Cyclicity and gestation length ofMacaca fascicularis

Menstrual cycle records were kept on all of the females in the colony for a period of 14 months. The mean cycle length was 30.8 days; the median, 33 days; and, the mode, 28 days. Cycles ranging from 27 to 32 days in length comprised 66.4% of all cycles. Regular cycles were scored on the basis of menses beginning within 2 days of a projected date based on an average of 6 previous cycles. Regular cycles were observed in 6.24% of the cases. The mean cycle length for regular cycles was 29.2 days. Forty-five percent of all females had regular cycles at least 70% of the time. The duration of menstrual flow for 150 cycles averaged 2.8 days. Menses ranged from 1 to 8 days in length, with 90.7% of the cases ranging from 1 to 4 days in length. For a given duration of menses, the percentage of cases of light flow increased as the end of the menstrual period was reached. The mean gestation length of 3 pregnancies was 164.4 days, with implantation bleeding beginning on day 19 of pregnancy and lasting from 4 to 9 days.This work supported by National Institute of Child Health and Human Development, Center for Population Research Contract No. 70-2061; USPHS Grant No. 5-PO6-RR 00366-04, to the Center for Laboratory Animal Resources, and, NIH Career Development Award No. 1-K4-HD35, 306-01. Journal Series Article No. 5668. Approved by the Director, Michigan State University Agricultural Experiment Station.