An overview on follicular dynamics in mare

Abstract

The mare is a seasonally polyestrous, long-day breeder exhibiting unique ovarian follicular dynamics characterized by distinct patterns of follicular wave development and mono-ovulation. Follicular growth in mares occurs in waves classified as major (ovulatory or anovulatory) and minor waves, each influenced by photoperiod, endocrine regulation, age, pregnancy, and season. Following wave emergence, follicles undergo a common growth phase, after which deviation occurs, resulting in the selection of a single dominant follicle while subordinate follicles regress. Deviation typically occurs when the future dominant follicle reaches approximately 22-25 mm in diameter, followed by continued growth to ovulation at 35-55 mm under the influence of luteinizing hormone (LH). Follicular selection is governed by complex interactions between systemic hormones such as follicle-stimulating hormone (FSH), LH, estradiol, inhibin, and androgens, along with local intrafollicular factors including the insulin-like growth factor (IGF) system, activin-follistatin balance, and vascular endothelial growth factor (VEGF). Advances in ultrasonography and intrafollicular manipulation techniques have greatly enhanced understanding of equine ovarian physiology. Seasonal anestrus, pregnancy, puberty, and aging significantly alter follicular activity and wave patterns in mares. A comprehensive understanding of follicular dynamics in the mare is essential for improving reproductive management, fertility control, and assisted reproductive technologies in equine practice.