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The aim of this study was to determine the time course for adaptation of the reticulo-rumen, omasum, abomasum, and small intestine in response to an abrupt increase in the proportion of grain in the diet. Adaptive responses include tissue and digesta mass, small intestinal length, and brush border enzyme activity in the duodenum, proximal jejunum, and ileum. Twenty-five Holstein steers (213 ± 23 kg; 5 to 7 mo of age) were blocked by body weight, and within block were randomly assigned to 1 of 5 treatments: the control diet (CTRL; 92% chopped grass hay and 8% mineral and vitamin supplement on a dry matter basis) or a moderate grain diet (MGD; 50% chopped grass hay, 42% rolled barley grain, and 8% mineral and vitamin supplement) that was fed for 3 (MGD3), 7 (MGD7), 14 (MGD14), or 21 d (MGD21). Dry matter intake was limited to 2.25% of body weight to ensure that changes in dry matter intake did not confound the results. On the last day of the dietary exposure, steers were slaughtered 2 h after feeding. Reticulo-rumen tissue mass and ruminal epithelium mass in the ventral sac of the rumen were not affected by the MGD. Wet reticulo-ruminal digesta mass decreased from CTRL to MGD7 and then increased, but reticulo-ruminal digesta dry matter mass did not differ between treatments. Omasal mass, omasal tissue mass, and omasum digesta mass decreased linearly with the number of days fed MGD, but abomasal tissue mass tended to increase linearly. Duodenal tissue mass tended to increase linearly, and ileal length increased linearly with the number of days fed MGD. Lactase activity in the proximal jejunum increased linearly and maltase activity in duodenum tended to increase linearly with days fed MGD. Aminopeptidase N activity in the proximal jejunum increased cubically with days fed MGD, and dipeptidylpeptidase IV activity in ileum tended to decrease from CTRL to MGD14 and then tended to increase. Adaptation to a diet with a greater proportion of concentrate involves changes in the mass and length of regions of the gastrointestinal tract and brush border enzyme activity. These changes take place gradually over at least 3 wk., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This short review deals with some basic aspects concerning the physiology of the ruminant forestomachs and the abomasum. Following the discussion of the motoric activities, the major aspects of microbial carbohydrate and nitrogen metabolism within the reticulorumen are treated. Thereafter, some functions of the abomasum are presented in some more detail. These include the composition of abomasal contents, the mechanisms and regulation of hypochloric acid and enzyme secretion, and the mechanisms responsible for protection of the mucosa against digestion by gastric secretions.

1. The normal passage to the abomasum of liquid sucked by lambs and calves was confirmed in radiographic studies to be changed to passage of liquid to the reticulum and rumen after cervical or abdominal vagotomy.2. The effects of hexamethonium (8-10 mg kg(-1) I.V.) were similar to those of vagotomy.3. Atropine (200-800 mug kg(-1) I.V.) had either no detectable effect on the destination in the stomach of liquid sucked by lambs or caused a partial failure of the reticular groove mechanism.4. Fluid sucked by lambs passed wholly to the abomasum after adrenaline (5-40 mug kg(-1) I.V.).5. Atropine and adrenaline caused a greater dysfunction of the reticular groove mechanisms in calves than in lambs.6. Contraction of the reticular groove was observed via rumen fistulae in three lambs. Eversion of the caudal oesophagus into the reticulum which occurred when saliva was swallowed into the reticulum and rumen was not observed when liquids were sucked from a bottle.7. The continued passage to the abomasum of sucked liquid in atropinized lambs has been taken as an indication of the importance of caudal oesophageal reactions, tonic activity of the reticular groove and the atropine-resistant vagally induced opening of the reticulo-omasal orifice in the reticular groove mechanism.

In the majority of experiments the ruminal preparations did not exhibit spontaneous electrical and contractile activity but showed a Ca-dependent spike-free myogenic tone. Ba2+ or Sr2+ evoked spike activity and phasic contractions and increased the muscle tonic tension. Tetraethylammonium (TEA) exerted no effect on the ruminal preparations but potentiated the effect of Ba2+. Acetylcholine (ACh) induced dose-dependent spike-free tonic contractions which were verapamil resistant and were suppressed by sodium nitroprusside. When applied to BaCl2- or TEA-pretreated preparations ACh caused spike activity and phasic contractions. The antral abomasum exhibited a spontaneous electrical activity--slow waves on which spike potentials were superimposed. ACh and TEA induced membrane depolarization and increased the spike activity and the phasic contraction amplitude.

