Some Bill Haley rockers recorded before 1954:
Compare Haley's version of "Rocket 88" with Jackie Brenston's original on this website. Compare his "Rock The Joint" with earlier versions on this website by Jimmy Preston (1949) Chris Powell (1949) and Jimmy Cavallo (1951). The other two selections are Haley originals.
Some very early country and western ventures into rock 'n' roll, even before Haley:
Hardrock Gunter, from Birmingham Alabama, wrote and recorded some of the very first rock and roll songs in the C&W music scene. His "Birmingham Bounce," which he recorded in 1949, was covered by many black artists such as Amos Milburn and Lionel Hampton (with Albert Ammons on piano!). Gunter's first records were on the Bama (short for Alabama) label, although he recorded some of these same songs for Sun Records in the 1950's. His name "Hardrock" was not a reference to his hard rocking music, but was a nickname he acquired in childhood. He still plays live today.
Tennessee Ernie Ford, as was typical among country singers of the 30's and 40's, picked up on the boogie woogie movement. There were so many country and western singers doing boogies that music writers refer to "hillbilly boogie" and a style of music. Hillbilly boogie was popular from around 1946 to the early 50's when it was overshadowed by rockabilly. The main difference between the two was the backbeat. If you take any hillbilly boogie tune from the 40's and add a drummer playing a backbeat, it becomes rockabilly automatically. However, country and western bands of the 40's traditionally had no drummer. This tradition was about to change.
It's hard to say who was the first C&W artist to record rock and roll, since so much of the "hillbilly boogie" music of the late 1940's comes really close to sounding like it. The hillbilly boogie genre began after the war, and was made popular by Hank Williams and was influenced by the western swing of the 1930's, and it paralleled the advances in the black boogie woogie music which was still popular at that time. But it is this author's opinion that boogie woogie, either black or hillbilly, is not true rock and roll, because it lacks that hard solid backbeat which originated in black gospel music and first came into vogue in secular music, in my opinion, due to Wynonie Harris' 1947 version of "Good Rocking Tonight." But C&W music started to develop a backbeat on its own, due to recordings such as "Move It On Over" by Hank Williams, recorded in 1947, which really set the stage for rockabilly music of the early 50's. When the hard-rocking R&B of 1949 and 1950 was mixed with C&W music during that same time period, the product was rockabilly, which was the earliest form of white rock and roll (if you don't count the anachronistic Louis Prima, or the very early and unusually (for its time) wild rocking boogie of Harry Gibson).