Abstract :
In the ewe, ovarian antral follicles emerge or grow in a wave-like pattern and each wave is
preceded by a peak in the serum FSH level. The purpose of the current study was to investigate
whether in anestrous Western White Face ewes, a combination of progesterone and
estradiol affects the circulating FSH peak secretion and the number of small ovarian follicles.
Five ewes were treated with subcutaneous silastic rubber implants (10cm×0.47 cm), containing
10% estradiol-17 w/w (controls) and 5 ewes were treated with the same estradiol
implant, along with subcutaneous implants (11cm×0.48 cm) containing 10% progesterone
w/w for 12 days. Daily transrectal ovarian ultrasonography and blood sampling was performed
from 5 days before, to 9 days after the period of implantation. Blood samples were
also taken every 12 min for a 6 h period on day −2, 6 and 13 prior to or after implant insertion
(day 0, day of implant insertion). Pulsatility in the serum LH levels was eliminated by
the implants (P < 0.05). During the implantation period, the serum FSH peak amplitude was
lower in ewes treated with implants releasing estradiol and progesterone, compared to
ewes treated with implants releasing only estradiol (P < 0.05). No follicular waves emerged
during implant treatment in both groups (P < 0.05) and the number of serum FSH peaks did
not differ during implantation, compared to before implantation. During the implantation
period, the number of small follicles did not differ in ewes with implants releasing estradiol
and progesterone, compared to ewes treated with implants releasing only estradiol. To conclude,
supra-physiological concentrations of estradiol completely eliminated the serum LH
pulsatality and suppressed the follicular wave emergence, while the FSH secretory peaks
that preceded the follicular waves were not affected. Supra-physiological concentrations of
estradiol-17 with physiological concentrations of progesterone decreased the serum FSH
peak amplitude, eliminated the serum LH pulses, but did not decrease the size of the small
follicle pool in anestrous ewes.
