Effects of monensin on volatile fatty acid metabolism in periparturient dairy cows using compartmental analysis

Eight multiparous periparturient Holstein cows fitted with ruminal cannulas were used in a split plot design to evaluate effects of monensin on ruminal volatile fatty acid (VFA) metabolism. Diets were supplemented with 300 mg/day of monensin, or no monensin, both prepartum and postpartum. Isotopic tracers, Na-1-¹³C-acetate (Ac), Na-1-¹³C-propionate (Pr), or Na-1-¹³C-butyrate (Bu) were used as markers to describe VFA kinetics in the rumen. The Windows version of SAAM software (WinSAAM) was used to develop a steady state VFA model. A 9-compartment model was adequate to comprehensively describe ruminal VFA metabolism. The main VFA compartments consisted of Ac, Pr and Bu. The model estimated lower Bu and Ac interconversions with monensin, postpartum (Bu to Ac; 0.14 versus 0.12; P=0.04, and Ac to Bu; 0.32 versus 0.25; P=0.11) compared to when measured prepartum. Results demonstrate that dilution studies employing stable isotopes of VFA can be used to provide information on VFA metabolism of the periparturient dairy cow. A time frame of 320 min of labeled VFA infusion employing a single injection allows accurate quantification of VFA metabolism in the rumen. Compartmental kinetic analysis of major VFA in the rumen indicate that monensin reduced about 0.125 the portion of the Ac that contributes to Bu by reducing movements of Bu originated carbons to the Ac pool. Monensin may affect certain biochemical pathways of interconversion of Bu and Ac in the rumen. Propionate kinetic data suggests that Pr behaves as a single pool in the rumen. Monensin did not affect Pr production in the rumen suggesting that monensin improves the metabolic status of the transition cow in a way other than increasing Pr production in the rumen.     

Effect of rumen ciliates on the digestive utilization of various carbohydrate-rich diets and on the end-products formed in the rumen. II. Utilization of inulin, saccharose and lactose

Three diets rich in inulin, saccharose and lactose, respectively, were given to 10 rumen-fistulated sheep. Two animals were defaunated, two were inoculated with either Polyplastron multivesibulatum or Entodinium sp., and two others were inoculated with both. The latter two were bred in conventional conditions. All animals ingested the same amounts of carbohydrates in the three diets (21-22 g/kg P0.75/day). Dietary nitrogen content was similar (table 1). The ciliate population was improved with the inulin diet (fig. 1; table 2). With a mixed population, the Entodinium improved with the inulin diet (fig 1; table 2). With a mixed population, the Entodinium sp. genus was always predominant. Holotrich protozoa (mainly Isotricha) in the rumen of the conventional sheep represented 15 to 30% of the total ciliate biomass, indicating that they were able to metabolize these soluble sugars. We also observed that P. multivesiculatum can ferment cellulose and all the soluble carbohydrates proposed in these diets. However, Entodinium sp. development occurred mainly in the presence of the sugard produced during carbohydrate hydrolysis by other ciliates or bacteria. The highest organic matter digestibility, noted in faunated animals (table 3) was confirmed by the VFA concentration in the rumen (table 4). This could be explained either by an activation of bacterial metabolism due to predation or by the direct effect of ciliates on fermentations, or both. Modifications in the VFA composition varied with ciliate inoculation, showing that ciliate metabolism may vary with the nature of the energy in the diet or that the observed results depended on various opposite effects in which the intensity of each component was influenced by the diet. In general, the acetic acid molar proportion increased and propionic acid decreased when there was a considerable Entodinium sp. population. The effect on butyric acid was low with these diets. Higher ammonia and lactic acid concentrations were observed in the rumen of faunated than defaunated sheep, irrespective of the ciliate inoculum.     

