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).     

Ovarian follicular dynamics during the estrous cycle in buffalo (Bubalus bubalis)

The growth, selection, regression and ovulation of ovarian follicles was ultrasonically monitored in 30 Murrah buffalo throughout a spontaneous estrous cycle during the breeding season (autumn). Examinations revealed that follicular growth during the estrous cycle occurs in waves; the buffalo showed 1-wave (3.3%, n = 1), 2-wave (63.3%, n = 19) or 3-wave (33.3%, n = 10) follicular growth. The first wave began at 1.00, 1.16 +/-0.50 and 1.10 +/- 0.32 d in buffalo with 1, 2 and 3 waves, respectively (ovulation = Day 0). The second wave appeared at 10.83 +/- 1.09 and 9.30 +/- 1.25 d (P < 0.01) for the 2 and 3 wave cycle animals, respectively. The third wave started at 16.80 +/- 1.22 d. Structural persistence of the first dominant follicle was longer in the 2- than 3-wave cycles (20.67 +/- 1.18 vs 17.90 +/- 3.47 d ; P < 0.05). The duration of the growth and static phases of the first dominant follicle differed between the 2 and 3 wave cycles (P < 0.05), whereas there were no differences in linear growth rates (cm/d). Two and three wave cycles differed (P < 0.05) with respect to the maximum diameter of both the first dominant follicle (1.51 +/- 0.24 vs 1.33 +/- 0.18 cm) and the ovulatory follicles (1.55 +/- 0.16 vs 1.34 +/- 0.13 cm). No relationship was found between dominant follicle development and the presence of either a CL or a previous dominant follicle in either ovary. Two and three wave cycles also differed with respect to the mean length of intervals between ovulation (22.27 +/- 0.89 vs 24.50 +/- 1.88 d; P < 0.01) and the mean length of luteal phases (10.40 +/- 2.11 vs 12.66 +/- 2.91 d; P < 0.05). These results demonstrate that buffalo have estrous cycles with 1, 2 or 3 follicular waves; that 2-wave cycles are the most common; and that the number of waves in a cycle is associated with the luteal phase and with estrous cycle length.     

Ovarian follicular dynamics in heifers during early pregnancy

Daily ultrasonic monitoring of individual follicles was used to compare follicular wave characteristics of nonbred (n = 6) and pregnant heifers (n = 6). The dominant follicle of the first wave (Wave 1) did not differ significantly between reproductive statuses for any endpoint. The dominant follicle of Wave 2 was the ovulatory follicle in all nonbred heifers. The maximum diameter of the dominant follicle of Wave 2 was greater (p less than 0.05) for the nonbred heifers (14.8 mm) than for the pregnant heifers (13.0 mm). The dominant follicle of Wave 3 was detected later (p less than 0.003; Day 19.7 vs. Day 17.3) and reached a greater diameter (p less than 0.05; 16.6 mm vs. 12.0 mm) in the nonbred than in the pregnant heifers. On the mean day of onset of luteolysis (Day 15.2) in the nonbred heifers, the dominant follicle was similar in diameter for the two groups. Within a few days, the follicle began to regress in the pregnant heifers but maintained or increased in diameter in the nonbred heifers so that a greater maximum diameter was attained. During Days 0 70 of pregnancy, the interval from emergence of a wave to the emergence of the next wave was constant (not significantly different; mean intervals, 8.5 9.8 days). The mean maximum diameter attained by the dominant follicles differed significantly among the first 6 follicular waves; diameter was greatest for Wave 1 (15.7 mm), smallest for Waves 2 (13.1 mm) and 3 (12.6 mm), and intermediate for Waves 4 (14.0 mm), 5 (13.7 mm), and 6 (14.5 mm).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicular dynamics in suckled zebu (Bos indicus) cows monitored by real time ultrasonography

