# Rumen

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{{Short description|First compartment of ruminant stomach}}
{{For|the given name|Rumen (given name)}}
{{more footnotes|date=January 2015}}
The '''rumen''', also known as a '''paunch''', is the largest stomach compartment in [ruminant](/source/ruminant)s.<ref name=":6">{{Cite web |last1=Parish |first1=Jane |last2=Rivera |first2=Daniel |last3=Boland |first3=Holly |date=November 18, 2024 |title=Understanding the Ruminant Animal Digestive System |url=https://extension.msstate.edu/publications/understanding-the-ruminant-animal-digestive-system |access-date=November 18, 2024 |website=Mississippi State University Extension. Service}}</ref> The rumen and the reticulum make up the [reticulorumen](/source/reticulorumen) in [ruminant](/source/ruminant) animals.<ref name=":0">{{Cite web|title=The ruminant digestive system|url=https://extension.umn.edu/dairy-nutrition/ruminant-digestive-system|access-date=2021-02-21|website=extension.umn.edu|language=en}}</ref> The diverse [microbial](/source/microbial) communities in the rumen allows it to serve as the primary site for microbial [fermentation](/source/fermentation_(food)) of ingested feed, which is often fiber-rich roughage typically indigestible by [mammalian](/source/Mammal) digestive systems.<ref name=":0" /><ref name=":7">{{Cite journal |last1=Baldwin |first1=Ransom L. |last2=Connor |first2=Erin E. |date=2017-11-01 |title=Rumen Function and Development |url=https://linkinghub.elsevier.com/retrieve/pii/S0749072017300543 |journal=Veterinary Clinics of North America: Food Animal Practice |series=Digestive Disorders of the Forestomach |volume=33 |issue=3 |pages=427–439 |doi=10.1016/j.cvfa.2017.06.001 |pmid=28807474 |issn=0749-0720|url-access=subscription }}</ref> The rumen is known for containing unique microbial networks within its multiple sac compartments to break down nutrients into usable energy and fatty acids.<ref name=":5">{{Cite journal |last1=Soltis |first1=Macey P. |last2=Henniger |first2=Madison T. |last3=Egert-McLean |first3=Amanda M. |last4=Voy |first4=Brynn H. |last5=Moorey |first5=Sarah E. |last6=Schnieder |first6=Liesel G. |last7=Shepherd |first7=Elizabeth A. |last8=Christopher |first8=Courtney |last9=Campagna |first9=Shawn R. |last10=Smith |first10=Joe S. |last11=Mulon |first11=Pierre-Yves |last12=Anderson |first12=David E. |last13=Myer |first13=Phillip R. |date=2023-03-21 |title=Rumen biogeographical regions and their impact on microbial and metabolome variation |journal=Frontiers in Animal Science |language=English |volume=4 |article-number=1154463 |doi=10.3389/fanim.2023.1154463 |doi-access=free |issn=2673-6225}}</ref> 

== Brief anatomy ==

thumb|200px|Rumen of a sheep from left. 1 Atrium ruminis, 2 Saccus dorsalis, 3 Saccus ventralis, 4 Recessus ruminis, 5 Saccus cecus caudodorsalis, 6 Saccus cecus caudoventralis, 7 Sulcus cranialis, 8 Sulcus longitudinalis sinister, 9 Sulcus coronarius dorsalis, 10 Sulcus coronarius ventralis, 11 Sulcus caudalis, 12 Sulcus accessorius sinister, 13 Insula ruminis, 14 Sulcus ruminoreticularis, 15 Reticulum, 16 Abomasum, 17 Oesophagus, 18 Spleen.

