Did you know? Dogs have a special gland on their tail known as the supracaudal gland. At times, the dog's supracaudal tail gland may get infected. Stud tail, also known as tail gland hyperplasia or supracaudal gland infection, is caused by the inflammation or infection of this gland and it's often found in intact male dogs as there's belief it's testosterone induced.https://en.wikipedia.org/wiki/Violet_gland#/media/File:Viol-Gland-dog.jpg