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)

Passage route into stomach compartments of liquid feeds containing a marker was studied by feeding a liquid supplement and molasses from a lick-wheel feeder and by infusing the liquid supplement into the reticulorumen 30 min prior to sampling contents of the reticulorumen and abomasum and 4 h prior to sampling blood for plasma glucose. Recovery from reticulorumen and concentration of marker in abomasal ingesta gave no evidence of rumen bypass, this supported by a gross correlation of .92 between rumen ammonia nitrogen and nonprotein nitrogen intake from liquid feeds. Plasma glucose values were not different. Preinfusion and postinfusion plasma glucose values were similar for abomasal infusion of about 454 g of molasses, 20% crude protein liquid supplement, and for the basal diet. Values were lower for abomasal infusion of the 35% crude protein liquid supplement (Pro-Lix) than for the 20% crude protein liquid supplement. When complete rations containing 11.5, 13.0, and 14.5% crude protein were supplemented with either molasses or a 20% crude protein liquid supplement fed from lick-wheel feeders, intake averaged .53 and .34 kg per animal daily for the respective liquid feeds. There was no effect on milk yield, solids-corrected milk, milk fat content, protein content, solids-not-fat percent, or body weight change. There was an interaction of protein level and liquid feeds in which plasma glucose was increased by liquid feeds in higher but not in lower protein diets.

The experiments are carried out on chloralose-anaesthesized sheep (50-70 mg/kg). The increase in the force, frequency and duration of the stimulating impulses in a geometric progression leads to an increase in the amplitude of the contractions in all sections of the complex stomach. The amplitude and nature of the evoked contractions for one and the same parameters of stimulation are different in the different sections. The latency of the response in the reticulum is always shorter and its contractions increase faster than in the other sections. The relaxation of the muscles after elimination of the stimulation to the initial level is slowest in the rumen and in the case of high parameters of stimulation it takes more than 10 min.

Hexamethonium, which inhibits cholinergic transmission by preventing acetylcholine release, has been considered an ideal reference drug for the blockade of autonomic ganglia, Auerbach plexus and reflex gastrointestinal secretions. The degree of inhibition of ruminant gastrointestinal functions with this reference drug were as follows: cyclical contractions of the reticulo-rumen and abomasal motility greater than gastric acid secretion and duodenal migrating myoelectrical complexes. Although reduced at high dosages, the initiation of migrating myoelectric complexes was enhanced at clinically used dosages. The duration of the inhibition of reticular contractions was dose-related varying from 0.5 to 5 h for 1.25 to 20 mg/kg subcutaneously. Abomasal motility and acid secretion were similarly reduced but exhibited strong and long-lasting rebound effects. Inhibition of the reticulum by the blockade of muscarinic receptors by atropine was also dose-related lasting from 0.5 to 3 h for 0.5 to 2 mg/kg, whereas inhibition of the abomasal motor and secretory functions lasted from 1 to 6 h. These results suggest a higher degree of impingement of the parasympathetic pathways on abomasal acid secretion and motility than on the cyclical activity of the reticulum and only a modulatory role of the extrinsic neural activity on the cyclical motor events of the duodenum.

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.

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.

1. Fistulated sheep given a concentrate diet were used to study the behaviour of solute ([51Cr]EDTA) and particle ([103Ru]phenanthroline) markers in the stomach under conditions of continuous feeding. 2. An injection of a mixed dose of [51Cr]EDTA and [103Ru]phenanthroline was given into the rumen and the time course of marker concentrations in the rumen and the abomasum was recorded. The curves were analysed on the assumption that the stomach of the sheep could be represented as two mixing compartments (reticulo-rumen and abomasum) and a time delay (omasum). This model provided a very good description of the data. 3. [103Ru]phenanthroline associated with small particles was retained in the rumen much longer than [Cr]EDTA. Although exchange of [103Ru]phenanthroline occurred between large and small particle fractions, the results suggested that small particles may have been retained somewhat longer in the rumen than solutes. However, it was clear from the results that the mean retention times for particulate matter in the rumen could not be simply obtained using adsorbable markers. 4. Cyclical fluctuations in the concentration of [51Cr]EDTA in the rumen indicated that there were daily variations in net water flux in the rumen. 5. The presence of protozoa was associated with much shorter retention times of both solutes and particles in the rumen. Protozoa were also associated with reduced rumen volumes.

1. Sheep equipped with rumen and abomasal cannulas were given ad lib. access to ground and pelleted lucerne (Medicago sativa) hay except for periods of up to 6 h immediately before experimental sessions in which food intake was measured while various stomach compartments were either distended or subjected to tactile stimulation from a probe. 2. Inserting a probe, consisting of two collapsed balloons tied onto the end of a polyethylene tube, into the reticulum depressed intake by 24% after 30 min of feeding (P less than 0.025). Compensatory feeding was observed during the 30 min period immediately following removal of the probes. There were no effects of having a probe in the abomascum. 3. Distension of the reticulum with 0-800 ml water in a balloon depressed intake by 0.2 g/ml after 30 min of feeding (P less than 0.05). Removing the balloons from the animals allowed them to make up the deficit in intake completely within 30 min. Distending the rumen by 800 ml had no effect on intake (P greater than 0.05). Distending the abomasum with up to 1000 ml water in a balloon depressed intake by 0.11 g/ml after 30 min of feeding with compensatory feeding being significant (P less than 0.05) but incomplete. 4. Combinations of reticular distension up to 800 ml and of abomasal distension up to 1200 ml did not have additive depressing effects on intake.