The first experiment was repeated to confirm the ovulations that occurred during sponging and the effects of MAP treatment on ovulation rate after sponge withdrawal. In addition, we examined the gonadotropin dependency of the ovulations that occurred during MAP treatment. Ewes were treated later in the breeding season (December-January) than they were in experiment 1, but general animal husbandry, handling of the ewes, and data analyses were similar in both experiments.
Ovarian ultrasonography was performed for 30 days from the beginning of the second estrus after the synchronization treatment using a realtime, high-resolution ultrasound scanner (Aloka SSD-900; Aloka Inc., Japan) connected to a stiffened, 7.5-MHz transducer. From 1 day before MAP treatment to 1 day after sponge removal, ultrasonography was performed every 12 h. The ability to detect and enumerate ovarian antral follicles >1 mm in diameter using the Aloka SSD-900 scanner has been verified in our laboratory. Ultrasonographic detection of ovulations and corpora hemorrhagica (CH) has also been recently validated in our laboratory by laparotomy and postoperative examinations of dissected ovaries (unpublished observations). Eight ewes were treated with PGF2„/MAP on Day 8 after ovulation. Blood samples (10 ml) were collected during ultrasonographic examinations, and also every 4 h from 1 day before to 1 day after the 6-day treatment with MAP sponges (5 ml), in order to determine serum concentrations of LH and FSH.
Using the higher resolution echo camera (Aloka SSD-900), ovarian follicles smaller than 1 mm (>0.4 mm) in size could be visualized, and 2-mm follicles were accurately assigned at the origin and end of sequential follicular waves.