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Temporal range: Early Eocene - present
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Clade: Cetruminantia
Clade: Ruminantiamorpha
Spaulding et al., 2009
Suborder: Ruminantia
Scopoli, 1777

Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. [2] [3] The word "ruminant" comes from the Latin ruminare, which means "to chew over again".


The roughly 200 species of ruminants include both domestic and wild species. [4] Ruminating mammals include cattle, all domesticated and wild bovines, goats, sheep, giraffes, deer, gazelles, and antelopes. [5] It has also been suggested that notoungulates also relied on rumination, as opposed to other atlantogenates that rely on the more typical hindgut fermentation, though this is not entirely certain. [6]

Taxonomically, the suborder Ruminantia is a lineage of herbivorous artiodactyls that includes the most advanced and widespread of the world's ungulates. [7] The suborder Ruminantia includes six different families: Tragulidae, Giraffidae, Antilocapridae, Moschidae, Cervidae, and Bovidae. [4]

Taxonomy and evolution

An impala swallowing and then regurgitating food – a behaviour known as "chewing the cud"

Hofmann and Stewart divided ruminants into three major categories based on their feed type and feeding habits: concentrate selectors, intermediate types, and grass/roughage eaters, with the assumption that feeding habits in ruminants cause morphological differences in their digestive systems, including salivary glands, rumen size, and rumen papillae. [8] [9] However, Woodall found that there is little correlation between the fiber content of a ruminant's diet and morphological characteristics, meaning that the categorical divisions of ruminants by Hofmann and Stewart warrant further research. [10]

Also, some mammals are pseudoruminants, which have a three-compartment stomach instead of four like ruminants. The Hippopotamidae (comprising hippopotami) are well-known examples. Pseudoruminants, like traditional ruminants, are foregut fermentors and most ruminate or chew cud. However, their anatomy and method of digestion differs significantly from that of a four-chambered ruminant. [5]

Monogastric herbivores, such as rhinoceroses, horses, and rabbits, are not ruminants, as they have a simple single-chambered stomach. These hindgut fermenters digest cellulose in an enlarged cecum. In smaller hindgut fermenters of the order Lagomorpha (rabbits, hares, and pikas), cecotropes formed in the cecum are passed through the large intestine and subsequently reingested to allow another opportunity to absorb nutrients.


Ruminantia is a crown group of ruminants within the order Artiodactyla, cladistically defined by Spaulding et al. as "the least inclusive clade that includes Bos taurus (cow) and Tragulus napu (mouse deer)". Ruminantiamorpha is a higher-level clade of artiodactyls, cladistically defined by Spaulding et al. as "Ruminantia plus all extinct taxa more closely related to extant members of Ruminantia than to any other living species." [11] This is a stem-based definition for Ruminantiamorpha, and is more inclusive than the crown group Ruminantia. As a crown group, Ruminantia only includes the last common ancestor of all extant (living) ruminants and their descendants (living or extinct), whereas Ruminantiamorpha, as a stem group, also includes more basal extinct ruminant ancestors that are more closely related to living ruminants than to other members of Artiodactyla. When considering only living taxa (neontology), this makes Ruminantiamorpha and Ruminantia synonymous, and only Ruminantia is used. Thus, Ruminantiamorpha is only used in the context of paleontology. Accordingly, Spaulding grouped some genera of the extinct family Anthracotheriidae within Ruminantiamorpha (but not in Ruminantia), but placed others within Ruminantiamorpha's sister clade, Cetancodontamorpha. [11]

Ruminantia's placement within Artiodactyla can be represented in the following cladogram: [12] [13] [14] [15] [16]


Tylopoda (camels) Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png


  Suina (pigs) Recherches pour servir a l'histoire naturelle des mammiferes (Pl. 80) (white background).jpg

 Ruminantia (ruminants) 

  Tragulidae (mouse deer) Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg

  Pecora (horn bearers) Walia ibex illustration white background.png


  Hippopotamidae (hippopotamuses) Voyage en Abyssinie Plate 2 (white background).jpg

