Answer by taking a quote from the following article:

"Hound Dog" is a twelve-bar blues song written by Jerry Leiber and Mike Stoller. Recorded originally by Willie Mae "Big Mama" Thornton on August 13, 1952, in Los Angeles and released by Peacock Records in late February 1953, "Hound Dog" was Thornton's only hit record, selling over 500,000 copies, spending 14 weeks in the R&B charts, including seven weeks at number one. Thornton's recording of "Hound Dog" is listed as one of the Rock and Roll Hall of Fame's "500 Songs That Shaped Rock and Roll", and was inducted into the Grammy Hall of Fame in February 2013. "Hound Dog" has been recorded more than 250 times. The best-known version is the July 1956 recording by Elvis Presley, which is ranked number 19 on Rolling Stone magazine's list of the 500 Greatest Songs of All Time; it is also one of the best-selling singles of all time.

"Hound Dog" (G2WW-5935) was initially released as the B-side to the single "Don't Be Cruel" (G2WW-5936) on July 13, 1956. Soon after the single was re-released with "Hound Dog" first and in larger print than "Don't Be Cruel" on the record sleeve. Both sides of the record topped Billboard's Best Sellers in Stores and Most Played in Jukeboxes charts alongside "Don't Be Cruel", while "Hound Dog" on its own merit topped the country & western and rhythm & blues charts and peaked at number two on Billboard's main pop chart, the Top 100. Later reissues of the single by RCA in the 1960s designated the pair as double-A-sided.  While Presley was performing "Hound Dog" on television and his record was scaling the charts, Stoller, who had been on vacation in Europe, was returning on the ill-fated final voyage of the Andrea Doria. On July 26, 1956, Leiber met the just-rescued Stoller on the docks and told him, "We got a smash hit on Hound Dog," Stoller said, "Big Mama's record?" And Leiber replied: '"No. Some white guy named Elvis Presley." Stoller added: "And I heard the record and I was disappointed. It just sounded terribly nervous, too fast, too white. But you know, after it sold seven or eight million records it started to sound better." Leiber and Stoller tired of explaining that Presley had dropped most of their lyrics. For example, Leiber complained about Presley adding the line, "You ain't caught a rabbit, and you ain't no friend of mine", calling it "inane...It doesn't mean anything to me." Forty years later, Leiber told music journalist Rikky Rooksby that Presley had stamped the hit with his own identity: "(A) white singer from Memphis who's a hell of a singer--he does have some black attitudes--takes the song over ... But here's the thing: we didn't make it. His version is like a combination of country and skiffle. It's not black. He sounds like Hank Snow. In most cases where we are attributed with rock and roll, it's misleading, because what we did is usually the original record--which is R&B--and some other producer (and a lot of them are great) covered our original record."  By August 18, 1956, Peacock Records re-released Big Mama Thornton's original recording of "Hound Dog", backing it with "Rock-a-Bye Baby" (Peacock 5-1612), but it failed to chart.

When was the song hound dog released ?
July 13, 1956.