Most dogs who eat cat food will be absolutely fine, especially if it’s just a one-off. But cat food is high in protein and fat and will be too rich for some dogs. You should be especially careful about letting your dog eat cat food if your dog has a sensitive stomach, kidney disease, liver disease, or a history of pancreatitis.
Unless your dog has an underlying illness, it’s ok to feed a dog cat food in an emergency. However, some dogs will get vomiting or diarrhea as cat food is richer than dog food. If your dog has an underlying illness like kidney disease or liver disease, or is prone to an upset stomach, it’s best not to feed them cat food.
Cat food is usually higher in protein and fat compared to dog food. This makes it more palatable (tasty), so it’s common for dogs to prefer cat food to dog food. If your dog isn’t enjoying his food consider looking for something a little higher in protein, assuming they don’t have any conditions that would make this a bad idea of course!