NZALA then filed charges against Robinson under the Animal Welfare Act.
Lyal Cocks, president of the New Zealand Rodeo Cowboys' Association, said Robinson's behaviour was totally unacceptable and that was why he'd been found guilty.
"It's totally unacceptable anywhere, it's totally unacceptable in the rodeo industry. He's no longer a member of either the New Zealand Rodeo Cowboys' Association or the Mid Northern Rodeo Association."
Cocks said live electric prodders could only be used on large, unrestrained cattle to get them to move but not at rodeo events.
The two events for which Robinson was found guilty involved steers who were used for a team roping competition.
While waiting in the chute, the animals became too distressed to take part in the rodeo, and knelt down on the ground in anxiety.
Both animals had no room to move away and did not react to the actions of rodeo cowboys who tried to get them up using manual methods.
The Rodeo Code of Welfare requires that animals in such situations must be released by opening the gate.
Instead, Robinson shocked the animals with a charged electric prodder, which jolted them and caused them to stand up in pain.
They were then sent into the arena and chased by two cowboys on horses.
An MPI spokeswoman said the ministry took various factors into account, including the degree of harm to the animals involved.
"It was decided it was not in the public interest to pursue a prosecution and a formal warning was issued."
NZALA said its video evidence showed MPI's existing reluctance to prosecute rodeo offences had created a false sense of immunity among rodeo cowboys like Robinson.
It said the prosecution, which cost the organisation about $10,000, and the guidance provided by the court on the use of prodders in rodeos opened the way for MPI to enforce the rodeo code through the courts.
NZALA said the court also found Robinson used his prodder unnecessarily on 22 other rodeo animals, including calves, but it could not be proved whether the prodder was turned on.
He will be sentenced in the Whangārei District Court early next year.