Dog food is formulated for omnivorous dogs with lower protein targets and typically no added taurine or sufficient arachidonic acid, so it misses feline requirements.
A cat sneaking a piece or two is usually fine; just watch for vomiting or diarrhea. The real danger is dog food serving as the long-term main diet.
Months of dog food can lead to taurine deficiency, poor coat, and muscle loss, with kittens and pregnant cats affected fastest.
In multi-pet homes, feed in separate zones, raise the cat's bowl, or use a selective feeder; if a cat has eaten dog food long term, get a vet assessment before transitioning.
