Follicle and systemic hormone interrelationships during induction of luteinized unruptured follicles with a prostaglandin inhibitor in mares

The objective was to determine differences in follicle and reproductive hormone characteristics in mares with ovulatory and flunixin meglumine (FM)-induced anovulatory cycles. Estrous mares were given 1500 IU hCG when the follicle was ≥ 32 mm (0 h). In Experiment 1, control mares (n = 7) were not treated further. The remaining mares (n = 11) were given 1.7 mg/kg FM i.v. twice daily, from 0 to 36 h after hCG treatment. Blood samples and ultrasonographic examinations were performed every 12 h. All control mares ovulated normally between 36 and 48 h. In contrast, eight of 11 FM mares did not ovulate, but developed luteinized unruptured follicles (LUFs). Three FM-treated mares did not develop conventional LUFs. Plasma progesterone concentrations were lower (P < 0.05) in LUF mares at 96, 120, and 216 h than in controls, whereas plasma LH concentrations were higher (P < 0.05) between 108 and 120 h in LUF mares than in controls. Plasma concentrations of PGFM and estradiol did not differ significantly between groups. In Experiment 2, the three mares that did not develop LUFs were treated, during the consecutive cycle, with the same dose of FM but with increased frequency at zero, 12, 24, 30, 36, and 48 h after hCG. One mare formed a LUF, whereas the other two did not. These two mares had lower LH concentrations than LUF or control mares in the two consecutive cycles. In conclusion, systemic treatment with FM blocked ovulation in 73% of treated mares. Mares with LUFs had lower progesterone and higher LH concentrations than control mares.     

Role of the double luteinizing hormone peak, luteinizing follicles, and the secretion of inhibin for dominant follicle selection in Asian elephants (Elephas maximus)

Elephants express two luteinizing hormone (LH) peaks timed 3 wk apart during the follicular phase. This is in marked contrast with the classic mammalian estrous cycle model with its single, ovulation-inducing LH peak. It is not clear why ovulation and a rise in progesterone only occur after the second LH peak in elephants. However, by combining ovarian ultrasound and hormone measurements in five Asian elephants (Elephas maximus), we have found a novel strategy for dominant follicle selection and luteal tissue accumulation. Two distinct waves of follicles develop during the follicular phase, each of which is terminated by an LH peak. At the first (anovulatory) LH surge, the largest follicles measure between 10 and 19.0 mm. At 7 ± 2.4 days before the second (ovulatory) LH surge, luteinization of these large follicles occurs. Simultaneously with luteinized follicle (LUF) formation, immunoreactive (ir) inhibin concentrations rise and stay elevated for 41.8 ± 5.8 days after ovulation and the subsequent rise in progesterone. We have found a significant relationship between LUF diameter and serum ir-inhibin level (r(2) = 0.82, P < 0.001). The results indicate that circulating ir-inhibin concentrations are derived from the luteinized granulosa cells of LUFs. Therefore, it appears that the development of LUFs is a precondition for inhibin secretion, which in turn impacts the selection of the ovulatory follicle. Only now, a single dominant follicle may deviate from the second follicular wave and ovulate after the second LH peak. Thus, elephants have evolved a different strategy for corpus luteum formation and selection of the ovulatory follicle as compared with other mammals.     

Systemic treatment with high dose of flunixin-meglumine is able to block ovulation in mares by inducing hemorrhage and luteinisation of follicles