  Cetacea (whales) Bowhead-Whale1 (16273933365).jpg

Within Ruminantia, the Tragulidae (mouse deer) are considered the most basal family, [17] with the remaining ruminants classified as belonging to the infraorder Pecora. Until the beginning of the 21st century it was understood that the family Moschidae (musk deer) was sister to Cervidae. However, a 2003 phylogenetic study by Alexandre Hassanin (of National Museum of Natural History, France) and colleagues, based on mitochondrial and nuclear analyses, revealed that Moschidae and Bovidae form a clade sister to Cervidae. According to the study, Cervidae diverged from the Bovidae-Moschidae clade 27 to 28 million years ago. [18] The following cladogram is based on a large-scale genome ruminant genome sequence study from 2019: [19]


Tragulidae Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg


Antilocapridae Antilocapra white background.jpg

Giraffidae Giraffa camelopardalis Brockhaus white background.jpg

Cervidae The deer of all lands (1898) Hangul white background.png

Bovidae Birds and nature (1901) (14562088237) white background.jpg

Moschidae Moschus chrysogaster white background.jpg


Digestive system of ruminants

Stylised illustration of a ruminant digestive system Abomasum (PSF).png
Stylised illustration of a ruminant digestive system
Different forms of the stomach in mammals. A, dog; B, Mus decumanus; C, Mus musculus; D, weasel; E, scheme of the ruminant stomach, the arrow with the dotted line showing the course taken by the food; F, human stomach. a, minor curvature; b, major curvature; c, cardiac end G, camel; H, Echidna aculeata. Cma, major curvature; Cmi, minor curvature. I, Bradypus tridactylus Du, duodenum; MB, coecal diverticulum; **, outgrowths of duodenum; +, reticulum; ++, rumen. A (in E and G), abomasum; Ca, cardiac division; O, psalterium; Oe, oesophagus; P, pylorus; R (to the right in E and to the left in G), rumen; R (to the left in E and to the right in G), reticulum; Sc, cardiac division; Sp, pyloric division; WZ, water-cells. (from Wiedersheim's Comparative Anatomy) Cambridge Natural History Mammalia Fig 041.png
Different forms of the stomach in mammals. A, dog; B, Mus decumanus; C, Mus musculus; D, weasel; E, scheme of the ruminant stomach, the arrow with the dotted line showing the course taken by the food; F, human stomach. a, minor curvature; b, major curvature; c, cardiac end G, camel; H, Echidna aculeata. Cma, major curvature; Cmi, minor curvature. I, Bradypus tridactylus Du, duodenum; MB, coecal diverticulum; **, outgrowths of duodenum; †, reticulum; ††, rumen. A (in E and G), abomasum; Ca, cardiac division; O, psalterium; Oe, oesophagus; P, pylorus; R (to the right in E and to the left in G), rumen; R (to the left in E and to the right in G), reticulum; Sc, cardiac division; Sp, pyloric division; WZ, water-cells. (from Wiedersheim's Comparative Anatomy)
Food digestion in the simple stomach of nonruminant animals versus ruminants Ruversin.jpg
Food digestion in the simple stomach of nonruminant animals versus ruminants

The primary difference between ruminants and nonruminants is that ruminants' stomachs have four compartments:

  1. rumen—primary site of microbial fermentation
  2. reticulum
  3. omasum—receives chewed cud, and absorbs volatile fatty acids
  4. abomasum—true stomach

The first two chambers are the rumen and the reticulum. These two compartments make up the fermentation vat and are the major site of microbial activity. Fermentation is crucial to digestion because it breaks down complex carbohydrates, such as cellulose, and enables the animal to use them. Microbes function best in a warm, moist, anaerobic environment with a temperature range of 37.7 to 42.2 °C (100 to 108 °F) and a pH between 6.0 and 6.4. Without the help of microbes, ruminants would not be able to use nutrients from forages. [21] The food is mixed with saliva and separates into layers of solid and liquid material. [22] Solids clump together to form the cud or bolus.

The cud is then regurgitated and chewed to completely mix it with saliva and to break down the particle size. Smaller particle size allows for increased nutrient absorption. Fiber, especially cellulose and hemicellulose, is primarily broken down in these chambers by microbes (mostly bacteria, as well as some protozoa, fungi, and yeast) into the three volatile fatty acids (VFAs): acetic acid, propionic acid, and butyric acid. Protein and nonstructural carbohydrate (pectin, sugars, and starches) are also fermented. Saliva is very important because it provides liquid for the microbial population, recirculates nitrogen and minerals, and acts as a buffer for the rumen pH. [21] The type of feed the animal consumes affects the amount of saliva that is produced.

