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At least 19 recordsLinked to original sources

PubMed2006

Ultrasonographic examination of the omasum in 30 healthy cows.

A 3.5 MHz linear transducer was used to scan the intercostal spaces of 30 healthy cows from dorsal to ventral on the right side, and the appearance, dorsal and ventral limits and size of the omasum were determined in each intercostal space. The size of the omasum determined ultrasonographically was compared with that determined postmortem. The distance between the omasum and the peritoneum of the lateral body wall was also determined electronically in each intercostal space by means of the two cursors. In the sixth to 11th intercostal spaces, the omasum had a crescent shape, with only the wall closest to the transducer visible as a thick echogenic line. The dorsal limit of the omasum appeared from cranial to caudal as the upper part of a circle, whereas the ventral omasal limit appeared as the lower part of a circle. The mean (sd) size of the omasum varied with the intercostal spaces from 16.3 (1.5) cm to 56.9 (10.0) cm; it was greatest in the ninth intercostal space and decreased cranially and caudally. The omasum was closest to the right abdominal wall in the eighth and ninth intercostal spaces, and was immediately adjacent to these spaces in 22 and 20 cows, respectively. There were significant correlations between the size of the omasum determined ultrasonographically in the ninth intercostal space and the weight, volume and largest and smallest diameters of the omasum determined postmortem, with correlation coefficients (r) between 0.38 and 0.55.

Animals↗

PubMed1988

A comparative study of the anatomy of the omasum in domesticated ruminants.

The structure of the omasum was compared in 10 water buffalo (Bubalus bubalis), 10 Shorthorn cattle (Bos indicus), 9 Merino sheep (Ovis aries) and 10 cross-bred goats (Capra hircus), and the functional significance of the differences is discussed. The weight of the omasum and area of the internal laminae appeared to be smaller in Brahman cattle than the buffalo and British cattle. When compared in relation to body weight, the omasums of caprid animals were smaller than those of bovids, by a factor of 0.33-0.67 but the omasums of goats were appreciably larger than sheep. The number of laminae ranged from 33 to 35 for the sheep and goats compared with 122 to 169 for the buffalo and cattle. It is suggested that the marked difference in structure of the omasum between the small and large ruminants may influence the food intake of these animals through the effects of this gut compartment on absorption of nutrients and passage of digesta.

Animals↗

PubMed2000

Functional anatomy of the omasum in high Arctic Svalbard reindeer (Rangifer tarandus platyrhynchus) and Norwegian reindeer (Rangifer tarandus tarandus).

The structure and fill of the omasum was investigated in summer and in winter in adult female reindeer living on the polar desert and tundra of the high Arctic archipelago of Svalbard and in sub-Arctic mountain habitats in northern Norway. The mean total mass of the omasum in non-lactating adult female Svalbard reindeer was 467 g (0.65 g per 100 g live body mass (BM)) in September and 477 g (1.03 g per 100 g BM) in April. By contrast, the mean mass of the omasum in non-lactating adult reindeer in northern Norway was 534 g (0.83 g per 100 g BM) in September but only 205 g (0.35 g per 100 g BM p < 0.05) in late March, owing to a decrease in both tissue mass and the wet mass of the contents of the organ. The mean absorptive surface of the omasum in Svalbard reindeer was 2300 cm2 in September and 2023 cm2 in April. In Norwegian reindeer, by contrast, the absorptive surface area decreased from 2201 cm2 in September to 1181 cm2 (p < 0.05) in late March. The marked seasonal decline of omasal tissue and contents in Norwegian reindeer probably results from intake of highly digestible forage plants, including lichens, in winter. Svalbard reindeer, a non-migratory sub-species, survive eating poor quality fibrous vascular plants in winter. The absence of any marked seasonal change in the mass, total absorptive surface area or filling of the omasum in Svalbard reindeer in winter despite a substantial decline in body mass presumably reflects their need to maintain maximum absorption of nutrients, including volatile fatty acids, when feeding on such poorly fermentable forage.

Absorption↗

PubMed1988

Transport of Na and Cl across the epithelium of ruminant forestomachs: rumen and omasum. A review.