Prostaglandins play an obligatory role during the process of ovulation in mammals. Ovulation can be blocked by intrafollicular administration of non-steroidal anti-inflammatory drugs (NSAIDs) in several domestic species including the mare as well as by systemic administration of these drugs in women. In the mare, the effect of systemic NSAIDs treatment on ovulation has not been critically studied. The objectives of this study were: a) to determine whether high dose of flunixin-meglumine (FM) administered systemically to mares during the periovulatory period was able to block ovulation; and b) to study the follicular ultrasound characteristics of FM treated mares. Six mares were used in the study during two consecutive estrous cycles. Each mare received 2 mg FM/kg i.v. twice a day starting at the time of treatment with hCG when the follicle reached a diameter of ≥ 32 mm and continuing until ovulation. During the consecutive control cycle (CON) the mares received the same dose of hCG but were not administered FM. During the FM cycles five of six mares failed to ovulate and collapse the preovulatory follicle; but echoic specks were observed within the follicles, which continued to grow until a mean diameter of 55 mm. Eventually, the follicular contents were organised and luteinised. All CON mares ovulated normally. In conclusion, when mares were treated with FM, they had a higher incidence of ovulatory failure and development of luteinised unruptured follicles (83%, P = 0.015) compared with untreated mares.     

Hemorrhagic ovarian follicles in llamas

The ovaries of 74 llamas were examined daily by transrectal ultrasonography for at least 30 d. Hemorrhagic follicles were observed in 13 (18%) llamas (incidence per anovulatory dominant follicle, 16%). The proportion of llamas in which a hemorrhagic follicle was detected was different among groups (nonmated, 8 25 ; mated to a vasectomized male, 4 21 ; mated to an intact male, nonpregnant, 1 10 ; mated to an intact male, pregnant, 0 18 ; P<0.05). A hemorrhagic follicle, observed grossly after ovariectomy, was large (13 mm) and fluctuant, with a thin translucent wall and dark red contents. No ovulatory stigma was detected, and after incising the wall, bloody fluid escaped and the follicle collapsed leaving only a small blood clot within the antrum. Ultrasonically, the formation of a hemorrhagic follicle was indicated by scattered free-floating echogenic spots within the follicular antrum which swirled upon ballottement of the ovary. The antral contents appeared to become organized (did not swirl when ballotted) after follicle growth ceased. Ultrasonic indications of antral hemorrhage were not observed in any follicles in which ovulation was later detected (0 45 ovulatory follicles). All of the hemorrhagic follicles (13 13 ) involved the dominant follicle of a wave during which no copulatory stimulus was applied. Hemorrhagic follicles were apparently anovulatory and were repeatable (P<0.05) within individuals. The interval from first detection to the first day of maximum diameter was longer (P<0.05) and maximum diameter was greater (P<0.0001) for hemorrhagic follicles than nonhemorrhagic follicles (16.4 versus 13.1 d and 22.1 versus 12.8 mm, respectively); however, the interwave interval was not affected by the presence of a hemorrhagic follicle. Luteinization of the hemorrhagic follicle was indicated (thickened wall) in two llamas by an elevated plasma progesterone concentration and/or by ultrasound. By their large size, hemorrhagic follicles may be interpreted as hemorrhagic follicular cysts; however, they were not associated with other ovarian irregularities or with infertility.     

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.     

Transition to the ovulatory season in mares: An investigation of antral follicle receptor gene expression in vivo

The inability to obtain in vivo samples of antral follicle wall layers without removing the ovaries or sacrificing the animals has limited more in‐depth studies on folliculogenesis. In this study, a novel ultrasound‐guided follicle wall biopsy (FWB) technique was used to obtain in vivo follicle wall layers and follicular fluid samples of growing antral follicles. The expression of proliferative, hormonal, angiogenic, and pro‐/antiapoptotic receptors and proteins in the follicular wall among three follicle classes were compared during the spring transitional anovulatory (SAN) and spring ovulatory (SOV) seasons in mares. The main findings observed in the granulosa, theca interna, and/or all follicle layers during the SOV season compared with the SAN season were (a) small‐sized follicles (10–14 mm) had greater epidermal growth factor receptor (EGFR) and Bcl‐2 expression; (b) medium‐sized follicles during the expected deviation/selection diameter (20–24 mm) had greater expression of EGFR, Ki‐67, luteinizing hormone receptor (LHR), and Bcl‐2; and (c) dominant follicles (30–34 mm) had greater EGFR, Ki‐67, vascular endothelial growth factor, LHR, and Bcl‐2 expression. Estradiol related receptor alpha expression and intrafollicular estradiol concentration increased, along with an increase in follicle diameter in both seasons. In this study, the application of the FWB technique allowed a direct comparison of different receptors’ expression among follicles in different stages of development and between two seasons using the same individuals, without jeopardizing their ovarian function. The successful utilization of the FWB technique and the mare as an experimental animal offer a great combination for future folliculogenesis studies on mechanisms of follicle selection, development, and ovulation in different species, including women.     

