Editing Ruminant (section)

==Rumen microbiology==
{{Further|Methanogens in digestive tract of ruminants}}
[[Vertebrate]]s lack the ability to hydrolyse the beta [1–4] glycosidic bond of plant cellulose due to the lack of the enzyme [[cellulase]]. Thus, ruminants completely depend on the microbial flora, present in the rumen or hindgut, to digest cellulose. Digestion of food in the rumen is primarily carried out by the rumen microflora, which contains dense populations of several species of [[bacteria]], [[protozoa]], sometimes [[yeasts]] and other [[fungi]] – 1 ml of rumen is estimated to contain 10–50 billion bacteria and 1 million protozoa, as well as several yeasts and fungi.<ref>{{cite web|url=http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/herbivores/microbes.html|title=Fermentation Microbiology and Ecology|access-date=25 January 2011|archive-date=26 September 2011|archive-url=https://web.archive.org/web/20110926050349/http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/herbivores/microbes.html|url-status=dead}}</ref>

Since the environment inside a rumen is [[:wikt:anaerobic|anaerobic]], most of these microbial species are [[Obligate anaerobe|obligate]] or [[Facultative anaerobic organism|facultative]] anaerobes that can decompose complex plant material, such as [[cellulose]], [[hemicellulose]], [[starch]], and [[Protein (nutrient)|protein]]s. The hydrolysis of cellulose results in sugars, which are further fermented to acetate, lactate, propionate, butyrate, carbon dioxide, and [[methane]].

As bacteria conduct fermentation in the rumen, they consume about 10% of the carbon, 60% of the phosphorus, and 80% of the nitrogen that the ruminant ingests.<ref name="Callewaert">{{cite journal|last1=Callewaert|first1=L.|last2=Michiels|first2=C. W.|title=Lysozymes in the animal kingdom|journal=Journal of Biosciences|date=2010|volume=35|issue=1|pages=127–160|doi=10.1007/S12038-010-0015-5|pmid=20413917|s2cid=21198203}}</ref> To reclaim these nutrients, the ruminant then digests the bacteria in the [[abomasum]]. The enzyme [[lysozyme]] has adapted to facilitate digestion of bacteria in the ruminant abomasum.<ref name="Irwin">{{cite journal|last1=Irwin|first1=D. M.|last2=Prager|first2=E. M.|last3=Wilson|first3=A. C.|title=Evolutionary genetics of ruminant lysozymes|journal=Animal Genetics|date=1992|volume=23|issue=3|pages=193–202|doi=10.1111/j.1365-2052.1992.tb00131.x|pmid=1503255}}</ref> [[Pancreatic ribonuclease]] also degrades bacterial RNA in the ruminant small intestine as a source of nitrogen.<ref>{{cite journal|last1=Jermann|first1=T. M.|last2=Opitz|first2=J. G.|last3=Stackhouse|first3=J.|last4=Benner|first4=S. A.|title=Reconstructing the evolutionary history of the artiodactyl ribonuclease superfamily |url=http://64.238.189.139/pubs/Reconstructing%20the%20evolutionary%20history%20of%20the%20artiodactyl%20ribonuclease%20superfamily.pdf|archive-url=https://web.archive.org/web/20190521104301/http://64.238.189.139/pubs/Reconstructing%20the%20evolutionary%20history%20of%20the%20artiodactyl%20ribonuclease%20superfamily.pdf|url-status=dead|archive-date=21 May 2019|journal=Nature|date=1995|volume=374|issue=6517|pages=57–59|doi=10.1038/374057a0|pmid=7532788|bibcode=1995Natur.374...57J|s2cid=4315312}}</ref>

During grazing, ruminants produce large amounts of saliva – estimates range from 100 to 150 litres of saliva per day for a cow.<ref>{{cite journal | last1 = Reid| first1 = J.T.| last2 = Huffman| first2 = C.F.| year = 1949 | title = Some physical and chemical properties of Bovine saliva which may affect rumen digestion and synthesis | url = http://www.journalofdairyscience.org/article/S0022-0302%2849%2992019-6/abstract | journal = Journal of Dairy Science | volume = 32 | issue = 2| pages = 123–132 | doi=10.3168/jds.s0022-0302(49)92019-6| doi-access = free}} {{open access}}</ref> The role of saliva is to provide ample fluid for rumen fermentation and to act as a buffering agent.<ref>{{cite web|url=http://arbl.cvmbs.colostate.edu:80/hbooks/pathphys/digestion/herbivores/rumination.html|archive-url=https://web.archive.org/web/19980129111027/http://arbl.cvmbs.colostate.edu:80/hbooks/pathphys/digestion/herbivores/rumination.html|url-status=dead|archive-date=29 January 1998|title=Rumen Physiology and Rumination}}</ref> Rumen fermentation produces large amounts of organic acids, thus maintaining the appropriate pH of rumen fluids is a critical factor in rumen fermentation. After digesta passes through the rumen, the omasum absorbs excess fluid so that digestive enzymes and acid in the abomasum are not diluted.<ref name="Clauss2014">{{cite journal|last1=Clauss|first1=M.|last2=Rossner|first2=G. E.|title=Old world ruminant morphophysiology, life history, and fossil record: exploring key innovations of a diversification sequence|journal=Annales Zoologici Fennici|date=2014|volume=51|issue=1–2|pages=80–94|doi=10.5735/086.051.0210|s2cid=85347098|url=http://www.zora.uzh.ch/id/eprint/94203/1/AnnZoolFenn_omasum_2014.pdf}}</ref>