Ruminal fatty acid outflow in dry cows fed different sources of linoleic acid: reticulum and omasum as alternative sampling sites to abomasum

This study was designed to determine the rumen outflow of fatty acids (FA) and biohydrogenation (BH) extent using alternative sampling sites (reticulum and omasum) to abomasum in dry cows fed different sources of FA. Four Holstein non-pregnant dry cows (≥3 parturitions, and 712 ± 125 kg BW), cannulated in the rumen and abomasum, were randomly assigned to a 4 × 4 Latin square design experiment, containing the following treatments: 1) control (CON); 2) soya bean oil (SO), dietary inclusion at 30 g/kg; 3) whole raw soya beans (WS), dietary inclusion at 160 g/kg; and 4) calcium salts of FA (CSFA), dietary inclusion at 32 g/kg. Rumen outflow of nutrients was estimated using the three markers reconstitution system (cobalt-EDTA, ytterbium chloride, and indigestible neutral detergent fibre [NDF]). Diets with FA sources decreased feed intake and increased FA intake. No differences in nutrient intake and digestibility were detected among cows fed diets supplemented with different FA sources. Diets with FA sources reduced the rumen outflow of DM and NDF, hence decreasing their passage rates. In addition, SO diet reduced the ruminal outflow of DM and NDF in comparison with WS and CSFA. Omasal sampling yielded the highest values of rumen outflow of NDF and potentially degradable NDF (pdNDF), whereas the reticular and abomasal samplings yielded intermediate and least values, respectively. The interaction effect between diet and sampling site was observed for rumen outflow of majority FA (except for C16:0, C18:0, and C18:2 trans-10, cis-12) and BH extension of C18:1 cis, C18:2, and C18:3. Calculations derived from abomasal sampling revealed that WS and CSFA diets had lower BH extent of C18:1 cis and C18:2 in comparison with SO, whereas cows fed CSFA had greater BH extent of C18:3 and lower BH extent of C18:1 cis compared to those fed WS. However, the latter results were not similar when calculations were performed based on the reticular and omasal samplings. Thus, there is evidence that neither reticular nor omasal samplings are suitable for estimating rumen outflow of FA in dry cows. In addition, WS and CSFA diets can increase the abomasal flow of polyunsaturated FA in dry cows.

Localization of CCK-1R in the omasum and role of CCK in the regulation of omasal contractions in sheep

The present study examined localization of cholecystokinin receptor (CCK-R) mRNA in the muscle layer of the ovine omasum and role of CCK-R type 1 (CCK-1R) in the regulation of muscle contraction of the omasum. We demonstrated that not only CCK-R type 2 (CCK-2R) mRNA but also CCK-1R mRNA is highly expressed in the muscle layer of the ovine omasum. Application of CCK-8 to muscle strips of the greater curvature of the ovine omasum at 1-100 nM induced tonic contraction in a concentration-dependent manner, and the contractile effect of CCK-8 was inhibited by both CCK-1R antagonist lorglumide (IC(50) 2.7 and 7.9 microM in the longitudinal and circular muscle, respectively) and CCK-2R antagonist PD135,158 (IC(50) 51.4 microM in the longitudinal muscle), indicating that not only CCK-2R but also CCK-1R is functionally expressed in the plasma membrane of smooth muscles in the omasum and mediates action of exogenous CCK. Contractile effect of intravenous infusion of CCK-8 (1-30 pmol/kg/min) on omasal contraction was also confirmed in the in vivo experiments using conscious sheep in the absence and presence of atropine infusion (14.4 nmol/kg/min), and showed that circulating CCK increases omasal electromyographic (EMG) activity at lower plasma concentration than that it inhibits ruminal contractions. Taking account of our previous results in the in vivo study using other CCK-1R antagonist, it is suggested that circulating CCK, even at normal range of plasma concentration, plays a physiological role as a regulator of omasal contractions in sheep and CCK-1R mediates the action of CCK.

Effect of intravenous infusion of proglumide on ruminal motility in conscious sheep (Ovis aries)

The effects of intravenous infusion of proglumide on regular ruminal contractions were examined in conscious sheep using doses that inhibit pancreatic exocrine secretion. After a control period of 20 min, proglumide was infused intravenously for 40 min at a dose of 15, 30 or 60 micromol/kg per min and venous blood was collected. The intravenous infusion of proglumide significantly increased the frequency of ruminal contractions at 15 micromol/kg per min without altering the amplitude, while it significantly decreased the frequency and amplitude of ruminal contractions at 30 and 60 micromol/kg per min in a dose-dependent manner. Proglumide did not increase contractile activity of the omasum, abomasum and duodenum or the plasma concentration of immunoreactive cholecystokinin (CCK). Application of proglumide at 1-30 mmol/L inhibited bethanechol-induced contraction in both longitudinal and circular muscle strips of the dorsal sac of the rumen. These results suggest that proglumide at a low dose acts indirectly on the rumen as a CCK receptor antagonist to increase the frequency of contractions, whereas at higher doses it inhibits cholinergic-induced contraction of the ruminal muscles or acts as an agonist to inhibit contractions in sheep. Hence, proglumide at high doses seems unsuitable for research or therapeutic use as a CCK receptor blockade in sheep.