Evaluation of the ultrasound image attributes of developing ovarian follicles in the four follicular waves of the interovulatory interval in ewes

Computer-assisted quantitative echotextural analysis was applied to ultrasound images of antral follicles in the follicular waves of an interovulatory interval in sheep. The ewe has three or four waves per cycle. Seven healthy, cyclic Western White Face ewes (Ovis aris) underwent daily, transrectal, ovarian ultrasonography for an interovulatory interval. Follicles in the third wave of the ovulatory interval had a longer static phase than that of those in Waves 1 and 2 (P < 0.05). The numeric pixel value for the wall of anovulatory follicles emerging in the third wave of the cycle was significantly higher than that for Waves 1 and 2 at the time of emergence (156.7 ± 8.09, 101.6 ± 3.72, and 116.5 ± 13.93, respectively), and it decreased as follicles in Wave 3 reached maximum follicular diameter (P < 0.05). The numeric pixel value of the antrum in the ovulatory follicles decreased as follicular diameter increased to ≥5 mm in diameter (P < 0.05). The pixel heterogeneity of the follicular antrum in Wave 1 increased from the end of the growth phase to the end of the regression phase for follicles in that wave (P < 0.05). The total area for the wall and antrum of the follicles studied were correlated with follicular diameter in all follicular waves (r = 0.938, P < 0.01 and r = 0.941, P < 0.01 for the wall and antrum, respectively). Changes in image attributes of the follicular wall and antrum indicate potential morphologic and functional differences among antral follicles emerging at different stages of the interovulatory interval in cyclic ewes.     

Aberrant blood flow area and plasma gonadotropin concentrations during the development of dominant-sized transitional anovulatory follicles in mares

Color Doppler transrectal ultrasound was used to evaluate blood flow area in the wall of dominant anovulatory follicles versus ovulatory follicles in mares during the transition between anovulatory and ovulatory seasons. Daily examinations were done in 11 control mares toward the end of the anovulatory season. In 13 separate mares, follicular fluid was collected from 30-mm follicles, and blood flow areas from control mares were used as a basis for designating the sampled follicle as either anovulatory or ovulatory. Blood flow area in the controls ranged from 0.18 to 0.35 cm(2) in six mares on the day of a 30-mm anovulatory follicle and from 0.25 to 0.86 cm(2) in 11 mares on the day of a 30-mm ovulatory follicle; the ranges did not overlap except for one follicle. In the controls, mean blood flow area was lower (P < 0.05) in the anovulatory group than in the ovulatory group for each day beginning with the first Doppler examination at 25 mm. For plasma LH in controls, an effect of follicle group (P < 0.0001) and an interaction (P < 0.0001) of group by day reflected lower (P < 0.05) concentrations in the anovulatory group on Days -6, -2, and 5-8 (Day 0 = 30-mm follicle). For plasma FSH, an interaction (P < 0.0001) reflected higher (P < 0.05) concentrations in the anovulatory group on Days -3 and 1-4. More (P < 0.05) statistically identified FSH surges occurred in the anovulatory group during Days -7 to 8. In the sampled mares, follicular-fluid concentrations of estradiol, free insulin-like growth factor-1, inhibin-A, and vascular endothelial growth factor were lower (P < 0.05) in 30-mm designated anovulatory follicles than in 30-mm designated ovulatory follicles. Results were interpreted as follows: 1) The future anovulatory dominant-sized follicle developed under an LH deficiency, 2) the LH deficiency led to reductions in blood flow area and in concentrations of follicular-fluid factors, and 3) the reduction in follicle production of FSH suppressors resulted in higher plasma FSH concentrations.     

