76 Which End? Gas in Cattle – Instructor Guide
Which End? Gas in Cattle
by Sarah Yvon Russell, Finn Schaeffer, Katie Davis
Instructional Guide
This unit is an introduction to cattle digestion and offers a comparative view of human and cattle physiology with a focus on a topic middle schoolers find interesting. Cattle burps are related to microbial activity, which is a good foundation for cell activity and very basic microbiology. It is also a good integration of animal science material with ‘big picture’ issues, as it ties something students already know is important (global warming) to something they’ve likely never thought about (cattle and their digestion).
Intended Grade Level
Students should be in middle school, grades 6-8. Students should have a basic understanding of how food is used in digestion– simply, that food is turned into nutrients and processed by the body for energy.
Learning objectives
- Students should learn that cows digest things differently than humans do, and that a big part of this is their unique foregut anatomy and the microbes that help them break down their food.
- Students should be aware that gas is a big byproduct of this digestion process, and that this digestive gas has a bigger impact on the world around them.
- Students should be able to connect individual learning objectives to create a “big picture” diagram of a cow.
Lesson Format
It is group work, where students will watch learning videos together and then brainstorm together in a way that helps them think through the learning objectives. They will then complete a final integrative learning activity where they trace the passage of food and gas through a cow’s foregut.
This will be a lesson that ideally should be able to be completed in an average 45-55 minute class period but can be adjusted to fit longer or shorter lesson times by eliminating some of the discussion questions or expanding them to include the optional activities.
Instructors will first go over the basic anatomy of a cow, including a quick summary of the foregut (rumen, reticulum, omasum, and abomasum). The instructor will then discuss microbes and their function in cattle digestion plus how they contribute to gas production. Finally, these topics will be linked by explaining why cattle burping contributes to global warming.
Students will need access to a partner for discussing ideas during brainstorming, a copy of the above image, and potentially a whiteboard to note ideas.
Lesson Background
Cattle are ruminants, which means they have four chambered stomachs. They are also herbivores, which means they only eat plants. The food (mostly silage, grain, and plant-based ingredients) will enter the mouth (oral cavity) and undergo mastication, which is the chewing of food. Cows have hypsodont, or flat teeth, to help them grind up the tough plant matter. Once chewed, the food particles (ingesta) flow down the esophagus and into the rumen, which is the first chamber of the stomach. In this chamber, rumen microbes are present to break down the ingesta. Through this process, the rumen microbes produce Volatile Fatty Acids (VFAs) and microbial proteins. Then ingesta then travels to the reticulum, which is the second chamber. Here, it is further digested. A special thing about cows is that they often regurgitate, meaning the ingesta travels back up through the rumen/reticulum and into the mouth for further chewing. The regurgitated food is now called cud. This allows for proper digestion of the food since it can be chewed into even smaller pieces. After multiple regurgitations, the ingesta flows past the reticulum and into the omasum (the third chamber of the stomach). Finally, the ingesta will travel to the abomasum, which is the cow’s “true” stomach. It acts similarly to a human stomach. After final processing in this last chamber, the ingesta will travel through the small intestine, cecum, large intestine, colon, and finally, the rectum where it will pass out as manure. The ingesta is moved between chambers/intestines due to peristalsis, which is the involuntary contraction/relaxation of gastrointestinal muscles to move the ingesta. This process usually takes one to three days to complete.
It is in the rumen that gas is made, and is typically expelled through burping!
Activities
Students will read through the presentation, stopping to watch videos, and participate in interactive games when prompted during the presentation.
Students will identify where in a cow the major microbe site is by clicking on it in an image.
Common misconceptions and challenge points
- Students may have difficulty conceptualizing the way the rumen functions
- Students may not grasp the different quadrants of the foregut
- Small and large intestinal function are not the main point of this lesson, but may be mentioned in passing to help students gather where colonic gas comes from and why cows don’t produce it
Assessment
Students will take a short quiz in order to assess their new knowledge.
Further exploration
Check out some of the following other pages for more information on topics such as this one:
Every Digestive System Is Unique
