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Abstract
In the ewe, ovarian follicular waves emerge every 4 to 5
d and are preceded by a peak in FSH secretion. It is
unclear whether large antral follicle(s) in a wave
suppress the growth of other smaller follicles during the
inter-wave interval, as seen in cattle. In this study,
anoestrous (N = 6; Experiment 1) and cyclic (N = 5;
Experiment 2) Western-White-Face ewes were given oFSH
(0.5 µg/kg; 2 s.c. injections, 8 h apart) during the
growth phase (based on ultrasonography) of a follicular
wave (Wave 1) Control ewes (N = 5 and 6, respectively)
received vehicle. In oFSH-treated ewes, serum FSH
concentrations reached a peak (P < 0.05) by 12 h after
oFSH treatment and this induced FSH peak did not differ
(P> 0.05) from the endogenous FSH peaks. In all ewes
emergence of follicular Waves 1 and 2 was seen (P >
0.05). However, in oFSH-treated ewes, an additional
follicular wave emerged ~5 d after treatment during the
inter-wave interval of Waves 1 and 2 without delaying the
emergence of Wave 2. The growth characteristics and serum
estradiol concentrations did not differ (P > 0.05) between
oFSH-induced waves and waves induced by endogenous FSH
peaks. We concluded that, unlike in cattle, the largest
follicle of a wave in sheep has limited direct effect on
the growth of other follicles induced by exogenous oFSH.
In addition, the largest follicle of a wave may possibly
not influence the rhythmicity of follicular wave
emergence, as it does in cattle.
Key words:
Estradiol •
Follicle-stimulating hormone •
Follicular development
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