Regions in the brainstem and frontal cortex where electrical stimulation elicits parotid and submandibular saliva secretion in sheep.

Acute experiments were conducted in sheep anaesthetized with sodium pentobarbital to identify regions in the brain where electrical stimulation would elicit secretion by the parotid and submandibular salivary glands. This was a prerequisite for single unit studies in the future. In the brainstem, parotid and submandibular secretions were evoked on average between 7 and 16 mm rostral to obex and from 1 to 11 mm lateral to midline, with the parotid gland being active on the caudal and the submandibular on the rostral sides of this region. Overlap of the two sites was common. The combined region was either between cranial nerves VII and IX or adjacent to either one of them. Stimulating the caudal edge of the parotid sites evoked relatively high parotid secretion rates compared with other areas whereas secretions were uniform throughout the submandibular sites. The combined sites were from 2 to 5 mm deep, the dorsal edge being 1 mm below the floor of the fourth ventricle near midline and 6 mm below it at the lateral extremes. From a dorsal perspective, their orientation was essentially in the lateral plane except that the submandibular site angled slightly rostrally from midline. Profuse parotid secretion was also consistently evoked by stimulating the frontal cortex 15-20 mm from midline and 0-15 mm under the apex. Weak submandibular responses were observed in about half of the sheep. There were no effects on either gland of stimulating the olfactory bulbs. This is the first report of the regions in the brain which increase parotid and submandibular saliva secretion in ruminants. The three-dimensional representation of both sites in the brainstem of individual animals is more precise than the composite representations published to date for other species.

Electrical stimulation of the medial frontal lobe elicits a pattern of body movements in sheep.

Acute experiments were conducted in sheep anaesthetized with sodium pentobarbital to identify regions in the brain where electrical stimulation would elicit movements of body parts. Stimulating the dorsal frontal cortex 2 mm from midline from the front of the brain backward for 30 mm caused movements, in order, of the lower jaw, face in general, neck, shoulder and front and back legs.

Technical note: reversible re-entrant cannulation of the parotid duct in cattle using a new injection anesthesia regimen.

A new method for reversible reentrant cannulation of the parotid duct in cattle by use of an injectable anesthetic regimen is described. Ruminal contents were removed before anesthesia instead of food deprivation. The parotid duct was dilated by means of a long hemostatic forceps: its jaws were encased in a piece of plastic tube, and the tip was extended by a piece of flexible wire. A polyethylene parotid catheter was inserted into the dilated duct and passed through the cheek. The saliva was re-directed back into the mouth via a silicone tube through another fistula in the cheek. The cannulations were maintained for 3 to 11 wk and two cows were recannulated three to five times in both parotid ducts without problems. No pathological changes of the mouth epithelium were found at slaughter. The rate of flow from the ducts during rest, ruminating, and eating were 5 to 20, 25 to 50, and 40 to 75 mL/min, respectively.

Attempts to modify reperfusion injury of equine jejunal mucosa using dimethylsulfoxide, allopurinol, and intraluminal oxygen.

This study compared the severity of ischemic injury to the equine jejunal mucosa caused by arteriovenous obstruction (AVO) or venous obstruction (VO) with that caused by reperfusion after ischemia. The degree of mucosal damage and regeneration was scored according to a modified version of an established light microscopic classification for ischemic injury. Biopsy specimens taken after 3 and 4 hours of obstruction, and after 3 hours of obstruction and 1 hour of reperfusion, were compared. There were no changes in the severity of mucosal injury (characterized by epithelial sloughing, loss of villus architecture, and necrosis of crypt cells) at 4 hours of ischemia when compared with 3 hours of ischemia. The mucosal injury score increased by one grade in three of six and five of eight segments during reperfusion for the VO and AVO models, respectively; however, only the scores for the AVO model were significantly different from the injury caused by ischemia alone. Modification of reperfusion injury was attempted by the administration of intravenous (IV) allopurinol, dimethyl sulfoxide (DMSO), or intraluminal oxygen insufflation at the time of release of the AVO and VO. Treatments did not significantly alter either the severity of injury noted after 1 hour of reperfusion or the degree of mucosal regeneration after 48 hours of reperfusion. In this group of ponies, the severity of mucosal damage was greater after 1 hour of reperfusion for both AVO and VO.

Factors affecting the voluntary intake of food by sheep. 6. The effect of monosodium glutamate on the palatability of straw diets by sham-fed and normal animals.

