Preliminary investigation into long‐term stress by isolated captivity‐related changes of reproduction hormones in Cynomolgus monkey

Background Stress profoundly affects physical and emotional well‐being, extending its physiological influence to the female menstrual cycle, impeding the hypothalamus–pituitary–gonadal (HPG) axis, and affecting fertility by suppressing sex‐stimulating hormones. Methods In this study, we meticulously analyzed menstrual cycles and corresponding hormonal fluctuations in three female Cynomolgus monkeys. Results The preliminary findings indicated lower‐than‐normal levels of cortisol, follicle‐stimulating hormone (FSH), and estradiol. Anovulatory bleeding occurred in one monkey, which could be linked to stress. In contrast to cortisol, alkaline phosphatase (ALP), which is correlated to cortisol levels, was consistently elevated in menstruating monkeys, suggesting its potential as a stress indicator. The non‐menstruating group exhibited stress‐related weight loss, emphasizing the observed ALP trends. Conclusions Non‐menstruating monkeys may experience more stress than menstruating monkeys. The implications of this study extend beyond the confines of primate studies and offer a valuable method for enhancing the welfare of female Cynomolgus monkeys.