Two-time Horse of the Year and classic sire Curlin will not cover mares for the remainder of the breeding season after developing an ulcer and a brief illness. The 22-year-old son of Smart Strike stands at Hill 'n' Dale Farm in Paris, Ky., which is hopeful that the stallion will be able to return to service in 2027. The story was first reported by the Thoroughbred Daily News. Hill 'n' Dale owner John Sikura told the TDN that Curlin exhibited discomfort about 10 days ago, and an ulcer was found outside of his stomach, an unusual location. The stallion also developed a minor temperature. He was given several days off of breeding mares, and returned to the breeding shed once he was off all medication. When Curlin's most recent mares bred were not checked in foal, Dr. Dickson Varner, a renowned reproductive expert from Texas A&M, was summoned. “Dr. Varner came today, examined his dismount sample, and found it subnormal in motility and the number of live semen," Sikura said. "Based on the science of how the body produces a sperm cell to a viable ejaculate, we thought it was only fair to give the horse a chance to regenerate on his own, and not to cover mares, which wouldn't be fair to outside breeders or to syndicate members.” :: DRF Kentucky Derby Package: Save on Past Performances, Clocker Reports, Betting Strategies, and more. Sikura said that Curlin was "a normal horse" prior to this incident, despite his age, and has over 20 mares checked in foal for this season, which began in early February. Mares are still continuing to be checked. "There is an accumulation of issues in an older horse, and those stress factors have compromised him," Sikura said. "There's not a direct, specific diagnosis. These things are somewhat mysterious at any stage, but with older horses, they're more susceptible to illness and injury, elevated temperatures, and treatment. Hopefully he can regroup and cover mares next year. But it's the right decision to make at this time." Curlin has ranked among North America's top 10 sires six times in his career, and has been a regular presence in the American classics ever since 2013 Belmont Stakes winner Palace Malice emerged from his first crop. He is also the sire of 2016 Preakness Stakes winner Exaggerator, last year's Preakness winner Journalism, and several other classic-placed runners. Curlin's 125 career stakes winners to date also include 2023 Horse of the Year Cody's Wish, two-time winner of the Breeders' Cup Dirt Mile; two-time Eclipse Award champion Malathaat, winner of the Kentucky Oaks and Breeders' Cup Distaff; two-time Breeders' Cup Sprint winner and divisional Eclipse champion Elite Power; Breeders' Cup Classic winner and champion Vino Rosso; Breeders' Cup Distaff winner and two-time Eclipse champion Idiomatic; Breeders' Cup Juvenile winner and champion Good Magic; and additional Eclipse champions Nest and Stellar Wind. Good Magic has gone on to become a classic sire in his own right, represented by 2023 Derby winner Mage and 2024 Belmont winner Dornoch in his first two crops. Good Magic stands alongside his sire at Hill 'n' Dale, which will now offer space in the stallion's book for mares previously booked to Curlin for the remainder of this season. :: Want to learn more about handicapping and wagering? Check out DRF's Handicapping 101 and Wagering 101 pages.