Change in the Size of Pre-Ovulatory Follicles During the Mare Breeding Season
Keywords:
follicle, mare, photoperiod, reproduction, temperatureAbstract
The mare is a seasonally polyestrous animal whose reproductive activity is regulated by hormonal mechanisms and influenced by environmental factors such as temperature and photoperiod. The aim of this study was to monitor seasonal changes in the size of preovulatory (PO) follicles of mares during the breeding season and to evaluate their relationship to the average daily temperature and the length of the daylight period. The study was carried out on 247 mares of different breeds aged 3–24 years, which were examined between April and September over a five-year period at the Equine Clinic of the University of Veterinary Medicine and Pharmacy in Košice. Follicle development was monitored ultrasonographically, supplemented by the determination of progesterone levels. The average size of PO follicles ranged from 5.00 ± 0.51 cm in April to 4.70 ± 0.42 cm in September, with no significant differences confirmed between individual months (p = 0.28). However, a multifactorial analysis based on individual measurements (n = 247) demonstrated a significant effect of average daily temperature on follicle size (p = 0.008), whereas day length did not show a significant effect (p = 0.233). Overall, follicle size showed a decreasing trend during the season and towards the end of the breeding season ovulation occurred at smaller diameters. The results indicate temperature as a key factor influencing seasonal changes in follicle size. These findings have practical importance for veterinarians and reproductive specialists, as reliance on a fixed follicle size threshold may lead to incorrect determination of the time of ovulation and lower insemination success attheend of the season.
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