uti

I have a 7 1/2 month old lab with constant urinary tract infections.  She's been on meds for most of her life and has had an ultrasound. I just came from a different doctor.  I believe he has diagnosed the problem, I can't think of the name of it. I just had her urine retested and all is cleared up for now except the crystals.    She still has the crystals in her urine and he believes that is causing the problem   She's on different antibiotics and presciption dog food.  I have to have her retested in a month.  My question is, what causes the crystals?

[Aleda M Cheng, D.V.M., C.V.A]

Dogs can produce crystals such as struvite and calcium oxylate, among others just from their diets, and the individual dogs propensity to use the ingredients to produce stones.  The ultrasound was performed to determine if she had urotiths which are crystals that have combined to cause stones.  These stones can be too large to pass in her urine and she would need to have them surgically removed.  The ultrasound would also help to determine if she has an anatomical problem to her bladder and urethra.  Some stones form more easily in acidic urine and others form more easily in alkaline urine.  Your veterinarian will try to manipulate your dogs diet to help prevent the production of whichever crystals she is producing.  Some female dogs can also have something anatomically wrong with their vaginas.  This kind of problem allows urine to collect in the vaginal opening and sit too long which can also cause infections.  This problem may pass as your dog matures or may have to be surgically corrected at the time of spaying.