Ovarian follicular activity and hormonal profile during estrous cycle in cows: the development of 2 versus 3 waves

Most estrous cycles in cows consist of 2 or 3 waves of follicular activity. Waves of ovarian follicular development comprise the growth of dominant follicles some of which become ovulatory and the others are anovulatory. Ovarian follicular activity in cows during estrous cycle was studied with a special reference to follicular waves and the circulating concentrations of estradiol and progesterone. Transrectal ultrasound examination was carried out during 14 interovulatory intervals in 7 cows. Ovarian follicular activity was recorded together with assessment of serum estradiol and progesterone concentrations. Three-wave versus two-wave interovulatory intervals was observed in 71.4% of cows. The 3-wave interovulatory intervals differed from 2-wave intervals in: 1) earlier emergence of the dominant follicles, 2) longer in length, and 3) shorter interval from emergence to ovulation. There was a progressive increase in follicular size and estradiol production during growth phase of each wave. A drop in estradiol concentration was observed during the static phase of dominant anovulatory follicles. The size of the ovulatory follicle was always greater and produced higher estradiol compared with the anovulatory follicle. In conclusion, there was a predominance of 3-wave follicular activity that was associated with an increase in length of interovulatory intervals. A dominant anovulatory follicle during its static phase may initiate the emergence of a subsequent wave. Follicular size and estradiol concentration may have an important role in controlling follicular development and in determining whether an estrous cycle will have 2 or 3-waves.     

Follicular populations during the estrous cycle in heifers. II. Influence of right and left sides and intraovarian effect of the corpus luteum

Ovarian follicles ≥2 mm were studied in 22 Holstein heifers by daily ultrasound examinations. Data were partitioned by right vs. left ovary and corpus luteum bearing ovary vs. the contralateral ovary. There were significantly more (P < 0.03) follicles 4–6 mm, > 13mm and total ≥2 mm in the right ovary, regardless of the presence of a corpus luteum. Significantly more (P < 0.05) follicles 2–3 mm, > 13 mm and total ≥2 mm were observed in the ovary bearing the corpus luteum. Interactions between day and corpus luteum appeared to be due to a greater number of follicles in the ovary bearing the corpus luteum during the first part of the interovulatory interval. There was also a day by right side vs. left side interaction for the number of follicles > 13 mm. Interpretation of the interactions was that the presence of a corpus luteum was conducive to the development of more anovulatory diestrous follicles > 12 mm. However, as regression of the corpus luteum progressed, there was an apparent proclivity for preovulatory follicular development in the right ovary. There was no apparent pattern of alternating sides of ovulation or of alternating sides of development of anovulatory diestrous follicles and preovulatory follicles in heifers observed for more than one interovulatory interval. There was not a significant difference in the maximum diameter attained by the anovulatory diestrous follicle or preovulatory follicle between ovaries ipsilateral or contralateral to the corpus luteum; however, the maximum diameter attained by the preovulatory follicle was greater (P < 0.05) than that attained by the anovulatory diestrous follicle.     

Ovarian follicle development in wapiti (Cervus elaphus) during the anovulatory season

The ovaries of 12 mature wapiti hinds were studied by transrectal ultrasonography during the anovulatory season to characterize follicular dynamics and to test the hypothesis that follicle development occurs in a wave-like fashion. The hinds were examined daily, standing without sedation. Follicle size and numbers were recorded, and individual follicles were identified serially. Follicle development was considered wave-like if periodic changes in follicle numbers could be associated temporally with the development of a dominant follicle. There were non-random changes (P<0.01) in the number of follicles > or =4 mm in diameter detected per day. Each peak in follicle numbers was associated with the development of a single dominant follicle. The dominant follicle of the cohort was larger (P<0.05) than the other follicles 1 day after its emergence. Intervals between successive peaks (6.8 +/- 0.4 day) and troughs (6.8 +/- 0.4 day) in follicle numbers, and emergence of sequential dominant follicles (7.1 +/- 0.5 day) were not different (P=0.86). Results confirmed the hypothesis that ovarian follicles develop in a wave-like fashion in wapiti during the anovulatory season.     

