The rodeo code of welfare states electric prodders must not be used on animals other than adult cattle.
Mr Rodwell said alternative approaches to prodding were available and they are confident there is no reason to believe he will not comply in the future.
"We also concluded that the Rodeo Committee was not complicit in this individual's actions."
Animal activists SAFE welcomed the warning but said it was not enough.
SAFE campaigns director Mandy Carter said MPI must take urgent action to prohibit rodeo events, starting with calf roping.
"This kind of treatment of those who must need our protection cannot be allowed to continue."
She said in calf roping, young calves are chased, wrenched off their feet by ropes, slammed into the ground and have their legs tied together.
"Even worse, at the Mid Northern Rodeo they were goaded with painful electric shocks before entering the arena."
NZ Rodeo Cowboys Association national spokesman Michael Laws said their understanding is that the man misinterpreted the rules and that evidence was accepted by the authorities.
"An error of judgment was made, an investigation completed and a satisfactory outcome arrived at. Despite some media mischief and some degree of provocation, NZ Rodeo considers that lessons have been absorbed and learned."
He said rodeo remains a very popular family entertainment with a strong welfare code, repeatedly endorsed by academic studies and scientific research.
"There is no sport in which 100 per cent of participants get it right 100 per cent of the time."
He said there was no sanction, outside the warning, which prevented the man being involved next year.
Mr Laws said they full support and endorse the rodeo code of welfare and said this incident actually proves it is working well.