Assessing reproductive status in orang-utans by using urinary estrone

The aim of this work was to compare normal menstrual cycle patterns of urinary estrone excretion in orang‐utans with those of an orang‐utan in her late 40s, an orang‐utan before and after rehabilitation for anorexia, and an orang‐utan during prolonged lactation. A detailed menstrual and sexual activity record was kept for each orang‐utan subject. Urine samples for estrone radioimmunoassay were collected daily for two cycles whenever possible. “Mawas,” in her late 40s, was monitored for two cycles in each of 3 successive years. While the normal pattern of estrone excretion was initially seen, some of the later cycles were shorter and appeared to lack the large luteal‐phase peak. “Puspa,” anorexic and amenorrhoeic at the age of 9½ years, had very low urinary estrone concentrations. After rehabilitation, followed by a late menarche, she had regular menstrual cycles with a normal estrone excretion pattern. She gave birth to a normal infant in 1990. “Puteri,” who had been lactating for 2 years, had consistently low estrone concentrations during an 8‐week monitoring period, with no evidence of cyclic variation in estrone excretion. Daily urinary estrone measurements, together with observation, were found to be useful in assessing the reproductive status of orangutans.