Does follicular dominance occur in ewes?

Area of Science:

• Reproductive Biology
• Ovarian Physiology
• Endocrinology

Background:

• The mechanism of dominant follicle selection and its effect on subordinate follicles in ewes remains unclear.
• A potential inhibitory role of the dominant follicle could impact superovulation responses to exogenous gonadotropins.

Purpose of the Study:

• To investigate the role of follicular dominance in ewe ovulation.
• To determine if dominant follicles secrete inhibitory substances affecting other follicles.

Main Methods:

• Administration of pregnant mares' serum gonadotropin (PMSG) at various stages and in different ovarian conditions.
• In vitro co-culture of small and large follicles to assess growth and steroidogenic potential.
• Comparison of ovarian responses with and without a dominant follicle.

Main Results:

• PMSG administration did not alter ovulatory response based on dominant follicle presence or ovarian status.
• In vitro studies showed no difference in granulosa cell proliferation or steroid production between follicles.
• Increased ovulation rate was observed with PMSG during the mid-follicular phase, irrespective of dominance.

Conclusions:

• Follicular dominance does not appear to be an active regulatory process in sheep.
• The passive nature of dominance can be overcome by elevated gonadotropin levels.
• This suggests a potential for manipulating ovulation rates in ewes.