Persistent Dominant Follicle Research Articles

FRI422 The Fates Of Ovarian Dominant Follicles In The First Two Gynecologic Years: An Investigation Of Morphologic And Endocrinologic Features

Abstract Disclosure: M. Calvert: None. S. Molsberry: None. S. Denslow: None. H. Vanden Brink: None. M.E. Lujan: None. N. Shaw: None. Introduction: Irregular menses are common during the early, post-menarchal years owing to the immaturity of the hypothalamic-pituitary-ovarian axis. Few studies have attempted to delineate the factors that contribute to cycle irregularity during this time. In the current study, we aimed to characterize the fate of ovarian dominant follicles in a longitudinal cohort of healthy, early post-menarchal girls. Methods: Participants contributed daily urine samples for reproductive hormone profiling (Cr-corrected LH, estrone conjugates [E1C], and pregnanediol-3-glucuronide [PdG]), and underwent periodic transabdominal ultrasound scans and body composition analysis. The current analysis includes cycles: 1) with an LH surge and ultrasounds performed 1-9 days before and/or <11 days after the surge, or 2) without an LH surge but with ultrasound documentation of a dominant follicle. LH surge requirements were > 40 mIU/mg Cr with concentrations > mean+3sd of the preceding 5 days. Ultrasounds were evaluated offline by two investigators using a standardized rubric for ovarian structures. Results: 26 participants contributed 74 ultrasound scans, spanning 45 cycles. Participants were 12.6 (range 9.8-14.7) years-old, 2.7 (range 0.3-9.6) months post-menarche, predominantly non-Hispanic White (65.4% vs. 26.9% Black, 3.8% Asian, 3.8% Multiracial), and of normal weight (76.9% with BMI <85th percentile). In 41/45 cycles, there was morphological (antral follicle diameter > 10 mm observed ultrasonographically, n=22) and/or endocrinological (LH surge, n=38) evidence for the presence of a dominant follicle. In 4/45 cycles, a dominant follicle was observed but peak LH did not meet LH surge criteria. In 17/41 cycles, dominant follicle fate could not be determined for technical reasons. In the remaining 24/41 cycles, dominant follicles fates post LH-surge were: corpus luteum (CL, 15/24, 71%), CL or luteinized unruptured follicle [LUF] (2/24, 8%), persistent dominant follicle (3/24, 13%), or no structure observed, implying follicular regression/collapse (4/24, 17%). In logistic GEE models, there was no association between peak E1C or LH, follicular phase length, gynecologic age, or free testosterone with odds of having a CL versus any other dominant follicle outcome. There were marginally significant associations between peak PdG (OR: 1.0003, 95% CI: 0.9999, 1.00008) and total body fat percent (OR: 0.86, 95% CI: 0.74, 1.01) with odds of having a CL versus any other dominant follicle outcome. Conclusion: In the first two gynecologic years, dominant follicles develop in most cycles and frequently ovulate. A variety of mechanisms, however, contribute to anovulation, including an absent LH surge, the formation of LUFs, and follicle regression. Whether degree of adiposity is related to ovulatory success of a dominant follicle early in gynecological life will be pursued in future research. Presentation: Friday, June 16, 2023

Ovarian length and persistence in cattle dominant follicle nellore chelate supplemented with chrome

The objective determine the length and diameter of ovarian follicular Nellore heifers supplemented with chelate of chromium in the rearing. We used 80 (eighty) Nellore heifers at 12 months of age with an average live weight of 220 kg, under to rotational grazing with Brachiaria brizantha Marandu , where they received mineral supplements with or without the chromium chelate. The animals were divided into two experimental groups: chromium treatment - 40 Nellore heifers subjected to supplementation with chromium chelate and control treatment - 40 Nellore heifers without chromium chelate. Ultrasound examination was performed in two experimental moments at the beginning (D0) and end (D200) of the experiment, to evaluate the chromium effect on ovarian activity; twenty animals were selected from each treatment according to the inclusion of chrome in the diet. Data were subjected to analysis of variance (ANOVA) at 5% significance level. The results showed that there was no difference in body weight, and 330.4 kg for the control group and 325.5 kg for the group chrome. There was no difference between the length of the ovaries, the evaluation of the control group was 17.9 mm and 20.0 mm for group chrome in the rights ovaries, and in left ovaries 19.4 mm in the control group, and 20.7 mm in group chrome. There was a difference in the diameter of the largest follicle, with 8.9 mm for the control group, and 11.0 mm for group chrome. There were also differences between groups in the percentage of animals with corpus luteum, being 100% in control group, and 68% in the chrome. The mineral supplementation associated with chromium in the growing phase was a decrease in the percentage of females with corpus luteum, and was able to increase the presence of persistent dominant follicles in Nellore heifers.

