Rabbits have a taste for their own faeces – and now we know why. The small mammals produce both soft and hard faeces, and will routinely eat the soft ones. It turns out that eating soft faeces helps the rabbits digest their food and gain weight at a healthy rate.
To test what effect a faeces-containing diet has on rabbits, Ming Li at the Henan Agricultural University in China and his team raised two groups of New Zealand rabbits. Some were allowed to eat their own faeces freely and others wore a cone-shaped collar that stopped them from eating anything but the food they were given by the researchers.
Previous work has shown that rabbits prohibited from eating faeces take in 15 to 22 per cent less microbial protein, as their digestive system may not be efficient enough to absorb nutrients quickly before food is expelled as waste. Rabbit faeces include a variety of microorganisms that may be required to populate the gut and aid in digestion.
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Rabbit habits
When Li’s team compared their two groups of rabbits after 90 days, they found that those that were prohibited from eating faeces had significantly lower body weight. Their weight gain over the three-month study was 32 per cent less than the rabbits without collars, even though both groups took in the same amount of food.
The collared rabbits also had livers that weighed less than the livers of rabbits in the control group. Retinoic acid – formed from ingested vitamin A – is stored in the liver, and a lack of retinoic acid can lead to abnormal organ development.
The team analysed the genes expressed in the livers of both groups of rabbits, and found that genes related to retinoic acid were less active in the rabbits that didn’t eat their own faeces. Collectively, this suggests that rabbits must ingest their faeces to develop a healthy liver – and ensure healthy organ development.
Scott Weese at the University of Guelph in Canada thinks there are some problems with the approach Li’s team used. The collars used in the experiment could potentially result in stress that might have affected the rabbits’ food or water intake, he says.
“A study of colony rabbits has limitations since they don’t likely reflect the microbiota of rabbits in other situations,” he adds.
Reference: Biorxiv, DOI:
