Researchers from the University of Southern California, Los Angeles (USC) have found that the poop of older donors rejuvenated the ovaries of younger mice. The researchers initially thought that transplanting the gut microbes from'menopausal' mice into younger mice would age their ovaries, but the opposite happened. The transplant of older poop boosted the health of these young mice's ovaries. The study is the first to show that poop transplants can directly remodel gene expressions associated with ovarian health and function. It is also possible that gut bacteria may replace lost estrogen in older age, potentially providing new treatment targets for infertility or menopause.