Struvite bladder sludge

Question
On Aug. 31, my neutered 6-year-old boybun was found to have significant struvite bladder sludge on palpation and radiography, to the extent we almost thought he had urolithiasis.  Urinalysis showed normal pH and few bacteria.  I began to give him 50 ml Lactated Ringer's Solution SC twice daily.  Repeat x-ray and physical exam on Sept. 4 showed improvement, so I decreased his fluids to 50 ml once daily.  We plan a repeat physical and x-ray on Oct. 2.  His daily diet consists of unlimited grass hay, two big handfuls of fresh wet greens (no spinach, kale, swiss chard, beet greens, carrot tops, dandelions, kale, collards, or bok choy), a pineapple chunk, several fresh cranberries, and willow tree twigs.  The question is, what is causing the struvite crystalluria and what can we do to treat it and to prevent a recurrence?  I've heard it suggested that cystocentesis and urine culture might reveal a UTI as a possible cause, despite the absence of significant bacteria on his previous urinalysis.  Is this a risk worth taking?

Answer
Dear Wendy,

Some rabbits develop bladder sludge simply because they have metabolic bone disease.  It comes with age, and there is little to be done about it except make sure bun gets plenty of Vitamin D (indirect sunlight for 15 minutes a day will help) and exercise to keep his bones healthy and his bladder sludge suspended so it can easily pass.

It's true that sludge can sometimes be triggered by a cryptic infection, but whether a cystocentesis will reveal it is questionable.  If there are signs of a UTI (straining to urinate, white blood cell casts in the urine, strong smell to the urine, etc.), then ask the vet about simply treating with an antibiotic that is likely to have a broad enough spectrum to kill the most likely bacterial culprits.  Baytril/ciprofloxacin might be a good first choice.  Coupled with amikacin (with lots of subQ fluids, and usually for no more than 5 days), you should be able to nail just about any of the most common bacteria that cause UTIs.

If this were my bun, I'd skip the cysto.  I've just never had a cysto reveal anything helpful.

Hope that helps.

Dana