This lesson introduces students to the microbial world and provides insight on their function by examining bacteria that both help and harm cows. Although multiple bacteria inhabit the cow’s rumen, this lesson focuses on two harmless microbes; Ruminococcus and Selenomonas, which break down cellulose and starch in plant matter, respectively. These bacteria obtain nutrients from the cow’s diet, and the cow gains energy from the products of bacterial metabolism. Therefore, these bacterial species are in a symbiotic relationship with the cow. Other bacterial species can harm cows. Such is the case with Escherichia coli, a non-ruminant bacterium that can cause the udder infection known as mastitis.

Intended Audience

Grades K-4

Learning Objectives
At completion of this activity, the learner will be able to:

  • Define the term microorganism.
  • Understand the effect ruminant bacteria on foods.
  • Differentiate three bacterial species based on cell shape and location in a cow’s rumen.
  • Understand the difference between symbiosis and pathogenesis

Necessary Student Background 
Students should have some understanding about the basic needs of mammalians: food, shelter, water, oxygen, and sunlight. They should also know that livestock are able to feed on grass and silage as their main dietary component. These needs will be extended to note their differences and similarities, and the needs of microbes that live in the rumen or on injured udders. Students should also have a general knowledge about the basics of milk production, i.e., the sources of milk and how milk is collected. This activity will extend information about milk production and look at how microbes aid or deter in this process. Students will also use a microscope to observe the different microorganisms that can exist in dairy cows. 


Ruminants, Microorganisms, Symbiosis, Pathogenesis

Print a PDF of this activity

Bacteria That Can Help or Hurt Cows (16 pages)