Effect of Varying Dietary Ratios of Alfalfa Silage to Corn Silage on Omasal Flow and Microbial Protein Synthesis in Dairy Cows

Eight ruminally cannulated multiparous Holstein cows that were part of a larger production trial were used to study the effects of varying dietary ratios of alfalfa silage (AS) to corn silage (CS) on omasal flow of nutrients and microbial protein. Cows were blocked by DIM and randomly assigned to 2 replicated 4 x 4 Latin squares (28-d periods). Diets fed contained (dry matter basis): A) 51% AS, 43% rolled high-moisture shelled corn (HMSC), and 3% solvent soybean meal (SSBM); B) 37% AS, 13% CS, 39% HMSC, and 7% SSBM; C) 24% AS, 27% CS, 35% HMSC, and 12% SSBM; or D) 10% AS, 40% CS, 31% HMSC, and 16% SSBM. Crude protein (CP) contents were 17.2, 16.9, 16.6, and 16.2% for diets A, B, C, and D. All 4 diets were high in energy, averaging 49% nonfiber carbohydrates and 24% neutral detergent fiber. Total microbial nonammonia nitrogen flow was lower on diet D (423 g/d) compared with diets A (465 g/d), B (479 g/d), and C (460 g/d). A significant quadratic effect indicated that microbial protein synthesis was maximal at 38% AS. Supply of rumen-degraded protein decreased linearly from 3,068 g/d (diet A) to 2,469 g/d (diet D). Omasal flow of rumen-undegraded protein did not differ among diets and averaged 1,528 g/d. However, when expressed as a percentage of dry matter intake, rumen-undegraded protein increased linearly from 5.59% (diet A) to 6.13% (diet D), probably because CP from SSBM was more resistant to degradation than CP from AS. Essential AA flow was lowest on diet D, and Lys flow tended to be lower on diet D, which may explain the lower milk and protein yields observed on that diet.

Retention of different sizes of electronic identification boluses in the forestomachs of sheep1,2

Twelve types of electronic identification ruminal boluses of different dimensions were used to obtain a model for predicting their retention in the forestomachs of sheep. Boluses (n = 1,662) were made of ceramic materials, and their dimensions varied in o.d. (9 to 21 mm), length (37 to 68 mm), volume (2.5 to 21.0 mL), and specific gravity (0.85 to 3.91). Each bolus contained a half-duplex, standardized, glass-encapsulated transponder (32 x 3.8 mm). Boluses were administered to sheep (n = 1,497) of different ages by using the appropriate balling guns, and their retention under semiintensive conditions was recorded for at least 2 yr. When a bolus was lost, the sheep was rebolused with a heavier bolus. All sheep wore 2 plastic ear tags: one for the official control of health programs and the other for farm use. To determine the anatomical limit for a bolus passing through the gastrointestinal tract, the size of the reticulo-omasal orifice was measured in 46 adult sheep (male, n = 14; female, n = 32) that died by causes not related to bolus administration during the experiment. No signs of disease or growth alteration were detected in the bolused sheep. Total ear tag losses during the experiment period were 7.5% on average. Bolus retention (5 to 100%) varied according to bolus features and age of the sheep, but it showed a plateau after 18 mo. Inadequately dimensioned boluses were regurgitated or passed through the gastrointestinal tract and were excreted with the feces. The diameter of the reticulo-omasal orifice in adult sheep differed between male and female (23.1 and 21.8 mm, respectively; P < 0.01) and was greater than the o.d. of the retained boluses. Retention rate was predicted from bolus weight and volume by a logistic regression (R2 = 0.997; P < 0.001). When retention data from the literature (59.0 to 100%) were included in the model, the adjustment was slightly lower (R2 = 0.967). As a result, the minimum bolus weight estimated to reach a 99.5% retention rate in sheep varied between 16 and 45 g when volume varied between 3 and 22 mL, for boluses with a specific gravity between 2.0 and 5.2. In conclusion, bolus retention rate in sheep varied dramatically according to their features. For safe and efficient retention of electronic identification boluses in sheep, boluses of small volume and diameter (e.g., < 15 mm) with specific gravity and weight greater than 3.0 and 20 g, respectively, are recommended.

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.

Determination of digesta flow entering the omasal canal of dairy cows using different marker systems

Four studies were conducted to compare the effect of four indigestible markers (LiCoEDTA, Yb-acetate, Cr-mordanted straw and indigestible neutral-detergent fibre (INDF)) and three marker systems on the flow of digesta entering the omasal canal of lactating dairy cows. Samples of digesta aspirated from the omasal canal were pooled and separated using filtration and high-speed centrifugation into three fractions defined as the liquid phase, small particulate and large particulate matter. Co was primarily associated with the liquid phase, Yb was concentrated in small particulate matter, whilst Cr and INDF were associated with large particles. Digesta flow was calculated based on single markers or using the reconstitution system based on combinations of two (Co + Yb, Co + Cr and Co + INDF) or three markers (Co + Yb + Cr and Co + Yb + INDF). Use of single markers resulted in large differences between estimates of organic matter (OM) flow entering the omasal canal suggesting that samples were not representative of true digesta. Digesta appeared to consist of at least three phases that tended to separate during sampling. OM was concentrated in particulate matter, whilst the liquid phase consisted mainly of volatile fatty acids and inorganic matter. Yb was intimately associated with nitrogenous compounds, whereas Cr and INDF were concentrated in fibrous material. Current data indicated that marker systems based on Yb in combination with Cr or INDF are required for the accurate determination of OM, N and neutral-detergent fibre flow. In cases where the flow of water-soluble nutrients entering the omasal canal is also required, the marker system should also include Co.

