A Cowboy's Dog

A cowboy rides into town on a hot blistering day riding his horse with his dog following. He ties his horse and dog under the shade of a tree and goes into the bar for a cold beer.
About twenty minutes later a policeman comes in and asks who owns the dog tied under the tree.
The cowboy tells him that its his.
The policeman says, "Your dog is in heat."
The cowboy answers, "No way the dog's in heat; he's cool cause he's tied under the shade of the tree."
The policeman says, "No! you don't understand, your dog needs to be bred."
The cowboy shakes his head and says, "No way dog needs bread, he's not hungry, I gave him beef jerky this morning."
The policeman finally gets mad and says, "Look, your dog wants to have sex."
The cowboy looks at him and says, "Go ahead; I always wanted a policedog!"