They're Off(1948)

At the race track, various spectators (all Goofy lookalikes) are playing the ponies. A posh rich Goofy bets on the equally posh Snapshot III while another more common looking Goofy bets on the bedraggled Old Moe. When the race begins, Snapshot and the rider are so overconfident they wait a few minutes after the race has begun to start running. When they finally do get going, Snapshot is not above stooping to dirty tricks such as tripping and biting the other horses. Sadly, Snapshot's vanity is what costs him winning the race (he stops to pose for the photo finish) and Old Moe is declared the winner.