135 SHORT-TERM OVARIAN EFFECTS OF UNILATERAL OVARIECTOMY IN COWS

Classical studies established that the removal of one of the paired organs produces a compensatory effect on the remaining organ. In the bovine ovary this aspect has not been examined in detail. We took advantage of follicular and luteal profiles from a previous study to retrospectively examine the effects of ovariectomy before and after ovulation on follicular dynamics of the remaining ovary in cattle. To characterise the prevalence and distribution of tyrosine kinase receptor A in the bovine ovary, the original design involved unilateral ovariectomy of cows at different stages of the periovulatory period. For the purposes of the present study, we combined data into 2 groups, a preovulatory group (n = 6 cows) and a post-ovulatory group (n = 5 cows), to provide sufficient data for statistical interpretation. The cows were examined daily by transrectal ultrasonography to determine the ovarian status. For the preovulatory group, a luteolytic dose of prostaglandin was administered when the dominant follicle of the second follicular wave reached ≥10 mm, and the ovary containing the dominant follicle was removed within 48 h. For the post-ovulatory group, ovariectomy was performed on the ovary containing the newly formed corpus luteum between Days 2 to 6 (Day 0 = ovulation). Unilateral ovariectomy was performed by colpotomy under caudal epidural anaesthesia using a chain ecraseur. After ovariectomy, cows were examined daily by ultrasonography from ovariectomy to the completion of an interovulatory interval (period between 2 ovulations). Single-point data were compared between groups by t-test, and binomial data were compared between groups by Fisher’s exact test. Double ovulations were detected in 3/6 ovariectomized in the preovulatory period and 2/5 ovariectomized in the post-ovulatory period. The first ovulation after ovariectomy tended to occur earlier in the preovulatory group than in the post-ovulatory group (P = 0.08), which was attributed primarily to the development of oversized persistent dominant follicles (~20 mm in diameter for ≥7 days in absence of a corpora lutea) in 2 of 5 cows in the post-ovulatory ovariectomy group. The interovulatory interval after ovariectomy was shorter in the post-ovulatory group than in the preovulatory group (14.6 ± 0.3 v. 20.3 ± 0.6 days; P = 0.01). No distinct patterns were detected in follicular and luteal dynamics between the pre- and post-ovulatory ovariectomy groups. The number of follicles ≥3 mm detected by ultrasonography was greater in the post-ovulatory ovariectomy group than in the preovulatory group on Days 6, 7, 8, and 16 of the first interovulatory interval after ovariectomy. In conclusion, results of this retrospective study support the concept that follicular and luteal effects of removal of one ovary are influenced by the timing of ovariectomy relative to ovulation. A prospective study involving a comparison of ovarian dynamics of the same cows before and after unilateral ovariectomy will provide a better understanding of the disruption that take place and the mechanisms controlling it. Research was supported by the Natural Sciences and Engineering Research Council of Canada.

Short communication: Presynchronization for timed artificial insemination in grazing dairy cows by using progesterone for 14 days with or without prostaglandin F2α at the time of progesterone withdrawal

Progesterone-containing devices can be inserted intravaginally for 14 d to presynchronize the estrous cycle for timed artificial insemination (TAI) in beef heifers (“14-day CIDR-PG” or “Show-Me-Synch” program). The progesterone treatment is effective for presynchronization because cattle develop a persistent dominant follicle during treatment that ovulates within 3 d after progesterone removal. The subsequent estrous cycle can be effectively used for a TAI program. Some cattle will retain a functional corpus luteum (CL) for the entire 14-d treatment period and will not be synchronized effectively because the interval to ovulation depends on the lifespan of their existing CL. The objective was to test the effect of a luteolytic dose of PGF2α at progesterone removal for improving synchrony of estrus after treatment and increasing conception rate to a subsequent TAI in dairy cows. Postpartum cows (n = 1,021) from 2 grazing dairy herds were assigned to 1 of 2 presynchronization programs that used a controlled internal drug releasing (CIDR) device containing progesterone: 14dCIDR (CIDR in, 14 d, CIDR out; n = 523) or 14dCIDR+PGF2α (CIDR in, 14 d, CIDR out, and PGF2α; n = 498). Cows were body condition scored (BCS; 1 to 5, thin to fat) and tail painted at CIDR removal. Paint score (PS) was recorded after CIDR removal [PS = 0 (all paint removed, indication of estrus), PS = 3 (paint partially removed), or PS = 5 (no paint removed; indication of no estrus)]. At 19 d after CIDR removal, all cows were treated with PGF2α, 56 h later treated with GnRH, and then 16 h later were TAI. Treating cows with PGF2α at CIDR removal increased the percentage with PS = 0 within 5 d (58.1% vs. 68.9%; 14dCIDR vs. 14dCIDR+PGF2α). We found no effect of treatment, however, on conception rate at TAI (41.1% vs. 43.6%; respectively). The TAI conception rate increased with increasing BCS and was greater for cows that had PS = 0 within 5 d after CIDR removal. In summary, treating cows with PGF2α at CIDR removal increased the percentage of cows with all tail paint removed but did not increase percentage of pregnant cows after TAI.

