Storm1974
Junior Guinea Pig
My boys love the leaves of this (Common variety, not Giant!) and I was just reading about the health benefits of them (for people) and it sounds like they could be very good for preventing bladder stones (as well as the stated kidney stones), so a good addition to our piggies diets IF they like them! 
'Benefits for Kidney Disorders
Ancient ayurvedic texts such as Charaka Samhita and Sushruta Samhita have mentioned punarnava as an excellent medicine for renal diseases. In addition, Punarnava is believed to have anti-urolithiasis properties, thanks to the prevention of deposition of calcium oxalate stones owing to its ability to counter the oxidative stress that results in excessive oxalate excretion in the urine.
Moreover, punarnava contains the diuretic compound punarnavine, which can further help flush kidney stones by increasing urination. Other benefits associated with flushing out excess water from the body also come to the fore, such as preventing conditions like dropsy and ascites'. (3)
10 Best Punarnava Benefits and Side Effects - Weight Loss, Kidney, Liver, Eyes

'Benefits for Kidney Disorders
Ancient ayurvedic texts such as Charaka Samhita and Sushruta Samhita have mentioned punarnava as an excellent medicine for renal diseases. In addition, Punarnava is believed to have anti-urolithiasis properties, thanks to the prevention of deposition of calcium oxalate stones owing to its ability to counter the oxidative stress that results in excessive oxalate excretion in the urine.
Moreover, punarnava contains the diuretic compound punarnavine, which can further help flush kidney stones by increasing urination. Other benefits associated with flushing out excess water from the body also come to the fore, such as preventing conditions like dropsy and ascites'. (3)
10 Best Punarnava Benefits and Side Effects - Weight Loss, Kidney, Liver, Eyes