Sheep with oesophageal fistulas were used in sham-feeding experiments to assess how sham intakes were affected by (a) physical form of straw (finely and coarsely ground; ground and pelleted), (b) type of food (straw pellets v. lucerne (Medicago sativa) hay pellets) and (c) additions of monosodium glutamate (MSG) with or without NaCl to the various straw diets. Normal animals were also fed on diets with and without MSG. Sham intakes of fine-ground loose straw (25 g/30 min) were markedly less (P = 0.002) than those of ground and pelleted straw (711 g/30 min). However, MSG at 5-40 g/kg fine and coarse ground straw increased sham intakes by 146 (P = 0.04) and 164% (P = 0.01) respectively. These findings indicated that the intakes of poor-quality diets can be increased by compacting them or by improving their palatability with MSG, or both. Sham intakes of straw pellets in two experiments were 32 (P = 0.02) and 45% (P = 0.008) of those of lucerne pellets (436 v. 1366 and 737 v. 1640 g/30 min). However, MSG at 20 g/kg straw pellets increased sham intakes from 674 to 1100 g/30 min (P = 0.05). When the MSG was mixed with NaCl (20 g/kg), the intakes of straw pellets were increased from 1089 to 1512 g/30 min (P = 0.02). Thus, the addition of MSG with or without NaCl increased the intakes of straw pellets. The highest intakes of the straw pellets treated with MSG were similar to those for lucerne pellets. When MSG-treated ammoniated barley straw (10 g/kg) was fed to normal sheep, the MSG increased DM intakes by 10% (719-789 g/d; P = 0.04). MSG sprayed onto grass hay (10 g/kg) did not, however, affect daily DM intakes by these sheep. In general, the findings indicate that the intake of straw by ruminants may be increased by compressing it to form pellets or cubes and by adding MSG.

A review of the physiological significance of hypertonic body fluids on feed intake and ruminal function: salivation, motility and microbes.

Mechanisms exist in the ruminant to detect changes in osmolality and volume of plasma during feeding to maintain fluid and electrolyte homeostasis. Feed intake during a meal can be limited by the rise in osmolality of ruminal fluid, which is sensed in the wall of the rumino-reticulum. Ruminal microbes appear to be resilient to the short-term changes in ruminal fluid tonicity, but in vitro growth rates are inhibited when the tonicity of the culture medium is increased beyond physiological levels. Although mixing contractions of the rumen are not inhibited by the normal increases in tonicity of ruminal fluid, time to first rumination is increased. This aspect of motility requires further research. The tonicity of plasma increases toward the end of a large meal as a consequence primarily of absorption of VFA and Na+ from the rumen and fluid shifts into the gut. This hypertonicity is sensed centrally to inhibit parotid secretion by a reduction in the parasympathetic stimulation to the gland. Increases in animal production may result from future research directed toward developing ways of counteracting these negative effects of hypertonicity in body fluids on feed intake and ruminal function.

Digesta kinetics in sheep and cattle fed diets with different forage to concentrate ratios at high and low intakes.

Effect of maintenance and ad libitum intakes on digesta kinetics was studied with six ruminally fistulated cows and six ruminally fistulated wethers to validate the use of sheep as a model of cattle. Complete diets were made up of ratios of alfalfa:cracked corn and soybean meal of 80:20, 55:45, and 30:70. The rate of passage of Cr-mordanted alfalfa and soybean meal in the reticulorumen was negatively related to percentage of concentrate in the diet in both species at low intakes. Passage values of particulate and liquid markers were faster at high than at low intakes in both species for all diets. Rumen liquid volume increased with intake only in the cows on the low and intermediate concentrate diets. No substantial differences were found in particulate passage values between sheep and cattle. However, liquid passage rates from the rumen and the differentials between liquid and particulate dilution rates were higher in cows than in sheep for all diets at both intakes. These results together with those for digestibility data reported in a previous communication suggest that caution should be exercised when extrapolating results from one species to the other.

Factors affecting the voluntary intake of food by sheep. 5. The inhibitory effect of hypertonicity in the rumen.

The site where osmotically active substances act to depress food intake was determined in sheep. After 5.5 h of food deprivation, solutions of sodium chloride or polyethylene glycol-200 (PEG-200) were added to either the reticulo-rumen or the abomasum. The sheep were then immediately offered pelleted lucerne (Medicago sativa). Water was withheld during the first 60 min of feeding but was available from 60 to 90 min. There was a linear inhibition in food intake in the first 10 min after loading 2.37, 6.25, 12.5, 25.0 or 50.0 g NaCl into the rumen according to a 5 x 5 Latin square design (P = 0.0001). The intake reduction was 3.49 g food/g NaCl. An osmotic load of PEG-200 equivalent to 50 g NaCl also significantly inhibited food intake in the first 10 min of the meal compared with a control treatment. The inhibition of food intake after loading 55 g NaCl into the rumen was not affected by injecting lidocaine hydrochloride into the reticulum immediately before NaCl loading. NaCl injected into the abomasum did not significantly affect food intake in the first 10 min of feeding even though the tonicity of abomasal digesta was increased to unphysiological levels. There was no consistent relationship between food intake and the change in the tonicity of jugular plasma following solute loading and drinking. The sensing site of hypertonicity was localized to the wall of the reticulo-rumen where neuronal receptors appear to be capable of detecting osmotic pressure within the physiological range to depress food intake. These receptors should be identified and characterized because of their possible significance in limiting food intake by ruminants.

