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)     

Selection of the dominant follicle in cattle: establishment of follicle deviation in less than 8 hours through depression of FSH concentrations

Deviation in follicle diameter in cattle is characterized by continued growth of the largest follicle of a follicular wave and a reduction or cessation of growth of the smaller follicles. Deviation begins when the largest follicle reaches about 8.5 mm. Two experiments were done to test the hypothesis that the deviation mechanism is established in < 8 h, as indicated by the temporal relationships between follicle removal and an increase in FSH concentrations (Experiment 1) and between a decrease in FSH concentrations and follicle inhibition (Experiment 2). In Experiment 1, the role of the first follicle to reach 8.5 mm was studied by follicle ablation (Hour 0). The combined mean FSH concentrations for the control group (n = 8) and ablation group before ablation (n = 7) progressively decreased (P < 0.02) over two 8-h intervals before the largest follicle reached > or = 8.5 mm (Hour-16, 1.77 +/- 0.11 ng/mL; Hour 0, 1.49 +/- 0.08 ng/mL). In controls, the concentrations continued to decrease (P < 0.02) until Hour 10 (1.21 +/- 0.09 ng/mL). Ablation of the largest follicle at > or = 8.5 mm resulted in increased (P < 0.02) circulating FSH concentrations between Hours 5 (1.34 +/- 0.04 ng/mL) and 8 (1.61 +/- 0.09 ng/mL). Growth rate of the second-largest follicle between Hours 0 and 8 was greater (P < 0.05) in the ablation group than in the controls, and the second largest follicle became dominant in 7 of 7 heifers following ablation of the largest follicle. In Experiment 2, a minimal single injection of a depressant of FSH concentrations (4.4 mL of steroid-reduced follicular fluid) was given when the largest follicle was a mean of 8.4 mm (Hour 0; controls, n = 4; treated, n = 4). An interaction of group and hour (P < 0.005) for FSH concentrations was attributable to an FSH decrease (P < 0.002) by Hour 6 and an increase (P < 0.002) between Hours 9 and 12 in the treated group. The growth rate of the largest follicle between Hours 0 and 12 was less (P < 0.05) in the treated group (0.2 +/- 0.2 mm/12 h) than in the control group (1.2 +/- 0.4 mm/12 h). The reduced diameter was recorded within 6 h after suppression of FSH concentrations, supporting the hypothesis. Our preferred interpretation is that when the largest follicle reaches a critical diameter of about > or = 8.5 mm, FSH concentrations continue to decrease and become lower than required by the smaller follicles but not the largest follicle. The results further indicate that a close temporal coupling between a change in FSH concentrations and the follicular response could establish the deviation mechanism in < 8 h or before the second largest follicle reaches a similar critical diameter.     

Morphological and biochemical characteristics during ovarian follicular development in the pig

Ovaries were recovered from groups of naturally cyclic pigs (N = 5) on each of Days 16, 18, 20 and 21 of the oestrous cycle. Follicular diameter, follicular fluid volume and concentrations of oestradiol, testosterone and progesterone, and granulosa cell number were determined in all follicles greater than or equal to 2 mm in diameter (n = 511). In alternate follicles either granulosa cell aromatase activity and theca testosterone content or 125I-labelled hCG binding to granulosa and theca were determined. The mean total number of follicles recovered per animal decreased as the follicular phase progressed and a strong positive relationship (P less than 0.001) existed between follicular diameter and volume on all days. The number of granulosa cells recovered per follicle was variable, and not related to oestrogenic activity of the follicles. Mean follicular fluid oestradiol, testosterone and 125I-labelled hCG binding all increased until Day 20 and decreased on Day 21, whereas mean theca testosterone content, 125I-labelled hCG binding to theca tissue and aromatase were all maximal on Day 21. On Days 20 and 21 a subset of 14-16 large follicles was readily distinguishable from the remaining smaller, less oestrogenically active population in each animal. Yet, consistently within these subsets there was a difference in follicular diameter of approximately 2.0 mm and also a considerable range of biochemical development even among follicles of equal size. These results indicate asynchrony at the time of recruitment and selection among follicles destined to ovulate and suggest that heterogeneity continues into the immediate preovulatory period.     

Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Ultrasonic evaluation of the preovulatory follicle in the mare

Ultrasonically visible characteristics of preovulatory follicles in mares which single ovulated were studied daily for 79 preovulatory periods in 40 mares. The preovulatory follicle became the largest follicle in the ovary from which ovulation later occurred six or more days before ovulation in 65 of 79 (82%) preovulatory periods; the mean was day -7 (range, day -14 to day -4). The increase in mean diameter of the preovulatory follicle was linear (R(2)=99.5%) over day -7 (29.4 +/- 0.8 mm) to day -1 (45.2 +/- 0.5 mm; growth rate, 2.7 mm/day). Follicles which double-ovulated were smaller (P<0.05) on day -1 (36 +/- 1.6 mm; n=12 follicles). Preovulatory follicles exhibited a pronounced change in shape from a spherical to a conical or pear-shaped structure in 84% of the preovulatory periods. Remaining follicles retained a spherical shape. Scores representing thickness of the follicular wall increased (P<0.05) as the interval to ovulation decreased. There was no significant difference among days in mean gray-scale value of the follicular wall or in echogenicity of the follicular fluid. Although diameter and shape of the follicle and thickness of the follicular wall changed during the preovulatory period, no reliable ultrasonically visible predictor of impending ovulation was found.     

Follicular activity and hormonal secretory profile in vicuna (Vicugna vicugna)

The objective of the present study was to characterize ovarian activity in non-mated vicunas, relating ovarian structures (evaluated by transrectal ultrasonography, daily for 30 days) to changes in plasma concentrations of estradiol-17beta and progesterone. Ovarian follicular activity occurred in waves, characterized by the follicle emergence, growth and regression. The mean duration of follicular waves was 7.2+/-0.5 days (mean+/-S.E.M.), with a range of 4-11 days. The follicular growth phase averaged 3.0+/-0.2 days, the static phase 1.4+/-0.1, the regression phase 2.9+/-0.3 days, and the inter-wave interval was 4.2+/-0.3 days. The mean growth rate during the growing phase was 1.8+/-0.1mm/day, while the duration of the interval from 6mm to maximum diameter was 1.4+/-0.1 days. The mean maximum diameter of the dominant follicle was 8.4+/-0.3mm (range: 6.2-11.2) and mean diameter of the largest subordinate follicle was 5.4+/-0.1mm. There was an inverse relationship between the size of the largest follicle and the total number of follicles (r=-0.21, P=0.002). Follicle activity alternated between ovaries in 77% of the waves, with 40% of dominant follicles present in the left ovary and 60% in the right ovary. Plasma estradiol-17beta concentrations also had a wave-like pattern, varying between 12.0 and 62.8 pmol/l. Plasma progesterone concentrations remained below 5.0 nmol/l and there was no ultrasonographic evidence of ovulation during the study.     

Influence of different doses of progesterone treatments on ovarian follicle status in beef cows

