Event director Mary Adams said afterwards that the injury was purely an accident: "the horse has hit his leg going over the jump, he's landed wrong and broken a leg."
Howie, 14, an intermediate rider, is from the Hawea-Wanaka pony club.
Of the accident, cross-country judge Bill Bates said organisers had been well prepared for any issues on the course. "All the possible problems were talked about and discussed beforehand and were eliminated. We were well prepared, I believe, for anything untoward happening. You don't want accidents to happen."
Another rider at the same event was taken to hospital with minor injuries after a rotational fall. Jessica Poole's mount, China Arrow, hit the 17th jump when two fences from home, and flipped. Poole, riding for Wyndham, broke her collarbone in the fall and suffered bruising.
Adams said Poole was one of the region's six top riders, and had ridden at the Pony Club Championships last year for the Otago-Southland team.
"Accidents are accidents," Adams said.