Though the rumen and reticulum have different names, they have very similar tissue layers and textures, making it difficult to visually separate them. They also perform similar tasks. Together, these chambers are called the reticulorumen. The degraded digesta, which is now in the lower liquid part of the reticulorumen, then passes into the next chamber, the omasum. This chamber controls what is able to pass into the abomasum. It keeps the particle size as small as possible in order to pass into the abomasum. The omasum also absorbs volatile fatty acids and ammonia. [21]

After this, the digesta is moved to the true stomach, the abomasum. This is the gastric compartment of the ruminant stomach. The abomasum is the direct equivalent of the monogastric stomach, and digesta is digested here in much the same way. This compartment releases acids and enzymes that further digest the material passing through. This is also where the ruminant digests the microbes produced in the rumen. [21] Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. The small intestine is the main site of nutrient absorption. The surface area of the digesta is greatly increased here because of the villi that are in the small intestine. This increased surface area allows for greater nutrient absorption. Microbes produced in the reticulorumen are also digested in the small intestine. After the small intestine is the large intestine. The major roles here are breaking down mainly fiber by fermentation with microbes, absorption of water (ions and minerals) and other fermented products, and also expelling waste. [23] Fermentation continues in the large intestine in the same way as in the reticulorumen.

Only small amounts of glucose are absorbed from dietary carbohydrates. Most dietary carbohydrates are fermented into VFAs in the rumen. The glucose needed as energy for the brain and for lactose and milk fat in milk production, as well as other uses, comes from nonsugar sources, such as the VFA propionate, glycerol, lactate, and protein. The VFA propionate is used for around 70% of the glucose and glycogen produced and protein for another 20% (50% under starvation conditions). [24] [25]

Abundance, distribution, and domestication

Wild ruminants number at least 75 million [26] and are native to all continents except Antarctica and Australia. [4] Nearly 90% of all species are found in Eurasia and Africa. [26] Species inhabit a wide range of climates (from tropic to arctic) and habitats (from open plains to forests). [26]

The population of domestic ruminants is greater than 3.5 billion, with cattle, sheep, and goats accounting for about 95% of the total population. Goats were domesticated in the Near East circa 8000 BC. Most other species were domesticated by 2500 BC., either in the Near East or southern Asia. [26]

Ruminant physiology

Ruminating animals have various physiological features that enable them to survive in nature. One feature of ruminants is their continuously growing teeth. During grazing, the silica content in forage causes abrasion of the teeth. This is compensated for by continuous tooth growth throughout the ruminant's life, as opposed to humans or other nonruminants, whose teeth stop growing after a particular age. Most ruminants do not have upper incisors; instead, they have a thick dental pad to thoroughly chew plant-based food. [27] Another feature of ruminants is the large ruminal storage capacity that gives them the ability to consume feed rapidly and complete the chewing process later. This is known as rumination, which consists of the regurgitation of feed, rechewing, resalivation, and reswallowing. Rumination reduces particle size, which enhances microbial function and allows the digesta to pass more easily through the digestive tract. [21]

Rumen microbiology

Vertebrates lack the ability to hydrolyse the beta [1–4] glycosidic bond of plant cellulose due to the lack of the enzyme cellulase. Thus, ruminants completely depend on the microbial flora, present in the rumen or hindgut, to digest cellulose. Digestion of food in the rumen is primarily carried out by the rumen microflora, which contains dense populations of several species of bacteria, protozoa, sometimes yeasts and other fungi – 1 ml of rumen is estimated to contain 10–50 billion bacteria and 1 million protozoa, as well as several yeasts and fungi. [28]

Since the environment inside a rumen is anaerobic, most of these microbial species are obligate or facultative anaerobes that can decompose complex plant material, such as cellulose, hemicellulose, starch, and proteins. The hydrolysis of cellulose results in sugars, which are further fermented to acetate, lactate, propionate, butyrate, carbon dioxide, and methane.