To determine a dose of progesterone (P4) that allow ovarian follicular wave control, Aberdeen Angus cows were randomly assigned into four groups: T600 (n=5), 600 mg of P4/day; T400 (n=5), 400 mg of P4/day; T200 (n=4), 200mg of P4/day and Control (n=4) (excipient only). Progesterone was injected from day 3 to 9 of estrous cycle. Ultrasonographies and blood sample collections were performed daily from day 2 to 10 and on day 15 of the estrous cycle. Additionally, an ultrasonographic study was conducted on day 13. Progesterone concentrations were different among all groups (P<0.01). The diameter of the dominant follicle was greater for control than for T200, T400 and T600 groups (P<0.01); there was no difference between T200 and T400 (P>0.05), but they had a greater diameter follicle than the T600 group (P<0.01). The growth rate of the dominant follicle between day 3 and 7 of estrous cycle was greater for control group (1.63+/-0.3 mmday(-1)) than for T200 (0.56+/-0.19 mmday(-1), P<0.05), T400 (0.6+/-0.23 mmday(-1), P<0.05) and T600 (0.11+/-0.13 mmday(-1), P<0.01) groups. The mean number of class I follicles (3-4mm) per day for the entire experimental period was less for the control group than for T200 (P<0.05), T400 and T600 (P<0.01) groups (3.7+/-1.3; 5.3+/-1.3; 6.6+/-1.8 and 8.1+/-1.9, respectively). The mean number for the T200 group was less than for T600 (P<0.05) and similar for T400 and T600 groups (P>0.05). The number of class III follicles was greater for control group than for the other groups (P<0.01). T200 and T400 groups had similar numbers of class III follicles (P>0.05) and both had greater numbers of follicles than the T600 group (P<0.05). The diameter of the corpus luteum of the T600 group (15.8+/-1.6 mm) was less than for control (21.0+/-2.5 mm, P<0.01), T200 (19.3+/-2.7 mm, P<0.01) and T400 (20.0+/-2.2 mm) groups (P<0.05). The mean diameter of corpus luteum of T200 was similar to T400 (P>0.05), but different from the control group (P<0.05). In conclusion, the daily intramuscular administration of 200mg or more of progesterone from day 3 to 9 of the estrous cycle indicates that plasma concentrations of progesterone can be used to modify the pattern of follicular development during the follicular wave. From day 5 of the estrous cycle, progesterone concentrations greater than 15 ng/ml (T600 group: 600 mg/day of progesterone from day 3 to 9 of the estrous cycle) inhibit dominant follicle development, increase the class I follicle populations (3-4 mm) and diminish the development of the corpus luteum.     

Decreased superovulatory responses in heifers superovulated in the presence of a dominant follicle

Dairy heifers were superovulated in the presence (dominant group, N = 8) or absence (non-dominant group, N = 6) of a dominant follicle at the start of a a superovulatory treatment on Days 7-12 of the oestrous cycle (Day 0 = oestrus). Daily ultrasonographic observations of ovaries (recorded on videotape) starting on Day 3 were used to assess the presence or absence of a dominant follicle (diameter greater than 9 mm, in a growing phase or at a stable diameter for less than 4 days) and to monitor follicular development before and during treatment. The number of CL estimated by ultrasonography (7.1 +/- 1.8 vs 13.5 +/- 1.4) or by rectal palpation (6.9 +/- 2.0 vs 16.3 +/- 1.6) and mean progesterone concentrations (32.5 +/- 19 vs 80.7 +/- 16 ng/ml) after treatment were lower (P less than 0.01) in the dominant than in the non-dominant group. Based on number of CL, two populations of heifers were identified in the dominant group, i.e. those that had a high (dominant-high, N = 4; greater than 7 CL) or a low (dominant-low, N = 4; less than 7 CL) response to treatment. During treatment, the increases in number of follicles 7-10 mm and greater than 10 mm in diameter occurred sooner and were of higher magnitude in the non-dominant than in the dominant-high or dominant-low groups (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Follicular growth monitoring in the female cat during estrus

Follicular growth in the feline ovary is usually detected indirectly, through behavior observation, vaginal smears, or more invasively, by estradiol assay in blood. This study was designed to describe follicular dynamics by transabdominal ultrasonography. Secondly, the stage of follicular growth was associated to behavioral and vaginal changes. Ovarian ultrasonography was performed during nine anovulatory and 12 ovulatory cycles. Forty-eight follicles were followed during anovulatory cycles: on the first day of estrus behavior, 4.8 ± 0.2 follicles (2 to 7 per female) of 2.3 ± 0.01 mm mean diameter were present. Follicular growth continued at a rate of 0.2 ± 0.04 mm per day. At least one follicle in the cohort reached a diameter greater than 3.0 mm. Maximal follicular growth (when one follicle of the cohort reached the maximal diameter observed for the whole estrus) was reached 3.8 ± 0.3 days after the onset of estrus with the largest follicle reaching a diameter of 3.5 ± 0.04 mm. Growth of the various follicles within a cohort was not exactly synchronous. When no ovulation took place, the follicular diameter decreased by 0.1 ± 0.01 mm per day until the end of estrus. The first day after the end of behavioral estrus, the diameter of the largest follicle in each cohort was 2.7 ± 0.05 mm. No correlation was found between follicular development and either vaginal smear characteristics, or time elapsed since the onset of estrus. When ovulations were mechanically induced after one follicle had reached 3.0 mm in diameter, artificial insemination produced normal pregnancy rate and litter size: four pregnant females out of nine, and 2 to 4 kittens per litter. Ultrasonography proved thus to allow the monitoring of follicular growth in the female cat, with low correlation with behavior and vaginal smear modifications. Further studies are needed to evaluate the interest of an ultrasonographic ovarian follow-up to determine the optimal moment for ovulation induction prior to artificial insemination.     

