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.     

Is one-wave follicular growth during the estrous cycle a usual phenomenon in water buffaloes (Bubalus bubalis)?

The pattern of growth and regression of ovarian follicles was monitored once daily for one complete estrous cycle in eight individual water buffaloes by ultrasonographic scanning of the ovaries for an entire interovulatory interval of normal cycle length. One-wave follicular growth was observed in five animals and two-wave follicular growth in three buffaloes during the estrous cycle. The first follicular wave of a two-wave cycle emerged significantly earlier (P < 0.05) than the emergence of the solitary wave of a one-wave cycle. One- and two-wave cycles differed significantly (P < 0.05) with respect to the mean interovulatory interval (21.0 +/- 0.54 days versus 22.7 +/- 0.33 days) and the mean interestrus interval (20.8 +/- 0.58 days versus 22.3 +/- 0.66 days). The overall linear growth rate of the ovulatory follicle was significantly greater (P < 0.01) in a two-wave cycle compared to that of a one-wave cycle (1.17 +/- 0.33 mm/day versus 0.32 +/- 0.01 mm/day). In a one-wave pattern, the growth profile of the solitary dominant follicle was atypical, showing three distinct phases, i.e. growth phase, regression phase and regrowth phase culminating in ovulation. The level of plasma progesterone steadily increased from day 0 of estrous cycle, attained peak level on day 14 and declined thereafter. A slower growth rate of the dominant follicle was observed in the presence of higher plasma progesterone concentration. The present study shows that one-wave follicular growth is a normal phenomenon in suckled water buffaloes.     

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

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

Ovarian follicular and luteal dynamics in wapiti during the estrous cycle

The reproductive tracts of 13 mature hinds were examined daily by transrectal ultrasonography and blood samples were taken daily from October to January to characterize follicular, luteal, and endocrine dynamics in wapiti during the estrous season. Follicle development occurred in waves characterized by regular, synchronous development of a group of follicles in temporal succession to a surge in serum FSH concentration. The mean interovulatory interval was 21.3 +/- 0.1 d, but was shorter in hinds exhibiting two follicular waves than in hinds exhibiting three and four waves (P < 0.05). The interwave interval was similar among waves in two-wave cycles and the first wave of three-wave cycles. All other interwave intervals in three- and four-wave cycles were shorter (P < 0.05). The maximum diameter of the dominant follicle of the first wave was similar among two-, three-, and four-wave cycles. For all other waves in three- and four-wave cycles, the maximum diameter was smaller (P < 0.05). Corpus luteum diameter and plasma progesterone concentrations were similar between two- and three-wave cycles, but the luteal phase was longer (P < 0.05) in four-wave cycles. The dominant follicle emerged at a diameter of 4 mm at 0.4 +/- 0.1 and 0.8 +/- 0.1 d before the largest and second largest subordinate follicles, respectively. The follicle destined to become dominant was larger (P < 0.05) than the largest subordinate follicle one day after emergence, which coincided with the first significant decrease in serum FSH concentration. We concluded that the estrous cycle in wapiti is characterized by two, three, or four waves of follicular development (each preceded by a surge in circulating FSH), that there is a positive relationship between the number of waves and the duration of the cycle, and an inverse relationship between the number of waves and the magnitude of follicular dominance (diameter and duration of the dominant follicle).     

Modification of follicular dynamics by exogenous FSH and progesterone, and the induction of ovulation using hCG in postpartum beef cows

