Laboratory testing on dead bighorn sheep doesn’t reveal why animals perished

Friday, Sept. 9, 2005 | 9:55 a.m.

Nevada wildlife officials know what did not cause 22 desert bighorn sheep to die in the Southern Nevada mountains in July, but they may never know what actually killed the animals.

The Nevada Department of Wildlife said Thursday that extensive laboratory testing on the sheep found dead on July 25 in the McCullough mountain range 20 miles south of Henderson were inconclusive.

"We did all the testing we reasonably could, for 13 different factors including diseases, metals, bacteria, poisons and toxins," Dr. Dan Crowell, a state veterinarian with the state Agriculture Department, wrote in an Aug. 31 report to state wildlife officials.

Desert bighorn sheep are Nevada's state mammal. More than 5,400 desert bighorns live in mountain ranges in the southern, western and central part of the state, wildlife officials said.

Initial reports that lightening killed the McCullough sheep seems unlikely because decomposition of the animals showed they died at least 24 to 48 hours prior to a lightning storm on the weekend prior to the animals' carcasses being discovered, wildlife officials said.

The carcasses were found by ATV riders near one of the man-made watering holes established by the Wildlife Department and volunteers throughout Southern Nevada.

Researchers could find no reports of lightning strikes in the area for the week prior to the discovery. And there was no evidence of lightning wounds on the carcasses, wildlife officials said, noting some of the animals were as far apart as 200 yards.

Other causes of death that were ruled out include anthrax, heavy metals, toxicity, antifreeze, strychnine, respiratory viruses, fertilizer-type chemicals, and compound 1080, which is used in predator control. There also was no evidence the animals were shot, officials said.

Considering the sheep were found near a "drinker" fixture, wildlife officials say the sheep could have died by consuming blue-green algae or from dehydration or botulism -- or some combination of the three. But that too is not conclusive, they say.

Although water samples were negative for toxins associated with blue-green algae and botulism, it is possible the toxins could have been present and were subsequently flushed from the water system with the rain, Crowell wrote in his report.

Also, the watering device could have been dry prior to the storm, officials said.

"We have read reports of similar cases in Arizona and California that showed animals occasionally die near dry water sources, even with other water sources available within reasonable distances," Mike Cox, big game staff biologist for the Wildlife Department, said in a news release.

Also, temperatures in the area neared 120 degrees, which also may have been a factor. However, officials said, tests for elevated sodium in brain tissue, which is indicative of dehydration, proved inconclusive.

Nevada Bighorns Unlimited-Reno paid for the laboratory costs, the wildlife department said.

In the 1990s the bighorn sheep population in the McCullough area was estimated at about 130. Through the addition of water developments and other favorable conditions, the population had increased to an estimated 320 animals, state wildlife officials said.