Omasum Of Sheep Research Articles

HISTOLOGICAL CHARACTERISTICS OF THE WALL OF THE OMASUM OF SHEEP OF THE EDILBAEV BREED IN THE AGE ASPECT

To date, sheep breeding in the Russian Federation is a promising branch of agriculture, in this regard, one of the priorities is to increase the number of livestock. First of all, agro-industrial complexes, farms of the Russian Federation engaged in breeding certain breeds of animals, not infrequently encounter diseases of the gastrointestinal tract of non-infectious etiology. On the basis of the Department of Animal Anatomy of the St. Petersburg State University of Veterinary Medicine, we examined 16 corpses of sheep of the Edilbaevsky breed aged from 10 days to 14 months. Cadaveric material was obtained during slaughter from the farm "Slaughter point" IP Yusubov O.M. located in the Vsevolozhsky district of the Leningrad region. The cadaverous material for the study was the pre-ventricles of small cattle, namely a omasum. In the course of the study, histological and morphological data were obtained and processed, as well as the features of the histostructures of the book wall in sheep of the Edilbaevsky breed in the age aspect were revealed. In our study, a complex of traditional histological methods and staining was used: hematoxylin-eosin and Masson trichrome. The purpose of our study is to study the histological structure of the omasum wall in sheep of the Edilbaevsky breed in the age aspect, to clarify morphometric indicators and to characterize the histostructures of this organ. Thus, during the study, it was found that the wall of the omasum in sheep of the Edilbaev breed developed evenly, and was not accompanied by a slowdown in its differentiation throughout the studied period of postnatal ontogenesis. This pattern is associated with the glycogen-depositing and transport functions of the mucous membrane and the high contractile function of the muscular membrane of the laminae omasi.

Carbonic anhydrase influences asymmetric sodium and acetate transport across omasum of sheep.

ObjectiveOmasum is an important site for the absorption of short chain fatty acids. The major route for the transport of acetate is via sodium hydrogen exchanger (NHE). However, a discrepancy in the symmetry of sodium and acetate transport has been previously reported, the mechanism of which is unclear. In this study, we investigated the possible role of carbonic anhydrase (CA) for this asymmetry.MethodsOmasal tissues were isolated from healthy sheep (N = 3) and divided into four groups; pH 7.4 and 6.4 alone and in combination with Ethoxzolamide. Electrophysiological measurements were made using Ussing chamber and the electrical measurements were made using computer controlled voltage clamp apparatus. Effect(s) of CA inhibitor on acetate and sodium transport flux rate of Na22 and 14C-acetate was measured in three different flux time periods. Data were presented as mean±standard deviation and level of significance was ascertained at p≤0.05.ResultsMucosal to serosal flux of Na (JmsNa) was greater than mucosal to serosal flux of acetate (JmsAc) when the pH was decreased from 7.4 to 6.4. However, the addition of CA inhibitor almost completely abolished this discrepancy (JmsNa ≈ JmsAc).ConclusionThe results of the present study suggest that the additional protons required to drive the NHE were provided by the CA enzyme in the isolated omasal epithelium. The findings of this study also suggest that the functions of CA may be exploited for better absorption in omasum.

Absorption of bicarbonate in sheep omasum

Transport of bicarbonate across the isolated epithelium of sheep omasum was studied in vitro in Ussing chambers in combination with the pH-Stat method. The transport of HCO3– occurred in both directions, but Jms HCO3– was significant larger than Jsm. Reducing the activity of the apical Na/H exchanger by a low mucosal Na concentration caused a significant reduction of Jms HCO3−. Mucosal amiloride or short chain fatty acids (25 mmol l−1 SCFA) numerically decreased Jms HCO3−, but their combination (amiloride + SCFA) caused a significant reduction, which was also observed after addition of the carboanhydrase inhibitor ethoxyzolamide. Concentrations of 5 or 15 mmol·l−1 mucosal ammonia did not change transport rates. The obtained results indicate the importance of an undisturbed cytosolic pH for transcellular HCO3– transport, which is probably mediated by an anion exchanger in both the apical and basolateral membranes. Possible impairment of HCO3– transport appears to be an overlooked factor in the pathogenesis of displacement of the abomasum.

