MILWAUKEE — Officials at Milwaukee County Zoo are trying to determine whether the recent deaths of two of the zoo's gorillas are related.

WITI-TV reports the zoo's other gorillas weren't on exhibit Wednesday. Zoo officials announced the death Monday of Naku, a 17-year-old Western lowland gorilla. Her partner, a 31-year-old gorilla named Cassius, died earlier in April.

Zookeepers noticed Naku appeared more tired than normal. She was found to be septic, and emergency surgery showed a portion of her intestine had died. She was euthanized.

Cassius died April 12. Officials don't know what caused his death.

Zoo animal management and health director Beth Rich says initial necropsy results showed some similar findings, but officials don't have concrete evidence that the deaths are related.

The zoo's remaining five gorillas are receiving antibiotics.