Pattern Of Ovarian Follicular Development Research Articles

Pattern of Ovarian Follicular Development and Steroid Hormone Concentrations during Estrous Cycle of Lohi Sheep

Pattern of Ovarian Follicular Development and Steroid Hormone Concentrations during Estrous Cycle of Lohi Sheep

Dual ovarian stimulation and random start in assisted reproductive technologies: from ovarian biology to clinical application.

The opportunity to use gonadotropins to stimulate the growth of antral follicles coming from different follicular waves available in different moment of the menstrual cycle allowed the implementation of innovative protocols in assisted reproductive technologies. The purpose of this review is to explore the possible advantages related to these new controlled ovarian stimulation (COS) strategies. Women exhibit major and minor wave patterns of ovarian follicular development during the menstrual cycle, as it is in animal species. These observations led to the introduction of two new strategies for COS: the random start and the double ovarian stimulation within a single menstrual cycle. The use of gonadotropin-releasing hormone antagonist COS protocols, started randomly at any day of the menstrual cycle, is today a standard procedure in those cases where obtaining oocytes is an urgent task, such as in case of fertility preservation for malignant diseases or other medical indications.On the other hand, in poor prognosis patients, double ovarian stimulation has been suggested with the aim of maximizing the number of oocytes retrieved within a single menstrual cycle and, in turn increasing the chance to obtain a reproductively competent embryo. Randomized control trials are necessary to confirm these preliminary findings.

The conflict between hierarchical ovarian follicular development and superovulation treatment

In mammals with a low ovulation rate phenotype, ovarian follicular development is thought to be hierarchical with few, if any, antral follicles at similar stages of development. The hypothesis being tested herein was that if most follicles are in a functionally different state, then the application of exogenous hormones to increase ovulation rate will not overcome the hierarchical nature of follicular development. Using sheep as the experimental model, the functional states of all non-atretic antral follicles > or =2 mm diameter were assessed in individual ewes (N=10/group) during anoestrus with or without pregnant mare's serum gonadotrophin (PMSG) treatment, or after a standard superovulation regimen, or during the follicular phase of the oestrous cycle. The functional states of these follicles were assessed by measuring the FSH- or human chorionic gonadotrophin (hCG)-induced cAMP responses of granulosa cells in vitro. There were significant overall effects across the treatment groups on the responses of granulosa cells to either FSH or LH (both P<0.001). It was concluded that for anoestrous ewes with or without PMSG treatment, and ewes during the follicular phase, granulosa cell populations of many follicles (> or =2 mm diameter) did not share a similar cAMP response to FSH ( approximately 50% of follicles) or hCG (>90% of follicles) either on a per cell or total cell basis. After superovulation, < or =30 and 10% respectively of the granulosa cell populations shared similar responses to FSH and LH with regard to follicular diameter and cAMP output. Thus, exogenous hormone treatments used routinely for increasing oocyte yield do not effectively override the hierarchical pattern of ovarian follicular development during the follicular phase.

Repeatability of 2-wave and 3-wave patterns of ovarian follicular development during the bovine estrous cycle

Characteristics predictive of a 2-wave versus 3-wave pattern of ovarian follicular development during the interovulatory interval (IOI) were examined by ultrasonographic monitoring of 91 IOIs from 31 beef heifers. Repeatability of the wave pattern within individuals and the effects of season and age were determined using a subset of 75 IOIs from 15 heifers examined for multiple IOIs. The 2-wave pattern was detected in 62 of 91 (68%) IOIs, and the 3-wave pattern was detected in 29 of 91 (32%) IOIs. The preponderance of the 2-wave versus 3-wave pattern (P < 0.05) was not influenced by season (P = 0.61) but was even greater in the more mature age group (P = 0.02). The majority of IOIs ≤21 d was of the 2-wave pattern (88%; P < 0.05), whereas the majority of IOIs ≥22 d was of the 3-wave pattern (78%; P < 0.05). The proportion of nonalternating patterns (repeatability) was more than twofold greater than the proportion of alternating patterns (70% vs. 30%; P < 0.01). This relationship was consistent among seasons (P < 0.01) and even more marked in the more mature age group (P = 0.01). Emergence and follicular dominance of Wave 2 were delayed (P < 0.01), and the onset of corpus luteum regression was earlier (P < 0.01) in 2-wave versus 3-wave IOI. In conclusion, the duration of the IOI was predictive of the wave pattern, and the pattern was repeatable within individuals. Factors influencing the period of follicular dominance of Wave 1 in 2-wave versus 3-wave IOI may be responsible for regulating the wave pattern and may be associated with heifer maturity or relative nutritional demand during the postpubertal period. The impact of greater follicular attrition recorded in 3-wave versus 2-wave IOI on ovarian depletion and reproductive senescence is worthy of critical evaluation.