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.

Role of nitric oxide in in vitro contractile activity of the third compartment of the stomach in llamas

OBJECTIVE

To determine the role of nitric oxide and an apamin-sensitive nonadrenergic-noncholinergic inhibitory transmitter in in vitro contractile activity of the third compartment in llamas.

SAMPLE POPULATION

Isolated strips of third compartment of the stomach from 5 llamas.

PROCEDURE

Strips were mounted in tissue baths containing oxygenated Kreb's buffer solution and connected to a polygraph chart recorder to measure contractile activity. Atropine, guanethidine, and indomethacin were added to tissue baths to inhibit muscarinic receptors, adrenoreceptors, and prostaglandin synthesis. Responses to electrical field stimulation following addition of the nitric oxide antagonist Nwo-nitro-L-arginine methyl ester (L-NAME) and apamin were evaluated.

RESULTS

Electrical field stimulation (EFS) resulted in a reduction in the amplitude and frequency of contractile activity, followed by rebound contraction when EFS was stopped. Addition of L-NAME resulted in a significant reduction in inhibition of contractile activity. Addition of apamin also resulted in a significant reduction in inhibitory contractile activity at most stimulation frequencies. The combination of L-NAME and apamin resulted in a significant reduction in inhibition at all frequencies.

CONCLUSION

Nitric oxide and a transmitter acting via an apamin-sensitive mechanism appear to be involved in inhibition of contractile activity of the third compartment in llamas.

CLINICAL RELEVANCE

Results suggest that nitric oxide plays an important role in mediating contractile activity of the third compartment in llamas. Use of nitric oxide synthase inhibitors may have a role in the therapeutic management of llamas with lesions of the third compartment.

Omasal anatomy in New Zealand red and fallow deer: an exploratory multivariate analysis

We measured the weight and volume of omasae, and the number, weight and area of omasal laminae from wild fallow (Cervus dama), and wild and farmed red deer (Cervus elaphus) whose diet, as indicated by rumen content, was known. A multivariate analysis yielded two principal components, interpreted as indices of overall omasal size and laminar leafiness. The second component showed significantly greater variance in wild red deer than in farmed red or wild fallow deer. Deer feeding on a mixed diet of browse and grasses may have greater variability of omasal from than those feeding on grass alone. A relationship is derived by which the laminar area can be estimated from counts of laminae in different size classes.

Omasal sampling technique for assessing fermentative digestion in the forestomach of dairy cows

A procedure allowing digesta sampling from the omasum via a ruminal cannula without repeated entry into the omasum was developed. The sampling system consisted of a device inserted into the omasum via the ruminal cannula, a tube connecting the device to the ruminal cannula, and a single compressor/vacuum pump. Eight cows given ad libitum access to a total mixed diet were used in a crossover design to evaluate the effects of the sampling system on digestive activity, animal performance, and animal behavior. Results indicated that the omasal sampling system has minimal effect on normal digestive and productive functions of high-producing dairy cows. Dry matter intake was reduced (24.0 vs 21.8 kg/d; P < .02) and seemed related more to the sampling procedures than to the device in the omasum. Observations of animal behavior indicated that cows with the sampling device were similar to control cows, although rumination and total chewing times were reduced slightly. The composition of digesta samples was biased toward an over-abundance of the liquid phase, but using a double-marker system to calculate digesta flow resulted in fairly small coefficients of variation for measurements of ruminal digestion variables. This technique may prove useful for partitioning digestion between the fermentative portion of the forestomach and the lower gastrointestinal tract. The omasal sampling procedure requires less surgical intervention than the traditional methods using abomasal or duodenal cannulas as sampling sites to study forestomach digestion and avoids potentially confounding endogenous secretions of the abomasum.

[Comparative ontogenic analysis of the epithelium of the non-glandular stomach compartments of merino sheep]

A total of 74 embryos and fetuses were used in a comparative analysis of the epithelium of the non-glandular stomach compartments of merino sheep during development. The mechanical protection showed by the tegumentary epithelium in the superficial layers of the rumen, reticulum and omasum is supported by a buffer system of neutral mucopolysaccharides secreted by the deeper strata. Neutral mucopolysaccharides first appeared in epithelial cells at 46 days of fetal life. Acid mucopolysaccharides, mucins, and mucoid compounds were not detected. Growth curves and formulas were constructed for the epithelial layers.

