Effect and absorption of histamine in sheep rumen: significance of acidotic epithelial damage

A single mild episode of subacute ruminal acidosis does not affect ruminal barrier function in the short term

Twenty-four German Merino sheep (72.3±10.1 kg of body weight) were fed an all-hay diet and assigned to either the subacute ruminal acidosis (SARA) treatment (n=17) or sham treatment (n=7). The SARA sheep were orally dosed with a 2.2 M glucose solution to supply 5 g of glucose/kg of body weight, whereas sham sheep received an equal volume of water. Ruminal pH was measured for 48 h before and 3 h after the oral dose. Sheep were then killed and ruminal epithelia from the ventral sac were mounted in Ussing chambers. The serosal-to-mucosal flux rate of partially (3)H-labeled mannitol (J(mannitol-SM)), an indicator of barrier function, was measured while epithelia were exposed to 3 sequential in vitro measurement periods lasting 1 h each. The measurement periods consisted of baseline, challenge, and recovery periods and were interspersed by 30-min periods for treatment equilibration. Baseline conditions were pH 6.1 (mucosal solution) and pH 7.4 (serosal solution) with a bilateral osmolarity of 293 mOsm/L. During the challenge period, the mucosal side of the epithelia was exposed to either an acidotic challenge (pH 5.2, osmolarity 293 mOsm/L) or an osmotic challenge (pH 6.1, osmolarity 450 mOsm/L); a third group served as control (pH 6.1, osmolarity 293 mOsm/L). The mucosal buffer solution was replaced for the recovery period. In vivo, sheep on the SARA treatment had lower mean (5.77 vs. 6.67) and nadir (5.48 vs. 6.47) ruminal pH for the 3h following the oral drench compared with sham sheep, indicating the successful induction of SARA with the oral glucose dose. Despite the marked reduction in pH in vivo, induction of SARA had no detectable effects on the baseline measurements of J(mannitol-SM), tissue conductance (G(t)), and short-circuit current (I(sc)) in vitro. However, reducing mucosal pH to 5.2 in vitro had negative effects on epithelial barrier function in the recovery period, including increased J(mannitol-SM), increased G(t), and decreased I(sc). The osmotic challenge increased J(mannitol-SM) and G(t) and decreased I(sc) during the challenge period, which was reversible in the recovery period except for slight reduction in I(sc). Interactions between the in vitro treatment and measurement period were detected for J(mannitol-SM), G(t), and I(sc). These data indicate that a mild episode of SARA (nadir pH, 5.48; duration ruminal pH <5.8, 111 min relative to the 180-min measurement period) does not affect ruminal epithelial barrier function immediately after the episode but that a rapid and more severe acidification (pH 5.2) in vitro increases epithelial permeability following the insult.

Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Highly fermentable diets are rapidly converted to organic acids [i.e., short-chain fatty acids (SCFA) and lactic acid] within the rumen. The resulting release of protons can constitute a challenge to the ruminal ecosystem and animal health. Health disturbances, resulting from acidogenic diets, are classified as subacute and acute acidosis based on the degree of ruminal pH depression. Although increased acid production is a nutritionally desired effect of increased concentrate feeding, the accumulation of protons in the rumen is not. Consequently, mechanisms of proton removal and their quantitative importance are of major interest. Saliva buffers (i.e., bicarbonate, phosphate) have long been identified as important mechanisms for ruminal proton removal. An even larger proportion of protons appears to be removed from the rumen by SCFA absorption across the ruminal epithelium, making efficiency of SCFA absorption a key determinant for the individual susceptibility to subacute ruminal acidosis. Proceeding initially from a model of exclusively diffusional absorption of fermentation acids, several protein-dependent mechanisms have been discovered over the last 2 decades. Although the molecular identity of these proteins is mostly uncertain, apical acetate absorption is mediated, to a major degree, via acetate-bicarbonate exchange in addition to another nitrate-sensitive, bicarbonate-independent transport mechanism and lipophilic diffusion. Propionate and butyrate also show partially bicarbonate-dependent transport modes. Basolateral efflux of SCFA and their metabolites has to be mediated primarily by proteins and probably involves the monocarboxylate transporter (MCT1) and anion channels. Although the ruminal epithelium removes a large fraction of protons from the rumen, it also recycles protons to the rumen via apical sodium-proton exchanger, NHE. The latter is stimulated by ruminal SCFA absorption and salivary Na(+) secretion and protects epithelial integrity. Finally, SCFA absorption also accelerates urea transport into the rumen, which via ammonium recycling, may remove protons from rumen to the blood. Ammonium absorption into the blood is also stimulated by luminal SCFA. It is suggested that the interacting transport processes for SCFA, urea, and ammonia represent evolutionary adaptations of ruminants to actively coordinate energy fermentation, protein assimilation, and pH regulation in the rumen.

