Horny, Horny Hippos- Gonads Make Hippos Go-Nuts

Hippo Aggression

Two male hippopotami showing their aggressive tendencies taken by Nils Rinaldi in Katavi National Park, Tanzania.

The world’s first successful hippopotamus castration, completed by veterinary researchers at the University of Veterinary Medicine in Vienna, Austria, proved to diminish male aggression and control hippo populations.

Initially, in 2006, the common hippopotamus was listed as a threatened species by the International Union for the Conservation of Nature Red.  Fortunately, the hippo made an expeditious comeback due to their reproductive success in captivity.  The average female hippo can have up to 25 calves in her lifetime. The problem then became that there were too many hippos for zoos to adequately accommodate.  The lack of enclosure space caused copious amounts of male-male aggression. The tight living quarters also left the animals unhappy and unhealthy.

The location of the male sex organs, specifically testes, and problems with anesthesia previously prevented veterinarians from successfully neutering hippos.  The male hippos reproductive tract has been a mystery to veterinarians due to its “internal” anatomy.  All the male sex organs that are found externally on most mammals are found in the vaginal pathway.  The anesthesia was shot into the hippo’s muscle, directly behind the ear with a carbon dioxide- launched dart gun.  The hippos received extensive oxygen throughout the entire procedure.  Once asleep, the hippos were laid on their side with their back legs secured to provide access to the surgical site.  Sterile, surgical utensils were placed in the vaginal pathway to arouse the testes to become visible.  An ultrasound machine was used to locate the precise location of the testes.  Once located, two incisions were made and the testes were extracted. The bleeding was stopped and the tissues were stitched together.  The entire procedure took, on average, 97 minutes.

Ten male hippos ranging from 2-14 years of age were included in the study.  They were all surgically castrated.  Post-surgery, no hippos developed further complications and passed medical examination. Zoo staff were given post surgical instructions to ensure a quick recovery. Nine out of the 10 hippos were returned to their living spaces within 30 minutes post surgery.  The tenth hippo was returned one hour after surgery due to an excessive amount of blood loss.

Six months after castration all the male hippo aggression in subjects had ceased.  Ironically, females became much more aggressive towards the castrated males.

Veterinarians were stunned by the lack of infection in the healing process since hippos live in bodies of water filled with fecal material.  Waltzer attributes the lack of infection to hippos’ “good wound healing.”  He says, “Good wound healing is a clear necessity for the common hippopotamus, because interindividual aggression often results in significantly large and numbers [sic] of wounds.”

The study and surgeries were completed following all the University of Veterinary Medicine Vienna’s ethics guidelines.

For more information  visit:

http://www.sciencedirect.com/science/article/pii/S0093691X13004275

Journal Source:

“Surgical castration of the male common hippopotamus (Hippopotamus amphibius)” by Christian Walzer, Thierry Petit, Gabrielle L. Stalder, Igal Horowitz, Joseph Saragusty, and Robert Hermes is published in the journal Theriogenology.http://www.sciencedirect.com/science/article/pii/S0093691X13004275

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