Concentrations of insulin-like growth factor-I in blood and ovarian follicular fluid of cattle selected for twins

Recent studies have implicated insulin-like growth factor I (IGF-I) as an intraovarian regulator of follicular growth and differentiation. Therefore, we investigated the possibility that cattle selected for twin births may have increased concentrations of IGF-I within the ovarian follicle and(or) in peripheral blood. The estrous cycles of 14 cows with histories of producing twins and 12 control monotocous cows were synchronized with 35 mg of prostaglandin F2 alpha (PGF2 alpha). Blood and follicular fluid were collected 48-50 h post-administration of PGF2 alpha (follicular phase of the estrous cycle). Concentrations of IGF-I were measured by RIA after acid-ethanol treatment of serum or follicular fluid. Twin-producing cows had a greater (p less than 0.05) number of large (greater than or equal to 4 mm) follicles and 47% greater (p less than 0.05) concentrations of IGF-I in peripheral blood than control cows. Cattle selected for high twinning frequency also had greater (p less than 0.05) concentrations of IGF-I (+/- SE) in the two largest follicles than control (unselected) cows (327 +/- 28 vs. 243 +/- 29 ng/ml). IGF-I concentrations in pooled small (1-3.9 mm) follicles were less (p less than 0.05) than in large follicles but did not differ between control and twin-producing cattle. In addition, the percentage of IGF-I concentrations measured in follicular fluid to that of serum was lower (p less than 0.05) in small follicles than in large follicles, and was greater (p less than 0.05) in large follicles of control (93.2 +/- 5.3%) than twin-producing (76.2 +/- 4.4%) cattle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal associations among ovarian events in cattle during oestrous cycles with two and three follicular waves

For 18 two-wave interovulatory intervals in heifers, the follicular waves were first detected on Days -0.2 +/- 0.1 and 9.6 +/- 0.2, and for 4 three-wave intervals on Days -0.5 +/- 0.3, 9.0 +/- 0.0 and 16.0 +/- 1.1 (ovulation is Day 0). The day-to-day mean diameter profile of the dominant follicle of the 1st wave and the day of emergence of the 2nd wave were not significantly different between 2-wave and 3-wave intervals. There were no indications, therefore, that events occurring during the first half of the interovulatory interval were associated with the later emergence of a 3rd wave. The dominant ovulatory follicle differed significantly (P less than 0.05 at least) between 2-wave and 3-wave intervals in day of emergence (Day 9.6 +/- 0.2 and 16.0 +/- 1.1), length of interval from emergence of follicle to ovulation (10.9 +/- 0.4 and 6.8 +/- 0.6 days), and diameter on day before ovulation (16.5 +/- 0.4 and 13.9 +/- 0.4 mm). The mean length of 2-wave interovulatory intervals (20.4 +/- 0.3 days) was shorter (P less than 0.01) than for 3-wave intervals (22.8 +/- 0.6 days). The mean day of luteal regression for 2-wave and 3-wave intervals was 16.5 +/- 0.4 and 19.2 +/- 0.5 (P less than 0.01). For all intervals, luteal regression occurred after emergence of the ovulatory wave, and the next wave did not emerge until near the day of ovulation at the onset of the subsequent interovulatory interval. In conclusion, the emergence of a 3rd wave was associated with a longer luteal phase, and the viable dominant follicle present at the time of luteolysis became the ovulatory follicle.     

