Minor FSH surge,minor follicular wave,and resurgence of preovulatory follicle several days before ovulation in heifers

Blood samples were collected and follicle diameters were determined daily beginning on Day 12 (Day 0 = ovulation) in 35 interovulatory intervals (IOIs) in heifers. A minor follicular wave with maximal diameter (6.0 ± 0.3 mm) on Day −4 was detected in six of seven IOIs that were scanned for follicles 4 mm or greater. The number of IOIs with a CV-identified minor FSH surge toward the end of the IOI was greater (P < 0.03) in two-wave IOIs (10/17) than in three-wave IOIs (4/18). The 17 two-wave IOIs were used for study of the temporal relationships among preovulatory follicle, FSH, LH, and estradiol. Daily growth rate of the preovulatory follicle was maximum on Days −11 to −7, minimum (P < 0.05) on Days −7 to −4, and increased (resurged, P < 0.05) on Days −4 to −3. A transient increase in FSH was maximum on mean Day −4, and the peak of a minor FSH surge occurred on Day −4.5 ± 0.2. Concentration of LH and estradiol increased between Days −5 and −4. Results demonstrated resurgence of the preovulatory follicle apparently for the first time in any species. Resurgence seemed more related temporally to the minor FSH surge than to the LH increase, but further study is needed. Results supported the novel hypotheses that a minor FSH surge near the end of the IOI is temporally associated with (1) the emergence of a minor follicular wave and (2) the resurgence in growth rate of the preovulatory follicle.     

Two-way coupling between FSH and the dominant follicle in heifers

Follicular Wave 1 and 2 and the associated FSH Surge 1 and 2 were used to designate the first two waves and surges of the interovulatory interval in two experiments in heifers. In experiment 1, a group with early (group E, N = 9) and late (group L, N = 5) development of the dominant follicle of Wave 1 were used as natural models to study FSH/follicle coupling. The day of wave emergence and the day of deviation in diameters between the two largest follicles were not different between groups. Emergence of Wave 2 and maximal FSH concentration in Surge 2 was approximately 1 day later (P < 0.03) in group L. Diameter of the dominant follicle of wave 1 (13.8 ± 0.3 mm vs. 12.0 ± 0.3 mm) and FSH concentrations in Surge 2 (0.29 ± 0.02 ng/mL vs. 0.21 ± 0.03 ng/mL) were first greater (P < 0.05) in group E than in group L at 4 and 5 days, respectively, after wave emergence. In experiment 2, treatment with estradiol (N = 8) when the dominant follicle of Wave 1 was ≥11 mm (Hour 0) resulted in a decrease (P < 0.02) in FSH and slower (P < 0.05) growth rate of the follicle between Hours 0 and 4. Results supported the following hypotheses: (1) the FSH surge that stimulates emergence of a follicular wave is associated with final growth of the dominant follicle of the previous anovulatory wave; and (2) suppression of FSH Surge 2 when the dominant follicle of Wave 1 is ≥11 mm is associated with a decrease in diameter. It is concluded for the first time that two-way FSH/follicle coupling in heifers continues during final growth of the dominant follicle of Wave 1 and that Surge 2 is the FSH source.     

Complex interrelationships among CL,preovulatory follicle,number of follicular waves,and right or left ovaries in heifers

The diameter of the dominant follicle (DF) of wave 1 was studied on Days 9 to 17 (Day 0 = ovulation) in a survey of the ipsilateral and contralateral relationships between the location of the DF and CL, and number of follicular waves per interovulatory interval (IOI). For contralateral relationships, regardless of number of waves the diameter of the DF of wave 1 decreased (P < 0.03) between Days 11 and 13 when referenced to the follicle–CL relationship of wave 1 and decreased (P < 0.008) between Days 9 and 11 when referenced to the preovulatory follicle (PF)–CL relationship. For wave 2 in two-wave IOIs, the CL ovary of ipsilateral relationships had more (P < 0.05) follicles that reached at least 6 mm than the non-CL ovary. In three-wave IOIs, frequency of IOIs with the DF in the CL ovary was greater (P < 0.02) for wave 2 than for wave 3. In wave 3, the preovulatory and the largest subordinate follicles were located more frequently (P < 0.005) in the contralateral ovary. Ovulation in two-wave IOIs occurred more frequently (P < 0.0009) from the right ovary. In three-wave IOIs with a contralateral relationship ovulation occurred more frequently (P < 0.003) from the left ovary; a negative intraovarian effect of the CL on location of the PF may account for more ovulations from the left ovary and a reported greater frequency of the contralateral relationship. The hypothesis was supported that the ipsilateral versus contralateral relationship between the PF and CL is affected by the DF–CL relationship during the previous follicular waves and by the number and identity of waves per IOI.     