Follicular growth and ovulation in response to FSH, progesterone and hCG were evaluated in postpartum beef cows. In Experiment 1, on Day 21 post partum, cows received an injection of either saline (control; n = 6), FSH (200 mg; n = 6), or a PRID (n = 5) for 10 d. Both FSH and PRID prolonged maintenance of a dominant follicle (15.5 +/- 1.16 and 14.4 +/- 1.29 d, respectively, vs 8.4 +/- 1.22 d in control; P < 0.01), and increased the maximum diameter of the dominant follicle (14.0 +/- 0.91 and 16.4 +/- 1.01 mm, respectively, vs 10.9 +/- 0.95 mm in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 60% of cows, followed by normal estrous cycles (vs 0% in control; P = 0.01), whereas the dominant follicle ovulated in 33% of FSH-treated cows (P = 0.08). The PRID regimen shortened the interval to first ovulation preceding a normal cycle and continued cyclicity (44 +/- 4.1 vs 60 +/- 4.4 d in control; P = 0.02). In Experiment 2, on Day 21 post partum, cows received either saline (control), saline + PRID, or FSH + PRID (n = 16/group). Sixty hours after PRID withdrawal, cows received either saline or hCG (1,500 IU, n = 8/treatment). The FSH + PRID regimen increased the number of large (> 10 mm in diameter) follicles (3.6 +/- 0.43 vs 1.9 +/- 0.39 in control; P = 0.005). Both PRID and FSH + PRID prolonged maintenance of the largest follicle (11.0 +/- 0.82 and 11.2 +/- 0.91 d, respectively, vs 8.7 +/- 0.81 d in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 50% of cows, followed by normal estrous cycles. The FSH + PRID-maintained largest follicle had become atretic at PRID withdrawal and was anovulatory. The FSH + PRID + hCG regimen increased the incidence of ovulation preceding a cycle of normal duration and continued cyclicity (100 vs 50% in PRID; P = 0.03), and reduced the interval to first ovulation preceding a cycle of normal duration and continued cyclicity (38 +/- 6.5 vs 58 +/- 6.3 d in control; P = 0.04). The area under the progesterone curve during the induced cycle was reduced after (PRID +/- FSH) + hCG than after PRID +/- FSH (P = 0.002). These results indicate that PRID alone or with FSH/hCG has the potential to modify the dominant follicle and initiate cyclicity in postpartum beef cows.     

Waves of follicle development during the estrous cycle in sheep

The pattern of ovarian follicle development in maiden cyclic lambs was characterized using the definition of a follicle wave as the changes in the number of follicles among the days of the estrous cycle, as originally defined in cattle by Rajakoski in 1960. We also examined the steroid content relationships among follicles on Days 5 (Wave 1) and 14 (Waves 2 and 3) of the estrous cycle. In Experiment 1, the ovaries of 20 cyclic lambs (40 to 45 kg) were examined daily using transrectal ultrasonography for 1 or 2 estrous cycles (n = 31 cycles). The number of small (2 and 3 mm in diameter), medium (4 and 5 mm) and large (> or = 6 mm) follicles were aligned with the beginning and end of the average length estrous cycle and then compared among days. Identified follicles were defined as those that grew to > or = 4 mm and remained at > or = 3 mm for > or = 3 d. The number of identified follicles emerging (retrospectively identified at 2 or 3 mm) per ewe per day was also aligned with the average length estrous cycle. In Experiment 2, ewe lambs were ovariectomized on Day 5 (n = 6) or 14 (n = 5) of the estrous cycle, then follicle diameters and follicular fluid concentrations of estradiol and progesterone were compared among follicles. Data were analyzed by repeated measures ANOVA and compared among days using Fisher's LSD. In Experiment 1, either 2 (n = 10 cycles), 3 (n = 20 cycles) or 4 (n = 1 cycle) periods of emergence of identified follicles occurred during individual cycles, with estrous cycle lengths of 15.6 +/- 1.6, 16.1 +/- 1.1 and 17 d respectively. In animals with 2 or 3 periods of emergence of identified follicles, the total number of small, medium and large follicles differed (P < 0.05) among days of the estrous cycle showing a wave-like pattern. In Experiment 2, a single follicle collected on each of Days 5 and 14 of the cycle (6.2 +/- 0.2 and 3.9 +/- 0.2 mm in diameter) had a higher (P < 0.05) concentration of follicular fluid estradiol (36.2 +/- 4.4 and 50.9 +/- 21.6 ng/mL) than other follicles collected on the same day (next largest follicle: 4.3 +/- 0.3 and 3.5 +/- 0.4 mm; 4.3 +/- 0.9 and 18.2 +/- 6.7 ng/mL estradiol). The results showed that 1) there was a synchronous emergence of follicles associated with fluctuations in the number and size of follicles during the estrous cycle; 2) within a wave there was a hierarchy among follicles for diameter and steroid content; 3) ovarian follicle growth in ewe lambs occurred in 2 or 3 organized waves during the estrous cycle.     

