Characteristics of the menstrual cycle in nonhuman primates. I. Similarities and dissimilarities between Macaca fascicularis and Macaca arctoides.

Comparative studies of reproductive characteristics were carried out on a colony of Macaca fascicularis and M. arctoides. Seasonal differences were not significant between species, and conceptions occurred throughout the year. The occurrence of short cycles ('luteal phase defect') was found in 2.9% of all M. fascicularis cycles and 1.5% of all M. arctoides cycles. Long cycles (40-50 days) were found in 4.0% of all M. fascicularis cycles and 3.5% of all M. arctoides cycles. Gestation lengths averaged 172.4 and 165.3 days, respectively, for M. arctoides and M. fascicularis. Ovulation in M. fascicularis occurred at a day of ovulation/cycle length ratio of 0.48 +/- 0.08 compared with 0.48 +/- 0.09 for M. mulatta data previously published.