Commonly heard in smoke filled gambling holes in reference to a horse who has performed in a sub par manner and has usually cost a bearded old coot his fortnightly welfare cheque.
Often implies the animal in question may be only a short trip away from the glue factory.
Carn ya nag daddy needs a new bottle o moonshine!
Damned old nag! now i'm gonna have to beat my kids for their pocket money so i can get drunk tonight!