Epithelia of the ovine and bovine forestomach express basolateral maxi-anion channels permeable to the anions of short-chain fatty acids

It has long been established that the absorption of short-chain fatty acids (SCFA) across epithelia stimulates sodium proton exchange. The apically released protons are not available as countercations for the basolateral efflux of SCFA anions and a suitable transport model is lacking. Patch clamp and microelectrode techniques were used to characterize an anion conductance expressed by cultured cells of the sheep and bovine rumen and the sheep omasum and to localize the conductance in the intact tissue. Cells were filled with a Na-gluconate solution and superfused with sodium salts of acetate, propionate, butyrate, or lactate. Reversal potential rose and whole cell current at +100mV decreased with the size of the anion. Anion-induced currents could be blocked by diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), NPPB (200 μmoll(-1)), or pCMB (1mmoll(-1)). In patches of bovine ruminal cells, single channels were observed with a conductance for chloride (327 ± 11 pS), acetate (115 ± 8 pS), propionate (102 ± 10 pS), butyrate (81 ± 2 pS), and gluconate (44 ± 3 pS). Channels expressed by sheep rumen and omasum were similar. Microelectrode experiments suggest basolateral localization. In conclusion, forestomach epithelia express basolateral maxi-anion channels with a permeability sequence of chloride > acetate > propionate > butyrate. SCFA absorption may resemble functionally coupled transport of NaCl, with the Na(+)/K(+)-ATPase driving the basolateral efflux of the anion through a channel. Since protons are apically extruded, the model accurately predicts that influx of buffers with saliva is essential for the pH homeostasis of the ruminant forestomach.

Ontogenesis of the omasum:: a comparative analysis of the Merino sheep and Iberian red deer

The aim of this study is to describe differences in the ontogenesis of the omasum in sheep (domestic ruminant) and deer (wild ruminant). A total of 50 embryos and fetuses of Merino sheep and 50 Iberian deer were used, from the first stages of prenatal life until birth. For the study, the animals were divided into five experimental groups according to the most relevant histological characteristics. The appearance of the omasum from the primitive gastric tube was earlier in sheep (22% gestation, 33 days) than in deer (25% gestation, 66 days). In both cases it displayed a primitive epithelium of a stratified, cylindrical, non-ciliary type. The appearance of four laminae of different sizes was always earlier in sheep than deer. At around 36% gestation in sheep (53 days) and 36% (97 days) in deer, the omasum consisted of 4 clearly-differentiated layers: mucosa (with epithelial layer and lamina propria), submucosa, tunica muscularis and serosa. The temporal order of appearance of the four order laminae and omasal papillae was always earlier in sheep than deer. The tegumentary mucosa of the omasum was without secretion capability in the first embryonic phases. From 67 days (26% gestation) the neutral mucopolysaccharides appeared in deer and at 46 days (30% gestation) in sheep. In both cases they continued to decrease until birth, this decrease being more pronounced in deer. Finally, the presence of neuroendocrine and glial cells was detected in deer at earlier stages than in sheep.

Transport of acetate and sodium in sheep omasum: mutual, but asymmetric interactions

We have studied the transport of acetate across the isolated epithelium of sheep omasum; no net transport was observed (J(ms) approximately = J(sm)) under Ussing chamber conditions. Low mucosal pH (pH 6.4) significantly enhanced J(ms) acetate and the transport rates of acetate increased linearly and significantly (r2=0.99) with the luminal acetate concentration. The presence of another short chain fatty acid (propionate) did not affect J(ms) acetate significantly. Neither addition of 1 mmol l(-1) DIDS to the mucosal side nor HCO3 replacement caused changes of J(ms) acetate; this does not support the assumption of acetate transport via anion exchange. Addition of 1 mmol l(-1) amiloride to the mucosal side significantly decreased acetate fluxes at high mucosal acetate concentration (100 mmol l(-1)) and low pH (6.4) indicating interaction between acetate uptake in the undissociated form, intracellular release of protons and activation of Na+/H+ exchange (NHE). However, the mutual interaction between Na transport via NHE and acetate transport is asymmetric. Stimulation or inhibition of Na transport via NHE is much more pronounced than the corresponding changes of acetate fluxes. Thus, the obtained results support the conclusion that acetate is transported via simple diffusion and probably predominantly in the protonated form, thereby explaining the positive and mutual interaction between Na transport and short chain fatty acids.

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.

