Carbohydrates molecular structure profiles in relation to nutritional characteristics of newly developed low and normal tannin faba bean varieties in dairy cows analysed by using standard methods and the vibrational molecular spectroscopy (Ft/IR‐ATR)

Abstract

To our knowledge, there was no study on interactive relationship between CHO molecular structure spectral profiles of newly developed cool-season adapted faba bean and nutritional characteristics in ruminants. The aim of this study was to evaluate the impact of genotypes and tannin levels on the physicochemical and nutritional characteristics of faba bean as an alternative protein and energy source for ruminants and its relation to CHO molecular structure spectral profiles using vibrational molecular spectroscopy (Ft/IR-ATR). Eight genotypes with two tannin levels (low and normal) grown at three different locations in Saskatchewan (CDC crop research fields) were analysed. Chemical analyses were performed using AOAC standards and energy was evaluated using NRC standards. Rumen degradation kinetics were determined using in situ dairy trial. Intestinal digestion was analysed by a modified three-step in vitro technique with 12h pre-rumen incubation in dairy cows. Molecular spectral study was performed using Ft/IR-ATR, and the molecular structural features were analysed at ca. 4000-800cm-1 using the Spectra ManagerII. CHO-related functional groups were analysed with OMNIC 7.3. The results showed low-tannin faba bean (LT) presented a highly significant difference (p<0.05) on rumen bypass starch (BSt) compared to normal tannin faba bean (NT). On the other hand, NT had more total tract digested starch (TDST) compared to LT. No significant differences (p>0.10) were observed for total digestible nutrients (TDN1x ), metabolizable protein (MP), feed milk value (FMV) or rumen undegraded crude protein (RUP). Results showed differences in physicochemical characteristics among faba bean varieties; however, the predicted production performance was not different within faba bean genotypes. These outcomes suggest that faba bean can be used as nutritive ingredient for dairy cattle without a significant genotype or tannin level effect on metabolic characteristics. Results from vibrational spectroscopic study showed a higher ATR-Ft/IR absorbance (p<0.05) in NT on inherent structural CHO (STCHO), total CHO (TCHO) area and peaks (H_1015, H_1076, H_1145), and cellulosic compounds (CEC) to total CHO (TCHO) ratio. Significant correlations could be found between CHO spectral profiles and metabolic characteristics of faba bean, which indicates that structural spectral features of faba bean could be used to predict metabolic characteristics in ruminants.