An 81-year-old Montana man was sentenced on Monday to six months in federal prison for illegally using tissue and testicles from large sheep hunted in central Asia and the US to create hybrid sheep for captive trophy hunting in Texas and Minnesota.

The US district court judge Brian Morris said he struggled to come up with a sentence for Arthur "Jack" Schubarth of Vaughn, Montana. He said he weighed Schubarth's age and lack of a criminal record with a sentence that would deter anyone else from trying to "change the genetic makeup of the creatures" on the Earth.

Morris also fined Schubarth $20,000 and ordered him to make a $4,000 payment to the US Fish and Wildlife Foundation. Schubarth will be allowed to self-report to a federal bureau of prisons medical facility.