Officials at Keeneland announced it will offer a share in Upstart (r, 10, Flatter-Party Silks, by Touch Gold), sire of leading classic prospects GISW Zandon and MGSW Kathleen O. in his second crop, at its April Horses of Racing Age Sale, to be held following the races on closing day Friday, Apr. 29 . The share will be the final offering of the sale. Shareholder involvement will begin with the 2023 breeding season. Upstart, who stands at Airdrie Stud in Midway, Kentucky, is a graded stakes-winner who earned $1.7 million....