Alan Jackson and Shania Twain have been added to the list of performers at the 38th annual Academy of Country Music Awards show. Reba McEntire hosts the May 21 awards show at the Mandalay Bay Resort and Casino in Las Vegas. Previously announced performers include Brooks & Dunn, Kenny Chesney, Toby Keith, Martina McBride and Willie Nelson. Also performing are George Strait (who will receive the ACM's Special Achievement award) and Alabama (who will be presented the ACM's Pioneer award). Voting is still underway for the second annual Home Depot Humanitarian Award. This year's nominees are Brooks & Dunn, Lonestar and Wynonna. Fans can cast their votes at CMT.com.