http://www.sciencedaily.com/releases/2010/03/
     100302142331.htm  
Baby Monkeys Receive Signals Through Their Mother's Breast Milk That Affect Behavior and Temperament
ScienceDaily (Mar. 3, 2010) — Among rhesus macaque monkeys, mothers who weigh more and have had
previous pregnancies produce more and better breast milk for their
babies than mothers who weigh less and are less experienced.
Scientists from the Smithsonian Institution and the University of
California, Davis are using this natural variation in breast milk
quality and quantity to show that a mother's milk sends a reliable
signal to infants about their environment. This signal may program the
infant's behavior and temperament according to expectations of
available resources and discourages temperaments that prove risky when
food is scarce.
The study was published in the American Journal of Primatology.
Researchers used large groups of rhesus macaques living in an
outdoor enclosure at the California National Primate Research Center at
UC Davis. Researchers collected milk two different times from 59
mothers: once when their infants were 1 month old and again when the
infants were 3 1/2 months old. They recorded the quantity of milk
produced by each mother, and the energy value of each one's milk was
analyzed for its content of sugars, proteins and fat. These figures
were combined to calculate the available milk energy generated by each
mother.
Although all of the monkeys in the study were fed the same diet, the
researchers found natural variation in the quantity and richness of the
milk generated by the 59 mothers. Milk from mothers who weighed more
and had had previous pregnancies contained higher available energy when
their infants were 1 month old than the milk of lighter, less
experienced mothers.
"This is the first study for any mammal that presents evidence that
natural variation in available milk energy from the mother is
associated with later variation in infant behavior and temperament,"
said Katie Hinde, the study's lead author and anthropologist at the
California National Primate Research Center and the nutrition
laboratory at the Smithsonian's National Zoo. "Our results suggest that
the milk energy available soon after birth may be a nutritional cue
that calibrates the infant's behavior to environmental or maternal
conditions."
At 3 to 4 months old, each infant was temporarily separated from its
mother and assessed according to its behavior and temperament. The
study found that infants whose mothers had higher levels of milk energy
soon after their birth coped more effectively (moved around more,
explored more, ate and drank) and showed greater confidence (were more
playful, curious and active). Infants whose mothers had lower milk
energy had lower activity levels and were less confident when separated
from their mother. Mothers and infants were reunited immediately after
the experiment.
Rhesus macaques are found throughout mainland Asia: from Afghanistan
to India and from Thailand to southern China. A free-ranging colony of
rhesus macaques was established in 1938 on Cayo Santiago -- a small
island off of the east coast of Puerto Rico. The only primates with a
broader geographic distribution than rhesus macaques are humans.
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Story Source:
Adapted from materials provided by Smithsonian.
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Journal Reference:
	1. Katie Hinde, John P. Capitanio. Lactational programming? Mother's milk energy predicts infant behavior and temperament in rhesus macaques (Macaca mulatta). American Journal of Primatology, 2010; DOI: 10.1002/ajp.20806
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Smithsonian
(2010, March 3). Baby monkeys receive signals through their mother's
breast milk that affect behavior and temperament. ScienceDaily. Retrieved March 3, 2010, from http://www.sciencedaily.com­/releases/2010/03/100302142331.htm 
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