The pattern of follicular growth was studied in 17 suckled zebu cows with average body condition and under extensive management in a tropical environment (23 degrees C, 78% humidity; 2200 mm annual rainfall; 1000 m altitude). The study covered the period from parturition to weaning at 12 months postpartum (PP). Data were collected by transrectal ultrasonography (7.5 MHz) at 48 h intervals, and progesterone (P4) measurements were performed by RIA. The sequential development of ovarian follicles greater than 4 mm was followed until regression or ovulation. Ovarian activity as characterized by growth and regression of follicles of 4 to 6 mm, with sporadic dominance, and a long interdominance interval was observed in every cow and from as early as 26 +/- 2 days PP. This follicular pattern was highly variable during the first 6 months: cows presented 2 to 20 follicular waves (FW) in which a dominant follicle (DF) grew to 8 +/- 1 mm with daily growth rates of 1.1 +/- 0.5 mm/day. The duration of dominance varied from 2 to 8 days and the interdominance time interval was 0 (overlapped waves) to 60 days. Neither behavioural oestrus nor ovulation was observed during this period. From 6 to 12 months PP, cows presented 7 to 20 FW, some with ovulation and/or corpora lutea (CL) formation. The ovulation was preceded by oestrus in some cases (43%). The mean (+/- sem) diameter of DF was 9 +/- 2.7 mm, their mean growth rate 1.4 +/- 0.2 mm/day, their duration of dominance was 2 to 8 days and the interdominance interval was 0 to 14 days. Progesterone concentrations (P4) from 1.0 to 13 ng/ml were found when a CL was present. Once cyclicity re-commenced at 217 to 278 days PP, the cows presented either normal (21 +/- 3 days), short (10 +/- 2 days), or long (50 +/- 4 days) cycles. The resumption of cyclicity was characterized by an increased frequency of emerging follicular waves. Under the conditions of this study, the suckled Bos indicus cows re-commenced ovarian follicular activity as early as described in B. taurus breeds, but the establishment of cyclicity was substantially later. These data add further to the panorama of postpartum reproductive physiology in tropical cattle.     

Surges of FSH during the follicular and early luteal phases of the estrous cycle in heifers

Surges of FSH were characterized in each of 12 Holstein heifers using a computerized cycle detector program, and as mean changes averaged over all heifers. Blood samples were collected 6 times a day at 4-h intervals beginning at late diestrus. Concentrations of FSH were adjusted relative to the preovulatory LH peak (Hour 0) and profiled beginning 48 h before and ending 120 h after the LH peak. Peak concentrations of FSH and LH occurred synchronously in 11 of 12 (92%) heifers, and only a 4-h interval separated peak concentrations in the remaining heifer. The FSH surge that was synchronous with the LH surge was designated FSH Surge 1 and was used as a reference to designate other FSH surges. Surge -1 of FSH was detected in 58% of the heifers at mean Hour -21.2, and Surges 2, 3 and 4 were detected in 92%, 92% and 75% of the heifers, respectively, at mean Hours 25.1, 57.8 and 78.7. Mean peak levels and duration of FSH Surges-1, 2, 3 and 4 were significantly lower than for FSH Surge 1. Mean concentrations of FSH significantly increased and decreased before and after the LH peak, resulting from the synchrony between FSH Surge 1 and the LH surge in individual heifers. Additionally, there was a tendency (P < 0.08) for a second and third increase in mean FSH concentrations at Hours 24 and 60, which was attributed to FSH Surges 2 and 3 that occurred in individuals. Peak FSH concentrations of Surge 2 occurred (mean, Hour 25.1) within 8 h of maximal mean concentrations at Hour 24 in 91% of the heifers. Correspondingly, peak FSH concentrations of Surge 3 occurred (mean, Hour 57.8) within 8 h of maximal mean concentrations at Hour 60 in 64% of the heifers. Surges -1 and 4 of FSH occurred less frequently and at various times within and among heifers compared with Surges 1 to 3; therefore, they were not detected as mean increases in FSH concentrations but were masked as a result of concentrations being averaged over all heifers. In summary, FSH surges were detected in individual heifers before and after the combined FSH/LH surge. The interpeak intervals for FSH Surges 1 to 2 (25 h), 2 to 3 (33 h) and 3 to 4 (21 h) suggests a rhythmic nature to the surges.     

Ovarian follicular populations during early pregnancy in heifers

Ovarian follicles >/=2mm were studied in 14 pregnant and 14 nonpregnant Holstein heifers by daily ultrasound examinations. There were significant differences among days, from Day 0 (day of ovulation) to Day 21, in the diameter of the largest follicle and the diameter of the second largest follicle in pregnant and nonpregnant heifers. There was an interaction of day and reproductive status (P < 0.001) for the diameter of the largest follicle. Significant differences among days were also observed in the numbers of follicles 2 to 3 mm, 4 to 6 mm, 7 to 10 mm, 11 to 13 mm, and >13 mm, and the total number of follicles >/=2 mm. There was a significant main effect of reproductive status for the number of follicles 11 to 13 mm. An interaction of day and reproductive status was observed for the number of follicles >13 mm, but not for any of the other diameter categories. The effect of reproductive status for number of follicles 11 to 13 mm and the interactions for the number of follicles >13 mm and the diameter of the largest follicle seemed due to the selective growth and ovulation of the follicle destined to ovulate in nonpregnant heifers. The differences in ovarian follicular populations between pregnant and nonpregnant heifers were attributed solely to the presence of a physiological mechanism for the selection of an ovulatory follicle in nonpregnant heifers. There were no significant differences among days for any follicular endpoint during Days 22 to 60 in the pregnant heifers.     

