"Porky and Teabiscuit" is a parody of the real racehorse, Seabiscuit...the winningest horse of the 1930s. The film was made a year before this horse was retired and at the time, practically everyone knew who Seabiscuit was....so a cartoon parodying the horse isn't surprising.
When the story begins, some crook cheats Porky...or thinks he does...by selling him a broken down horse. However, this was similar to Seabiscuit's early life and by the end, he of course, proves his worth.
This is just an okay. Cartoon. While it's animated well, it has one gaping problem...there are very few laughs. Because of this and that most people don't remember Seabiscuit, I'd consign this to the category of a time-passer...worth seeing but also worth skipping.