Effects of vasoactive intestinal polypeptide on electromyographic activity of the reticulo-omasal orifice in sheep at two levels of intake

The effects of intragastric arterial infusions (1 mL/min) of physiological saline, vasoactive intestinal polypeptide (VIP), or VIP-antagonist [4Cl-D-Phe6, Leu17]VIP (1 nmol/mL) on electromyographic (EMG) activities of the reticulum and reticulo-omasal orifice (ROO) in conscious ewes fed to meet either their net energy for maintenance (NEm) or twice maintenance requirements were studied. Intragastric arterial infusions (1 mL/min) of 15-min durations were conducted before, during, and after feeding. The aims of the study were to elucidate the relationships between EMG activities of the reticulum and ROO and their potential regulation by VIP in sheep fed solid feed and how the relationships could be affected by different feeding levels. At both levels of feed intake, reticular EMG spiking activity was associated with high-amplitude EMG spiking activity of the ROO, and lack of spiking activity or quiescence of the ROO was never fully observed until the reticulum became quiescent. Irrespective of feeding level, infusions of VIP were associated with a marked reduction in reticular EMG and ROO spiking activities after 3 to 4 min and a complete cessation of ROO spiking activity 8 min after commencement of VIP infusion. Three to four minutes after initiation of VIP-antagonist infusion, EMG spiking activity of the ROO was enhanced and quiescence of the ROO activity was markedly diminished. The data suggest that 1) VIP may be involved in mediation of quiescence of the ROO and increases the duration of the quiescence in sheep fed at twice maintenance compared with maintenance-fed sheep, 2) the ROO EMG activity is influenced differently by different phases of the feeding cycle, and 3) VIP-antagonist enhances the EMG activity of the ROO.

Demonstration and characterization of dipeptide transport system activity in sheep omasal epithelium by expression of mRNA in Xenopus laevis oocytes

Research from this laboratory has recently demonstrated that the omasal epithelium of sheep is capable of absorbing dipeptides. In order to express proteins potentially responsible for the mediated absorption of small peptides, size-fractionated poly(A)+RNA (RNA) isolated from omasal epithelial tissue of sheep (average BW 67.5 kg) were injected into defolliculated Xenopus laevis oocytes. The ability of oocytes injected with RNA or water to absorb [14C]glycyl-L-sarcosine (Gly-Sar) from media (usually pH 5.5) was compared. After 4 d (P < .02) of culture, specific RNA fractions induced an increased (P < .02) rate of Gly-Sar absorption, as compared with water-injected oocytes. The dependency of Gly-Sar uptake on the presence of a pH gradient was evaluated at pH 5.0, 5.5, 6.0, 6.5, and 7.5. Inducible uptake increased (P < .001) in the presence of increasing proton concentrations, whereas endogenous uptake of Gly-Sar decreased (P < .001). At pH 5.5, induced Gly-Sar uptake was saturable (Kt = .4 mM), but endogenous uptake was not. The specificity of Gly-Sar absorption was studied by the co-incubation of .1 mM Gly-Sar with 5 mM levels of competing substrates (pH 5.5). Induced uptake was inhibited (P < .05) 44% by carnosine, 94% by methionylglycine, and 91% by glycylleucine, but not by glycine. Incubation of RNA with DNA oligomers that were complementary to the rabbit intestinal transporter completely inhibited (P < .05) induced Gly-Sar uptake. These results indicate that sheep omasal epithelial cells express messenger RNA that encode for proteins that are capable of H(+)-dependent dipeptide transport activity.

Myoelectrical activity of the gastrointestinal tract of sheep analysed by computer

The myoelectrical activity of several sections of the digestive tract of sheep has been studied as an estimation of the gastrointestinal motility. Nickel/chromium electrodes were implanted chronically in the reticulum, rumen, omasum, antrum and duodenum. The myoelectrical signals were then recorded simultaneously and stored in a computer which calculated the integrated activity, duration and period (interval) of each separate reticuloruminal spike burst and the integrated activity (over one minute intervals) in the omasum, abomasum and duodenum. The different electromyographic parameters were standardised in sheep during a period of non-ingestion (resting period), and the physiological changes in these parameters associated with rumination and feeding were measured. The main effect induced by rumination was an increase in the myoelectrical parameters in the reticulum. Feeding enhanced the total activity in all regions studied. In the reticulorumen this increase was due to a rise in the frequency of the spike bursts, although there was a decrease in the integrated activity and duration of each individual spike burst.

Absorption of L-carnosine, L-methionine, and L-methionylglycine by isolated sheep ruminal and omasal epithelial tissue

The absorption of carnosine, methionine, and methionylglycine (using 35S-methionine and 35S-methionylglycine as representative markers) across ruminal and omasal epithelia collected from four (carnosine) and seven sheep (methionine and methionylglycine) were studied using parabiotic chambers that were repeatedly sampled over a 240-min incubation. The quantity of all substrates transferred was linearly (P < .01) dependent on initial substrate concentration and time. More (P < .01) carnosine, methionine, and methionylglycine was transferred across omasal than across ruminal epithelia. Carnosine was absorbed across both tissues without hydrolysis. Methionylglycine was transferred intact across both tissues. A greater (P < .01) quantity was hydrolyzed by omasal than by ruminal epithelia, after 240 min of incubation. Greater (P < .06) quantities of methionine and methionylglycine accumulated in ruminal tissue after 240 min. Total absorption of methionine and methionylglycine did not differ within tissues, but total absorption of both substrates was greater (P < .01) by omasal tissues. There was little evidence for saturable absorption. These results indicate that omasal epithelial tissue possesses a greater ability to absorb both free and peptide-bound amino acids than does ruminal epithelial tissues.