Rumen: 1. It is generally accepted that sodium and chloride is transported across the rumen epithelium of ruminants in the mucosal-serosal direction by an active transport mechanism. In all in vitro studies the short circuit current, Isc, was significantly lower than the net transport of sodium, JNanet. It was concluded that most of the sodium is transported by an electrically silent mechanism. A Na, Cl cotransport and/or a double exchange system Na/H and Cl/HCO3 was proposed. 2. Recent in vitro studies in our laboratory revealed that the Na/H exchange inhibitor amiloride (1 mmol/l) reduced JNanet by 70%. The Na/K/2Cl-cotransport inhibitor bumetanide or furosemide (1 mmol/l) had no effect. 3. Replacement of permeable anions led to an inhibition of JNanet by 87%. However, under these experimental conditions Isc and JNanet were not significantly different. The remaining small electrogen transport of sodium was not influenced by mucosal amiloride. 4. It is concluded that two transport systems are operating in the ruminal epithelium: a Na/H exchange system which accounts for 80-90% of JNanet and an electrogen Na transport which is not sensitive against amiloride. Omasum: 1. The data concerning the transport of sodium and chloride in the omasum are very limited. In vivo measurements of flow rates demonstrated that sodium is absorbed by the omasum (40-60% of inflow in bull calves, 10-20% in sheep) and chloride is secreted. 2. In vitro studies with isolated preparation of sheep omasum epithelium demonstrated a net transport of Na and Cl in the mucosal-serosal direction. JNanet is completely abolished by ouabain (0.1 mmol/1) and JClnet by replacement of Na.

Animals↗

PubMed2005

Morphometric and immunohistochemical study of the omasum of red deer during prenatal development.

The red deer is an important study species because of its value in the national economy and because it provides a wealth of genetic material. To date, there has been little research into the prenatal development of the stomach of ruminants, and none of the red deer. We therefore performed a histological evaluation of the ontogenesis of the omasum in the red deer. Histomorphometric and immunohistochemical analyses were carried out on 50 embryos and fetuses of deer from the initial stages of prenatal life until birth. For test purposes, the animals were divided into five experimental groups: Group I (1.4-3.6 cm crown-rump length, CRL; 30-60 days, 1-25% of gestation); Group II (4.5-7.2 cm CRL; 67-90 days, 25-35% of gestation); Group III (8-19 cm CRL; 97-135 days, 35-50% of gestation); Group IV (21-33 cm CRL; 142-191 days, 50-70% of gestation); and Group V (36-40 cm CRL; 205-235 days, 75-100% of gestation). At 67 embryonic days, the omasum wall was differentiated, and comprised three layers: the epithelial layer, pluripotential blastemic tissue and serosa. The stratification of the epithelial layer was accompanied by changes in its structure, with the appearance of four laminae of different sizes; in order of appearance these were: primary at 67 days, secondary at 90 days, tertiary at 97 days and quaternary at 135 days. At around mid-gestation, lateral evaginations were formed from the stratum basale of the primary and secondary smaller laminae. These were the primitive corneum papillae. From 205 days, the corneum papillae were present in all four sizes of laminae. The histodifferentiation of the lamina propia-submucosa, tunica muscularis and serosa showed patterns of development similar to those reported for the rumen and reticulum of red deer. The omasum of red deer during prenatal life, especially from 67 days of gestation, was shown to be an active structure with full secretory capacity. Its histological development, its secretory capacity (detected by the presence of neutral mucopolysaccharides) and its neuroendocrine nature (detected by the presence of positive non-neuronal enolase cells and the neuropeptides vasoactive intestinal peptide and neuropeptide Y) were parallel to the development of the rumen and the reticulum. However, its prenatal development was later than that of the omasum in sheep, goat and cow.

Animals↗

PubMed1974

The cyclic motility of the omasum and its control in sheep.

1. The mechanical activity of different parts of the omasum was recorded by means of small balloons and/or strain-gauges in conscious sheep. These events were related to the electrical activity of the omasal body, the omasal groove and the leaves and to the changes in diameter of the reticulo-omasal orifice. Humoral, behavioural and nervous influences were examined.2. Two patterns of contraction of the omasum were found. One, confined to the oral and middle thirds of the organ, originated at the omasal groove and proceeded to the right and then the left surfaces of the body and ceased at the onset of reticular contraction. The other was limited to the aboral third of the organ near the abomasum; in this part the contractions were prolonged regardless of the reticular contraction and some gave rise to a reversed propagation over the organ. The characteristic cyclic motility of the omasum was slightly reduced in sheep fasted for 48 hr and in those fed on pelleted food, and it persisted after vagotomy.3. The reticulo-omasal orifice always dilated strongly during the second phase of reticular contraction. It also dilated noticeably during the extra-contraction associated with regurgitation. In each case alternating opening and closing movements at a frequency of 5-7/min followed. Contractions of the omasal leaves, which were independent of those of the omasal body, occurred at a rate of approximately 2-3/min. They passed from the free border to the base and travelled in an aboral direction. After local application of fatty acids the frequency of their contractions increased to approximately the same rate as that of the orifice.4. It is concluded that the motility of the omasum in sheep involves a wave of contraction starting at a point on the omasal groove just posterior to the reticulo-omasal orifice and passing slowly over the omasal body. With the exception of the occasional reversed contractions this pattern is closely associated with rumino-reticular cycles even though the omasal contractions and the movements of the leaves are partially independent of vagal innervation.