Progesterone concentration, follicular development and induction of cyclicity in dairy cows receiving intravaginal progesterone inserts

Objectives were to evaluate progesterone concentrations after cows had initiated estrous cycles following calving and induction of estrous cycles in postpartum anovular high-producing Holstein dairy cows treated with controlled internal drug releasing (CIDR). In experiment 1 (EXP1), 62 cows that had initiated estrous cycles received a new CIDR (NCIDR) containing 1.38 g of progesterone or a 7-d used autoclaved CIDR (UCIDR) 48 h after luteolysis for 7 d. Ovaries were examined by ultrasonography, and plasma analyzed for concentrations of progesterone. In experiment 2 (EXP2), 515 cows diagnosed as anestrus were randomly assigned to untreated control, NCIDR or UCIDR for 6 d. Plasma was analyzed for concentration of progesterone 12 d after CIDR removal to determine ovulation. In EXP1, milk yield and body condition did not influence progesterone concentrations. Concentration of progesterone tended to increase faster ( P = 0.10) in cows receiving UCIDR than NCIDR, but both treatments reached a plateau at 90 min. Cows receiving the NCIDR had greater ( P = 0.04) concentrations of progesterone during the 7-d treatment, but they were mostly subluteal (<1.0 ng/mL) after d 2. After removal, concentrations of progesterone were greater for NCIDR than UCIDR for the first 45 min, and were similar thereafter. Multiparous cows had lesser ( P = 0.004) concentrations than primiparous cows throughout the study. The pattern of ovarian follicular development was not affected by treatment. In EXP2, induction of onset of estrous cycles increased ( P < 0.01) with progesterone treatments, but was similar between NCIDR and UCIDR. Proportion of cows experiencing shorter than typical length estrous cycles after first AI tended to be greater ( P = 0.09) for control cows than those receiving the CIDR, and for cows remaining anestrous than those in which onset of estrous cycles was induced. Pregnancy per AI and pregnancy loss were similar among treatments. Cows that resumed estrous cyclicity prior to first AI had greater ( P = 0.01) pregnancy per AI. Treatment of high-producing Holstein cows that had previously initiated onset of estrous cycles with CIDR resulted in subluteal concentrations of progesterone, but in anestrous high-producing cows increased induction of estrous cycles with no effect on fertility at first insemination.

Associations between the manipulation of patterns of follicular development and fertility in cattle

The wave-like patterns of ovarian follicular development in cattle can be manipulated by shortening the luteal phase with prostaglandin F 2α (PGF), lengthening the period of follicle dominance with progesterone or curtailing follicle development with GnRH or oestradiol as 17β, benzoate or cypionate. These hormones can also be used to synchronise ovulation allowing timed inseminations without detected oestrus. Progesterone, PGF, GnRH and oestradiol benzoate have each been used to increase conception rates in some situations, but their use has reduced them in others. For example, inseminations made within 96 h of a single injection of PGF administered during the luteal phase were associated with increased conception rates in dairy cows whereas double injection protocols reduced conception rates. The three forms of oestradiol and GnRH have greater effects on follicular development following divergence and dominance than following wave emergence. This can mean that follicles of differing maturity will be present about 7 days later and can result in varied intervals to the onset of oestrus following a PGF injection. The consequent variation in ovulation time can be reduced by injecting GnRH or an oestradiol during pro-oestrus. This means that some less mature follicles will ovulate, forming corpus luteum (CL) associated with a slower rise in plasma progesterone and lower mid-luteal concentrations. The lower conception rates recorded with single timed inseminations with synchronised ovulations have been associated with increased prevalences of short cycles in lactating dairy cows (with GnRH), with long luteal phases in cows and heifers (with oestradiol benzoate) and with embryo loss following positive pregnancy diagnosis (as with Ovsynch in lactating Holstein cows). Extensive Canadian studies have demonstrated that these same hormones can be successfully used without these limitations and reliably obtaining conception rates over 50% and up to 70% in beef cattle that have been supplemented with a progestin during the period of ovarian follicle synchronisation. The inherently lower fertility of Holstein cows during early lactation may be contributing to the reduced effectiveness of hormonal treatments for synchronised follicle development and ovulation. The role of reduced dose rates of GnRH in compromising this effectiveness needs to be determined if the potential of these treatments realised with beef cattle is to be achieved with lactating Holstein cows.

