Temporal variation in reproductive activity in mares during September: A retrospective analysis of ultrasonographic records from Chile, 2015-2024
DOI:
https://doi.org/10.30972/vet.3719729Keywords:
Fisiología reproductiva, Estrous cycle, Photoperiod, Mare, Reproductive physiologyAbstract
Reproductive efficiency is key to the equine industry and is supported by various tools to ensure its success, with transrectal ultrasound monitoring being essential to optimize reproductive programs. The mare is a long-day seasonal polyestrous species whose reproductive activity depends on the hypothalamic-pituitary-ovarian axis, regulated by the hormones GnRH, FSH, and LH, which control follicular growth, ovulation, and corpus luteum formation. During the estrous cycle, follicular waves and hormonal changes occur that allow the identification of the transition, estrus, and diestrus phases. An observational, descriptive, longitudinal study was conducted using 223 ultrasound records of mares that were admitted to a reproductive center during September from 2015 to 2024 in Chile. The spring transition phase predominated (48.4%), followed by diestrus (38.1%) and estrus (13%). Additionally, the average diameter of the dominant follicle was 33.5 ± 7.7 mm, close to the preovulatory size. A functional corpus luteum was observed in 38.1% of the mares. Significant intramonthly variations were observed, with the proportion of mares in transition decreasing toward the end of September, while estrus and diestrus increased, reflecting ovarian reactivation associated with the increase in photoperiod. The findings confirm the physiological progression of spring reproductive activity and highlight the importance of individualized ultrasound monitoring to optimize reproductive management.
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Copyright (c) 2026 Eliannys Rodríguez Sivira, Daniel Inostroza Briones, Katherinne Escobar Chihuaillán, Daniela Moraga Alarcón, Valentina Maluenda Carilao
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