Amherst, Wisconsn -- Preliminary results show acute interstitial pneumonia is to blame for a mass death of cattle outside of Wausau.

The University of Wisconsin-Madison's Veterinary Diagnostic Lab is studying tissue samples from two of the 200 dead Amherst steers.

The steers all came from one farm, and while the lead veterinarian said the preliminary results pointed to pneumonia as the cause of death, associate lab director Peter Vanderloo said nothing is being ruled out until the final tests are completed.

"We can approach the problem both from looking at what's going on microscopically in the animal, to identifying a pathogen, viral or bacterial, or looking for a toxin that might be causing deaths," Vanderloo said.

The cattle were found on a farm in Amherst, which is about 50 miles south of Wausau.

The farm's veterinarian said the steers began to die early last week with the last dying Saturday.

Vanderloo said the incident was rare and couldn't remember ever studying so many cattle dying in just a matter of four days.

"I can think of a few pretty significant die-offs but not to this extent," Vanderloo said.

Vanderloo said he did not know when testing would be completed.