'After competing in the Barnbougle Polo Club event in early January, the horses were transported to Victoria on the Spirit of Tasmania ferry', an Australian Maritime Safety Authority spokesperson said. 

The ponies were all reported to have been in good health after competing. There is great confusion as to how "A-grade" ponies ended up “cold dead” only an hour after disembarking in Melbourne. Tasmania's Department of Primary Industries, Parks, Water and the Environment has launched an investigation into the deaths.

A probe by the Australian Maritime Safety Authority found the Spirit Of Tasmania operator TT-Line "complied with AMSA requirements relating to the carriage of livestock".

Andrew Williams former owner and manager of Willo Polo Club, Richmond north of Sydney before moving to Forbes to manage Jemalong Polo Club, stated he was 'gutted' by the mystery and has released a statement about the voyage and how it all went wrong. 

"I have done this trip 11 times in the same truck, but I knew something was wrong as I drove through the city of Melbourne a short time after disembarking. So I rang my other truck and asked if his load was travelling well," Mr Williams said.

"My head groom said 'his horses couldn't wait to get off his truck' so I knew then that something was potentially wrong, as mine were not indicating the usual activity. I then arrived in Yarra Glen at a friend's property. It was my worst nightmare."

"Within an hour of leaving the boat, I had 16 horses that were cold dead and two fighting to survive," Mr Williams said in a statement.

It is not known if the horses died on the ferry or after they disembarked.

The other puzzling piece of information refers to a similar number of horses who did survive the trip back to the mainland in a second horse trailer that was also managed by Williams.

Some sources highlight a potential reason maybe related to the dates the horses were transported coinciding with a heatwave that swept through both Tasmania and Victoria.

Action from the Barnbougle Polo competition, in north east Tasmania, in January. Photo - ABC News

According to the Australian Bureau of Meteorology, Tasmania experienced record warm nights at the end of January with a heatwave that peaked on January 28 recording temperatures in the high 30s in parts of the state. 

Melbourne's daytime and overnight temperatures in January were also warmer than average.

Investigations are underway on the tragic death of these horses.