Effect of hCG administration on day 7 of the estrous cycle on follicular dynamics and cycle length in cows

The use of hCG in cattle at breeding or at different times after breeding has been associated with extension in estrous cycle length among cows that do not become pregnant. The objective of this study was to determine whether the increase in estrous cycle length observed in hCG-treated cows that fail to become pregnant is due to changes in ovarian follicular dynamics. Twelve nonbred lactating cows were randomly assigned either to receive hCG on Day 7 of the cycle (Day 0 = day of estrus, n = 6) or to serve as controls (n = 6). Ultrasound scanning was conducted daily from Day 0 until the onset of the next ovulation to monitor follicular and corpus luteum (CL) dynamics. Blood samples were collected for progesterone analysis at each ultrasound session. Ovulation of the Day 7 follicle occurred in all 6 hCG-treated cows. The time of emergence of the second-wave of follicular growth was advanced in hCG-treated cows but was not statistically different (P > 0.05) from that of the control cows (10.8 +/- 0.3 vs 12.7 +/- 1.4 d). The mean diameter of the second-wave dominant follicle from Days 15 to 18 was not different (P > 0.05) between the treatment groups. However, the second-wave dominant follicle had a slower growth rate (0.8 vs 1.3 mm/d) among cows treated with hCG compared with that of the controls. The second-wave dominant follicle was the ovulatory follicle in 5 control cows, but only in 3 hCG-treated cows. The dominant follicle from the third wave ovulated in 1 control and in 3 hCG-treated cows. The lifespan of the spontaneous CL and the time to low progesterone levels (< 1 ng/ml) were not different between the control and hCG-treated cows. These results suggest an altered follicular dynamic but no extension in estrous cycle length when hCG is administered on Day 7 of the cycle in postpartum cows.     

Standardization and validation of an induced ovulation model system in buffalo cows: Characterization of gene expression changes in the periovulatory follicle

In bovines characterization of biochemical and molecular determinants of the dominant follicle before and during different time intervals after gonadotrophin surge requires precise identification of the dominant follicle from a follicular wave. The objectives of the present study were to standardize an experimental model in buffalo cows for accurately identifying the dominant follicle of the first wave of follicular growth and characterize changes in follicular fluid hormone concentrations as well as expression patterns of various genes associated with the process of ovulation. From the day of estrus (day 0), animals were subjected to blood sampling and ultrasonography for monitoring circulating progesterone levels and follicular growth. On day 7 of the cycle, animals were administered a PGF(2alpha) analogue (Tiaprost Trometamol, 750 microg i.m.) followed by an injection of hCG (2000 IU i.m.) 36 h later. Circulating progesterone levels progressively increased from day 1 of the cycle to 2.26+/-0.17 ng/ml on day 7 of the cycle, but declined significantly after PGF(2alpha) injection. A progressive increase in the size of the dominant follicle was observed by ultrasonography. The follicular fluid estradiol and progesterone concentrations in the dominant follicle were 600+/-16.7 and 38+/-7.6 ng/ml, respectively, before hCG injection and the concentration of estradiol decreased to 125.8+/-25.26 ng/ml, but concentration of progesterone increased to 195+/-24.6 ng/ml, 24h post-hCG injection. Inh-alpha and Cyp19A1 expressions in granulosa cells were maximal in the dominant follicle and declined in response to hCG treatment. Progesterone receptor, oxytocin and cycloxygenase-2 expressions in granulosa cells, regarded as markers of ovulation, were maximal at 24h post-hCG. The expressions of genes belonging to the super family of proteases were also examined; Cathepsin L expression decreased, while ADAMTS 3 and 5 expressions increased 24h post-hCG treatment. The results of the current study indicate that sequential treatments of PGF(2alpha) and hCG during early estrous cycle in the buffalo cow leads to follicular growth that culminates in ovulation. The model system reported in the present study would be valuable for examining temporo-spatial changes in the periovulatory follicle immediately before and after the onset of gonadotrophin surge.     

