Dog licking fur off tail (near butt).

Question
QUESTION: My 5 year old sheppard has been licking and licking his under tail, now the fur is removed to a 2 inch diameter, I recently moved to Florida, he is on heartguard and advantic, and we recently changed his food to Purina one, is it the food, and insect, what? So far I think there's no infection, its pink skin only?
Thanks, John
Thanks

ANSWER: I highly doubt it is the food.  It is always possible he is allergic to the lamb or chicken in it.

More likely it is his anal glands.  Take him to the vet.  The vet should empty them and perhaps do some other tests taking some skin scrapings.  If he has a reoccuring problem with the anal glands, you many find a groomer that will empty them for less than the vet.

---------- FOLLOW-UP ----------

QUESTION: since the under tail licking, the dog started in a new spot above his butt, hip would be a better place I guess, he licked and bit it so much a lump is there now, but the fur isn't licked off, I put a vid. E oil on the bald area and bought Tee  Tree Oil to put in the area that he's licking, so far its working, do you still think it's the Anal Gland now that he's licking some where else?
Thank, Merry Christmas,
John

Answer
He has tried licking one spot, and it didn't work, so he is trying another.  I can't say for sure if it is the problem.  It is easy to check, and if it isn't the anal glands, he is going to have to see the vet to find out what it is.  it is highly unliky it is anything a home remedy will clear up.