A sheriff's deputy in northeastern Arizona used a stun gun to drive off a large cow that was stepping on him in a field after he rescued a woman pinned to the ground by the mammal.

Navajo County Sheriff's officials said Tuesday that a woman telephoned for help last week while pinned as the large black cow was continually pressing her if she moved or tried to get away.

The incident occurred around 9 p.m. Friday in the Antelope Valley area about 10 miles north of Heber, and it's believed the barking of the woman's dog may have provoked the cow, Chief Deputy Randy Moffitt said.

He said it's still unclear why the unidentified adult woman was in the field that night.

Deputy Vincent Palozzolo arrived on the scene and used his stun gun to get the cow to release the woman.

But the cow then charged Palozzolo, striking his chest and forcing him to the ground before he was able to again use his stun gun to drive away the cow.

Paramedics examined both people, but they refused further medical attention.

Sheriff's officials said Palozzolo's ballistic vest helped protect him from serious injury.