This is the solution for healthier toddlers: going naked. At least this is what the team led by John Speakman at the University of Aberdeen, UK, found and presented in the Journal of Experimental Biology: nursing female mice with a shaved back delivered more milk, which enabled them to have heavier litters (11 offspring on average) than their "hairy" counterparts.

"Normally mice need their fur to keep warm, but while nursing, making more milk and digesting the extra food needed for the production of it, generates so much waste heat that the mouse risks overheating." said Speakman.

But "nude" females lose easier heat through the skin and can ingest higher food amounts. The team determined that about 55 % of the ingested food was processed by the females' body into milk. But "naked" mice females ingested 12 % more food, produced 15 % more milk and their offspring were 15 % heavier than those of their full-coat peers.

"If prevention of overheating is important for animals that need to keep a constant body temperature, like mammals and birds, then this could for example explain why litter and clutch sizes are bigger in cooler regions," Speakman told New Scientist.

However, since mice are small and have a large surface to volume ratio, they will rather struggle to keep warm than to lose heat.

"Nursing females with their high metabolism may be a special case, but the idea that excess heat from digestion or milk production may limit food intake is more valid in large animals. I would like to see how this applies to sheep or bison", said Polly Phillips, a physiologist at Florida International University in Miami, US.

Thus, should human mothers go naked? Phillips says we deal with overheating by sweating, while Speakman signals that there are human mothers that have a sensation of overheating during the breastfeeding period.