Estimation of ruminal outflow in buffaloes fed diets with different energy and protein sources by use of reticular and omasal sampling.

This study aimed to evaluate the effects of different traditional or alternative energy and protein sources, associated or not, on feeding behavior, ruminal kinetics, and post-ruminal flow of nutrients. Besides, it was assessed diets' effects on different sites (reticulum and omasum) of buffaloes. Four ruminally cannulated male Murrah buffaloes (average initial weight of 637 ± 66.37 kg) were randomly distributed in a 4 × 4 Latin square design. Treatments were arranged as 2 × 2 factorial arrangement. The first factor evaluated was the inclusion of energy sources (ground corn and crude glycerin), and the second factor was the inclusion of protein sources (soybean meal and cottonseed cake). Buffaloes fed cottonseed cake had a higher content of neutral detergent fiber (NDF) and potentially digestible detergent fiber (pdNDF) in the rumen environment than buffaloes fed soybean meal. There was a sampling site effect on rumen digestion rates of pdNDF, passage rates of indigestible neutral detergent fiber (iNDF), and pdNDF, and flow of iNDF. In this study, omasal collections were more representative. Total replacement of ground corn by crude glycerin promoted less NDF ruminal digestibility, and care should be taken to include this energy source. The cottonseed cake does not cause a difference in rumen dynamics and can totally replace soybean meal in feedlot buffaloes' diet.

Effect of exogenous butyrate on the gastrointestinal tract of sheep. I. Structure and function of the rumen, omasum, and abomasum.

The aim of this study was to determine the effect of exogenous butyrate on the structure and selected functions of the stomach in sheep. Eighteen rams (30.8 ± 2.1 kg; 12 to 15 mo of age) were allocated to the study and fed a diet for 14 d without (CTRL) or with sodium butyrate (BUT; 36 g/kg of offered DM). Neither DMI nor initial BW differed between treatments (P ≥ 0.61), but final BW was greater for BUT compared with CTRL (P = 0.03). Butyrate concentration in the reticuloruminal fluid and abomasal digesta was greater for BUT compared with CTRL (P ≤ 0.01), but total short-chain fatty acids (SCFA) concentration, as well as concentration of other SCFA, did not differ between treatments (P ≥ 0.07). Relative to BW, reticuloruminal tissue mass tended (P = 0.09) to be greater and omasal digesta was less (P = 0.02) for BUT compared with CTRL. Dietary butyrate did not affect ruminal papillae length, width, and density nor did it affect ruminal epithelium thickness (P ≥ 0.12) in the ventral sac of the rumen. However, the DM of ruminal epithelium (mg/cm2) tended (P = 0.06) to be greater for BUT compared with CTRL. Omasal and abomasal epithelium thicknesses were greater (P ≤ 0.05) for BUT compared with CTRL. Mitosis-to-apoptosis ratio in the abomasal epithelium was less for BUT compared with CTRL (P = 0.04). Finally, the mRNA expression of peptide transporter 1 in the omasal epithelium was less (P = 0.02) and mRNA expression of monocarboxylate transporter 1 in the abomasal epithelium tended (P = 0.07) to be greater for BUT compared with CTRL. It can be concluded that exogenous butyrate supplementation affected not only the rumen but also omasum and abomasum in sheep.

Relationship between glucocorticoids and prolactin during mammary gland stimulation in dairy cows.