ERGOVALINE MOVEMENT ACROSS CACO-2 CELLS

Ergovaline's role in the direct causation of fescue toxicosis first requires establishment of its dietary absorption. Therefore, ergovaline movement across human intestinal cells was assessed using Caco-2 cells derived from human colon carcinoma. A pre-equilibrated mixture of ergovaline/ergovalinine (60:40 ratio of isomers) was added to the apical compartment, and isomer movements were assessed by high-performance liquid chromatography (HPLC) of extracted media (initial pre-isomerized ergovaline concentrations of 6 and 22 microM, two doses). Mathematical models for ergot alkaloid movement were developed. Rates of movement were not different for the isomers. In the absence of cells, basal accumulation of isomers was essentially linear for 3 h regardless of loading concentration, after which basal accumulation of ergovaline/ergovalinine plateaued. Rates of ergovaline/ergovalinine movement in the presence of cells slowed to about 25% the rate of movement in the absence of cells (22 microM, kt = 0.0133 no cells, 0.0036 with cells, P < 0.05). Mass transfer rate was 7.5 ng x cm(-2) x min(-1) and was similar to that reported for ergovaline using a parabiotic chamber with sheep omasum. After 6 h in the presence of cells, approximately 25 and 40% of the total ergovaline/ergovalinine administered had accumulated in the basal compartment for 6.6 and 22 microM treatments, respectively. Ergovaline and its naturally occurring isomer, ergovalinine, readily crossed intestinal cells intact and at similar rates. Either isomer, or a combination of both, could be involved in the pathogenesis of fescue toxicosis at sites distal to the intestine.

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.

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.

Tissue distribution of a peptide transporter mRNA in sheep, dairy cows, pigs, and chickens.

A 446-bp cDNA fragment encoding a peptide transport protein was cloned from sheep omasum and used as a probe to study the distribution of the peptide transport protein mRNA in various tissues of sheep, dairy cows, pigs, and chickens. Because the predicted amino acid sequence of this fragment was 85.8, 90.5, and 90.5% identical to rabbit, human, and rat intestinal peptide transporter (PepT1), respectively, it is believed that this cloned fragment represents PepT1 from sheep. In sheep (n = 5) and lactating Holstein cows (n = 3), hybridization was observed with mRNA from the omasum, rumen, duodenum, jejunum, and ileum. The estimated size of mRNA was 2.8 kb. No hybridization was observed with mRNA from the abomasum, cecum, colon, liver, kidney, and semitendinosus and longissimus muscles of either species or the mammary gland of the dairy cows. In pigs (n = 6), the probe hybridized with mRNA from the duodenum, jejunum, and ileum. There was no hybridization with mRNA from the stomach, large intestine, liver, kidney, and semitendinosus and longissimus muscles. Two bands, 3.5 and 2.9 kb, were observed with northern blot analysis, indicating two RNA transcripts that may result from alternative mRNA processing. In White Leghorns (n = 15) and broilers (n = 20), the strongest hybridization was found in the duodenum, but the jejunum and ileum showed faint bands. The size of mRNA in chickens was 1.9 kb. Other tissues, including the crop, proventriculus, gizzard, ceca, liver, kidney, and muscles showed no hybridization to the probe. In conclusion, mRNA for PepT1 is present in the small intestine of all animals examined and the omasal and ruminal epithelium of sheep and dairy cows. The size of the mRNA varied among species.

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.

Comparative gross anatomy of the omasum of sheep and goats

The omasum of 50 adult sheep (Madras Red Cross) and 50 adult Desi goats (of similar body size in each group) was collected from the local slaughter house. Different parameters (greater curvature, lesser curvature, weight and volume of the organ), in addition to various gross anatomical features, were studied. Difference in weight (19.6 g) and volume (19.52 ml) of the omasum between the two species was highly significant ( P < 0.01); the omasum of sheep being heavier and having a greater volume. There was no correlation between these parameters in sheep or goats. A definite and constant sequence of laminae was found in sheep and goats. The advantage of such a sequence is discussed. Different anatomical features of the laminae and papillae studding them have been related functionally. Relevance of the classification of laminae by thickness and position of their pedunculated bases of the various orders of the laminae has been confirmed.

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

1. 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. 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. 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. 4. Little or no acid detergent fibre was degraded in the omasum.

