After racing, many thoroughbred horses retire to a life of breeding.
Even though some of them make millions during their racing career, it's actually their breeding life that produces the most money for their owners.
In 2018, the most expensive stud fees produce some pretty gaudy numbers.
Galileo is the most expensive stallion. Although the fee has been listed as private since 2008, reports suggest the figure has been almost $700,000 to stud.
The most expensive American horse is Tapit, who charges a $300,000 fee to stud and makes nearly $12.6 million in an average year.
American Pharoah, the most recent Triple Crown winner, also has a private fee, but many believe the price is over $200,000.