Follicle Selection in Mares as a Model for Illustrating the Many Hormonal and Biochemical Interactions That Drive a Single Physiological Mechanism.
Authors: Ginther O J
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Follicle selection in mares—the process by which one dominant follicle emerges from a cohort of growing follicles—represents a masterclass in endocrine coordination, as demonstrated in Ginther's 2023 analysis of diameter deviation (the point at which the future ovulatory follicle abruptly accelerates growth relative to subordinate follicles). The mechanism integrates multiple overlapping hormonal signals: FSH initially promotes growth of all follicles within the cohort, but as the dominant follicle emerges, responsiveness to LH becomes selective, allowing preferential stimulation of only the future ovulatory follicle whilst subordinate follicles plateau. Concurrently, the dominant follicle's increasing oestradiol production provides negative feedback to suppress FSH concentrations to levels that favour its continued development, whilst simultaneously preventing LH from rising to concentrations that would become inhibitory—all whilst intrafollicular factors such as inhibin and insulin-like growth factor modulate these systemic signals locally. Understanding follicle selection as an integrated physiological mechanism rather than isolated hormonal events has direct relevance for practitioners managing reproductive performance: it explains why follicle growth patterns vary considerably between cycles and individuals, and underscores how nutritional status, stress, or metabolic imbalances affecting hormone production or sensitivity can disrupt the precise coordination required for reliable ovulation.
Read the full abstract on PubMed
Practical Takeaways
- •Understanding follicle selection mechanisms via diameter deviation can help veterinarians time reproductive interventions and predict ovulation more accurately in mares
- •The complex hormonal interplay during follicle selection demonstrates why single-hormone treatments may be insufficient; practitioners should consider the broader endocrine context when managing mare fertility
- •Recognition that estradiol plays a dual regulatory role (reducing FSH while preventing LH elevation) explains why careful monitoring of hormonal concentrations is critical during fertility management protocols
Key Findings
- •Diameter deviation represents an abrupt separation in growth rates between the future dominant follicle and subordinate follicles during follicle selection
- •FSH positively affects all follicles during the growing phase, while LH appears to selectively affect only the future dominant follicle
- •Estradiol produced by the developing dominant follicle reduces FSH concentrations and prevents LH from reaching adverse levels at appropriate times and degrees
- •Follicle selection involves coordinated interactions of multiple hormonal and biochemical factors including inhibin and insulin-like growth factor operating simultaneously within the same tissue