For giant pandas, there’s nothing like having friends in low places. The bears rely on chummy relations with their gut microbes to extract nutrients from their vegetarian diet, but an annual switch from noshing bamboo stalks to leaves can plunge the pandas' gut microbes into disarray. According to a study of panda poop, this switch potentially causes one grizzly problem.

The authors of the study suggest that the microbial mayhem explains why the bears occasionally poop out their intestinal mucosal linings amid that seasonal shift. The slimy dumps likely expunge broken microbiomes, clearing the way for the bears to forge fresh microbial alliances. Based on the numbers of gooey poops in captive bears, however, that yearly bowel reboot often doesn’t go well, leaving many pandas suffering from chronic inflammation, intestinal ulcers, and unpleasant gastrointestinal symptoms. And those gut troubles often coincide with mating season and pregnancies, the researchers report in Frontiers in Microbiology.

If the hypotheses hold up in further studies, the findings may help explain why pandas are notoriously bad breeders—it’s likely hard to get in the mood if you’re battling stomach cramps, bloating, and mucus poops. Currently, there are only a couple thousand giant pandas in the wild.

There have been hints in the past that pandas may suffer from some unusual gastrointestinal problems. The gentle bears have the gut structure of carnivores despite going vegetarian around 2 to 2.4 million years ago. Unlike other herbivores, the pandas don’t have the gut chambers needed to process plant-based fare and extract all the nutrients. A study last year also found that the bears don’t even count normal plant-digesting microbes among their intestinal allies. Instead, the bears’ gut microbiomes still resemble those of carnivorous relatives.

For these reasons, researchers speculate that the bears munch on bamboo mostly for the easy-to-digest hemicellulose content rather than the harder-to-digest lignin and cellulose. The bears also require an impressive amount of bamboo—up to a third of their body weight a day—which they can spend up to 14 hours a day munching.

For much of the year, pandas seem to prefer bamboo stalks (culm) over the leaves. Researchers think that this is because the leaves often have high levels of silica, an anti-herbivory defense by the plants. But during the fall, the silica levels in the foliage drop and the bears ditch the stalks and go for the leaves.

It’s at this switch that the pandas begin experiencing their yearly flush of mucus poops.

For the study, researchers at the University of Wisconsin and Mississippi State University collected the feces of two giant pandas at the Memphis Zoo—Le Le, a male, and Ya Ya, a female—from 2013 and 2014. Next, the researchers analyzed the microbial content of poops and mucus dumps throughout the year with a total of 34 samples.

In line with previous data, the researchers found that normal panda poop has low levels of microbial diversity compared to other animal poop. But right before the mucus poops began, the panda’s gut microbe diversity dropped even lower, suggesting an upset in the gut community.

The mucus-filled dropping, on the other hand, had huge spikes in microbial levels, particularly of bacteria that cling to mucosal linings and some linked to inflammatory bowel disease. This again suggested that the panda’s microbial communities were out of whack and being shed wholesale in the mucus poops.

In the winter, when the pandas went back to eating the stalks, the microbial content of their non-slimy droppings returned to normal.

While the study is just on two animals and doesn’t point to any clear solutions, the authors are hopeful that it’s a starting point to study better care for the animals, such as dietary supplements or offering different food sources.

Frontiers in Microbiology, 2016. DOI: 10.3389/fmicb.2016.00661 (About DOIs).