Rabbits and cecotrophy
Rabbit in a grassy cage, by Madeleine / Flickr
Rabbits, are unique in the sense that they practice cecotrophy. Cecotrophy is the act of eating cecotropes or "soft feces". This sounds similar to coprophagy, but it is not the same process. In the rabbit, small fiber particles are "selected" in the GI tract and sent to the cecum where they are fermented to synthesize proteins and vitamins, which will be part of the cecotropes. On the other hand, large particles are sent to the colon to form the regular or hard feces. Cecotropes are different from feces in that they are higher in moisture and protein than feces. Cecotropes are consumed directly from the anus in the early morning hours, therefore making difficult to see these feces. The function of cecotrophy is to provide the rabbit with the proteins and vitamins that were synthesized in the cecum and prevents these nutrients from being lost. It is a very important process, because it can provide up to 20% of their daily protein requirement.