Skip to main content

Oregon in Agriculture in the Classroom Foundation

Agricultural Literacy Curriculum Matrix

Lesson Plan

The Ultimate Efficient Recycler

Grade Level
3 - 5

Students examine how cows help conserve natural resources by identifying the important role dairy cattle have in reducing, reusing, and recycling food processing by-products. Students identify each stage of the ecological cycle and the important role of decomposers. Grades 3-5

Estimated Time
50 minutes
Materials Needed

For class:

  • 5-10 brown paper bags
  • 5-10 different feed stuffs 
    • Almond hulls, cottonseed, barley, culled carrots, etc. Many feed mills, dairies, universities or animal nutritionists will donate.

For each group:


by-product: an incidental or secondary product made in the manufacture or synthesis of something else

compost: a mixture made of decaying organic material used to fertilize plants and amend soils

decomposer: an organism that feeds on and breaks down dead plant or animal matter

efficient: achieving maximum productivity with minimum wasted effort or expense

fertilizer: any material of natural or synthetic origin that is applied to soils or plant tissues to supply one or more nutrients essential to plant growth

macroorganism: an organism large enough to be seen with the naked eye

manure: animal waste used for fertilizing land

microorganism: any organism, such as a bacterium, protozoan, or virus, of microscopic size

nutrient: a substance that provides nourishment essential for growth and the maintenance of life

Background Agricultural Connections

This lesson is part of a series called, Milk Matters: Discovering Dairy. These lessons introduce students to the history, production, nutritional value and economic significance of the dairy industry. Other related lessons include:

Dairy cows are truly efficient recyclers. Because of their complex multi-compartment stomachs, they can consume feedstuffs that would be difficult or impossible for humans to digest, and then convert the feed into dairy products that humans can consume. The ingredients used for cattle feed include food processing by-products that would otherwise be sent to landfills. More than 25 percent of food processing by-products are fed to cattle. These feed products may include sugar beet pulp, almond hulls, canola seed pulp, citrus pulp, potato peels, culled vegetables, bakery waste, corn stalks, tomato pulp, grape skins, cottonseed, soy hulls and more. Eighty-five percent of what cattle eat is material that people cannot digest.

Not only do dairy cows recycle our unwanted leftovers to produce delicious dairy products, they also produce waste that we re-use for a variety of purposes. One way we “re-use” is applying properly composted manure from dairy cows to crops for fertilizer.

Macroorganisms and microorganisms play a vital role in turning cattle waste into a useful resource for humans. Worms, grubs and microbes are all examples of organisms that chew and break down material such as twigs, roots, manure and leaves.

Earthworms are macroorganisms that eat their way through their surroundings, consuming anything that is soft enough for them to chew. All “food” that is consumed is ground up in the gizzard, leaving the worm’s body in the form of dark, nutrient-rich castings. These castings are an important contribution to soil fertility. When macroorganisms die and decay, their bodies also add nitrogen and other elements to the compost.

Microorganisms, like bacteria, begin the breakdown of material, making it easier for worms and other macroorganisms to do their job. Many different types of microorganisms are at work in composted manure. Given the right environmental conditions--such as proper moisture, temperature, air, a favorable balance of carbon and nitrogen and lots of surface area to work on--bacteria will thrive. Since bacteria are smaller and less mobile than other organisms, they are less able to escape an environment that becomes unfavorable. A decrease in the temperature of the compost pile or a drastic change in pH can kill these decomposers. Once undergoing the process of decomposition, dairy farmers are able to use properly composted manure to enrich the soil, aiding in healthy plant growth.

Dairy farmers add composted manure to crops, which acts like a “homemade” fertilizer. Plants grow healthy and strong with the added nutrients. Dairy farmers use these crops to produce more feed ingredients, such as corn stalks, and the cycle begins again from the beginning.

Answers to commonly-asked questions about the dairy industry:

  • How much does it cost to produce one gallon of milk? 
    Input costs, such as processing, labor, transportation, and raw product costs, vary considerably. Even the type of milk will have an impact on the final cost, making the cost of producing a gallon of milk inconsistent. However, researchers estimate that it costs between $1.96 and $2.35 for processors to produce a gallon of milk, before transport to the retail store.
  • How and why is milk pasteurized? 
    All milk intended for direct consumption  should be pasteurized for food safety. Pasteurization is a simple, effective method of killing potentially harmful bacteria without affecting the taste or nutritional value of milk. With standard pasteurization, milk is heated to a temperature of at least 161 degrees Fahrenheit for not less than 15 seconds, followed by rapid cooling.
  • How should milk and dairy products be stored and handled? 
    After arriving home from the grocery store, dairy products should immediately be transferred to the refrigerator. With proper handling, milk should last five to seven days after its "sell-by" date. The refrigerator should be 38° to 40°F to slow bacterial growth. Store milk in the back of the refrigerator and away from the refrigerator door. This keeps the temperature lower and more constant. The sealed container will prevent contamination and absorption of flavors from other foods in the fridge. If the milk develops an off-odor smell, it should be discarded. Storing dairy products in their original packaging with a securely closed lid will help decrease spoilage.

