What is the name of the partly digested cellulose?

December 2, 2025 •

2 min read

Over 150 different species of ruminant animals rely on a specialized digestive process to survive on a diet of fibrous plants. A key component of this process is cud, the name for the partly digested cellulose these animals regurgitate and re-chew.

Quick Summary

Partly digested cellulose is known as cud, a semi-degraded food mass regurgitated by ruminant animals such as cows and sheep to be re-chewed and fully broken down by symbiotic microbes residing in the rumen.

Key Points

Name: The name for partly digested cellulose, especially in ruminants like cows, is cud.
Ruminants: Ruminant animals have a specialized four-chambered stomach, with the rumen being the first chamber where initial digestion occurs.
Microbial Action: Cellulose digestion is performed by symbiotic microorganisms that live in the rumen.
Rumination: Cud is regurgitated and re-chewed by the animal in a process called rumination.
Humans: Humans cannot digest cellulose because they lack the specific enzymes required.
Hindgut Fermenters: Non-ruminant herbivores digest cellulose in the cecum through hindgut fermentation.
End Products: The main energy-yielding byproducts of microbial cellulose fermentation are volatile fatty acids (VFAs).

The Ruminant Digestive Process

Animals like cows, sheep, and goats are known as ruminants, and they have a unique, multi-chambered stomach designed to process large quantities of fibrous plant material. The digestion of cellulose, a complex carbohydrate that forms the structural component of plant cell walls, is a multi-step process that starts with the rapid ingestion of food. Ruminants quickly swallow their food with minimal chewing and store it in the rumen.

The Role of the Rumen and its Microbes

Within the rumen, symbiotic microorganisms produce cellulase, an enzyme that breaks down cellulose. This anaerobic fermentation process converts plant fiber into volatile fatty acids (VFAs), methane, and carbon dioxide. VFAs serve as the primary energy source for the ruminant.

How Cud is Formed and Digested

Partly fermented fibrous material from the rumen is known as cud. This cud is regurgitated for re-chewing, a process called rumination. Re-chewing physically breaks down fibers, increases saliva production to buffer rumen pH, and enhances microbial action. After re-chewing, the cud is swallowed again, bypassing the rumen and reticulum and entering the omasum and abomasum for final digestion.

Cud vs. Other Forms of Digested Cellulose

Different herbivores process cellulose differently. The table below compares cellulose digestion in ruminants, non-ruminant herbivores, and humans.


Feature	Ruminants (Cattle, Sheep)	Non-Ruminant Herbivores (Horses, Rabbits)	Humans
Primary Digestion Site	Foregut (Rumen)	Hindgut (Cecum and Colon)	No significant digestion
Microbial Fermentation	Occurs before the true stomach, allowing for efficient nutrient absorption.	Occurs after the small intestine, making nutrient absorption less efficient.	Minimal fermentation occurs in the large intestine.
Regurgitation (Rumination)	Yes, to re-chew cud.	No.	No.
Main Energy Source	VFAs from microbes.	VFAs from microbes, absorbed less efficiently.	No energy from cellulose.
Cellulose Function	Primary energy and nutrient source.	Source of energy and nutrients, less efficiently.	Indigestible dietary fiber for bowel health.

Beyond Cud: The End Products of Fermentation

Rumen fermentation produces VFAs for energy, as well as amino acids and B-vitamins. Ruminants also digest the microbes themselves as a protein source. A byproduct of this fermentation is methane, a greenhouse gas released through belching.

The Significance of Cellulose Breakdown

The ability to digest cellulose allows ruminants and other herbivores to utilize abundant plant matter. Without symbiotic microbes, the energy in cellulose would be unavailable. For humans, cellulose is indigestible but vital as dietary fiber. Some modern hunter-gatherer populations retain cellulose-degrading gut bacteria, suggesting an evolutionary link tied to diet.

Conclusion

The partly digested cellulose in ruminants is called cud, a key element in the rumination process powered by symbiotic microbes in the rumen. This efficient digestion allows ruminants to thrive on fibrous plants. Humans cannot digest cellulose, but it serves as essential dietary fiber for gut health. These differing digestive strategies demonstrate the diverse ways animals utilize cellulose. You can find more information about the relationship between ruminants and their gut microbes in the journal Science.

Frequently Asked Questions

Cud is partially digested food regurgitated by ruminants for re-chewing as part of their normal digestive process. Vomit is the expulsion of undigested or partially digested food due to illness.

Humans cannot digest cellulose because our digestive system does not produce the enzyme cellulase needed to break its bonds.

No. Ruminants are foregut fermenters that produce cud, while hindgut fermenters like horses digest cellulose in their cecum but do not regurgitate food.

Rumination is the process where a ruminant animal regurgitates food from its rumen, re-chews it, and then re-swallows it for final digestion.

After re-chewing and mixing with saliva, the cud is swallowed and goes to the omasum and abomasum for further digestion and absorption.

Energy-yielding byproducts include volatile fatty acids (VFAs). Methane and carbon dioxide gases are also produced.

Even though humans cannot digest cellulose for energy, it's essential as dietary fiber, providing bulk for bowel health and preventing constipation.