Observations on Determination of Dysprosium in Labeled Digesta Samples by Near Infrared Spectroscopy

¹ Nutrient Conservation and Metabolism Laboratory, Livestock and Poultry Sciences Institute, ARS, USDA, Building 200, Room 124, BARC-East, Beltsville, MD 20705

The objective of this work was to determine whether the Dy content of ruminal digesta samples labeled by pulsedosing intra-ruminally with Dy-labeled forages could be determined by near infrared reflectance spectroscopy. Ruminal grab samples were obtained from four steers. Equal numbers of alfalfa and orchardgrass samples were collected at 17 times (0 to 165 h) after dosing and analyzed (total of 272 samples). Dysprosium was determined by direct current plasma emission spectrometry. Spectra were obtained by scanning ground samples on a scanning monochromator. Calibrations for Dy (0 to 349.5 ppm; mean = 44.5 ppm) were carried out using both step-wise and partial least squares regressions. Wavelength selections using step-wise regression included characteristic Dy wavelengths and resulted in R² and standard error of analysis of .9 and 20 ppm, respectively. Partial least squares regressions, although more robust, were not significantly better. Sample ashing to increase relative Dy concentrations did not improve the results. Further investigations indicated that interference by Co marker, also present in the samples, was a problem. Although near infrared reflectance spectroscopy is capable of determining Dy in labeled forages, further work is needed to increase its accuracy.

Key Words: near infrared • dysprosium forages • in situ

Submitted on January 9, 1995
Accepted on May 12, 1995