Authorities are still trying to figure out what caused the deaths of two dozen cows in the Heber-Overgaard area, in the Apache-Sitgreaves National Forest.

Samples taken after the cows were found dead last week have tested negative. That’s according to the Navajo County Sheriff's Office.

Law enforcement previously ruled out foul play, saying it was likely a naturally occurring ecological poisoning.

Further testing will be done by a veterinarian. Arizona Game and Fish and the U.S. Forest Service continue to work on the investigation.