The objectives of this study were to determine the role of glucocorticoids in the regulation of prolactin (PRL) release induced by mammary gland stimulation and to investigate whether the milk depression induced by glucocorticoids in dairy cows is due to a decrease in PRL release. In experiment 1, 8 dairy cows were used in a 4 × 4 Latin square design. Four hours after the morning milking, the cows received 1 of the following treatments: (1) a 5-min manual stimulation of the mammary gland; (2) an i.v. injection of 1 mg of dexamethasone; (3) 2 infusions of 2.5 g of metyrapone (an inhibitor of cortisol biosynthesis) in the omasum 4 and 2 h before a 5-min stimulation of the mammary gland; or (4) no treatment. Sixty minutes later, the mammary gland of each cow was stimulated for 5 min. Blood samples were collected from 20 min before to 120 min after the start of the treatment. When the mammary gland was stimulated twice in 60 min, less PRL and cortisol were released during the second stimulation. Metyrapone did not affect PRL or cortisol release. Dexamethasone decreased serum cortisol concentration but did not affect PRL concentration. In experiment 2, 16 cows were used in a crossover experimental design consisting of 2 experimental weeks separated by 1 resting week. During the first week, cows were treated as follows: (1) 4 cows were injected with 0.5 g of domperidone (a PRL secretagogue) in canola oil on d 1 and 2 and 20 mg of dexamethasone on d 1; (2) 4 cows were injected with 0.5 g of domperidone on d 1 and 2; (3) 4 cows were injected with canola oil on d 1 and 2 and with 20 mg of dexamethasone on d 1; and (4) 4 cows were injected with canola oil on d 1 and 2. During the second experimental week, the same 4 treatments were repeated, except the cows that did not receive dexamethasone in the first week received it on d 1 of the second week, and cows that did receive it in the first week did not receive it in the second week. On d 1 and 2 of each week, blood samples were collected during morning milking for PRL determination. Dexamethasone reduced milk production and decreased both basal and milking-induced PRL release. It also increased milk fat and protein percentages and decreased milk lactose content. Domperidone increased basal PRL levels in serum and milk but did not affect milk yield. Although we cannot rule out the possibility that inhibition of PRL secretion or reduction of mammary gland PRL responsiveness play a role in the inhibition of milk production by glucocorticoids, the fact that enhancement of PRL secretion by domperidone could not prevent the depression of milk yield suggests that other mechanisms are involved.

Role of tachykinins and neurokinin receptor subtypes in the regulation of motility of the forestomach and abomasum in conscious sheep.

The present study was planned to evaluate role of tachykinins (TKs) and neurokinin (NK) receptors in the regulation of gastric motility in sheep. We examined the effects of intravenous (i.v.) injection of neurokinin A (NKA) and substance P (SP) on motility of the rumen, omasum, and abomasum in conscious sheep and the effects of NK receptor blockade on the effect of TKs using NK-1 receptor antagonist L-732,138 and NK-2 receptor antagonist SR48968. Moreover, the effect of NK receptor blockade on omasal cyclic contractions was examined. Intravenous injection of NKA and SP induced tonic contraction of rumen, omasum, and abomasum, and the contractile effect of NKA was more potent than that of SP in all the gastric regions. Although the effect of SP was not inhibited by L-732,138, the effect of NKA was significantly inhibited by SR48968. However, single infusion of SR48968 and L-732,138 did not alter cyclic electromyographic activity and basal intraluminal pressure in the omasum. These results imply that NKA and NK-2 receptors play a primary role in non-cholinergic regulation of ovine gastric motility, though NK-2 and NK-1 receptors seem unlikely to be involved in the physiological regulation of omasal cyclic contractions.

Interaction of unsaturated fat or coconut oil with monensin in lactating dairy cows fed 12 times daily. II. Fatty acid flow to the omasum and milk fatty acid profile.