Relationship between days of the luteolytic period and locations of the preovulatory follicle and CL in interovulatory intervals with two or three follicular waves in heifers

Diameter of follicles was determined every 12 hours and progesterone (P4), FSH, and LH concentrations were determined every 6 hours from Day 12 (Day 0 = ovulation) to the ovulation at the end of the interovulatory interval (IOI). Groups were assigned on the basis of an ipsilateral (Ipsi) versus contralateral (Contra) relationship between the preovulatory follicle and CL and two follicular waves (2W) versus three waves (3W) per IOI. Numbers of IOIs were Ipsi-2W (n = 6), Ipsi-3W (n = 6), and Contra-3W (n = 8). Normalization to the end of luteolysis (day that P4 was closest to 1.0 ng/mL) indicated for the first time that concentrations of P4 and FSH were greater (P < 0.05) in 3W IOIs than in 2W IOIs for the 3 days before the beginning of a P4 decrease. The beginning of a P4 decrease occurred about 5 days and 6 hours after emergence of the preovulatory wave at 6 mm in 2W and 3W IOIs, respectively. On the day of diameter deviation between the future dominant and largest subordinate follicles in wave 3 of 3W IOIs, the future dominant follicle had the following characteristics: (1) distribution of diameters differed (P < 0.01) from unimodality; (2) diameter was greater (P < 0.05) in the Contra-3W group (9.8 ± 0.4 mm) than in the Ipsi-3W group (8.8 ± 0.3 mm); (3) diameter was similar to the diameter at the beginning of the P4 decrease (9.6 ± 0.9 mm); and (4) diameter was as small or smaller than diameter of the largest subordinate in seven of 14 heifers compared with zero of seven heifers in wave 2 of 2W IOIs. The differences involving deviation may be related to a reported greater frequency of the Contra-3W group than Ipsi-3W group. Results supported the hypothesis that emergence of the ovulatory wave occurs well before the beginning of luteolysis in 2W IOIs and near the beginning of luteolysis in 3W IOIs.     

Intraovarian effect of dominant follicle and corpus luteum on number of follicles during a follicular wave in heifers

The intraovarian relationships among dominant follicle (DF), corpus luteum (CL), and number of follicles between Days 0 to 5 (Day 0 = ovulation) in wave 1 (n = 65 waves) and Days 9 to 13 in wave 2 (n = 62) were analyzed in separate experiments in Bos taurus heifers. Ovaries were grouped into intraovarian patterns of DF–CL, DF alone, CL alone, and neither DF nor CL. In wave 1, the pattern frequencies of DF–CL or neither DF nor CL (34% each) were greater (P < 0.0004) than for DF alone or CL alone (16% each). The number of growing follicles ≥5.0 mm, was greater (P < 0.0001) in ovaries with the DF, even when the DF was removed from the tally (P < 0.03). In a factorial analysis of wave 1, there was a positive main effect of DF (3.9 ± 0.2 vs. 2.2 ± 0.2 follicles; P < 0.0001), but the main effect of CL and the interaction of DF and CL were not significant. In a factorial analysis of wave 2, there were more (P < 0.0001) follicles greater than 6 mm in ovaries with a DF when the DF was included and an approaching difference (P < 0.09) when the DF was excluded. The main effect of CL and the interaction of DF and CL were not significant. The hypothesis that both the DF and CL have a positive intraovarian effect on number of follicles in waves 1 and 2 was only partly supported; the DF, but not the CL, had an effect in the factorial analyses. Previous reports in cattle and sheep of a positive intraovarian effect of CL on number of follicles are questionable in that location of the DF was not considered.     

