How Chewing the Cud Works


You might be familiar with the term “chewing the cud.” It is an expression that is used to refer to mulling over an idea in your head or thinking intensely about something. The picture you get is of someone rotating a thought over and over in their head, and that’s how the phrase came to be. If you have ever been to a farm, you might have noticed how some of the animals were continuously chewing. Animals like cows literally chew the cud. They keep turning the food they have eaten in their stomachs in an interesting and unique process. This article looks at how that works and answers many often-asked questions about this.

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A Stomach Made for This

Cows are not the only animals that chew their food over and over again. They are part of a special group of mammals that feed on plant matter. These are known as ruminants and include herbivores such as sheep, cattle, goats, antelopes, deer, and giraffes. All in all, around 200 species of mammals fall into this category. Their plant-based diet requires them to be able to get all the nutrients from the grass and leaves that they eat. This makes them different from meat-eating animals like lions and omnivores that feed on everything like human beings.

Ruminants are wired differently. They have a specialized digestive system that allows them to process the food they eat. Their stomachs have four different compartments known as the rumen, the reticulum, the omasum, and the abomasum. Each plays a role in the special digestive pathway of these animals.

Another unique part about the ruminants is that they have enzymes that can breakdown complex carbohydrates such as cellulose. Cellulose makes up the cell walls of plants, but animals such as human beings are not able to fully break these down because we do not have the requisite enzymes. Instead, after chewing different plants such as fruits and vegetables, the cellulose makes up the roughage that is egested, still intake chemically, as waste.

In ruminants, the plant matter eaten is broken down through fermentation. Microbes present in the stomach cause the chewed food to start fermenting. This is regurgitated back to the mouth for a second round of chewing to further break it down. It is an intricate digestive process which takes some time, but it allows the animals to prepare the food eaten to be fully digested in the intestines.

What Is the Cud and When Is It Chewed?

The cud that these ruminants are so famous for chewing is the partly digested food that is brought back to the mouth from the first stomach. This allows for a second round of chewing.

Food that is taken in is chewed and moistened, then swallowed. It goes to the rumen where it is softened with digestive liquids. This soft cud is returned to the mouth through the muscle action of the rumen. There it is chewed and swallowed and proceeds to the omasum where the moisture is squeezed out. It enters the abomasum, mixes with more digestive juices, then heads to the intestines.

Interesting Facts

Thankfully, the detailed process of digestion happens naturally without having to think through each step, because for ruminants, there are quite a lot of them! Interestingly, a cow chews the cud for as many as eight hours a day. Add to that the time it takes for them to chew the food the first time around. This is because cellulose in the plant cells is a very strong and rigid substance, so it takes a lot of physical and chemical effort to break it down. It is estimated that cows undergo over 40,000 jaw movements per day.

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