Ashburton-based Sumotori, trained by Pam Gerard and owned by Greg Jones, was injured when the horse in front ran through a barrier about 450m into the second race of the day.
The impact caused a metal section of the barrier to come loose, which Sumotori, running his first race, was then forced to jump.
What happened next, said Dunedin horse veterinarian Pete Gillespie from VetEquine Otago, were the worst injuries he had seen on a horse that survived.
As Sumotori jumped, the metal railing ran "like a knife" along the horse's belly, opening a 1.2m-long slice in the skin on the left of his belly.
Rider Daniel Stackhouse, of Ashburton, was unhitched, but uninjured, while Sumotori, bleeding heavily, ran another 1000m to finish the race. Once he was stopped, veterinarian Annemarie Wezenbeek worked to stem the bleeding with wadding and bandaging, but the horse's blood pressure was too low to use an ananaesthetic straight away.
In a three-hour surgery at Mosgiel the following day, Mr Gillespie and Ms Wezenbeek administered hundreds of stitches, patching muscles and stitching skin back together where they could.
"Essentially he ran into a blade. He had three to four feet [90 to 120cm] of lacerations, and some parts were too jagged to put back together and patches of skin were missing. It was quite a difficult surgery," Mr Gillespie said.
"I've been doing this for 30 years and it is the worst [injury], where the horse survived, that I've seen."
Yesterday, a week after his surgery, Sumotori was recovering "remarkably well" in the care of Zoe Miller on her lifestyle block at Mosgiel, and was even starting to regain a bit of his cheekiness, he said.
He still had lots of drains in and was on regular doses of antibiotics, but was expected to make a full recovery within 10 to 12 weeks.
"Physically he's doing well, it's the mental scars that might be worse, but we won't know that until later."
Ms Gerard said she was thankful Mr Stackhouse had escaped injury and the horse was recovering well.
She said she loved racing at the country courses, but it would be nice to see some of the metal railings replaced with plastic material like that used at city tracks. However, she realised the cost might be prohibitive for the smaller courses.
She was confident Sumotori he would be back racing one day.
"It was just some bad luck for him that day."