Efeito do intervalo entre recrutamentos foliculares na superovulação de vacas da raça Holandesa não-lactantes

Vacas da raça Holandesa não-lactantes, distribuídas em dois grupos, foram sincronizadas com o protocolo Ovsynch modificado. No dia sete (dia 0 = dia do segundo GnRH), o grupo 7 (G-7; n=19) recebeu CIDR usado previamente por cinco dias e 100mcg de GnRH, e o grupo 14 (G-14; n=21), CIDR e 25mg de PGF2alfa. No dia 14 foi aspirado o folículo dominante (FD), trocado o CIDR usado por um novo e foram aplicados 25mg de PGF2alfa. Iniciou-se o tratamento com FSH 36h depois, removeu-se o CIDR com o sétimo FSH e aplicou-se GnRH 36h depois. As inseminações foram feitas 12 e 24h depois. Recuperaram-se os embriões sete dias depois da inseminação artificial. O diâmetro do FD no G-7 foi 13,1±0,57mm no dia sete e 11,2±0,57mm no dia 14. O diâmetro FD persistente no G-14 aumentou de 12,6±0,55mm no dia sete para 16,4±0,55mm no dia 14 (P<0,001). O número de folículos >8mm, 48h após o início do tratamento com FSH, foi maior (P<0,05) no G-7 (15,6±0,05) que no G-14 (12,5±0,05). Não foi detectado efeito de tratamento sobre o número de corpos lúteos e de embriões. O menor intervalo entre recrutamentos foliculares aumentou o número de folículos recrutados, porém não alterou a quantidade e a qualidade dos embriões produzidos.

The effect of different doses of Gonadorelin on ovarian follicle dynamics in river buffalo ( Bubalus bubalis)

The objective of this study was to determine the response of the ovarian dominant follicle to the different doses of GnRH in river buffalo. The estrous cycle of 12 river bufflaloes was synchronized using norgestomet implant for 12 days in association with two injections of prostaglandin F 2α analogue on Days 0 and 7 of implant insertion. On Day 6 or 7 of the ensuing cycle (Day 0 of the experiment), females received a norgestomet implant in conjunction with two prostaglandin injections on Days 0 and 1. On Day 6 of the experiment, females were randomly allocated into three groups. At this time, Group 1 and 2 females were given an i.m. injection of 50 or 100 μg Gonadorelin, respectively. Group 3 females did not receive any further treatment and were considered as control. All females were given prostaglandin on Day 12 and implants were removed on Day 13 of the experiment. The results revealed that in the control group, ovarian dominant follicle became persistent throughout the experiment; whereas, the persistent dominant follicle in all females belonging to Group 2 (100 μg GnRH) and one female in Group 1 (50 μg GnRH) ovulated within 48 h, subsequent with an emergence of a new follicular wave and an increase in plasma progesterone concentration within 72 and 96 h after GnRH injection, respectively. In conclusion, 100 μg of Gonadorelin seems to be the most effective dose to induce ovulation followed by an emergence of a new follicular wave in river buffalo.

Alterations in peripheral concentrations of inhibin A in cattle studied using a time-resolved immunofluorometric assay: relationship with estradiol and follicle-stimulating hormone in various reproductive conditions.

The aims of this study were to develop a sensitive and specific assay for bovine inhibin A using europium and to investigate the endocrine role of inhibin A in various reproductive conditions by characterizing the relationship between profiles of inhibin A, FSH, and estradiol and follicle growth during the postpartum period, during the intact estrous cycle, and in cows with follicular cysts. The time-resolved immunofluorometric assay (Tr-IFMA) for bovine inhibin A, using purified polyclonal antibodies to alpha and beta(A) subunits, was specific for bovine inhibin A and did not cross-react with bovine activin A, activin AB, activin B, pro-alphaC or human recombinant inhibin B. The detection limit of the IFMA was 3.3 pg/ml expressed in terms of bovine 32-kDa inhibin A. Dose-response curves of plasma samples obtained from intact and FSH-stimulated cows and cystic cows were parallel to the standard without any preassay processing of samples. Plasma inhibin A levels increased (P < 0.01) concomitant with emergence of nonovulatory or ovulatory follicular waves during the postpartum period. In cystic cows, plasma inhibin A was sustained at high levels for a longer period, associated with growth of persistent dominant follicles. The highest levels of inhibin A were noted during the growth phase of normal and persistent dominant follicles; however, inhibin A levels declined (P < 0.01) as these dominant follicles ceased to grow or ovulated. An inverse relationship between patterns of plasma inhibin A and FSH existed during each follicular wave in the three physiologic conditions. Increases in plasma inhibin A levels were associated with increases in plasma estradiol levels during most follicular waves; however, there was no increase in plasma estradiol level and no relationship between patterns of estradiol and FSH during follicular waves observed during the early postpartum period or midluteal phase of the estrous cycle. In conclusion, the Tr-IFMA does not require pretreatment of samples and can be used for precise measurement of bovine inhibin A without interference with free inhibin alpha subunits. Inhibin A, produced primarily during growth of the dominant follicle, functions as a negative feedback regulator for FSH secretion throughout the postpartum period and the estrous cycle, whereas estradiol appears to have a minor role in regulation of FSH compared with inhibin A, especially during the early postpartum period and midluteal phase of the estrous cycle. The results also indicate that a persistent dominant follicle sustains inhibin A production for a longer period than the dominant follicle emerging in the estrous cycle and establishes long-term dominance by suppressing emergence of a new follicular wave.

