The "brown chicken, brown cow" joke is a joke consisting of a sexy question related to farming and followed by the punch line "brown chicken, brown cow." For example, one version of the joke asks, "What are the sexiest animals on a farm?" And the punch line is "brown chicken, brown cow." This is meant to be funny as "brown chicken, brown cow" sounds like "bow chicka bow wow."
When said quickly, the words "brown chicken, brown cow" sound like the classic music from a pornographic film, and this phrase is easily applied to a number of sexy farming situations to make a joke. Another version of the joke asks, "What animals did Farmer Joe and Farmer Betty see while they were alone in the barn?" The punch line is the same.
The line is also included in a Trace Adkins song. The song tells the story of two rural residents, Bobby Joel and Betty. After working hard in the hot sun, these two people climb into the hay loft. In spite of hay, cows and corn that need their attention, the couple shucks off their work clothes in the barn loft, and the chorus of the song gives a glimpse of what they may be doing: "Singin' brown chicken, brown cow/ (Ain't nobody watchin' but the) / Brown chicken, brown cow / Yeah."