Blood flow to follicles and CL during development of the periovulatory follicular wave in heifers

The hemodynamics of the developing CL and the future dominant follicle (DF) was studied in 22 heifers during wave 1 on Days 0 to 5 (Day 0 = ovulation). Color-Doppler ultrasonography was used to determine the resistance index (RI) at the most prominent Doppler signal in an ovarian arterial branch before entry into the ovary; a decrease in RI indicates a downstream increase in vascular perfusion. The RI for each of four intraovarian patterns averaged over days was different (P < 0.05) from each of the other patterns as follows: DF–CL (DF and CL in the same ovary), 0.52 ± 0.02; CL alone, 0.60 ± 0.01; DF alone, 0.67 ± 0.01; neither DF nor CL, 0.78 ± 0.01. The differences in RI among intraovarian patterns began on Day 0 or 1, indicating that the extent of vascular perfusion on Days 0 to 5 for the various patterns may have been influenced by events that occurred before ovulation. The percentage of the DF wall with color-flow signals was greater (P < 0.05) in the DF–CL pattern than in the DF pattern on each of Days 2 to 5 and was greater (P < 0.0001) in the DF–CL pattern when the DF was adjacent to the CL (40.2 ± 2.0%) than when separated (24.5 ± 1.9%). Dimensions of DF (P < 0.01) and CL (P < 0.02) were greater when adjacent to each other. The results supported the hypotheses for wave 1 that (1) vascular perfusion is greater for the DF–CL intraovarian pattern than for the DF or CL pattern and (2) the extent of blood-flow Doppler signals in the wall of the developing DF is greater for the DF–CL pattern than for the DF pattern. Our preferred interpretation is that a change in vascular perfusion of the CL is accompanied by a similar change in perfusion of the DF when the two structures are in the same ovary especially adjacent.     

Alterations in follicular IGFBP mRNA expression and follicular fluid IGFBP concentrations during the first follicle wave in beef heifers

The objective was to determine the pattern of IGFBP-2, -3 and -4 gene expression and follicular fluid concentrations of IGFBP-2, -3, -4 and -5 during emergence, selection and dominance of the first follicle wave of the estrous cycle in cattle and during exogenous steroid treatment. Heifers (n = 35) were ovariectomized at 36 (n = 7), 66 (n = 8), 84 (n = 12) and 108 (n = 8) h after the onset of estrus. Heifers in the 84 h ovariectomy group were sub-divided to receive either no treatment (n = 6) or were treated with a progesterone-releasing intravaginal device (n = 6, PRID) and 0.75 mg estradiol benzoate i.m. at the approximate time of ovulation, 30 h post estrus until ovariectomy. Within heifers the four largest follicles recovered following ovariectomy were ranked on size (F1, F2, F3 and F4). At 36 h IGFBP gene expression and follicular fluid IGFBP concentrations were similar in all follicles (F1-F4). Mean diameter of the F1 follicle increased (P < 0.05) between 36 and 84 h with no difference between 84 and 108 h. The F1 follicle had the highest (P < 0.05) concentration of estradiol compared with the F2, F3 and F4 at 84 and 108 h. There was no granulosa cell IGFBP-2 mRNA in F1 follicles at 84 or 108 h. Intrafolliclar IGFBP-2 concentrations were lower (P < 0.05) in the F1 compared with F3 and F4 follicles at 108 h. There was no difference in theca cell IGFBP-4 mRNA expression at 108h, but amounts of follicular fluid IGFBP-4 were lower (P < 0.05) in F1 follicles compared with F3 and F4 follicles at 108 h. IGFBP-3 mRNA was localized in the theca layer of all follicles examined with no difference in expression or follicular fluid concentrations during emergence, selection and dominance of the first follicle wave. IGFBP-5 concentrations were higher (P < 0.05) in follicular fluid of F3 follicles at 108 h compared with the F3 at 36 h. In conclusion follicular dominance was associated with low or decreased follicular fluid concentrations of IGFBP-4 and -5, increased estradiol and differential regulation of IGFBP production.     

Diurnal variation in LH and temporal relationships between oscillations in LH and progesterone during the luteal phase in heifers

Diurnal variation in progesterone and LH during the luteal phase and the temporal relationships between oscillations of the two hormones were studied in 10 heifers by collection of blood samples at 0100, 0700, 1300, and 1900 h each day, beginning on Day 1 (Day 0 = ovulation). Concentration of LH on Days 5-9, but not on Days 10-14, was lower (P < 0.05) at 0700 h (0.25 ± 0.02 ng/mL) than at each of the other three hours (combined, 0.32 ± 0.02 ng/mL). An oscillation was defined as an uninterrupted increase and decrease in concentrations. The number of LH oscillations/heifer with the peak at 1900 h (6.1 ± 0.7) throughout the luteal phase was greater (P < 0.01) than for each of the other hours (combined, 4.0 ± 0.2). Diurnal variation in progesterone was not detected. Only statistically defined LH oscillations were used to determine the temporal association between the peak of an LH oscillation and various components of a progesterone oscillation. On Days 5-14, the frequency of the peak of an LH oscillation occurring at the same hour as the peak of a progesterone oscillation (26/48, 54%) was greater (P < 0.0001) than at the progesterone nadir (3/48, 6%). The frequency of the LH peak occurring during increasing (11/34, 32%) and decreasing (8/25, 32%) progesterone concentrations was intermediate (P < 0.05). Results indicated the following: 1) diurnal variation occurred in LH as determined by concentration and by the hour of the peak of an oscillation; and 2) LH oscillations were temporally and positively related to progesterone oscillations.     