Regulation of ovarian follicular dynamics in farm animals. Implications for manipulation of reproduction

In this review, the main features of folliculogenesis are summarized and compared among species. In the past few years, ultrasonography has clarified follicle growth patterns, and our understanding of follicle maturation has improved considerably. As the follicles develop towards the ovulatory stage, three features appear to be highly conserved across all species: 1) the sequence of events (recruitment, selection and dominance); 2) the sequential need for gonadotropins (FSH for recruitment, LH for dominance) and 3) the large variability of numerical parameters (number of waves per cycle, number of follicles per wave) as well as temporal requirements (time of selection, duration of dominance). In addition, specific follicles may also have variable gonadotropin requirements (thresholds). When patterns of follicle development at different physiological states are compared across species, follicular waves were detected in cattle, sheep and horses and during the prepubertal period in swine, suggesting that ovaries of all species operate on a wave basis unless they are prevented from doing so. Efficient estrus control treatments should have the ability to affect 1) the wave pattern by preventing the development of persistent dominant follicles containing aging oocytes, and 2) the recruitment of the future ovulatory follicle whatever the stage of the wave at the time of treatment. This would allow synchronous ovulation of a growing dominant follicle. Manipulation of the luteal phase follicular waves after mating or AI may also optimize fertility. Superovulation is still an efficient technique to obtain progeny from genetically valuable females. Administration of exogenous gonadotropins acts to reveal the underlying ovarian variability. Ovarian response of each female depends on the number of gonado-sensitive follicles present at the time when treatment is initiated. Identification of the number of such follicles for each female would improve efficacy of superovulation, by allocating potential nonresponders to other techniques (OPU/FIV). One of the main components of the within female response to superovulation is the stage of the wave when gonadotropins are injected. Treatment in the absence of a dominant follicle ensures a response close to the female's specific maximum. The development of practical approaches to achieve this still requires further research.

Effect of long-term and short-term progestagen treatment on follicular development and pregnancy rate in cyclic ewes

The aim of this study was to evaluate the effect of the length of a progestagen treatment (12 d vs. 6 d) on follicular dynamics, estrus synchronization and pregnancy rate using medroxyprogesterone acetate (MAP) with or without an eCG dose at the end of MAP treatment. One hundred sixty Polwarth ewes were divided into four equal groups: long-term treated (LT, n=40); short-term treated (ST, n=40); long-term treated plus eCG (LTeCG, n=40); and short-term treated plus eCG (STeCG, n=40). Five ewes of each group were separated to undergo daily transrectal ultrasonography, and blood samples were taken for hormone determination. Until 96 h after sponge withdrawal the number of ewes in estrus was higher in both long-term—treated groups than in both short-term—treated groups but at the end of the observational period (144 h) no significant differences were found among groups. The pregnancy rate was higher in the ST group (87%) than in the other groups (LT, 63%; LTeCG, 67%; and STeCG, 58%; P≤0.03). The ovulatory follicle emerged before sponge withdrawal in long-term—treated ewes (−3.8 ± 0.4 d and −2.2 ± 0.8 d for LT and LTeCG, respectively), whereas in short-term—treated ewes it emerges around sponge removal (0.4 ± 1.1 and 0.5 ± 0.5 d for ST and STeCG, respectively; P≤0.01). The ovulatory follicle in the LT group had a longer lifespan and attained a larger (P≤0.05) maximum diameter than in the ST group. We conclude: a) that the lower pregnancy rate observed after long-term progestagen treatment was related to a slower follicular turnover that promoted the ovulation of persistent dominant follicles; (b) that short-term treatment resulted in a higher pregnancy rate probably due to the ovulation of newly recruited growing follicles; and (c) treatment with eCG had no advantage in association with long-term treatment and had a deleterious effect in combination with short-term treatment with MAP.

Effects of the Persistent Dominant Follicle on the Ability of Follicle Stimulating Hormone to Induce Follicle Development and Ovulatory Responses

Three experiments were conducted to evaluate the effect of an induced first wave persistent dominant follicle on folliculogenesis and ovulatory responses induced by FSH. On d 6 of asynchronized estrous cycle (d 0=estrus), cows were treated with a Syncromate-B implant and two injections of PGF2α (25mg, 0700h; 15mg, 1900h, i.m.). Cows in the control group retained a first-wave persistent dominant follicle, but in the aspirated group, the first-wave dominant follicle was removed via transvaginal aspiration on d 10 (d 0=estrus). Beginning on d 12, cows received 32mg of FSH-P i.m. in decreasing doses at 12-h intervals over a 4-d period. On d 15, the Syncromate-B implant was removed, and cows were ovariectomized (experiment 1, n=8) or inseminated (experiment 2, n=11) at 10 and 22h after the onset of estrus. Cows in experiment 3 received a used controlled intravaginal drug releasing (CIDR) device and two injections of PGF2α (25mg, 0700h; 15mg, 1900h; i.m.) on d 6. On d 8, the first-wave dominant follicle was aspirated (n=6) or left intact (n=5), and FSH treatment was initiated (20mg of Folltropin in decreasing doses at 12-h intervals over a 4-d period), and on d 10 the used CIDR device was removed from all cows. Ovarian follicle size and number were examined daily by ultrasonography from d 5 of the estrous cycle. The persistent dominant follicle increased in size from 10.7mm on d 5 to 15.4mm on d 10 (experiments 1 and 2), and from 9mmon d 5 to 20.4mmon d 11 (experiment 3). From d 11 to 14, the number of class 1 (2 to 5mm) follicles was lower in the aspirated group than in the control group; the number of class 2 (6 to 9mm) follicles was higher on d 12 and 13 for the aspirated group (experiments 1 and 2). The number of class 3 (≥10mm) follicles was higher in the aspirated group on d 14 to 16, but the same on d 17. Ovarian and embryo responses to superovulation did not differ between groups. In experiment 3, the numbers of class 1, 2, and 3 follicles, as well as ovarian and embryo responses following ovulation did not differ between groups. Initiation of exogenous FSH treatment appears to override any systemic inhibitory effect that a persistent dominant follicle may be exerting at the pituitary and possibly the ovary.

