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Ash in forage, esophageal, and fecal samples analyzed using near-infrared reflectance spectroscopy

Windham, W.R., Hill, N.S., Stuedemann, J.A.
Crop science 1991 v.31 no.5 pp. 1345-1349
alfalfa, Medicago sativa, Festuca arundinacea, forage, nutritive value, esophagus, ash, spectral analysis, infrared spectroscopy, prediction, organic matter, digestibility, accuracy, calibration, chemical constituents of plants, feces composition
In study of the plant-animal interface, knowledge of the organic fraction of pasture, esophageal, and fecal samples can help predict energy intake and digestion. Ashing of the large sample volumes necessary to conduct interface studies, however, is cumbersome and impractical. This study was initiated to examine the use of near-infrared reflectance spectroscopy (NIRS) as a means of predicting ash concentration in pasture, esophageal, and fecal samples. Pasture mixtures of alfalfa (Medicago sativa L.) and tall fescue (Festuca arundinacea Schreb.) were defoliated by grazing animals. Pasture, esophageal and fecal samples were collected and scanned by NIRS. A calibration subset was selected, samples were ashed, and the data used for equation development. The optimum equation was developed using log 1/reflectance (R) spectral data and produced standard errors of calibration (SEC) and validation (SEP) of 14.4 and 14.2 g kg-1, respectively, regardless of whether ash or organic matter data were used. Equations selected during calibration contained three wavelength pairs within 40 mn of one another. New calibration equations were generated by forcing in one wavelength in the neighboring pair +/- 20 nm from the selected band. Validation error of calibration equations with forced wavelengths was not different from that of the original calibration equation. It was concluded that wavelength pairs were necessary to calculate slope differences of spectra from samples varying in ash concentration. Recalibration of the instrument with a subset of pasture and esophageal samples improved SEC and SEP to 9.5 and 9.8 g kg-1, respectively, recalibration with a subset of fecal samples improved SEC and SEP to 10.6 and 12.7 g kg-1, respectively.