The carcasses of 250 cattle were found dead of apparent poisoning on a ranch in northeast Nebraska, authorities said.

The state patrol was investigating the deaths north of Richland with the Colfax County Sheriff's office, the state Department of Agriculture and the University of Nebraska.

``We don't really know if it's accidental or intentional yet,'' said Terri Teuber, a spokeswoman for the state patrol.

The cattle were yearlings owned by Jack Barta of Fremont who said he received word of the deaths Sunday morning.

Organic phosphate may have poisoned the cattle because about 30 that survived were responding to a drug used to combat nerve gas in soldiers, Barta said. The chemical is commonly used as an insecticide.

The chemical could have come in a sack of mislabeled minerals or someone may have intentionally put it in the cattle's feed, Barta said.