Five meerkats died at the Philadelphia Zoo last week after they were exposed to an unknown toxin from a dye routinely used to identify them, a zoo official said.
The zoo has used the topical agricultural dye called Nyanzol-D for over 30 years, said Rachel Metz, the zoo's vice president of animal well-being.
"So the question is what is the difference that caused these animals’ deaths," she said. "We’ve been implementing a robust internal and external fact-finding mission."
The dye is used on other animals at the zoo, Metz said. Zookeepers mark different parts of the animals’ bodies with the dye so they can be easily identified, she said, calling it a routine practice.
The zoo has suspended use of the dye until officials find out what happened to the meerkats.
Necropsy results are pending to determine exactly how the meerkats died.