Prosecutors say Ziniuk hit his horse in the head with a sledgehammer and decapitated it in the remote mountain community of Anza.
Ziniuk has pleaded not guilty. He said he loved the horse named Grizzle and that the animal was already dead.
A vet pathologist determined the horse was still alive when it was decapitated.
Ziniuk could face up to three years and eight months in prison if convicted.
