I just switched to fleece bedding and noticed some white gritty urine recently over the past week or two. I'm relating it to too much calcium in their diet. I have two 5-month old piggies so I'm feeding them unlimited
Cavy Performance which is alfalfa (more calcium than timothy) based, and in addition to the usual lettuce/tomato/carrot/fruit, for the past 2 weeks I was feeding them about 15-20 grams of parsley (high calcium) to each piggy every 2-3 days. If any of you think it's another reason, please say so!