Use of Fourier transform infrared (FTIR) spectroscopy to predict VFA and ammonia from In vitro rumen fermentation

The aim of the present study was to develop a FTIR method to quantify amounts and proportions of volatile fatty acids (VFA) and ammonia nitrogen (N-NH3) in fermen- tation fluids collected in vitro using innovative Bayesian models as chemometric technique. A set of 170 fluids, collected before and after 4 in vitro incubations of 8 diets in 5 replication plus 5 blanks, were analysed for VFA, N-NH3 and scanned using the MilcoScan FT2 (Foss Electric, Hillerød, Denmark) in the spectral range between 5000 and 900 cm-1. A Bayes B model was used to calibrate equations for each fermentative trait. The calibration equation predicts well VFA and N-NH3 amounts in calibration and also in validation (R2VAL ranged from 0.93 to 0.83 for iso- valeric and n-butyric acid, respectively). However, the prediction of VFA expressed as proportions of total amount was much less accurate (R2VAL ranged from 0.81 to 0.52 for iso-valeric and n-butyric acid, respectively). In conclusion, FTIR and Bayesian models can be used as tools to accurately predict VFA amounts in vitro.