Since, chicken don't have teeth, they swallow small stones which are stored in gizzard for grinding of food that they eat.
Rabbits are herbivorous. Bacteria in their gut digests the food and packs it into green spherical pellets.
Dogs have a very short digestive tract and hence, they can process, absorb and release the waste in just 6 hours.
Cows belong to the class of animals called ruminants who regurgitate the partially digested food to chew it again. This helps them to break down huge load of fibers in their food.