The rumen is composed of five muscular sacs: cranial sac, ventral sac, dorsal sac, caudodorsal sac, and caudoventral blind sac. Each of these areas contain unique microbial communities, environments, and physical abilities that influence digestion.<ref name=":6" /><ref name=":5" />

The outer lining of the rumen, known as the epithelium, serves as a protective layer and contributes to the metabolic processing of [fermentation](/source/fermentation) products.<ref name=":7" />

The inner lining of the rumen wall is covered in small fingerlike projections called papillae, which aid in nutrient absorption.<ref name=":6" /> The [reticulum](/source/Reticulum_(anatomy)) is lined with ridges that form a [hexagonal](/source/hexagonal) [honeycomb](/source/honeycomb) pattern.<ref name=":6" /> These features increase the surface area of the [reticulorumen](/source/reticulorumen) wall, facilitating the absorption of [volatile fatty acids](/source/volatile_fatty_acids) and capture of smaller digesta particles.<ref name=":6" />

The rumen and the [reticulum](/source/Reticulum_(anatomy)) differ with regard to the makeup of the lining but account for approximately 80% of total [ruminant](/source/ruminant) stomach volume.<ref name=":6" />

== Digestion ==
Digestion in the rumen and [reticulorumen](/source/reticulorumen) occurs through [fermentation](/source/fermentation) by diverse [microbe](/source/microbe) communities to optimize resources from nutrient dense feed.<ref name=":8">{{Cite journal |last1=McCann |first1=Joshua C. |last2=Elolimy |first2=Ahmed A. |last3=Loor |first3=Juan J. |date=2017-11-01 |title=Rumen Microbiome, Probiotics, and Fermentation Additives |url=https://linkinghub.elsevier.com/retrieve/pii/S0749072017300622 |journal=Veterinary Clinics of North America: Food Animal Practice |series=Digestive Disorders of the Forestomach |volume=33 |issue=3 |pages=539–553 |doi=10.1016/j.cvfa.2017.06.009 |pmid=28764865 |issn=0749-0720|url-access=subscription }}</ref> Millions of [microorganisms](/source/Microorganism), including [bacteria](/source/bacteria), [archaea](/source/archaea), [viruses](/source/Virus), [fungi](/source/Fungus), and [protozoa](/source/protozoa), are known to reside in the [reticulorumen](/source/reticulorumen) and are essential to digest structural [carbohydrates](/source/Carbohydrate), like [lignocellulose](/source/Lignocellulosic_biomass) ([hemicellulose](/source/hemicellulose) and [cellulose](/source/cellulose)), non-structural [carbohydrates](/source/Carbohydrate) ([starch](/source/starch), [sugar](/source/sugar), and [pectin](/source/pectin)), [lipids](/source/Lipid), and [nitrogenous compounds](/source/Nitrogenous_compound) ([protein](/source/protein)s, [peptide](/source/peptide)s, and [amino acid](/source/amino_acid)s).<ref name=":8" /> 

Both non-structural and structural carbohydrates are [hydrolysed](/source/Hydrolysis) to [monosaccharide](/source/monosaccharide)s or [disaccharide](/source/disaccharide)s by microbial [enzymes](/source/Enzyme). The resulting [mono](/source/Monosaccharide)- and [disaccharides](/source/Disaccharide) are transported into the microbes.  Once within microbial cell walls, the [mono](/source/Monosaccharide)- and [disaccharides](/source/Disaccharide)  may be assimilated into microbial biomass or fermented to [volatile fatty acids](/source/volatile_fatty_acids) (VFAs), such as [acetate](/source/acetic_acid), [propionate](/source/propionic_acid), [butyrate](/source/butyric_acid), [lactate](/source/lactic_acid), [valerate](/source/valeric_acid) and other [branched-chain](/source/Branching_(polymer_chemistry)) VFAs via [glycolysis](/source/glycolysis) and other biochemical pathways to yield energy for the microbial cell.<ref name=":6" /><ref name=":7" />  Most VFAs are absorbed across the [reticulorumen](/source/reticulorumen) wall, directly into the bloodstream, and are used by the ruminant as substrates for energy production and [biosynthesis](/source/biosynthesis).<ref name=":6" /><ref>{{Cite journal|last1=Matthews|first1=Chloe|last2=Crispie|first2=Fiona|last3=Lewis|first3=Eva|last4=Reid|first4=Michael|last5=O'Toole|first5=Paul W.|last6=Cotter|first6=Paul D.|date=2018-09-12|title=The rumen microbiome: a crucial consideration when optimising milk and meat production and nitrogen utilisation efficiency|journal=Gut Microbes|volume=10|issue=2|pages=115–132|doi=10.1080/19490976.2018.1505176|issn=1949-0976|pmc=6546327|pmid=30207838}}</ref> Some [branched chain VFAs](/source/Branched-chain_fatty_acid) are incorporated into the [lipid membrane](/source/lipid_membrane) of rumen microbes. VFAs provide large amounts of energy for ruminants and are critical to the health of the rumen and its microbiome.<ref name=":9">{{Cite journal |last1=Soltis |first1=Macey P. |last2=Henniger |first2=Madison T. |last3=Egert-McLean |first3=Amanda M. |last4=Voy |first4=Brynn H. |last5=Moorey |first5=Sarah E. |last6=Schnieder |first6=Liesel G. |last7=Shepherd |first7=Elizabeth A. |last8=Christopher |first8=Courtney |last9=Campagna |first9=Shawn R. |last10=Smith |first10=Joe S. |last11=Mulon |first11=Pierre-Yves |last12=Anderson |first12=David E. |last13=Myer |first13=Phillip R. |date=2023-03-21 |title=Rumen biogeographical regions and their impact on microbial and metabolome variation |journal=Frontiers in Animal Science |language=English |volume=4 |article-number=1154463 |doi=10.3389/fanim.2023.1154463 |doi-access=free |issn=2673-6225}}</ref>  

