The impala struggled to break free for 18 seconds, according to the zoo’s director of animal health, Dr. Doug Armstrong. Once it untangled itself, the animal rejoined its herd for about 30 minutes before it collapsed.

Zookeepers found the animal unconscious but still alive near a mud wallow. But it died before it could reach the zoo’s hospital.

The zoo is still trying to determine the impala’s cause of death. A necropsy (animal autopsy) was performed but didn’t show any clear signs explaining the death.

“Right now, the hypothesis is that he’s an impala, and they are more stress-susceptible than other hoofstock,” Armstrong said.

The electric hot wire fencing could have contributed to the impala’s death, Armstrong said, but it’s more likely that it died because the stress of being trapped caused breathing or heart problems. The animal also could have had pre-existing health problems exacerbated by the stress. Lastly, the electricity could have thrown the animal’s heart into an irregular rhythm.

“If he had been electrocuted, he would have died right there,” Armstrong said.

The zoo said in a statement that it has had no animal die from electric shock in 45 years.

“Animal death from engaging with hot wire is extremely rare and to our knowledge has not happened at the zoo in the preceding 45 years,” the statement says.

Electric fencing is commonly used not only in zoos, but in agriculture as well, according to Association of Zoos and Aquariums spokesman Rob Vernon. The AZA does not regulate zoos’ use of electric fencing.

“It is a fairly common tool used for keeping animals in an area that we want them to stay,” he said. “In particular, it’s used to try to keep animals away from areas where they might hurt themselves.”

Armstrong said the zoo has already started shrinking the distance between the cables and the fence to prevent another animal from becoming trapped.

A histopathology report providing further details about the animal’s death should be complete by mid-December.