Suckling behaviour and fertility in rhesus macaques (Macaca multatta)

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Abstract
Lactation has been proposed as the main proximate mechanism regulating female fertility among non–seasonally breeding mammals. Less is known about the effects of lactation upon fertility among seasonal species, where photoperiodic control of reproduction is widely believed to have an overriding influence. In neither case is it clear which of the different components of lactation influence fertility and in which ways. In this paper, the links between suckling patterns and the likelihood of conception during the following breeding season are examined. Data were collected at the Madingley rhesus colony, where reproduction is strictly seasonal. It is shown that fertility was depressed in lactating females when compared to non–lactating ones. Within the lactating group, mothers who suckled their infants frequently, and with a great number of independent nipple contacts in each bout, failed to conceive during the following breeding season. It is suggested that early differences in suckling patterns might reflect differences in maternal condition; and that differences during the breeding season may affect the quality of the ovulations. A considerable decrease in both the frequency of suckling and the number of nipple contacts per bout seemed to be required for conception to occur. On the other hand, neither the duration of the suckling bouts, nor the duration of the intervals between bouts, were found to be associated with the likelihood of conception.