The rumors have been around for years about 2002 Kentucky Derby winner War Emblem, given his disinterest in mares. The NYT explores the topic but concludes that War Emblem just has "finicky taste." Others call him quirky or temperamental:
"He is isolated from the other studs at Shadai Stallion Station in the hope that he will feel safe and more confident in his sexuality. Mares surround him in an effort to revive a long-dormant libido. In nearly five and a half years of contact with hundreds of mares, War Emblem, now 9, has managed to mate with only 70 of them, which is half of most stallions’ yearly output. He has not produced a live foal since 2005, and the last time it was confirmed that he ejaculated in the company of a mare was in 2006. He did it once. 'We know he is fertile, but he has no interest in mares,' said Dr. Nobuo Tsunoda, the director of the farm."
Said Anne Peters, the matings adviser at Three Chimneys in Midway, Ky: "It’s very abnormal to have no sexual interest in mares."
Unless, of course...