Using Mid-IR Spectroscopy (ATR-FTIR) as a Fast Analytical Tool to Reveal Association between Protein Spectral Profiles and Metabolizable Protein Supply, Protein Rumen Degradation Characteristics and Estimated Intestinal Protein Digestion Before and After Rumen Incubation of Faba Bean Partitions and Faba Bean Silage

To our knowledge, there is little research done in using vibrational MID-IR molecular spectroscopy- attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) for ruminant system study. The objective of this study was to use ATR-FTIR as a fast analytical tool to reveal association between protein molecular structure in faba and metabolizable protein supply and nutrient delivery, and to explore the relationship between protein molecular structure in original and ruminal degraded residue and in situ rumen protein degradation and protein metabolism characteristics of faba bean samples (whole crop, stem, leaf, whole pods, and faba silage). The experiment for ruminant nutrition research was RCBD. Fourier transform Infrared (FTIR) spectra of faba samples before and after 12 and 24 h rumen incubations were collected with JASCO FT/IR-4200 with ATR at mid-IR range (ca. 4000-700 cm-1) with 128 scans and at 4 cm-1 resolution. The univariate molecular spectral analysis was carried using OMNIC software. Protein related spectral parameters before and after rumen degradation included amide region (ca. 1730-1480 cm-1), amide I region (ca. 1713-1558 cm-1) and amide II region (ca. 1558-1485 cm-1). Within amide I region, α-helix (ca. 1644 cm-1) and β-sheet (ca. 1630 cm-1) were studied. The results showed that ATR-FTIR protein molecular spectral features were significantly different before and after rumen incubation. Protein availability and digestion characteristic are mainly determined by original ATR-FTIR spectral profiles. Total truly digestible protein value (DVE) of faba partitions could be predicted with this equation: DVE (g/kg DM) = 1207.7 HAII12 + 228.7 alpha_beta24 - 310.8 (with R-square = 0.94, RSD = 8.06, model P < 0.001). The study shows that vibrational MID-IR molecular spectroscopy (ATR-FTIR) show a high potential to be a fast analytical tool to predict nutrient delivery.