Not all nutrient sources are equally digestible. For example, the iron in organ meats has higher bioavailability than iron from plant sources, and calcium from bone meal absorbs differently than calcium carbonate. Pet food quality depends not just on listed nutrient percentages but on how much the animal actually absorbs. Factors affecting bioavailability include ingredient quality, processing methods, nutrient interactions (vitamin C enhances iron absorption), and the individual pet's digestive health. This is why two foods with identical guaranteed analyses can produce different health outcomes. Choosing foods with named animal protein sources and minimal heavy processing generally supports better nutrient absorption.