Hi Anna, my bridge bun Oliver had long term sludge issues with urine infections. The last time he had bad sludge none actually came out when he peed so just because it can't be seen dies not mean it's not there. The treatten for sludge when bad is a bladder flush to remove the sludge but xray needed to confirm enough sludge present to warrent the bladder flush. Oliver had this done 3 times once every year. He was alays more comfortable after the flush. I think sludge buns are more prone to uti's.