How Do Cows Eat Grass

January 15, 2014

Digestion is the process our bodies use to break down and absorb nutrients stored within food, but the ability to digest food is not the same for all animals. Cows, for example, have a very different digestive system than our own, and this allows them to thrive on a diet mainly made up of grass.

Let’s explore how cows are able to eat grass. The key to this ability lies in the cow’s four-compartment stomach. As humans when we chew and swallow our food, the stomach serves as a holding tank where digestion begins and food begins separation into individual nutrients. Next, food passes into the small intestine where the breakdown continues and where the body absorbs nutrients. This basic digestive process is also true of cows, but there are a few extra steps along the way.

 When a cow first takes a bite of grass, it is chewed very little before it is swallowed. This is a characteristic feature of the digestion in cows. Cows are known as “ruminants” because the largest pouch of the stomach is called the rumen. Imagine a large 55-gallon trash can.

In a mature cow, the rumen is about the same size! Its large size allows cows to consume large amounts of grass. After filling up on grass, cows find a place to lie down to more thoroughly chew their food. “But they have already eaten,” you might be thinking. This is true, but cows are able to voluntarily “un-swallow” their food. This process of swallowing, “un-swallowing”, re-chewing, and re-swallowing is called “rumination,” or more commonly, “chewing the cud.” More on cud chewing here. Rumination enables cows to chew grass more completely, which improves digestion.

1. The Rumen - this is the largest part and holds up to 50 gallons of partially digested food. This is where the 'cud' comes from. Good bacteria in the Rumen helps soften and digest the cow's food and provides protein for the cow.

2. The Reticulum - this part of the stomach is called the 'hardware' stomach. This is because if the cow eats something it should not have like a piece of fencing, it lodges here in the Reticulum. However, the contractions of the reticulum can force the object into the peritoneal cavity where it initiates inflammation. Nails and screws can even perforate the heart. The grass that has been eaten is also softened further in this stomach section and is formed into small wads of cud. Each cud returns to the cow's mouth and is chewed 40 - 60 times and then swallowed properly.

3. The Omasum - this part of the stomach is a 'filter'. It filters through all the food the cow eats. The cud is also pressed and broken down further.

4. The Abomasum - this part of the stomach is like a human’s stomach and is connected to the intestines. Here, the food is finally digested by the cow's stomach juices and essential nutrients that the cow needs are passed through the bloodstream. The rest is passed through to the intestines and produces a 'cow pat'.

The rumen efficiently extracts nutrients from food other animals cannot digest. For this reason, cows can eat plant materials (such as shells, and stems) that remain after grains are harvested for human consumption. These remaining materials are sometimes called “by-products.” Feeding by-products helps farmers and businesses save money by not having to pay to dispose of these extra materials and make money by selling the by-products as animal feed.

When oil is extracted from grains (for example, soybean oil from soybean seed and Canola oil from rapeseed), or grains are used to brew alcohol or make fuel-ethanol, plant by-products are made. Although key nutrients (like fat, sugar, and protein) are removed from the plant materials during processing, when used properly, these by-products can be fed to cows. The complex nature of their four-compartment stomachs and their rumen bacteria allow cows to eat and thrive on plant by-products that other animals cannot digest.

The better we understand the cow’s digestive system, the better we are able to formulate diets and manage our herds for the optimal production of the nutritious meat and milk we routinely enjoy. So, the next time you have a cool glass of milk, a cup of ice cream, or a juicy hamburger, you will know that these products came from cows fed grass, grain, or by-products, and you will know, How Cows Eat Grass.


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