Hills DD, Hills Prescription Diet DD is designed for the nutritional management of cats & dogs with food allergy and or food intolerance. Hills Prescription Diet DD comes with novel / new protein sources to help manage pets with such adverse reactions to food. Commonly, food allergy and food intolerance is often caused by beef, dairy products and wheat. Hills Prescription DD foods contain none of these. Once you have been advised to use one particular flavour it is advised you do not alter this unless specified by your vet.