As bacteria conduct fermentation in the rumen, they consume about 10% of the carbon, 60% of the phosphorus, and 80% of the nitrogen that the ruminant ingests. [29] To reclaim these nutrients, the ruminant then digests the bacteria in the abomasum. The enzyme lysozyme has adapted to facilitate digestion of bacteria in the ruminant abomasum. [30] Pancreatic ribonuclease also degrades bacterial RNA in the ruminant small intestine as a source of nitrogen. [31]

During grazing, ruminants produce large amounts of saliva – estimates range from 100 to 150 litres of saliva per day for a cow. [32] The role of saliva is to provide ample fluid for rumen fermentation and to act as a buffering agent. [33] Rumen fermentation produces large amounts of organic acids, thus maintaining the appropriate pH of rumen fluids is a critical factor in rumen fermentation. After digesta passes through the rumen, the omasum absorbs excess fluid so that digestive enzymes and acid in the abomasum are not diluted. [1]

Tannin toxicity in ruminant animals

Tannins are phenolic compounds that are commonly found in plants. Found in the leaf, bud, seed, root, and stem tissues, tannins are widely distributed in many different species of plants. Tannins are separated into two classes: hydrolysable tannins and condensed tannins. Depending on their concentration and nature, either class can have adverse or beneficial effects. Tannins can be beneficial, having been shown to increase milk production, wool growth, ovulation rate, and lambing percentage, as well as reducing bloat risk and reducing internal parasite burdens. [34]

Tannins can be toxic to ruminants, in that they precipitate proteins, making them unavailable for digestion, and they inhibit the absorption of nutrients by reducing the populations of proteolytic rumen bacteria. [34] [35] Very high levels of tannin intake can produce toxicity that can even cause death. [36] Animals that normally consume tannin-rich plants can develop defensive mechanisms against tannins, such as the strategic deployment of lipids and extracellular polysaccharides that have a high affinity to binding to tannins. [34] Some ruminants (goats, deer, elk, moose) are able to consume food high in tannins (leaves, twigs, bark) due to the presence in their saliva of tannin-binding proteins. [37]

Religious importance

The Law of Moses in the Bible allowed the eating of some mammals that had cloven hooves (i.e. members of the order Artiodactyla) and "that chew the cud", [38] a stipulation preserved to this day in Jewish dietary laws.

Other uses

The verb 'to ruminate' has been extended metaphorically to mean to ponder thoughtfully or to meditate on some topic. Similarly, ideas may be 'chewed on' or 'digested'. 'Chew the (one's) cud' is to reflect or meditate. In psychology, "rumination" refers to a pattern of thinking, and is unrelated to digestive physiology.

Ruminants and climate change

Methane is produced by a type of archaea, called methanogens, as described above within the rumen, and this methane is released to the atmosphere. The rumen is the major site of methane production in ruminants. [39] Methane is a strong greenhouse gas with a global warming potential of 86 compared to CO2 over a 20-year period. [40] [41] [42]

As a by-product of consuming cellulose, cattle belch out methane, there-by returning that carbon sequestered by plants back into the atmosphere. After about 10 to 12 years, that methane is broken down and converted back to CO2. Once converted to CO2, plants can again perform photosynthesis and fix that carbon back into cellulose. From here, cattle can eat the plants and the cycle begins once again. In essence, the methane belched from cattle is not adding new carbon to the atmosphere. Rather it is part of the natural cycling of carbon through the biogenic carbon cycle. [43]

In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world, [44] 26% of the total greenhouse gas emissions from agricultural activity in the U.S., and 22% of the total U.S. methane emissions. [45] The meat from domestically raised ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies. [46] Methane production by meat animals, principally ruminants, is estimated 15–20% global production of methane, unless the animals were hunted in the wild. [47] [48] The current U.S. domestic beef and dairy cattle population is around 90 million head, approximately 50% higher than the peak wild population of American bison of 60 million head in the 1700s, [49] which primarily roamed the part of North America that now makes up the United States.

