Dog birthmarks

[Snappy]

My 6month black lab bitch has a patch at the top of her tail where the roots of the hairs are grey. Its about the size of a 50p and feels very coarse, its only at the roots so you cant see it unless you part the hairs. Is this a birthmark?

[Noweia]

Dogs have a gland located at the top side of the tail, near the body, called the supracaudal gland, or supracaudal organ. The hair over the gland can be coarser and a different colour to the rest of the body coat. Could this be what you're seeing?

[Snappy]

I though this was only present in foxes?

[Noweia]

All dogs have them, cats too, it's just more prominent in wild canids e.g. foxes and wolves.