Relationships of changes in B-mode echotexture and colour-Doppler signals in the wall of the preovulatory follicle to changes in systemic oestradiol concentrations and the effects of human chorionic gonadotrophin in mares

Follicle and hormone dynamics in single versus double ovulating heifers

Follicles ≥5 mm were ablated at 4 day post-ovulation in heifers to induce a follicular wave, and prostaglandin F2α was given at day 6 to increase the incidence of double ovulations. Follicle diameters and plasma hormone concentrations were compared between single ovulators (n=12) and double ovulators (n=8). In double ovulators, the interval from follicle deviation to the peak of the pre-ovulatory LH surge was shorter (1.9±0.2 vs 2.5±0.2 days; P<0.02) and diameter of the largest pre-ovulatory follicle was smaller (12.2±0.5 vs 13.3±0.3 mm; P<0.02). The LH concentrations of the pre-ovulatory surge did not differ between single and double ovulators for 24 h on each side of the peak. When data were normalised to LH peak, the peak of the pre-ovulatory FSH and oestradiol (E2) surges occurred in synchrony with the peak of LH surge for both groups. Concentration of FSH for 24 h on each side of the peak showed a group effect (P<0.0001) from lower concentration in the double ovulators. A group-by-hour interaction (P<0.008) for E2 reflected greater concentration in the double ovulators before and at the peak. Results indicated that two pre-ovulatory follicles resulted in an earlier and greater E2 increase, leading to lower FSH concentration, an earlier LH surge, and ovulation at a smaller diameter. In conclusion, the difference in hormone concentrations during the pre-ovulatory period was an effect rather than a cause of double ovulations.

Efficiency of superovulation and in vivo embryo production in eFSH-treated donor mares after estrus synchronization with progesterone and estradiol-17beta

Reliable methods of regulating estrus and stimulating superovulations in equine embryo transfer programs are desirable. Our objectives were to investigate the efficacy of a progesterone and estradiol-17beta (P&E) estrus synchronization regimen in mares with and without subsequent equine follicle-stimulating hormone (eFSH) treatment and to examine the effects of eFSH on folliculogenesis and embryo production. Cycling mares were treated with P&E daily for 10 d. On the final P&E treatment day, prostaglandin F(2alpha) was administered, and mares were randomly assigned to one of two treatment groups (n=20 mares/group). In both groups, mares were examined daily by transrectal ultrasonography. In the eFSH group, twice-daily eFSH treatments were initiated at follicle diameter 20 to 25 mm and ceased at follicle > or =35 mm; human chorionic gonadotrophin (hCG) was administered after 36 h. In the control group, eFSH treatments were not given, but hCG was administered at follicle > or =35 mm. Mares were inseminated with fresh semen, and embryo recovery attempts were performed 8 d postovulation. Synchrony of ovulations within each group appeared to be similar. Six mares in the eFSH group failed to ovulate. The eFSH treatment resulted in higher (P<0.05) numbers of preovulatory follicles and ovulations; however, embryo recovery rate did not increase (eFSH 1.0+/-0.4 vs. control 0.95+/-0.1 embryos/recovery attempt), and embryo per ovulation rate was significantly lower (36% vs. 73%). The eFSH-treated mares had significantly higher frequency of nonovulatory follicles (28% vs. 0) and higher periovulatory serum concentrations of estradiol-17beta. Based on our findings, combined P&E and eFSH regimens cannot be recommended for cycling donor mares.

Relationship of vascular perfusion of the wall of the preovulatory follicle to in vitro fertilisation and embryo development in heifers

The effect of the extent of vascular perfusion of the wall of the preovulatory follicle on in vitro cleavage rate of the recovered oocyte and embryo development to >8 cells was studied in 52 heifers. Heifers received a luteolytic dose of prostaglandin F2α (PGF2α) when the largest follicle was ≥11 mm. An ovulation-inducing injection of GnRH was given 36 h later (hour 0), and collection of follicular fluid and the oocyte was done at hour 26. Vascular perfusion of the follicular wall was assessed by colour Doppler ultrasonography at hours 0 and 26. Each of the recovered oocytes (41/52; 79%) was mature (extruded polar body). Cleavage and embryo development were assessed at 48 h and 120 h respectively, after in vitro fertilisation (IVF). The percentage of cleaved oocytes and >8 cell embryos was 80% (31/39) and 55% (17/31) respectively. Vascular perfusion of the follicular wall was greater (lower pulsatility index; P<0.001) for follicles that produced cleaved versus non-cleaved oocytes and greater (P<0.04) for follicles that produced >8 cell versus ≤8 cell embryos. Percentage of follicular wall with Doppler signals of blood flow was greater (P<0.001) for >8 cell versus ≤8 cell embryos. Follicular-fluid concentration of free IGF1 was lower for cleaved oocytes (P<0.001) and >8 cell embryos (P<0.05), and oestradiol was lower (P<0.05) for >8 cell embryos. Results supported the hypothesis that greater vascular perfusion of the wall of the preovulatory follicle was positively associated with IVF and embryo development.

