Fluctuations of antimüllerian hormone, ovarian follicular reserve, and antioxidant status throughout the estrous cycle in aged mares.

Background: Senility influences fertility in women and companion animals, especially horses.

Aim: This study aimed to investigate the effect of aging in horses on the daily changes in the dominant follicle (DF) dynamics and hemodynamics, antimüllerian hormone (AMH), enzymes, antioxidants, and ovarian hormones during the estrous cycle.

Methods: Ovaries of old mares ( = 5, age >20 years) and young native mares ( = 6, age <10 years) were scanned during 6 different estrous cycles from March 2022 to August 2023 with Doppler ultrasound. The DF diameter and color area, the corpus luteum (CL) diameter, and the uterine horn area and color area were determined. In collected blood samples with each ultrasound and Doppler scanning, AMH, estradiol (E2), progesterone (P4), cholesterol, myeloperoxidase, catalase, glutathione peroxidase, lactate dehydrogenase (LDH), alkaline phosphatase, and nitric oxide (NO) concentrations were determined.

Results: Age significantly affected the DF area ( < 0.0001), color area ( < 0.0001), color area % ( = 0.020), CL area ( = 0.033), uterine horn area ( < 0.0001), ovarian artery pulsatility index (PI, < 0.05), E2 ( < 0.001), cholesterol ( < 0.0001), LDH ( < 0.0001), and NO ( < 0.0001). Aging tended ( > 0.05) to decrease the DF antrum diameter but significantly decreased ( < 0.05) its area, antrum area, and color area % in addition to the decrease ( < 0.01) in the uterine horn diameter and area, estradiol, total cholesterol, LDH, NO, aging increased ( < 0.05) CL area and the ovarian artery PI, and tended ( > 0.05) to increase the ovarian artery resistance index.

Conclusion: Aging in mares did not disturb AMH, the ovarian macro-environmental dynamics, follicle growth, and recruiting but the disrupted blood flow mediators, enzymes, and antioxidant status may affect the intrafollicular mediators and influence the oocyte quality.