Dogs can eat cabbage, and many enjoy doing so. Cabbage is rich in vitamins such as K and B6 and contains a large amount of dietary fiber. However, long-term consumption of raw cabbage can cause hypothyroidism in dogs.
Dogs are primarily meat-eaters, but they still need a certain amount of vegetable matter to get all the nutrients they need. In particular, fiber keeps the digestive system running at an even pace, but it is hard to come by in a diet based entirely on meat.
Cabbage provides plenty of fiber, though not without some side effects. It can cause flatulence and loose feces in dogs. The sulphur compounds in cabbage cause feces to become unpalatable to dogs that frequently eat animal waste. Cabbage also contains a compound called thiocyanate that suppresses thyroid function, but this effect can be avoided by only feeding cooked cabbage, never raw.