DISCOVERY BAY (CBS SF) — Contra Costa County sheriff’s deputies fatally shot a bull Thursday in a rural field after it was believed it have killed a local rancher.

East Contra Costa Fire Protection District firefighters responded to a field just west of the 2300 block of Bixler Road about a half-mile south of Point of Timber Road around noon on reports of a man down.

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When they arrived, they were confronted by an aggressive bull. Sheriff’s deputies and county animal-control officers were called to the scene.

When the bull approached first responders attending to the injured man, a shot was fired to drive it away. When it didn’t respond and continued to be aggressive, deputies shot the bull.

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The man was declared dead at the scene.

His name was not released pending next-of-kin notification. The coroner’s office will determined the man’s cause of death.

“It is believed that the bull may have attacked the rancher,” said Steve Aubert, a fire marshal public information officer with the East Contra Costa Fire Protection District.

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Deputies were investigating the incident.