Occational urine odor

Question
My Shitzu, 15 month spaded female. On occasion, about once every 2 week, she produces a very strong urine/amonia smell. The odor appears to come from her anal area, like a fart (excuse my french). There is no liquid of any kind and what ever she is laying on the odor becomes attached and must be washed immediately. We immediately bathe her bottom area and clean her and dry her. She is then fine until the next time. This has been going on for about 9 months. We feed her only "Natural Choice" chicken meal, lamb and rice, and biscuits from the same company. Never any thing else, only dog food.
Any idea what may be causing this and is this normal with Shitzu's?

Answer
Hello Ed,  I believe you might be smelling the results of her anal glands.  Some dogs drag their rear to express the anal gland sacks and some of this may be still on her hair in that area.  And yes, this will smell similar to a "fart"  When she is groomed the groomer should express the anals for you.  This would reduce the lilkely hood of her dragging her rear and getting it on her hair.  If you do not get her groomed then a visit to the vet will solve this problem.  Good luck with this.  Thank you, Cindy Lou :)