In vivo production and molar percentages of volatile fatty acids in the rumen: a quantitative review by an empirical approach

Despite their major contribution to the energy supply of ruminants, the production of volatile fatty acids (VFA) in the rumen is still poorly predicted by rumen models. We have developed an empirical approach, based on the interpretation of large bibliographic databases gathering published in vivo measurements of ruminal VFA production rate (PR), rates of duodenal and faecal digestion and molar percentages of VFA in the rumen. These databases, covering a wide range of intake levels and dietary composition, were studied by meta-analysis using within-experiment models. We established models to quantify response laws of total VFA-PR and individual VFA molar percentages in the rumen to variations in intake level and dietary composition. The rumen fermentable organic matter (RfOM) intake, estimated from detailed knowledge of the chemical composition of diets according to INRA Feed Tables, appears as an accurate explanatory variable of measured total VFA-PR, with an average increment of 8.03 ± 0.64 mol total VFA/kg RfOM intake. Similar results were obtained when total VFA-PR was estimated from measured apparent RfOM (total VFA-PR/RfOM averaging 8.3 ± 1.2 mol/kg). The VFA molar percentages were related to dry matter intake and measured digestible organic matter (OM), digestible NDF and rumen starch digestibility, with root mean square error of 1.23, 1.45, 0.88 and 0.41 mol/100 mol total VFA for acetate, propionate, butyrate and minor VFA, respectively, with no effect of pH on the residuals. Stoichiometry coefficients were calculated from the slopes of the relationships between individual VFA production (estimated from measured apparent RfOM and individual VFA molar percentages) and measured fermented fractions. Coefficients averaged, respectively, 66, 17, 14 and 3 mol/100 mol for NDF; 41, 44, 12 and 4 mol/100 mol for starch; and 46, 35, 13 and 6 mol/100 mol for crude protein. Their use to predict VFA molar percentages appear relevant for most dietary conditions, that is, when the digested NDF/digested OM ratio exceeded 0.12. This study provides a quantitative review on VFA yield in the rumen. It contributes to the development of feed evaluation systems based on nutrient fluxes.     

Use of compartmental analysis to study ruminal volatile fatty acid metabolism under steady state conditions in Holstein heifers

Four rumen-cannulated Holstein heifers were used to quantify volatile fatty acid (VFA) kinetics in the rumen using ¹³C stable isotopes. Heifers were fed either a low (L) or high (H) concentrate diet with level of concentrate of 250 or 700 g/kg dry matter, respectively. Isotopic tracers, Na-1-¹³C-acetate (Ac), -propionate (Pr), or -butyrate (Bu) were infused as a bolus into the rumen. Three days prior to sampling, cows were fed equal meals every 4 h for 2 days followed by 2 h feeding intervals 1 day prior to and on the day of sampling. The rumen was sampled 26 times (3 times prior to tracer infusion; background samples and 23 times during 8 h after tracer infusion). Isotopic enrichment was expressed as Tracer/(Tracee + Tracer) or F value. F values were corrected for skewness and graphed against time. A three-compartment model was adequate to describe VFA kinetics in the rumen. It was estimated that there was a flux of Ac to the Pr pool [0.05 g/min (L) versus 0.03 g/min (H)], resulting in an average conversion fraction of Ac to Pr of 0.051 in both groups. The model predicted that the fraction of Ac which contributed to the Pr pool was 0.198 (L) versus 0.145 (H). Although the fraction of the Ac conversion to Bu ranged from 0.367 (L) to 0.448 (H), only a small fraction [0.0137 (L) and 0.0160 (H)] of the Bu was converted to Ac. A major portion of the Bu was coming from Ac in both diet groups. The portion of Bu coming from Ac in the rumen varied between 0.95 and 0.65 in (L) and (H) diets, respectively. Turnover time of all VFA was calculated to be longer in H. Results indicate that Ac and Bu exchange, and that Ac contributes to the Pr pool. However, Pr does not contribute to the Ac or Bu pools. This study demonstrates the usefulness of ¹³C isotopes to study VFA kinetics and metabolism in cattle.     