Effect of treatment with progesterone and oestradiol when starting treatment with an intravaginal progesterone releasing insert on ovarian follicular development and hormonal concentrations in Holstein cows

Ovarian follicular development and concentrations of gonadotrophin and steroid hormones were studied in non-lactating Holstein cows following administration of progesterone (P 4) or oestradiol benzoate (ODB) at the start of treatment with an intravaginal progesterone releasing insert (IVP 4) in a 2 by 2 factorial experiment. Cows were treated at random stages of the oestrous cycle with an IVP 4 device (Day 0) and either no other treatment ( n=8), 200 mg of P 4 IM ( n=9), 2.0 mg of ODB IM ( n=8) or both P 4 and ODB ( n=9). Seven days later devices were removed and PGF 2α was administered. Twenty-four hours later 1.0 mg of ODB was administered IM. Oestrus was detected in 97.1% and ovulation in 64.7% (effect of treatment, P=0.41) of cows within 96 h of removing inserts. In the cows that ovulated, day of emergence of the ovulatory follicle was delayed ( P<0.01) and more precise ( P<0.05) in cows treated with ODB compared to the cows treated with P 4. Interval from wave emergence to ovulation and the diameter of the ovulatory follicle was less ( P<0.05) in cows treated with ODB compared to cows treated with P 4. Combined treatment with P 4 and ODB at the time of starting treatment with an IVP 4 device did not significantly change the pattern of ovarian follicular development compared to treatment with ODB alone. Concentrations of LH and FSH in plasma were less in cows treated with ODB between Days 0 and 4 ( P<0.05) while treatment with P 4 increased concentrations of FSH in plasma between Days 0 and 4 ( P<0.05). When anovulatory cows were compared to ovulatory cows, diameters of follicles ( P<0.001) and growth rate of follicles ( P<0.01) were less in anovulatory cows between Days 7 and 9, while concentrations of FSH in plasma were greater ( P<0.01), concentrations of LH similar ( P>0.90) and concentrations of oestradiol were less ( P=0.01) in the anovulatory cows between Days 4 and 10. Our findings support a hypothesis that ovarian follicular development following administration of P 4 or ODB at the start of treatment with an IVP 4 device differs. Anovulatory oestrus may have been associated with reduced maturity and/or later emergence of ovarian follicles.

Use of a small dose of estradiol benzoate during diestrus to synchronize development of the ovulatory follicle in cattle.

