Absence of seasonal variation in the length of the menstrual cycle and the fertility of the crab-eating macaque (Macaca fascicularis) raised under natural daylight ratio

Abstract

Fifty-five Macaca fascicularis females are raised in the laboratory at relatively constant humidity and temperature but under natural daylight ratio in Paris. Their 275 menstrual cycles studied over 3 years show no variation in mean length during the year (fig. Dividing the year into four different daylight ratio lengths (short, 8-9 hours ; increasing from 9 to 15 hours ; long, 15-16 hours ; decreasing from 16 to 8 hours), we find no difference in the conception rate which is 35 p. 100 (table Contrary to lemurs, the daylight ratio seems to play no role in the reproduction of macaque females. The length of the menstrual cycle of Macaca fascicularis is 34.5 ! 1 .3 days ; the median is 32 days and the mode 29 days (fig.