Organisers of the annual Gisborne Rodeo Association event said it was a "freak accident".
"Something like this has not happened for 30 years to animals at the Gisborne rodeo," said secretary Marsala Dalziel.
"We had a vet onsite and he made the call to put the bull down, and did it professionally."
When asked about the 25 minutes it took to put the bull down, she said it was the vet's call.
"How do the protesters know what is good for the animals? Are they trained vet specialists?"
A video of the incident had been shared 287 times on Facebook and watched almost 10,000 times as of this morning.
East Coast Farm Vets had a veterinarian of 20 years experience on site at the event all day.
Owner and veterinarian Andrew Cribb said he spoke to the vet who felt what happened after the bull was injured was appropriate.
The bull dislocated its hock, which is like a human ankle joint, which is a common injury on a farm, said Cribb.
He was satisfied there was prompt treatment.
"First there had to be a diagnosis, and upon that diagnosis, euthanasia became the only option. To do that effectively you have to find the appropriate pen.
"The other thing you have to have in the back of your mind is human safety. You can't just go firing a rifle off in the middle of an event like that."
Cribb confirmed no pain relief was administered to the bull because that would have heightened the stress and prolonged the outcome.
"The time for the drug to work would be approximately two hours, so there was little point in giving the drugs if euthanasia was the only option."
NZ Rodeo Cowboys Association president Lyal Cocks said he was contacted immediately after it happened.
"It's terrible. The last thing you want is to get a call like that. It's a devastating incident to have any animal lost at a rodeo, especially for the animal and the people involved. But we have a lot of other successful rodeos going on and you have to balance it out."
Cocks said he was waiting for the official report on the incident.
"We will see if there are any lessons learnt from that. We are in a sport using animals like many other sports in New Zealand. We have got to remember not to let this overshadow the successful side of rodeo and all the good it does for local communities, the thousands of spectators who enjoy it, the hundreds of animals involved and the hundreds of people who compete.
"Regrettably this does happen sometimes in sports that use animals; it's not just rodeo."
Cocks said the association worked with the Ministry for Primary Industries to continually monitor their sport, to keep an eye on animal welfare but also keep it an exciting competition.
Changes had been brought into the sport recently, including the introduction of a minimum qualification for riders — so not anyone could just turn up and ride a bull.
This is the second death this rodeo season. A horse at Methven Rodeo died at the opening weekend of the season.
A protest is planned on January 1 outside the Warkworth Rodeo.
Direct Animal Action spokesman Apollo Taito said the protests were to highlight the harm of rodeo.
"This death is a clear indication of that. We've had enough of seeing animals dying for entertainment at rodeos. This situation needs urgent action."
A report from the National Animal Welfare Advisory Committee (NAWAC) in October recommended a new rodeo animal welfare committee be established to monitor the use and help improve the welfare of animals.
Gisborne Rodeo Association president Graeme Fogarty did not want to discuss the bull's death, other than to say it was a "freak accident."
"It was a good day, and everything else ran smoothly."