Effect of duration of dominance of the ovulatory follicle on onset of estrus and fertility in heifers.

In cattle, prolonged progestogen treatments following luteolysis result in persistent dominant follicles (DF) that are associated with precise onset of estrus but marked reductions in pregnancy rate (PR). The aim was to determine whether increasing duration of dominance of the ovulatory follicle in heifers affected 1) precision of onset of estrus and 2) the timing and nature of the decline in PR. In Exp. 1, duration of dominance of the ovulatory follicle was controlled by causing corpus luteum (CL) regression at emergence of the second follicle wave (mean duration of dominance of 2.1+/-.3 d, Dm2, n = 11) or first day of dominance of the second DF of the cycle; the latter was combined with insertion of a 3-mg norgestomet ear implant for 2 to 10 d to maintain the second DF for 4 (Dm4, n = 32), 6 (Dm6, n = 19), 8 (Dm8, n = 49), 10 (Dm10, n = 28), or 12 d (Dm12, n = 20). Heifers detected in estrus were inseminated approximately 12 h later with frozen-thawed semen. Durations of dominance of the ovulatory follicle of up to 8 d did not affect (P>.05) PR (Dm2 8/9, Dm4 19/28, Dm6 14/18, and Dm8 34/48 heifers pregnant), but PR in Dm10 heifers (12/23 heifers pregnant) was reduced (P = .05) compared with Dm2 heifers; PR in Dm12 heifers (2/17 pregnant) was less compared with all other treatments (P<.01). Fitting a logistic regression model to the pooled PR data to examine the trend in PR showed that extending the duration of dominance from 2 to 9 d and from 10 to 12 d resulted in a predicted decline in PR of 10 to 25% and a further decline of 35 to 75%, respectively. Onset of estrus was delayed in heifers assigned to Dm4 treatment relative to all other treatments (P<.001); it was less variable than that for heifers on Dm6, Dm8, and Dm10 treatments (P<.1). In Exp. 2, heifers received a PGF2alpha analogue and a norgestomet implant on d 12 of the cycle for 3 or 7 d to give approximate durations of dominance of the preovulatory follicle of 2 to 4 d (Dm2-4, n = 29) or 6 to 8 d (Dm6-8, n = 24), respectively. The PR did not differ (P>.05) between heifers on Dm2-4 (22/29) and Dm6-8 (15/24) treatments, but the interval to onset of estrus was delayed (P<.05) by 7 h in the Dm2-4 heifers. In conclusion, restricting the duration of dominance of the preovulatory follicle to < or =4 d at estrus, results in a precise onset of estrus and a high PR following a single AI at a detected estrus.

Comparison of three methods of acute administration of progesterone on ovarian follicular development and the timing and synchrony of ovulation in bos indicus heifers

The aim of this study was to induce the formation of a persistent dominant ovarian follicle and to compare the effects of 3 methods of acute administration of P 4 on ovarian follicular development and on the timing and synchrony of ovulation. Stage of the estrous cycle was initially synchronized in Bos indicus heifers with a norgestomet implants (3 mg) for 10 d and with an analogue of PGF 2α (15 mg) on the first and last day of norgestomet treatment. Eight days after removal of the implants, heifers were randomly assigned to 4 groups. All heifers received a norgestomet implant (Day 0), which was removed 17 d later (Day 17); PGF 2α was administered on Days 0 and 4. Heifers in the control group (n =5) received no other treatment. On Day 10 heifers in Group P 4C (n = 5) were treated with a CIDR for 24 h; heifers in Group P 4O (n = 5) were administered 100 mg im of P 4 in oil, while heifers in Group P 4S (n = 5) were administered 100 mg im of P 4 in saline/alcohol. Data were analyzed using bootstrap estimates of location (mean) and spread (standard deviation; SD). Compared with the control heifers, day of emergence of the ovulatory follicle was delayed, and age and duration of dominance of the ovulatory follicle were reduced in the P 4C and P 4O heifers (P < 0.05) but not in the P 4S heifers (P > 0.05). In all groups treated with P 4 both the mean and variability (SD) in the timing of ovulation did not differ with that of the control group (P > 0.05) but there was less variability in the day of emergence, age, duration of dominance and diameter of the ovulatory follicle than in the control group (P < 0.05). Delayed timing and reduced synchrony (SD) of ovulation and greater age of the ovulatory follicle (P < 0.05) occurred in P 4S heifers than in P 4C heifers. We conclude that administration of 100 mg of P 4 in oil is as effective as treatment with a CIDR for synchronizing emergence and ovulation of a newly recruited dominant follicle. However, reduced synchrony of ovulation, greater age of the ovulatory follicle and delayed timing of ovulation occurred following administration 100 mg of P 4 in saline/alcohol compared with the CIDR device.

Characteristics of prolonged dominant versus control follicles: follicle cell numbers, steroidogenic capabilities, and messenger ribonucleic acid for steroidogenic enzymes.

