Near-infrared reflectance analysis of the fermentation characteristics of silage prepared by chemical treatment to prevent volatilisation of fermentation end products

Abstract

In this investigation, silage fermentation characteristics were predicted by near-infrared reflectance (NIR) analysis. Silage was prepared by drying in a microwave oven and milling through a 1 mm sieve. Volatilisation of the fermentation end products was prevented by previous chemical treatment with NaOH (10 moles l −1) and H 2SO 4 (5 moles l −1). Treatment of silage with different amounts of these chemicals showed that treatments associated with pH values of 8.5 and 3.5 were optimal with respect to a minimal loss of total volatile fatty acids (TVFA) and ammonia-nitrogen (ammonia-N), respectively. Silage samples prepared for NIR calibration/validation were all chemically treated to obtain pH values of 8.5 and 3.5 before drying and milling. Prepared silage samples with a pH of 8.5 were used to calibrate a Neotec model 51A NIR spectrophotometer with the reflection data (log 1/ R) and the corresponding lactic acid, TVFA, acetic acid and butyric acid values. Silage with a pH of 3.5 was used for calibration with ammonia-N. R 2 values for lactic acid, TVFA, acetic acid, butyric acid and ammonia-N, for calibration and prediction (validation), respectively, were: 0.89, 0.93, 0.90, 0.68, 0.95 and 0.85, 0.86, 0.92, 0.65, 0.88. Corresponding standard error values (g kg −1 dry matter) were 17.0, 10.4, 6.7, 4.7, 0.9 and 21.1, 18.7, 6.5, 5.8, 1.5, respectively. It is concluded that silage fermentation characteristics can be predicted with a fair amount of accuracy by NIR analysis if volatilisation of fermentation end products is prevented by conversion to their corresponding salts before drying.