Weaning, body weight, and postpartum amenorrhea duration in pigtailed macaques (Macaca nemestrina)

Early permanent infant separation or weaning decreases the time interval be tween pregnancies and interbirth intervals for many female primates. At lea st part of the interpregnancy interval consists of postpartum amenorrhea, a period of non-menstruation lasting from the time of birth until the female begins to ovulate. This study investigated the effects of weaning age and dam's body weight on the duration of the interval between pregnancies, the duration of postpartum amenorrhea, and the number of cycles to conception i n a year-round breeder. Female pigtailed macaques (Macaca nemestrina) have an observable perineal swelling that fluctuates throughout the menstrual cy cle and provides a means of detecting ovulation. The perineal swelling reco rds of socially housed pigtailed macaques were studied from July 1996 to Se ptember 1998. Postpartum amenorrhea data were obtained on 44 females who ga ve birth to normal, viable infants. As weaning age increased and dam's weig ht decreased, postpartum amenorrhea, and consequently the interval between pregnancies, increased in duration. The interpregnancy interval consisted a lmost entirely of the postpartum amenorrhea phase. Our finding that a highe r dam's body weight decreased the length of postpartum amenorrhea duration lends support to the hypothesis that a minimum body weight is necessary for menstrual cycles to occur. Most females became pregnant on their first ovu lation regardless of weaning age and whether or not they were carrying an i nfant. As the weaning age of the infant and the dam's weight increased, ovu lation went from occurring after separation to occurring before separation. Am. J. Primatol. 52:81-91, 2000. (C) 2000 Wiley-Liss, Inc.