We tested the hypothesis that a small dose of estradiol benzoate (EB) at the midstage of the estrous cycle in cattle would synchronize the subsequent pattern of ovarian follicular development, estrus, and ovulation. Nonlactating Friesian cows received either 1 mg of EB i.m. on d 13 of the estrous cycle (T; n = 12; estrus = d0) or served as untreated controls (C; n = 12). Their ovaries were examined daily with transrectal ultrasonography from d 7, and blood samples were collected 0, 2, 4, 8, 24, and 48 h after treatment on d 13. Plasma concentrations of estradiol-17beta were elevated to 12 pg/mL during the initial 24 h following treatment, compared with a baseline of 1 pg/mL in untreated controls (P < .001). Progesterone concentrations in cows of the T group declined between 24 and 48 h after treatment (-3.2 +/- .5 ng/mL) compared with little change in concentrations of progesterone in cows of the C group at this time (P < .01). This difference was coincident with an earlier time to regression of the corpus luteum in cows of the T group. Disregarding treatment groups, the second dominant follicle of the estrous cycle (DF2) emerged on d 10.6 +/- .3 and was 9.4 +/- .4 mm in diameter on d 13. Further growth of the DF2 was halted by EB treatment on d 13. Cessation of growth occurred irrespective of whether the DF2 was in the early or late growth phase, and a new follicular wave emerged 4.5 +/- .2 d later. The dominant follicle from this wave (DF3) ovulated 5 d after emergence in most cases. During the estrous cycle of every cow in the T group, there were three waves of follicular development (3-wave), whereas the ratio of 2:3 waves of follicular development in cows of the C group was 1:3. Consequently, the interval from emergence to ovulation of the ovulatory dominant follicle in cows of the C group ranged from 3 to 11 d. The dynamics of ovarian follicular wave development during the estrous cycle can be strategically manipulated by treating with a small dose of EB to synchronize proestrous development of the ovulatory follicle.

Secretion of inhibin A and follicular dynamics throughout the estrous cycle in the sheep with and without the Booroola gene (FecB).

The identification of a single gene (Booroola FecB) associated with a significant increase in the ovulation rate in sheep provides a powerful tool for the study of factors regulating the selection of preovulatory follicles. The ovarian secretion of dimeric inhibin A was investigated and related to the secretion of ovarian steroids, the concentration of gonadotropins, and the pattern of ovarian follicular development during the follicular and early luteal phases in ewes with an ovarian autotransplant with or without the FecB gene. The secretion of inhibin A was related to the presence of large estrogenic follicles, being high during the follicular phase and falling after the LH surge (P < 0.05) before increasing during the early luteal phase (P < 0.05). There were no differences in the timing of the onset of the LH surge, the concentrations of FSH and progesterone, or the rates of inhibin A, estradiol, and androstenedione secretion during the follicular or luteal phase between ewes with and without the Booroola gene. Although the overall pattern of follicular development was similar between the genotypes, the ovulation rate was higher (P < 0.05) in the gene carrier ewes, and the ovulatory follicles and corpora lutea were significantly smaller (P < 0.05) than those in noncarrier animals. During the luteal phase, the diameter of the large follicles from the first wave was smaller (P < 0.05) in the gene carrier than in noncarrier ewes. Because there are no qualitative or quantitative differences in the pattern of secretion of pituitary gonadotropins or ovarian hormones between the two genotypes, we conclude that is likely that the FecB gene exerts its action at the level of ovary.

Effect of 48 h treatment with 17 beta-oestradiol or progesterone on follicular wave emergence and synchrony of ovulation in Bos indicus cows when administered at the end of a period of progesterone treatment.

