Research shows that bamboo nutrition causes such digestive problems for pandas that reproduction becomes secondary for them.
Pandas are bears belonging to the family Ursidae, which also includes grizzly bears and polar bears. Unlike their relatives, all other members of this family are omnivorous, while pandas evolved into strict vegetarians about 2 million years ago. During this time, they developed some adaptations characteristic of herbivores: powerful jaws capable of effectively chewing fibers and opposable thumbs that allow them to hold stems conveniently.
However, the digestive system of pandas remains the same as that of omnivorous bears. Food passes through their intestines in 10 hours (for comparison, the complete digestive cycle for cows and horses takes 24 hours or more). During this period, the panda's intestine, which is evolutionarily designed to process more nutritious food, does not manage to extract all the necessary nutrients from bamboo. This is likely why pandas spend so much time eating: they chew bamboo for about 16 hours a day.
Millions of years ago, such a diet may have made sense. Bamboo was abundant, and foraging for it was not difficult. However, with changes in ecology, bamboo forests are becoming increasingly rare, and the pandas' strategy no longer seems so successful.
In captivity, pandas receive bamboo that is available to humans, and this is not always high-quality vegetation. To compensate for the lack of nutrients, zookeepers have to add baked goods and fruits to the bears' diet. In zoos, pandas often suffer from digestive disorders, which scientists believe may be one of the reasons for their reproductive problems. In particular, constant discomfort hinders females from carrying cubs and sometimes leads to miscarriages.
The research findings are published in the journal Frontiers in Microbiology.
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