Characteristics of peaks in serum concentrations of follicle-stimulating hormone and estradiol, and follicular wave dynamics during the interovulatory interval in cyclic ewes

There are three or four ovarian follicular waves in the interovulatory interval of cyclic ewes. Each follicular wave is preceded by a transient peak in serum follicle-stimulating hormone (FSH) concentrations. Serum concentrations of estradiol also increase concurrent with the growth of follicle(s) in each wave. In the current study, we investigated the patterns of follicular wave development and characteristics of FSH and estradiol peaks in all follicular waves of the interovulatory interval and after induction of a supraphysiologic FSH peak in cyclic ewes (Ovis aris). In Experiment 1, 19 ewes underwent daily ovarian ultrasonography and blood sampling for a complete interovulatory interval. In Experiment 2, seven ewes received two administrations of ovine FSH (oFSH), 8 h apart (1 μg/kg; sc), at the expected time of the endogenous FSH peak preceding the second follicular wave of the interovulatory interval. In Experiment 1, the amplitude of the FSH peaks decreased (up to 50%), whereas basal serum FSH concentrations increased across the interovulatory interval (P < 0.05). Maximum follicular diameter was greater (P < 0.05) for Wave 1 and the Ovulatory wave (6.0 ± 0.3 and 6.1 ± 0.2 mm, respectively) than for Waves 2 and 3 (5.3 ± 0.1 and 5.4 ± 0.3 mm, respectively). Life span was greater for follicles in Wave 1 compared with other waves (P < 0.05). Treatment with oFSH increased the amplitude of an FSH peak by 5- to 6-fold. This treatment increased estradiol production (P < 0.05) but had little effect on other characteristics of the subsequent follicular wave. We concluded that changes in the amplitude and duration of the peaks in serum concentrations of FSH that precede follicular waves across the interovulatory interval do not influence the characteristics of the follicular waves that follow.     

Relationship between plasma beta-carotene concentrations during the peripartum period and ovulation in the first follicular wave postpartum in dairy cows

Beta-carotene functions independently of vitamin A in the reproductive performance of dairy cows. The concentrations of beta-carotene in plasma decrease during the dry period, and reach a nadir in about the first week postpartum. This coincides with a negative energy balance, which affects the onset of the first ovulation in early postpartum cows. Thus, we hypothesised that plasma beta-carotene concentrations during the peripartum period may affect ovulation in the first follicular wave postpartum in dairy cows. The aim of the present study was to investigate changes in the profiles of plasma beta-carotene concentrations during the peripartum period in ovulatory and anovulatory cows during the first follicular wave postpartum. We used 22 multiparous Holstein cows, which were fed a total mixed ration consisting of grass, corn silage and concentrate, and collected blood samples for beta-carotene and progesterone analysis from week 3 prepartum to week 3 postpartum when the period of day 0-6 after parturition was regarded as the parturient week (week 0). The first ovulation was confirmed using the profile of plasma progesterone concentrations and colour Doppler ultrasound. Thirteen cows ovulated during the first postpartum follicular wave. Parity, the dry-off period, calving interval, mastitis episodes, and actual 305 days' milk yield during the previous lactation, and milk composition in the last month during the previous lactation in this study did not differ between ovulatory and anovulatory cows. Differences in the plasma beta-carotene profile were observed between ovulatory and anovulatory cows. Plasma beta-carotene concentrations at week 3 prepartum were greater in ovulatory cows (2.97+/-0.24 mg/L) than in anovulatory cows (1.53+/-0.14 mg/L; P<0.001), after that its concentrations in ovulatory cows decreased and reached the lowest level at week 1 postpartum, although its concentrations in anovulatory cows remained unchanged. No differences in plasma beta-carotene concentrations between the two groups were observed postpartum. The present study indicates for the first time that the lower beta-carotene concentrations in plasma during the prepartum period is associated with anovulation during the first follicular wave postpartum.