* No official organization tracks the heights of all horses worldwide.
* Horse height records are often based on anecdotal evidence and individual owners' claims.
* Even if a horse is considered "tall," there is no guarantee that it is the second tallest in the world.
While there have been horses claimed to be incredibly tall, there is no universally accepted list of the tallest horses.
If you are interested in learning more about giant horses, I suggest searching for information about specific breeds known for their size, like the Shire horse or the Clydesdale horse.