Relation between progesterone concentrations during the early luteal phase and follicular dynamics in goats

We studied the relationship between progesterone (P4) concentrations early in the estrus cycle and follicular dynamics in dairy goats. We used seven untreated goats (control group) and six progesterone treated goats (P group) with a controlled internal drug release device from Days 0 to 5 (Day 0: day of ovulation). We performed daily ultrasonograph during the interovulatory interval to determine ovarian change and took daily blood samples to determine serum estradiol 17beta (E2) and P4 concentrations by RIA. We divided the control goats into 3- (n = 4) and 4-wave goats (n = 3), according to the number of follicular waves recorded during the ovulatory cycle. Mean progesterone concentrations between Days I and 5 were higher and mean estradiol concentrations between Days 3 and 5 were lower in 4-wave goats (P4: 3.8+/-0.2 ng/ml; E2: 1.6+/-0.2 pg/ml) than in 3-wave goats (P4: 2.0+/-0.5 ng/ml, P < 0.05; E2: 4.4+/-0.9 pg/ml, P < 0.05). Wave 2 emerged earlier in 4-wave (Day 4.2+/-0.3) than in 3-wave goats (Day 7.3+/-0.3, P < 0.05). Three out of six of the progesterone-treated goats had short cycles (mean 8.0+/-0.0 days) and ovulated from Wave 1. The other three goats had shorter cycles (mean 18.3+/-0.3 days) than the control group (20.0+/-0.2 days; P < 0.05), although they were within the normal range of control cycles (shortened cycles). In the three treated goats with shortened cycles (two with four waves, one with three waves), mean progesterone concentrations between Days I and 5 were higher (4.7+/-0.6 ng/ml) than in the 3-wave control goats. In these goats, Wave 2 emerged at Day 4.3+/-0.3, similar to the time observed in 4-wave goats but earlier (P < or = 0.05) than in 3-wave control goats. Overall results confirm a relationship between the progesterone levels and the follicular wave turnover during the early luteal phase in the goat. Higher progesterone concentrations may accelerate follicular turnover probably by an early decline of the negative feedback action of the largest follicle of Wave 1. This is followed by an early emergence of Wave 2.     

Folliculogenesis during the transitional period and early ovulatory season in mares

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

Follicular dynamics in Serrana goats

Twenty-two Serrana goats were studied through two successive estrous cycles in order to characterize their follicular dynamics during the breeding season. The ovaries of the goats were scanned daily by real-time ultrasonography and all follicles >or=3mm were measured and classified. The data were classified by the number of follicular waves per goat to test the hypothesis that temporal and morphological differences between the last follicular wave of an ovary, irrespective of ovulation, will affect the selection of the next ovulatory wave. The mean interovulatory interval was 20.7+/-1.0 days (mean+/-S.D.). Three to five waves per estrous cycle were observed and 61.3% (19/31) of cycles had four waves. In estrous cycles with four waves, the day of onset of the first, second, third and fourth wave was 1.4+/-1.0, 6.9+/-1.4, 11.6+/-1.8 and 16.8+/-1.6, respectively. No differences (P>0.05) were found between the day of onset of the first and second waves for estrous cycles with three, four or five waves. However, the day of onset of the third and fourth waves occurred later when the number of waves per estrous cycle increased (P<0.001). The duration of the interwave interval (time between the day of onset of two consecutive waves) was longer when the second wave was ovulatory. The length of the growth phase (2.4+/-0.9 days) and size (5.9+/-0.7 mm) of the dominant follicle in the second wave were lower (P<0.01) than for the first wave (3.3+/-1.2 days and 6.6+/-0.9 mm, respectively) and the fifth wave (4.1+/-1.2 days and 7.5+/-1.0mm, respectively). Within pairs of ovaries, the onset of the last wave occurred later (P<0.05) and was less variable in ovulatory ovaries (day 16.8+/-1.4, n=20) than in anovulatory ovaries (day 15.1+/-3.7, n=20). The length of the growing phase was longer (P<0.001) in the last waves of ovulatory ovaries (3.1+/-0.9 days) than in the last waves of anovulatory ovaries (1.7+/-0.8 days). These results support the hypothesis that the day of onset of the ovulatory wave is related to or, at least, conditioned by the luteolysis and the decrease in plasma progesterone. In summary, the estrous cycle of Serrana goats is characterized by sequential follicular wave growth with a great variability in their onset and duration, with the exception of the ovulatory wave. The temporal and morphological differences observed in the last wave of estrous cycle provide strong evidence for the role of progesterone in their regulation.     

