Cud is a portion of food that returns from a

ruminant 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. Th ...

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

bolus Bolus may refer to: Geography * Bolus, Iran, a village in Ardabil Province, Iran * Bolus, or Baulus, an Anatolian village on the site of ancient Berissa Medicine * Bolus (digestion), a ball-shaped mass moving through the digestive tract * Bolus ...

of semi-degraded food regurgitated from the reticulorumen of a

. Cud is produced during the physical digestive process of rumination.

Rumination

The

alimentary canal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

of ruminants, such as

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

giraffe The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, '' Giraffa cameloparda ...

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of ...

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated sh ...

alpaca The alpaca (''Lama pacos'') is a species of South American camelid mammal. It is similar to, and often confused with, the llama. However, alpacas are often noticeably smaller than llamas. The two animals are closely related and can success ...

s, and

antelope The term antelope is used to refer to many species of even-toed ruminant that are indigenous to various regions in Africa and Eurasia. Antelope comprise a wastebasket taxon defined as any of numerous Old World grazing and browsing hoofed mamm ...

, are unable to produce the enzymes required to break down the

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

and

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...

of plant matter. Accordingly, these animals rely on a symbiotic relationship with a wide range of microbes, which largely reside in the reticulorumen, and which are able to synthesize the requisite enzymes. The reticulorumen thus hosts a microbial fermentation which yields products (mainly volatile fatty acids and microbial protein), which the ruminant is able to digest and absorb. This allows the animals to extract nutritional value from cellulose which is usually undigested. The process of rumination is stimulated by the presence of

roughage Dietary fiber (in British English fibre) 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 the ...

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

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

. From the esophagus it is taken back to the mouth with retro peristaltic 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 so the cattle can extract the minerals present in the cud brought to the surface during rumination. 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 secretion to buffer the rumen pH. When food has been degraded sufficiently it passes from the reticulorumen through the reticulo-omasal orifice to the omasum followed by the

abomasum The abomasum, also known as the maw,The Cham ...

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, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

are only secreted from the

abomasum The abomasum, also known as the maw,The Cham ...

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

Chemistry

The reticulorumen has an optimum pH of 6.5 for the microbe population to thrive. 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 is a process causing increased acidity in the blood and other body tissues (i.e., an increase in hydrogen ion concentration). If not further qualified, it usually refers to acidity of the blood plasma. The term ''acidemia'' describes ...

, where the rumen pH can fall to 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 An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

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. Some dairy cows in intensive systems of milk production may have sub-acute acidosis because of the high rates of cereals in their diets relative to an insufficient amount of forage. However, most producers provide adequate

fodder Fodder (), also called provender (), is any agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food given to the animals (including ...

in the form of hay to prevent this.

References

{{reflist Digestive system Articles containing video clips Ruminants

Rumination

Chemistry

See also

References