Concentrations of inhibin, progesterone and oestradiol in fluid from dominant and subordinate follicles from mares during spring transition and the breeding season.

The study examines the concentrations of specific hormones in dominant and subordinate follicles in mares during the transition into spring and the breeding season. The research finds that the hormone levels influence continuous follicle growth and ovulation, with lower hormone levels indicating early deficiencies in production.

Objective of the Study

• Researchers aimed to explore the regulation of folliculogenesis during spring transition and the breeding season in mares. They did this by analyzing the concentrations of specific hormones in dominant and subordinate follicles when the dominant follicle reached 30 mm in diameter.

Key Findings of the Research

• The levels of oestradiol-17beta, progesterone, and inhibin A were found to be significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. However, inhibin isoforms with pro- and alpha C-immunoreactivity did not show any significant difference.
• Through the spring transition, the dominant follicles gradually regained their steroidogenic activity after successive anovulatory waves.
• The dominant follicles held greater concentrations of oestradiol, progesterone, and inhibin A during both the spring transition and the cyclicality phase as opposed to the subordinate follicles. No difference was observed in the levels of inhibin pro- and alpha C-isoforms between the two types of follicles.

Implications of the Findings

• High follicular levels of oestradiol, progesterone, and inhibin A were found to be associated with sustained follicle growth and ovulation, indicating the crucial role these hormones play.
• The lower concentrations of oestradiol and progesterone in transitional follicles indicated that a deficiency in steroidogenesis, or hormone production, was present early in the steroidogenic pathway.
• The observed similarity between the profiles of follicular hormone during spring transition and cyclicity implied that the dominance mechanism applies equally to both types of follicles.