Feeding animal-vegetable (AV) fat or medium-chain fatty acids (FA) to dairy cows can decrease ruminal protozoal counts. However, combining moderate to large amounts of AV fat with monensin (tradename: Rumensin, R) could increase the risk for milk fat depression (MFD), whereas it is not known if diets supplemented with coconut oil (CNO; rich in medium-chain FA) with R would cause MFD. In a 6 × 6 Latin square design with a 2 × 3 factorial arrangement of treatments, 6 rumen-cannulated cows were fed diets without or with R (12 g/909 kg) and either control (no fat), 5% AV fat, or 5% CNO. Diets were balanced to have 21.5% forage neutral detergent fiber, 16.8% crude protein, and 42% nonfiber carbohydrates. Omasal flows of FA were characterized by an increased percentage of trans 18:1 for AV fat and CNO diets compared with the control, a higher percentage of 12:0 and 14:0 for CNO, and higher cis 18:1 for AV fat. Milk FA composition reflected the changes observed for omasal FA digesta flow. The de novo FA synthesis in the mammary gland was decreased by the main effects of R compared without R (averaged over fat treatments) and for added fat (AV fat and CNO) versus control (averaged over R). The percentages of 6:0, 8:0, and 10:0 in milk fat were lower for R and for AV fat and CNO compared with the control. The percentage of trans 18:1 FA in milk fat also higher for AV fat and CNO compared with the control. Against our hypotheses, the feeding of CNO did not prevent MFD, and few interactions between R and fat source were detected. The feeding of CNO did compromise ruminal biohydrogenation, with accumulation of trans 18:1 in the rumen and in milk fat.

Role of tachykinin and neurokinin receptors in the regulation of ovine omasal contractions.

The present study investigated a role of tachykinins (TK) and neurokinin (NK) receptors (NK-R) in the non-cholinergic regulation of omasal contractions in sheep. Semiquantitative reverse transcription (RT)-PCR revealed that both preprotachykinin (PPT)-A and PPT-B mRNA were distributed in the omasal muscle layers and that NK-R type-1 (NK-1R) and type-2 (NK-2R) mRNA were largely expressed in the same tissues. Cumulative application of substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) at 0.03-10µM induced tonic contractions of omasal muscle strips, and the contractile amplitude increased in order of NKB

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.

Omasal flow of soluble proteins, peptides, and free amino acids in dairy cows fed diets supplemented with proteins of varying ruminal degradabilities.

Three ruminally and duodenally cannulated cows were assigned to an incomplete 4 x 4 Latin square with four 14-d periods and were fed diets supplemented with urea, solvent soybean meal, xylose-treated soybean meal (XSBM), or corn gluten meal to study the effects of crude protein source on omasal canal flows of soluble AA. Soluble AA in omasal digesta were fractionated by ultrafiltration into soluble proteins greater than 10 kDa (10K), oligopeptides between 3 and 10 kDa (3-10K), peptides smaller than 3 kDa (small peptides), and free AA (FAA). Omasal flow of total soluble AA ranged from 254 to 377 g/d and accounted for 9.2 to 15.9% of total AA flow. Averaged across diets, flows of AA in 10K, 3-10K, small peptides, and FAA were 29, 217, 50, and 5 g/d, respectively, and accounted for 10.3, 71.0, 17.5, and 1.6% of the total soluble AA flow. Cows with diets supplemented with solvent soybean meal had higher flows of Met, Val, and total AA associated with small peptides than those whose diets were supplemented with XSBM, whereas supplementation with corn gluten meal resulted in higher total small peptide-AA flows than did XSBM. Averaged across diets, 27, 75, and 93% of soluble AA in 10K, 3-10K, and peptides plus FAA flowing out of the rumen were of dietary origin. On average, 10% of the total AA flow from the rumen was soluble AA from dietary origin, indicating a substantial escape of dietary soluble N from ruminal degradation. Omasal concentrations and flows of soluble small peptides isolated by ultrafiltration were substantially smaller than most published ruminal small peptide concentrations and outflows measured in acid-deproteinized supernatants of digesta.

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.

Ca-sensitive Na transport in sheep omasum.

Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current (Isc), with a range of 1-4 microeq. h-1. cm-2. A Michaelis-Menten-type kinetic was found between the Na concentration and the Isc (Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 microeq. h-1. cm-2). Mucosal amiloride (1 mM), phenamil (1 or 10 microM), or serosal aldosterone (1 microM for 6 h) did not change Isc. Removal of divalent cations (Ca and Mg) enhanced Isc considerably from 2.61 +/- 0.24 to a peak value of 11.18 +/- 1.1 microeq. h-1. cm-2. The peak Isc (overshoot) immediately declined to a plateau Isc of approximately 6-7 microeq. h-1. cm-2. Na flux measurements showed a close correlation between changes in Isc and Na transport. Transepithelial studies demonstrated that K, Cs, Rb, and Li are transported, indicating putative nonselective cation channels, which are inhibited by divalent cations (including Ca, Mg, Sr, Ba) and by (trivalent) La. Intracellular microelectrode recordings from the luminal side clearly showed changes of voltage divider ratio when mucosal divalent cations were removed. The obtained data support the assumption of a distinct electrogenic Na transport mechanism in sheep omasum.

