Bacterial action in the cecum breaks down the large cellulose molecules into simpler organic compounds, like starches and sugars. The same thing happens to your lettuce or celery in the plastic grocery bag in the refrigerator and in the rumen of ruminants. Since the food bolus has already passed the absorption point, it must be recycled. On the second visit through the stomach and small intestine, additional substances are absorbed and the fecal pellet that eventually emerges is hard and dry. It is not known how the animals know which pellet-production cycle they are on.
Many rodents are notoriously prolific animals.
It is their prodigious reproductive rate that provides for their great adaptability and for our inability to control them. Litter size can be as high as 20 offspring, depending upon species. Biologists refer to these large litters as r- selected rapid reproductive rate. A large number of offspring ensures a few will survive. They are instinct driven and little care is given after the initial post-natal period.