Vascular endothelial growth factor production in growing pig antral follicles

Angiogenesis is the process that drives blood vessel development in growing tissues in response to the local production of angiogenic factors. With the present research the authors have studied vascular endothelial growth factor (VEGF) production in ovarian follicles as a potential mechanism of ovarian activity regulation. Prepubertal gilts were treated with 1250 IU equine chorionic gonadotropin (eCG) followed 60 h later by 750 IU of human chorionic gonadotropin (hCG) in order to induce follicle growth and ovulation. Ovaries were collected at different times of the treatment and single follicles were isolated and classified according to their diameter as small (<4 mm), medium (4-5 mm), or large (>5 mm). VEGF levels were measured in follicular fluid by enzyme immunoassay, and VEGF mRNA content was evaluated in isolated theca and granulosa compartments. Equine chorionic gonadotropin stimulated a prompt follicular growth and induced a parallel evident rise in VEGF levels in follicular fluid of medium and large follicles. Analysis of VEGF mRNA levels confirmed the stimulatory effect of eCG, showing that it is confined to granulosa cells, whereas theca cells maintained their VEGF steady state mRNA. Administration of hCG 60 h after eCG caused a dramatic drop in follicular fluid VEGF that reached undetectable levels in 36 h. A parallel reduction in VEGF mRNA expression was recorded in granulosa cells. The stimulating effect of eCG was also confirmed by in vitro experiments, provided that follicles in toto were used, whereas isolated follicle cells did not respond to this hormonal stimulation. Consistent with the observation in vivo, granulosa cells in culture reacted to hCG with a clear block of VEGF production. These results demonstrate that while follicles of untreated animals produce stable and low levels of the angiogenic factor, VEGF markedly rose in medium and large follicles after eCG administration. The increasing levels, essentially attributable to granulosa cells, are likely to be involved in blood vessel development in the wall of growing follicles, and may play a local key role in gonadotropin-induced follicle development. When ovulation approaches, under the effect of hCG, the production of VEGF is switched off, probably creating the safest conditions for the rupture of the follicle wall while theca cells maintained unaltered angiogenic activity, which is probably required for corpus luteum development.     

Expression of proopiomelanocortin-related peptides in human follicular fluid

In order to evaluate the expression of the opioid precursor proopiomelanocortin (POMC) in the ovarian follicle, we measured 6 of its main end-products in 23 follicular fluids. We coupled high performance liquid chromatography (HPLC) to specific radioimmunoassays. Seven follicles were immature (diameter less than 9 mm), 10 were obtained from superovulated patients during an in vitro fertilization-embryo transfer program (greater than 22 mm) and six were persistent follicles, collected during the luteal phase [15-31 mm, luteinized unruptured follicles (LUF)]. Follicular fluids were extracted by mean of Sep-pak cartridges and then purified by HPLC with a reverse-phase C-18 column eluted in a linear gradient with acetonitrile/0.01 M hydrochloric acid (from 18:82 to 40:60). Fractions were tested with specific antisera for ACTH (1-39), alpha-MSH, beta-lipotropin (beta-LPH), beta-endorphin (beta-EP) and gamma-endorphin (gamma-EP) immunoreactivities. No presence of beta-LPH, beta-EP and ACTH was confirmed, while gamma-EP, alpha-MSH and des-alpha-MSH were detected for the first time in follicular fluid. In every class of follicles shorter chain peptides predominate over their longer chain precursor. Immature follicles are characterized by the highest amounts of gamma-EP, ACTH, alpha-MSH and des-alpha-MSH if compared to superovulated and LUF. On the contrary, beta-EP amount was highest after superovulation. Apart from this finding, peptide levels in superovulated patients and LUF are similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Concentrations of inhibin,progesterone and oestradiol in fluid from dominant and subordinate follicles from mares during spring transition and the breeding season

