I will share a personal experience regarding sludge in the bladder. I had a sow who had a stone that we could see in her urethra and the Vet assumed that she was in the process of passing it. She also had loads of sludge in her bladder. X-ray taken on a Friday confirmed this. She was scheduled for an ultrasound on the following Tuesday. Over the weekend, I syringed copious amounts of water and unflavored Pedialyte (adds good electrolytes) to her in an attempt to move large quantities of fluid through her bladder and possibly flush out the sludge.
Comes Tuesday and the ultrasound revealed that the stone was lodged in the wall of her urethra......it was still there when she crossed the Rainbow Bridge.
However, there was NO sludge in her bladder! You may want to try this with your sow........it certainly won't hurt her and could do a world of good. If you're lucky, your cavy may just have a UTI. However, generally we see bacteria and cells if it is a UTI. Blood and protein may indicate that her kidneys aren't functioning properly.
All the best......please keep us posted.