    In the case of other dairy products, such as cheese and yogurt, bacteria play an important role in flavor, function, and good health. Most yogurts are made by the addition of two or more types of bacteria, including Lactobacillus bulgaricus and Streptococcus thermiphilus. These types of bacteria are called "cultures" and work to create distinct flavors and textures in the yogurt. To ensure the safety of yogurt, store it in the refrigerator in its original sealed container. Moldy yogurt should be discarded.

    Cheese is also the product of cultures and an aging process that causes fermentation. There is a wide range of production methods that yield many different flavors and forms of cheese. In general, you should follow the same storage tips as milk and yogurt. If mold is on cheese, the block of cheese can generally still be eaten. If a small patch of mold appears on a piece of cheese, trim it off completely by cutting off and discarding at least one-quarter inch below the mold. Plan to consume the rest of the cheese soon. Always check the "sell-by" date before you purchase cheese. If there is mold on fresh cheese, do not purchase it.
  • How can people be assured the dairy products they eat are safe?
    Personnel from the United States Department of Agriculture, the United States Environmental Protection Agency, and other governmental agencies continually meet with research scientists, technical experts, farmers, ranchers, and the general public to discuss food safety issues. They establish guidelines and standards for all food processors, handlers, and others involved in food production and distribution. Inspections occur on a regular basis to make sure that dairy products meet government standards and regulations. The United States currently has the safest food supply in the world and continues to work hard to maintain this position. By practicing safe food handling and storage, consumers also play a significant role in food safety.
  • Why do farmers treat cows with antibiotics?
    Sometimes, cows get sick just as some humans do. Without proper medical care, the cows could become seriously ill or die. It is a dairy farmer's job to treat them and make them well again with medications prescribed by a veterinarian. Sick cows still have to ne milked, but during treatment their milk is thrown away. Strict U.S. regulations and standards are in place to monitor antibiotic use and assure food safety.
  • Are there antibiotics in milk? 
    No. All milk is tested for antibiotics. Any tanker that tests positive is disposed of immediately.
  • Are there hormones added to milk?
    No. Hormones are naturally present in many foods that come from plants and animals, including milk, but farmers don't add hormones to the milk. Some farmers choose to give some of their cows a supplement called bST to increase milk production, but research shows that this practice has no effect on hormone levels in the milk itself.
  • What is the difference between whole and fat-free milk?
    Fat-free milk is made by skimming off the fat. A cup of fat-free milk contains less than one-half gram of fat and is fortified with vitamin A and usually with vitamin D. In the United States, skim or fat-free milk is also known as nonfat milk. Nonfat milk contains comparable amounts of protein, calcium, potassium, phosphorous, and other key nutrients found in higher-fat milks such as whole milk.
  • What is the difference between organic and regular milk?
    Organic milk is identical in composition to regular milk. Organic dairy farmers use only organic fertilizers and organic pesticides, and their cows are not given supplemental hormones. The milk itself, however, is identical to milk produced conventionally. Stringent government standards that include testing all types of milk for antibiotic and pesticide residues ensure that both organic milk and conventional milk are safe and nutritious.
  • How are dairy farmers practicing sustainable agriculture?
    Many dairy farmers have been practicing "new" sustainability methods for generations. Here are some of the ways dairy farmers practice sustainable agriculture:
    • Homegrown Feed:  Many dairies grow much of their own feed. Locally grown and fertilized crops save water, fuel, and fertilizer.
    • Waste Watchers: Many food products that were once sent to landfills are now being fed to cows, including culled tomatoes, almond hulls, bakery crumbs, and more.
    • Water Wise: Water is a precious commodity. Clean water is used to care for cows and recycled water is used to wash barns and irrigate crops.
    • Powering Up: More and more dairies are exploring the opportunities of biogas digestion. This promising technology can generate power for the dairy and its neighboring communities, all while reducing greenhouse gases.
  1. In this lesson, the students examine dairy cattle’s role in conserving natural resources. To introduce the topic ask the students what it means to recycle. Help guide them to understand that recycling means putting waste through a process so the material can be used again. Ask the students if they think that a dairy cow could recycle. Give a few examples of how a dairy cow can use items that we would consider to be waste.
    • Cottonseed: Most students wear clothes made out of cotton. Inside of a cotton boll (flower) are seeds that are extracted because they are not needed to make cotton fabric.  These seeds are used to feed dairy cows, who then produce milk and milk products that are a healthy addition to our diets.
    • Sugar Beet Pulp: Some of the sugar we use in cooking is produced by a sugar beet. Once the sugar is extracted from the beet the pulp remains.  Sugar beet pulp is a valuable feed for cattle that is high in energy.  It takes a lot of energy for a cow to produce milk. They can obtain some of this energy from beet pulp, a by-product that cannot be digested well or provide nutrition to us as humans.
    • Almond Hulls: Almonds grow on trees. The nut is encased in both a shell and a fibrous cover called a "hull." Cattle have four chambers in their stomach which allow them to digest and gain nutrients from items that humans cannot. Dairy cows can eat almond hulls as part of their specially formulated diet. Cows use this energy to produce milk.
    • There are many more examples of how dairy cattle help recycle and preserve valuable resources.
Explore and Explain
  1. Place several types of food processing by-products used for dairy feed in separate, brown paper bags. Have the students take turns feeling inside the bags and guessing the feed ingredient. Review with students, identifying the original product and the changes that happened to create each by-product foodstuff.
  2. Explain to the students that dairy cows help us recycle materials that would normally be considered waste. We call these materials “by-products.” For example, after farmers harvest ears of corn, the stalks remain. These stalks are a nutritious addition to animal feed. Re-using products is an important way for humans to reduce the amount of waste sent to landfills. By recycling the material and using it as nutritious ingredients for dairy feed, we reduce our impact on the environment. Work with students to identify other waste products that are used in the dairy industry as feed.
  3. Being a resourceful consumer of by-products is not the only way dairy cows are ultimate, efficient recyclers. In a moment, students will break into groups and discover the other ways dairy cows reduce, reuse and recycle.
  4. Break students into cooperative learning groups of four. Read the following script to students: (The following journal entry was written by 5th grader Lily Longacre.)