Action Potentials↗

PubMed1989

The significance of water absorption and fibre digestion in the omasum of sheep, goats and cattle.

1. The omasal dry matter contents constituted 0.6, 1.2 and 3.3% of the body weight in the sheep, goats and cows, respectively. 2. A large part of the fluid leaving the reticulo-rumen passed quickly through or along the omasum to the abomasum in sheep (43%). The proportion was much less in goats (17%). 3. The absorption of water from the fluid delayed in the omasum was low: 15, 18 and 19% in sheep, goats and cows, respectively. 4. Little or no acid detergent fibre was degraded in the omasum.

Absorption↗

PubMed2004

Sodium transport across the isolated epithelium of sheep omasum is influenced by luminal ammonia.

Ammonia is a physiological fermentation product in the forestomachs and is absorbed from the rumen and omasum. Cellular uptake of ammonia affects the intracellular pH of polar and non-polar cells. The effect of the uptake on the pH of the cytosol depends on the predominant form of ammonia. NH(3) uptake and its intracellular protonation tend to alkalinize the cytoplasm, whereas the uptake of NH(4)(+) acidifies the cytoplasm by reversing this reaction. Consequently, the absorption of ammonia across the omasal epithelium could cause a change of the intracellular pH and pH-dependent transport mechanisms like Na/H exchange. Because no information is available about the form of ammonia absorbed in the omasum and, hence, possible modulation of Na transport by ammonia, the effect of increasing luminal ammonia concentrations (0, 5, 15 and 30 mmol/l) on Na transport were studied. In epithelia of hay-fed animals, ammonia linearly inhibited Na transport in a dose-dependent manner, at a luminal pH of 7.40, but not at a pH of 6.40. Ammonia did not influence Na transport in epithelia of concentrate-fed animals. Because luminal ammonia did not consistently change the short circuit current or tissue conductance absorption of ammonia as NH(4)(+) appears to be unlikely. The predominant form of ammonia absorbed in the omasum is probably NH(3), which is protonated in the cytosol. The reduced availability of protons may be the cause of inhibition of Na transport via Na/H exchange.

Ammonia↗

PubMed1980

[Spontaneous motility and contractile response of the sheep omasum (author's transl)].

Spontaneous motility of the sheep omasum longitudinal muscular layer its responses to the periarterial and transmural electric stimulus have been studied in vitro. Three parts of the organ were chosen: a) the greater curvatura; b) omasum lateral wall, and c) omasum canal. The preparations always showed a great spontaneous motility with elevated contractions followed by relaxations. The electric stimulation caused contractile responses followed by relaxation. The lesser the spontaneous motility, the greater becomes the response, which disappears when the spontaneous motility is very high.

Animals↗

PubMed1996

The surface morphology of the omasum of the African goat.

The microstructure of the omasum of the African goat was investigated macroscopically, as well as by scanning electron microscopy to determine how the omasum is anatomically specialised to enable the goat to graze and browse so successfully in the harsh environments of Africa. The omasum of the African goat was found to be more simple in structure than that of other domesticated ruminants. The omasal laminae were arranged in only 3 orders with the number of laminae varying between 27 and 33, considerably fewer than previously described for other goats, sheep or cattle. The large conical and unguiculiform papillae surrounding the reticulo-omasal orifice, as well as the hooked papillae present on the laminae, were more similar to those of wild ruminants that browsed than domestic grazing species. The papillae on the laminae were also found to be directionally orientated towards the orifices, which may suggest a "sieve mechanism' at the reticulo-omasal orifice and interlaminar spaces. In addition, it may suggest a directional movement of ingesta between the laminae. The stratified squamous epithelium lining the laminae and papillae was lightly keratinised which, along with the microplicae-like surface folds and pits of the superficial cells, indicated that it was functionally structured for absorption. These morphological specialisations of the omasal surfaces of the indigenous African goat demonstrated similarities with that of wild ruminants that are able to graze and browse.

Animals↗

PubMed1987

Immunohistochemical study on the distribution of neuron-specific enolase- and peptide-containing nerves in the omasum of cattle.