The role of GABA receptors in the control of the omasal myoelectrical activity in sheep

Gamma-aminobutyric acid (GABA) receptor-mediated modification of omasal spiking activity (SA) was studied in six conscious ewes at rest, chronically fitted with electrodes implanted in the reticular and omasal walls and a cannula placed in the left cerebral lateral ventricle. Intracerebroventricular (0.1 microgram kg-1) but not intravenous (25 micrograms kg-1) administration of muscimol increased both the duration of omasal SA and the frequency of groups of spiking bursts (GSB) from the reticulum and oral omasum; the frequency of GSB from the aboral omasum decreased. These responses were antagonised by intracerebroventricular pretreatment with bicuculline (0.5 microgram kg-1). Both intravenous (500 micrograms kg-1) and intracerebroventricular (1 microgram kg-1) administration of baclofen inhibited reticular SA; in both the oral and aboral omasum, while the duration of SA increased, the frequency of GSB decreased. Reticuloomasal responses to intravenous or intracerebroventricular baclofen were greatly antagonised or abolished, respectively, by a previous intracerebroventricular injection of phaclofen (80 micrograms kg-1). The main conclusion which could be drawn from these results is that exclusively central GABAA and mainly central GABAB receptors mediate a prolongation of omasal body motility in sheep.

Substance P-immunoreactive neurons of the bovine forestomach mucosa: their presumptive role in a sensory mechanism

Substance P-immunoreactive nerve fibers and cell bodies were examined in the forestomach mucosa of the calf and cow pretreated with colchicine, using thick (100 microns) floating sections. Intraepithelial nerve fibers were identified, appearing only rarely in the rumen and reticulum, and completely absent from the omasum. Nerve fibers were observed in the lamina propria of all the regions of the forestomach examined. A few thin nerve fibers were seen in the core of the ruminal papillae of the calf, whereas in the cow they appeared very coarse in nature. Flocculent and complicated nerve fiber networks were seen in the connective tissue of the reticular papillae. Mucosal nerve fibers formed a peculiar glomerulus-like architecture in the omasal papillae of the calf, while in the cow, the nerve fibers were largely restricted in distribution to the vicinity of the epithelium within the connective tissue pegs. Immunoreactive nerve cell bodies were found in the ruminal atrium, the dorsal sac and the ventral sac of the rumen of the calf and in the reticulum of both the calf and cow. Some of these neurons exhibited processes that appeared to course toward the papillae. In total, substance P-immunoreactive nerve fibers and cell bodies were more abundant in the calf than in the cow. These distributions demonstrate that the neural circuitry of the bovine forestomach contains substance P immunoreactivity in the mucosa as well as in the muscle layer, pointing to its possible importance in the regulation of the forestomach function. Substance P-immunoreactive nerve fibers were numerous in the reticular papillae of the calf and cow and in the omasal papillae of the calf. The positive fibers at these localities may act as mucosal receptors.

The effect of size and density on mean retention time of particles in the gastrointestinal tract of sheep

The selective retention of particles in the reticulo-rumen and in the gastrointestinal tract distal to the reticulo-rumen was studied in fistulated sheep maintained on a roughage diet. Polyethylene glycol and plastic particles of different lengths (1 and 10 mm) and densities (0.92, 1.03, 1.22 and 1.44 g/ml) were either fed or were introduced into the omasum. The mean retention time in the reticulo-rumen (MRTRR) of 1 mm long particles with a density of approximately 1.0 g/ml was about 67 h, that is eight times longer than the MRTRR of fluid; the heavier particles were retained only three times longer than fluid. Particles with a length of 10 mm were retained in the reticulo-rumen 19-28 h longer than 1 mm long particles of the same density. Particles with a length of 10 mm were reduced to smaller particles (0.5-4 mm) due to rumination. Multiple regression analysis indicated that particle density and particle size accounted for 59 and 28% of the total variation of MRTRR respectively. The mean retention time distal to the reticulo-rumen (MRTGut) of 1 and 10 mm long particles with a density near 1.0 g/ml was 18-19 h, similar to that of fluid (16 h). The heavier particles were retained about 3-8 h longer.

Involvement of alpha-adrenoreceptors in the regulation of omasal cyclic myoelectrical activity in sheep

In five conscious adult ewes at rest, chronically implanted with electrodes in the musculature of the omasal wall, intravenous (i.v.) infusion for 30 min of alpha 1- or alpha 2-adrenergic receptor blockers, prazosin (20 micrograms/kg/min) and yohimbine (30 micrograms/kg/min), respectively, had no significant effects on omasal myoelectrical activity. The i.v. administration for 15 min of alpha 1- or alpha 2-agonists phenylephrine (4 micrograms/kg/min) or naphazoline (2.5 micrograms/kg/min), respectively, increased the frequency and the amplitude of groups of myoelectrical discharges of omasum, as well as the duration of its activity. Pretreatment of animals with prazosin blocked the responses to phenylephrine. Yohimbine prevented the effects of naphazoline dose-dependently. It is suggested that both alpha 1- and alpha 2-adrenoreceptors are involved in regulation of the sheep's omasal notility. This regulation did not seem to be a simple consequence of the changes in the reticular motility.

