The deaths of two Malayin tapirs last week have been connected to an accidental overdose of a copper supplement, Denver Zoo officials confirmed.

An internal review done by the zoo concluded that the tapirs, JonHi, 16, and Rinny, 18, ingested too much of the dietary supplement, used to as of their care protocol to maintain their health, the zoo said on social media Friday.

The zoo first posted about the animals’ deaths a week prior on Jan. 16, but did not provide more details about the incident at that time.

“We have a very extensive internal review process that is standard protocol across the zoo anytime when something like this happens,” Denver Zoo spokesperson Jake Kubié
said Saturday. “There will be a deep dive investigation to identify what went wrong and what improvements we can make in the future to make sure this never happens again.”

Kubié
added that the deaths have been especially difficult for the care team, who pride themselves on making sure the animals are healthy and well-cared for.

The zoo added in the post that the incident was isolated to just the two tapirs and that no other animals, staff, volunteers or guests are in any danger.