A vet is warning pet owners to beware after seeing an unexpected rise in the number of guinea pigs with bladder stones.

It is very rare for the tiny rodents to develop the condition, and Julia Mewes hasn’t seen a case for 25 years.

However in recent weeks she has treated two guinea pigs for the problem.

Ms Mewes, who runs the Mewes Veterinary Clinic in Haywards Heath, said: “Of all the uncommon conditions I might be asked to treat, bladder stones in a guinea pig is one of the most unusual. I have not seen a single case since I was a newly qualified vet but in the past three weeks I have seen two.”

Guinea pigs Zola and Tufty, from different families, were both brought into the clinic for treatment.

They have each had surgery to remove the stones and are recovering well, but the reason behind how they developed the stones is still a mystery.

Ms Mewes said: “I can’t help but wonder why they have both developed this ultra-rare condition, and why now? Will I be seeing any others in the near future?

“Guinea pig bladders are about the size of my little fingernail, and stones can only be removed by surgery.

“Of course, the owners will also need to be willing to pay for the procedure to be done and to help their little pet to recuperate afterwards.”

Bladder stones are typically formed from calcium deposits so owners are recommended to feed their pets low-calcium diets to reduce the risk of stone formation.

It is also important to keep fluid intake high, by wetting their food and adding cucumber to the diet.

Filtering hard water to reduce calcium levels and impurities can also be beneficial.