Why do cows chew cud?

Cows chew cud to efficiently digest fibrous plant material, such as grass, which they cannot break down directly because their bodies lack the necessary enzymes to digest cellulose.12

When a cow eats, it swallows food quickly without thorough chewing, storing it in the rumen—the first of four stomach compartments—where the material softens and undergoes fermentation by microbes. Later, while resting, the cow regurgitates this partially digested food, known as cud, to chew it again. This process breaks down the tough plant fibers, allowing the food to pass into the remaining stomach chambers for further digestion and nutrient absorption.132

Beyond digestive efficiency, scientists believe this behavior evolved as a survival strategy. By consuming food rapidly in the wild, cows could minimize their time spent exposed to predators, retreating to a safe location to chew and digest their food later.3