Kentucky Derby (gr. I) winning rider, Jorge Chavez, will be one of eight leading jockeys coming to Prairie Meadows May 21 to compete in Riding Cup IV, a charity fundraising event. Jockey Chavez won the May 5 Derby aboard the John Oxley-owned Monarchos, trained by John Ward. The first post on May 21 is 4:30 p.m., with a jockey autograph session to be held on the track apron from 4:30-5:30 p.m. In case of inclement weather, the autograph signing will be moved inside the grandstand facility on track level.Laffit Pincay, Jr., the winningest jockey in history, joins Chavez in Riding Cup IV, along with nationally known riders Jerry Bailey, Pat Day, Victor Espinoza, and Corey Nakatani. Terry Thompson and Luis Quinonez, the two leading jockeys at Prairie Meadow currently with 19 wins and 18 wins, respectively, have earned berths to compete with the incoming riders. Quinonez will ride with Bailey, Day, and Chavez for Team East. Thompson will join Laffit Pincay, Jr., Corey Nakatani, and Victor Espinoza on Team West.The three-race Riding Cup series, based on an inverse scoring format, will be races 5, 7, and 9 on the card, with the Riding Cup races to go of at approximately 6:06 p.m., 6:54 p.m., and 7:44 p.m.Following the ninth race, the jockeys will meet with Prairie Meadows officials in the winners circle to present a check totaling $10,000 from the day's proceeds to the Des Moines Ronald McDonald House.