The SPCA says complaints of animal suffering and death during the filming of The Hobbit are useless if they are not reported at the time.
People for the Ethical Treatment of Animals (Peta) says it will hold protests at three premieres around the world after alleging that five horses, a pony, and several goats, sheep and chickens were maimed or killed at a Wellington farm they were housed at during the movies.
The film's producers reject the accusations, which they say were made by wranglers dismissed during production, and that hundreds of thousands of dollars were spent improving facilities for the animals.
SPCA chief executive Robyn Kippenberger says it had been made aware of the complaints last year, but too late to establish if there were any truth behind them.
The American Humane Association - which looks after animals on set but not where they are trained - had responded quickly and Ms Kippenberger was confident they were doing a good job on behalf of the animals.
However, she was scathing of the anonymous whistleblower, who had complained months after the alleged incidents, without any specific details that could be properly and promptly investigated.
"People who report after the fact are just as bad as those perpetrating it because they are not making it any better.
"It's just rubbish, and now Peta are protesting The Hobbit but nobody has done anything... because nobody stood up and said this is happening.
"This whistleblower hasn't had the courage of their convictions to get in touch in the first place, or give us a name or give us something to go on.
"Peta can march up and down until the cows come home, it's not going to help the animals if they were abused."