Cattle with low (subluteal) levels of plasma progesterone develop a persistent dominant follicle; plasma estradiol and LH pulse frequency are elevated, and fertility subsequent to the ovulation of a prolonged dominant follicle is compromised. The hypotheses were 1) that prolonged dominant follicles produce more estradiol because they have theca and granulosa cells with an enhanced capacity to produce androgen and estradiol, respectively, and 2) that these changes in steroidogenic capacity are paralleled by concomitant changes in mRNA for the appropriate steroidogenic enzymes. Prolonged dominant follicles were induced by treating Holstein heifers with exogenous progesterone via an intravaginal controlled internal drug-release device (CIDR) from Day 14 to 28 of the cycle. Prolonged dominant follicles were collected just before (CIDRb, Day 28; n=4) or 24 h after (CIDRa, Day 29; n=4) CIDR removal, and their steroidogenic capacity was compared to that of growing, control dominant follicles obtained just before (CONTb, n=4) or 24 h after (CONTa, n=4) a luteolytic injection of prostaglandin F2alpha during the late luteal phase. After natural luteolysis, CIDR heifers maintained subluteal concentrations of progesterone (1-2 ng/ml) and had higher estradiol and LH pulse frequency than control heifers, as expected. In CIDR heifers, prolonged dominant follicles were present on the ovary for a longer time, reached a larger diameter, and had more granulosa cells and a larger mass of theca than dominant follicles from control heifers (p < 0.05). Concentrations of steroids in follicular fluid, estradiol secretion by granulosa cells in vitro, and levels of mRNA for steroidogenic enzymes in theca and granulosa cells provided no evidence for greater capacity of theca and granulosa cells of CIDR follicles to produce androgen and estradiol. In fact, follicular fluid estradiol and mRNA for P450 aromatase were higher after luteolysis than before in control animals (p < 0.05) but not after CIDR removal in treated animals. Therefore, the data do not support the hypotheses. Rather it is suggested that prolonged dominant follicles produce more estradiol because they have more granulosa cells and a larger mass of theca than control dominant follicles. In contrast, progesterone concentrations in the follicular fluid increased in CIDRa relative to CIDRb follicles (p < 0.05), a change that did not occur in control follicles; and granulosa cells from CIDRa follicles secreted more progesterone than granulosa cells from any other group. The increased capacity of CIDRa follicles to secrete progesterone suggests premature luteinization, which could contribute to decreased fertility in cattle that ovulate a prolonged dominant follicle.

Persistence of the dominant follicle during melengestrol acetate administration and its regression by exogenous estrogen treatment in beef cattle.

Experiments were conducted to test the hypothesis that estrogen treatment will regress a persistent dominant follicle developed during melengestrol acetate (MGA) treatment in the absence of a functional corpus luteum (CL) with normal fertility following development and ovulation of a newly recruited follicle. In Exp. 1, nonlactating beef cows (n = 31) were administered .5 mg.cow-1.d-1 of MGA (d 0) for 14 d with 25 mg of prostaglandin F2 alpha (PGF2 alpha) administered on d 6 and 8 to regress the CL. On d 11 of treatment, approximately half the MGA-treated cows received 5 mg of estradiol valerate (EV) i.m. (MGAEV, n = 14) and the remainder were maintained on MGA (n = 17). Ovaries were checked with ultrasound on d 8, 10, 12, and 14 of MGA treatment and every day until ovulation. A persistent dominant follicle developed in 90% of the MGA-treated cows by d 10 of treatment. Most of the MGA-treated cows ovulated the persistent dominant follicle (n = 13/17), whereas EV treatment regressed the persistent dominant follicle (n = 10/14) with the recruitment of a new follicle that ovulated (n = 8/10). Diameter of the ovulatory follicle was larger (P < .05) for the MGA (19.8 +/- .6 mm) than for the control (15.1 +/- .8 mm) and MGAEV (14.8 +/- .7 mm) cows. In Exp. 2, nonlactating, multiparous beef cows (n = 97) and yearling heifers (n = 38) were equally allotted to either a control, MGA alone, or MGA + estradiol-17 beta (MGAE) group with the same dose of MGA as administered in Exp. 1. The 1st d of MGA feeding was the 1st d of treatment. On d 10 of treatment half the MGA-treated animals were injected i.m. with 5 mg of estradiol-17 beta. In controls, behavioral estrus was detected and animals were artificially inseminated (AI) for 5 d (d 10 to 14 of experiment). All controls not exhibiting estrus by d 15 of experiment were injected with 25 mg of PGF2 alpha. The remaining controls and all MGA cows were observed for behavioral estrus and AI commenced for 7 d following withdrawal of MGA (d 15 to 21 of experiment). More (P < .05) controls (90.3%) than MGA (84.8%) or MGAE (63.6%) cows showed estrus within 7 d after MGA withdrawal. The percentage of animals conceiving to the synchronized estrus did not differ (P > .05) among treatments. The data support our hypothesis that a persistent dominant follicle developed and can be regressed with exogenous estrogen treatment followed by the recruitment and ovulation of a new follicle after MGA withdrawal and fertility of that estrus does not seem to be significantly compromised.

Influence of varied progestogen treatments on ovarian follicle status and subsequent ovarian superstimulatory responses in cows.

