The composition of milk from free-living common marmosets (Callithrix jacchus) in Brazil.

Common marmosets, one of the smallest anthropoid primates, have a relatively high reproductive rate, capable of producing twins or triplets twice per year. Growth and development of infants is relatively rapid, and lactation is relatively short at less than 3 months. Although mean values for the proximate composition (dry matter, protein, fat and sugar) of captive common marmoset milks fall within anthropoid norms, composition is highly variable among individual samples, with concentrations of milk fat ranging from below 1 to over 10%. To examine the extent to which this variation might be a consequence of captive conditions, we collected milk samples from wild common marmosets freely living on a farm in the state of Rio de Janeiro, Brazil. The proximate composition of the milk samples was assayed using identical techniques as used for the captive marmoset milks. The composition of the milk of wild common marmosets was also variable, but tended to be lower in dry matter, fat, protein and gross energy, and higher in sugar than milks from captive animals. Interestingly, the percentage of estimated gross energy from the protein fraction of the milks was relatively constant in both wild and captive marmosets and did not differ between wild and captive animals: 1 kcal of common marmoset milk contains on average (+/-SEM) 0.035+/-.001 g of protein regardless of the gross energy content of the milk or whether the milk was from a wild or captive animal. In contrast, in 1 kcal of low-energy milks, the amount of sugar was significantly higher and the amount of fat significantly lower than in 1 kcal of high-energy milks. Thus, common marmoset milk exhibits axes of variability (especially fat concentration) as well as a significant stability in the relative amount of protein.

The composition of milk from Bolivian squirrel monkeys (Saimiri boliviensis boliviensis).

Squirrel monkeys (genus Saimiri) give birth to relatively large neonates with large, fast-growing brains. Maternal energy expenditure during gestation and infant development is argued to be high, but may be offset by the provisioning of offspring by females other than the mother (allonursing). Milk composition is an important component of maternal energy expenditure, but has been examined in only a small number of primate species. Here, we report on the milk composition from laboratory-housed Bolivian squirrel monkey (Saimiri boliviensis boliviensis) dams (n = 6) and allomothers (n = 2). Milk samples (n = 16) representing mid-lactation were assayed for fat, sugar, dry matter (DM), crude protein (CP), and fatty acids. Gross energy (GE) was calculated from these constituents (excepting fatty acids). The goals of this project were: (1) to provide descriptive data on milk composition of squirrel monkeys, including the range of intraspecific variation; (2) to determine if milk produced by allomothers differs from milk from dams; and (3) to compare squirrel monkey milk to that of other small New World monkeys, the callitrichines. Squirrel monkey samples averaged 4.56% fat, 3.59% CP, 6.98% sugar, 16.59% DM, and 0.91 kcal/g. The proportion of the medium chain fatty acids 8:0 and 10:0 was 40 times greater than that reported for human milk samples, and 18:1 and 18:2n-6 comprise more than 60% of total fatty acids. Milk from allomothers was lower than dams in fat, DM, and GE, which may relate to variation in maternal condition between these two groups. Excluding allomothers, milk from squirrel monkeys was higher in mean GE than captive common marmosets, but did not differ in the proportion of energy from fat, CP, and sugar relative to total GE. The consistency in energy from protein between species suggests this may be a shared-derived trait of New World monkeys.