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Research article2009Peer reviewed

Estimating volatile fatty acid concentrations in rumen samples by Fourier transform mid-IR transmission spectroscopy

Uden, P.; Sjaunja, L. -O.


This paper investigates the possibility of determining concentrations of acetate, propionate and butyrate in rumen fluid by Fourier transform mid-infrared (FIR) transmission spectroscopy. A total of 308 samples were used for calibration of the FIR instrument, normally used for milk analysis. The samples consisted of semi-artificial rumen fluids, spiked with acetate, propionate and butyrate with and without added bicarbonate and phosphate. The Test set consisted of 123 rumen in vitro samples with a mean value for the sum of the three volatile fatty acids of 5.5 g/L (84 mM), determined by high-performance liquid chromatography (HPLC). Stepwise regression was applied to find suitable wavelengths for predictions, mainly in the region of 6.3-10 mu m. A total of 12-13 wavelengths were used for the prediction equations and resulted in mean prediction errors (MPE) ranging from 0.031 to 0.043 g/L (approximately 0.5 mM) for the three VFAs and ratios of population standard deviation (SD) to SD of the regressions> 11.6. The calibration equation predicted the Test set well, with a MPE of 0.074, 0.066 and 0.119 for acetate, propionate and butyrate, respectively. More than 0.5 of the mean square prediction error was due to non-random errors which it should be possible to adjust for by use of calibration samples. A rough estimate also indicated that 0.09-0.16 of the mean square prediction error was due the HPLC method. The FTIR method is recommended for applications were required measurement accuracies are in the range of 1 mM. (C) 2009 Elsevier B.V. All rights reserved.


Prediction; VFA; FTIR; Rumen fluid

Published in

Animal Feed Science and Technology
2009, Volume: 152, number: 1-2, pages: 123-132
Publisher: Elsevier Masson

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      Animal and Dairy Science
      Veterinary Science

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