Ruminating White-tailed Deer

White-tailed deer are ruminants; that is to say, they ruminate. Rumination is the process of chewing and swallowing food, regurgitating it in a partially-digested form called "cud," then chewing and swallowing it again. It may sound gross, but it is a key part of a fascinating digestive system.

Here is video of a white-tailed deer doe ruminating. Watch her throat after she swallows, and you can see the cud come up! 

Pretty cool, huh?

There are about 150 species of ruminants in the world, including cattle, goats, sheep, giraffes, yaks, deer, antelopes, and even some marsupials. Excepting the marsupials, all ruminants are ungulates, or hoofed mammals. Ruminants have crazy, multi-chambered stomachs. You may have heard that cows have four stomachs, which is not strictly true; they have four-chambered stomachs.

Below is an MS Paint masterpiece, by yours truly, that shows how food passes through the ruminant digestive system.

First, the plant matter is chewed and swallowed and enters the rumen, by far the largest compartment, where it is attacked by billions of bacteria and begins to ferment. Then, the food particles pass into the reticulum. This chamber acts like a filter, only allowing tiny food particles to pass into the omasum. If the food particles are too large to pass on, they are regurgitated, chewed and swallowed again, often multiple times, until the combination of chewing and bacterial fermentation breaks them down enough. In the omasum, water and salts are absorbed from the food before it finally enters the abomasum, the "true stomach." The abomasum contains acid that breaks down the food before it enters the intestine, much like our own monogastric (single-chambered) stomach.

So, there you go. That was your biology lesson for the day. Now, since this is supposed to be a wildlife photography blog, enjoy these photos of white-tailed deer (with a few raccoon interlopers):