Stock animals such as cows, pigs, rabbits and chickens that are raised in large agricultural businesses typically are sustained on compound feed, a highly nutritive blend of grains, vitamins, minerals and other substances. Assuring the quality of compound feed during production traditionally has been a laborious process of sampling by hand and taking the sample to a laboratory for physicochemical analysis. Recently, the process was sped up by using near-IR spectroscopy, but testing still must be performed off-site.Researchers at the University of Córdoba in Spain have found that near-IR spectrometry based on a diode laser array instrument is suitable for measuring animal feed as it moves on a conveyor belt. The inset shows a sample of the feed being tested. Courtesy of Elvira Fernández-Ahumada.Making the process of sampling and testing quick enough to be done on the production line with spectrometry is possible by switching from a grating monochromator to a diode laser array. However, little has been known about how well the latter technique compares with the former at testing compound feeds. Recently, researchers at the University of Córdoba in Spain gathered calibration data using both spectrometry methods, finding that online systems are feasible under certain conditions.Over a span of five years, the investigators — Elvira Fernández-Ahumada, Ana Garrido-Varo and José Emilio Guerrero-Ginel — collected feed samples made in various forms for several animal species. They tested all of the samples with two devices: a near-IR scanning grating monochromator from Foss NIRSystems Inc. of Laurel, Md., and a Carl Zeiss Inc. diode array spectrometer attached to a stationary module made by J. Haldrup a/s of Løgstør, Denmark, that simulated a production line.The diode array spectrometer recorded absorbance spectra between 400 and 1690 nm at 2-nm steps. The grating monochromator can scan up to 2498 nm, also in 2-nm steps, but the researchers trimmed the range from 400 to 1690 nm to obtain comparable data. They scanned the same samples with both instruments and used the data to predict the amounts of constituents such as crude protein and crude fiber as well as ingredients such as sunflower meal and a mineral-vitamin premix.After data analysis, the researchers concluded that the calibrations recorded with the diode array spectrometer were remarkably accurate, even when the feed was in motion. In particular, results for crude protein, sunflower meal and the premix achieved by the diode array system exhibited accuracy similar to or greater than that achieved with the monochromator-based system. However, some indicators for crude fiber content were better from the monochromator instrument.The scientists believe that the diode array may offer high accuracy because of its data-acquisition speed — which allows a large amount of sample to be scanned — and that future investigations should show whether diode array spectrometers with larger acquisition ranges will offer even better performance or could be used to look for other types of feed ingredients.Journal of Agricultural and Food Chemistry, May 14, 2008, pp. 3185-3192.