I've heard that it takes cows and other ruminants a lot longer to digest their food, compared with animals such as wolves or humans. Time of digestion depends largely on the type of food an animal ingests. Carnivores live high on the food chain. They eat only other animals, which turn out to be relatively easy to digest. Hence, their digestive systems are short and uncomplicated and the process of digestion is rapid.
Omnivores eat at all levels of the food chain.
As a result, they require a balanced digestive system that can handle both plant and animal. Herbivores eat plants, which form the foundation of the food chain but are the toughest to digest. Thus, herbivores sometimes employ a variety of digestive tricks to do the job, from multiple stomachs to reliance on certain kinds of microorganisms to do the bulk of their digestive work. For them, extracting nutrients and reducing food to waste is a long process. In one study, for example, it took deer 15 hours to digest a meal of dry alfalfa.