Repeat breeding in dairy heifers: follicular dynamics and estrous cycle characteristics in relation to sexual hormone patterns

Repeat breeding occurs at an incidence of 10% in the Swedish dairy cow population.Evidence is available for a hormonal asynchrony around estrus in repeat-breeder heifers (RBH). This asynchrony seems to be the underlying cause for a series of dysfunctions such as prolonged standing estrus and delayed ovulation, leading to fertilization failure. For further determinations of repeat-breeder estrous cycle characteristics, seven strictly selected RBH and six virgin heifers (VH) were studied during 3-7 consecutive cycles, with particular attention paid to the estrous period. Follicular dynamics were studied by ultrasonography and related to estrous behavior and pattern of sexual hormones (progesterone, estradiol-17beta, and LH) in peripheral circulation. Mean group data were compared and a classification model was designed. The most prominent findings for RBH were prolonged duration of estrus, delayed LH peak, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in plasma progesterone. There was also a strong tendency for peri-ovulatory suprabasal progesterone levels in RBH. It is suspected that these deviations cause changes in the microenvironment of the preovulatory follicle, negatively affecting the final maturation of the oocyte. The heterogeneity of the RBH group underlines the multifactorial cause of the repeat-breeder syndrome. The VH formed a homogenous group with data varying within physiological limits. A classification model based on three characteristic variables managed to identify 81% of the VH and 79% of the RBH correctly. Results from this study propose that some heifers have general, consistent problems in synchronizing estrous events, displayed as varying symptoms in the course of consecutive estrous cycles. These subfertile animals could be classified as repeat-breeders.     

Effects of oxytocin on follicular development and duration of the estrous cycle in heifers

Holstein heifers were used to study effects of exogenous administration of oxytocin on luteal function and ovarian follicular development. Twelve heifers were monitored for 1 estrous cycle to confirm normal ovarian function. At the subsequent estrus, these animals were randomly assigned to 1 of 3 treatments: saline control, (Group 1, n=4), oxytocin (Group 2, n=4) and saline pregnant (Group 3, n=4). Group 2 received continuous infusion of oxytocin (1.9 mg/d) from Days 14 to 26 after estrus, while Groups 1 and 3 received saline infusion during the same period. Group 3 were artificially inseminated at estrus. Daily blood samples were collected for oxytocin and progesterone assay. Ovarian follicles and corpus luteum (CL) development were monitored daily by transrectal ultrasonography until Day 32 after estrus. Plasma progesterone (P4) concentrations prior to initiation of infusion were 7.6+/-1.3 ng/mL on Day 14. They then decreased to <1 ng/mL on Day 19 for Group 1 and on Day 28 for Group 2. The interestrous interval was longer (P <0.05) for heifers that received oxytocin infusion. During the infusion period P4 concentrations were not different (P >0.05) between Group 2 and 3 but declined gradually from Day 20 in Group 2 despite the presence of high plasma oxytocin concentrations. Control heifers had 2 waves of follicular growth, with the second dominant follicle ovulating. Three of the 4 oxytocin-infused animals had an additional wave, with the third dominant follicle ovulating. Oxytocin infusion had no effect on size of the ovulating follicle (P >0.05) and the number of Class 1 follicles (3 to 5 mm, P >0.1). Differences in the number of Class 2 follicles (6 to 9 mm) among treatments on Days 15 to 22 after estrus were not detected (P >0.1) except on Days 23 to 26, when Group 2 had fewer follicles than Group 3 (P <0.05). The results show that continuous infusion of oxytocin during normal luteolysis delays luteal regression without inhibiting follicular development.     

