China's "Space Mouse" Births Third Healthy Litter | China Space Station
A female mouse that spent time aboard China's Tiangong Space Station last year has birthed her third consecutive healthy litter back on Earth, providing scientists with invaluable data on mammalian reproduction after spaceflight. Four mice were sent to the Tiangong space station as part of the Shenzhou-21 mission on Oct. 31, 2025, marking China's first small-mammal experiment in orbit. The rodents spent approximately two weeks in a specialized habitat in microgravity conditions before returning to Earth on Nov. 14, 2025.
Shortly after their return, one female conceived and delivered her first litter of nine pups on Dec. 10. She has since birthed two additional healthy litters, the second of which resulted in 10 pups and the third in another nine.
"What we see now are the male mouse and female mouse that returned from space mission. This is the first litter of male and female pups born on Dec. 10, 2025. This is the second litter of male and female pups, born to our space mice on Jan. 5 of this year. Currently, the third litter has also been born. They were born on Feb. 18 of this year and are still in the nursing period, so they are being housed in the same cage as the female space mouse," said Wang Yixi, an engineer at the Institute of Zoology (IOZ) of the Chinese Academy of Sciences (CAS).
Researchers at the Institute of Zoology have observed intriguing behavioral variations across the three litters.
The first exhibited more cautious, "socially anxious" behavior, hiding in sheltered areas frequently. The second showed greater confidence, exploring their environment more readily. By the third litter, the offspring demonstrated progressively improved adaptation to ground living conditions, according to the report.
Overall, each successive litter has shown improved adaptation to ground living conditions compared to the previous one. These subtle changes provide important evidence for the study of space life reproduction, according to the researchers.
"The pups from the second litter, born on Jan. 5, are now showing less fear of people. They build their own cotton-made nest in the red room, but unlike the first litter, they don't drag all the cotton into the red room. They spend more time foraging for food freely and are more active. This also indicates that our mice are gradually adapting to the ground environment with each generation," Wang said.
The size of each litter has exceeded typical terrestrial litters of five to seven pups, China Media Group reported on Saturday.
"Normally, our strain of mice can have only five to seven pups per litter. However, the female mouse that returned from space station had nine pups in her first litter, 10 in her second, and nine in her third, significantly more than the offspring produced by our ground mice that have never been to space. We will also analyze the hormone levels and some blood parameters of the mice, hoping to uncover more mechanisms from these observations," said Li Tianda, associate researcher at the Institute of Zoology.
Mice have approximately 85 percent genetic similarity to humans and have rapid reproductive cycles, making them ideal models for the study of potential risks to human reproduction during long-term space missions.
Researchers will continue to monitor these "space pups" closely, tracking growth curves and testing whether they themselves can reproduce normally, searching for potential generational impacts.
According to the research plan, the scientific team will conduct longer-duration space experiments with mice, mirroring human orbital missions that last over six months to study their physiological responses and spatial adaptability, per the report.
Video Credit: CCTV
Duration: 2 minutes
Release Date: March 1, 2026
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