Apheromone that helps a baby rabbit find its mother’s nipple may also help to set its day-and-night cycle and facilitate digestion. It’s the first time that an olfactory cue has been shown to affect a newborn mammal’s behaviour and physiology.
Rabbit pups nurse just once a day, and some of them manage to down a third of their body weight in rich, high-fat milk. More remarkable, the feed usually lasts no longer than three minutes. No young bunny wants to miss out on its one and only meal, so the pups emerge from their nest about an hour before feeding time, which happens at the same time each day. Their temperatures rise and they start to move around in anticipation of their mother’s visit. When the mother enters the nest, they make straight for a nipple.
Newborn rabbits, who are born blind, find the nipple with the help of their mother’s “nipple search pheromone”. Last week, Robyn Hudson of the National Autonomous University of Mexico in Mexico City, who first identified that chemical signal, told the annual meeting of smell and taste scientists, AChemS, in Sarasota, Florida, that the pheromone also appears to induce circadian rhythms.
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“The nipple search pheremone, which helps newborn rabbit find the nipple, appears to induce circadian rhythms”
Hudson’s team took two groups of newborn rabbits and fed them equal quantities of food through a tube. Just like mother, the feeding tube appeared for only a few minutes, at exactly the same time each day. Pups in one of the groups, however, were first treated to a whiff of the nipple-search pheromone.
Hudson and her colleagues found that pups exposed to the pheromone behaved like normally fed animals: they roused themselves in anticipation of feeding time, casting off their nesting material and becoming active. The rabbits who did not get the pheromone failed to get ready for their meal. Implanted sensors revealed that they had not established a normal 24-hour temperature cycle, unlike the other group.
Despite being fed the same amount, the pheromone-deprived animals appeared to have more digestive problems and were less likely to thrive. “They remain restless and agitated, they keep moving around, and don’t flop to sleep,” says Hudson. She wonders if a human pheromone might have a hand in infant digestive disorders, particularly in bottle-fed babies, or even colic, which is largely unexplained. Baby rabbits with disrupted circadian rhythms remind her of babies with colic, she says.
Charles Wysocki, of the Monell Chemical Senses Center in Philadelphia, says the hypothesis about circadian rhythm is “not implausible”. But he is more intrigued by the findings about impaired digestion. “It has profound ramifications in mammals in general. These findings have the potential to be ground-breaking.”
