Magistrate Leanne Topfer, in October, found the ferry operator guilty of 29 animal welfare charges related to the 2018 incident.
Sixteen horses, which had just competed at the annual Barnbougle Polo Tournament, were found dead inside a converted refrigeration trailer after crossing the Bass Strait from Devonport and Melbourne.
Ms Topfer said the voyage was on a "warm evening where there was a clearly inadequately ventilated transport unit stationary for 10 hours".
There were too many horses in the unit and 16 horses were exposed to the risk of acute heat stress and asphyxiation and died from respiratory failure, she said.
Former Australian polo captain Andrew Williams is also expected to be sentenced after pleading guilty in July to criminal charges relating to the same 16 deaths on the 2018 voyage.
Mr Williams has pleaded guilty to 16 counts of failing to ensure a horse was individually stalled.
He also pleaded guilty to one count of using a method of management reasonably likely to result in unreasonable and unjustifiable pain and suffering.
TT-Line has already lodged an appeal in the Full Court of the Supreme Court over its guilty verdict.
On Tuesday, Chief Justice Alan Blow said the matter would be heard in a one-day hearing on February 27 next year.
TT-Line will argue it shouldn't have been found guilty of animal welfare offences.
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