Kentucky cops will write you a DUI if you ride a horse drunk. The fellow whose circumstances proved this to the rest of us was carrying a jar of "moonshine" at the time. Lowering the Bar has some legal analysis of the bust. Good thing the horse was sober when he got pulled over, or there would have been an additional count of cruelty to animals.
And things are not looking good for him otherwise. The statutory language is better than the title: "No person under the influence of intoxicating beverages or any substance which may impair one's driving ability shall operate a vehicle that is not a motor vehicle anywhere in this state." Okay, but what is a "vehicle not a motor vehicle"? I think a skateboard or scooter would qualify, or even a Big Wheel. The Flintstones car would count. Surely someone in Kentucky has one of those. But can a living thing be a "vehicle"? Yes, people ride around on them, but to me the common meaning of "vehicle" just doesn't include a horse (elephant, lion, Sasquatch, whatever). A vehicle is a machine.
There is some support for this elsewhere in the statutes. The one above refers to "driving" ability. "Driving" is not the same as "riding" when it comes to animals, according to television. You would "ride" a horse during a cattle "drive," for example; you don't "drive" a horse. And look over here at Section 189.310, "Vehicles meeting other vehicles and animals," which not only distinguishes between "vehicles" and "animals" but also makes the riding/driving distinction. That seems unnecessary if every animal you could ride is also a vehicle, doesn't it?
All very interesting, said no one, but aren't there often statutes that define certain legal terms? Yes, and there's one here. And sadly for Rooster Cogburn, it defines "vehicle" as including "All agencies for the transportation of persons or property over or upon the public highways of the Commonwealth.…" So while I still like my "animal is not a vehicle" argument, Kentucky has precluded it.