The bluehorn was a herd animal native to the Skagaran colony planet.
Bluehorns were considered very hardy animals and could be raised on ranches even in the harshest climate. (ENT: "North Star")
This animal was thought up by Chris Black, when he wrote references to them into the "North Star" script. Their name was based on the fact that several breeds of cattle are, in reality, called "longhorn". With a laugh, the episode's official writer, David A. Goodman, described bluehorns as "some kind of bull animal [...] that is blue". Black imagined that "bluehorn ranching" might be an industry on the Skagaran colony planet. Concerning bluehorns in general, he reckoned, "On the one hand, I guess that kinda makes sense, that there would be indigenous livestock or wildlife here, that they would raise and eat and whatever. But [...] also, when you write these things, you sort of tickle yourself with these [references]." ("North Star" audio commentary, ENT Season 3 Blu-ray special features)
According to the Star Trek Encyclopedia, 4th ed., vol. 1, p. 89, the bluehorn was used for meat, dairy products, and hides. In a note to this entry, the authors raised the possibility that the bluehorn were brought to the planet, along with Humans and horses.