Establishment of cellulolytic bacteria and development of fermentative activities in the rumen of gnotobiotically-reared lambs receiving the microbial additive Saccharomyces cerevisiae CNCM I-1077

We studied the effects of a yeast additive used in ruminant nutrition on the establishment of cellulolytic bacteria, on plant cell wall degradation and on digestive functions in the rumen of gnotobiotically-reared lambs. Cellulolytic bacteria inoculated to the lambs tended to become established earlier in the presence of Saccharomyces cerevisiae CNCM I-1077 (SC). In addition, their population was maintained at a higher level, when the physico-chemical conditions of the biotope were altered. In these lambs, specific activities of fibrolytic enzymes were greater, and in sacco degradation of wheat straw tended to increase. In the presence of SC there was a decrease in ruminal ammonia concentration and a higher volatile fatty acid (VFA) concentration when lambs were 20 to 50 days old. These data suggest that this yeast strain may stimulate the development of cellulolytic microflora and enhance microbial activity in the rumen of young ruminants. Such activity could be beneficial in preventing microbial imbalance and a reduction of rumen function efficiency in the case of nutritional transitions. Further studies with conventional animals will soon be performed in order to verify these dings.     

Maternal versus artificial rearing shapes the rumen microbiome having minor long-term physiological implications

Increasing productivity is a key target in ruminant science which requires better understanding of the rumen microbiota. This study investigated how maternal versus artificial rearing shapes the rumen microbiota using 24 sets of triplet lambs. Lambs within each sibling set were randomly assigned to natural rearing on the ewe (NN); ewe colostrum for 24 h followed by artificial milk feeding (NA); and colostrum alternative and artificial milk feeding (AA). Maternal colostrum feeding enhanced VFA production at weaning but not thereafter. At weaning, lambs reared on milk replacer had no rumen protozoa and lower microbial diversity, whereas natural rearing accelerated the rumen microbial development and facilitated the transition to solid diet. Differences in the rumen prokaryotic communities disappear later in life when all lambs were grouped on the same pasture up to 23 weeks of age. However, NN animals retained higher fungal diversity and abundances of Piromyces, Feramyces and Diplodiniinae protozoa as well as higher feed digestibility (+4%) and animal growth (+6.5%) during the grazing period. Nevertheless, no correlations were found between rumen microbiota and productive outcomes. These findings suggest that the early life nutritional intervention determine the initial rumen microbial community, but the persistence of these effects later in life is weak.     

Factors stimulating migration of holotrich protozoa into the rumen

The effects of feeding and various reticular infusions on ruminal holotrich concentrations were studied in an attempt to identify possible factors stimulating their migration into the rumen. It was concluded that glucose entering the reticulo-rumen shortly after feeding could stimulate migration of holotrich protozoa.     

Anaerobic degradation of dehydrodiisoeugenol by rumen bacteria

The degradation of dehydrodiisoeugenol (DDIE) by cow rumen bacteria was studied under strictly anaerobic conditions. After two days of cultivation, about 23% of DDIE (1.2 mM) was degraded to volatile fatty acids (VFA) such as acetic acid, propionic acid and butyric acid. The aromatic intermediates were vanillic acid, 5-methylvanillin and 3-methyl-4-hydroxybenzaldehyde, which suggested that the coumaran ring in DDIE was cleaved during degradation. These results indicate that the rumen anaerobes can degrade this lignin-related dimer to monoaromatic compounds and VFA.     

Factors stimulating migration of holotrich protozoa into the rumen.

The effects of feeding and various reticular infusions on ruminal holotrich concentrations were studied in an attempt to identify possible factors stimulating their migration into the rumen. It was concluded that glucose entering the reticulo-rumen shortly after feeding could stimulate migration of holotrich protozoa.     

Effects of strontium on the absorption of calcium, magnesium and phosphate ions from the ovine reticulo-rumen

The net absorption rates of strontium ions from the ovine reticulo-rumen, isolated in situ in trained conscious animals, were measured under controlled conditions. A linear positive response was obtained from the addition of Sr²⁺ ions to the artificial rumen fluid. This increase in the absorption of Sr was reflected in an increase in the plasma Sr concentration. In contrast to the discrimination observed elsewhere in favour of the absorption of Ca relative to Sr, the absorption rate of Sr from the reticulo-rumen was significantly greater than that of Ca, from solutions containing the same molar concentration. A graded increase in the Sr concentration in the ruminal fluid from 1 mmol/l to 4 mmol/l led to a corresponding reduction in the absorption rate of Ca but an increase in that of phosphate. The latter result is similar to that observed when the intra-ruminal concentration of Ca²⁺ ions is increased. It is suggested that Ca and Sr share a common pathway for absorption from the reticulo-rumen and that this may involve coupling with the absorption of phosphate ions. Accepted: 18 January 2000     