Dominant and subordinate follicles were collected from mares on the day after the dominant follicle reached 30 mm in diameter, to investigate regulation of folliculogenesis during spring transition and the breeding season. Concentrations of oestradiol-17beta, progesterone and inhibin A, but not inhibin isoforms with pro- and alpha C-immunoreactivity, were significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. Steroidogenic activity was regained gradually in the dominant follicles of successive anovulatory waves through spring transition. The dominant follicles, during both spring transition and cyclicity, contained higher concentrations of oestradiol, progesterone and inhibin A, but not inhibin pro- and alpha C-isoforms, than subordinate follicles. The results indicate that high follicular levels of oestradiol, progesterone and inhibin A are associated with continued follicle growth and ovulation. The low concentrations of oestradiol and progesterone in transitional follicles indicate that the deficiency in steroidogenesis exists early in the steroidogenic pathway. The similarity in patterns of follicular hormones in spring transition and during cyclicity strongly suggests that the mechanism of dominance is the same in both types of follicle.     

Ultrasonography and hormone profiles of adrenocorticotrophic hormone (ACTH)-induced persistent ovarian follicles (cysts) in cattle

The objective of this study was to develop a model for the study of abnormal ovarian follicles in cattle by treating heifers with adrenocorticotrophic hormone (ACTH) (100 iu at 12 h intervals for 7 days, beginning on day 15 of the oestrous cycle). Cortisol concentrations increased (P < 0.05) within 24 h after beginning ACTH treatment and cortisol and progesterone concentrations remained elevated after cessation of ACTH treatment for 8 and 4 days, respectively. The pulses and surges of LH decreased during ACTH treatment, but FSH profiles were similar to those in controls and persistent or prolonged follicles were eventually observed in all heifers. In five heifers, prolonged dominant follicles ovulated after 10 days, whereas in six heifers, persistent follicular structures were present for 20 days, but ceased to secrete oestradiol after approximately 12 days. In the heifers with persistent follicular structures, new follicles emerged when the persistent follicle became non-oestrogenic. During the last 2 days of normal follicular growth, the concentration of oestradiol was greater than it was during prolonged or persistent follicle development (P < 0.05). There were no differences in the growth rates or maximum diameters of abnormal follicles that had different outcomes, but oestradiol concentrations were greater in prolonged follicles that ovulated compared with those follicles that persisted (P = 0.06). In conclusion, stimulation with ACTH resulted in a marked deviance from normal follicular activity. The aberrations were probably caused by the interruption of pulsatile secretion of LH (but not FSH) leading to decreased but prolonged oestradiol secretion.     

Quantitative echotexture analysis of bovine ovarian follicles

Computer-assisted image analysis was used to evaluate ultrasound images of bovine ovarian follicles. The ovaries of 8 sexually mature heifers were examined daily by transrectal ultrasonography for 2 estrous cycles. Ultrasonographic examinations of the ovaries were then videotaped, and the dominant and subordinate follicles of successive waves were individually identified and monitored. Recorded images of the dominant anovulatory follicle of the first wave (n = 15) and the ovulatory follicle of the last wave (n = 15) of the estrous cycle were subsequently digitized for computer analysis of echotexture (mean pixel value and pixel heterogeneity). Regions of the image spanning the breadth of the follicle wall were selected, and image analysis revealed that mean pixel value of the dominant anovulatory follicle changed over time (P = 0.0005). Mean pixel value decreased (P = 0.0005) dramatically during the early static phase (Days 6 to 8, Day 0 = day of ovulation), increased (P = 0.0005) at the onset of the regressing phase (Day 12), and reached maximal levels (P = 0.0005) on Day 14. Similarly, image echotexture of the ovulatory follicle revealed a time-dependent effect (P = 0.0001) due to a rapid decrease in mean pixel values between 7 and 4 d before ovulation, followed by an increase until the day before ovulation. The echotexture of images of the follicular antrum were also evaluated and with regard to the dominant anovulatory follicle, a time-dependent effect was not detected for mean pixel value (P = 0.62) but was observed for pixel heterogeneity (P = 0.02). In addition, there was a positive correlation between mean pixel value and heterogeneity (r = 0.61, P = 0.0001). Heterogeneity initially decreased (P = 0.02) and remained low until the emergence of the second follicular wave (mean Day 9). Values subsequently increased and became variable during the late static and regressing phases (> Day 9). Mean pixel value of the antrum of the dominant ovulatory follicle increased (P = 0.0001) as the day of ovulation approached. Heterogeneity did not change (P = 0.14), nor was there any correlation between mean pixel value and heterogeneity for the antrum of the ovulatory follicle (r = 0.06, P = 0.49). We concluded that changes in echotexture (mean pixel value and heterogeneity) of bovine ovarian follicles assessed by computer analysis of ultrasound images were temporally related to functional status (i.e., anovulatory versus ovulatory; growing, static or regressing). The results were strongly supportive of the concept that ultrasonographically detected image attributes are a reflection of physiologic status.     

