Rabbits do not get kidney failure like dogs from ingesting grapes. However, I do not recommend feeding your rabbit grapes. Fruits are high in sugars and grapes are not normally a part of a rabbit's diet. They do not need nor can they handle much fruit. They have a very sensitive gastrointestinal tract and the normal bacterial flora is easily disturbed. A rabbit's diet should be high in fiber consisting most of fresh timothy hay available at all times. A pelleted rabbit diet should also be fed. Vegetables and treats should be fed sparingly and comprise no more than 10% of the diet.
