This essay analyses the similarities and differences between the monogastric and ruminant digestive systems, including the mechanisms of each system and the physiological roles.
All animals are consumers, which means they cannot produce their own food and therefore must eat other products.
The digestive system’s primary function is to break down the food and send essential nutrients to the body’s cells. This then allows the body to develop energy and adenosine triphosphate and other biomolecules. 
The digestive system of a ruminant has many different factors in comparison to the monogastric. Within this essay, the monogastric digestive system relates to a dog and the ruminant digestive system focuses on a cow. 
A pivotal point is that a cow’s stomach is defined as a compound stomach and is found in the digestive system’s cranial region. (Aspinall, 2015) Whereas in a dog, the stomachs location is on the left side of the cranial abdomen and classed as a simple stomach.
In a ruminant, the stomach is defined as a compound due to its four compartments: The rumen, reticulum, omasum, and abomasum. Within the digestive system, each compartment serves a particular purpose.  Whereas in a monogastric it is classed as a simple stomach and is made up of one chamber with “large muscular folds” (NDSU, ND)
The rumen and reticulum are the main chambers in ruminants, forming a compartment known as the fermentation chamber. Microorganisms begin to “break down complex carbohydrates such as cellulose” at this stage (Aspinall, 2015). “These microbes digest or ferment feed in the rumen and create volatile fatty acids.” (Linn 2018) The reticulorumen is made up of the rumen and the reticulum. The reticular fold divides the reticulorumen from the rumen, allowing the two compartments to mix.
The rumen consists of several muscular sacs, including the cranial sac, ventral sac, ventral blind sac, and reticulum. (2020, RUBENRIOSA) The rumen wall is lined with papillae, which increases the surface area and allows for further absorption. The papillae may be rounded or conical in shape.
The reticulum is a pouch-like structure in the forward region of the body, near the heart. A honeycomb effect is created by the creation of 1cm high folds (Aspinall, 2015). Papillae cover the bottom of these folds to aid absorption and maximise surface area. A thin tissue fold separates the reticulum from the rumen. The rumen and reticulum are referred to as the rumino-reticulum when they are combined.
The omasum is a globe-shaped structure that contains tissue leaves. The omasum wall is heavily folded, resulting in a wide surface area that enables efficient water and salt absorption from partially digested food. The omasum also functions as a pump, transporting food from the reticulorumen to the abomasum’s true stomach. 
The only compartment with glands is the abomasum. Hydrochloric acid and digestive enzymes are released by these glands, which are necessary for feed breakdown. The abomasum resembles the stomach of a nonruminant mammal. Cells in the abomasum wall contain enzymes and hydrochloric acid, which hydrolyse proteins in the food and microbes inside the food.
In contrast to the ruminant digestive system, the stomach is a C-shaped sac-like organ covered by the visceral peritoneum. A dogs stomach walls are thick and easily swollen by food. The monogastric digestive system has three regions of the stomach: the cardia, fundus, and pylorus, rather than the ruminant digestive system’s different compartments.
Many gastric glands are located in the fundus region, and the mucous membrane that lines the stomach walls protects the chief cells and underlying tissue from the digestive juices.
The duodenum, ileum, and jejunum are used in both the monogastric and ruminant digestive systems. Like that of the ruminant digestive system, the jejunum’s lining is intended to help in the digestion of carbohydrates and proteins. The jejunum has much longer villi than the duodenum or ileum, which increases the surface area required to absorb nutrients from the gut contents. Similarly, the jejunum plays a role in the digestion and absorption of nutrients in the ingesta in the monogastric system. In addition, the jejunum’s mesentery (mesojejunum) is long, allowing the jejunum to travel across the abdomen.
The monogastric system’s liver and pancreas secrete substances into the duodenum through ducts. Bile salts are transported through the bile duct and released into the duodenum to aid fat digestion. The primary pancreatic duct transports high-enzyme and nutrient-rich digestive secretions.
The ileum function in both the ruminant and monogastric systems is to absorb vitamin B12, bile salts, and any other nutrients not absorbed by the jejunum. On the other hand, the ileum has a secondary role in a dog’s digestive system: it secretes hormones that control the motility and adaptation of the small intestine.
Microbes digest undigested feed in the large intestine of a cow’s digestive system, but the purpose of the large intestine is to absorb water. In addition to the caecum, the ascending colon, transverse colon, sigmoid colon, rectum, and anus are all members of the large intestine.
The colon is a large part of the large intestine that is shorter in length but greater in diameter than the small intestine. The colon is involved in active sodium transport and osmosis water absorption from the digested material it contains. In contrast to a dog’s digestive system, the large intestine absorbs all liquids, electrolytes, and water-soluble vitamins. The anus is where any undigested matter is removed.
Figure one: A ruminants digestive system

Figure two: A monogastric digestive system

Table one: Main differences between a ruminants digestive system and a monogastric digestive system.

Ruminant

Monogastric

4 chambered stomach

Simple stomach

Prominent microbial digestion

Enzymatic digestion

Saliva lacks carbohydrate digestive enzyme

Saliva contains carbohydrate digestive enzyme

Digestion duration is 4- 7 days

Digestion duration is 12-24 hours

Herbivores

All food types

Regurgitate food

Do not regurgitate food

Foregut fermenter

Monogastric herbivores are hindgut fermenters

Can synthesise protein

Cannot synthesise protein

References
Linn, J. (2020). The Ruminant Digestive System: The RUMEN. Available: https://rubenriosa.com/science-corner/the-ruminant-digestive-system-the-rumen. Last accessed 16th April 2021.
Aspinall, V (2015). Introduction to Veterinary Anatomy and Physiology Textbook. London: Elsevier Health Sciences. p99- 211.
NDSU. (ND). Stomach. Available: https://www.ndsu.edu/pubweb/~tcolvill/stomach.htm. Last accessed 16th April 2021.
Britannica. (2014). Chyme. Available: https://www.britannica.com/science/chyme. Last accessed 16th April 2021.