March 22, 2012
Rhino Diet May Affect Reproduction
The once thriving captive-born southern white rhinoceros population is being threatened by their diet, according to new research. San Diego Zoo Global researchers predict that phytoestrogens in the rhinoceros´ food may be causing reproductive failure in the females.
In a press release detailing the research, Christopher Tubbs, researcher with the San Diego Zoo Institute for Conservation Research explained the importance of the study.“Understanding why the captive white rhinoceros population has been dwindling for decades is an important part of protecting the future of this species. Our work is the first step toward determining if phytoestrogens are involved in this phenomenon and whether we need to reevaluate captive white rhino diets.”
Zoologists have only recently found the northern and southern white rhinoceros to be different species´ rather than a subspecies of the African white rhinoceros. As such, conservation efforts have been specifically designed to increase the population of the southern white rhino.
According to SanDiegoZooGlobal.org, The San Diego Safari Park has had great success in conserving the southern white rhino population and has bred more than 88 rhino calves since the Park´s establishment in the early 1970s.
While there have been successes in conservation efforts, scientists at San Diego Zoo have noticed a decline in reproduction in females born into captivity.
Reproductive issues such as cystic endometrial hyperplasia; cervical, ovarian, and uterine cancers; and ovarian cysts have placed the sustainability of the captive rhinos is jeopardy. In trying to find the cause of these issues, San Diego Zoo scientists began to look at every aspect of the rhino´s daily life, such as social experiences, animal density, enclosure size, premature copulations, and diet. Their research suggests examining the rhino´s diet as a starting point for unlocking these reproductive mysteries.
The captive southern white rhinoceros´ eat a diet of alfalfa hay and soy-based, commercially made pellets. Scientists believe that these foodstuffs may contain phytoestrogens such as isoflavinoids. Previous research has shown abnormalities to occur in livestock exposed to these phytoestrogen-rich foods. The abnormalities occur particularly during embryonic development and are similar to those found in captive-born rhinos. The phytoestrogens activate estrogen sensors in the female southern white rhinos, making it difficult to conceive and reproduce. As the southern white rhino is genetically different from other species of African white rhino, the phytoestrogens affect them much differently than other rhinos, such as the one-horned rhinoceros.
Second only to elephants, the southern white rhinoceros is one of the world´s largest land animals. While captive-born populations now face the threat of reproductive difficulty, wild rhinos face the threat of poachers and sport hunting. These factors have placed the southern white rhinoceros on the International Union for Conservation of Nature´s “near-threatened species” list. According to the San Diego Zoo, there are currently 17,500 southern white rhinos in the wild, with 500 rhinos in captivity.
The study compares healthy reproducing rhinos in the wild with non-reproducing rhinos in captivity. The study has been published in the March issue of Endocrinology.