Babies learn mum's smell to breastfeed

In a new study, researchers have shown that a mammal begins to suckle its mother’s milk through a learned response built on learning her unique combination of smells.

When a mammal is born, it is exposed to the smell of its mother’s amniotic fluid and the baby then responds to those smells to feed.  Prevailing thought has been that pheromones – chemicals that trigger an innate behaviour – drove the suckling response as an automatic behaviour.

The new work determines that, in mice, the smells must be learned before the behaviour can occur.  Suckling is a critical step for survival in mammals, which are defined by giving birth to offspring that need to feed from their mother’s milk. The newborn must begin to feed soon after birth or it will die. It is a crucial, defining behaviour in mammals and offers researchers an opportunity to investigate the biology of instinct.

Previous research into suckling has shown that European rabbit mothers use a pheromone to initiate suckling in their newborn babies. This led most scientists to think that all mammals were likely to use the same mechanism.

Keen to discover the pheromone involved in other mammals, the team chose the mouse
because they have a parenting style similar to that of humans, nurturing and caring for their young.  “We were expecting to find a pheromone controlling suckling in mice, but we found a completely different mechanism at work,” Dr Darren Logan, lead author of the study from Wellcome Trust Sanger Institute, said.

“We have shown for the first time that it is not a pheromone response in mice, but a learned response, founded on a mix of odours: the unique signature smell of the mother,” Logan said.

“Our work shows us that there is no species-wide pheromone that makes newborn mice feed, but that the mouse pups are actually learning their mother’s unique and variable mix of smells at birth,” Lisa Stowers, senior author said.