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.

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.

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.

Oral administration of calcium chloride-containing products: testing for deleterious side-effects.

Two products that contain CaCl2 and that are intended for oral administration were tested for safety aspects. One product contained CaCl2 as a gel, the other contained CaCl2 in an oil emulsion. Oral administration of the CaCl2-containing products caused minor to severe damage to the mucosa of the forestomach and abomasum. The gel solution especially proved to be highly caustic, while the oil emulsion appeared to be relatively safe.

Relaxation of muscle strips from the reticular groove and reticulo-omasal orifice by vasoactive intestinal peptide (VIP).

The effect of Vasoactive Intestinal Peptide (VIP) on muscle strips from the reticular groove, the reticulo-omasal orifice (ROO) and the omasal canal was studied. VIP caused a concentration-dependent (10(-8)-5 x 10(-7) mol/l) reduction of the acetylcholine-induced (55 x 10(-6) mol/l) contraction of the reticular groove muscle preparations from calves and adult cattle. VIP was more effective in the muscle strips from calves than in those from adult cattle. Moreover, the circular muscle strips from the reticular groove were more sensitive to VIP than the longitudinal muscle strips. VIP also induced a concentration-related (10(-8)-5 x 10(-7) mol/l) relaxation of muscle strips from the calf ROO. Furthermore, both circular and longitudinal muscle strips from the omasal canal of the calf were relaxed by VIP (10(-7)-5 x 10(-7) mol/l). The relaxing effect of VIP on the circular muscle strips from the reticular groove of the calf was not significantly affected during incubation with 5 x 10(-6) mol/l tetrodotoxin. The relaxing effect of VIP therefore seems to be mediated by VIP receptors of smooth muscle cells. These properties of VIP in conjunction with its presence in nerve fibres located in the wall of the reticular groove and ROO are consistent with a role of VIP as inhibitory transmitter in this region of the bovine stomach.

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.

Effects of prostaglandin F2 alpha and indomethacin on the contractile activity of different compartments of the complex stomach.

In vitro experiments have shown that PGF2 alpha or indomethacin produces different effects on muscle strips isolated from different compartments of sheep complex stomach. PGF2 alpha (10(-6) - 10(-5) M) increases the tone of the ruminal preparations and exerts a negligible effect on the reticulum and omasum strips. Indomethacin (5 X 10(-6) M) inhibits the mechanical activity of the rumen and omasum and has no effect on that of the reticulum. More pronounced are the effects on the different parts of the abomasum: PGF2 alpha (10(-9) - 10(-6) M) markedly increases the tone of the proximal abomasum and decreased the amplitude and the phasic contractions of the antral abomasum; indomethacin (5 X 10(-6) M) inhibits the tone and the phasic contractions of the middle abomasum. PGF2 alpha (10(-9) - 10(-6) M) inhibits while indomethacin (5 X 10(-6) M) stimulates the contractile activity of the antral abomasum.

Forestomach motility in adult sheep when reticular groove closure is provoked by copper sulphate solution.

Forestomach motility in adult sheep when reflex reticular groove closure is provoked by 10 ml of 10% copper sulphate solution was studied electromyographically. Rumen and omasum motility disappeared with the administration of the stimulant, while some muscular activity of the reticulum was always present but was manifested by monophasic, more frequent and weaker contractions than before stimulation; between these contractions very frequent small discharges appeared in the electromyogram from the reticulum. Cyclic activity of the forestomach reappeared 3 to 5 min later and returned gradually to normal. The functional significance of these findings is discussed.

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.