The influence of ovarian follicle status and follicle dominance on the response to superstimulatory treatment with FSH was examined in cows. In Experiment 1, oestrus was synchronised using Crestar and on Days 4-6 of the ensuing oestrous cycle cows were assigned to: Group NO (n = 9), control, endogenous CL and no treatment; Group N1 (n = 15), injected with a luteolytic dose of cloprostenol (500 micrograms) and implanted with one implant (3 mg) of the synthetic progestogen, norgestomet; Group N8 (n = 18), injected with 500 micrograms cloprostenol and implanted with eight (24 mg) implants of norgestomet. On Days 9-11, seven implants were removed from six cows in Group N8 and these cows, plus eight Group N1 and all Group N0 cows, were superstimulated with porcine FSH (Folltropin-V) over 4 days (360 mg total dose). The remaining implants were removed from cows in Groups N1 and N8 on Days 11-13, and all cows received 500 micrograms cloprostenol. Numbers and sizes of ovarian follicles, and CL, were recorded by trans-rectal ultrasonography; the largest follicle > 10 mm in diameter was considered morphologically dominant (DF). On Days 9-11, the proportions of cows with a DF were: Group N0, 3/9; Group N1, 14/15; Group N8, 0/18. Total follicles on the 4th day of FSH treatment were greater (P < 0.05) for cows in Group N1 (21.6 +/- 4.2) compared with Group N0 (10.9 +/- 2.4), with cows in Group N8 (13.2 +/- 0.9) not different from the other two groups. Subsequent numbers of CL were lower (P < 0.05) for cows in Group N1 (5.0 +/- 1.3) compared with Group N0 (9.4 +/- 2.0), with cows in Group N8 (8.5 +/- 1.0) not different from the other two groups. In Experiment 2, oestrus was synchronised in cows and on Days 4-6, cows were assigned to: Group C0 (n = 7), control, endogenous CL and no treatment; Group C3 (n = 6), received three CIDR-B intra-vaginal devices that delivered progesterone. On Days 9-11, two CIDR-B were removed from cows in Group C3 and all cows treated with FSH as in Experiment 1. The remaining CIDR-B was removed from cows in Group C3 on Days 11-13 and all cows injected with 500 micrograms cloprostenol. Proportions of cows with a DF on Days 9-11 and diameter of largest follicle were: Group C0, 6/7 and 12.6 +/- 0.9 mm; Group C3, 2/6 and 9.6 +/- 0.8 mm. Numbers of CL on Day 8 after oestrus were: Group C0, 20.0 +/- 7.1; Group C3, 14.8 +/- 4.8 (P > 0.05). Exposure to low dose norgestomet allowed development of a persistent dominant follicle, resulting in a reduced response to superstimulation with FSH. High dose progestogen restricted follicle growth without apparent effects on responses to superstimulation.

Estrus synchronization and fertility after the control of formation and regression of the corpus luteum, and emergence of the ovarian dominant follicle in cattle

Three experiments were conducted with the aim of improving estrus synchronization and conception rates to AI after progestogen-based estrus synchronization. In Experiment 1, stage of the estrous cycle was synchronized in heifers, and on Day 6 of the ensuing cycle (Day 0 of treatment) heifers (n = 14) received a norgestomet implant with prostaglandin (PG) administered on Days 0 and 1. This resulted in an increase in pulsatile secretion of LH and continued growth of the dominant follicle. On Day 4, groups of heifers received 500 (n = 4), 1,000 (n = 4), 1,500 (n = 3) or 3,000 (n = 3) IU hCG, which induced the dominant follicle to ovulate. This was followed within 48 h by the emergence of a newly-recruited dominant follicle that ovulated after the removal of norgestomet and injection of PG on Day 10. The dose of 500 IU hCG was sufficient to ovulate the dominant follicle on Day 4, and this dose was used in subsequent experiments. In Experiment 2, stage of the estrous cycle was synchronized in cows, and on Day 6 of the ensuing cycle (Day 0 of treatment) the cows were given PG and a single norgestomet implant On Day 4 of treatment cows were divided into 2 groups: Group 2A (n = 17), injection of PG; Group 2B (n = 13), injection of PG plus 500 IU hCG. Norgestomet implants were removed on Day 10, coinciding with an additional injection of PG. Cows were inseminated 12 h after estrus. Cows that received hCG (ovulated a newly-recruited dominant follicle) had a higher (P < 0.05) pregnancy rate than control cows (ovulated a persistent dominant follicle; 61 and 23%, respectively). In Experiment 3, heifers at different stages of the estrous cycle were given PG and a norgestomet implant on Day 0, and a second injection of PG plus 500 IU hCG on Day 4. The heifers were divided into 2 groups and those in Group 3A (n = 9) were given PG on Day 10, with the norgestomet implant removed on Day 11. Heifers in Group 3B (n = 9) were given PG at implant removal on Day 11. Injection of PG 24 h before norgestomet implant removal induced an earlier onset of estrus and tended to improve the closeness of estrus synchrony, but pregnancy rates (89%) were the same for both groups of heifers. The norgestomet/hCG regimen allows tor control of the development and regression of the corpus luteum (CL), together with ovulation of a newly-recruited dominant follicle. This protocol can be further developed for estrus synchronization programs to consistently achieve close synchrony of estrus and high fertility in cattle.

