The biggest concern with cranberry juice is the sugar in it. Otherwise, it has been used for urinary issues, with mixed results. There is a more concentrated extract you can find in health food stores but it would be best to contact your veterinarian for a dosage of this. I would follow your veterinarian's instructions for diet, as a urinary-specific veterinary diet is often very helpful to help control symptoms. Encouraging more fluid intake through canned food can also help. I'm glad Chase is doing better but don't forget that if he is straining in the box and not producing any urine...this is an absolute emergency! And best of luck to your daughter in her desire to become a veterinarian.
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