Relationships between ultrasonographic image attributes, histomorphology and proliferating cell nuclear antigen expression of bovine antral follicles and corpora lutea ex situ

The aim of this study was to examine the relationships between quantitative ultrasonographic image characteristics, histological attributes and cell proliferating ability of bovine antral follicles and corpora lutea (CL) ex situ. Bovine ovaries (n = 30) from animals at various reproductive states (metoestrus-early dioestrus, n = 8; mid-dioestrus, n = 12; oestrous phase of peripubertal heifers, n = 6; and pregnancy, n = 4) were collected at the slaughterhouse. High-resolution ultrasonographic images of the ovaries were obtained in the water bath, digitized and subjected to computerized image analyses. The analyses utilized line and spot techniques designed to determine pixel values of the follicular wall (the largest follicles >2 mm in diameter in each ovary) and CL, respectively. Individual ovarian structures were dissected and processed for histology and immunohistochemical detection of proliferating cell nuclear antigen (PCNA). The mean follicular diameter was negatively correlated with total cell density (r = -0.45, p < 0.05), granulosa layer thickness (r = -0.67, p < 0.001) and the percentage of PCNA-positive cells (r = -0.57, p < 0.001). Numerical pixel values and heterogeneity of the follicular wall were positively correlated with total cell density (r = 0.42, p < 0.05 and r = 0.62, p < 0.05; respectively), granulosa layer thickness (both r = 0.39, p < 0.05), and the percentage of PCNA-positive cells (r = 0.54, p < 0.01 and r = 0.69, p < 0.001, respectively). Estimates of cell density and proliferating cell index were not correlated with the ultrasonographic image attributes of CL. We conclude that follicular size and echotextural variables, as determined by computer-assisted image analysis of ovaries ex situ, are reliable markers of the histophysiological properties of bovine antral follicles, but the ultrasonographic characteristics are not indicative of cell density and proliferation in the bovine CL.

Miniature ponies: 1. Follicular, luteal and endometrial dynamics during the oestrous cycle

Follicular dynamics were studied during 12 interovulatory intervals (IOIs) and 36 preovulatory periods in Miniature mares. The percentage of IOIs with the following follicle events was: ovulatory wave with only one follicle ≥10 mm (55%), diameter deviation similar to previous reports in larger mares (25%) and minor waves emerging before or after the ovulatory wave (55%). Follicle data were compared among Miniature ponies, large ponies and Breton horses (n = 12 IOIs per breed). The IOI was longer (P < 0.001) in Miniature ponies (23.3 ± 0.9 days) and in large ponies (23.9 ± 0.5 days) than in Breton horses (20.3 ± 0.7 days). The Miniature ponies had fewer (P < 0.0001) growing follicles ≥10 mm per ovulatory wave (1.5 ± 0.3) and more (P < 0.0004) ovulatory waves (6/11) with only one follicle ≥10 mm than large ponies (9.8 ± 0.8 and 0/12) and horses (5.8 ± 0.9 and 0/12). Maximum diameter of the preovulatory follicle was smaller (P < 0.003) in the Miniature ponies (38.3 ± 0.7 mm) than in the horses (44.5 ± 1.4 mm), but the difference between breeds was slight (6%) compared with the difference in bodyweight (65%). Considering the small number of follicles per ovulatory wave, Miniature mares are a potential model for comparative studies in folliculogenesis within and among species.

