Why don't rats do not have a gallbladder?

Rats, like some other rodents, lack a gallbladder because their diet is primarily herbivorous and consists of high-fiber plant materials. This diet allows for a continuous flow of bile directly from the liver into the intestines, which is more efficient for digesting such fibrous foods. The absence of a gallbladder means they do not need to store bile, as their feeding habits allow for constant digestion and nutrient absorption.