The effect of feeding frequency and meal size on amounts of total and parotid saliva secreted by sheep.

Total and unilateral parotid saliva production during eating were measured in response to offering sheep a fixed amount of lucerne (Medicago sativa) hay as one, two, four or eight meals. Total saliva measurements were obtained using sham-fed oesophageal-fistulated sheep. Unilateral parotid saliva was collected from sheep fitted with reversible re-entrant cannulas. Dry matter intakes and eating times were measured for each meal but were not constrained to particular values. Total and unilateral parotid saliva production during eating increased linearly with the log of the number of meals (P = 0.0001). The amounts corresponding to one, two, four and eight meals of lucerne hay were 1553, 1737, 1851 and 2087 ml during total collections and 209, 248, 307 and 352 ml during unilateral parotid collections. The time-period spent eating and the amount of food consumed both increased as meal number increased. Total saliva collections when lucerne hay was sham-fed as one, two, four or eight meals were associated with eating times of 56.9, 57.4, 70.8 and 86.0 min and intakes of 562, 622, 629 and 638 g dry matter respectively. For unilateral parotid collections, eating times and dry matter intakes were 64.2, 71.3, 78.0, 82.1 min and 515, 579, 614 and 627 g for one, two, four and eight meals of lucerne hay respectively. The saliva production response appeared to be determined through the effects of the time-period spent eating and amounts consumed, but other undetermined effects of feeding frequency contributed to the response. The importance of meal duration on total saliva production was assessed by sham-feeding of 800 g lucerne as stem, leaf, hay, chopped hay or ground and pelleted hay. Increasing meal duration by feeding with stems resulted in the production of 1808 ml saliva, whereas the rapid consumption of pellets resulted in only 442 ml being produced.

Parotid secretion patterns during meals and their relationships to the tonicity of body fluids and to gastrin and pancreatic polypeptide in sheep.

The flow pattern of unilateral parotid saliva in sheep was compared when a total of 800 g lucerne (Medicago sativa) hay was offered as one, two, four or eight distinct meals. These patterns were related to changes in the tonicity of rumen fluid and plasma and to plasma concentrations of gastrin and pancreatic polypeptide. Sheep having ad lib access to hay overnight were offered fresh hay from 08.00 to 09.00 hours and were then given one, two, four, or eight meals of fresh hay according to a schedule such that the mean deprivation period was 6.5 h for each meal frequency-size. Neither the peak in saliva flow rate nor the time of this peak differed among the different meal sizes. The flow rate decreased rapidly after reaching a maximum at 3.2 min into the meal. After 7 min of eating, the tonicity of plasma and rumen fluid had increased by only 2.2 and 8.2 mosmol/kg respectively. These increases would not cause the rapid decline in parotid flow observed after 3.2 min of eating. There was no postprandial change in the concentration of gastrin in jugular plasma. However, it did increase significantly (P = 0.0043) from 16 to 4 min before eating commenced. There was a postprandial peak in plasma pancreatic polypeptide concentration after 4.5 min of eating. However, the parotid flow rate remained low after the concentration of this peptide returned to prefeeding levels. The rapid decrease in parotid secretion rate observed early in the meal may be due to subsiding central excitation rather than to an inhibitory factor limiting production.

Comparative digestion in sheep and cattle fed different forage to concentrate ratios at high and low intakes.

Effect of maintenance and ad libitum intakes on digestibility of different feed fractions was studied with six ruminally fistulated cows and six ruminally fistulated wethers to validate the use of sheep as a model for cattle. Complete diets were made up of ratios of alfalfa:cracked corn and soybean meal of 80:20, 55:45, and 30:70. The regression coefficient of the line relating organic matter digestibility with proportion of concentrate in the diet was smaller for the cows at ad libitum intake than for the other groups. Increasing the intake caused a decrease in digestibility of different fractions. The depression in digestibility was greater for the 30:70 forage:concentrate diet than for the others. At high intake, digestion values in the cows were less than those in the sheep for all diets. An increase in intake depressed the digestion of cell wall fractions and cell solubles including starch in cows, whereas in sheep, an increase in intake reduced cell wall digestion and to a lesser extent cell solubles, without affecting starch digestion. The digestive physiology of these species is sufficiently different to preclude the use of sheep data in formulating nutrient requirements for cows.

