A 26-year-old South Australian man has pleaded not guilty to the fatal shooting of a police officer who was responding to an emergency call at a rural property.

Jadyn Stimson is accused of murdering Brevet Sergeant Jason Doig, 53, at a property in Senior, about 15km north of Bordertown in November.

Police were responding to reports an animal had been shot when Stimson allegedly opened fire.

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Doig, 53, of Lucindale Police Station, died of gunshot wounds at the scene.

One of his colleagues, Sergeant Michael Hutchinson, was also shot and taken to hospital for treatment of non-life threatening injuries.

Police then fired on Stimson, who suffered life-threatening injuries and was flown to the Royal Adelaide Hospital for treatment.

His lawyers argued the 26-year-old had an undiagnosed mental health condition at the time of the incident.

Stimson will stand trial in the Supreme Court.

He remains in custody at mental health facility James Nash House.

More to come...