36 Fore stomach, true stomach, red stomach, blue stomach

Introduction

Have you ever driven by a farm and seen a horse or cow munching on grass? Have you ever thought about why we can’t eat grass?

Grass can’t be digested normally because it is made up of particles that are really hard to break down in normal stomachs. If you can’t break down grass into little pieces, then your body isn’t able to receive all of the important nutrients from it. Some animals have very special parts in their digestive system that allow them to break down grass.

Learning objectives

1. Identify the important GI structures in the horse
2. Identify the important GI structures in the cow
3. Compare and contrast the functional anatomy of the GI tract in a horse and cow

Review material

Horse Anatomy

When a horse eats food, it moves through their esophagus to their stomach where digestive particles that break down food are secreted. Next, the food will move to the small intestine where it is further broken down. The small intestine is also an important location for nutrient absorption. After the small intestine, the food is moved to the large intestine where grasses can be fully digested and used for energy. The large intestine is made up of the cecum, colon, and rectum. The cecum is an extension off of the colon. Once food is done digesting in the large intestine, leftover food is turned into poop. Poop will pass through the rectum and then be excreted.

The cecum and the colon contain good and helpful bacteria (microbes) that allow the horse to break down the grass they ate. The colon is very long to allow the horse maximum time for their body to absorb nutrients from their food.

Cow Anatomy

When a cow eats, the food moves through their esophagus to the four chambers in their stomach, first the rumen, then the reticulum. The reticulum will spit the food back up to be chewed more and after the cow swallows the food again, it passes through the rumen and reticulum again. Then, the food goes to the omasum, then the abomasum, then to the small intestines, and then to the large intestine where the leftover food material is turned into poop.

The four-chambered stomach is made up of the rumen, reticulum, omasum, and abomasum. The rumen is large and has small organisms (microbes) that eat and break down components of the grass into molecules that can be absorbed for energy. The reticulum sorts through the particles that have been broken down. The reticulum sorts the food into two categories. It sends the smaller particles to the omasum and spits the larger particles back up so the cow can chew it again, to make sure that all of the grass has been broken down into small pieces. The omasum squeezes all the water out of the food so the body can absorb it. The rumen, reticulum, and omasum are known as the “fore stomach“.  The abomasum is known as the “true stomach” because it produces the particles that break down what is leftover in the food. This includes protein, fats, and carbohydrates. This has similar functions to the stomach in the horses.

Activities

1. Pair up into groups of 2 or 3 people.
2. Put the cut-out pictures of the GI tract in the correct order for both cows and horses. The different organs are printed individually and labeled with what structure it is.
3. Match the listed functions with the appropriate anatomical structure(s) and species:
   1. “Because this animal is a herbivore and has a small stomach, these structures are important to break down the grass”
   2. “This large structure contains microbes and is part of a four-chambered stomach”
   3. “This structure plays an important role in water absorption and is part of a four-chambered stomach”
   4. “This structure produces digestive particles and is part of a four-chambered stomach”
   5. “This structure sorts food into two categories; food that needs to be broken down more and food that is small enough to move through the rest of the digestive system”

Knowledge check

Good effort! The correct order for the horse anatomy is: the esophagus first, the stomach second, the small intestine third, the large intestine fourth (cecum and colon), and finally the rectum. If you get this correct, you get one gold star. The correct order for the cow anatomy is rumen, reticulum, omasum, abomasum, small intestine, large intestine, and rectum. If you get this correct, you get another gold star.

You will get one gold star for each correct match. The key is:

Cecum and colon in the horse: “Because this animal is a herbivore and has a small stomach, these structures are important to break down the grass”

Rectum in the cow: “This structure contains microbes and is part of a four-chambered stomach”

Omasum in the cow: “This structure plays an important role in water absorption”

Abomasum in the cow: “This structure produces digestive particles and is part of a four-chambered stomach”

Reticulum in the cow: “This structure sorts food into two categories; food that needs to be broken down more and food that is small enough to move through the rest of the digestive system”

If every student gets at least one gold star, the entire class gets a free pizza lunch day!