The director used real horses in place of the stage play's famous life-size theatrical puppets for the adaptation of the Michael Morpurgo children's novel about a boy separated from his beloved pet during World War I.
Co-director of the original stage play Tom Morris told The Daily Telegraph: "We didn't have any input into the film, but we saw Mr Spielberg and he was a straightforward and very nice man.
"He was telling us that, when they were in the middle of filming, he was quite frustrated as the real horses weren't nearly as expressive as the puppets. They wouldn't do what you wanted them to do."
Spielberg said recently that he considers himself an "old-fashioned director", describing film-making in the past as a "craft".
The horse in the theatrical production was played by three different actors, garnering high praise for its realistic appearance from critics.
Jeremy Irvine will be making the transition from the stage to star in the film.
War Horse opens in US cinemas on December 28 and on January 13, 2012 in the UK.
Watch the trailer for Steven Spielberg's War Horse below: