Cooking spinach releases some of the nutrients that are bounded in the plant's cell wall and makes it more bioavaialble for your pup. Cooking spinach also makes it easier for dogs to digest and absorb the nutrients. Spinach are high in nutrients such as vitamins A, C, K, iron and calcium - which are all essential for your pup's overall health. Adding cooked spinach can promote healthy digestion and also help keep your pup hydrated as spinach has very high water content.