Rumen
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The rumen, also known as a paunch, is the largest stomach compartment in
, which is fully continuous with the rumen, but differs from it with regard to the texture of its lining.Brief anatomy
The rumen is composed of several muscular sacs, the cranial sac, ventral sac, ventral blind sac, and reticulum.
The lining of the rumen wall is covered in small fingerlike projections called papillae, which are flattened, approximately 5mm in length and 3mm wide in cattle. The
Digestion
Digestion in the reticulorumen is a complex process. It occurs through fermentation by microbes in the reticulorumen rather than the animal per se. The reticulorumen is one of the few organs present in animals in which digestion of cellulose and other recalcitrant carbohydrates can proceed to any appreciable degree.
The main substrates of digestion in the reticulorumen are non-structural carbohydrates (
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
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, then expelled 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, which leads to the next chamber in the ruminant animal's alimentary canal, the 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
Reticulorumenal microbes
Microbes in the reticulorumen include
Ruminal fungi make up only 5-10% of microbes and are absent on diets poor in fibre. Despite their low numbers, the fungi still occupy an important niche in the rumen because they hydrolyse some ester linkages between
Microbes in the reticulorumen eventually flow out into the omasum and the remainder of the alimentary canal. Under normal fermentation conditions the environment in the 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 flora and fauna as they flow into it. Subsequently, microbial biomass is digested in the small intestine and smaller molecules (mainly amino acids) are absorbed and transported in the portal vein to the liver. The digestion of these 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.
Ruminal Acidosis: In cattle the ruminal acidosis is characterized by the decreased blood pH and bicarbonate due to the over production of ruminal D-lactate. It can appear as acute rumen acidosis due to lactic acid accumulation to sub-acute acidosis due to accumulation of VFAs in the rumen, although acute acidosis is more fatal than sub-acute rumen acidosis. The decrease in ciliated protozoal population of the ruminal fluid is a common feature of both acidosis and can be a good indicator of the ruminal acidosis. Acidosis in rumen occurs when the cattles consume excessive amount of rapidly fermentable non-structural carbohydrates and high grain-based diets with low fiber content. This leads to rapid fermentation of the organic substrates contributing to massive formation of VFAs and lactic acids leading to lower pH and subsequent reactions by the microbes of rumen.
Major differences between the two clinical forms of acidosis:
Remarks | Acute acidosis | Sub-acute acidosis |
---|---|---|
Presence of clinical signs | Yes | Maybe |
Mortality | Yes | No |
Ruminal Changes | ||
a.Rumen pH | Below 5 | 5.0-5.4 |
b.Lactic acid | Increase | Normal |
c.Volatile Fatty Acids | Decrease | Increase |
d.Gram negative bacteria | Decrease | Normal |
e.Gram positive bacteria | Increase | Normal |
f.Streptococcus bovis | Increase | Normal |
g.Lactobacillus spp | Increase | Normal |
h.Lactic acid producers | Increase | Increase |
i.Lactic acid consumers | Decrease | Increase |
Blood parameters | ||
a.Blood pH | Low | Borderline |
b.Bicarbonate | Low | Borderline |
c.Lactate | Increase | Normal |
Human uses
The feed contained within the reticulorumen, known as "paunch waste", has been studied as a fertiliser for use in sustainable agriculture.[4]
Rumen development
At birth, the rumen
Due to ruminants being born with a sterile gastrointestinal tract, the developing rumen must be exposed to an array of microflora at an early stage. This is why a specific diet in which microflora that promote an anaerobic environment in the rumen are favored. Furthermore, feeds must be tailored to the needs of the specific ruminants. Developing ruminants who have been on a strict liquid feed diet will possess different microflora when compared to that of a developing ruminant fed with a combination of a dry and liquid feed. 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 groove.[5]
The most abundant bacteria present in the rumen microbiome include
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.[12] Sampling microbial DNA from rumen epithelial cells has led to the identification of microbial genes and functional pathways associated with animal growth factors.[13] 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.[12] Furthermore, vitamin B12 related genes, including cobD, tolC, and fliN, are also related to the daily feed intake of the animal.[12]
References
- ^ a b "The ruminant digestive system". extension.umn.edu. Retrieved 2021-02-21.
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- doi:10.13031/aim.202460831 (inactive 31 January 2024). Paper No. 16-2460831.)
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- ^ "Dairy Calf Rumen Development". Purina Animal Nutrition. Retrieved 2021-04-11.
- ^ PMID 30207838.
- PMID 26528276.
- ^ PMID 31357433.
- PMID 28761933.
- PMID 1875947.
- ^ PMID 31440274.
- PMID 32473013.
- Nagaraja, T. G.; Titgemeyer, E. C. (2007-06-01). "Ruminal Acidosis in Beef Cattle: The Current Microbiological and Nutritional Outlook1, 2". Journal of Dairy Science. Electronic Supplement. 90: E17–E38. PMID 17517750.
- Hernández, Joaquín; Benedito, José Luis; Abuelo, Angel; Castillo, Cristina (2014). "Ruminal Acidosis in Feedlot: From Aetiology to Prevention". The Scientific World Journal. 2014: 702572. PMID 25489604.
- Cronjé, P.; E.A. Boomker (2000). Ruminant Physiology: Digestion, Metabolism, Growth, and Reproduction. Wallingford, Oxfordshire, UK: CABI Publishing. ISBN 0-85199-463-6.
- Dijkstra, J.; J.M. Forbes; J. France (2005). Quantitative Aspects of Ruminant Digestion and Metabolism, 2nd edition. Wallingford, Oxfordshire, UK: CABI Publishing. p. 736 pages. ]
- Hobson, P.N.; C.S. Stewart (1997). The Rumen Microbial Ecosystem, 2nd edition. New York: Springer. ISBN 0-7514-0366-0.