[Lipid](/source/Lipid)s, [lignin](/source/lignin), [minerals](/source/minerals), and [vitamin](/source/vitamin)s play a less prominent role in digestion than carbohydrates and protein, but they are still critical in many ways. [Lipid](/source/Lipid)s are partly hydrolysed and hydrogenated, and [glycerol](/source/glycerol), if present in the lipid, is fermented. Lipids are otherwise inert in the rumen. Some carbon from carbohydrate or protein may be used for [de novo synthesis](/source/de_novo_synthesis) of microbial lipid.  High levels of lipid, particularly unsaturated lipid, in the rumen are thought to poison microbes and suppress fermentation activity. [Lignin](/source/Lignin), a phenolic compound, is recalcitrant to digestion, through it can be solubilized by fungi. Lignin is thought to shield associated nutrients from digestion and hence limits degradation. Minerals are absorbed by microbes and are necessary to their growth.  Microbes in turn synthesize many vitamins, such as [cyanocobalamin](/source/cyanocobalamin), in great quantities—often great enough to sustain the ruminant even when vitamins are highly deficient in the diet.

The protein ingested is either [degradable intake protein](/source/degradable_intake_protein) or [undegradable intake protein](/source/undegradable_intake_protein), or [rumen bypass protein](/source/rumen_bypass_protein).<ref name=":6" /> Protein is hydrolysed to [peptide](/source/peptide)s and [amino acids](/source/amino_acids) by microbial enzymes, which are subsequently transported across the microbial cell wall for assimilation into cell biomass, primarily.  Peptides, amino acids, ammonia, and other sources of nitrogen originally present in the feed can also be used directly by microbes with little to no hydrolysis. In situations in which nitrogen for microbial growth is in excess, protein and its derivatives can also be fermented to produce energy, yielding [ammonia](/source/ammonia). Excess [ammonia](/source/ammonia) is absorbed by the rumen and converted into [urea](/source/urea) in the liver. Non-amino acid nitrogen is used for synthesis of microbial amino acids.<ref name=":6" />

[Ruminants](/source/Ruminant) have access to food-sourced protein and microbial proteins produced by the [microbes](/source/microbes) in the rumen.<ref name=":6" /> This creates a [symbiotic](/source/Symbiosis) relationship between the [ruminant](/source/ruminant) and the [microbial](/source/Microorganism) communities, as the [microbes](/source/microbes) can be used as a protein source when washed into the [abomasum](/source/abomasum) section of the digestive tract.<ref name=":6" />

== Stratification and mixing of digesta ==
Digested food (digesta) in the rumen is not uniform, but rather stratified into gas, liquid, and particles of different sizes, densities, and other physical characteristics. Additionally, the digesta is subject to extensive mixing and complicated flow paths upon entry into the rumen. Though they may seem trivial at first, these complicated stratification, mixing, and flow patterns of digesta are a key aspect of digestive activity in the ruminant and thus warrant detailed discussion.

