A magistrate says she cannot sentence the operator of the Spirit of Tasmania or former Australian polo captain Andrew Williams over the 2018 deaths of 16 polo ponies until fresh evidence of them "whinnying in distress" is considered.
The ponies had been competing at a polo event in Barnbougle in Tasmania's north in January 2018 and were travelling back to New South Wales on the Spirit of Tasmania.
Sixteen of the 18 horses were found dead inside the converted refrigerator trailer they were travelling in after the ship docked in Melbourne.
Magistrate Leanne Topher was due to sentence ferry operator TT-Line and Mr Williams on Wednesday.
Mr Williams pleaded guilty to 17 counts of breaching the animal welfare act in July, while TT-Line was found guilty of 29 charges in October.
But in the Burnie Magistrates Court, Magistrate Topfer said she would not proceed with the sentence because a significant issue had arisen from a report provided by Mr Williams' lawyers.
The court heard the report from a veterinary surgeon with more than 40 years' experience, which stated the truck's ramp should have been lowered to allow for greater ventilation.
The report said the horses would have been exposed to a "vicious cycle" of rising air temperature and deteriorating air quality, which would have led to them panicking and trying to escape.
It said there would have been "violent movement of the vehicle, [and] kicking against walls of the vehicle".
"It would have been apparent to anyone hearing them that this was an emergency situation," Magistrate Topfer read.
The report said because TT-Line had a policy of not allowing passengers access to the decks, it was responsible for ensuring the horses were inspected at regular intervals.
It found lowering the ramp of the vehicle on the deck could have "saved these horses lives".
Magistrate Topfer said the extent of the pain and suffering endured by the horses was relevant to sentencing and may have made a difference to her finding in October.
At the time, she said she was "not satisfied that the aspect of TT-Line's method of management so far as it involved a failure to inspect the horses either by the passengers or TT-Line during the voyage exposed the horses to any further risk of pain and suffering".
"There is insufficient evidence that it would have made any difference to the outcome."
She said she could not sentence TT-Line and Mr Williams based on different facts.
TT-Line defence lawyer David Neal said the company would consider its next move.
"We would want to consider the position, look at the report and then give a considered response," he said.
The matter is scheduled to appear before the court later this month.
The ferry operator had already lodged an appeal in the Supreme Court of Tasmania over the guilty finding.
Mr Williams also launched actions against TT-Line in the Supreme Court of Victoria, with a trial set for March.
