The four-year-old, who had also been a smart performer on the Flat for O’Brien’s father Aidan, had to be euthanised after suffering an injury during the JCB Triumph Hurdle, for which he had been a hot favourite.
While admitting his devastation at the loss of Sir Erec, O’Brien felt Friday’s Christchurch mosque shootings that killed 49 people in New Zealand helped to put matters into context.
He told Racing TV: “We’re devastated – everyone at home, the owners and everyone. It’s one of those things.
“It was documented he had a stone bruise during the week and he seemed perfect the last couple of days. He had a full set of X-rays two days ago just to make sure there was nothing else going on, and they were perfectly clean.
“Mark (Walsh, jockey) said he jumped the hurdle awkwardly and landed extremely awkwardly and obviously he got injured.
“It’s one of those things, but I suppose when you see what happened in New Zealand last night, it kind of brings it into perspective a little and we’ll move on.”
Sir Erec had won both of his starts over hurdles and while he had spread a plate on the way to the start, he stood perfectly motionless and calm while the farrier fitted a new one.
All had looked to be going to plan until after the fourth flight and David Sykes, director of equine welfare at the British Horseracing Authority, felt Sir Erec’s injury could not possibly have been predicted.
He told ITV Racing: “Sometimes there are catastrophic injuries. This morning he was examined by a veterinary surgeon and trotted up and he said he moved very well.
“There was no indication of lameness, there was no indication of injuries.
“Whether he made a mistake at that hurdle or not and landed awkwardly – there was no reason we could predict that injury to that horse today.
“He was shod and the veterinary surgeon trotted him up in the same way. The shoe was having no effect. Putting a shoe on wasn’t going to cause that sort of injury.
“It’s one of those catastrophic injuries that occur unexpectedly. We are not able to predict those.”
There were six deaths at the Festival last year, with another horse subsequently put down due to his injuries, and while the number of fatalities has halved, chief executive Nick Rust says the BHA will not rest on its laurels as it attempts to further reduce the risks of racing.
He said: “I would like to offer my gratitude to the veterinary team and to all the trainers who have competed at the Festival.
“The process of liaison in the build-up and the carrying out of the various veterinary checks on all 450+ runners has been an immense logistical challenge, as have the requirements regarding equine flu controls, particularly for international runners.
“It has been a collaborative process and we are grateful for the role that trainers have played in this, which has been first class. The event has run smoothly despite our setting a very high threshold in terms of the preparation required for every runner.
“I would also like to thank the overwhelming majority of jockeys who have demonstrated skill, professionalism and care throughout.
“The requests we sent out ahead of the Festival to act responsibly with regard to welfare and use of the whip have been followed and this has contributed significantly to the success of the week.
“We share in the sadness of everyone involved in the sport about the fatal injuries incurred by Ballyward, Sir Erec and Invitation Only this week.
“Our thoughts are with everyone connected to the horses. While the overall injury rate has reduced significantly this year, there will always be an element of risk that can never be entirely eliminated.
“It is the role of the BHA and everyone in the sport to try to reduce that level of risk as much as possible, and do all we reasonably can to prevent injuries that could have been avoided.
“As such, all the racing incidents from this year’s Festival will undergo a rigorous process of review and evaluation.
“We will analyse the evidence alongside the extensive data collected by the 2018 Cheltenham Festival Review to see if any emerging trends can be identified. This will include post-mortem reports, video analysis of incidents and speaking to trainers and jockeys to seek their feedback.”