A 26-year-old zebra named Shani began showing signs of weakness and neurological disease. Officials say because of the rapid progression of Shani’s condition and the poor prognosis for recovery, veterinarians decided to put her down Wednesday. But they still don’t know what caused the animal’s sickness.

Leslie Field is lead zookeeper. She says Shani was leader-of-the-pack. 

“She certainly had a lot of character, a lot of presence. And being the lead mare she would teach new zebras into the herd sort of what the hierarchy was and teach them their place."

Field says it may take a couple of months before veterinarians determine why the zebra got sick. Shani was a Grevy’s zebra – an endangered species native to Kenya and Somalia. In captivity, Grevy’s zebras usually live to between 20 and 30-years old.