Near Infrared Spectroscopic Analysis of Forage Samples Digested In Situ (Nylon Bag)

¹ Ruminant Nutrition Laboratory, Livestock and Poultry Science Institute, Beltsville Agricultural Research Center, Agricultural Research Service, USDA, Beltsville, MD 20705

The objective was to investigate the feasibility of using near infrared reflectance spectroscopy to determine the composition of samples generated in situ. Five alfalfa and five orchardgrass hays of differing maturities were incubated for 0, 6, 24, 48, and 72 h (Experiment 1) or for 0, 2, 4, 8, 12, 24, 48, and 96 h (Experiment 2) in rumen-fistulated, lactating cows, using nylon bags. After washing to remove rumen contents, samples were analyzed using a nonrotating circular cell in a scanning monochromator. All samples then were dried at 55°C and analyzed for CP and ADF by wet chemistry and rescanned in the dry state. The degree of DM digestion of the original sample was calculated from duplicate bags. Results for spectral analysis of dried samples (Experiment 1), with one-half the samples for validation, were typical of results found for dry forages. The results for scanning wet samples were less accurate than for dry ones. Analysis of samples from Experiment 2 by equations developed in Experiment 1 often resulted in extremely large biases, but these were corrected by including six samples of each forage from Experiment 2 in the calibration set (from Experiment 1) and redeveloping the equations. Although it is possible to use near infrared reflectance spectroscopy to determine the composition of wet samples generated in situ, results are more accurate if the samples are scanned after drying.

Key Words: in situ • near infrared reflectance spectroscopy • nylon bag

Submitted on October 10, 1990
Accepted on March 4, 1991