Effects of a dominant follicle on ovarian follicular dynamics during the oestrous cycle in heifers

Two hypotheses were tested: (1) a dominant follicle causes regression of its subordinate follicles, and (2) a dominant follicle during its growing phase suppresses the emergence of the next wave. Cyclic heifers were randomly assigned to one of four groups (6 heifers/group): cauterization of the dominant follicle of Wave 1 or sham surgery (control) on Day 3 or Day 5 (day of ovulation = Day 0). Ultrasonic monitoring of individually identified follicles was done once daily throughout the interovulatory interval. The onset of regression (decreasing diameter) of the largest subordinate follicle of Wave 1 was delayed (P less than 0.01) by cauterization of the dominant follicle of Wave 1 on Day 3 compared to controls (mean onset of regression, Days 10.8 +/- 2.1 vs 4.3 +/- 0.4). Cauterization of the dominant follicle of Wave 1 on Days 3 or 5 caused early emergence (P less than 0.01) of Wave 2 when compared to controls (Day-3 groups: Days 5.5 +/- 0.4 vs 9.6 +/- 0.7; Day-5 groups: Days 7.0 +/- 0.3 vs 9.1 +/- 0.4). The results supported the two hypotheses. In addition, cauterization of the dominant follicle of Wave 1 on Days 3 or 5 increased the incidence of 3-wave interovulatory intervals.     

Estrogen and LH dynamics during the follicular phase of the estrous cycle in the Asian elephant

Pituitary and corpus luteum hormone patterns throughout the elephant estrous cycle have been well characterized. By contrast, analysis of follicular maturation by measurement of circulating estrogens has been uninformative. This study tested the ability of a urinary estradiol‐3‐glucuronide radioimmunoassay to noninvasively assess follicular development during the nonluteal phase of the elephant estrous cycle, and to determine the relationship between estrogen production and the “double LH surge.” Daily urine and serum samples were collected throughout seven estrous cycles from three Asian elephants, and urine was collected from an additional three females, for a total of 13 cycles. Serum was analyzed for luteinizing hormone (LH), and urine was analyzed for estrogens and progestins. Elephants exhibited a typical LH pattern, with an anovulatory LH (anLH) surge occurring approximately 21 days before the ovulatory LH (ovLH) surge. The urinary estrogen pattern indicated the presence of two follicular waves during the nonluteal phase. The first wave (anovulatory) began 5 days before the anLH surge and reached a maximum concentration the day before the peak. Thereafter, urinary estrogens declined to baseline for 2 weeks before increasing again to peak concentrations on the day of the ovLH surge. Urinary progestins were baseline throughout most of the follicular phase, increasing 2–3 days before the ovLH surge and continuing into the luteal phase. These results support previous ultrasound observations that two waves of follicular growth occur during the nonluteal phase of the elephant estrous cycle. Each wave is associated with an increase in estrogen production that stimulates an LH surge. Thus, in contrast to serum analyses, urinary estrogen monitoring appears to be a reliable method for characterizing follicular activity in the elephant. Zoo Biol 22:443–454, 2003. © 2003 Wiley‐Liss, Inc.     

Ovarian steroidogenic enzyme activities during the rat estrous cycle

We have correlated the concentrations of serum LH, estradiol and progesterone with the activities of 2 ovarian steroid biosynthetic enzymes during the rat estrous cycle. Ovarian 3 β-hydroxysteroid dehydrogenase isomerase (3-βHSD) activity decreased from 29 ± 6 nmol/mg protein/ min (mean ± SEM) in diestrus, to 7 ± 0.4 nmol/mg protein/min in late proestrus (p < 0.005), and subsequently increased to 36 ± 9 nmol/mg protein/min in metestrus (p < 0.01). Ovarian 17-hydroxylase (17-OH) activity decreased from early to late proestrus (3.3 ± 0.2 vs 2.2 ± 0.2 nmol/mg protein/min, p <0.0025), and subsequently increased to 3.9 ± 0.2 in metestrus (p<0.001). Serum LH, estradiol and progesterone peaked during proestrus, and reached a nadir during estrus. We conclude that the activities of 3-βHSD and 17-OH in the rat ovary vary markedly during the estrous cycle. These changes may underlie the pattern of steroid secretion characteristic of this process.     

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.     

Plasma inhibin A in heifers: relationship with follicle dynamics, gonadotropins, and steroids during the estrous cycle and after treatment with bovine follicular fluid