Ruminal acidosis in beef cattle: the current microbiological and nutritional outlook

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.

The effects of lactic acid bacteria inoculants and formic acid on the formation of biogenic amines in grass silages

Silages were prepared in six laboratory experiments from four direct-cut grassland swards and pure swards of perennial ryegrass and false oat with dry matter contents ranging between 180 and 325 g/kg. Grass was fermented at 22 degrees C and silages were stored at the same temperature for 4 months. Untreated silages (negative control) and silages preserved with 3 g/kg of formic acid (positive control) were compared with silages inoculated with commercial strains of Lactobacillus plantarum, Lactobacillus buchneri and a mixed preparation Microsil. The inoculants were applied at a dose of 5.10(6) CFU/g of grass. Seven biogenic amines were extracted from silages with perchloric acid and determined as N-benzamides by micellar electrokinetic capillary chromatography. Common chemical quality parameters of silages were also determined. Tyramine, cadaverine and putrescine were the amines occurring at the highest concentration. As compared to untreated silages, formic acid was most effective to suppress formation of the main amines. Also the inoculants often decreased amine contents significantly (P < 0.05). The inoculants decreased levels of polyamine spermidine more efficiently than formic acid. Contents of histamine, tryptamine and polyamine spermine were very low, commonly below the detection limits.

Allisonella histaminiformans gen. nov., sp. nov. A novel bacterium that produces histamine, utilizes histidine as its sole energy source, and could play a role in bovine and equine laminitis

When cattle and horses are fed large amounts of grain, histamine can accumulate in the gastrointestinal tract, and this accumulation can cause an acute inflammation of the hooves (laminitis). When ruminal fluid from dairy cattle fed grain supplements was serially diluted in anaerobic MRS medium containing histidine (50 mM), histamine was detected at dilutions as high as 10(-7). The histidine enrichments were then transferred successively in an anaerobic, carbonate-based medium (50 mM histidine) without glucose. The histamine producing bacteria could not be isolated from the rumens of cattle fed hay; however, histamine producing bacteria could be isolated the feces of cattle fed grain and the cecum of a horse. All of the histamine producing isolates had the same ovoid morphology. The cells stained Gram-negative and were resistant to the ionophore, monensin (25 microM). The doubling time was 110 min, and the yield was 1.5 mg cell protein per mmol histidine. The G+C content was 46.8%. Lysine was the only other amino acid used, but lysine did not allow growth if histidine was absent. Because carbohydrate and organic acid utilization was not detected, it appeared that the isolates used histidine decarboxylation as their sole mechanism of energy derivation. 16s rRNA gene sequencing indicated that the isolates were most closely related to low G+C Gram-positive bacteria (firmicutes), but similarities were < or = 94%. Because the most closely related bacteria (Dialister pneumonsintes, Megasphaera elsdenii and Selenomonas ruminantium) did not produce histamine from histidine, we propose that these histamine producing bacteria be assigned to a new genus, Allisonella, as Allisonella histaminiformans gen. nov., sp. nov. The type strain is MR2 (ATCC BAA610, DSM 15230).

Glucose uptake via SGLT-1 is stimulated by beta(2)-adrenoceptors in the ruminal epithelium of sheep

Glucose absorption via the sodium glucose-linked transporter (SGLT)-1, decreases the glucose concentration in the ruminant forestomach and may ameliorate or prevent ruminal lactic acidosis. Because acidotic ruminants show increased sympathetic activity, the possibility of adrenergic modulation of SGLT-1 was investigated. Glucose uptake into ovine ruminal epithelia was measured in Ussing chambers after the addition of 200 micromol/L (14)C-labeled glucose to the mucosal solution. Glucose uptake decreased (P < 0.05) by >50% in comparison with control after mucosal addition of the SGLT-1 inhibitor, phlorizin (100 micromol/L). Serosal preincubation with 100 micromol/L epinephrine increased (P < 0.05) the phlorizin-sensitive glucose uptake in the absence and presence of indomethacin (10 micromol/L). The effect of epinephrine was simulated by beta- (100 micromol/L isoproterenol) and beta(2)-receptor agonists (10 micromol/L terbutaline), as well as by direct stimulation of adenylyl cyclase (10 micromol/L forskolin). The serosal addition of methoxamine, clonidine, dobutamine or BRL 37344 had no effect. Inhibition of protein kinase A with 2 micromol/L H 89 completely abolished the stimulation of glucose uptake by epinephrine. We conclude that ruminal SGLT-1 can be stimulated via beta(2)-dependent generation of cyclic adenosine monophosphate.