After being swallowed, food travels down the [oesophagus](/source/oesophagus) and is deposited in the [dorsal](/source/Dorsum_(biology)) part of the reticulum. Contractions of the reticulorumen propel and mix the recently ingested feed into the ruminal mat.  The mat is a thick mass of digesta, consisting of partially degraded, long, fibrous material.  Most material in the mat has been recently ingested, and as such, has considerable fermentable substrate remaining.  Microbial fermentation proceeds rapidly in the mat, releasing many gases.  Some of these gases are trapped in the mat, causing the mat to be buoyant.  As fermentation proceeds, fermentable substrate is exhausted, gas production decreases, and particles lose buoyancy due to loss of entrapped gas.  Digesta in the mat hence goes through a phase of increasing buoyancy followed by decreasing buoyancy.  Simultaneously, the size of digesta particles–relatively large when ingested–is reduced by microbial fermentation and, later, rumination. Incomplete digestion of plant material here will result in the formation of a type of [bezoar](/source/bezoar) called Phytobezoars. At a certain point, particles are dense and small enough that they may "fall" through the rumen mat into the ventral sac below, or they may be swept out of the rumen mat into the reticulum by liquid gushing through the mat during ruminal contractions. Once in the ventral sac, digesta continues to ferment at decreased rates, further losing buoyancy and decreasing in particle size.  It is soon swept into the ventral reticulum by ruminal contractions.

In the ventral reticulum, less dense, larger digesta particles may be propelled up into the oesophagus and mouth during contractions of the reticulum.  Digesta is chewed in the mouth in a process known as [rumination](/source/ruminant), then impelled back down the oesophagus and deposited in the dorsal sac of the reticulum, to be lodged and mixed into the ruminal mat again.  Denser, small particles stay in the ventral reticulum during reticular contraction, and then during the next contraction may be swept out of the reticulorumen with liquid through the [reticulo-omasal orifice](/source/reticulo-omasal_orifice), which leads to the next chamber in the ruminant animal's alimentary canal, the [omasum](/source/omasum).

Water and saliva enter through the rumen to form a liquid pool.  Liquid will ultimately escape from the reticulorumen from absorption through the wall, or through passing through the reticulo-omasal orifice, as digesta does.  However, since liquid cannot be trapped in the mat as digesta can, liquid passes through the rumen much more quickly than digesta does.  Liquid often acts as a carrier for very small digesta particles, such that the dynamics of small particles is similar to that of liquid.

The uppermost area of the rumen, the headspace, is filled with [gas](/source/gas)es (such as [methane](/source/methane), [carbon dioxide](/source/carbon_dioxide), and, to a much lower degree, [hydrogen](/source/hydrogen)) released from [fermentation](/source/fermentation_(biochemistry)) and [anaerobic respiration](/source/anaerobic_respiration) of food. These gases are regularly expelled from the reticulorumen through the mouth, in a process called [eructation](/source/eructation).

== Microbes in reticulorumen ==
thumb|upright=1.75|Bacteria dominate rumen microbiome; composition can change substantially with diet.<ref name="Kibegwa2023">{{cite journal |last1=Kibegwa |first1=Felix M. |last2=Bett |first2=Rawlynce C. |last3=Gachuiri |first3=Charles K. |last4=Machuka |first4=Eunice |last5=Stomeo |first5=Francesca |last6=Mujibi |first6=Fidalis D. |date=13 January 2023 |title=Diversity and functional analysis of rumen and fecal microbial communities associated with dietary changes in crossbreed dairy cattle |journal=PLOS ONE |volume=18 |issue=1 |article-number=e0274371 |doi=10.1371/journal.pone.0274371 |doi-access=free |pmid=36638091 |bibcode=2023PLoSO..1874371K |pmc=9838872 }}</ref>
{{Further|Methanogens in digestive tract of ruminants}}
The different sacs of the rumen allow for varying ecological niches for microbes in the reticulorumen, including [bacteria](/source/bacterium), [protozoa](/source/protozoa), [fungi](/source/fungus), [archaea](/source/archaea), and [virus](/source/virus)es.<ref name=":9" /> Each microbial community depends on a variety of enzymes to breakdown [lignocellulose](/source/lignocellulose), nonstructural [carbohydrates](/source/Carbohydrate), [nitrogenous compounds](/source/Nitrogenous_compound), and [lipids](/source/Lipid).<ref name=":8" />  

