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B Vlaeminck

Publications and source records attributed to B Vlaeminck.

13 recordsLinked to original sources
PubMed2006

Projection of multidimensional GC data into alternative dimensions-exploiting sample dimensionality and structured retention patterns.

Comprehensive multidimensional gas chromatography (GCxGC) is a powerful separation technique. One of the features of this technique is that it offers separations with more apparent structure than that offered by conventional one-dimensional GC (1-D GC). While some previous studies have alluded to this structure, and used structured retention patterns for some simple classifications, the topic of structured retention in GCxGC has not been studied in any great detail. Using the separation of fatty acid methyl esters (FAME) on both nonpolar/polar and polar/nonpolar column sets, the interaction between the separation dimensions and the sample dimensions is explored here. The GCxGC separation of a series of compounds is presented as a projection of the sample from sample space, a p-dimensional space with dimensions defined by the dimensionality of the sample, into separation space: for GCxGC, a two-dimensional plane passing through the sample space in an orientation defined by the separation conditions. Using this conceptual model and some a priori knowledge of the sample, it is shown how the image of the sample in the separation space can be used to construct an image of the sample in alternate dimensions, such as second dimension retention factor ((2)k) vs. chain length in the case of FAME. These projections into alternate dimensions should facilitate the interpretation of the complex patterns found within the GCxGC chromatogram for the identification and classification of compounds.

Journal Article↗
PubMed2006

Effect of forage:concentrate ratio on fatty acid composition of rumen bacteria isolated from ruminal and duodenal digesta.

Four dairy cows were used to examine the effect of the dietary forage:concentrate ratio [35:65, 50:50, 65:35, and 80:20 on a dry matter (DM) basis] on the fatty acid composition of rumen bacteria isolated from the liquid (LAB) and solid (SAB) phase of the rumen and duodenal digesta. Rumen contents were sampled 4 h after the morning feeding. Solid and liquid phases were separated from rumen contents and duodenal bacteria from a composite duodenal sample by differential centrifugation. Total fatty acid content in bacterial DM was 1.6 to 2.8 times higher in SAB compared with LAB, and increased with dietary concentrate. In combination with published reports, the data show that bacterial fatty acid content and composition is closely related to dietary fatty acids except for C18:2n-6 and C18:3n-3. A decrease in forage:concentrate ratio increased bacterial concentration of trans-10 C18:1, and this increase was 3.4 times higher in LAB compared with SAB. Analysis of odd- and branched-chain fatty acids showed large differences between SAB and LAB, which probably reflected a difference in species composition. The variation in odd- and branched-chain fatty acids between SAB and LAB was used to estimate their relative proportions in duodenal bacteria by means of linear programming, and showed an increased proportion of SAB from 64.7 to 74.8% with increasing forage:concentrate ratio. In addition, increasing the proportion of dietary forage was closely related to the proportion of anteiso C15:0 in total odd- and branched-chain fatty acids (r(pearson) = -0.771). The bacterial concentration of iso C17:0 closely reflected the bacterial growth rate as shown by the relation with cytosine:N (r(pearson) = -0.729). These strong relationships suggest that odd- and branched-chain fatty acids might be used as tool to evaluate nutrient supply to rumen bacteria.

Animal Feed↗
PubMed2006

Milk odd- and branched-chain fatty acids in relation to the rumen fermentation pattern.