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

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

Intraovarian relationships among dominant and subordinate follicles and the corpus luteum in heifers

Previous studies demonstrated that waves of follicular activity develop approximately every 9 d in cattle during the estrous cycle and early pregnancy. A dominant follicle develops from each wave and the remaining follicles (subordinates) begin to regress after a few days. In this study, intraovarian luteal and follicular interrelationships were examined during the follicular waves of the estrous cycle and pregnancy using data obtained by ultrasonography. During the estrous cycle, no intraovarian relationships were found between the ovary containing the corpus luteum and the ovary containing the dominant follicle (n = 165), or between the location of the corpus luteum and the characteristics of the dominant follicle. During pregnancy, however, the frequency distribution for the number of follicular waves with the dominant follicle and corpus luteum on the same or opposite ovaries differed (P<0.05) among Waves 1 to 10. The two structures (dominant follicle and corpus luteum) were more often in opposite ovaries during Waves 3 to 10 (combined frequency, 75%) than during Waves 1 and 2. During pregnancy, dominant follicles of consecutive waves differed (P<0.05) among Waves 1 to 8 in the frequency with which they appeared in the same versus the opposite ovary. The difference seemed primarily due to an increased frequency of consecutive follicles on the same ovary for Waves 4 to 8 (combined frequency, 80%). During both the estrous cycle and pregnancy, there was no significant intraovarian effect of the dominant follicle on the day of detection of the next dominant follicle, on the growth rate of the largest subordinate follicle, or on the length of the interval from wave origin to cessation of growth of the largest subordinate; these results indicate that previously postulated suppressive effects between follicles are exerted through systemic channels.     

Ovarian follicular dynamics in Nelore breed (Bos indicus) cattle

The most common beef cattle raised in Brazil is the Nelore breed (Bos indicus). Information obtained by ultrasonography on follicular growth in Bos taurus cattle has been accumulating rapidly. However, there are few publications to date on follicular development in Bos indicus breeds. The follicular dynamics in Nelore heifers and cows during natural or prostaglandin (PG)-induced estrous cycle were studied. From the detection of estrus onward, all animals were examined daily by ultrasonography for one (n = 35) or two (n = 10) consecutive estrous cycles. The follicular dynamic in Nelore cattle was characterized by the predominance of 2 follicular waves in the cows (83.3%, n = 18, P < 0.05) and 3 waves in the heifers (64.7%, n = 16, P < 0.05). Most of the cattle observed over 2 consecutive estrous cycles presented the same pattern of follicular waves in the first and second cycle, and only 30% showed variation in the number of waves from one cycle to the other. Most of the follicular parameters analyzed were not affected by PG treatment or age but were altered by follicular waves. Consequently, data on cows and heifers were combined according to the number of follicular waves. The ovulatory follicle was larger than the other dominant follicles (P < 0.05), and the ovulatory wave was shorter than the preceding waves (P < 0.05). The interovulatory interval was longer in animals showing 3 waves than those exhibiting 2 waves (P < 0.05). Maximum diameter of the dominant follicle (around 11 mm) and of the corpus luteum (CL, approximately 17 mm) were smaller than those reported for European breeds. In conclusion, the results demonstrate that although the dominant follicle and corpus luteum are smaller than in European breeds, the follicular dynamics in Nelore cattle were similar to those observed in European breeds and were characterized by 2 or 3 follicular waves for cows and heifers, respectively, during the natural or prostaglandin-induced estrous cycle.     

Ovarian responses to progesterone and oestradiol benzoate administered intravaginally during dioestrus in cattle