Characterization of ovarian follicular dynamics in dromedary camels (Camelus dromedarius)

Ovarian follicular dynamics was monitored by transrectal ultrasonography, for a period of 60 to 90 days, and its correlation with plasma estradiol-17β (E2) and progesterone (P4) were studied in seventeen, multiparous, non-lactating, 12 to 20-year-old dromedary camels. The average number of follicles recruited (12.77 ± 0.93) in each wave between animals varied (P < 0.001). The number of follicles recruited during different follicular waves was highly repeatable (0.95) within individual animals. The growth and mature phase periods of the dominant follicle (DF) were 6.10 ± 0.15 and 10.20 ± 0.47 days, respectively with a linear growth rate of 1.17 ± 0.02 mm/day between Day 0 and 10 of the follicular wave. There was an inverse relationship between the diameter of the largest DF and number of follicles (r = −0.95, P < 0.001). The DF development did not regularly alternate between the ovaries and the incidence of codominance was 45%. The mean maximum diameter of DF during its mature phase was 27.30 ± 0.78 mm and oversized follicle was 38.43 ± 1.41 mm. In 73.3% waves, the DF continued its growth for a period of 10.64 ± 1.53 days even after losing its dominance and developed into oversized follicle. The duration of the regression phase of DF and oversized follicle were 24.71 ± 3.79 and 18.50 ± 2.23 days. The mean duration of a complete follicular wave was 47.11 ± 2.94 days with an interwave interval (IWI) of 16.36 ± 0.37 days. The IWI within an individual was repeatable (0.88) and between the animals was variable (P < 0.001). Plasma E2 concentration profiles showed a wave like pattern. The peak plasma E2 concentrations were attained approximately 12 days after beginning of the growth phase, when the largest DF grew to a diameter of 18.7 mm. Plasma concentration of P4 was below 1.0 ng/mL in 85% of waves and above 1.0 ng/mL in 15% of the waves for a period of 3 to 6 days in the absence of spontaneous ovulation. It is concluded that ovarian follicular development and plasma E2 concentrations occurs in a wave like pattern in dromedary camels and the IWI and follicle numbers recruited per wave are variable between the animals and repeatable within an individual animal.     

Follicular and FSH dynamics in ewes with a history of high and low ovulation rates

Daily transrectal ultrasound scanning and twice-daily blood sampling were used to monitor the temporal relationships between FSH concentrations and follicle development during complete interovulatory intervals for ewes in which the ovulation rate in each of the 2 previous years was high or low (> or = 3 and < or = 2 ovulations, respectively). Follicles that reached > or = 5 mm were used to define a follicular wave and were tracked retrospectively to 3 mm (emergence). The hypothesis that FSH surges (identified with a computer program) and follicular waves (retrospectively determined based on ultrasound scanning) are temporally associated was supported in both groups by the emergence of an anovulatory or ovulatory follicular wave near the peak of an FSH surge. Further support for the hypothesis was a significant increase in FSH concentrations before and a significant decrease after follicular-wave emergence in both groups independent of the identification of FSH surges. Ewes with a history of high ovulation rates had smaller follicles (anovulatory and ovulatory) and more ovulations, but the 2 groups were similar in the number of ovulatory follicular waves and associated FSH surges, number and characteristics of the FSH surges, and mean FSH concentrations per interovulatory interval. Surges of FSH were periodic (every 3 or 4 d) regardless of the ovulation-rate group or follicle response. In ewes with a low ovulation rate, the nonovulatory FSH surges were most frequently associated with emergence of detected anovulatory follicular waves. In ewes with a high ovulation rate, more FSH surges were not associated with a detected follicular wave, as defined, presumably because the largest follicle did not reach 5 mm. The results indicated that the factors resulting in a high ovulation rate were not exerted through circulatory patterns or concentrations of FSH but involved a shorter growth phase and smaller maximal diameter of follicles.     