Gastric electromyographic activity in the milk-fed lamb

1. Electromyographic (EMG) activity of the reticulum, reticulo-omasal orifice (ROO) and abomasum was recorded from conscious lambs. 2. In fasted lambs diphasic reticular EMG bursts occurred at intervals of 60 +/- 13 s. In association with the second phase of the reticular EMG burst there was consistently a period of inactivity of the EMG of the ROO of 2.4-11.0 s (5.5 +/- 2.0 s, mean +/- S.D.). This period of quiescence ended with the onset of a burst of EMG activity of the ROO of 4.1 +/- 0.8 s termed here a long burst of activity. Preceding the following reticular EMG burst there were further long bursts of EMG activity of the ROO at intervals of 11.1 +/- 1.3 s or intermixing or replacement of long burst activity with short bursts which were of duration 1.1 +/- 0.3 s and which occurred at intervals of 2.4 +/- 0.5 s. 3. When the lambs were shown milk and at times when they could be expected to anticipate milk being provided, a period of inactivity of the EMG of the ROO developed for up to 60 s. In association with this there was commonly an increase in the frequency of reticular EMG bursts which at times became monophasic. 4. With the start of sucking there was quiescence of the EMG of the ROO which persisted throughout periods of sucking for up to 90 s. Simultaneously with the disappearance of activity of the ROO there was a monophasic burst of the reticular EMG, which was followed by either quiescence or disorganized low voltage activity. Inactivity of the EMG of the ROO still developed when lambs sucked milk after administration (I.V.) of atropine, phentolamine or propranolol, but not after hexamethonium. 5. In lambs observed over a period 30-60 min after feeding the diphasic reticular bursts occurred every 85 +/- 24 s and the duration of the period of inactivity of the EMG of the ROO associated with each reticular burst (3.7 +/- 1.2 s) was significantly less (P less than 0.001) than in fasted lambs. Short bursts of EMG activity of the ROO occurred more frequently than in fasted lambs. 6. In fasted lambs bursts of EMG activity of the body of the abomasum occurred at frequencies of 6-12 min-1 and those of the antrum and pylorus at ca. 6 min-1 but episodes of such activity were intermittent.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of the muscle coat at the omasoabomasal junction and its vicinity in cattle

Detailed studies on the distribution of the muscle coat at the omasoabomasal junction in cattle, especially in the pila omasi, were carried out in order to clarify the mechanism of closing of the ostium omasoabomasicum. Anatomical and histological observations revealed that the muscle coat forming the circumference of the ostium omasoabomasicum is composed of inner circular and outer longitudinal layers. The former was particularly thickened at the end of the sulcus omasi (pila omasi). Joined to the pila omasi was a thick muscle bundle which extended from the labium sinistrum (left lip) of the sulcus reticuli and ran obliquely along the floor of the sulcus omasi. Moreover, on the abomasal side of the ostium omasoabomasicum, vela abomasi were formed in such a manner as to surround the ostium omasoabomasicum. These were continuous with the edges of the sulcus omasi. Judging from its location and muscular structure, the pila omasi may contract in accordance with the contraction of the reticulum. As a result, the ostium omasoabomasicum may be narrowed and the vela abomasi pulled toward the omasum, perhaps obstructing the ostium omasoabomasicum. Accordingly, it is presumed that the retention of contents in the omasum may effectively prevent abomasal contents from moving backward into the omasum.

Gastro-intestinal tract function in sheep infused with somatostatin

The effect of a 5-day continuous intravenous infusion of somatostatin (4.6 ng min-1 kg-1) was studied, using anoestrous ewes given 791 g dry matter per day of a 60:40 lucerne hay:oat grain pelleted diet from a continuously moving belt. 51Cr-EDTA, 103Ru-phenanthroline and lignin were used as markers to determine digesta mean retention times (MRT) by a continuous infusion-total sampling procedure. The somatostatin infusion increased the concentration of somatostatin in venous plasma within the physiological range from 10 to 76 ng/l, decreased plasma concentrations of prolactin and thyroxine, but had no effect upon plasma concentrations of insulin and glucagon. It had no effect upon digesta-free weight of the rumen and omasum but consistently decreased the weight of all post-ruminal segments of the gastrointestinal (GI) tract. The infusion increased the accumulation of digesta in the abomasum and caecum. Total MRT of all three markers in the entire GI tract was unaffected by somatostatin infusion, but the proportion of total MRT spent in the abomasum + small intestine + caecum increased and the proportion spent in the large intestine and rumen decreased. Somatostatin infusion decreased apparent endogenous abomasal secretion, increased water flow from the rumen and into the abomasum and decreased voluntary water consumption. It is proposed that the prime site of somatostatin action was in the abomasal to caecal region, where somatostatin-secreting D cells are found in greatest concentration, that effects observed in the large intestine and rumen may represent secondary compensatory mechanisms and that the effects observed were due to direct action of somatostatin and were not mediated by other GI hormones.

