Author
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Reeves Iii, James |
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Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/10/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Mid-infrared spectroscopy is a non-destructive assay method using a form of light which can be used to determine the composition and quality of materials. Samples of tall fescue (a forage or grass used as animal feed) from three growing years, ground by two methods, and oven and freeze dried were analyzed chemically and by mid-infrared spectroscopy for protein, fiber and digestible dry matter. Results indicated that the same principles which govern the development of near-infrared calibrations (another method using light, which has been widely used to determine the composition of materials such as fescue) apply to the development of calibrations using mid-infrared spectra. In both of these methods spectra (graphical representation of how the light interacts with the sample) are used to develop equations which can then be used to determine the composition of other samples. Overall, results indicated that spectra collected at a higher resolution (more detailed spectra) produced better results, that oven and freeze dried samples yield equally good results, but, unlike previous near-infrared results, that how the samples are ground can affect the results, with more finely and consistently ground samples giving better results. Reducing the size of the calibration set (number of samples used to develop the equations) resulted in a decrease in calibration accuracy similar to that found with near-infrared calibrations. In conclusion, the results presented in this paper show that mid-infrared spectra can be used for the determination of the composition of forages and behave similar to those developed using near-infrared spectra. Technical Abstract: Tall fescue samples from three years, ground by two methods, and oven and freeze dried were analyzed chemically and by mid-infrared diffuse reflectance spectroscopy for CP, NDF, ADF and in vitro digestible dry matter. Results indicated that the same principles which govern the development of near-infrared calibrations apply to the development of calibrations using mid-infrared spectra. Overall, results indicated that spectra collected at a resolution of 4 cm-1 produced better calibrations than spectra collected at 16 cm-1, that a wide variety of data treatments needed to be tested, that oven and freeze dried samples calibrated the same, but, unlike previous near-infrared results, UDY ground were preferred over Christy-Norris ground samples. Reducing the size of the calibration set resulted in a decrease in calibration accuracy similar to that found with near-infrared calibrations with approximately 56 out of 223 samples needed for acceptable calibrations. Finally, results from predicting samples from one year by calibrations developed using samples from another year indicated that mid-infrared calibrations, at least as developed in this work, may be less robust than their near-infrared counterparts. The results presented in this paper show that mid-infrared spectra can be used to develop calibrations for the determination of the composition of forages and behave similar to those developed using near-infrared spectra. In conclusion, while further work is needed to determine the best way to develop mid-infrared calibrations, including questions not addressed, such as spectral resolutions other than 4 or 16 cm-1 and the number of scans needed to achieve acceptable results, the mid-infrared can be used for quantitative determinations in materials such as forages. |
