Asian elephants (Elephas maximus) are considered an endangered species, and their reproduction in captivity is important for their conservation. In this study, we analyzed the impact of social pressure on stress status and the estrous cycle of captive female Asian elephants with the aim of determining the reason for their prolonged anestrous status. The levels of estradiol and progesterone indicate the estrous phase, and those of cortisol show stress status; therefore, we measured estradiol and cortisol in urine and feces, and progesterone in the urine of female elephants by radioimmunoassay. Social pressure was determined by the degree of aggressive and nonaggressive behavior. The results indicate the following: (1) females in a dominant position were more frequently engaged in aggressive behavior compared with those in a subordinate position; (2) cortisol levels in dominant females were significantly higher than those in subordinate females; (3) the levels of estradiol and progesterone in dominant individuals showed cyclic fluctuations, but those in subordinate individuals did not. These data suggest that among captive Asian elephants, social pressure may be the cause of low sex hormone levels and prolonged anestrus in subordinate females, which are therefore not engaged in reproductive behavior for a long time.

亚洲象是中国一级濒危保护动物，改善圈养亚洲象的繁殖状况是亚洲象保护工作的重要内容之一。本研究旨在通过分析社群压力对圈养雌性亚洲象应激和动情状况的影响，从而探究圈养雌性亚洲象长期不动情的原因。通过放射性免疫法检测雌性亚洲象尿液中皮质醇、孕酮和雌二醇水平以及粪便中皮质醇和雌二醇水平，以雌激素水平反映亚洲象的动情状况，以皮质醇水平反映亚洲象的应激状态，以争斗行为和友好行为的发生情况反映圈养群体的社群压力。研究发现：(1)处于优势地位的个体表现出更多的斗争行为，处于从属地位的个体受到更多的攻击行为；(2)优势个体的皮质醇水平显著高于处于从属地位个体的皮质醇水平；(3)优势个体的雌二醇和孕酮具有小幅周期性波动，而从属个体的雌二醇和孕酮水平没有表现出明显的波动。从本研究结果可以看出圈养亚洲象群体中优势个体对从属个体的行为抑制可能是导致从属个体雌激素水平低，长期不能参与繁殖的原因。