Why does cow eat grass

The rumen has a capacity of approximately 40 gallons and is the primary site of digestion and absorption of nutrients.

It is covered with finger-like papillae which increase the surface area and allow for greater absorptive capacity. The rumen is home to a diverse microbial community made up of many species of bacteria, protozoa, and fungi. The relationship between the microorganisms and the cow is symbiotic, meaning it is beneficial to both. The wet, warm, anaerobic environment is a place that microorganisms can thrive, and the cow derives energy and protein to meet its nutrient requirements.

Microorganisms secrete enzymes with break down large pieces of fibrous material, specifically cellulose, and create volatile fatty acids or VFAs.

Volatile fatty acids acetate, propionate, and butyrate are absorbed as an energy source for the cow. Microbial protein is also produced in the rumen and is passed on to be digested later. The cow also gets rid of excess gases created by the microorganisms through eructation.

Eating vegetable matter only does not provide many calories. We all know this-think dieters and salads. Cows eat grass because grass and other forages plants the cow can eat are the food source cattle are biologically designed to eat.

Grass grows all over the world. Cows can eat the grass fresh from the plant or can eat it dried and stored in a barn to be feed later in the year. This dried and stored grass is called hay.

Grass has the ability to remain nutritious through the winter. Even when the grass is dormant not growing cows can eat any of the plant that is still standing from the previous growing season. Many farmers keep their cows out of some of the pastures leaving the grass to grow then be eaten by the cows in the winter. This is also why wild herds of grass eaters move around-they are looking to find an area of grass to eat in the non growing season.

Eating grass is called grazing. When a cow gets her lunch from the grass out in the field she is grazing. She eats by wrapping her tounge around a hunk of grass to hold it then kind of sawing off the blades of grass with a sideways motion of her lower teeth against the top ridge of her jaw.

Cows can survive on grass because of a special digestive system that makes a cow and other grass eaters like her able to digest things that animals like us cannot digest. A cow has a four compartment stomach that allows her and other animals with the same special stomach to get nutrition from plants.

Animals like us with a more simple stomach cannot get nutrients from the plants the cow is eating. The ability to digest these plants is what makes the cow a ruminant. A ruminant is an animal capable of digesting plants that we cannot because of her digestive system-specifically the four compartment stomach. Her stomach has millions of organisms mostly bacteria that allow her to get nutrition from grass.

She will eat grass or other forages until she feels full then she will chew her cud. Chewing her cud means she makes little bundles of grass and brings it back up to her mouth in order to more completely chew the forage fibers. Her single celled workforce all the organisms in her stomach need well chewed food so they can utilize all of the energy and nutrients the forage has to offer. Cows like to take in all of their grass as quickly as they can so they can get to chewing their cud.

A cow is actually only eating if you are seeing the grass or hay go into her mouth and be swallowed. These tiny organisms then release nutrients into the rumen. Some nutrients are absorbed right away; others have to travel to the small intestine before being absorbed. In Figure 2, notice that the rumen wall resembles a shag carpet or the imitation wool on the inside of a winter coat.

The papillae give the rumen wall this texture. The next pouch in the stomach is the omasum letter D, Diagram 1. This pouch acts like a giant filter to keep plant particles inside the rumen while allowing water to pass freely.

By keeping grass pieces and other feed inside the rumen, bacteria have more time to break them down, providing even more nutrients for the cow. Figure 3 shows the multiple layers of the omasum.

After the grass pieces and other feed are broken down to a small enough size, they eventually pass through the omasum and enter the abomasum letter E, Diagram 1. The abomasum, then, is located just beyond the omasum. This illustrates a similarity in function. You see, the abomasum has the same basic function as the stomach of the dog, man, or other mammal, which is the production of acids, buffers, and enzymes to break down food.

After passing through the abomasum, partially digested food enters the small intestine where digestion continues and nutrients are absorbed. The rumen efficiently extracts nutrients from food other animals cannot digest. For this reason, cows can eat plant materials such as seed coats, shells, and stems that remain after grains are harvested for human consumption. 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.

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. CVM Kid's Page.