Length of Menstrual Cycles in Relation to Time of Successful Mating in Macaca Mulatta

Abstract

Menstrual cycles of Macaca mulatta ranged from 21 to 57 days in length with little individual variation. More than half the cycles were 27 to 31 days, with the modal length, 28 days. Results of matings conducted on day 11 of the menstrual cycle were tabulated. More than 70% of the monkeys conceived after no more than 2 confinements with a male for 24 hours on day 11 of the menstrual cycle. Absence of menstruation for several months after arrival from India, and failure to conceive following first matings after menstruation started have been observed.