The relationship between follicle growth and plasma inhibin A, FSH, LH, estradiol (E), and progesterone was investigated during the normal bovine estrous cycle and after treatment with steroid-free bovine follicular fluid (bFF) to arrest follicle development. In the first study, four heifers were monitored over three prostaglandin (PG)-synchronized cycles. Blood was collected every 2-8 h, and ovaries were examined daily by ultrasonography. Inhibin A was measured using a modified enzyme-linked immunosorbent assay that employed a new monoclonal antibody against the alpha subunit of bovine inhibin. Plasma inhibin A ( approximately 50 pg/ml before luteolysis) rose steadily during the induced follicular phase (P < 0.05) to a peak ( approximately 125 pg/ml) coincident with the preovulatory E/LH/FSH surge. After ovulation, inhibin A fell sharply (P < 0.05) to a nadir ( approximately 55 pg/ml) coincident with the secondary FSH rise. During the next 3 days, inhibin A increased to approximately 90 pg/ml in association with growth of the new dominant follicle (DF). Plasma E also rose twofold during this period, whereas FSH fell by approximately 50%. Inhibin A was negatively correlated with FSH (r = -0.37, P < 0.001) and positively correlated with E (r = 0.49, P < 0.0001). Observations on eight cycles (two cycles/heifer), in which growth of the ovulatory DF was monitored from emergence to ovulation, showed that the first-wave DF (DF1) ovulated in three cycles and the second-wave DF (DF2) in five cycles. After PG, plasma inhibin A and E increased similarly in both groups, with concomitant falls in FSH. In the former group, the restricted ability of DF1 to secrete both inhibin A and E was restored after luteolysis. Results indicate that dynamic changes in the secretion of both E and inhibin A from the DF contribute to the fall in FSH during the follicular phase and to the generation and termination of the secondary FSH surge, both of which play a key role in follicle selection. In the second study, bFF (two dose levels) was administered to heifers (n = 3-4) for 60 h starting from the time of DF1 emergence. Both doses suppressed FSH (P < 0.05) and blocked DF1 growth to the same extent (P < 0.01), although inhibin A levels were only marginally raised by the lower dose (not significant compared to controls). The high bFF dose raised (P < 0.001) inhibin A to supraphysiological levels ( approximately 1 ng/ml). A large "rebound" rise in FSH occurred within 1 day of stopping both treatments, even though the inhibin A level in the high-dose bFF group was still approximately threefold higher than that in controls. This indicates that desensitization of gonadotropes to inhibin negative feedback is a contributory factor, together with reduced ovarian output of E, in generation of the post-bFF rebound in FSH.     

Ovarian atrial natriuretic peptide during the rat estrous cycle.

The changes in ovarian levels of immunoreactive atrial natriuretic peptide (irANP) and arginine vasopressin (irAVP) were observed during the estrous cycle of rat. We also demonstrated the synthesis of ovarian ANP. In adult 4-day cycling rats, ovarian level of irANP was found to be the highest on proestrus and was to be the lowest on diestrus. Ovarian irANP level inversely correlated with ovarian level of irAVP. On reverse-phase HPLC, two distinct peaks of ovarian irANP, high and low molecular weight forms, existed in the each stage of the estrous cycle. However, no significant changes in plasma and atrial concentrations of ANP were observed during the cycle. The rat ovary contained mRNA coding for ANP. These data showing the synchronized cyclic change of ovarian irANP and irAVP with the estrous cycle suggest that the ovary locally synthesizes ANP and ovarian ANP may play regulatory roles on the follicular fluid dynamics.     

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 and hormonal dynamics during the first follicular wave in heifers

A few days after the first follicular wave emerges as 4-mm follicles, follicular deviation occurs wherein 1 follicle of the wave continues to grow (dominant follicle) while the others regress. The objectives of this study were to characterize follicle growth and associated changes in systemic concentrations of gonadotropins and estradiol at 8-h intervals encompassing the time of follicle deviation. Blood samples from heifers (n = 11) were collected and the ovaries scanned by ultrasound every 8 h from 48 h before to 112 h after the maximal value for the preovulatory LH surge. The follicular wave emerged at 5.8 +/- 5.5 h (mean +/- SEM) after the LH surge, and at this time the future dominant follicle (4.2 +/- 0.8 mm) was larger (P < 0.001) than the future largest subordinate follicle (3.6 +/- 0.1 mm). There was no difference in growth rates between the 2 follicles from emergence to the beginning of the deviation (0.5 mm/8 h for each follicle), indicating that, on average, the future dominant follicle maintained a size advantage over the future subordinate follicle. Deviation occurred when the 2 largest follicles were 8.3 +/- 0.2 and 7.8 +/- 0.2 mm in diameter, at 61.0 +/- 3.7 h after wave emergence. Diameter deviation was manifested between 2 adjacent examinations at 8-h intervals. Mean concentrations of FSH decreased, while mean concentrations of LH increased 24 and 32 h before deviation, respectively, and remained constant (no significant differences) for several 8-h intervals encompassing deviation. In addition to the increase and decrease in circulating estradiol concentrations associated with the preovulatory LH surge, an increase (P < 0.05) occurred between the beginning of deviation and 32 h after deviation. The results supported the hypotheses that deviation occurs rapidly (within 8 h), that elevated systemic LH concentrations are present during deviation, and that deviation is not preceded by an increase in systemic estradiol.     