Temporal relationships among LH, estradiol, and follicle vascularization preceding the first compared with later ovulations during the year in mares

Diameter of the preovulatory follicle, plasma concentrations of LH and estradiol, and vascularization of the follicle wall, based on color-Doppler signals, were characterized in 40 pony mares for 6 days preceding ovulation (Days -6 to -1; preovulatory period). Comparisons between the preovulatory periods preceding the first compared with a later ovulation during the year were used to study the relationships between LH and estradiol and between vascularization and estradiol. Diameter of the preovulatory follicle was greater (P<0.02) and concentration of LH was less (P<0.02) during the first preovulatory period, whereas concentration of estradiol was not different between the first and second preovulatory periods. Vascularized area (cm(2)) of the follicle wall increased at a reduced rate during the first preovulatory period, as indicated by an interaction (P<0.03) between day and group. Vascularized area was similar between the preovulatory groups on Day -6, and a reduced rate of increase resulted in a lesser (P<0.001) area on Day -1 before the first ovulation (1.4+/-0.1cm(2)) than before a later ovulation (2.2+/-0.2 cm(2)). Results demonstrated that follicle vascularization and the LH surge were attenuated preceding the first ovulation of the year with no indication that estradiol was involved in the differences between the first and later ovulations.

Negative Effect of Estradiol on Luteinizing Hormone Throughout the Ovulatory Luteinizing Hormone Surge in Mares1

The negative effect of estradiol-17beta (E2) on LH, based on exogenous E2 treatments, and the reciprocal effect of LH on endogenous E2, based on hCG treatments, were studied throughout the ovulatory follicular wave during a total of 103 equine estrous cycles in seven experiments. An initial study developed E2 treatment protocols that approximated physiologic E2 concentrations during the estrous cycle. On Day 13 (ovulation = Day 0), when basal concentrations of E2 and LH precede the ovulatory surges, exogenous E2 significantly depressed LH concentrations to below basal levels. Ablation of all follicles > or = 10 mm when the largest was > or =20 mm resulted in an increase in percentage change in LH concentration within 8 h that was greater (P < 0.03) than for controls or E2-treated/follicle-ablated mares. Significant decreases in LH occurred when E2 was given when the largest follicle was either > or =25 mm, > or =28 mm, > or =35 mm, or near ovulation. Treatment with 200 or 2000 IU of hCG did not affect E2 concentrations during the initial portion of the LH surge (largest follicle, > or =25 mm), but 2000 IU significantly depressed E2 concentrations before ovulation (largest follicle, > or =35 mm). Results indicated a continuous negative effect of E2 on LH throughout the ovulatory follicular wave and may be related to the long LH surge and the long follicular phase in mares. Results also indicated that a reciprocal negative effect of LH on E2 does not develop until the E2 surge reaches a peak.

Relationships of Follicle Versus Oocyte Maturity to Ultrasound Morphology, Blood Flow, and Hormone Concentrations of the Preovulatory Follicle in Mares1

The effects of ultrasound morphology, vascularity, and follicular-fluid hormones of the preovulatory follicle on oocyte recovery rate and on follicle and oocyte maturity rates were studied for 60 spontaneous and solitary preovulatory follicles in mares. An ovulation-inducing dose of hCG was given when the follicle was >or=32 mm (Hour 0), and a procedure for oocyte recovery was done 30 h later (Hour 30). Between Hours 0 and 30, diameter of the follicle increased less and circulating estradiol (E2) concentrations decreased more in groups with successful versus nonsuccessful oocyte recovery and in groups with mature versus immature recovered oocytes, as indicated by significant interactions of group and hour. Significant differences in blood-flow end points between groups were not detected. At Hour 30, the frequency of granulosa serration, an indicator of impending ovulation, was higher (P < 0.001), and the number and expansion of granulosa cells in the lavaging fluid, indicators of follicle maturity, were greater in the oocyte-recovery group and in the oocyte-mature group. Follicular-fluid concentrations of E2, progesterone, and free insulin-like growth factor (IGF) 1 were not different between the oocyte-recovery and -nonrecovery groups. Concentration of progesterone was significantly greater, and E2 and free IGF1 were less in the oocyte-mature than in the immature groups. Results indicated that the post-hCG oocyte-recovery and oocyte-maturity rates were positively affected by follicle maturity. Greater follicular-fluid progesterone and lower E2 and free IGF concentrations were associated temporally with maturation of the oocyte but not with maturation of the follicle.