Estimation of the stoichiometry of volatile fatty acid production in the rumen of lactating cows

The purpose of this study was to improve the prediction of the quantity and type of Volatile Fatty Acids (VFA) produced from fermented substrate in the rumen of lactating cows. A model was formulated that describes the conversion of substrate (soluble carbohydrates, starch, hemi-cellulose, cellulose, and protein) into VFA (acetate, propionate, butyrate, and other VFA). Inputs to the model were observed rates of true rumen digestion of substrates, whereas outputs were observed molar proportions of VFA in rumen fluid. A literature survey generated data of 182 diets (96 roughage and 86 concentrate diets). Coefficient values that define the conversion of a specific substrate into VFA were estimated meta-analytically by regression of the model against observed VFA molar proportions using non-linear regression techniques. Coefficient estimates significantly differed for acetate and propionate production in particular, between different types of substrate and between roughage and concentrate diets. Deviations of fitted from observed VFA molar proportions could be attributed to random error for 100%. In addition to regression against observed data, simulation studies were performed to investigate the potential of the estimation method. Fitted coefficient estimates from simulated data sets appeared accurate, as well as fitted rates of VFA production, although the model accounted for only a small fraction (maximally 45%) of the variation in VFA molar proportions. The simulation results showed that the latter result was merely a consequence of the statistical analysis chosen and should not be interpreted as an indication of inaccuracy of coefficient estimates. Deviations between fitted and observed values corresponded to those obtained in simulations.     

Studies on the absorption of sodium and chloride from the rumen of sheep

The net absorption of Na and Cl from the temporarily isolated rumen of sheep was studied using an artificial ruminal fluid with different Na and K and constant Cl concentrations. The net absorption of Na and Cl was linearly correlated. The net absorption of Cl was abolished and a small net secretion was observed when no sodium was in the artificial rumen fluid. The net absorption of Na was significantly reduced under chloride free conditions. It is concluded that the active transport of Na and Cl is coupled. The mechanism of an Na-Cl cotransport can not be deduced from these studies.     

Transfer of plasmids between strains of Escherichia coli under rumen conditions

K. P. SCOTT AND H.J. FLINT. 1995. Strains of Escherichia coli originally isolated from the rumen of sheep were shown to be capable of exchanging a 60kb plasmid, conferring resistance to tetracycline and ampicillin, at low frequencies (below 10^-6 per recipient) under anaerobic conditions in the presence of (a) autoclaved and clarified rumen fluid, (b) raw clarified rumen fluid, or (c) whole rumen fluid. Under anaerobic conditions the two rumen strains showed no inhibition of growth rate when 50 mmol 1^-1 volatile fatty acids were added to LB medium at pH 7, although significant inhibition resulted with 100 mmol 1^-1 VFA. The two rumen strains, and four strains from the pig gut, showed less inhibition of anaerobic growth by volatile fatty acids than did three laboratory strains examined for comparison. These findings indicate that plasmid transfer between certain E. coli strains can occur under conditions that closely simulate an anaerobic gut environment.     

Methane production and diurnal variation measured in dairy cows and predicted from fermentation pattern and nutrient or carbon flow