Ovarian response to hCG treatment during the oestrous cycle in heifers

The aims of this study were to investigate whether treatment with a single ovulatory dose of hCG, between the day of oestrus and the end of the luteal phase, could induce extra ovulations in heifers and whether the presence of an existing corpus luteum (CL) affected the response. Heifers (N = 32) were injected with 1500 i.u. hCG or saline on a given day of the oestrous cycle. Treatments were repeated during subsequent cycles to provide a total of 71 observations, 57 of which followed an injection of hCG, given between Day 0 (oestrus) and Day 16, and 14 of which followed saline injections as controls. Ovulatory responses were noted by laparoscopy 2 days after hCG treatment. No heifers injected with saline produced additional CL. Of the hCG-treated cycles, 23 resulted in the formation of an additional CL, and this was significantly affected by the stage of the oestrous cycle when hCG was given; a greater response was observed during the early (Days 4-7) and late (Days 14-16) stages of the luteal phase than at the mid-luteal phase of the oestrous cycle. Two heifers were also treated with hCG on Days 17 or 18 of the oestrous cycle, but before oestrus; both had induced CL. There were no significant differences between the left-right orientation of the existing CL or the hCG-induced CL. These results demonstrate that the large, luteal-phase follicle of the cow is capable of ovulating in response to hCG and that the induced CL is not affected by the presence of an existing CL.     

Pattern of follicular development during the estrous cycle of aged rats

Summary The pattern of follicular development during the estrous cycles of aged rats was examined and compared with that of mature rats. In both, preovulatory follicles are derived from a select group of small pre-Graafian follicles which begin to develop at estrus and reach the preovulatory size by the morning of proestrus, but the rate of growth, as judged by an increase in the percentage of granulosa cells incorporating ³H-thymidine, is accelerated in the follicles of aged rats. A second mechanism, which accounts for preovulatory follicles in aged rats, involves the rescue from atresia of pre-Graafian and preovulatory follicles. The existence of this mechanism is supported by the observation that at metestrus in aged rats virtually all follicles, regardless of their state of atresia, possess a high percentage of granulosa cells incorporating ³H-thymidine, indicating that the follicles are growing rapidly. However, some of these rapidly growing follicles show signs of atresia such as pyknotic nuclei within their granulosa cell layers. Since follicles in the initial stage of atresia contain defective oocytes (Peluso et al. 1979b), their rescue and development into preovulatory follicles would result in the ovulation of defective oocytes, a fact which accounts in part of the lower fertility in these older animals.     

Behavioral, follicular and gonadotropin changes during the estrous cycle in donkeys

Sexual behavior, follicular development and ovulation, and concentrations of circulating gonadotropins during the estrous cycle were studied during the summer in 7 jennies. Mean behavioral estrous length was 6.4 +/- 0.6 days (mean +/- SEM, n=19; 5.6 +/- 0.5 days preovulatory and 0.8 +/- 0.2 days post-ovulatory). Mean diestrous length was 19.3 +/- 0.6 days (n=14). Females in estrus typically showed posturing, mouth clapping, clitoral winking, urinating and tail raising. Mouth clapping began approximately one day sooner and lasted approximately one day longer than winking and tail raising, so that the total duration of clapping was significantly greater than for the other two signs. Follicular changes and concentrations of gonadotropins were determined for 14 estrous cycles (2 per jenny). The follicular end points [diameter of the largest follicle and number of large (>25 mm), medium (20-24 mm), and small follicles (<20 mm)] showed a significant day effect. The diameter of the largest follicle and the number of large follicles began to increase significantly 7 days prior to ovulation with a maximum value the day before ovulation. Medium follicles reached a maximum number 4 days prior to ovulation, and small follicles decreased significantly prior to ovulation. After ovulation, all follicular end points, except the number of small follicles, remained low for the next 12 days. Mean values of FSH were low during estrus and high during diestrus with 2 significant peaks, one 3 days and one 9 days after ovulation. In contrast, mean levels of LH were low during diestrus and high during estrus with a maximum value the day after ovulation. The LH profile showed a more prolonged gradual increase prior to ovulation, than that which has been reported for ponies and horses.