Do cows really have four stomachs?

How do intestinal parasites infect and impact cows?

What you can learn from this lesson

At the end of this lesson you should be able to….

• Understand that there are many kinds of parasites and be able to give a few examples
• Understand the basic life cycle of an intestinal parasite
• Understand the GI tract of a cow and the 4 “stomachs”
• Understand the negative effects of parasites in cows and how this relates to physiology

Lesson

Key terms

What is a parasite?

An organism that lives in or on another species (host) and benefits from taking nutrients from that organism at the other’s cost.

What is a host?

An organism that a parasite lives on or in.

Test your knowledge

Can you identify parasites?

If you had some troubles, review the illustration below to clarify your understanding.

Parasites can be external (outside the host) or internal (inside the host). A common name for internal parasites is worms! These are different than the earthworms you may see outside on the sidewalk after it rains!

The Life Cycle

Most parasites have a life cycle with different forms like butterflies do! For roundworms (which are one type of intestinal worm), they have to enter a cow’s GI tract in order to lay eggs.

Here is an example life cycle for several roundworm species that infect cows:

The Cow GI Tract

A cow’s GI tract starts at the mouth! After the cow swallows the food, it travels down the esophagus to the stomach.

You may have heard that cow’s have 4 stomachs!

Cows actually have 4 stomach compartments. They are the rumen, reticulum, omasum, and abomasum.

Microbes live in the rumen and help the cow break down grass and hay. These microbes produce gas in the rumen, so cows burp a lot to release the gas.

The reticulum compartment helps separate different size food particles. If the food particles are too big, they go back to the rumen to be broken down more or are regurgitated up the esophagus to be chewed more. When the food particles are small enough, they go to the next stomach chamber, the omasum.

The omasum’s main job is to absorb water from the food particles. After the omasum, the food particles go to the abomasum.

The abomasum is acidic and helps break down the food even more before it goes to the intestines. The intestines are where most nutrients are absorbed. Nutrients can only be absorbed when food is broken down. The abomasum is most similar to a human stomach!

After the food leaves the abomasum, it goes through the small intestine, which is where most nutrients and water are absorbed. Cows have a cecum, which is the area where the small and large intestines meet. The exact purpose of the cecum is not known. Following the cecum, food moves through the large intestine and finally comes out of the body as poop at the anus.

Check your understanding

What Order Do Cows Digest Food?

Hint: There is one answer per blank spot and every word should be used only once.

3 Intestinal Worm Examples

Barber pole worm (species name: Haemonchus placei)   

Appearance

Barber pole worms are red and white-striped, kind of like a candy cane (or a barber’s pole). They can be up to 30 millimeters (1.18 inches) long and are usually at least 10 millimeters (0.4 inches) long. They also have “mouthparts” that they use to take in their food, but they are not quite the same as human or cow mouths.

What do they do?

Barber pole worms are very unique intestinal worms because they require blood as food. These worms use their “mouthparts” to bite into the cow’s stomach to get blood, kind of like a vampire! If the infection is severe enough, this can cause a problem for the cow called anemia. Anemia occurs when there are no longer enough healthy red blood cells in the blood to transport as much oxygen as the body and tissues need. Barber’s pole worms can cause anemia if the cow loses enough blood due to the worms’ bites.

Signs of infection

If a cow is infected with barber pole worms, the cow will most likely appear sick or unhealthy compared to normal. They may also be physically weaker and more tired. Due to the anemia, the cow’s gums and the area around her eyes may be paler than normal. Most cows infected with barber pole worms will not have diarrhea. Diarrhea is only likely if they are also infected with another intestinal worm.

Interesting fact

Female barber pole worms can produce up to 10,000 eggs per day!

Brown stomach worm (species name: Ostertagia ostertagi)

Appearance

Brown stomach worms are skinny and reddish-brown in color. The males are usually 6-7 millimeters (0.25 inches) long and the females are usually 8-11 millimeters (0.4 inches) long. 

What do they do?

