An engineer who modelled the conditions horses would have experienced on a Spirit of Tasmania journey in 2018 has told a court the temperature meant they were "going to cook".
Warning: details in this story may be distressing for some readers.
Sixteen polo ponies were found dead inside a trailer after a Bass Strait crossing between Devonport and Melbourne. Two more ponies survived.
Ferry operator TT-Line is fighting 29 charges of breaching the Animal Welfare Act, including that it failed to ensure the horses were individually stalled and that there was adequate ventilation.
Engineer Conrad Stacey told the Burnie Magistrates Court his modelling showed the temperature inside the horse trailer would have been at best, very uncomfortable, and at worst, fatal.
He said the horses would have generated 20 kilowatts of heat inside the trailer.
"The maximum heater sold draws 10 amps which is 2.4 kilowatts, and it will put all of that out as heat," he said.
"If you have eight of them in a room, like this trailer, that's about the same amount of heat the horses were putting out."
He said due to the trailer's small ventilation openings, the temperature would have risen quickly.
"The horses could not reject their heat so they were going to cook," he said.
Dr Stacey concluded the trailer did not have adequate ventilation for 18 ponies when stationary.
The court has previously heard because the ponies were exposed to high temperatures, their respiratory demand was increased, and they likely died about eight hours into the voyage across the Bass Strait.
The two horses loaded closest to the trailer's tailgate, which had an extra opening that allowed more air in, survived.
Tense exchange over qualifications
The court heard Dr Stacey had a background in studying ventilation on live export ships, which resulted in a fiery exchange over whether he had adequate qualifications to give evidence in this case.
TT-Line defence lawyer Robert Taylor asked Dr Stacey about the differences between livestock vessels and ships such as the Spirit of Tasmania, that don't predominantly carry animals.
Dr Stacey said it was no different from an animal's perspective.
"I'm not asking what you think cows think," Mr Taylor replied.
Magistrate Leanne Topfer noted Dr Stacey had not mentioned cows and asked Mr Taylor to "please stay pleasant".
The court also heard a recording of an interview with Spirit of Tasmania representatives that was conducted following the deaths.
The Spirit's general managers for port and marine operations, Stuart Michael and Paul Davis, said the only time they would inspect the inside of a freight or livestock trailer would be in an emergency situation.
The court heard there would need to be a visual or audio cue that something was out of the ordinary for an inspection to take place.
During the interview, they told Biosecurity Tasmania officers that someone would inspect the freight decks around halfway through the journey, however they said they would not go in or open horse trailers.
Instead, they would look into the trailer through ventilation openings, but admitted that these were often located too high for that to occur.
Dr Stacey was the last witness to be called by the prosecution, with several people to be called by the defence over the next three days.
Former Australian polo captain Andrew Williams, who was driving the trailer, changed his plea to guilty in July to charges arising from the incident.
He is due to be sentenced at a later date.