Ovarian dynamics, serum estradiol and progesterone concentrations during the interovulatory interval in goats

Ovarian changes determined by daily transrectal ultrasonic scanning, and its correlation with serum progesterone (P4) and estradiol (E2) concentrations were studied in seven cyclic Saanen goats. Estrous cycles were synchronized with 2 injections of a PGF2 alpha analogue 9 d apart. All follicles > or = 2 mm in diameter and CL were measured each day. One goat showed a longer interestrous interval, associated with development of a cystic-luteinized structure. The mean interovulatory interval for the other 6 goats was 20.8 +/- 0.4 d. The incidence of goats with 4, 3, and 2 follicular waves was 3, 1 and 2 respectively; follicular waves emerged on Days 0.5 +/- 0.6, 7.2 +/- 0.7, 10.7 +/- 0.5 and 13.7 +/- 0.8 for Wave 1, 2, 3 and the Ovulatory wave, respectively. The largest follicle of Wave 2 was smaller (4.9 +/- 0.1 mm) than the largest follicles of Wave 3 (6.2 +/- 0.1 mm; P < or = 0.01) and of the Ovulatory wave (7.0 +/- 0.5 mm; P < or = 0.01), and tended to be smaller than the largest follicle of Wave 1 (6.3 +/- 0.6 mm; P < or = 0.09). Interval between emergence of Wave 1 and Wave 2 was longer than interval between emergence of Wave 2 and Wave 3 (7.3 +/- 0.9 d vs 4.0 +/- 0.4 d; P < or = 0.01), and between Wave 3 and the Ovulatory wave (3.8 +/- 1.1 d; P < or = 0.05). Two days before ovulation, the diameter of the ovulatory follicle was larger (P < or = 0.01) than the first subordinate follicle. Serum E2 concentrations increased from the day of ovulation (2.7 +/- 0.3 pg/mL) to Day 2 (7.6 +/- 0.9 pg/mL; P < or = 0.01), associated with the early-mid growing phase of the largest follicle of Wave 1, and then decreased to basal levels on Day 5 (P < or = 0.01) and peaked again (16.5 +/- 2.4 pg/mL) 2 d before ovulation. The CL were detected ultrasonically on Day 3 post ovulation and attained a mean maximum diameter of 13.5 +/- 0.8 mm between Days 8 and 14. The following characteristics were observed: 1) ovarian follicular development in goats is wave-like; 2) increased P4 concentrations may be promoting follicular wave turnover; 3) it is suggested that the presence of follicular dominance and the production of E2 are different among waves. While in Wave 1 and in the Ovulatory wave, follicular dominance is present and production of E2 is consistent, no changes in serum E2 concentrations were found in other stages of the interovulatory interval. In the intervening waves, no indicators of follicular dominance could be firmly documented.     

Pattern of follicular growth and resumption of ovarian activity in post-partum beef suckler cows

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.     

Origin and Differentiation of the Inner Follicular Cells during Oogenesis in Molgula pacifica (Urochordata), an Ascidian without Test Cells

In Molgula pacifica small previtellogenic oocytes are found between cells of the ovarian epithelium. Each oocyte subsequently grows within a compartment of the epithelium known as a primary follicle. The wall of the primary follicle is composed of outer follicular epithelial cells. While growing from about 15–70 μm in diameter, each oocyte gradually recruits a set of about 950 non-epithelial inner follicular cells. These cells co-differentiate in sets with each oocyte, but test cells never appear. The first filamentous components of the vitelline coat appear on the surface of an oocyte in places where it is in contact with undifferentiated (stage 2) inner follicular cells. Each fully differentiated inner follicular cell stores adhesive precursors in a large compartment of the endoplasmic reticulum and probably secretes components of the vitelline coat. There is no evidence that the outer follicular epithelial cells transform into inner follicular cells by dedifferentiation as has often been assumed. Inner follicular cells, in stage 1, are nearly identical to hemoblasts. Hemoblasts may form the inner follicular cells, but to do this they would have to cross the outer follicular epithelium and this phenomenon has not yet been seen.     