Brown stomach worms eat part of the stomach lining (mucosa) of the abomasum, which causes irritation and messes up the abomasum’s function (to digest and break down food). Stomach acid is not properly released when the stomach lining is damaged, so the pH of the abomasum goes up, which is bad for the cow too.

Signs of infection

Cows with a brown stomach worm infection often have watery diarrhea. They may also have weight loss or not be able to gain weight because they can’t fully digest food which means they can’t absorb all of its nutrients. They may also have lack of appetite and look sick. Some dairy cows may produce less milk when they have a brown stomach worm infection.

Interesting fact

Brown stomach worms are the most economically important parasite for cattle since an infection can cause farmers to lose money due to less production.

Stomach hairworm (species name: Trichostrongylus axei)

Appearance

Adult worms are very thin, like a strand of hair! They are also very short, about 5 millimeters (0.20 inches) long.

What do they do?

Stomach hairworms cause swelling and irritation to the lining (mucosa) of the stomach. This irritation can cause the mucosa to be eaten away, and can lead to a loss of protein that a cow’s body requires.

Signs of infection

Interestingly, cows usually do not show signs when they are infected with the stomach hairworm. Cows that are already more vulnerable due to lack of proper nutrition or being exposed to high levels of stress are more likely to show signs than otherwise healthy animals. Cows with a heavy infection of stomach hairworm are also more likely to show signs. The most common signs, when they are seen, are diarrhea, loss of appetite, and weight loss.

Things worms do

There are also things that all three of these intestinal worms have in common

1. They all infect the abomasum, or the fourth stomach chamber!
2. They can all be treated with similar medications, called “dewormers.” Dewormers are anti-parasitic medications that kill worms. Benzimidazoles or “white dewormers” are a type of dewormer that can by given by mouth (like a pill). These worms can also be treated with macrocyclic lactones, another type of dewormer, which can also be given by mouth, as an injection (like a shot) under the skin, or as a liquid poured over food.
3. There is always the possibility of a cow appearing healthy when infected with intestinal worms!
4. There is also the possibility that a cow may become extremely ill and even die, if the intestinal parasite infection is severe enough.

Got worms? 

Farmer Jo comes to you and tells you she has 3 sick dairy cows, all showing different symptoms. You are concerned about internal parasites, specifically worms!

Read through the 3 cows’ symptoms below. Then, use the information above to determine which cow is likely to be infected with each worm (the barber pole worm, the brown stomach worm, or the stomach hairworm). 

Cow A: Betsy

CC BY-NC 2.0, Image Source

Farmer Jo tells you that she is worried about Betsy because she has been sleeping more than normal. She is usually very active and sometimes difficult to handle! When Farmer Jo went to take a closer look at Betsy earlier, she realized her gums were not their normal pink color. She also noted that Betsy usually doesn’t allow people to touch her mouth as easily as she did today.

Cow B: Matilda

Matilda was rescued by Farmer Jo from an owner that was not providing her with accurate care, including food. She was underweight when she arrived to Farmer Jo’s but was slowly gaining weight until recently. She has not shown interest in eating much since yesterday and Farmer Jo says Matilda is noticeably thinner than she was last week.

Cow C: Georgia

Farmer Jo has had Georgia since she was a cute little calf! She is worried that Georgia doesn’t seem like her normal self! She is one of Farmer Jo’s best milk producing cows, but Farmer Jo tells you that she produced less milk than she normally does in the last 2 weeks. Yesterday, Georgia started having diarrhea. She also only ate a little bit of food this morning.

Excellent job on this activity! You correctly matched the three cows with the parasite they are most likely to be infected with! Farmer Jo is very grateful for your help, and all three parasite infections can be treated with dewormers!

Assessment

Practice what you learned in today’s lesson!

Further Exploration

Do you want to learn more about what you learned in this lesson? Check out these links to additional resources to explore.

• Texas A&M Common Cattle Parasites paper
• Morris Vet Center Bovine Parasite website
• Purdue website: Treating for Internal Parasite of Cattle
• University of Minnesota website: the Ruminant Digestive System

If these resources don’t answer your questions, try researching on your own or ask your teacher or librarian. Happy learning!

All graphics were created using biorender.