The objective of this study was to determine the effect of treatment with additional progesterone (P4) or 17 beta-oestradiol (E2) at the end of a period of P4 treatment on ovarian follicular development, ovulation time, and plasma gonadotrophin and steroid hormone concentrations of Bos indicus cows. Initially, two injections of PGF2 alpha were given 14 days apart, and at the time of the second injection (Day 0) all cows received a single P4-releasing controlled internal drug release (CIDR) device that was removed 10 days later. Control cows (Group 1, n = 8) received no other treatment. On Day 8, cows in Group 2 (n = 8) and Group 3 (n = 8) received either a s.c. implant containing E2, or a second CIDR device, respectively. All CIDR devices and E2 implants were removed at a similar time on Day 10. Treatment with E2 or P4 delayed mean (+/- SD) time of ovulation (113.1 +/- 25.6 h, 153.4 +/- 44.5 h and 150.8 +/- 25.1 h for Groups 1, 2 and 3, respectively; P < 0.05) and the mean time (+/- SD) of the luteinising hormone (LH) peak (87.4 +/- 24.5 h, 124.3 +/- 45.0 h and 122.3 +/- 25.04 h for Groups 1, 2 and 3, respectively; P < 0.05). Both treatments delayed the mean (+/- SD) day of emergence of the ovulatory follicle (7.7 +/- 3.6 days, 11.3 +/- 1.7 days and 11.1 +/- 1.5 days for Groups 1, 2 and 3, respectively; P < 0.05), and reduced the variability in the day of emergence of the ovulatory follicle (P < 0.05) compared with the control cows. Variability in age and duration of dominance of the ovulatory follicle was greater in control animals compared with treated animals (P < 0.05). Treatment with E2 on Days 9 and 10 did not alter mean concentrations of gonadotrophins in the cows in Group 2 compared with control cows (P > 0.05), whereas treatment of cows with an additional CIDR device resulted in greater mean concentrations of FSH and lesser concentrations of LH on Day 9 (P < 0.05) compared with cows in Groups 1 and 2. By Day 10 mean concentrations of gonadotrophins were similar among cows in all three groups. Concentrations of E2 were less in cows in Group 3 compared with cows in Groups 1 and 2 from Day 9 to Day 11 (P < 0.05). We conclude that treatment with either E2 or P4 can influence the pattern of ovarian follicular development and ovulation in cattle; however, the mechanism of action of the two treatments may differ. Atretogenic treatments for ovarian follicles applied at the end of a period of progesterone treatment did not improve synchrony of ovulation.

The recruitment of ovarian follicles is enhanced by increased dietary intake in heifers.

The objective of this study was to determine whether dietary-induced changes in growth hormone (GH), insulin, and IGF-I alter the pattern of ovarian follicular development in heifers. Twenty-eight 2- to 3-yr-old Hereford-Friesian heifers were equally allocated (n = 7) to one of four dietary treatments: 1) Control (C) fed a maintenance diet as two meals per day; 2) twice maintenance (2M2) given as two meals per day; 3) twice maintenance (2M6) given as six meals per day; 4) feed-deprived (F) fed maintenance requirements as for C, changed to straw ad libitum for 3 d from a synchronized estrus. On d 4 (estrus = d 0) heifers were transferred to grass silage (ad libitum access) until the end of the experiment. Blood samples were collected hourly for 10 h on d 1 and 3 and daily for an additional 14 d. Follicular development was monitored daily by ultrasonography until d 14. The number of small follicles (< 4 mm) was increased (P < .05) by 37% on d 1 and 2 in 2M2 and 2M6 heifers, with no carryover effect of nutrition to the second follicular wave. Number of medium-sized (4 to 8 mm) and large (> 8 mm) follicles did not vary (P > .05) among treatments. The FSH concentrations were not different (P > .05) among treatments. Insulin concentrations were higher (P < .05) in 2M2 and 2M6 heifers than in C or F heifers, with no carryover after the diet was changed. Increase in number of small follicles was independent of changes in FSH and IGF-I, negatively associated with GH, but positively associated with circulating insulin. These results indicate that a short-term increase in nutritional plane can affect follicular recruitment in cycling heifers.

Relationship of fertility to patterns of ovarian follicular development and associated hormonal profiles in dairy cows and heifers. Cooperative Regional Research Project.

Ovarian follicular development, hormonal patterns, and fertility were compared for growing and persistent follicles in 98 lactating dairy cows and in 89 heifers. Pregnancy rates were greater in animals that ovulated the first-wave dominant follicle while it was growing (GF) vs persistent (PF; for cows 54.2 vs 14.0%, P < .001; for heifers 62.0 vs 35.9%, P < .05). Follicles were larger in cows than in heifers (P < .05). Preovulatory growth rate (mm/d) for PF in cows was parallel to that of GF in both groups; in heifers, PF grew more slowly. At estrus, PF were larger than GF in cows and overall (P < .001), but not in heifers. Estradiol in plasma was greater (P < .05 in animals with PF than in those with GF before estrus (for 6 d in heifers, 8 d in cows). During d -6 through -2, progesterone in plasma tended to be lower (P = .12) in cows with PF than in heifers with PF. Pulse frequency of LH in plasma increased on d 7 in animals with GF and more frequent LH pulses continued through d 13 and 14 in animals with PF. After AI, progesterone in plasma did not differ between GF and PF, in either cows or heifers. However, among cows with GF, progesterone was greater (P < .01) by d 6 to 7 after estrus in pregnant than in nonpregnant cows. In summary, fertility was lower in animals that ovulated a persistent rather than a growing follicle, especially in lactating cows. Lower fertility in animals with PF was associated with prolonged increases in concentrations of LH and estradiol in plasma before estrus and ovulation.

