I’m sitting here watching my rabbit consume his own poop like it’s the last meal he’ll ever get but all I can do is watch him with a disgusted face since I know it’s necessary or something.
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Rabbits make a special kind of poop at night that’s really tasty and good for them so they eat it. They don’t eat all of their poop.
Camels and true ruminants like cattle and deer chew the cud. horses and rhinos ahve an enormous appendix. Rabbits do coprophagy. Ways to get a livable amount of nutrients from low-density plant matter like grass
Digesting plants is hard.
I’m not talking about all those succulent fruits and nuts. I mean stuff like grass, leaves, stalks – anything “structural”.
These items include very large amounts of a material called cellulose (and related compounds), which gives plants most of their structure. Any animal that lives primarily by eating such items must find a strategy for digesting cellulose, which it turns out is very hard to do and no mammal can do “naturally”.
Most mammals have developed strategies which rely on storing microorganisms somewhere in the digestive system and having them break down the cellulose into something that the mammal can digest. For animals like cows, deer, sheep, and camels (“even-toed hooved animals”, even though not all of them have hooves or an even number of them), they have a complicated multi-chambered stomach, and they pass grass (etc) back and forth between the chambers, occasionally “vomiting” it up into the mouth for further mechanical processing – this is what we call “chewing cud” in cows. These are called “foregut fermenters”, because the breakdown happens near the start of their digestive tract. Kangaroos also do something similar.
Some other animals like horses and rhinos (“odd-toed hooved animals”), elephants, rodents, and rabbits instead need their cellulose-digesting microorganisms further back – typically in an organ called a *cecum* (from a Latin word meaning “blind”) between the small intestine and large intestine. Here, the food is passed back and forth between the large intestine and cecum like foregut fermenters pass it back between their various stomach chambers.
Now, this means that the large intestine is doing most of the heavy lifting when it comes to absorbing the nutrients. But as it happens, the large intestine isn’t great at that. In most mammals, the absorption of bulk nutrients is done in the small intestine, and the large intestine mostly absorbs trace nutrients like vitamins and minerals, as well as water.
So some hindgut fermenters (rabbits, hares, and a closely related animal called the pika) instead found a way to take this post-fermentation food and give it another pass through the small intestine. Instead of shoving it all the way back inside the body, the material goes to the large intestine where it is dried out and compacted…and then it goes out the anus and back into the mouth. It’s quite analogous to a cow chewing its cud, just with an “outdoors” component. This pellet is called a *cecotrope* (“in the style of the cecum”) and is quite different from normal poop. We call animals that do this, *cecophages* which means “those who eat from the cecum”.
In hindgut fermenters that are not cecophages, the cecum itself and the front part of the large intestine are adapted to better absorb nutrients.
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