The distribution of nerves containing immunoreactivity for substance P (SP), vasoactive intestinal polypeptide (VIP), leucine-enkephalin (LENK), and gastrin-releasing polypeptide (GRP) in the margin of the reticulo-omasal orifice, omasum, and omasal pillar of calves and cows was studied by immunohistochemistry. The general distribution of nerves was determined by means of neuron-specific enolase (NSE) antiserum and then compared to the distribution of immunoreactive (IR) nerves stained for the four peptides. Marked differences in the distribution of immunoreactive nerves were associated with age and the segment examined. SP-IR fibers were abundant in the musculature of the ungulate papillae at the reticulo-omasal orifice and in the smooth muscle of the omasal leaves, moderately dense in the omasal pillar, and low in density in the inner muscle layer of the reticulo-omasal orifice and in the muscle of the omasal wall. In order of decreasing abundance, the cell bodies of SP-IR nerves were found at the reticulo-omasal orifice, in the omasal wall, and in the omasal pillar. LENK-IR fibers, though less abundant, showed a pattern of distribution that was similar to that of SP-IR fibers. Nerve cell bodies showing weak immunoreactivity for LENK were detected rarely. Abundant VIP-IR fibers were present in the inner muscle layer of the reticulo-omasal orifice and in the omasal wall, while moderate numbers were seen in the omasal pillar: they were low in density in the ungulate papillae and omasal leaves. Cell bodies of VIP-IR nerves decreased in number through the omasum, reticulo-omasal orifice, and omasal pillar. The distribution of GRP-IR nerve fibers was similar to that of VIP-IR fibers, although GRP-IR fibers were less abundant. Nerve cell bodies showing weak immunoreactivity for GRP were detected rarely. The individual distribution of peptide-IR nerves was similar in the calf and cow, but immunoreactive nerves were far more abundant in the calf. The present study provides valuable information for discussion of the possible role of nerves in the regulation of omasal function.

Animals↗

PubMed1986

An omaso-abomasal cannula used to assess efflux from the omasum of sheep.

An omaso-abomasal cannulation technique was developed for sheep to assess efflux from the omasum. The procedure enabled the collection of the total omasal effluent and avoided transection of the innervation and circulation of this region of the gut. Eating was associated with an increase in flow of the fluid and dry matter fractions of digesta passing from the omasum but efflux was unaffected by rumination. There were few protozoa and flagellated organisms in the omasal effluent relative to the numbers in ruminal fluid. The preparation was used over 3 months of study.

Ammonia↗

PubMed1977

Partition of capillary blood flow in rumen, reticulum, and omasum of sheep.

Using radioactive microspheres, mucosal and muscular capillary blood flow have been measured in the rumen, reticulum, and omasum of conscious sheep. Total forestomach capillary blood flow (7.7 ml min(-1) kg body wt(-1)) was about 7% of cardiac output; 95% of the flow was in the mucosa and only 5% in muscle layers. Blood flow in the rumen was 6 times higher than in the reticulum and 4.4 times higher than in the omasum. Mucosal capillary flow per unit area of mucosal epithelium in the omassum (disregarding the increment in area due to papillae) was only one-third of that in the ventral rumen (long papillae); flow in the dorsal rumen (short papillae) was about half the flow in the ventral rumen. Mucosal flow seems to provide a convenient, indirect estimate of the increase in mucosal surface due to papillae and, thereby, of the functional forestomach surface area. Heat stimuli resulted in decreased capillary blood flow--primarily in mucosa during exposure to a warm environment and, also, in muscle during hypothalamic or spinal cord heating.

Animals↗

PubMed1999

Ca-sensitive Na transport in sheep omasum.

Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current (Isc), with a range of 1-4 microeq. h-1. cm-2. A Michaelis-Menten-type kinetic was found between the Na concentration and the Isc (Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 microeq. h-1. cm-2). Mucosal amiloride (1 mM), phenamil (1 or 10 microM), or serosal aldosterone (1 microM for 6 h) did not change Isc. Removal of divalent cations (Ca and Mg) enhanced Isc considerably from 2.61 +/- 0.24 to a peak value of 11.18 +/- 1.1 microeq. h-1. cm-2. The peak Isc (overshoot) immediately declined to a plateau Isc of approximately 6-7 microeq. h-1. cm-2. Na flux measurements showed a close correlation between changes in Isc and Na transport. Transepithelial studies demonstrated that K, Cs, Rb, and Li are transported, indicating putative nonselective cation channels, which are inhibited by divalent cations (including Ca, Mg, Sr, Ba) and by (trivalent) La. Intracellular microelectrode recordings from the luminal side clearly showed changes of voltage divider ratio when mucosal divalent cations were removed. The obtained data support the assumption of a distinct electrogenic Na transport mechanism in sheep omasum.

