I think that this 1988 classic of a train wreck would be perfect. It stars Bobcat Goldthwait, Dabney Coleman and the voice of John Candy.
The IMDB Synopsis:
Fred P. Chaney (Goldthwait) receives as inheritance after the death of his mother a speaking horse (Voiced by Candy) that also has good knowledge about the stock-market. With the help of this horse Fred gains a lot at the stock-market of Chicago.
It also features an incredible climactic horse race, which is easily one of the more profane talking animal sequences in history.