Following the ovulation after sponge withdrawal, four of eight animals had fewer CL than ovulated follicles. One ewe ovulated two follicles but no CL was detected by Day 5 after ovulation, and serum progesterone concentrations were ± 0.10 ng/ml. In the remaining three ewes, some ovulated follicles failed to form observable CL. One ewe with two CL formed a luteinized, unovulated follicle that was first detected 3 days after ovulation. The mean number of CL per ewe (1.6 ± 0.2) was less than the mean ovulation rate (2.8 ± 0.4; P < 0.05). The total number of all luteal structures per ewe (1.8 ± 0.2) was also less (P < 0.05) than the ovulation rate above.
Within 3 to 6 days of the injection of PGF2a and insertion of MAP sponges, 6 of 11 ewes ovulated, giving a total of 11 ovulations (Table 1). No ewes were marked by rams. All of the ovulations detected with ultrasonography were subsequently confirmed by laparotomy (Fig. 5). On the basis of ultrasonographic records, 28% (9/32) of all follicles >5 mm in diameter present on the day of PGF2a injection ovulated during MAP treatment. In addition, one ewe had a follicle that emerged on Day 1 and ovulated on Day 4, and in one other ewe a follicle that emerged on Day 2 ovulated on Day 5 after PGF2a. Ruptured ovarian follicles with distinct bloodstained ovulatory sites, from 1 to 5 mm in diameter, protruding above the surface of the ovary, were observed at laparotomy (Fig. 5, A and C). Histological micrographs of the dissected CH are shown in Figure 5, B and D.
FIG. 4. Mean (± SEM) concentrations of FSH (•) and LH (o) in serum samples collected every 4 h, and analyzed for the period from 48 h before to 12 h after breakthrough ovulations (n = 7) detected with ultrasonography in five of eight Western white-faced ewes, between Days 1 and 6 after PGF2a/MAP treatment (experiment 2).
FIG. 5. Photographs of ovaries at laparotomy conducted in two Western whitefaced ewes (A and C; experiment 3) 1 day after follicular rupture detected with ultrasonography 5 and 3 days after PGF2„ injection and insertion of MAP impregnated sponges, respectively. The ewes received PGF2„ and a MAP sponge on Day 8 after ovulation. Arrows indicate ovulatory sites observed during the inspection of ovaries just before dissection. B and D depict histological sections through the CH illustrated in (A) and (C) (X40). Arrowheads delineate outlines of the CH/ruptured follicles. For comparison, a section through the CL of a ewe 24 h after normal ovulation (Duggavathi et al., unpublished data) showing darkly stained thecal cells, the hypertrophied granulosa cells, and the innermost connective tissue with the reminder of a blood clot, is shown in (E) (X40). Note differences in diameter and cell differentiation (luteinization) between the growing CL (E) and transient CH in the present study (B and D). Scale bars in (B), (D), and (E) represent 1 mm.