Bacteria, along with [protozoa](/source/protozoa), are the predominant microbes and by mass account for 40-60% of total microbial matter in the rumen.<ref name="Kibegwa2023" /><ref name=":10">{{Cite journal |last1=Cammack |first1=Kristi M. |last2=Austin |first2=Kathleen J. |last3=Lamberson |first3=William R. |last4=Conant |first4=Gavin C. |last5=Cunningham |first5=Hannah C. |date=2018-03-06 |title=RUMINANT NUTRITION SYMPOSIUM: Tiny but mighty: the role of the rumen microbes in livestock production |journal=Journal of Animal Science |volume=96 |issue=2 |pages=752–770 |doi=10.1093/jas/skx053 |issn=1525-3163 |pmc=6140983 |pmid=29385535}}</ref> They are categorized into several functional groups, such as [fibrolytic](/source/fibrolytic), [amylolytic](/source/amylolysis), and [proteolytic](/source/proteolysis) types, which preferentially digest structural carbohydrates, non-structural carbohydrates, and protein, respectively. [Protozoa](/source/Protozoa) (40-60% of microbial mass) derive their nutrients through [phagocytosis](/source/phagocytosis) of other microbes, and degrade and digest feed [carbohydrates](/source/Carbohydrate), especially starch and sugars, and protein.<ref name="Kibegwa2023" />   

Ruminal [fungi](/source/Fungus) make up 5-10% of microbes and are absent on diets poor in fibre.<ref name=":10" />  Fungi occupy an important niche in the rumen because they hydrolyse some ester linkages between [lignin](/source/lignin) and [hemicellulose](/source/hemicellulose) or [cellulose](/source/cellulose), and help break down digesta particles.  [Archaea](/source/Archaea), approximately 3% of total microbes, are mostly [autotrophic](/source/autotrophic) methanogens and produce [methane](/source/methane) through [anaerobic respiration](/source/anaerobic_respiration).<ref name=":10" />  Most of the hydrogen produced by [bacteria](/source/bacteria), [protozoa](/source/protozoa) and [fungi](/source/Fungus) is used by these [methanogens](/source/Methanogen) to reduce [carbon dioxide](/source/carbon_dioxide) to [methane](/source/methane).<ref name=":10" /> [Viruses](/source/Virus) are present in unknown numbers and have not been well studied.  However, they can [lyse](/source/lysis) microbes, releasing their contents for other microbes to assimilate and ferment in a process called [microbial recycling](/source/microbial_recycling), although recycling through the predatory activities of protozoa is quantitatively more important.<ref name=":10" />

[Microbes](/source/Microbes) in the [reticulorumen](/source/reticulorumen) eventually flow out into the [omasum](/source/omasum) and the remainder of the [alimentary canal](/source/alimentary_canal).  Under normal [fermentation](/source/fermentation) conditions the environment in the [reticulorumen](/source/reticulorumen) is weakly acidic and is populated by microbes that are adapted to a pH between roughly 5.5 and 6.5; since the abomasum is strongly acidic (pH 2 to 4), it acts as a barrier that largely kills [reticulorumen](/source/reticulorumen) [flora](/source/flora) and [fauna](/source/fauna) as they flow into it.<ref name=":6" />  Subsequently, microbial [biomass](/source/biomass) is digested in the [small intestine](/source/small_intestine) and smaller molecules (mainly [amino acids](/source/Amino_acid)) are absorbed and transported in the portal vein to the liver.<ref name=":6" />  The digestion of these [microbes](/source/microbes) in the small intestine is a major source of nutrition, as microbes usually supply some 60 to 90% of the total amount of amino acids absorbed. On starch-poor diets, they also provide the predominant source of glucose absorbed from the small intestinal contents.<ref name=":6" /><ref name="Kibegwa2023" />

