Near Infrared Spectroscopy for Measuring in Situ Degradability in Barley Forages

Abstract

The Western Canadian dairy, beef cow and feeder cattle industries rely heavily on barley ( Hordeum vulgare) based forages for a major portion of the ruminant diet. The objective of this study was to investigate the use of near infrared (NIR) reflectance spectroscopy to determine: 1) the proportion of rapidly degradable and slowly degradable dry matter in the forage, and 2) the effective rumen dry matter degradablities at rumen passage rates ( Kp) of 3% and 6% per hour for the forages, as determined in situ using the nylon bag technique. For each incubation period a total of 195 straw samples from the 1994 to 1995 crops years were placed in each rumen of three lactating Holstein cows. The same cows were used to incubate 27 greenfeed and corresponding 27 silage samples from the 1995 crop year. Similarly, 27 greenfeed and corresponding 27 silage samples from the 1996 crop year were incubated in each rumen of three dry Holstein cows. The incubation times were 0, 4, 8, 12, 24, 72, 120 and 240 h. Residual dry matter (DM) in each bag was expressed as a percentage of original DM. Using an NIRSystems 6500 instrument and Infrasoft International, NIRS 3, version 3.11 software, calibration equations were developed for predicting rapidly degradable (A) and slowly degradable (B) rumen fractions and effective degradability at Kp of 3% (D) and 6% (E). Two-thirds of the 302 samples (202) were spectrally selected for NIR spectroscopy calibration and the remaining 100 samples were used for validation. Coefficients of multiple determination ( R2) between in situ experimental and NIR spectroscopy predicted results in the calibration set were 0.99, 0.92, 0.99 and 0.99 for A, B, D and E, respectively. Standard errors of calibration ( SEC) in the calibration set were 1.59, 2.57, 1.54 and 1.69 for A, B, D and E, respectively. The corresponding R2 and standard errors of prediction ( SEP) in the validation set were 0.95, 0.66, 0.96 and 0.94 and 3.47, 4.26, 3.04 and 3.63 for A, B, D and E, respectively. The RPD statistics, the ratio of the standard deviation of in situ data to SEP from the validation set, were 4.75, 1.73, 4.67 and 4.08 for A, B, D and E, respectively, indicating that the calibration equation is acceptable for predicting an in situ constituents accurately. Based on the high R2, low SEC, low SEP and the high RPD results, we conclude that the NIR spectroscopy equations developed in this study are valid for predicting the rapidly degradable (A) fraction and the effective rumen dry matter (DM) degradability at both 3% (D) and 6% (E) per hour rumen passage rates for barley forages.