Many feeding trials have been conducted to quantify enteric methane (CH₄) production in ruminants. Although a relationship between diet composition, rumen fermentation and CH₄ production is generally accepted, the efforts to quantify this relationship within the same experiment remain scarce. In the present study, a data set was compiled from the results of three intensive respiration chamber trials with lactating rumen and intestinal fistulated Holstein cows, including measurements of rumen and intestinal digestion, rumen fermentation parameters and CH₄ production. Two approaches were used to calculate CH₄ from observations: (1) a rumen organic matter (OM) balance was derived from OM intake and duodenal organic matter flow (DOM) distinguishing various nutrients and (2) a rumen carbon balance was derived from carbon intake and duodenal carbon flow (DCARB). Duodenal flow was corrected for endogenous matter, and contribution of fermentation in the large intestine was accounted for. Hydrogen (H₂) arising from fermentation was calculated using the fermentation pattern measured in rumen fluid. CH₄ was calculated from H₂ production corrected for H₂ use with biohydrogenation of fatty acids. The DOM model overestimated CH₄/kg dry matter intake (DMI) by 6.1% (R²=0.36) and the DCARB model underestimated CH₄/kg DMI by 0.4% (R²=0.43). A stepwise regression of the difference between measured and calculated daily CH₄ production was conducted to examine explanations for the deviance. Dietary carbohydrate composition and rumen carbohydrate digestion were the main sources of inaccuracies for both models. Furthermore, differences were related to rumen ammonia concentration with the DOM model and to rumen pH and dietary fat with the DCARB model. Adding these parameters to the models and performing a multiple regression against observed daily CH₄ production resulted in R² of 0.66 and 0.72 for DOM and DCARB models, respectively. The diurnal pattern of CH₄ production followed that of rumen volatile fatty acid (VFA) concentration and the CH₄ to CO₂ production ratio, but was inverse to rumen pH and the rumen hydrogen balance calculated from 4×(acetate+butyrate)/2×(propionate+valerate). In conclusion, the amount of feed fermented was the most important factor determining variations in CH₄ production between animals, diets and during the day. Interactions between feed components, VFA absorption rates and variation between animals seemed to be factors that were complicating the accurate prediction of CH₄. Using a ruminal carbon balance appeared to predict CH₄ production just as well as calculations based on rumen digestion of individual nutrients.     

Rumen microbial population dynamics in response to photoperiod

AIMS: This work was carried out to determine if there was a difference in the microbial population of the rumen associated with daylength at which sheep are housed. METHODS AND RESULTS: Denaturing gradient gel electrophoresis (DGGE) was used to study the ciliate and bacterial diversity in the rumen of Soay rams kept in long day (16 h light) or short day (8 h light) photoperiods. Bacterial diversity varied according to the daylength conditions where the host animal was housed, as did total volatile fatty acids (VFA) concentrations. No differences associated with daylength were detected in ciliate diversity, branched VFA concentrations or the ruminal ammonia concentrations. CONCLUSIONS: As diets had identical composition, yet voluntary intakes levels were higher during long days, it is proposed that the differences in bacterial populations arise because of the differences in amount of food consumed. SIGNIFICANCE AND IMPACT OF THE STUDY: The outcome of this study demonstrated that factors beyond dietary composition must be taken into account when trying to study microbial populations, even in what can be considered a fairly constant environment.     

产琥珀酸放线杆菌的分离鉴定及其对瘤胃微生物发酵的影响

采用厌氧分离技术从奶牛瘤胃中分离出1株细菌,通过对其形态、培养特性、生化特性、16S rRNA基因序列测定与同源性分析的研究,确定分离菌株为产琥珀酸放线杆菌（Actinobacillus succinogenes）,体外发酵实验表明,发酵液中挥发性脂肪酸浓度（VFA）明显升高,乳酸浓度明显降低,对反刍动物的能量代谢和酸中毒具有一定的调节作用。     

Factors influencing biohydrogenation and conjugated linoleic acid production by mixed rumen fungi

The objective of this study was to evaluate the effect of soluble carbohydrates (glucose, cellobiose), pH (6.0, 6.5, 7.0), and rumen microbial growth factors (VFA, vitamins) on biohydrogenation of linoleic acid (LA) by mixed rumen fungi. Addition of glucose or cellobiose to culture media slowed the rate of biohydrogenation;only 35-40% of LA was converted to conjugated linoleic acid (CLA) or vaccenic acid (VA) within 24 h of incubation, whereas in the control treatment, 100% of LA was converted within 24 h. Addition of VFA or vitamins did not affect biohydrogenation activity or CLA production. Culturing rumen fungi at pH 6.0 slowed biohydrogenation compared with pH 6.5 or 7.0. CLA production was reduced by pH 6.0 compared with control (pH 6.5), but was higher with pH 7.0. Biohydrogenation of LA to VA was complete within 72 h at pH 6.0, 24 h at pH 6.5, and 48 h at pH 7.0. It is concluded that optimum conditions for biohydrogenation of LA and for CLA production by rumen fungi were provided without addition of soluble carbohydrates, VFA or vitamins to the culture medium; optimum pH was 6.5 for biohydrogenation and 7.0 for CLA production.     

