Funktionen des Blättermagens bei kleinen Hauswiederkäuern*

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.

Passage of indigestible particles of various specific gravities in sheep and goats

1. Eight kinds of indigestible particles with specific gravities (SG) ranging from 0.92 to 1.87 (2 mm diameter and 4 mm length) were injected into the reticulo-rumen of sheep and goats in order to investigate the relation between SG and passage through the gastrointestinal tract, and the difference in passage time in the two species of animals. 2. The percentage of excreted particles significantly increased, while the percentage of ruminated particles in the excreted particles significantly decreased, as the SG increased. 3. The daily and cumulative recovery rates of particles of SG 1.38 were slower in sheep than in goats, while those with SG 0.92 were not different between species. 4. It is concluded that particles with SG higher than 1.27 would pass through the gastrointestinal tract of sheep and goats more quickly than those with SG lower than 1.21.

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.

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.

Exchanges of water and certain water-soluble minerals during passage of digesta through the stomach compartments of young ruminating bovines

1. Four ruminating bull calves were provided with cannulas in the rumen and abomasum and a sleeve sutured at the omosal-abomasal orifice that permitted digesta flowing from the omasum to be diverted and collected. 2. The calves were each given in turn a high-roughage (HR) and high-concentrate (HC) diet consisting mainly of dried grass and flaked maize in the proportions 3:2 and 1:2 by weight respectively. Water-soluble non-absorbable marker (polyethylene glycol) was also given and the diets were sometimes supplemented with magnesium sulphate. For each diet (HR(0), HR(Mg), HC(0), HC(Mg], collections were made from the rumen, reticulum, omasal outflow and abomasum, and flows of water, sodium, potassium and chloride calculated at these sites relative to intakes. 3. The general pattern of net exchange was similar for all the diets. Substantial additions of water and Na, a small addition of K and a small absorption of Cl occurred between mouth and reticulum. Substantial (approximately 40-60%) absorption of water and Na, a small absorption of K and considerable secretion of Cl occurred in the omasum. Quantitative comparisons indicated that addition of water and Na up to the reticulum, presumably in saliva, was significantly greater for the HR than the HC diets. Addition of Mg appeared to stimulate absorption of Na and water up to the reticulum for unknown reasons. Re-absorption of these components in the omasum varied for different calves and diets but appeared to be influenced primarily by a positive linear relation between amounts of digesta flowing into the omasum and amounts of water and Na absorbed from it. The proportion of water absorbed also increased with increasing entry rates of water. 4. Other findings showed that pH values rose slightly (about 0.2 pH units) but significantly in the reticulum compared with the rumen and that the value fell again by about the same amount during the passage of digesta through the omasum. Changes between omasal outflow and the abomasum were as expected, with marked additions of Cl, Na and water and a fall in pH.

Absorption of the toxins of Lantana camara L. from the digestive system of sheep

When lantana was given into different regions of the alimentary tract, absorption sufficient to cause intoxication occurred from the stomachs, small intestine and large intestine, but absorption from the small intestine was quantitatively the most important. However, it was shown that the passage of ingesta into the small intestine decreased markedly a few hours after the toxin was given and it is suggested that absorption from all areas of the gastrointestinal tract is important for the progression of the disease. When bile was diverted away from the small intestine, animals were still intoxicated by lantana. This indicates that bile is not important for absorption of lantana toxins. Other experiments indicated that the lantana toxins are transported to the liver mainly in the portal blood.