Feline Carnivorous? An Overview of Why Cats Can’t Be Vegetarian

Instructional Guide

Learners will understand the basics of the cat digestive system and why cats cannot survive on a vegetarian diet. The lesson includes a short video presentation followed by a case study with questions for students to answer and discuss in small groups. After, there is a short quiz to assess their understanding of the topic.

Intended Grade Level

9th-12th grade. Students should be familiar with the general dietary differences between herbivores, omnivores, and carnivores. They should be familiar with introductory information about biomolecules, specifically carbohydrates and proteins.

Learning objectives

• Students will be able to list the major components of the cat digestive system and have a basic understanding of what each part does.
• Students will be able to explain why herbivores can digest a vegetarian diet while cats cannot.
• Students will be able to tell the main reason that cats have a high dietary protein requirement.
• Students will be able to identify consequences of a vegetarian diet through clinical signs in a cat.

Lesson Format

This lesson can be done individually or in small groups. Students should follow along with the presentation and answer questions about a case study after

• First, students will listen to a presentation on the basic digestive system anatomy of a cat and the key reasons why they cannot survive on a vegetarian diet. (10 minutes)
• Next, in small groups of 3-5,  students will apply what they have learned from the presentation to a case study that focuses on why cats cannot survive on a vegetarian diet. (15-20 minutes)
• An individual quiz will assess the students’ understanding of the material covered. (15 minutes)

Lesson Background

Cats are carnivores. The cat gastrointestinal tract (and most carnivore GI tracts) consists of the oral cavity, the esophagus, the stomach, the small intestine, the large intestine, and the anus. The oral cavity is the first step of the digestive tract and produces proteins to begin breaking down the food chemically with enzymes. It also contains teeth that begin to physically break down the food. Cats have specific teeth that are not meant for grinding down plant foods, but rather for tearing their food. These teeth are sharp and long. The food then moves to the esophagus. The esophagus carries the food from the mouth to the stomach. It is a muscular tube that provides a passageway for the food to pass from the oral cavity into the stomach. No digestion occurs in the esophagus and it is rather a way to just transport the food. Then, in the stomach chemicals and enzymes further break down food. It uses hydrochloric acid and pepsin to chemically digest food. The stomach serves as a place for the food to be stored while it is being broken down. The food then moves to the small intestine where vitamins and nutrients are absorbed. The small intestine has three parts: the duodenum, the jejunum, and the ileum. Both the liver and pancreas play a role in aiding the small intestine with absorption and digestion of food by secreting enzymes. Finally, the food moves to the large intestine for any additional and final absorption. From the large intestine the completely broken down food goes to the anus where it is excreted as feces.

The digestive system of herbivores is designed to breakdown a vegetarian diet. Although specific organs within the digestive tract can vary in function and structure, they have the same components as the cat GI system (oral cavity, esophagus, stomach, small intestine, large intestine, and anus). Some herbivores have four parts, or chambers in their stomach, unlike cats (and carnivores in general) that only have one. The first three chambers make up the forestomach. This is where the majority of digestion happens in herbivores that have a forestomach. The last chamber is very similar to the stomach of carnivores, and almost no plant digestion occurs there. Cat stomachs are not made to digest fibrous plants and therefore do not have these extra three chambers of the stomach. In other herbivores that do not have these four stomach chambers, there are specific gut microbes throughout the GI tract that are specialized to break down fibrous plant foods. Cats do not have these gut microbes and therefore do not have a chemical mechanism to break down these plant foods either.

