The mean day of emergence of the follicles that ovulated during sponging was -3.9 ± 1.5 days before PGF2a (range, from 8 days before to 3 days after PGF2a injection). No ewes were marked by rams and none of the follicles that ovulated during the treatment with MAP formed a CL; however, CH were detected after ovulations occurred (Fig. 3, A-D) for —4 days (Table 1). For comparison, a CL detected with ultrasonography 48 h after ovulation posttreatment is shown in Figure 3E. In the five ewes that ovulated 1 to 6 days after PGF2a, there were no changes (p > 0.05) in serum concentrations of FSH or LH in blood samples taken every 4 h, from 48 h before to 12 h after ovulations (Fig. 4), and serum concentrations of LH remained basal (time effect, P > 0.05) from 1 day before to 1 day after treatment with MAP sponges.
The mean number of emerging follicular waves during MAP treatment was 1.7 ± 0.2 per ewe (range, 1 to 2), and the last wave before sponging emerged 1.9 ± 0.3 days before treatment (range, 1 to 3 days). After the sponges were withdrawn, the mean ovulation rate was 2.8 ± 0.4 (range, 2 to 5). The mean ovulation rate after treatment was greater (p < 0.05) than the pretreatment ovulation rate (1.9 ± 0.1; Table 2). All but one ewe were well marked by rams; one ewe was not marked. In four ewes, a total of nine ovulations were observed before estrus, and five ovulations were detected after the onset of behavioral estrus; in the remaining four ewes all ovulations occurred after estrus. However, in all but one ewe, ovulations occurred within a 48-h period, between 2 and 5 days after sponge withdrawal. A single ewe ovulated on Days 2, 3, 4 (before estrus), and again on Day 6 after MAP treatment (after the onset of estrus).
FIG. 3. Photographic reproductions of ultrasonograms of ovaries (left panels) with accompanying diagrams depicting the outlines of the ovary and intraovarian structures (right diagrams). Images obtained using an Aloka SSD-900 echo camera equipped with a 7.5-MHz transducer (experiment 2) were recorded on S-VHS, digitized, and then converted into gray scale bit-map images in order to delineate ovaries, antral follicles, CH, and CL. For illustrative purposes, ovarian stroma is shown in light gray, follicles in black, and CH/CL in dark gray. Sequential ultrasonograms (A-D) show an ovary recorded in a treated ewe at 0, 12, 24, and 48 h relative to ovulation, which was detected on Day 1 after PGF2a injection and insertion of a MAP sponge, and E depicts an ovary of a ewe 48 h after ovulation that was detected 3 days after the removal of MAP sponges. All ewes underwent transrectal ultrasonography of ovaries every 12 h, from 1 day before PGF2a/MAP treatment until 1 day after sponge withdrawal, and then daily for 8 days. Each scale bar represents 10 mm. Note the difference in the size and echogenicity (brightness) between demising CH (D) that did not form a CL, and a growing (full lifespan) CL (E) at 48 h postovulation.