Көкқарынның алғашқы бөлімі

First compartment of ruminant stomach
the given name

The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allows it to serve as the primary site for microbial fermentation of ingested feed. Some branched chained VFAs are incorporated into the lipid membrane of rumen microbes. Protein is hydrolysed to peptides and 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. Non amino acid nitrogen is used for synthesis of microbial amino acids. In situations in which nitrogen for microbial growth is in excess, protein and its derivatives can also be fermented to produce energy, yielding ammonia. Lipids, lignin, minerals, and vitamins play a less prominent role in digestion than carbohydrates and protein, but they are still critical in many ways. Lipids are partly hydrolysed and hydrogenated, and 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 of microbial lipid. High levels of lipid, particularly unsaturated lipid, in the rumen are thought to poison microbes and suppress fermentation activity. 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, in great quantities—often great enough to sustain the ruminant even when vitamins are highly deficient in the diet.

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 and is deposited in the dorsal 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 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, 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 gases (such as methane, carbon dioxide, and, to a much lower degree, hydrogen) released from fermentation and anaerobic respiration of food. These gases are regularly expelled from the reticulorumen through the mouth, in a process called eructation.

The feed contained within the reticulorumen, known as "paunch waste", has been studied as a fertiliser for use in sustainable agriculture.

At birth, the rumen organ, rumen epithelium, and rumen microbiota are not fully developed. Developing the rumen after birth is a critical aspect of the overall development of ruminants. This early, sensitive period of rumen development, will have life lasting effects on the overall health and productivity of the animal. Generally, the most receptive time for rumen development is between the postnatal and weaning periods. Over this period, rumen organ and epithelium growth, along with the establishment of rumen microbiota, will prove to be essential to rumen development. Papillae, or small, round projections protruding out of the tissue lining, growth in rumen epithelium is essential for rumen functionality. Papillae increase the surface area inside of the rumen. Therefore, papillae allow for a considerable increase in nutrient absorption inside of the rumen. Distinguishing a developed from an undeveloped rumen is simplified by observing the carpeting of tissue surrounding the interior of the rumen. An undeveloped rumen maintains a smooth, papillae lacking outer surface. A developed rumen possesses thick, papillae full walls. 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. 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 (VFAs). Previous research identified the significant impact of volatile fatty acids on rumen development through the effects of the inter ruminal insertion of acetate, propionate, and butyrate. 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. 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. In the epithelial wall of the rumen, butyrate regulates epithelial cell gene expression to increase blood flow and papilla proliferation. Sampling microbial DNA from rumen epithelial cells has led to the identification of microbial genes and functional pathways associated with animal growth factors. 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. Furthermore, vitamin B12 related genes, including cobD, tolC, and fliN, are also related to the daily feed intake of the animal.