The objectives of this study were 1) to determine whether a relationship exists between molar proportions of volatile fatty acids in the rumen and milk odd-and branched-chain fatty acid concentrations (i.e., iso C13:0, anteiso C13:0, iso C14:0, C15:0, iso C15:0, anteiso C15:0, iso C16:0, C17:0, iso C17:0, anteiso C17:0, and cis-9 C17:1); and 2) to evaluate the accuracy of prediction of the latter equations using an independent data set. For development of the regression equations, individual cow data from 10 feeding experiments with rumen-fistulated dairy cows were used, resulting in a data set of 148 observations. Milk odd- and branched-chain fatty acids were closely related to the molar proportions of acetate (SE = 15.3 mmol/mol), propionate (SE = 14.7 mmol/mol), and butyrate (SE = 9.2 mmol/mol). These regression equations were further validated using data from the literature (n = 14). Evaluation of these prediction equations using the independent data set resulted in a root mean square prediction error of 3.0, 9.0, and 8.9% of the observed mean for acetate, propionate, and butyrate, respectively. In addition, less then 5% of the mean square prediction error was due to line bias. This suggests that the currently developed prediction equations based on milk odd- and branched-chain fatty acids show potential to predict molar proportions of individual volatile fatty acids in the rumen.

Animals↗
PubMed2005

Use of odd and branched-chain fatty acids in rumen contents and milk as a potential microbial marker.

The objectives of this study were: 1) to determine if a correlation exists between rumen odd and branched-chain fatty acids (OBCFA, i.e., C(15:0), iso C(15:0), anteiso C(15:0), C(17:0), iso C(17:0), anteiso C(17:0), and C(17:1)), uracil, and purine bases (PB), 2) to evaluate the potential of milk OBCFA secretion to predict duodenal flow of microbial protein in lactating cows, 3) to evaluate the accuracy of the latter prediction equations using an independent data set, and 4) to determine whether these predictions were more accurate than predictions based on dry matter intake (DMI) and dietary characteristics. In the first experiment, 4 lactating dairy cows arranged in a 4 x 4 Latin square were offered diets based on grass silages of different botanical composition and a standard concentrate. The relationship between rumen pool size of OBCFA and microbial matter was investigated. Rumen pool size of microbial matter (g), determined 4, 12, and 17 h after feeding, using uracil and PB as microbial markers, was closely related to OBCFA (g) [r(2) = 0.716, root mean square error (RMSE) = 4.45]. To correct for differences in marker concentrations among strains of rumen microbes, C(17:0) was included in the regression equations, resulting in an increased predictive power (r(2) = 0.780, RMSE = 3.92). The relationship between microbial flow to the duodenum and milk OBCFA yield was evaluated in a second experiment with lactating dairy cows offered diets based on grass silage and concentrates differing in starch source. Similar to observations in the rumen, milk OBCFA yield was closely related to microbial flow to the duodenum (RMSE = 4.28), but predictive power of equations did not increase when straight-chain C(17)-fatty acids were included in the regression equations (RMSE = 4.92). Evaluation of the current prediction equations with 3 independent datasets resulted in a root mean square prediction error of 20.5 and 13.4% of the observed mean for equations based on milk secretion of total OBCFA and straight-chain C(17)-fatty acids, respectively. Comparison of the accuracy of the latter equations with 2 previously published equations based on DMI and dietary characteristics suggest the former to be more accurate. This first evaluation suggests that milk OBCFA could be used as a marker for duodenal flow of microbial matter, especially when accurate measurements of DMI are not available.

Animal Nutritional Physiological Phenomena↗
PubMed2004

Rumen odd and branched chain fatty acids in relation to in vitro rumen volatile fatty acid productions and dietary characteristics of incubated substrates.

A first aim of this batch in vitro experiment (21 h) was to use changes in odd and branched chain fatty acid (OBCFA) patterns to suggest shifts in microbial populations, associated with four types of incubated whole dairy cow diets. Principal component analysis suggested higher dietary starch increased the proportion of C15:0 and C17:0, whereas increased neutral detergent fibre content was positively related to anteiso C15:0 concentrations, which is in agreement with the importance of these fatty acids in respectively amylolytic and cellulolytic bacteria. A second aim of the experiment was to relate rumen volatile fatty acid proportions to OBCFA by principal component regression and to compare these relations with predictions based on diet proximate composition. The R2 values achieved for the regressions between acetate, propionate and butyrate, and OBCFA were 79.6%, 86.6% and 84.9% respectively. Moreover, in the current study, predictions of the rumen fermentation pattern showed higher R2 (p < 0.01) when based on OBCFA compared with proximate feed composition. If relations persist in vivo, there could be scope for milk OBCFA to predict the supply of specific rumen nutrients.