Suppression of plasma FSH concentrations with bovine follicular fluid blocks ovulation in GnRH-treated seasonally anoestrous ewes

The specific requirement for FSH in the final stages of preovulatory follicle development was assessed in seasonally anoestrous ewes given 2-h injections of GnRH (250 ng/injection), with (N = 10) or without (N = 10) concurrent treatment with bovine follicular fluid (bFF: 2 ml given i.v. at 8-h intervals). Treatment with bFF significantly (P less than 0.01) suppressed plasma FSH concentrations, but, at least for the first 30 h of treatment, did not influence the magnitude of GnRH-induced LH episodes (mean max. conc. 3.00 +/- 0.39 and 3.63 +/- 0.51 ng/ml for bFF-treated and control ewes, respectively). Of 10 animals treated with GnRH for 72 h, 5/5 control ewes showed oestrus and ovulated whereas 0/5 bFF-treated ewes showed oestrus or ovulated in response to GnRH treatment. There was, however, a transient (13.2 +/- 1.0 h) increase in plasma LH concentrations in the ewes given bFF (mean max. conc. 4.64 +/- 1.57 ng/ml), which was coincident with the preovulatory LH surge recorded in animals given GnRH alone. In 10 GnRH-treated ewes slaughtered after 32 h of treatment, the mean diameter of the largest antral follicle was significantly (P less than 0.001) greater in control ewes (5.92 +/- 0.17 mm) than in animals that were also given bFF (3.94 +/- 0.14 mm). In addition, the incidence of atresia in the 3 largest antral follicles present at this time was greater in bFF-treated ewes. These results show that, when plasma FSH concentrations are suppressed by administration of bFF, although the magnitude of GnRH-induced LH episodes is unchanged, preovulatory follicular development is impaired and ovulation does not occur.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 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.     

The mare: a 1000-pound guinea pig for study of the ovulatory follicular wave in women

The mare is a good comparative model for study of ovarian follicles in women, owing to striking similarities in follicular waves and the mechanism for selection of a dominant follicle. Commonality in follicle dynamics between mares and women include: (1) a ratio of 2.2:1 (mare:woman) in diameter of the largest follicle at wave emergence when the wave-stimulating FSH surge reaches maximum, in diameter increase of the two largest follicles between emergence and the beginning of deviation between the future dominant and subordinate follicles, in diameter of each of the two largest follicles at the beginning of deviation, and in maximum diameter of the preovulatory follicle; (2) emergence of the future ovulatory follicle before the largest subordinate follicle; (3) a mean interval of 1 day between emergence of individual follicles of the wave; (4) percentage increase in diameter of follicles for the 3 days before deviation; (5) deviation 3 or 4 days after emergence; (6) 25% incidence of a major anovulatory follicular wave emerging before the ovulatory wave; (7) 40% incidence of a predeviation follicle preceding the ovulatory wave; (8) small but significant increase in estradiol and LH before deviation; (9) cooperative roles of FSH and insulin-like growth factor 1 and its proteases in the deviation process; (10) age-related effects on the follicles and oocytes; (11) approximate 37-hour interval between administration of hCG and ovulation; and (12) similar gray-scale and color-Doppler ultrasound changes in the preovulatory follicle. In conclusion, the mare may be the premier nonprimate model for study of follicle dynamics in women.     

Effects of lactational and reproductive status on ovarian follicular waves in llamas (Lama glama)