Cats require a high protein diet. Protein amounts are very high in carnivorous diets but not vegetarian (herbivorous diets). Proteins are broken down into amino acids through the digestive tract. There are essential and non-essential amino acids. Essential amino acids must be obtained from the diet or supplementation because they cannot be synthesized by the body, while non-essential amino acids are able to be made by the body and therefore do not need to be obtained through the diet. Cats have eleven essential amino acids they must obtain through their diet. One key essential amino acid for cats is taurine. Unlike dogs, which are omnivores, or cows, which are herbivores, cats cannot make their own taurine and therefore must obtain it through their diet.  Taurine is not obtainable in adequate amounts in vegetarian diets, therefore cats must eat a carnivorous diet to survive, as they cannot survive without a source of taurine. Signs of taurine deficiency in cats include poor eyesight, tooth decay, reproductive issues, and digestive issues. Arginine is another key essential amino acid for cats that is not present in adequate amounts in vegetarian diets. Arginine deficiency signs include vomiting and salivation.

Due to the cat’s digestive tract (its inability to process vegetarian diets) and their taurine and arginine requirements, cats would not be able to survive on a vegetarian diet. Their bodies are designed to eat a carnivorous diet.

Activities

Video presentation: The link to the presentation is provided. Students can either watch individually with headphones or can watch on a big screen as a whole group.

*Optional*: Depending on the class’s comfort with the digestive system, consider having them create their own GI tract model/diagram. For less visual learners, a flow-chart can be another great option. This activity will help solidify the understanding of digestive flow and can help learners visualize the difference between herbivores and carnivores.

Case study: Information and questions are provided for the case study. Students should be broken up into smaller groups of 3-5, and read through the study while answering and discussing the given questions.

Assessment Quiz: This should be completed individually. Quiz questions are provided and the student should complete this after watching the presentation and completing the case study.

Common misconceptions and challenge points

If cats need protein, why do so many cat diets have other nutrients like carbohydrates as well?

• Like many animals, cats can eat pretty much everything, but their digestive system is not specifically formulated to digest and utilize certain nutrients. Like humans, cows, and many other animals, cats still possess enzymes and other mechanisms for digesting plants and vegetables. However, their body is better formulated for digesting protein. Together, this means that a cat can still digest and utilize nutrients from vegetables, but they cannot survive strictly off a veggie diet. To better clarify information, recommend the student examine the chart featured within the presentation comparing amino acid values of veggies and proteins. Despite vegetables having some amino acid content, the amount a cat would need to eat to survive is simply not feasible.

Could you replace a cat’s meat diet with amino acid supplements?

• While amino acid supplementation and even replacement sounds like a feasible option for cat diets, it unfortunately is not possible at this point in time. The complexities of amino acid absorption, formation, and utilization currently limit the amount of supplementation that can occur through non-dietary means. Depending on the point of curriculum, it may be beneficial to review how the body can utilize or synthesize amino acids. You can also direct students to vitamin labels they may have within their house. Have students recognize that some nutrients are supplied at nearly 3000% of the total daily value. Briefly explain how certain nutrients can only be absorbed with the right keys, nutrients, enzymes, etc. inside the body. Now, have students apply that same logic to cats. It simply is not feasible to input such an excessive amount of amino acids to a cat daily if other nutrient requirements are not being met.

What are the nutritional implications of a raw meat diet for cats?

• Although this question is not directly addressed in the chapter, it is a common discussion in today’s veterinary care. Like any diet, a raw diet should be appropriately balanced. Various meat types include differing quantities of nutrients and can be more or less pallative for individual animals. A balanced raw diet should include a minimum amount of the taurine and arginine while also supplementing other nutrients that students will learn about in later courses. Aside from nutritional requirements, raw diets can pose health risks to animals and humans. You may open a discussion on why raw diets can be dangerous because of bacteria and other pathogens. Recommend directing your students to reach out to their local veterinarian for a more nuanced perspective.

If cats are carnivorous, why do so many cats not have refined hunting skills?

• Cats, like dogs, and most of our pet animals have been domesticated. Remind students that domestication is an often long process that changes some sort of natural condition of a plant or animal. Explain that with the domestication of some bigger cats, certain behavioral traits are lost or minimized. It may be a good idea to expand and share how certain traits or behaviors can return if physiologically necessary. A good example could be to ask how many students like to run. For the students who do not like running, you could mention that the body would take over if a lion was chasing them. In other words, the students would inevitably start running. In cats that are outdoors or feral, they may readapt certain traits or behaviors. Like us, the extent and skill of behaviors may vary.

