Abstract :
To achieve successful embryo transfer programs, ewes must be hormonally stimulated to induce multiple follicular development.
Knowing the times of ovulation in these stimulated animals is critical for accurate timing of insemination. To determine
the timing of ovulation in ewes treated with Syncro-Mate-B (SMB) and FSH, ewes (n = 13) were implanted with SMB
for 14 days and were treated with FSH twice daily for 4 days, starting on day 11 after SMB implantation. Ewes underwent
laparoscopy at 36, 48, and 60 h after SMB removal (day 0) to count corpora hemorrhagica (CH), followed by laparotomy on
day 8 to count corpora lutea (CL). Blood samples were taken every 6 h to record plasma LH, estradiol-17 , and progesterone
concentrations on days 1–3, and one sample was collected before laparotomy on day 8. Ovulation rates (number of CH expressed
as a percentage of the total number of CL) increased (P <0.01) from 4±2% at 36 h, to 50±7% at 48 h, to 67±7%
at 60 h. Between 36 and 48 h after SMB removal, 50% of the follicles had ovulated, and between 48 and 60 h another 16% of
the follicles had ovulated. However, at 60 h after SMB removal, approximately 30% of the follicles still remained unovulated.
Plasma LH concentrations increased (P <0.05) from 1.4 ng/ml at 7:00 a.m. on day 1 to 10.1 ng/ml at 1:00 a.m. on day 2 and
then decreased (P < 0.05) to 0.6 ng/ml at the time of laparotomy (day 8). Plasma estradiol-17 concentrations increased
(P <0.05) from 8.5 pg/ml at 7:00 a.m. on day 1 to 24.3 pg/ml at 7:00 p.m. on day 1 and then decreased (P <0.05) to 8.6 pg/ml
on day 8. Progesterone concentrations were very low (<0.2 ng/ml) on days 1–3, but increased (P < 0.01) to 4.3 ng/ml on
day 8, after formation of the CL. These results demonstrate that the ovulation in SMB- and FSH-treated ewes occurs over an
extended period of time and that almost a third of follicles do not ovulate until more than 60 h after SMB removal.
© 2003 Elsevier Science B.V. All rights reserved.
