Relationship between sexual skin colour of female rhesus monkeys and midcycle plasma levels of oestradiol and progesterone

Abstract

Relative color changes within the cycle can help to determine whether the cycle is ovulatory and to identify the approximate time of the preovulatory estradiol surge and ovulation soon after they occur. The existence of an easily observable external sign reflecting conditions of fertility should prove a useful tool in endocrine and behavior studies, particularly for monitoring and identifying reproductive states of free-ranging rhesus females. Data suggest that the optimum time for insemination in the rhesus monkey is coincident with or soon after the estradiol peak.