The owner of six polo ponies that allegedly died during a Bass Strait crossing on the TT-Line's Spirit of Tasmania said he had seen the autopsy report and blamed the ferry service for their deaths.

Australian agribusiness multi-millionaire Johnny Kahlbetzer owned six of the 13 horses that died in January while, it is alleged, travelling from Devonport to Melbourne.

Mr Kahlbetzer said he and the owner of the other dead ponies, former Australian polo team captain Andrew Williams, arranged for autopsies to be done.

The pair, along with Mr Williams' wife Rebecca, are suing TT-Line and logistics company QUBE for negligence over the horses' deaths, alleging the companies failed to provide a safe environment, adequate checks and air flow.

Johnny Kahlbetzer says the autopsy showed his horses suffocated. ( AAP )

Mr Kahlbetzer said he and Mr Williams commissioned the autopsy and said the horses suffocated.

"We delivered the horses to the vets, who did that autopsy, etc — that's how I've seen it," he said.

"It's all in technical terms, and part of our legal case, but basically they died of lack of oxygen."

The Tasmanian Department of Primary Industries (DPIPWE) has repeatedly refused to release the autopsy report, saying it was part of their ongoing investigation.

The ponies, valued at almost $650,000, died in the horse float driven by Mr Williams.

"It's irrelevant if it's a $20 cat from the pound or if it's a bloody million-dollar race horse," Mr Kahlbetzer said.

"You're not allowed to let animals out of your car or truck or whatever, you can't go and visit them whilst you're on the ferry, so it's totally the responsibility of the ferry to provide a safe environment, and they're not doing it on an everyday basis.

"It's not as if you can say, 'I do it right 99 per cent of the time'. It has to happen 100 per cent of the time."

'I still have faith in Mr Williams'

Andrew Williams discovered the horses were dead. ( Facebook: Willo Polo )

Mr Kahlbetzer said he blamed conditions on the ship, not the truck, for the deaths.

"The truck wasn't going, so they didn't die because of the truck," he said.

"There's nothing the truck could do to actually cause them to have died.

"It's been in that ferry 10 times or 11 times … without any issues, it's been used for I don't know how many years in general transport of horses, so I have no problems with the truck or the trailer.

"I still have faith in Andrew Williams — I employ him today."

Mr Williams and his lawyer have both been contacted for comment but have not commented so far.

Mr Kahlbetzer said the former Australia polo captain had nightmares about the deaths.

"I didn't see the horses at all, I've seen pictures of them in the back of the truck … certainly it was not a pretty sight, not pleasant at all," he said.

Mr Kahlbetzer said he had been told by Mr Williams how distressing it was to discover the horses were dead.

"He was shattered for quite a while. I'm sure he has nightmares of it still today.

"I think anyone who works with horses and breeds them and trains them and uses them for the sport, whatever sport it is, is intimately attached and emotionally attached to them."

Mr Kahlbetzer says there was no issue with the horse float. ( Instagram: chelcroz )

'We won't use the ferry again'

The agribusiness giant said it was the end of any association he and Mr Williams would have with Tasmania.

"I certainly wouldn't use them [TT-Line] for transporting horses," Mr Kahlbetzer said.

"We still don't understand why this happened or exactly what caused it.

"These aren't the first animals that have ever died on that ferry, and there's obviously something that occurs at times on that ferry which is causing animals to die on them, so they need to have a really good look at their systems and improve them.

"Until there was a significant dedication by them to improve the system and understand what's happening in these cases, I certainly wouldn't put any livestock on the ferry."

The TT-Line said it could not comment until the official investigation by DPIPWE was concluded.

It also said it had not yet been formally notified of any legal action against it.

Primary Industries Minister Sarah Courtney has refused to put a timeline on when the results of the investigation would be revealed.