Impact of lactation upon fertility in the New World primate capuchin monkey (Cebus apella)

In the present paper, we have studied the impact of lactation upon fertilit y in the capuchin monkey, Cebus apella, under laboratory conditions. Nursin g females (ten females, 12 postpartum periods) presented lactational amenor rhea (first menses at 159.2 +/- 9.0 vs 42.6 +/- 5.8 days postpartum in five non-nursing females, seven postpartum periods). Plasma estradiol and proge sterone concentrations during lactational amenorrhea were lower than those during the follicular phase of the menstrual cycle. Prolactin was higher th an in non-nursing females at 31-60 days postpartum. Interbirth interval, st udied in three nonnursing (four intervals) and six nursing females (eight i ntervals) lasted for 349.5 +/- 11.8 and 613.4 +/- 30.8 days, respectively. In non-nursing females, early recovery of the menstrual cycle was followed by a residual infertility (mating but no pregnancy) lasting 152.8 +/- 7.9 d ays. In nursing females, recovery of the menstrual cycle was followed by an extended residual infertility of 301.5 +/- 22.7 days. Thus, in the capuchi n monkey, nursing prolongs the interbirth interval by inducing lactational amenorrhea and extending the residual infertility period.