Failure of the LH-releasing hormone agonist, deslorelin, to prevent development of a persistent follicle in heifers synchronized with norgestomet

The use of exogenous progestagens for estrus synchronization in cattle can result in a persistent dominant follicle which is associated with reduced fertility. We examined whether the LHRH agonist, deslorelin, would prevent the formation of a persistent follicle in heifers synchronized with norgestomet. The estrous cycles of heifers were synchronized with cloprostenol, and on Day 7 of the ensuing cycle the heifers received one of the following treatments for 10 d: Group C (n = 5), untreated control; Group N (n = 6), injection of a luteolytic dose of cloprostenol on Days 7 and 8 and implant of norgestomet from Day 7 to Day 17 (i.e. typical 10-day norgestomet implant period); Group D (n = 6), injection of cloprostenol on Days 7 and 8 and implants of deslorelin from Day 7 to Day 17; Group ND (n = 6), injections of cloprostenol and both norgestomet and deslorelin implants as above. Follicle growth was monitored using ultrasonography. Group-N heifers showed continued follicle growth and had larger follicles on Day 17 of the cycle than Group-C heifers (16.8 ± 1.6 and 10.4 ± 1.6 mm). Follicle growth for Group-D and ND heifers was similar and variable, and seemed to depend on follicle status at the initiation of treatment. Heifers with follicles of 5 to 10 mm (n = 9) in diameter either showed no follicle growth ( 2 9 ) or developed large follicles ( 7 9 ), while heifers with follicles approximately 12 mm (n = 3) in diameter showed follicle atresia with no further significant growth. On Day 17, size of the largest follicle was similar for Group-ND (14.3 ± 2.9) and Group-D (16.8 ± 1.6) heifers. Heifers in Group N showed estrous behavior 1.8 ± 0.2 d after treatment, whereas heifers in Groups D and ND did not show estrus for 2 to 4 wk. The results show that combined treatment with progestagen and an LHRH agonist does not consistently prevent the development of a persistent dominant follicle and that return to estrus can be delayed after treatment with an LHRH agonist.

Acute progesterone administration regresses persistent dominant follicles and improves fertility of cattle in which estrus was synchronized with melengestrol acetate

Experiments were conducted to determine whether acute progesterone administration would regress persistent follicles and improve fertility in heifers and postpartum cows fed melengestrol acetate (MGA). In Exp. 1, heifers (n = 13) were fed MGA for 11 d (1st d of MGA = d 1). Prostaglandin F2 alpha (PGF2 alpha) was administered to heifers on d 2 to regress the corpus luteum (CL). On d 9, heifers were randomly assigned to receive an injection of either 200 mg of progesterone (PROG) or no hormone (vehicle; VEH). Neither growth of the persistent follicle nor plasma estradiol concentrations were altered by administration of VEH, and the persistent follicle ovulated after cessation of MGA feeding. Administration of PROG regressed the persistent follicle, reduced (P < .05) systemic estradiol concentrations, and resulted in ovulation of a newly recruited follicle. In Exp. 2, heifers were fed MGA for 14 d and were administered either PROG (n = 30) or VEH (n = 31) on d 12. When the CL was absent on d 12, synchronization conception rate (SCR) and pregnancy rate (PR) were greater (P < .05) for heifers administered PROG than for those administered VEH. Neither SCR nor PR were different among treatments when the CL was present on d 12. In Exp. 3, cows (n = 49) were fed MGA for 14 d and were administered either PROG or VEH on d 12. In cows lacking a CL (n = 32), administration of PROG increased (P < .05) SCR, but not PR. We conclude that acute PROG administration induces turnover of persistent follicles and may increase fertility when estrus is synchronized with MGA.

Association between the duration of dominance of the ovulatory follicle and pregnancy rate in beef heifers.

After luteolysis, subluteal concentrations of progesterone or treatment with a synthetic progestagen result in an extended period of dominance (persistence) of the dominant follicle in cattle. Two experiments studied (1) the relationship between the duration of dominance of the ovulatory follicle and pregnancy rate and (2) the ability of a persistent dominant follicle to ovulate and form a normal functioning corpus luteum. In Expt 1, beef heifers were either untreated (n = 30) or given a synthetic progestagen implant (3 mg norgestomet) for 12 days starting on day 16 of their cycle (n = 32). The mean duration of dominance of the ovulatory follicle differed (P < 0.05) between treated and control heifers (10.8 +/- 1.2 and 3.3 +/- 0.8 days, respectively) and 20 of 26 control and 7 of 30 treated heifers were diagnosed pregnant 28 days after artificial insemination (P < 0.01). In Expt 2, on the first day of dominance of the second dominant follicle, heifers received either a PGF2 alpha analogue alone (controls; n = 18), or prostaglandin and a norgestomet implant for 6 (T6; n = 19) or 10 days (T10; n = 20). Increases in the duration of dominance of the second dominant follicle (controls, 4.1 +/- 0.2 days; T6, 8.6 +/- 0.2 days; T10, 12.1 +/- 0.2 days; P < 0.05) resulted in a decrease in pregnancy rate (controls, 14 of 16; T6, 11 of 19; T10, 0 of 13; P < or = 0.05). Progesterone concentrations on days 7 and 12 and the area of luteal tissue on day 12 after artificial insemination were not different (P > 0.05) between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of induction of low plasma progesterone concentrations with a progesterone-releasing intravaginal device on follicular turnover and fertility in cattle

The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF2 alpha (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (approximately 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF2 alpha injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 +/- 1.6 mm, 20 +/- 1.3 mm and 10 +/- 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5-9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)