US authorities are investigating how a US farmer was eaten by his hogs.

The district attorney's office says 70-year-old Terry Vance Garner never returned after he set out to feed his animals on Wednesday on his farm near the Oregon coast.

A relative later found Garner's dentures and pieces of his body in the pig enclosure, but most of his remains had been consumed.

The district attorney's office said in a statement that it is possible Garner had a medical emergency, such as a heart attack, or was knocked over by the animals before he was killed. But criminal activity has not been ruled out.

Authorities estimate the pigs weigh 320 kilograms each. The DA's office says one pig had either bitten or been aggressive with Garner previously.

AP