I thought a cat was healthy as long as it was being fed.

• This is a great segway into animal welfare and a conversation about health. Many veterinarians follow the sentiment that “fed is best” especially in families and cliets with lower income. Explain that while a cat may be active and appear physically healthy, inside they could be functioning less optimally. Consider comparing a diet of junk food and healthy food. Explain that although one could theoretically function off ice cream, the body does not feel as good or function as well. The same logic applies to our cats.

What is the flow of food through the digestive tract?

• The digestive tract is a lot to understand and move through with so many parts! It may be best to have students draw out their own diagram of digestive system flow and consider adding in arrows! For less visual students, recommend drawing a flow chart together as a class or in small groups. If confusion occurs between the model herbivore digestive system (cow) and the cat’s digestive system, it may be best to refer students to the supplemental resources. The diagrams representing the flow of the GI tract in the student presentations are shown below.

Why are non-essential amino acids still required by the body?

• The distinction between essential and non-essential amino acids can be difficult to grasp for students and non-students. A way to distinguish and remember the difference between essential and non-essential amino acids is to think about amino acids in terms of the diet. Both essential and non-essential amino acids are still needed by the body! However, non-essential amino acids are ones that can be synthesized by the body. In other words, essential amino acids are ones that must be present within the diet! If something is essential it must be there. So, if an amino acid is essential, and we consider amino acids to be related to a diet, then an essential amino acid must be present in the diet. Ask any other students if they have helpful ways of remembering the difference between the two amino acid types.

What do the supportive organs of the GI tract do?

• The supportive organs of the GI tract are starred on both the GI tract flow diagrams present in the student presentation. These organs include the liver, pancreas, and gallbladder. Ask students if they know the function of any of these organs. From there, you can start a brainstorm and mini lesson on each organ function. The liver is responsible for processing nutrients from the GI tract and secreting bile. Bile is a substance utilized to help digest fat. Explain the concept of solubility with fat to students by discussing how soap removes grease. Bile works in the same way. The gallbladder assistes the liver by storing excess bile for later! In this way, the body is able to quickly have bile on hand for extra fatty meals. Finally, the pancreas helps produce numerous enzymes that the body needs to digest and absorb foods.

What makes the microbes in a cow’s GI tract better at digesting plants than the microbes in a cat’s large intestine?

• Microbial populations within a GI tract can vary considerably from animal to animal and even more from species to species. Because of this population variability, there are different types of microbes with different functions. Another consideration is the placement of the microbes within the digestive tract. In cows, most of the microbes are present in the stomach, specifically the cow’s rumen. Meanwhile, most of the microbes in the cat’s GI tract are present in the large intestine. What this means is that cow microbes get an initial taste of food before any digestion can occur. The microbes in the cat get more second-hand offerings because the cat’s digestive system has already broken down most of what it can of the food. If you put both of these ideas together, the cow microbes are better at initially breaking down the ingested food, grass, than the cow’s own processes. The cat, on the other hand, can digest its food very well, and the microbes get what is left.

Further exploration

Here are some resources students can be provided with if they’re interested in learning more:

What are the other supportive organs of the GI tract that aid in digestion of biomolecules?

https://www.hopkinsmedicine.org/health/conditions-and-diseases/the-digestive-process-what-is-the-role-of-your-pancreas-in-digestion

https://courses.lumenlearning.com/suny-ap2/chapter/accessory-organs-in-digestion-the-liver-pancreas-and-gallbladder/

Differences between cat teeth and cow teeth

https://www.nku.edu/~whitsonma/Bio120LSite/Bio120LReviews/Bio120LAnimalRev.html

Compartments of a cow’s stomach

https://extension.umn.edu/dairy-nutrition/ruminant-digestive-system#stomach-compartments-1000460