Effect of starter diet supplementation on rumen epithelial morphology and expression of genes involved in cell proliferation and metabolism in pre-weaned lambs

Starter feeding is usually used in lamb production to improve rumen development and to facilitate the weaning process, but molecular mechanism of which is not well understood. Therefore, the objective of this study is to investigate the effect of starter feeding on the expression of ruminal epithelial genes involved in cell proliferation, apoptosis and metabolism in pre-weaned lambs. We selected eight pairs of 10-day-old lamb twins. One twin was fed ewe milk (M, n=8), while the other was fed ewe milk plus starter (M+S, n=8). The lambs were sacrificed at 56 days age. Results showed that the lambs fed M+S had lower pH in the rumen and a higher concentration of acetate, propionate, butyrate and total volatile fatty acid (VFA). Compared with the M group, the concentration of β-hydroxybutyric acid in plasma had an increased trend, and the concentration of IGF-1 in plasma had an decreased trend in the M+S group. The length, width and surface of rumen papillae increased in the M+S group compared with the M group; this was associated with increased cell layers in the stratum corneum, stratum granulosum and total epithelia. Messenger RNA (mRNA) expression of proliferative genes of cyclin A, cyclin D1 and cyclin-dependent kinase 2 in the ruminal epithelia of M+S lambs was increased compared with M only lambs. The mRNA expression of apoptosis genes of caspase-3, caspase-8, B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein (Bax) in the M+S group was decreased compared with M group, but the ratio of Bcl-2 to Bax were not changed between the two groups. Expression of IGF-1 mRNA was decreased, but the mRNA expression of IGF-1 receptor was higher in ruminal epithelia in the M+S group. Furthermore, the mRNA expression of VFA absorption and metabolism genes of β-hydroxybutyrate dehydrogenase isoforms 1 and 3-hydroxy-3-methylglutaryl-CoA lyase had an increased trend in the M+S group than in the M group, but the mRNA expression of 3-hydroxy-3-methylglutaryl-CoA synthase isoform 1, monocarboxylate transporter isoform 1 and putative anion transporter isoform 1 had a decreased trend in the M+S group than in the M group. These results suggest that starter feeding increased proliferation and inhibited apoptosis of ruminal epithelial cells, and may promote the VFA metabolism in ruminal epithelium in pre-weaned lambs. These findings provide new insights into improving rumen development by nutritional intervention strategies in pre-weaned lambs.     

Toxicity of volatile fatty acids at rumen pH prevents enrichment ofEscherichia coli by sorbitol in rumen contents

Attempts were made to establishEscherichia coli ML308 in the sheep rumen by inoculating it in combination with the slowly metabolized sugar alcohol, sorbitol. Numbers were determined by plating dilutions on nutrient agar containing the chromogenic -galactoside, 5-bromo-4-chloro-3-indolyl--d-galactoside. This strain, alac-constitutive mutant, produced distinctive blue colonies.E. coli ML308 failed to grow in rumen fluid, despite being able to grow rapidly on sorbitol and in rumen fluid at pH 7.0. Its growth rate was depressed by relatively small drops in pH in the presence of volatile fatty acids (VFA), such that normal pH's of 6.2–6.6 in rumen contents were inhibitory. The indigenous remen bacterium,Streptococcus bovis, was much more resistant to the combination of high VFA concentrations and low pH. The success of this and similar strategies for the introduction of new organisms with beneficial new properties will, therefore, depend on the organism's having a tolerance to VFA over a range of rumen pH that enables them to survive in the same way as native species.