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

Rumen: 1. 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, 4:, was significantly lower than the net transport of sodium, J Na net. 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/HCO 3, was proposed. 2. 2. Recent in vitro studies in our laboratory revealed that the Na/H exchange inhibitor amiloride (1 mmol/1) reduced J Na net by 70%. The Na/K/2Cl-cotransport inhibitor bumetanide or furosemide (1 mmol/1) had no effect. 3. 3. Replacement of permeable anions led to an inhibition of J Na net by 87%. However, under these experimental conditions I sc and J Na net, were not significantly different. The remaining small electrogen transport of sodium was not influenced by mucosal amiloride. 4. 4. It is concluded that two transport systems are operating in the ruminai epithelium: a Na/H exchange system which accounts for 80–90% of J Na net and an electrogen Na transport which is not sensitive against amiloride. Omasum: 1. 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. 2. In vitro studies with isolated preparation of sheep omasum epithelium demonstrated a net transport of Na and Cl in the mucosal-serosal direction. J Na net is completely abolished by ouabain (0.1 mmol/1) and J Cl net by replacement of Na. As in the rumen J Na net is significantly higher (3–4 times) than I sc. Replacement of Cl or HCO 3 demonstrated that Na is transported by a Cl-dependent mechanism. 3. 3. Bumetanide did not influence transport of Na. Thus a direct coupling between Na and Cl transport is unlikely. High mucosal concentrations of amiloride (1 mmol/1) significantly reduced J Na ms and J Na sm without a significant effect on J Na net. 4. 4. Although the transport of Na and Cl exhibits some similarities in rumen and omasum, it appears that the omasum is a distinct epithelium.

The passage of protozoa from the reticulo-rumen through the omasum of sheep.

1. Protozoa in rumen contents and omasal effluent of growing wethers were counted. The wethers were equipped with rumen and abomasal cannulas, and omasal sleeves attached to the omasal-abomasal orifice. Rumen fluid dilution rates were elevated by continuous infusions of hypertonic mineral solutions (3-4 litres/d) for 24 d. Rumen contents and omasal effluent were sampled between 9 and 21 h during the last 10 d of each experiment. 2. Protozoal concentrations in omasal effluent were only 0.2-0.3 those found in the rumen under normal conditions. The ratio of protozoal concentrations in rumen: those in omasal effluent was for small Diplodinium spp. 4.6 (SD 0.9), for Ophryoscolex spp. 4.3 (SD 1.0), for Dasytricha ruminantium 4.0 (SD 0.5), for Isotricha spp. 3.8 (SD 0.8), for Entodinium spp. 3.6 (SD 0.9) and for Polyplastron multivesiculatum 2.6 (SD 0.5). 3. Elevation of rumen fluid dilution rate by 20 and 55% respectively, increased protozoal concentrations in omasal effluents from 22 to 33% and from 31 to 47% those in rumen contents. The apparent residence times of protozoa in the rumen were decreased 50% by the infusion of a mineral-salt solution. The increase in rumen fluid dilution rate had no significant effect on concentrations of protozoa in the rumen or on the differences of the apparent residence times between different species. The apparent residence time of holotrichs remained the same before and after infusion of the mineral-salt solution. 4. Apparent residence times of individual species of protozoa in the rumen were, under normal feeding conditions, 2.55 d, and were four to six times longer than the mean residence time of CrEDTA in the rumen.

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.

Development of the omasum in sheep.

Data are presented on the histogenesis of the omasal mucosa in sheep from the 2.5 cm crown-rump (c-r) length fetus to the adult. 11 stages of fetal development, and 4 post-natal stages, were studies. The distribution of glycogen in the omasal epithelium was also studied. During fetal life the omasal epithelium was initially stratified cuboidal in type, but the superficial layers of cells became flattened in later stages of gestation. This epithelium became extremely thick by the late stages of fetal life, reaching a maximum of 358 micron, and consisting of greater than 20 layers of cells, in the 45 cm c-r fetus (approximatelay 140 days). After birth the epithelium became markedly reduced in thickness, being approximately 77 micron in the adult, and had differentiated into a cornified stratified squamous epithelium of the adult type by 12 weeks after birth. Glycogen was extremely abundant in the omasal epithelium of the 2.5 cm fetus, and declined gradually thereafter to be almost completely absent in post-natal specimens. 4 orders of laminae were present in the adult omasum, distributed in the seqeunce 1-4-3-4-2-4-3-4-1. The 1st order was already present in fetuses of 2.5 cm c-r length, with the 2nd, 3rd and 4th appearing by the 3.5, 5.5 and 11.0 cm stages, respectively. Initial stages in the development of conical papillae were first seen in 15.0 cm fetuses, but the development of these papillae was not completed until after birth.

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.

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.