Parotid secretion and associated efferent activity inhibited by pentagastrin in sheep.

The inhibition of parotid secretion by pentagastrin increased with dose for jugular and carotid injections (0.01-0.16 micrograms/kg) in acute preparations of 3 sheep anesthetized with sodium pentobarbital. The intracarotid effect exceeded that for the jugular both in magnitude across all doses and in slope relating % inhibition to ln dose (p less than 0.005). The greater depression from carotid injections indicated that the effect was mediated in the head in response to higher pentagastrin concentrations at any dose level. In other experiments, both secretion and associated efferent activity in the parotid nerve were depressed more by carotid than jugular injections of pentagastrin, secretion being reduced by 27.2 vs. 12.1% and efferent activity by 43.2 vs. 20.6% respectively (p less than 0.025). These results indicate that gastrin in the circulation may be able to inhibit parotid secretion in sheep by acting directly on the central nervous system.

Factors affecting the voluntary intake of food by sheep. 4. The effect of additives representing the primary tastes on sham intakes by oesophageal-fistulated sheep.

1. Sheep with oesophageal fistulas were sham-fed on pelleted lucerne (Medicago sativa) hay to assess the palatability of added chemicals representing the tastes of sweet (sucrose), sour (hydrochloric acid), salt (sodium chloride), bitter (urea) and umami (monosodium glutamate; MSG). 2. Plain pellets and four concentrations of each chemical were sham-fed for 30 min after 5.5 h deprivation in 5 x 5 Latin-square experiments following a period of adaptation feeding. 3. Sucrose, at concentrations of 15-120 g/kg air-dried pellets, depressed intakes with a linear relation between intake (I; g) and concentration (C; g/kg): I = 1001-3.42C. 4. HCl at 6.25-25.0 g/kg pellets had no effect on sham intakes but at 50 g/kg reduced them by 50% of control (P less than 0.05). 5. NaCl at 50 200 g/kg increased sham intakes by 26% (P less than 0.01) with no evidence of a dose-related effect. 6. Urea at 10-80 g/kg decreased sham intakes by 26.9% (P less than 0.01) with no evidence of a dose-related effect. 7. MSG at 5-40 g/kg in two experiments increased sham intakes by 16.1 and 40.8% (P less than 0.05). In another experiment at 1-8 g/kg there was no significant effect. 8. When palatability and post-ingestive effects are separated by sham-feeding, the effect of added chemicals on intake may be completely different from when they are ingested normally (e.g. NaCl and sucrose). This newly developed technique enables the palatability effect of feed additives to be tested critically and economically.

Effects of buffers on ruminal rate of passage and degradation of soybean meal in steers.

Eight rumen-fistulated steers were randomly assigned to medium- and high-concentrate diets supplemented with 0, .75, 2.5 and 5% of either sodium bicarbonate or an artificial saliva salts mixture. Each animal was fed for 21 d at 75 g dry matter/kg body weight . 75. Rates of soybean meal (SBM) degradation were predicted by adjusting digestion rates in nylon bags with respective passage rates of chromium-mordanted SBM particles. Measures of rumen fermentation were made during the incubation period. Liquid dilution rate was determined with 51Cr-EDTA. The high-concentrate diet produced higher (P less than .05) liquid dilution rates than the medium-concentrate diet, but there were no differences in response to the two buffers (P greater than .05). The liquid dilution rates averaged across diets for 0, .75, 2.5 and 5% levels of buffer were 6.2, 6.3, 8.5 and 8.7%/h (SE = .03) and passage rates for SBM were 5.2, 5.2, 6.5 and 6.7%/h (SE = .025). The 2.5 and 5% levels of buffer increased the rate of disappearance of SBM from the nylon bags and buffers fed at these levels also increased rumen pH and NH3-N concentration. Rumen pH was correlated with N disappearance from the nylon bag (r = .903, P less than .05). Buffer levels did not affect degradation rates of SBM.

Pentagastrin in the circulation acts directly on the brain to depress motility of the stomach in sheep.

