(Dietary) food for cats is specially formulated based on the nutritional requirements of cats. These are different from the requirements of dogs. Cats are not able to produce taurine. Feline diets are adjusted to compensate this inability to synthesis these metabolites/nutrients. It is not harmful to feed dog food to your cat for a short period. However, when feeding dog food to your cat for a longer period, deficiencies will develop and your cat can become ill.