Earlier story: Horses attempt to get to safety.
They took refuge on the roof of a house as the floodwaters rose, but could do little by that stage to help the horses.
"Horses are up to their chest in water ... they probably won't make it," he wrote at one stage.
"I've never felt like this in my life ... everything is gone .... pretty upset."
Just 14 minutes later he wrote: "Just witnessed a horse drown and get washed away .... this is the worst day of my life."
It was just before 6pm on Tuesday and Sullivan and his friends faced a night on the rooftop - 13 hours in all - as there was no means of escape, and rescue helicopters were unavailable.
Rescue came the next morning when stud owner Clive Palmer, Australia's fifth richest man, flew in his own company chopper to rescue the staff at the southeast Queensland stud, near Moore.
Palmer told Harnesslink.com that the four staff came close to perishing.
He told the website: "We flew in the company chopper and saved them but one staff member, 22-year-old Murray Sullivan, who drives a lot of our horses to and from venues, was absolutely devastated. Thank goodness we have lost no-one."
He said about 80 standardbreds, including 17 racehorses and 15 yearlings, had died in the flooding. The 15 yearlings were lost in one barn.
He said the equine toll could have been worse had all his team been in Queensland. Some of his horses were campaigning out of state and in New Zealand.
The Sydney Morning Herald reported that Palmer used his helicopter to rescue about 60 people from the wider area around his stud.
The human death toll is at 15.