RESUMO
Variation in the duration and pattern of breast-feeding contributes significantly to inter-population differences in fertility. In this paper, measures of suckling frequency and intensity are used to compare the effects of breast-feeding practices on the duration of lactational amenorrhoea, and on the length of the birth interval in three prospective studies undertaken during the 1980s, among Quechua Indians of Peru, Turkana nomads of Kenya, and Gainj of Papua New Guinea. In all three societies, lactation is prolonged well into the second year postpartum, and frequent, on-demand breast-feeding is the norm. However, the duration of lactational amenorrhoea and the length of birth intervals vary considerably. Breast-feeding patterns among Gainj and Turkana are similar, but Turkana women resume menses some 3 months earlier than do the Gainj. The average birth interval among the Gainj exceeds that of nomadic Turkana by over 15 months. Suckling activity decreases significantly with increasing age of nurslings among both Gainj and Quechua, but not among Turkana. Earlier resumption of menses among Turkana women may be linked to the unpredictable demands of the pastoral system, which increase day-to-day variation in the number of periods of on-demand breast-feeding, although not in suckling patterns. This effect is independent of the age of infants. The short birth intervals of Turkana women, relative to those of the Gainj, may be related to early supplementation of Turkana nurslings with butterfat and animals' milk, which reduces energetic demands on lactating women at risk of negative energy balance.
PIP: Between July 1989 and late February 1990. an anthropologist observed breast feeding patterns of 24 mother-infant pairs of the nomadic Ngisonyoka Turkana in Kenya to determine suckling frequency and intensity and their effect on the duration of lactational amenorrhea and the length of the birth interval. She compared her results with those of studies of the Gainj of Papua New Guinea and of the Quechua Indians of Peru, studies which used the same unite of analysis as the Turkana study. Prolonged lactation and frequent, on-demand ruled in each group. Turkana infants suckled all day and night, with each nursing period being 1-2 minutes long and with 10-15 minutes between each period. The Gainj also had prolonged lactation and similar nursing sessions. On the other hand, the Quechua clumped their breast feeding sessions, which were longer than those of both the Turkana and the Gainj. Turkana birth intervals were shorter than those of Gainj (29 vs. 44.3 months). Turkana women also had a higher fertility rate than did the Gainj (6.5 vs. 4 live births). Suckling activity fell considerably as age increased for Gainj and Quechua infants, but not for Turkana infants. Early introduction of butterfat from goats' and camels' milk during the first few weeks after birth and the daily difference in amount of suckling during the lactational period due to variable maternal work schedules (based on the labor demand of the pastoral system of the Turkana) reduced the effect of age. In conclusion, differences in the length and pattern of breast feeding practices account for much of the interpopulation variation in fertility.