This article is about the digestive process of a ruminant

Ruminant

A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...

. For other uses, see Cud (disambiguation)

Cud (disambiguation)

Cud is the portion of food regurgitated by a ruminant.Cud or CUD may also refer to:* Cud, a lump of metal on a coin caused by a die defect* Cud , an indie rock band formed in Leeds, England in 1987* Cannabis use disorders...

.

Cud is a portion of food that returns from a ruminant

Ruminant

A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...

's stomach in the mouth to be chewed for the second time. More accurately, it is a bolus

Bolus (digestion)

In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....

 of semi-degraded food regurgitated

Regurgitation (digestion)

Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...

 from the reticulorumen

Reticulorumen

The reticulorumen represents the first chamber in the alimentary canal of ruminant animals. It is composed of the rumen and reticulum. The reticulum differs from the rumen with regard to the texture of its lining. The rumen wall is covered in small, finger-like projections called papillae, which...

 of a ruminant

Ruminant

A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...

. Cud is produced during the physical digestive process of rumination

Rumination

The term rumination , meaning "to chew the cud," is used in several contexts:-Digestive rumination:* In animals, rumination is a part of normal digestion, in which the animal brings up swallowed food , chews it, and swallows it...

, or "chewing the cud". The idiomatic expression chewing one's cud means meditating or pondering; similar expressions such as "he chewed that over for a bit", or "chew on that!" likely have the same derivation.

Explanation

The alimentary canal of ruminants, such as cattle

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

, goat

Goat

The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s, sheep

Ovis

Ovis is a genus of mammals, part of the goat-antelope subfamily of the ruminant family Bovidae. Its five or more highly gregarious species are known as sheep...

, alpaca

Alpaca

An alpaca is a domesticated species of South American camelid. It resembles a small llama in appearance.Alpacas are kept in herds that graze on the level heights of the Andes of southern Peru, northern Bolivia, Ecuador, and northern Chile at an altitude of to above sea level, throughout the year...

s and antelope

Antelope

Antelope is a term referring to many even-toed ungulate species indigenous to various regions in Africa and Eurasia. Antelopes comprise a miscellaneous group within the family Bovidae, encompassing those old-world species that are neither cattle, sheep, buffalo, bison, nor goats...

, is unable to produce the enzymes required to break down the cellulose

Cellulose

Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

 and hemicellulose

Hemicellulose

A hemicellulose is any of several heteropolymers , such as arabinoxylans, present along with cellulose in almost all plant cell walls. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength...

 of plant matter. Accordingly, these animals have developed a symbiotic relationship with a wide range of microbes, which largely reside in the reticulorumen

Reticulorumen

The reticulorumen represents the first chamber in the alimentary canal of ruminant animals. It is composed of the rumen and reticulum. The reticulum differs from the rumen with regard to the texture of its lining. The rumen wall is covered in small, finger-like projections called papillae, which...

, and which are able to synthesize the requisite enzymes. The reticulorumen thus hosts a microbial fermentation which yields products (mainly volatile fatty acids

Volatile fatty acids

Volatile fatty acids are fatty acids with a carbon chain of six carbons or fewer. They are now usually referred to as short-chain fatty acids .They can be created through fermentation in the intestine.Examples include:* Acetic acid...

 and microbial protein), which the ruminant is able to digest and absorb. This allows digestion of less edible plants.

Process of ruminaton

The process of ruminaton is stimulated by the presence of roughage in the upper part of the reticulorumen

Reticulorumen

The reticulorumen represents the first chamber in the alimentary canal of ruminant animals. It is composed of the rumen and reticulum. The reticulum differs from the rumen with regard to the texture of its lining. The rumen wall is covered in small, finger-like projections called papillae, which...

. The chest cavity is stretched, forming a vacuum in the gullet that sucks the semi-liquid stomach content into the esophagus

Esophagus

The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

. From the esophagus it is taken back to the mouth with retro peristaltic

Peristalsis

Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 movements. When the stomach content, or the cud, arrives in the mouth of the ruminant, it is pushed against the palate with the tongue to remove excess liquid, the latter is swallowed and the solid material is chewed thoroughly. The function of rumination is that food is physically refined to expose more surface area for bacteria working in the reticulorumen, as well as stimulation of saliva

Saliva

Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

 secretion to buffer

Buffer solution

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a...

 the rumen pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

.

Chemistry

The reticulorumen has an optimum pH of 6.5 for the microbe population to live and function. Consumption by ruminants of an insufficiently fibrous diet leads to little cud formation and therefore lowered amounts of saliva production. This in turn is associated with rumen acidosis

Acidosis

Acidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....

, where the rumen pH can fall to as low as pH 5 or lower. Rumen acidosis is associated with a lowered appetite which leads to still lower rates of saliva secretion. Eventually, a collapse of the microbial ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

 in the rumen will occur because of the low pH. Acute rumen acidosis can lead to death of the animal, and will occur if the animal is allowed to eat a diet with no roughage but high levels of highly digestible starchy concentrate. It is thought that most dairy cows in intensive systems of milk production have sub-acute acidosis because of the high rates of cereals in their diets relative to an insufficient amount of forage.

Final digestion

When food has been degraded efficiently it passes from the reticulorumen through the reticulo-omasal orifice to the omasum

Omasum

The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants...

 followed by the abomasum

Abomasum

The abomasum, also known as the maw, and the rennet-bag, and the read, is the fourth and final stomach compartment in ruminants. It secretes rennin - the artificial form of which is called rennet, and is used in cheese creation....

 to continue the digestion process in the lower parts of the alimentary canal. No enzymes are secreted in the rumen. Enzymes and hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

 are only secreted from the Abomasum

Abomasum

The abomasum, also known as the maw, and the rennet-bag, and the read, is the fourth and final stomach compartment in ruminants. It secretes rennin - the artificial form of which is called rennet, and is used in cheese creation....

(fourth stomach) onwards, and ruminants function from that point onwards much like monogastric animals, such as pigs and humans.