Nevada Sen. Harry Reid is calling on U.S. Interior Secretary Dirk Kempthorne to conduct a “full and thorough investigation” into the nitrate contamination deaths of 71 wild horses in July at the Tonopah Test Range.

“There are strong concerns in southern Nevada that these deaths are the result of serious negligence in the management of the test range and the wild horse herds in the area,” Reid wrote in a letter sent Friday to the secretary.

“In light of this unfortunate event, I believe that this is also an appropriate time to take a close look at the land and wildlife management practices used on the larger Nellis Air Force Range,” Reid, the Senate majority leader, suggested.

The horses’ carcasses were found at a watering hole about a mile from the Tonopah Test Range airfield, about 210 miles northwest of Las Vegas