On a recent trip to Davis Farmland, my daughter and I were stunned to learn that goats have not one, not two, but four stomachs.
It was hard to imagine why such a small animal would need four different stomachs. (Not to mention how a pregnant goat could possibly fit a baby or two in with all those stomachs.) It was clearly time to Ask the iPhone.
Turns out “goats have four stomachs” is sloppy shorthand for “goats have one very large stomach split into four compartments”: the rumen, the reticulum, the omasum, and the abomasum.
There are lots of explanations of how goat stomachs work on the web, but I find I’m rather partial to the one provided by the New York State 4-H.
As the 4H explains, when a goat chomps down on a mouthful of grass or hay, it chews its feed long enough to soak it with saliva before swallowing it down. (The swallowed clump of food is referred to as a cud.) The cud is sent first to the goat’s rumen, the largest chamber in an adult goat stomach, which serves as a sort of fermentation vat. Microorganisms in the rumen produce enzymes that break down the fiber in the cud, converting it into proteins, B vitamins, and other necessary nutrients. Fermenting the cud is a multi-step process. Periodically the goat will regurgitate the cud and chew on it for a while before swallowing it down again.
Once the cud particles are small enough, they pass to the reticulum, which removes any foreign objects that the goat swallowed with the feed before pushing the cud to the omasum.
The omasum extracts water and more nutrients, particularly fatty acids, from the cud particles before forcing the particles into the abomasum.
The abomasum is often referred to as the goat’s true stomach, because it digests food particles using hydrochloric acid (HCL) just as our own stomachs do.
From the abomasum, the food particles pass to the small intestine, which makes the extracted nutrients available to the body.
You may have noticed that I said that the rumen was the largest of the stomach chambers in an adult goat. That’s because the relative size of these chambers changes as the goat matures and its diet changes. Kid goats depend on milk, not roughage, for their nutrition. Consequently, the abomasum, which digests the milk, is the largest (and most useful) chamber in a kid goat’s stomach. The rumen grows over time as roughage gradually replaces milk in the goat’s diet. In a mature goat, the rumen is roughly 8 times the size of the abomasum.