Differentiation of dominant versus subordinate follicles in cattle

Selection of a dominant follicle, capable of ovulating, from among a cohort of similarly sized follicles is a critical transition in follicular development. The mechanisms that regulate the selection of a species-specific number of dominant follicles for ovulation are not well understood. Cattle provide a very useful animal model for studies on follicular selection and dominance. During the bovine estrous cycle, two or three sequential waves of follicular development occur, each producing a dominant follicle capable of ovulating if luteal regression occurs. Follicles are large enough to allow analysis of multiple endpoints within a single follicle, and follicular development and regression can be followed via ultrasonographic imaging. Characteristics of recruited and selected follicles, obtained at various times during the first follicular wave, have been determined in some studies, whereas dominant and subordinate follicles have been compared around the time of selection in others. As follicular recruitment proceeds, mRNA for P450 aromatase increases. By the time of morphological selection, the dominant follicle has much higher concentrations of estradiol in follicular fluid, and its granulosa cells produce more estradiol in vitro than cells from subordinate follicles. Shortly after selection, dominant follicles have higher levels of mRNAs for gonadotropin receptors and steroidogenic enzymes. It has been hypothesized that granulosa cells of the selected follicle acquire LH receptors (LHr) to allow them to increase aromatization in response to LH, as well as FSH. However, LH does not appear to stimulate estradiol production by bovine granulosa cells, and the role of LHr acquisition remains to be determined. Recent evidence suggests a key role for changes in the intrafollicular insulin-like growth factor (IGF) system in selection of the dominant follicle. When follicular fluid was sampled in vivo before morphological selection, the lowest concentration of IGF binding protein-4 (IGFBP-4) was more predictive of future dominance than size or estradiol concentration. Consistent with this finding, dominant follicles acquire an FSH-induced IGFBP-4 protease activity. Thus, a decrease in IGFBP-4, which would make more IGF available to interact with its receptors and synergize with FSH to promote follicular growth and aromatization, appears to be a critical determinant of follicular selection for dominance.     

Changes in ovarian follicles following acute infection with bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) has been associated with several reproductive problems in cattle, including poor fertility, early embryonic deaths, abortion and congenital anomalies. Little is known about the cause of poor fertility in cows acutely infected with BVDV. The purpose of this study was to identify changes in ovarian function following acute infection with noncytopathic BVDV. The ovaries of 5 BVDV sero-negative and virus-negative pubertal heifers were monitored daily for 4 consecutive estrous cycles. The position and diameter of all follicles (> 5 mm) and luteal structures were recorded. Daily plasma samples were collected to measure peripheral progesterone and estradiol levels. Each heifer was infected intranasally with noncytopathic BVDV following ovulation of the second estrous cycle. The maximum diameter and growth rate of dominant anovulatory and ovulatory follicles were significantly reduced following acute BVDV infection. Similarly, the number of subordinate follicles associated with both the anovulatory and ovulatory follicle was reduced following infection. There were no significant differences in other follicle or luteal dynamic parameters or in peripheral progesterone or estradiol levels. Ovarian follicular growth was different during the first 2 estrous cycles following acute infection with BVDV when compared with the 2 estrous cycles preceding infection. These differences may be important in explaining reduced fertility in herds with acute BVDV infection.