The mechanism whereby pentagastrin inhibits the frequency of contractions of the reticulo-rumen in conscious sheep was studied by comparing the effects of a range of doses given by continuous infusion into the jugular vein and the carotid artery. The intracarotid infusions at rates of 1 and 2 micrograms/kg per h were more effective than the jugular infusions (P less than 0.05). This is the first report that pentagastrin administered intravenously acts directly on the brain to alter the motility of a portion of the digestive tract. This agrees with the fact that in sheep and other ruminants, the gastric centres in the medulla dictate the frequency of cyclical motility in the reticulum.

Factors affecting the voluntary intake of food by sheep. 3. The effect of intravenous infusions of gastrin, cholecystokinin and secretin on motility of the reticulo-rumen and intake.

1. Sheep given ground and pelleted lucerne hay (Medicago sativa) ad lib. were infused intravenously with pentagastrin, secretin, cholecystokinin (CCK) and its analogues to assess their effects on motility of the reticulo-rumen and on food intake. In the latter experiments the animals were deprived of their diet for periods of up to 6 h to induce hunger and the infusions were made before and during 3-10 min periods of feeding. 2. Pentagastrin, and analogue of gastrin, depressed intake by 35-50% (P less than 0.05) when it was infused at 9 microgram/kg per h during 30 min of feeding. The threshold may however be below 1 microgram/kg per h as this dose decreased intake of 12-17%. The frequency of reticular contractions decreased by 13, 35, 39 and 44% when 1, 3, 9, and 27 microgram pentagastrin/kg per h respectively was infused (P less than 0.025). 3. Secretin depressed food intake 38% after 30 min (P less than 0.025) when 8 Clinical Units (CU)/kg per h was infused but the threshold could be less than this dose since 0.5 CU/kg per h depressed intake by 12%. Contraction amplitude but not frequency decreased at 8 CU/kg per h. 4. CCK produced a 39% decrease in intake during the first 10 min of feeding (P less than 0.05) and the threshold was between 5 and 15 Ivy Dog Units (IDU) or 425 and 1276 pmol/kg per h. The frequency of reticular contractions was not affected by 1.7 IDU/kg per h but it was depressed 21 and 63% by 5 and 15 IDU/kg per h. Octapeptide at 1.5 and 3 microgram (1312 and 2624 pmol) kg per h depressed intake by 11 and 43% respectively after 10 min (not significant) and 1.5 microgram/kg per h depressed motility by 39% (P less than 0.01). Ceruletide at 810 ng (599 pmol)/kg per h depressed intake by 31% (not significant) after 10 min and decreased motility by 52% (P less than 0.05). The threshold dose for ceruletide on intake appeared to be about 90 ng or 66 pmol/kg per h which is considerably less than that for CCK or octapeptide. 5. The biological significance of gastrointestinal hormones as signals of satiety in normal sheep is not known since doses of pentagastrin and CCK that suppressed intake also interfered quite markedly with motility. However there is good reason to suspect that elevated concentrations of gastrin and CCK in blood of parasitized sheep may account at least in part for their symptoms of rumen atony and reduced food intakes.

Effect of ensiling whole plant corn on voluntary intake, rumen fermentation, retention time and rate of digestion in steers.

The study was designed to determine whether products of fermentation in corn silage could limit its voluntary intake. Six rumen-cannulated Hereford steers were assigned randomly to diets of corn silage (CS) and dried corn forage reconstituted either with water (DC + W) or with extracts from corn silage (DC + CSE) according to a crossover design with three experimental periods. During each period, steers were fed ad libitum for 18 days and then restricted to 65 g DM/kg BW.75 for another 13 days. During the restricted feeding period, measures of rumen fermentation were made, and mean retention time (MRT) of rumen digesta was estimated after a single injection of the liquid and solid phase markers, 51Cr-EDTA and 103Ru-Phenanthroline complex (103Ru-P), respectively. Daily voluntary intake of DM (g/kg BW.75) for diet DC + W (80.2) was not diffferent (P greater than .05) from that for CS (89.7) but was significantly lower than that for DC + CSE (93.5). The corresponding estimates of MRT were 16.1, 14.1 and 17.4 hr (SEM +/- .5) for 51Cr-EDTA and 23.2, 23.9 and 24.3 hr (SEM +/- .7) for 103Ru-P. Measurements of osmolality, pH and VFA concentrations in rumen fluid were not related to daily DM intake. A study of rate of DM digestion, conducted by the rumen bag technique with samples of freeze-dried corn silage residue obtained after liquid extraction, yielded rate constants (hr-1) of .039 +/- .0030, .055 +/- .0028, and .0030 when steers were fed CS, DC + W and DC + CSE, respectively.

Factors affecting the voluntary intake of food by sheep. 2. The role of distention and tactile input from compartments of the stomach.

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.