Hindgut fermentation

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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 microbes including bacteria, archaea, and eukaryotes [1] . The microbial fermentation occurs in the digestive organs that follow the small intestine: the cecum and large intestine. 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. [2] In contrast, foregut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, [3] as well as in sloths, macropodids, some monkeys, and one bird, the hoatzin. [4]

Contents

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. [5] Research on small cecum fermenters such as flying squirrels, rabbits and lemurs has revealed these mammals to have a GI tract about 10-13 times the length of their body. [6] This is due to the high intake of fiber and other hard to digest compounds that are characteristic to the diet of monogastric herbivores. [7]

Easily digestible food is processed in the gastrointestinal tract & expelled as regular feces. But in order to get nutrients out of hard to digest fiber, some smaller hindgut fermenters, like lagomorphs (rabbits, hares, pikas), ferment fiber in the cecum (at the small and large intestine junction) and then expel the contents as cecotropes, which are reingested (cecotrophy). The cecotropes are then absorbed in the small intestine to utilize the nutrients. [7]

This process is also beneficial in allowing for restoration of the microflora population, or gut flora. These microbes are found in the gastrointestinal tract and can act as protective agents that strengthen the immune system. Small hindgut fermenters have the ability to expel their microflora, which is useful during the acts of hibernation, estivation and torpor.

Efficiency

While foregut fermentation is generally considered more efficient, and monogastric animals cannot digest cellulose as efficiently as ruminants, [5] 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. While ruminants require a good deal of time resting between meals, hindgut fermenters are able to take in smaller meals more frequently, allowing them to eat and move more readily. [8] The large hindgut 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. [9]

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 megaherbivores, elephants and indricotheres (a type of rhino), respectively, have been hindgut fermenters. [10] 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, rodents and proboscids). [11]

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 fermenters tend to be larger species such as horses, and cecal fermenters are smaller animals such as rabbits and rodents. [2] However, in spite of the terminology, colonic fermenters such as horses make extensive use of the cecum to break down cellulose. [12] [13] 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, which are characterised by an enlarged "paunch" of the hindgut that also houses the bulk of the gut microbiota. [14] 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. [15]

See also

Related Research Articles

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<span class="mw-page-title-main">Large intestine</span> Last part of the digestive system in vertebrates

The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. The colon is the longest portion of the large intestine, and the terms are often used interchangeably but most sources define the large intestine as the combination of the cecum, colon, rectum, and anal canal. Some other sources exclude the anal canal.

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

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<span class="mw-page-title-main">Gastrointestinal tract</span> Organ system within humans and other animals

The gastrointestinal tract 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 other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as faeces. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.

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The cecum or caecum is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body. The word cecum stems from the Latin caecus meaning blind.

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References

  1. ↑ Liu, Ning; et, al (2022). "Oxidative cleavage of cellulose in the horse gut". Microbial Cell Factories. 21 (1): 38. doi: 10.1186/s12934-022-01767-8 . PMC   8917663 . PMID   35279161.
  2. 1 2 Grant, Kerrin Adaptations in Herbivore Nutrition, July 30, 2010. Lafebervet.com. Retrieved on 2017-10-16.
  3. ↑ Hindgut versus Foregut Fermenters. Vcebiology.edublogs.org (2011-04-30). Retrieved on 2011-11-27.
  4. ↑ Grajal, A.; Strahl, S. D.; Parra, R.; Dominguez, M. G.; Neher, A. (1989). "Foregut fermentation in the Hoatzin, a Neotropical leaf-eating bird". Science. 245 (4923): 1236–1238. Bibcode:1989Sci...245.1236G. doi:10.1126/science.245.4923.1236. PMID   17747887. S2CID   21455374..
  5. 1 2 Animal Structure & Function Archived 2012-05-02 at the Wayback Machine . Sci.waikato.ac.nz. Retrieved on 2011-11-27.
  6. ↑ Lu, Hsiao-Pei; Yu-bin Wang; Shiao-Wei Huang; Chung-Yen Lin; Martin Wu; Chih-hao Hsieh; Hon-Tsen Yu (10 September 2012). "Metagenomic analysis reveals a functional signature for biomass degradation by cecal microbiota in the leaf-eating flying squirrel (Petaurista alborufus lena)". BMC Genomics. 1. 13 (1): 466. doi: 10.1186/1471-2164-13-466 . PMC   3527328 . PMID   22963241.
  7. 1 2 James (14 May 2010). "Comparative Digestion". VetSci. Retrieved 3 May 2013.
  8. ↑ Budiansky, Stephen (1997). The Nature of Horses . Free Press. ISBN   0-684-82768-9.
  9. ↑ van der Made, Jan; Grube, René (2010). "The rhinoceroses from Neumark-Nord and their nutrition". In Meller, Harald (ed.). Elefantenreich – Eine Fossilwelt in Europa (PDF) (in German and English). Halle/Saale. pp. 382–394, see p. 387.
  10. ↑ Clauss, M.; Frey, R.; Kiefer, B.; Lechner-Doll, M.; Loehlein, W.; Polster, C.; Roessner, G. E.; Streich, W. J. (2003-04-24). "The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut, and adaptations of hindgut fermenters" (PDF). Oecologia . 136 (1): 14–27. Bibcode:2003Oecol.136...14C. doi:10.1007/s00442-003-1254-z. PMID   12712314. S2CID   206989975.
  11. ↑ Evans, A. R.; et al. (2012-01-30). "The maximum rate of mammal evolution". PNAS . 109 (11): 4187–4190. Bibcode:2012PNAS..109.4187E. doi: 10.1073/pnas.1120774109 . PMC   3306709 . PMID   22308461.
  12. ↑ Williams, Carey A. (April 2004), "The Basics of Equine Nutrition", FS 038, vol. The Equine Science Center, Rutgers University, archived from the original on 2007-04-08, retrieved 2017-04-02
  13. ↑ Moore, B. E.; Dehority, B. A. (1993). "Effects of diet and hindgut defaunation on diet digestibility and microbial concentrations in the cecum and colon of the horse". Journal of Animal Science. 71 (12): 3350–3358. doi:10.2527/1993.71123350x. PMID   8294287.
  14. ↑ Brune, A.; Dietrich, C. (2015). "The Gut Microbiota of Termites: Digesting the Diversity in the Light of Ecology and Evolution". Annual Review of Microbiology. 69: 145–166. doi: 10.1146/annurev-micro-092412-155715 . PMID   26195303.
  15. ↑ Mikaelyan, A.; Strassert, J.; Tokuda, G.; Brune, A. (2014). "The fibre-associated cellulolytic bacterial community in the hindgut of wood-feeding higher termites (Nasutitermes spp.)". Environmental Microbiology. 16 (9): 2711–2722. Bibcode:2014EnvMi..16.2711M. doi:10.1111/1462-2920.12425.
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