The effects of lactational status and reproductive status on patterns of follicle growth and regression were studied in 41 llamas. Animals were examined daily by transrectal ultrasonography for at least 30 days. The presence or absence of a corpus luteum and the diameter of the largest and second largest follicle in each ovary were recorded. Llamas were categorized as lactating (N = 16) or non-lactating (N = 25) and randomly allotted to the following groups (reproductive status): (1) unmated (anovulatory group, N = 14), (2) mated by a vasectomized male (ovulatory non-pregnant group, N = 12), (3) mated by an intact male and confirmed pregnant (pregnant group, N = 15). Ovulation occurred on the 2nd day after mating with a vasectomized or intact male in 26/27 (96%) ovulating llamas. Interval from mating to ovulation (2.0 +/- 0.1 days) and growth rate of the preovulatory follicle (0.8 +/- 0.2 mm/day) were not affected by lactational status or the type of mating (vasectomized vs intact male). Waves of follicular activity were indicated by periodic increases in the number of follicles detected and an associated emergence of a dominant follicle that grew to greater than or equal to 7 mm. There was an inverse relationship (r = -0.2; P = 0.002) between the number of follicles detected and the diameter of the largest follicle. Successive dominant follicles emerged at intervals of 19.8 +/- 0.7 days in unmated and vasectomy-mated llamas and 14.8 +/- 0.6 days in pregnant llamas (P = 0.001). Lactation was associated with an interwave interval that was shortened by 2.5 +/- 0.05 days averaged over all groups (P = 0.03). Maximum diameter of anovulatory dominant follicles ranged from 9 to 16 mm and was greater (P less than 0.05) for non-pregnant llamas (anovulatory group, 12.1 +/- 0.4 mm; ovulatory group, 11.5 +/- 0.2 mm) than for pregnant llamas (9.7 +/- 0.2 mm). In addition, lactation was associated with smaller (P less than 0.05) maximum diameter of dominant follicles averaged over all reproductive statuses (10.4 +/- 0.2 vs 11.7 +/- 0.3 mm). The corpus luteum was maintained for a mean of 10 days after ovulation in non-pregnant llamas and to the end of the observational period in pregnant llamas. The presence (ovulatory non-pregnant group) and persistence (pregnant group) of a corpus luteum was associated with a depression in the number of follicles detected and reduced prominence of dominant follicles (anovulatory group greater than ovulatory non-pregnant group greater than pregnant group).(ABSTRACT TRUNCATED AT 400 WORDS)     

Changes in morphological appearance and functional capacity of recruited follicles in cows treated with FSH in the presence or absence of a dominant follicle

This study was designed to determine the effect of the presence of a dominant follicle at the beginning of FSH stimulation on the morphological appearance and functional capacity of recruited follicles during FSH stimulation in cattle. Synchronized nonlactating dairy cows were assigned to 1 of 2 groups and treated with FSH in the presence (n = 5) or absence (n = 6) of a dominant follicle between Days 7 and 12 of the estrous cycle (Day 0 = estrus) to stimulate follicular growth. Dominant follicles were identified by daily ultrasonographic observations, beginning on Day 3 of the estrous cycle. Dominant follicle had an ultrasonographic diameter > or = 10 mm and were in a growing phase, or maintaining a constant diameter (> or = 10 mm) for less than 4 d. Ovaries were collected at slaughter on the morning of the third day following initiation of the FSH stimulation. All follicles > 2 mm were dissected, classified according to diameter (Class 1: 2 to 4.4 mm; Class 2: 4.5 to 7.9 mm; Class 3: > 8 mm), and incubated individually for 90 min in medium M-199 (37 degrees C, 5% CO2). Following incubation, integrity of each follicle was evaluated histologically to assess the level of atresia and biochemically to determine the in vitro release of estradiol (E2) and androstenedione in culture media. On Day 3 of the FSH treatment, mean number of follicles in each class was similar (P > 0.1) between the 2 groups. The percentage of atretic follicles in Classes 1 and 3 on Day 3 of the FSH stimulation did not differ (P > 0.1) between the 2 groups. However, the percentage of atretic follicles in Class 2 was higher (P < 0.005) in cows treated with FSH in presence than in absence of a dominant follicle (60.8 vs 38.2%). The release of E2 in culture media by small Class 1 atretic or healthy follicles, by Class 2 atretic and by Class 3 healthy follicles was not affected (P > 0.1) by the ovarian status. However (P < 0.001), the release of E2 in culture media of Class 2 healthy and Class 3 atretic follicles was less for follicles harvested from cows bearing than from those not bearing a dominant follicle. Within each follicular class, concentrations of androstenedione in the culture media did not differ between the 2 groups (P > 0.1). These results suggest that the presence of a dominant follicle at the beginning of FSH stimulation alters the population of follicles recruited FSH stimulation. This may be associated with the reported decrease of the superovulatory response in cows superovulated in presence of a dominant follicle.