Making over $35 million a year as a retiree is rather impressive — and it's maybe even more so when the retiree in question is a horse. But it's become the norm for the racing-stallion-turned-stud known as Tapit. The thoroughbred breeds with up to 125 mares a year at a record stud fee of $300,000 per mare, which brings Tapit's yearly earnings to over $35 million. "He's the most valuable stallion at stud in America," says Michael Hernon, director of sales at Gainesway, the Lexington, Ky., farm where Tapit resides.

Tapit takes a stroll at the Gainesway Farm in Lexington, Ky., where he headlines the stallion roster. Ian Tapp | Gainesway

It's a staggering figure considering the top-earning racehorse in 2016 netted just over $4 million in total earnings at the track, according to BloodHorse. But in the big business of thoroughbred racing, sometimes the real money is made in the breeding shed. Owners pay top dollar to ensure they are getting horses from a lineage of proven winners. Since 2014, Tapit has held the title of the nation's leading sire, meaning that the stallion's progeny have earned the most on the track every year for the previous three years. Most recently, in 2016, Tapit's progeny made $19.9 million in total earnings. Even the stud fee of recent Triple Crown winner American Pharoah fell short of Tapit's in 2016, since, as yet, Pharoah has no track record off of the track.

Tapit grazes in the barn area at Churchill Downs on April 29, 2004, in Louisville, Ky. Getty Images |