Believe it or not there was a time when ZZ Top were a serious blues-rock band, one of the best that squandered their talent, probably after 1979's Deguello.
The track was based on a common blues lick (see John Lee Hooker's "Boogie Chillen" and Slim Harpo's "Shake Your Hips") but it obvious the boys know how to kick some arse when it comes to the 'one-chord blues'
The song refers to a brothel in La Grange, Texas known as the 'Chicken Ranch' popularised in a pretty terrible movie with Dolly Parton and Burt Reynolds
In recent years, when the band played the song in concert, it has become a tradition for them to abruptly stop playing in the middle of it, at which point Gibbons and bassist Dusty Hill shout out, "Hell yeah!" before resuming the song.