This study examined the effects of administering progesterone and oestradiol benzoate (ODB) during mid-dioestrus, on ovarian follicular dynamics in cattle. Twelve cycling cows were used in a 4 x 4 latin square design, with the 4 treatments being initiated on Day 13 of the cycle (oestrus = Day 0) and comprising intravaginal insertion for 5 days of: (i) a progesterone releasing device (CIDR; 'P4'); (ii) a CIDR device with a gelatin capsule containing 10 mg ODB and 1 g lactose (CIDIROL; 'P4/ODB') attached; (iii) a placebo CIDR device with the 10 mg ODB capsule (ODB); and, (iv) a placebo CIDR device alone (CTRL). The ovaries of each cow were examined daily by transrectal ultrasonography from Day 7 of the cycle until subsequent ovulation. Blood samples were collected daily from Day 11, and at intervals of 2-4 h during the 24 h period either side of treatment initiation. The second dominant follicle (DF2) emerged on Day 10.7 +/- 0.2 (mean +/- SEM), and was 8.5 +/- 0.2 mm in diameter by Day 13. The DF2 developed through to ovulation (2-wave cycles) in half of the animals in the CTRL group; while in the other half of cases, the ovulatory follicle originated from the third follicle wave that emerged on Day 17.2 +/- 0.4. Administration of a CIDR device alone (P4 group) did not alter the 1:1 ratio of 2 and 3-wave cycles, but the third dominant follicle (DF3) in those cows with 3-wave cycles emerged earlier on Day 15.6 +/- 0.2. In contrast, the DF2 of every animal in the ODB and P4/ODB groups became atretic and was replaced by a DF3 which emerged 4.0 +/- 0.3 days later. The effects of ODB on luteal function were limited to an earlier decline in plasma progesterone concentrations from 2 to 4 days after device insertion and a reduction in diameter of the corpus luteum when administered concurrently with progesterone. Intravaginal administration of 10 mg ODB on Day 13 of the oestrous cycle, with or without progesterone, was effective in promoting follicle wave turnover. In the absence of ODB, progesterone administration alone (P4 group) did not alter the ratio of animals with 2 or 3-wave cycles from that observed in animals in the CTRL group, but did advance the timing of subsequent follicle wave emergence in those animals with 3-wave cycles.     

Follicular dynamics in water buffalo superovulated in presence or absence of a dominant follicle

The ovaries of 12 buffalo were examined daily by ultrasound beginning at Day 3 of the estrous cycle, followed by superovulation between Days 10 and 13 of the cycle. The buffalo were divided into 2 groups on the basis of the presence (dominant, n = 7) or absence (nondominant, n = 5) of a dominant follicle at the start of superovulation. Daily ultrasonographic observations of the ovaries were recorded on a videotape and were used to assess the progression of both the large (dominant) follicle and the next-to-the-large (subdominant) follicle as well as the numbers of follicles in the small (4 to 6 mm), medium (7 to 10 mm), and large (>10 mm) size categories, before and during the superovulation treatment. A greater number of small size (P < 0.05) follicles was available before the start of the superovulatory treatment in the buffalo superovulated in the absence of a dominant follicle. The turnover of follicles from medium to large size classes also occurred sooner (P < 0.01), and was of higher magnitude (P < 0.01) during treatment in buffalo of the nondominant follicle group. The number of corpora lutea at palpation per rectum was higher (P < 0.05) in buffalo of the nondominant than the dominant group (4.6 +/- 0.6 vs 2.7 +/- 0.5). However, there was no significant difference among the groups in the means of serum progesterone concentration (3.6 +/- 1.3 vs 2.2 +/- 0.6 ng/ml), total number of embryos (2.0 +/- 0.6 vs 1.1 +/- 0.7), transferable embryos (1.6 +/- 0.5 vs 1.0 +/- 0.6) and unfertilized ova recovered (0.4 +/- 0.2 vs 0) on Day 6. It is concluded that in buffalo, the superovulatory response could possibly be improved by ultrasongraphic observation of the status of follicular dominance prior to treatment.     

Ovarian follicular dynamics during the estrous cycle in heifers monitored by real-time ultrasonography

It is not clear whether the turnover of ovarian follicles during the estrous cycle in cattle is continuous and independent of the phase of the cycle, or whether waves of follicular growth occur at specific times of the cycle. To clarify this controversy, the pattern of growth and regression of ovarian follicles was characterized during a complete estrous cycle in ten heifers by daily ultrasonographic examinations. Follicles greater than or equal to 5 mm were measured and their relative locations within the ovary were determined in order to follow the sequential development of each individual follicle. Results indicated the presence of either two (n = 2 heifers), three (n = 7), or four (n = 1) waves of follicular growth per cycle. Each wave was characterized by the development of one large (dominant) follicle and a variable number of smaller (non-dominant) follicles. In the most common pattern observed (three waves/cycle), the first, second, and third waves started on Days 1.9 +/- 0.3, 9.4 +/- 0.5, and 16.1 +/- 0.7 (X +/- SEM), respectively. The dominant follicle in the third wave was the ovulatory follicle. The maximal size and the growth rate of the dominant follicle in the second wave were significantly lower than in the other waves, but no significant difference was observed between the first and third waves. For the two heifers that had two follicular waves/cycle, the waves started on Days 2 and 11, whereas in the remaining heifer (four waves/cycle), the waves began on Days 2, 8, 14, and 17, respectively. At 0, 1, 2, 3, and 4 days before estrus, the ovulatory follicle was the largest follicle in the ovaries in 100%, 95%, 74%, 35%, and 25% of follicular phases monitored, respectively. The relative size of the preovulatory follicle at the completion of luteolysis (progesterone less than 1 ng/ml) was negatively correlated (r = -0.90; p less than 0.0001) with the interval of time between the end of luteolysis and the luteinizing hormone surge, suggesting that the length of proestrus is determined by the size of the pre-ovulatory follicle at the beginning of proestrus. In conclusion, this study shows that the development of ovarian follicles greater than or equal to 5 mm in heifers occurs in waves and that the most common pattern is three waves per estrous cycle.     