== Human uses ==
The feed contained within the reticulorumen, known as "paunch waste", has been studied as a fertiliser for use in [sustainable agriculture](/source/sustainable_agriculture).<ref>{{cite conference |last1=McCabe |first1=Bernadette K. |last2=Antille |first2=Diogenes L. |last3=Birt |first3=Henry W. G. |last4=Spence |first4=Jennifer E. |last5=BFernana |first5=Jamal M. |last6=der Spek |first6=Wilmer Bvan |last7=Baillie |first7=Craig P. |date=July 17–20, 2016 |title=An Investigation into the Fertilizer Potential of Slaughterhouse Cattle Paunch |url=https://www.researchgate.net/publication/304244483 |conference=2016 American Society of Agricultural and Biological Engineers Annual International Meeting |location=Orlando, FL |id=Paper No. 16-2460831 |doi=10.13031/aim.202460831|doi-broken-date=12 July 2025 }}</ref>

== Development ==
At birth, the rumen [organ](/source/Organ_(anatomy)), rumen [epithelium](/source/epithelium), and rumen [microbiota](/source/microbiota) are not fully developed and are metabolically nonfunctional.<ref name=":7" /> The developing rumen does not display the level of keratinization seen in the mature organ.<ref name=":7" />  Generally, the most receptive time for rumen development is between the [postnatal](/source/Postpartum_period) and [weaning](/source/weaning) periods. Over this period, rumen organ and [epithelium](/source/epithelium) growth, along with the establishment of rumen [microbiota](/source/microbiota), will prove to be essential to rumen development.<ref name=":1">{{Cite journal|last1=Diao|first1=Qiyu|last2=Zhang|first2=Rong|last3=Fu|first3=Tong|date=2019-07-26|title=Review of Strategies to Promote Rumen Development in Calves|journal=Animals|volume=9|issue=8|page=490|doi=10.3390/ani9080490|issn=2076-2615|pmc=6720602|pmid=31357433|doi-access=free}}</ref> This process is influenced by the introduction of solid food and the establishment of [fermentation](/source/fermentation) in the rumen.<ref name=":7" /> Additionally, there must be an adequate amount of [short chain fatty acids](/source/Short-chain_fatty_acid), produced during [fermentation](/source/fermentation), to properly develop the papillae.<ref name=":7" /> 

[Papilla](/source/Dermal_papillae)e growth in rumen [epithelium](/source/epithelium) is essential for rumen functionality. Papillae increase the surface area inside of the rumen and allow for a considerable increase in nutrient [absorption](/source/Absorption_(biology)) inside of the rumen.<ref name=":6" /> Distinguishing a developed from an undeveloped rumen is simplified by observing the carpeting of tissue surrounding the interior of the rumen, as an undeveloped rumen maintains a smooth, papillae-lacking outer surface, and a developed rumen possesses thick, papillae-full walls.<ref name=":7" /><ref>{{Cite web|last1=Bradley |first1=Katie Klein |title=Dairy Calf Rumen Development|url=https://www.purinamills.com/dairy-feed/education/detail/rumen-development-in-dairy-calves-101|access-date=2021-04-11|website=Purina Animal Nutrition|language=en}}</ref>