The effects of nutritionally-induced liveweight differences on follicular development, ovulation rate, oestrous activity and plasma follicle-stimulating hormone levels in the ewe

Romney ewes of similar mean liveweight were differentially grazed to generate two treatment groups ( n = 35) differing in mean liveweight by approximately 15 kg. Oestrous cycles were synchronized by treatment for 14 days with intravaginal sponges, and the oestrous activity and ovulation rate (O.R.) for the cycle immediately following sponge withdrawal recorded. Patterns of preovulatory follicular development, ovarian antral follicle populations and plasma FSH levels were compared between the two treatment groups during the second cycle following sponge withdrawal. Ewes in the high-liveweight (HLW) group had a significantly ( P < 0.001) higher ovulation rate (1.73 ± 0.20, mean ± s.e.) than those in the low-liveweight (LLW) group (1.19 ± 0.13). Following sponge withdrawal, ewes in the LLW group came into oestrus significantly ( P < 0.05) later (56.6 ± 3.1 h) than those in the HLW group (43.9 ± 2.6 h). Compared with ewes in the LLW group, those in the HLW group had: more follicles ≥2 mm in diameter present on the ovarian surface late in the luteal phase (10.70 ± 1.19 vs. 7.66 ± 0.75; P < 0.001); a greater number of follicles being recruited (3.79 ± 0.19 vs. 2.80 ± 0.30; P < 0.05); and a lower intensity of selection through atresia (43.7 ± 4.2% vs. 53.9 ± 5.5%; P < 0.10). There were no differences between treatment groups in the total number of antral follicles ≥ 0.2 mm in diameter or their size distribution, but ewes in the HLW group had significantly more healthy follicles > 2 mm in diameter and more follicles in the terminal stages of atresia than those in the LLW group. There was no difference between the two groups in plasma FSH levels during the late luteal and follicular phases. These results suggest that variation in ovulation rate due to nutritionally-induced difference in liveweight is associated with changes in the patterns of ovarian follicular development, changes which appear to be independent of circulating levels of FSH.

Some aspects of thecal and granulosa cell function during follicular development in the bovine ovary.

The patterns of ovarian follicular development and the steroidogenic properties of individual follicles (greater than or equal to 2 mm diam.) were assessed in Angus cows from Day - 5 until Day + 1 of the oestrous cycle (oestrus = Day 0). Individual follicles were judged to be healthy or atretic using a new classification system incorporating assessments of thecal vascularity and colour, the number of granulosa cells, the presence or absence of debris in follicular fluid and the status of the oocyte. The results suggest that the theca interna of small antral follicles (less than 5 mm diam.) responds to LH and synthesizes androstenedione before the granulosa cells develop an appreciable ability to metabolize androgen to oestrogen. Regardless of follicle size, the output of thecal androstenedione per unit mass of tissue remained unchanged in healthy but not in atretic follicles. On a per cell basis, aromatase activity increased in granulosa cells from healthy but not from atretic follicles with increasing follicle size. Peak levels of aromatizing activity were consistently observed in dominant oestrogen-enriched follicles on Day 0 although similar activity was also observed in some healthy follicles (greater than or equal to 8 mm diam.) on other days of the cycle. Early atresia in bovine follicles was characterized by an absence or lowering of aromatase activity in granulosa cells which always preceded any reduction in the thecal steroidogenic response to LH. It was estimated that between 20 and 60 antral follicles (greater than or equal to 2 mm diam.) per cow may respond to LH by synthesizing androgen whereas only 1-3 follicles (greater than 5 mm diam.) have granulosa cells capable of metabolizing androstenedione or testosterone to oestradiol.