Effect of estradiol valerate on ovarian follicle dynamics and superovulatory response in progestin-treated cattle

Three experiments evaluated the effects of estradiol valerate (EV) on ovarian follicular and CL dynamics, intervals to estrus and ovulation, and superovulatory response in cattle. Experiment 1 compared the efficacy of two norgestomet ear implants (Crestar and Syncro-Mate B; SMB) for 9 d (with PGF at implant removal), combined with either 5 mg estradiol-17beta and 100 mg progesterone (EP) or 5 mg EV and 3mg norgestomet (EN) im at the time of implant insertion on CL diameter and follicular wave dynamics. Ovaries were monitored by ultrasonography. There was no effect of norgestomet implant. Diameter of the CL decreased following EN treatment (P < 0.01). Mean (+/- S.D.) day of follicular wave emergence (FWE) was earlier (P < 0.0001) and less variable (P < 0.0001) in EP- (3.6 +/- 0.5 d) than in EN- (5.7 +/- 1.5 d) treated heifers. Intervals from implant removal to estrus (P < 0.001) and ovulation (P < 0.01) were shorter in EN- (45.7 +/- 11.7 and 74.3 +/- 12.6 h, respectively) than in EP- (56.4 +/- 14.1 and 83.3 +/- 17.0 h, respectively) treated heifers. Experiment 2 compared the efficacy of EP versus EN in synchronizing FWE for superovulation in SMB-implanted cows. At random stages of the estrous cycle, Holstein cows (n = 78) received two SMB implants (Day 0) and were randomly assigned to receive EN on Day 0 or EP on Day 1. Folltropin-V treatments were initiated on the evening of Day 5, with PGF in the morning and evening of Day 8, when SMB were removed. Cows were inseminated after the onset of estrus and embryos were recovered 7 d later. Non-lactating cows had more CL (16.7 +/- 11.3 versus 8.3 +/- 4.9) and total ova/embryos (14.7 +/- 9.5 versus 7.9 +/- 4.6) than lactating cows (P < 0.05). EP-treated cows tended (P = 0.09) to yield more transferable embryos (5.6 +/- 5.2) than EN-treated cows (4.0 +/- 3.7). Experiment 3 compared the effect of dose of EV on ovarian follicle and CL growth profiles and synchrony of estrus and ovulation in CIDR-treated beef cows (n = 43). At random stages of the estrous cycle (Day 0), cows received a CIDR and no further treatment (Control), or an injection of 1, 2, or 5 mg im of EV. On Day 7, CIDR were removed and cows received PGF. Follicular wave emergence occurred within 7 d in 7/10 Control cows and 31/32 EV-treated cows (P < 0.05). In responding cows, interval from treatment to FWE was longer (P < 0.05) in those treated with 5 mg EV (4.8 +/- 1.2 d) than in those treated with 1 mg (3.2 +/- 0.9 d) or 2 mg (3.4 +/- 0.8 d) EV, while Control cows were intermediate (3.8 +/- 2.0 d). Diameter of the dominant follicle was smaller (P < 0.05) at CIDR removal and tended (P = 0.08) to be smaller just prior to ovulation in the 5 mg EV group (8.5 +/- 2.2 and 13.2 +/- 0.6 mm, respectively) than in the Control (11.8 +/- 4.6 and 15.5 +/- 2.9 mm, respectively) or 1mg EV (11.7 +/- 2.5 and 15.1 +/- 2.2 mm, respectively) groups, with the 2mg EV group (10.7 +/- 1.5 and 14.3 +/- 1.7 mm, respectively) intermediate. Diameter of the dominant follicle at CIDR removal was less variable (P < 0.01) in the 2 and 5mg EV groups than in the Control group, and intermediate in the 1mg EV group. In summary, treatment with 5mg EV resulted in a longer and more variable interval to follicular wave emergence than treatment with 5mg estradiol-17beta, which affected preovulatory dominant follicle size following progestin removal, and may have also affected superstimulatory response in Holstein cows. Additionally, 5 mg EV appeared to induce luteolysis in heifers, reducing the interval to ovulation following norgestomet removal. Conversely, intervals to, and synchrony of, follicular wave emergence, estrus and ovulation following treatment with 1 or 2 mg EV suggested that reduced doses of EV may be more useful for the synchronization of follicular wave emergence in progestogen-treated cattle.     