Due to ruminants being born with a sterile [gastrointestinal tract](/source/gastrointestinal_tract), the developing rumen must be exposed to an array of microflora at an early stage. Specific diets in which [microflora](/source/Microbiota) promote an [anaerobic](/source/Anaerobic_digestion) environment suitable for fermentation in the rumen are favored.<ref name=":1" /> Furthermore, feeds must be tailored to the needs of the specific [ruminants](/source/Ruminant), as developing [ruminants](/source/Ruminant) who have been on a strict liquid feed diet will possess different [microflora](/source/microflora) when compared to that of a developing [ruminant](/source/ruminant) fed with a combination of a dry and liquid feed.<ref name=":7" /> This is due to the nutrients ingested by the animal not entering into the rumen stomach compartment, as it is instead bypassed by the reflexive closure of the [esophageal](/source/esophagus) groove.<ref name=":1" />
thumb|Ruminant stomach structure
The most abundant bacteria present in the rumen microbiome include ''[Prevotella](/source/Prevotella), [Butyrivibrio](/source/Butyrivibrio)'', and ''[Ruminococcus](/source/Ruminococcus)''.<ref name=":2">{{Cite journal|last1=Matthews|first1=Chloe|last2=Crispie|first2=Fiona|last3=Lewis|first3=Eva|last4=Reid|first4=Michael|last5=O'Toole|first5=Paul W.|last6=Cotter|first6=Paul D.|date=2018-09-12|title=The rumen microbiome: a crucial consideration when optimising milk and meat production and nitrogen utilisation efficiency|journal=Gut Microbes|volume=10|issue=2|pages=115–132|doi=10.1080/19490976.2018.1505176|issn=1949-0976|pmc=6546327|pmid=30207838}}</ref> This is due to ruminant organisms ingesting high-forage, commonly grass-based diets. Their typical high-forage diets cause this significant demand for cellulose digesting bacteria to be ever-present. Other bacteria, such as ''Lachnospira multiparus, Prevotella ruminicola,'' and ''Butyrivibrio fibrisolvens'', play essential roles in the creation of [volatile fatty acids](/source/Short-chain_fatty_acid) (VFAs).<ref name=":2" /> Specific feeds can stimulate this extensive bacterial growth in the rumen and therefore aid in the production of these volatile fatty acids, which play a major role in rumen epithelium growth, capillary development, and papillae formation.<ref>{{Cite journal|last1=Yáñez-Ruiz|first1=David R.|last2=Abecia|first2=Leticia|last3=Newbold|first3=Charles J.|date=2015-10-14|title=Manipulating rumen microbiome and fermentation through interventions during early life: a review|journal=Frontiers in Microbiology|volume=6|page=1133|doi=10.3389/fmicb.2015.01133|issn=1664-302X|pmc=4604304|pmid=26528276|bibcode=2015FrMic...601133Y |doi-access=free}}</ref> Previous research identified the significant impact of volatile fatty acids on rumen development through the effects of the inter-ruminal insertion of [acetate](/source/acetate), [propionate](/source/propionate), and [butyrate](/source/butyrate).<ref name=":3">{{Cite journal|last1=Diao|first1=Qiyu|last2=Zhang|first2=Rong|last3=Fu|first3=Tong|date=August 2019|title=Review of Strategies to Promote Rumen Development in Calves|journal=Animals|language=en|volume=9|issue=8|page=490|doi=10.3390/ani9080490|pmid=31357433|pmc=6720602|doi-access=free}}</ref> The most visually notable and impactful of these volatile fatty acids was butyrate, which is synthesized naturally in ruminants through multiple anaerobic fermentation pathways of dietary substrates.<ref>{{Cite journal|last1=Esquivel-Elizondo|first1=S.|last2=Ilhan|first2=Z. E.|last3=Garcia-Peña|first3=E. I.|last4=Krajmalnik-Brown|first4=R.|title=Insights into Butyrate Production in a Controlled Fermentation System via Gene Predictions|journal=mSystems|year=2017|volume=2|issue=4|pages=e00051–17|doi=10.1128/mSystems.00051-17|doi-access=free|pmc=5516221|pmid=28761933}}</ref> Butyrate, mainly expressed in epithelial tissue lining, is involved in regulating a plethora of ruminant epithelial cell genes. Generally, butyrate regulates gene expression by acting on cell cycle control pathways.<ref>{{Cite journal|last1=Glauber|first1=J G|last2=Wandersee|first2=N J|last3=Little|first3=J A|last4=Ginder|first4=G D|date=1991-09-01|title=5'-flanking sequences mediate butyrate stimulation of embryonic globin gene expression in adult erythroid cells|journal=Molecular and Cellular Biology|volume=11|issue=9|pages=4690–4697|doi=10.1128/mcb.11.9.4690-4697.1991|pmid=1875947|pmc=361361}}</ref> In the epithelial wall of the rumen, butyrate regulates epithelial cell gene expression to increase blood flow and papilla proliferation.<ref name=":3" />

