Hindgut fermentation is a digestive process seen in monogastric

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

s, animals with a simple, single-chambered stomach.

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 ...

is digested with the aid of

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

.Animal Structure & Function
. Sci.waikato.ac.nz. Retrieved on 2011-11-27. The

microbial A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

occurs in the digestive organs that follow the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

: the large intestine and cecum. Examples of

hindgut The hindgut (or epigaster) is the posterior ( caudal) part of the alimentary canal. In mammals, it includes the distal one third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and up to the ano-rectal juncti ...

fermenters include

proboscidea The Proboscidea (; , ) are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. From ...

ns and large odd-toed ungulates such as

horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

and

rhino A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...

s, as well as small animals such as

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

rabbits Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit specie ...

and

koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the womb ...

s. In contrast,

foregut fermentation Foregut fermentation is a form of digestion that occurs in the foregut of some animals. It has evolved independently in several groups of mammals, and also in the hoatzin bird. Foregut fermentation is employed by ruminants and pseudoruminants, s ...

is the form of cellulose digestion seen in 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 mal ...

which have a four-chambered stomach, as well as in

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

s, macropodids, some

monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...

s, and one bird, the hoatzin..

Cecum

Hindgut fermenters generally have a cecum and large intestine that are much larger and more complex than those of a foregut or midgut fermenter. Research on small cecum fermenters such as

flying squirrel Flying squirrels (scientifically known as Pteromyini or Petauristini) are a tribe of 50 species of squirrels in the family Sciuridae. Despite their name, they are not in fact capable of full flight in the same way as birds or bats, but they ar ...

s, rabbits and lemurs has revealed these mammals to have a GI tract about 10-13 times the length of their body. This is due to the high intake of

fiber Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

and other hard to digest compounds that are characteristic to the diet of monogastric herbivores. Unlike in foregut fermenters, the cecum is located after the stomach and small intestine in monogastric animals, which limits the amount of further digestion or absorption that can occur after the food is fermented.

Large intestine

In smaller hindgut fermenters of the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Lagomorpha (rabbits, hares, and pikas),

cecotrope Cecotropes, also called caecotrophs, caecal pellets, or night fecs, are the product of the cecum, a part of the digestive system in mammals of the order Lagomorpha, which includes two families: Leporidae (hares and rabbits), and Ochotonidae (pika ...

s formed in the cecum are passed through the large intestine and subsequently reingested to allow another opportunity to absorb nutrients. Cecotropes are surrounded by a layer of mucus which protects them from stomach acid but which does not inhibit nutrient absorption in the small intestine.

Coprophagy Coprophagia () or coprophagy () is the consumption of feces. The word is derived from the grc, κόπρος , "feces" and , "to eat". Coprophagy refers to many kinds of feces-eating, including eating feces of other species (heterospecifics), of ...

is also practiced by some rodents, such as the

capybara The capybaraAlso called capivara (in Brazil), capiguara (in Bolivia), chigüire, chigüiro, or fercho (in Colombia and Venezuela), carpincho (in Argentina, Paraguay and Uruguay) and ronsoco (in Peru). or greater capybara (''Hydrochoerus hydro ...

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus ''Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ani ...

and related species, and by the marsupial

common ringtail possum The common ringtail possum (''Pseudocheirus peregrinus'', Greek for "false hand" and Latin for "pilgrim" or "alien") is an Australian marsupial. It lives in a variety of habitats and eats a variety of leaves of both native and introduced plants, ...

. This process is also beneficial in allowing for restoration of the microflora population, or

gut flora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...

. These microbes are found in the digestive organs of living creatures and can act as protective agents that strengthen the

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

. Hindgut fermenters do have the ability to expel their microflora, which is useful during the acts of

hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...

estivation Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and ...

and

torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...

Efficiency

While foregut fermentation is generally considered more efficient, and monogastric animals cannot digest cellulose as efficiently as ruminants, hindgut fermentation allows animals to consume small amounts of low-quality forage all day long and thus survive in conditions where ruminants might not be able to obtain nutrition adequate for their needs. Hindgut fermenters are able to extract more nutrition out of small quantities of feed. The large hind-gut fermenters are bulk feeders: they ingest large quantities of low-nutrient food, which they process more rapidly than would be possible for a similarly sized foregut fermenter. The main food in that category is grass, and grassland grazers move over long distances to take advantage of the growth phases of grass in different regions.

Speed

The ability to process food more rapidly than foregut fermenters gives hindgut fermenters an advantage at very large body size, as they are able to accommodate significantly larger food intakes. The largest extant and prehistoric

megaherbivore Megaherbivores (Greek μέγας megas "large" and Latin ''herbivora'' "herbivore") are large terrestrial herbivores that can exceed in weight. This polyphyletic group of megafauna includes elephants, rhinos, hippos, and giraffes. The largest bo ...

s, elephants and

indricothere Paraceratheriidae is an extinct family of long-limbed, hornless rhinocerotoids, commonly known as paraceratheres or indricotheres, that originated in the Eocene epoch and lived until the early Miocene. The first paraceratheres were only about the ...

s (a type of rhino), respectively, have been hindgut fermenters. Study of the rates of evolution of larger maximum body mass in different terrestrial mammalian groups has shown that the fastest growth in body mass over time occurred in hindgut fermenters ( perissodactyls,

s and

proboscid The Proboscidea (; , ) are a taxonomy (biology), taxonomic order (biology), order of afrotherian mammals containing one living family (biology), family (Elephantidae) and several extinct families. First described by Johann Karl Wilhelm Illiger ...

s).

Types

Hindgut fermenters are subdivided into two groups based on the relative size of various digestive organs in relationship to the rest of the system:

colonic Colon cleansing, also known as colon therapy, or colon hydrotherapy, or a colonic, or colonic irrigation encompasses a number of alternative medical therapies claimed to remove unspecified toxins from the colon and intestinal tract by remo ...

fermenters tend to be larger species such as horses, and cecal fermenters are smaller animals such as rabbits and rodents.Grant, Kerri
Adaptations in Herbivore Nutrition
July 30, 2010. Lafebervet.com. Retrieved on 2017-10-16. However, in spite of the terminology, colonic fermenters such as horses make extensive use of the cecum to break down cellulose. Also, colonic fermenters typically have a proportionally longer large intestine than small intestine, whereas cecal fermenters have a considerably enlarged cecum compared to the rest of the digestive tract.

Insects

In addition to mammals, several insects are also hindgut fermenters, the best studied of which are the

termites Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattode ...

, which are characterised by an enlarged "paunch" of the hindgut that also houses the bulk of the gut microbiota. Digestion of wood particles in lower termites is accomplished inside the phagosomes of gut flagellates, but in the flagellate-free higher termites, this appears to be accomplished by fibre-associated bacteria.

References

{{reflist, 2 Digestive system Biology terminology