Ruminal bypass of drinking water in lactating cows

Drinking water that does not equilibrate with ruminal fluid, i.e., bypasses the rumen, was studied qualitatively and quantitatively in eight rumen-fistulated lactating Holstein cows. Decreased temperatures in the sulcus omasi and abomasum shortly after initiation of drinking indicated that water had bypassed the rumen. Recovery of a water-soluble marker, included in drinking water offered after water was withheld for 4.5 or 9 h following feeding, was used to estimate ruminal bypass. For respective treatments, 18 and 5% of drinking water was calculated to have bypassed the rumen. Ruminal bypass in lactating cows drinking relatively large amounts of water could affect comparisons of water intake with total ruminal fluid outflow as measured by dilution of a water-soluble marker. Drinking water should not be assumed to equilibrate with ruminal fluid.

Forestomach motility in the chronically vagotomized sheep

1. The motility of the reticulo-rumen and omasum in conscious sheep was studied by electromyography from chronically implanted nichrome wire electrodes. The sheep were subjected to vagotomy and were maintained totally by intragastric infusion of liquid nutrients before and after vagotomy. Before vagotomy the motility of the forestomach was essentially similar to that seen in roughage-fed sheep.2. Bilateral thoracic vagotomy transiently abolished all electrical activity of the reticulo-rumen and omasum, but within 1 day some activity returned. Frequent periods of rhythmic local small group discharges were seen over the reticulo-rumen, while the omasum showed prolonged (1-5 min) bursts of mainly slow wave activity.3. Within 1-2 weeks of vagotomy strong contractions of the reticulo-rumen were visible by radiography. Electromyographically, they comprised a rhythmic series of some two to five large group discharges recurring approximately once a minute. Each series of activity was separated from the next by a short period of quiescence. The discharges occurred almost simultaneously over the whole reticulo-rumen and so contrasted with the progressive forward or backward spread of activity seen in the intact animal. The bursts of activity in the omasum, lasting 0.5-2 min, were not co-ordinated with the activity of the reticulo-rumen as they are in the intact animal.4. The activity in the reticulo-rumen and omasum was not affected by bilateral section of the splanchnic nerves and removal of the coeliaco-mesenteric ganglia. Reticulo-rumen but not omasal activity was abolished by atropine (0.1 mg/kg) or hexamethonium (2 mg/kg), while both were stimulated by pentagastrin (3 mug/kg).5. Following vagotomy reticulo-rumen motility was no longer influenced by feeding, or by tactile stimulation of the buccal cavity or oesophagus. Severe distension of the abomasum caused a slight acceleration of the motility rhythm compared to the inhibition seen before vagotomy.6. It is concluded that the reticulo-rumen motility observed after vagotomy is an intrinsic cholinergic motility which is dependent upon the activity of the myenteric plexus. The motility of the omasum after vagotomy is similar to that seen in the intact animal and differs from that of the rumen in that it appears not to depend wholly upon cholinergic control.

[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.

Sulfur and methionine metabolism in sheep. I. First approximations of sulfur pools in and sulfur flows from the reticulo-rumen

Sulfur pools in the rumen and sulfur flows from the rumen were investigated in two experiments with sheep on a diet containing equal parts of oaten and lucerne chaffs. The diet was fed at two levels, either chopped or pelleted, and with intraruminal DL-methionine supplements. Ruminal fluid volumes and fluid flows to the omasum were measured. None of the treatments influenced ruminal fluid volume. Fluid flow to the omasum, however, was increased by increasing dry matter intake (DMI), and was further enhanced by feeding chaffed hay rather than the same materials ground and pelleted; the DL-methionine supplement had no effect. First approximation of the ruminal sulfur pools and of sulfur flows to the omasum were derived from the concentration of sulfur in true digesta and the ruminal fluid volume or fluid flow. Increasing DMI from 500 to 1000 g/day resulted in larger ruminal pools of total (1096 v. 792 mg), neutral (1016 v. 731 mg) and protein (479 v. 419 mg) sulfur, but the reducible sulfur pools were not affected by the level of DMI. Infusions of DL-methionine increased the ruminal sulfide sulfur pool irrespective of level of DMI. The first approximation of total sulfur flow was increased by 1660 mg/day at the higher level of DMI, due mainly to increases of 710 mg S/day as protein sulfur and 859 mg S/day as non-protein neutral sulfur. Flows of inorganic sulfate and ester sulfate sulfur, although small in comparison with organic sulfur flows, increased with level of DMI. Sulfide sulfur flows were also increased at the higher level of DMI, and were almost doubled by intraruminal infusions of DL-methionine.

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.

