THE USE OF NEAR-INFRARED REFLECTANCE SPECTROSCOPY TO DEFINE NUTRIENT DIGESTION OF HAY BY CATTLE

Near-infrared reflectance spectroscopy (NIRS) has the potential to help redefine nutrient requirements and feeding standards. The spectral information obtained from a feed sample is much greater and more specific than the currently used conventional chemical procedures. Difference spectra between hays and feces from steers fed the hay were used to determine spectral areas of uniform digestion or indigestion. Digestion coefficients were calculated for each data point and the digestible absorption regressed on absorption for the hay. Above average apparent digestion occurred between 1450 and 1620 nm and between 2100 and 2200 nm. Below average apparent digestion occurred with sharp peaks at 1714, 2256, 2306, 2346 and 2382 nm. These represent aliphatic C-H stretch and bend first overtone and combination bands and are usually associated with lipids, but may result from either feeds, sloughed animal tissue, or microbial residue. High correlations of organic matter digestion and hay spectra were found at 1990 and 2192 nm. These probably represent protein fractions but are shifted slightly from the peak absorption of proteins at 2000 and 2180 nm. Results also suggest uniform digestible fractions near 1990 and 2190 nm. The 2086 nm region produced an R(2) of near zero indicating non-uniform digestion, probably from conflicting digestibilities of starch and cellulose.