Farmhand Gideon D Swartzentruber pleaded guilty to having "sexual gratification with an animal", according to court records. The 20-year-old was working in a Neillsville barn when the incident happened.
"He said that he kind of touched the donkey and was playing around being crazy," according to a detective.
When asked why he had intercourse with the donkey, Swartzentruber said his "privates were out of control" and that he "got crazy and carried away," according to Marshfield Herald News.
The Winsonsin man said he had not harmed the donkey and claimed that it was the first time he had done anything like this before. He was caught in the act by the animal's owner, who reported him to the police and then sacked Swartzentruber.
Clark County Circuit Judge Jon Counsell put Swartzentruber on probation, ordered him to pay $443 (£300, €408) and have therapy. But on Wednesday 30 December, the farmhand pleaded with the judge to put him in jail, resulting in Counsell sentencing him to 30 days.
Clark County Assistant District Attorney Kerra Stumbris, who prosecuted the case, told News-Herald Media that Swartzentruber did not say in open court why he asked for jail time. He represented himself in court and has gone without an attorney since being charged.
Bestiality — also known as zoophilia — is a felony in 16 US states, including Alabama, Mississippi, Tennessee and Georgia. Scott Heiser, an attorney with the Animal Legal Defence Fund, a California-based organisation that fights to protect animals through the legal system, said the lack of bestiality laws in states without them is down to a lack of awareness.
"I can't imagine that there are (legislators) out there who say as a policy we should be engaging in sexual acts with animals," he told Watchdog.org. "I think a lot of lawmakers think their animal cruelty laws cover this act, but in some states that's not the case."