No, cats cannot nurse from a dog. Cats are obligate carnivores, meaning that their bodies are designed to digest and use only animal-based proteins. Dogs are omnivores, meaning they can digest both plant and animal based proteins. The difference in digestive physiology between cats and dogs means that cat milk contains far higher levels of protein than dog milk. For a kitten, this high level of protein is essential for proper growth and development. Nursing from a dog would not provide the necessary nutrition for a kitten and could actually be harmful.