Animal Feed↗
PubMed2003

Use of principal component analysis to investigate the origin of heptadecenoic and conjugated linoleic acids in milk.

The aim of this paper was the application of principal component analysis (PCA) 1) to elucidate mutual metabolic relationships between milk fatty acids (FA) and 2) to illustrate the origin of milk FA, in particular C17:1 and cis-9,trans-11 conjugated linoleic acid. Data were combined from 3 experiments with lactating Holstein-Friesian cows offered diets based on grass or legume silage and concentrates. Loading plots of PCA based on milk FA concentrations showed 4 groups of milk FA, having similar precursors or metabolic pathways in the rumen and/or mammary gland: medium-chain saturated FA, de novo synthesized from acetate and beta-hydroxybutyrate; monoenoic milk FA, products of delta9-desaturase activity in the mammary gland; odd chain FA of rumen microbial origin and C18:0, n-6 C18:2, and n-3 C18:3 of dietary origin or the result of rumen biohydrogenation. Loading plots of PCA based on both milk and duodenal FA concentrations as well as on milk FA yields and duodenal FA flows further illustrated the importance of postabsorptive synthesis of the milk medium chain saturated and monoenoic FA and the direct absorption from the blood stream of odd chain FA, C18:0, n-6 C18:2, and n-3 C18:3. In all loading plots, milk oleic acid (C18:1) appeared intermediate between clusters of 18-carbon FA and monoenoic FA, illustrating its dual (dietary and endogenous production) origin. Milk C17:1 was suggested to be a desaturation product of C17:0, in common with other milk monoenoic FA. Finally, the PCA technique, based on milk FA patterns of one experiment, was applied to investigate factors determining cis-9,trans-11 conjugated linoleic acid concentrations in milk. Within the range of diets and cows studied here, we showed changes in cis-9,trans-11 conjugated linoleic acid to be mainly dependent on vaccenic acid supply and to a lesser extent on variation in desaturase activity.

3-Hydroxybutyric Acid↗
PubMed2001

Effect of N fertilisation rate, energy supplementation and supplementation strategy on efficiency of N utilisation in the sheep rumen.

The effect of nitrogen (N) fertilisation (200 vs. 400 kg N ha-1 year-1) of pasture cut in the beginning (end of May) and the end (end of August) of the grazing season and of simultaneous or separated feeding of maize and grass (400 kg N ha-1 year-1) on efficiency of N utilisation in the rumen has been studied using four rumen cannulated wethers. Doubling N fertiliser rate increased grass CP production by about 60%, but induced extensive excess of rumen degradable N, reflected in high urinary urea excretion (rpearson = 0.747). The latter was lower (74% at the maximum) when feeding less fertilised or older grass or when supplementing with maize silage. Although simultaneous feeding of maize silage with grass changed patterns of rumen ammonia concentrations, no change in urinary excretion of purine derivatives was observed. Hence, faecal or urinary N excretion was unaffected by the supplementation strategy. Microbial growth efficiency was estimated from urinary excretion of purine derivatives and fermented OM. The latter was calculated from total rumen CH4 production, based on rumen fermentation stoichiometry and taking into account proportional concentrations of individual volatile fatty acids. Higher levels of intake tended to improve rumen microbial growth efficiency slightly (rpearson = 0.406), which, however, could not compensate for the reduced effective rumen DM degradability (rpearson = -0.442). The latter was apparently associated with a partial shift of the fermentation from the rumen to the hindgut, as suggested from the negative correlation (rpearson = -0.745) between faecal RNA concentrations and rumen effective degradability.

Ammonia↗