The 67-year-old, whose name was suppressed on Tuesday by judge Lance Pilgrim at a County Court siting in Ballarat, used tethers and a milk crate to defile another animal in a separate incident. 

The man, who was previously convicted of bestiality in May 2013, pleaded guilty to two charges of bestiality after being filmed by members of the public performing lewd acts on his rural property near Ballarat. 

One witness, after spotting the man stood in an "unusually high" position behind a horse tethered to a shed on March 12, went to get a camera to film the incident.

Crown prosecutor Tania Bolton told the court on returning, the witness observed the man, stood on a milk crate, penetrating the horse with his forearm while masturbating. 

The court heard at around midday on January 15, 2014, a local worker saw the naked man in a paddock holding up the tail of a small horse while having sex with it. 

The man crouched down behind the horse when he observed the witness driving past, Ms Bolton said. 

Defence lawyer Amanda Hurst said the man's wife, who owns a horse stud, had got rid of all the ponies at the rural property. 

"They're only left with very big horses that would make it very difficult to carry out this type of offending," she said. 

Ms Hurst said the witness's decision to film the accused was questionable and borne out of suspicion from previous offending.

"It's not a case of him being out in the public having sex with an animal, he's doing it on a secluded property," she said. 

In ordering the man to complete a psychiatric evaluation, judge Pilgrim said confusion reigned over the man's mental health status. 

"He's behaving anti-socially in a very, very strange way, he needs help," Mr Pilgrim said. 

"We need to get a medical practitioner to figure out what's wrong with him."

A report will be prepared and the man is expected to reappear for sentencing at Melbourne County Court at a date to be fixed.