See also

Related Research Articles

<span class="mw-page-title-main">Even-toed ungulate</span> Order of mammals

The even-toed ungulates are ungulates—hoofed animals—which bear weight equally on two of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, odd-toed ungulates bear weight on an odd number of the five toes. Another difference between the two is that many other even-toed ungulates digest plant cellulose in one or more stomach chambers rather than in their intestine as the odd-toed ungulates do.

<span class="mw-page-title-main">Dietary fiber</span> Portion of plant-derived food that cannot be completely digested

Dietary fiber or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by their solubility, viscosity, and fermentability, which affect how fibers are processed in the body. Dietary fiber has two main components: soluble fiber and insoluble fiber, which are components of plant-based foods, such as legumes, whole grains and cereals, vegetables, fruits, and nuts or seeds. A diet high in regular fiber consumption is generally associated with supporting health and lowering the risk of several diseases. Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins, pectins, beta-glucans, and oligosaccharides.

<span class="mw-page-title-main">Digestion</span> Biological process of breaking down food

Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small molecules the body can use.

<span class="mw-page-title-main">Chewing</span> Mechanical procedure for crushing the food and its first enzymatic splitting

Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding. The muscles of mastication move the jaws to bring the teeth into intermittent contact, repeatedly occluding and opening. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down carbohydrates in the food. After chewing, the food is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs. Increasing the number of chews per bite increases relevant gut hormones. Studies suggest that chewing may decrease self-reported hunger and food intake. Chewing gum has been around for many centuries; there is evidence that northern Europeans chewed birch bark tar 9,000 years ago.

Cud is a portion of food that returns from a ruminant's stomach to the mouth to be chewed for the second time. More precisely, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the physical digestive process of rumination.

A monogastric organism has a simple single-chambered stomach. Examples of monogastric herbivores are horses and rabbits. Examples of monogastric omnivores include humans, pigs, hamsters and rats. Furthermore, there are monogastric carnivores such as cats. A monogastric organism is comparable to ruminant organisms, such as cattle, goats, or sheep. Herbivores with monogastric digestion can digest cellulose in their diets by way of symbiotic gut bacteria. However, their ability to extract energy from cellulose digestion is less efficient than in ruminants.

The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allows it to serve as the primary site for microbial fermentation of ingested feed. The smaller part of the reticulorumen is the reticulum, which is fully continuous with the rumen, but differs from it with regard to the texture of its lining.

<span class="mw-page-title-main">Omasum</span> Third stomach compartment in ruminents

The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants. The omasum comes after the rumen and reticulum and before the abomasum. Different ruminants have different omasum structures and function based on the food that they eat and how they developed through evolution.

<span class="mw-page-title-main">Enteric fermentation</span> Digestive process that emits methane

Enteric fermentation is a digestive process by which carbohydrates are broken down by microorganisms into simple molecules for absorption into the bloodstream of an animal. Because of human agricultural reliance in many parts of the world on animals which digest by enteric fermentation, it is one of the factors in increased methane emissions.

<span class="mw-page-title-main">Abomasum</span> Fourth and final stomach compartment in ruminants

The abomasum, also known as the maw, rennet-bag, or reed tripe, is the fourth and final stomach compartment in ruminants. It secretes rennet, which is used in cheese creation.

Cecotropes, also called caecotrophs, caecal pellets, or night feces, are the product of the cecum, a part of the digestive system in mammals of the order Lagomorpha, which includes two families: Leporidae, and Ochotonidae (pikas). Cecotropes are passed through the intestines and subsequently reingested for added nutrients in a process known as "cecotrophy", "cecophagy", "pseudorumination", "refection", coprophagia or "coprophagy". Reingestion is also practiced by a few species of rodent, some marsupials and one species of primate.

In biology, syntrophy, synthrophy, or cross-feeding is the phenomenon of one species feeding on the metabolic products of another species to cope up with the energy limitations by electron transfer. In this type of biological interaction, metabolite transfer happens between two or more metabolically diverse microbial species that live in close proximity to each other. The growth of one partner depends on the nutrients, growth factors, or substrates provided by the other partner. Thus, syntrophism can be considered as an obligatory interdependency and a mutualistic metabolism between two different bacterial species.