The site of magnesium absorption from the ruminant stomach

1. A low-magnesium diet was fed to four sheep, each of which had been surgically prepared with a rumen fistula, a tube into the cranial one-third of the omasum, a tube to the cranial one-third of the abomasum and a re-entrant duodenal cannula. Mg, as gluconate or acate or acetate, was continuously infused for 12-14 d in turn into (1) the caudal duodenal cannula, (2) the abomasum, (3) the omasum, (4) the rumen. A continuous infusion of the chromium-ethylenediaminetetraacetic acid complex (CrEDTA) was maintained to the rumen. The abomasal effluent which flowed through the cranial duodenal cannula was continually sampled and the flow of Mg calculated from the concentrations of Mg and CrEDTA. Blood and rumen fluid samples were taken and urine and faeces collected during each period of Mg infusion. 2. The Mg infused to either the abomasum or omasum was completely recovered at the duodenum, indicating a lack of net absorption of Mg from these stomach compartments. In contrast, 13-7-18-7 mmol (36-61%) of the Mg infused to the rumen was not recovered at the duodenum which suggested that a substantial net absorption of the infused Mg occurred from the reticulo-rumen. Absorption of Mg caudal to the pylorus was not related to the site of Mg infusion and averaged 3-28 +/- 0-56 (SEM) mmol/d. 3. Compared with the intraruminal infusion, the post-ruminal infusion of Mg was associated with decreased plasma and rumen fluid Mg concentrations, decreased urinary Mg exretion, decreased Mg balance and increased faecal Mg excretion. 4. It is concluded that no significant absorption of Mg occurs from either the omasum or abomasum in sheep and that the reticulo-rumen is the principal site of Mg absorption before the pylorus. Absorption of Mg post-ruminally is insufficient to maintain normal Mg status in the animal.

Cineradiography of the reticular groove mechanism

The use of cineradiographic studies in the interpretation of how sucked liquid passes to the abomasum in young sucking ruminants is described with special reference to experimental studies in lambs and calves. The work involved an examination of the movements of stainless steel wire or clips inserted via a gastrostomy into the mucosa of the caudal thoracic oesophagus, lips of the reticular groove and margins of the reticulo-omasal orifice. This assisted the interpretation of how these structures are involved in the passage into the abomasum of sucked liquid and into the reticulo-rumen of liquid or solid ingesta or saliva swallowed independently of sucking. An understanding of contributions made by the oesophagus, reticular groove and reticulo-omasal orifice to the passage of sucked liquid into the abomasum was aided by the use of the autonomic blocking agents, atropine and hexamethonium.

Health and performance of calves with forestomach-bypass fed milk replacer

Ten male Holstein calves were placed in groups of two calves each on similarity of age. On calf in each group was subjected to forestomach-bypass surgery at about 1 mo of age. Fortified commercial milk replacer with added minerals and vitamins was fed as the sole diet. The calves were housed indoors on slatted platforms. Weight gain was determined biweekly. Feed intake was determined daily. Necropsies were performed upon termination of the study. Recurrent ruminal bloat, fever, and anorexia of varying degrees and combinations occurred in four of the calves with forestomach bypass. Two of these calves showed slow weight gain. One of the four calves died following acute bloat while the other three calves were sacrificed following repeated episodes of bloat. The time of termination varied between 3 and 10 mo. One calf with forestomach bypass and all control calves appeared healthy throughout the experiment. Necropsies indicated that the ruminal bloat, seen in most of the forestomach-bypass calves, could be attributed to the back-flow of ingesta via the omasal-abomasal orifice. This ingesta appeared to produce gas which became trapped in the bypassed rumen.

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.

Effects of stimulation of efferent fibres of the vagus on the reticulo-omasal orifice of the sheep

1. The reticulo-omasal orifice has been observed and its activity recorded in decerebrate and spinal preparations of lambs and in lambs and sheep anaesthetized with chloralose.2. Spontaneous closure movements at about 6/min were seen, or recorded from balloons placed in the orifice in all types of preparation when both vagus nerves had been cut and after atropine, hexamethonium, phentolamine and propranolol had been given I.V.3. The effects on the reticulo-omasal orifice of stimulation in the neck of efferent fibres of the vagus nerves on either side differed according to the form of the stimulus applied.4. Threshold stimulation of the vagus nerve caused closing of the orifice which was blocked by atropine.5. Opening of the orifice and disappearance of spontaneous closing movements followed more intense stimulation of the vagus nerves.6. Vagal opening effects were obtained after atropine was given and after adrenergic opening and closure effects had been blocked with phentolamine and propranolol.

Movements of the stomach compartments of a young bull during sucking

1. Gastric motility was studied in a young bull and two sheep which had retained their sucking behaviour. Pressure tracings or electromyograms were recorded from all compart-ments of the stomach.

2. During the sucking of milk or water reticulum contractions either became more fre-quent but weak, or ceased altogether. After sucking, or after the introduction of fluid directly into the abomasum, reticulum contractions slowed down but retained their strength. The rumen and omasum were more fully inhibited than the reticulum.

3. It is concluded that the inhibitory response to sucking has two phases, a cephalic phase dependent upon the eagerness of sucking which mainly influences the strength of the contractions of the forestomach, and an abomasal phase dependent on the degree of distension of the abomasum which mainly affects the frequency of the contractions.