Zoo diets may be harming rhinos

Southern white rhinoceros populations in zoos have been showing severely reduced reproductivity and it may be down to their diet, US researchers say. San Diego Zoo researchers say they may have determined why the rhino populations in managed-care facilities are declining: phytoestrogens in their diet might be contributing to reproductive failure in the females. The southern white rhinoceros is on the International Union for Conservation of Nature's "near-threatened" species. Wild populations face poaching and sport hunting, but captive populations have been declining because of reproductive issues in the females including cystic endometrial hyperplasia; cervical, ovarian, and uterine cancers; and ovarian cysts, the Zoological Society of San Diego reported. Researchers say they believe the diets of the captive population is a concern and that phytoestrogens such as isoflavinoids found in the alfalfa and soy they eat activate their estrogen receptors more than those of the greater one-horned rhinoceros, another captive population that receives a similar diet but has better reproductive success. "Understanding why the captive white rhinoceros population has been dwindling for decades is an important part of protecting the future of this species," Christopher Tubbs, researcher with the San Diego Zoo Institute for Conservation Research, said. The researchers compared populations that are doing well with populations whose reproductivity is placing them at risk, and said diet is a key difference between the two. "Our work is the first step toward determining if phytoestrogens are involved in this phenomenon and whether we need to re-evaluate captive white rhino diets."