Neocallimastigomycota is a phylum containing anaerobic fungi, which are symbionts found in the digestive tracts of larger herbivores. Anaerobic fungi were originally placed within phylum Chytridiomycota, within Order Neocallimastigales but later raised to phylum level, a decision upheld by later phylogenetic reconstructions. It encompasses only one family.

<span class="mw-page-title-main">Cetruminantia</span> Taxonomic clade

The Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.

Fibrobacter succinogenes is a cellulolytic bacterium species in the genus Fibrobacter. It is present in the rumen of cattle. F. succinogenes is a gram negative, rod-shaped, obligate anaerobe that is a major contributor to cellulose digestion. Since its discovery in the 1950s, it has been studied for its role in herbivore digestion and cellulose fermentation, which can be utilized in biofuel production.

Hindgut fermentation is a digestive process seen in monogastric herbivores, animals with a simple, single-chambered stomach. Cellulose is digested with the aid of symbiotic bacteria. The microbial fermentation occurs in the digestive organs that follow the small intestine: the large intestine and cecum. Examples of hindgut fermenters include proboscideans and large odd-toed ungulates such as horses and rhinos, as well as small animals such as rodents, rabbits and koalas. In contrast, foregut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, as well as in sloths, macropodids, some monkeys, and one bird, the hoatzin.

Methanogens are a group of microorganisms that produce methane as a byproduct of their metabolism. They play an important role in the digestive system of ruminants. The digestive tract of ruminants contains four major parts: rumen, reticulum, omasum and abomasum. The food with saliva first passes to the rumen for breaking into smaller particles and then moves to the reticulum, where the food is broken into further smaller particles. Any indigestible particles are sent back to the rumen for rechewing. The majority of anaerobic microbes assisting the cellulose breakdown occupy the rumen and initiate the fermentation process. The animal absorbs the fatty acids, vitamins and nutrient content on passing the partially digested food from the rumen to the omasum. This decreases the pH level and initiates the release of enzymes for further breakdown of the food which later passes to the abomasum to absorb remaining nutrients before excretion. This process takes about 9–12 hours.

<span class="mw-page-title-main">Displaced abomasum</span>

Displaced abomasum in cattle occurs when the abomasum, also known as the true stomach, which typically resides on the floor of the abdomen, fills with gas and rises to the top of the abdomen, where it is said to be ‘displaced’. When the abomasum moves from its normal position it prevents the natural passage of gas and feed through the digestive system, creating a restriction. As cattle are ruminants, which have a 4 chambered stomach composed of a rumen, reticulum, omasum and abomasum. Ruminants require this specialized digestive system in order to properly process and break down their high fiber and cellulose rich diets. As this type of digestive system is quite complex it is at a greater risk for incidence. Due to the natural anatomy of cattle it is more common to have the abomasum displace to the left, known as a left-displaced abomasum, than to the right, right-displaced abomasum. When the abomasum becomes displaced there also becomes a chance of an abomasal volvulus, twist, developing. An abomasal volvulus occurs when the abomasum, which is already out of place, will rotate and cut off blood and nutrient supply to the abomasum. Cattle which develop an abomasal twist require immediate vet attention to regain blood supply and food passage through the digestive system or the abomasum will begin to shut down due to lack of blood supply and toxicity development.

<span class="mw-page-title-main">Jarman-Bell principle</span> Ecological concept linking an herbivores diet and size

The Jarman-Bell principle, coined by P.J Jarman (1968.) and R.H.V Bell (1971), is a concept in ecology offering a link between a herbivore's diet and their overall size. It operates by observing the allometric properties of herbivores. According to the Jarman-Bell principle, the food quality of a herbivore's intake decreases as the size of the herbivore increases, but the amount of such food increases to counteract the low quality foods.

<i>Anaeromyces robustus</i> Fungus living in the gut of cows and sheep

Anaeromyces robustus is a fungal microorganism that lives in the gut rumen of many ruminant herbivores such as cows and sheep. Previously thought to be protozoa from their flagellated zoospores, they are biomass degraders and help the animal by breaking down carbohydrates and plant materials from the food the animal ingests. This fungus, therefore, is anaerobic and lives without oxygen. Gut fungi are dramatically outnumbered by other organisms in the microbiome; however, they are important members of the gut microbiome in ruminants and hind-gut fermenters and play a key role in digestion.


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