Aldosterone↗

PubMed1994

Immunohistochemical study of the distributions of the peptide- and catecholamine-containing nerves in the omasum of the sheep.

The distribution in the sheep omasum of peptide- and catecholamine-containing neurons was investigated by an immunohistochemical technique using antibodies against six neuropeptides and two catecholamine-synthesizing enzymes. In the myenteric plexus, both nerve cell bodies and nerve fibers were positively immunostained for substance P (SP), methionine enkephalin (ENK), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and galanin (GAL). In contrast, immunoreactivity specific for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) was detected only in nerve fibers. In the omasal wall, nerve fibers with SP- and ENK-like immunoreactivity were prominent in the outer muscle layer, while numerous nerve fibers with VIP-, NPY- and GAL-like immunoreactivity were observed in the inner muscle layer. In the lamina propria mucosae, and in particular in the omasal papillae, a dense network of peptide-containing nerves was found. The distribution of nerves with CGRP-like immunoreactivity was different from that of other immunoreactive nerves. The networks of nerves with TH-, DBH- and NPY-like immunoreactivity were concentrated around the vascular components. The results of this study indicate the complexity of the enteric nervous system in the sheep omasum, reflecting the multiple functions of the nerves in the regulation of motility and/or absorption and secretion.

Animals↗

PubMed2005

The effect of concentrate supplementation on nutrient flow to the omasum in dairy cows receiving freshly cut grass.

An experiment was carried out to determine the effect of increasing the amount of grain-based concentrate (0, 3, or 6 kg/d) on nutrient flow to the omasum, rumen fermentation pattern, milk yield, and nutrient use of dairy cows. Harvested timothy-meadow fescue grass was fed individually 3 times daily to 6 rumen-cannulated Holstein-Friesian cows in a duplicated 3 x 3 Latin square experiment. Grass was offered as 6 equal meals daily, and concentrates were fed as 2 equal meals daily. Nitrogen, microbial N, and neutral detergent fiber (NDF) flow from the rumen were measured using an omasal sampling technique in combination with a triple marker method [CoEDTA, Yb, and indigestible NDF (INDF) as markers]. Concentrate supplementation linearly decreased ruminal pH, N degradability, ammonia N concentration, and molar proportion of acetate and increased the molar proportion of butyrate. Supplementation of grass with concentrates linearly increased dry matter intake (DMI), microbial N synthesis, N, and NDF flow to the omasum, and ruminal and total tract NDF digestibility decreased linearly. Decreases in NDF digestibility in response to concentrates was primarily related to a decrease in the rate of digestion. Increased DMI overcame the negative effects of concentrate on NDF digestion, resulting in a linear increase in total metabolizable energy intake and milk production. Physical constraints were found not to limit grass DMI. Concentrate supplementation increased the apparent use of dietary N for milk production because of a reduction in N intake, rather than thorough improvements in N capture in the rumen.

Animal Feed↗

PubMedDate not supplied

Regulation of motor activity of omasum after blockade of vagus nerves.

In 3 sheep with subcutaneously exposed vagus nerves and with chronic large fistula of the rumen pharmacological analysis of the motor activity of omasum was carried out after blockade of vagus nerves. The contractions of omasal canal, reticulum and rumen were recorded by the baloon method. After blockade of the vagus nerves with anesthetics the proper pharmacological agents were administered in intravenous injections. In the light of the obtained results it was found that contractions of the omsal canal, persisting after vagal blockade, are independent of the influence of the autonomic system and they are probably due to myogenic automatism. It has been also demonstrated that both alpha and beta adrenergic receptors participate in regulation of the tonous of omasum musclular layers.

Animals↗

PubMed1978

Effects of gastrin on emptying and composition of digesta of the omasum of sheep.

Three adult sheep were prepared with a denervated pouch of fundus of the abomasum and a reentrant fistula system that connected the remaining proximal and distal portions of the abomasum. The proximal cannula of the reentrant system was close to the omasoabomasal orifice, allowing for easy collection of fluid leaving the omasum. Intravenous injection of 0.5, 1.0, or 2.0 microgram/kg/hr of synthetic human gastrin I caused a marked decrease in flow rate of fluid from the omasum. The concentration of particulate matter in the digesta was inversely related to rate of omasal outflow. An increase in acid output from the denervated abomasal pouch during gastrin injection indicated that the hormone was given at pharmacologically effective doses. Results indicate that gastrin has a modulating effect on the flow of ingesta through the ruminant forestomachs. Actual sites of action were not identified.

Animals↗