Elevated plasma testosterone concentrations during stallion-like sexual behavior in mares (Equus caballus)

Mounting interactions in mares isolated from stallions and the relationship to stage of the estrous cycle and level of circulating hormones were studied for 3 years in a herd averaging 105 mares. Mares were assigned to mounting, standing, and control groups. A control mare was selected by being within 1 day of the number of days after ovulation in a mounting mare. A total of 15 mounting interactions were detected by chance observation during the 3 years. A blood sample was collected immediately after the mounting interaction from each mare in the three groups, and a transrectal ultrasonographic examination of the reproductive tract was done. Two mounting interactions occurred during the early luteal phase and 13 during the follicular phase. The interactions that occurred during the follicular phase were used for comparisons among groups. The interval between mounting and the next ovulation, diameter of the two largest follicles, and the number of follicles larger and smaller than 20 mm were not different significantly among the mounting, standing, and control groups. Testosterone concentrations were higher (P<0.01) in the mounting group (17.7+/-2.3 pg/ml) than in standing group (10.9+/-0.5 pg/ml), and the difference between the mounting group and the control group (12.8+/-0.6 pg/ml) approached significance (P<0.08). Concentrations of androstenedione, estradiol, estrone, and progesterone did not differ significantly among groups. Results indicated that mounting behavior between mares is rare, usually occurs during the follicular phase, and is related to high circulating concentrations of testosterone.

Ultrasonographic image attributes of non-ovulatory follicles and follicles with different luteal outcomes in gonadotropin-releasing hormone (GnRH)-treated anestrous ewes

Ultrasonographic images are composed of multiple square picture elements called pixels. Quantitative changes in numerical pixel values (echotexture) determined by computer-assisted analysis of digital images reflect discrete changes in the microscopic structure and physiological status of ovarian antral follicles. The objective of the present study was to determine and compare the ultrasonographic attributes of non-ovulatory antral follicles that grew to an ostensibly ovulatory diameter (> or =5mm) and follicles with different luteal outcomes in response to gonadotropin-releasing hormone (GnRH) in anestrous Western White Face ewes (n=34). All animals received GnRH injections (250ng i.v. every 2h for 24h) followed by a bolus injection of 125microg of GnRH i.v. Ovarian images obtained by repeated transrectal ultrasonography were digitized and subjected to computerized analyses to determine the changes in follicular size and echotexture of the follicular antrum and wall. At the beginning of GnRH treatment, follicles that formed inadequate corpora lutea following ovulation (ICL; n=22) had higher (P<0.001) pixel intensity of the central and peripheral antrum compared with non-ovulatory follicles (n=40). Pixel intensity of the central follicular antrum was greater (P<0.01) in follicles that formed ICL compared with follicles that formed normal (full-lifespan) CL post-treatment (NCL; n=20) and mean pixel heterogeneity of the follicular wall was greater (P<0.05) in non-ovulatory follicles compared with follicles that gave rise to NCL. At the time of GnRH bolus injection (i.e., induction of a synchronous LH surge), the mean diameter of non-ovulatory follicles was greater (P<0.01) than that of all ovulating follicles, and pixel heterogeneity of the central follicular antrum was lowest (P<0.05) in non-ovulatory follicles. The mean diameter of luteinized unovulated follicles (n=9) tended to be greater (P<0.10) at 2.5 and 3 days after emergence, and pixel intensity of the follicular wall was lower (P<0.05) compared with non-luteinized follicles (n=8) at 1.5 and 2.5 days after emergence (beginning of the growth from approximately 3mm onwards). In conclusion, ovarian antral follicles with different outcomes after GnRH treatment (in seasonally anestrous ewes) had distinctive ultrasonographic characteristics.

Studies of Follicular Vascularity Associated with Follicle Selection and Ovulation in Cattle

We reviewed recent in vivo studies of the real-time changes in the vasculature of the follicle wall during selection of the dominant follicle as well as during ovulation in cows. Changes in follicle diameter and vascularity were determined by transrectal ultrasonography. Blood flow within the walls of the two largest follicles was detected at the time of wave emergence (largest follicle=5 mm in diameter). Before selection of a follicle (largest follicle <8.5 mm in diameter), the degrees of vascularity of the two largest follicles were not significantly different. After the largest follicle reached a diameter of 10 mm, the vascularity of the largest (dominant) follicle was higher than that of the second largest (subordinate) follicle. In the preovulatory follicle, follicular vascularity gradually increased, and as ovulation approached, the LH-surge induced an increase in blood flow within the follicle wall. The above results suggest that maintenance of follicular vasculature and appropriate blood supplies to follicles are essential for establishment of follicular dominance. Consequently, only a dominant follicle with high vascularity may have a chance to reach final maturation and acquire ovulatory capacity.