing follicles with 3- to 4-d intervals was continued for an additional 3 mo in the remaining 4 animals. Twice-weekly puncturing of all tertiary follicles abolished estrous cycles and lead to an increase in follicular wave frequency without apparent negative effects on either the reproductive tract or ovaries. After puncture the new follicular wave attained full numerical development within 3 d. Two-day intervals resulted in a lower number of follicles than the 3-d interval (11.0 -/+ 3.8 vs 15.4 -/+ 6.1; P < 0.05). In contrast 4- and 5-d intervals between puncture resulted in an increase in follicle size when compared with that of the 3-d interval. The mean+SD number of recruited follicles varied between animals ranging between 78 +/- 2.5 to 19.2 -/+ 6.0. The mean number of follicles recruited increased from the first month (March) to the third month (May) of sampling (11.8 +/- 4.7 vs 16.4 +/- 6.5; P < 0.01), and then decreased between the third (May) and the sixth (August) month of sampling (21.5 +/- 4.7 vs 16.8 +/- 5.0; P < 0.01). During the experiment, the number of recruited follicles varied cyclically, with waves having a length of 6 puncture session (PS) or 3 wk (i.e., the mean length the bovine estrous cycle). Follicular recruitment after repeated ovum pick-up showed a high repeatability (r = 0.576) A model was also developed showing good predictability of the potential of animals to recruit follicles on the basis of the first 4 to 6 PS. Our results showed that despite large variation in follicular recruitment between animals, the high repeatability and good predictability of follicle recruitment demonstrates the possibility of characterizing animals on their potential for follicle growth.     

Ovarian follicular dynamics in heifers during early pregnancy

Daily ultrasonic monitoring of individual follicles was used to compare follicular wave characteristics of nonbred (n = 6) and pregnant heifers (n = 6). The dominant follicle of the first wave (Wave 1) did not differ significantly between reproductive statuses for any endpoint. The dominant follicle of Wave 2 was the ovulatory follicle in all nonbred heifers. The maximum diameter of the dominant follicle of Wave 2 was greater (p less than 0.05) for the nonbred heifers (14.8 mm) than for the pregnant heifers (13.0 mm). The dominant follicle of Wave 3 was detected later (p less than 0.003; Day 19.7 vs. Day 17.3) and reached a greater diameter (p less than 0.05; 16.6 mm vs. 12.0 mm) in the nonbred than in the pregnant heifers. On the mean day of onset of luteolysis (Day 15.2) in the nonbred heifers, the dominant follicle was similar in diameter for the two groups. Within a few days, the follicle began to regress in the pregnant heifers but maintained or increased in diameter in the nonbred heifers so that a greater maximum diameter was attained. During Days 0 70 of pregnancy, the interval from emergence of a wave to the emergence of the next wave was constant (not significantly different; mean intervals, 8.5 9.8 days). The mean maximum diameter attained by the dominant follicles differed significantly among the first 6 follicular waves; diameter was greatest for Wave 1 (15.7 mm), smallest for Waves 2 (13.1 mm) and 3 (12.6 mm), and intermediate for Waves 4 (14.0 mm), 5 (13.7 mm), and 6 (14.5 mm).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicular populations during early pregnancy in heifers

Ovarian follicles >/=2mm were studied in 14 pregnant and 14 nonpregnant Holstein heifers by daily ultrasound examinations. There were significant differences among days, from Day 0 (day of ovulation) to Day 21, in the diameter of the largest follicle and the diameter of the second largest follicle in pregnant and nonpregnant heifers. There was an interaction of day and reproductive status (P < 0.001) for the diameter of the largest follicle. Significant differences among days were also observed in the numbers of follicles 2 to 3 mm, 4 to 6 mm, 7 to 10 mm, 11 to 13 mm, and >13 mm, and the total number of follicles >/=2 mm. There was a significant main effect of reproductive status for the number of follicles 11 to 13 mm. An interaction of day and reproductive status was observed for the number of follicles >13 mm, but not for any of the other diameter categories. The effect of reproductive status for number of follicles 11 to 13 mm and the interactions for the number of follicles >13 mm and the diameter of the largest follicle seemed due to the selective growth and ovulation of the follicle destined to ovulate in nonpregnant heifers. The differences in ovarian follicular populations between pregnant and nonpregnant heifers were attributed solely to the presence of a physiological mechanism for the selection of an ovulatory follicle in nonpregnant heifers. There were no significant differences among days for any follicular endpoint during Days 22 to 60 in the pregnant heifers.     

Analyses for the presence of a major gene affecting uterine capacity in unilaterally ovariectomized rabbits

The presence of a major gene for uterine capacity (UC), ovulation rate (OR), number of implanted embryos (IE), embryo survival (ES), fetal survival (FS), and prenatal survival (PS) was investigated in a population of rabbits divergently selected for UC for 10 generations. Selection was performed on estimated breeding values for UC up to four parities. UC was estimated as litter size in the remaining overcrowded horn of unilaterally ovariectomized does. OR and IE were counted by means of laparoscopy. Bartlett's test, Fain's test, and a complex segregation analysis using Bayesian methods were used to test for the presence of a major gene. All three tests showed that the data appeared consistent with the presence of a major gene affecting UC and IE. The results of the complex segregation analysis suggested the presence of a major gene with large effect on IE and ES (a > 1sigma(p)), at high frequency (p = 0.70 and 0.68, respectively), and with a large contribution to the total variance (R(g) = 0.39 and 0.47, respectively); and the presence of a major gene with moderate effect on each of OR, FS, PS, and UC. The results suggest that the studied reproductive traits are determined genetically by at least one gene of large effect.