The short answer: It is not recommended.
The long answer: Though dog and cat food may look the same, their composition and nutritional content vary greatly. Dogs are omnivores and derive energy and nutrients from a diet consisting of plants and meats, so your pooch should get his daily recommended amount of carbohydrates, protein, fats, vitamins, and minerals from his kibble.
Meanwhile, cats are obligate carnivores who acquire energy and nutrients from a diet consisting of meat. Since cat food is made up mostly of protein, it is not wise to feed it to your dog because it may upset his stomach, causing vomiting or diarrhea. It may also be hard on his liver and kidney to have too much protein. If your dog is fed cat food regularly, he may be at greater risk of becoming obese and getting pancreatitis.
What to do if your dog accidentally eats cat food: If your dog munches on a piece or two of cat food, it should not be a problem. Some trainers and owners actually use cat food as training incentive for their dog because of its delicious, high-protein taste.
However, if your dog reacts badly to eating cat food, bring him to the veterinarian immediately. If he vomits or has a bad case of the runs, it means his gastrointestinal system cannot handle it.
In summary: Cat food is high in protein, fat, and taurine—all of which are not good for your dog in excessive amounts. For him to function at his best, he needs to eat a balanced diet packed with fiber, protein, and nutrients which he can get through his dog food. Make sure to segregate your dog and cat’s feeding areas to prevent your pets from eating something that isn’t meant for him. (Yes, your cat shouldn’t eat dog food, too!) Also, store your cat food properly so your dog won’t have easy access to it. Instead of feeding him cat food, discover what your pooch can safely eat in our “can dogs eat” category.