                                    Dear Journal,                                                                              June 5

                                    School is finally out for the summer, and today my mom and I drove 
                                    to my grandparents' house. They raise Holstein dairy cows and live 
                                    on a small farm called Green Meadow Ranch. Every summer I come 
                                    to spend two weeks with them out in the country. It's been a whole 
                                    year since I've seen their dogs, goats, chickens, horses, and my
                                    favorite dairy cows, Lola and Lacey. I'm especially excited to visit 
                                    this year because in science class, we learned a little bit about how
                                    dairy cows contribute much more than just milk. Through their eating
                                    and excreting, they actually help our food grown and help clean up 
                                    some of the earth's waste. I can't wait to see Lola, Lacey, and the 

                                    other cows hard at work!
  5. Give each learning group a packet of Ultimate Efficient Recycler journal entries. Have each student read one of the journal entries and respond to the reading comprehension questions at the bottom of the page.
  6. After several minutes, the students gather in their assigned cooperative learning groups. Each student summarizes what they read to the group and shares the answers to their questions. Review each of the questions as a class.
  7. Instruct the students to place their journal entries in the correct chronological order, identifying areas where they see the process of recycling, reducing, and reusing. Students should be able to review the process from beginning to end and recognize that these steps are repeated to form an effective cycle.
    • Cows consume feed, made of food processing by-products.
    • Dairy farmers create compost and collect manure.
    • Manure is used to fertilize fields.
    • Dairy farmers harvest fields and feed the by-products to dairy cattle.
  8. Some possible discussions about this lesson may include:
    • What type of diagram is appropriate to illustrate this process?
    • Is it a timeline or is it cyclical? Why?
    • What are some lessons we have learned from dairy cows that will help us reduce, reuse, and recycle in our own lives?
    • How are these interactions an example of a viable ecosystem?
    • How would life be different without decomposers?
  • As a class, create your own compost pile. Observe and monitor changes in pH, insect activity, heat, and size. Hypothesize future changes in the compost. Students can also create personal compost piles in plastic water bottles or milk cartons and monitor changes on a smaller scale.

  • Research the potential of “catching” methane gas from manure and using it as an energy source. Go on a field trip to a dairy with a methane digester.

  • Create a storybook about the efficient and resourceful dairy cycle. Students can also create a storybook sharing how they reduce, reuse, and recycle.

  • Write your own journal entry, written from the perspective of a dairy cow.


After conducting these activities, review and summarize the following key concepts:

  • Natural resources such as soil, water, air, plants, and minerals are required to produce milk.
  • Farmers take stewardship of the land and the natural resources they need to produce milk. 
  • Farmers recycle and reuse many resources and turn them into useable resources.

This lesson was funded in 2008 by the California Milk Advisory Board and the California Farm Bureau Federation. To meet the needs of California educators, Milk Matters: Discovering Dairy was created to meet the Curriculum Content Standards for California Public Schools. The unit also includes a collection of relevant resources about the dairy industry.

Executive Director: Judy Culbertson
Layout and Design: Imelda Muziom

Mandi Bottoms
California Foundation for Agriculture in the Classroom
We welcome your feedback! If you have a question about this lesson or would like to report a broken link, please send us an email. If you have used this lesson and are willing to share your experience, we will provide you with a coupon code for 10% off your next purchase at AgClassroomStore.