Regulation of follicular activity and ovulation in ewes by exogenous progestagen

The success of estrus synchronization programs using progestagen sponges, particularly for fixed-time AI, varies considerably. In view of the recent evidence in cattle that exogenous progestins alter follicular dynamics, it may be that the stage of the estrous cycle at which the synchronization protocol is begun affects the synchrony of ovulation. The goal of this study was to evaluate the effect of medroxyprogesterone acetate (MAP) intravaginal sponges on follicular dynamics, luteal function and interval to ovulation when inserted at 3 stages of the estrous cycle. Sponges were inserted for 12 d beginning on either Day 0, 6 or 12 (n = 5) following ovulation. Ovarian activity was monitored using real-time ultrasound imaging during the treatment and the post-treatment estrous cycles. Information from the post-treatment cycle was used as a baseline to compare with the treatment cycle. Most ewes (79%) in the post-treatment cycle exhibited 3 follicular waves in an estrous cycle of 16 d, with the second wave follicles having smaller diameter (P < 0.001). Treatment with MAP increased the number of follicular waves from 3 to 4 or 5 when sponges were inserted on Days 6 and 12, respectively. Size of the largest follicle was smaller (P > 0.01) in waves in the early and middle of the 12-d MAP treatment period when compared with the last 4 days. This effect was most pronounced when endogenous progesterone concentrations were elevated concurrently with the presence of the sponge. Persistence of the ovulatory follicle was increased (P < 0.001) when sponges were inserted on Day 12, the only treatment where these follicles were under the influence of MAP in the absence of functional corpora lutea. Follicles were regressing at sponge removal in the Day 6 treatment, which resulted in a delay in emergence of ovulatory follicles, the LH surge and ovulation (P < 0.08) in relation to Day 0 and Day 12. Treatment with MAP sponges does not adequately synchronize estrus and ovulation among cyclic ewes due to the different follicular patterns that result depending on the stage of cycle at the time of sponge insertion.     

Characteristics of ovarian follicular dynamics throughout the estrous cycle of Egyptian buffaloes

Data of 56 normal and 9 abnormal estrous cycles were collected from 9 Egyptian buffaloes (Bublus bublis) to describe the follicular growth wave pattern. Heat was checked twice daily while, ovaries were scanned daily to monitor the patterns of follicular waves. Day of ovulation was determined when the largest follicle was replaced by corpus haemorrhgicum (CH). Number of waves/cycle, day of emergence of the follicular wave, characteristics of the dominant follicle and corpus luteum (CL) growth features were monitored. Buffaloes displayed mainly two types of follicular waves; two (46.4%) and three (53.6%). In cycles of three wave pattern, time of emergence of the 1st wave post-heat was longer (P < 0.05) and number of recruited follicles/wave were larger (P < 0.05) compared to the corresponding values of the two wave pattern. Number of recruited follicles in early follicular waves (1st or the 2nd) had larger number (P < 0.05) compared to the subsequent ones. Follicles that reached ovulation in both types of estrous cycle had shorter life-span (P < 0.05) than the previous ones. Life-span of CH, growing and regressed CL were 3.6 ± 0.6, 11.2 ± 0.8 and 4.4 ± 0.5 days, respectively with no difference in both types of follicular wave. Three types of ovarian disorders were observed. Follicular waves and CL growth features showed unique pattern for each individual. These results demonstrate that buffaloes display two main types of follicular waves with dominance of three wave type.