== Rumen microbiome genetics ==
Developing feeds to support the microbiome growth of both production and pet ruminant animals is vital; both for the overall health of the maturing animal and for reducing the costs associated with raising that animal. In the production animal realm, feeding can account for up to 75% of the overall cost associated with that animal, making it crucial to identify and satisfy the nutritional demands of the rumen.<ref name=":4">{{Cite journal|last1=Lima|first1=Joana|last2=Auffret|first2=Marc D.|last3=Stewart|first3=Robert D.|last4=Dewhurst|first4=Richard J.|last5=Duthie|first5=Carol-Anne|last6=Snelling|first6=Timothy J.|last7=Walker|first7=Alan W.|last8=Freeman|first8=Tom C.|last9=Watson|first9=Mick|last10=Roehe|first10=Rainer|date=2019-08-08|title=Identification of Rumen Microbial Genes Involved in Pathways Linked to Appetite, Growth, and Feed Conversion Efficiency in Cattle|journal=Frontiers in Genetics|volume=10|article-number=701|doi=10.3389/fgene.2019.00701|issn=1664-8021|pmc=6694183|pmid=31440274|doi-access=free}}</ref> Sampling microbial DNA from rumen epithelial cells has led to the identification of microbial genes and functional pathways associated with animal growth factors.<ref>{{Cite journal|last1=Li|first1=Junhua|last2=Zhong|first2=Huanzi|last3=Ramayo-Caldas|first3=Yuliaxis|last4=Terrapon|first4=Nicolas|last5=Lombard|first5=Vincent|last6=Potocki-Veronese|first6=Gabrielle|last7=Estellé|first7=Jordi|last8=Popova|first8=Milka|last9=Yang|first9=Ziyi|last10=Zhang|first10=Hui|last11=Li|first11=Fang|date=2020-05-30|title=A catalog of microbial genes from the bovine rumen unveils a specialized and diverse biomass-degrading environment|journal=GigaScience|volume=9|issue=6|article-number=giaa057|doi=10.1093/gigascience/giaa057|issn=2047-217X|pmc=7260996|pmid=32473013}}</ref> Microbial clusters in the rumen possess genes associated with many animal growth-related factors. Protein encoding genes that encode for bacterial cell functions, such as ''aguA, ptb'', K01188, and ''murD'', also are associated with the animal's average daily weight gain.<ref name=":4" /> Furthermore, vitamin B12 related genes, including ''cobD, tolC, and fliN,'' are also related to the daily feed intake of the animal.<ref name=":4" />

== References ==
{{Reflist}}
*{{Cite journal|last1=Nagaraja|first1=T. G.|last2=Titgemeyer|first2=E. C.|date=2007-06-01|title=Ruminal Acidosis in Beef Cattle: The Current Microbiological and Nutritional Outlook1, 2|journal=Journal of Dairy Science|series=Electronic Supplement|language=en|volume=90|pages=E17–E38|doi=10.3168/jds.2006-478|pmid=17517750|issn=0022-0302|doi-access=free}}
*{{Cite journal|title=Ruminal Acidosis in Feedlot: From Aetiology to Prevention|last1=Hernández|first1=Joaquín|last2=Benedito|first2=José Luis|date=2014|journal=The Scientific World Journal|language=en|last3=Abuelo|first3=Angel|last4=Castillo|first4=Cristina|volume=2014|article-number=702572|doi=10.1155/2014/702572|pmid=25489604|pmc=4247954|doi-access=free}}
*{{cite book |title=Ruminant Physiology: Digestion, Metabolism, Growth, and Reproduction |last=Cronjé |first=P. |author2=E.A. Boomker  |year=2000 |publisher=CABI Publishing |location=Wallingford, Oxfordshire, UK |isbn=0-85199-463-6 }}
* {{cite book |title=Quantitative Aspects of Ruminant Digestion and Metabolism, 2nd edition |last=Dijkstra |first=J. |author2=J.M. Forbes |author3=J. France |year=2005 |publisher=CABI Publishing |location=Wallingford, Oxfordshire, UK |isbn=0-85199-814-3 |url=http://www.cabi.org/bk_BookDisplay.asp?PID=1868 |page=736 pages }}{{Dead link|date=March 2022 |bot=InternetArchiveBot |fix-attempted=yes }} 
* {{cite book |title=The Rumen Microbial Ecosystem, 2nd edition |last=Hobson |first=P.N. |author2=C.S. Stewart  |year=1997 |publisher=Springer |location=New York |isbn=0-7514-0366-0 |url=https://books.google.com/books?id=--OAI30q6NgC&q=The+Rumen+Microbial+Ecosystem+free+download&pg=PA123 }}

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Category:Digestive system
Category:Ruminants
Category:Mammal anatomy

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Adapted from the Wikipedia article [Rumen](https://en.wikipedia.org/wiki/Rumen) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Rumen?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.