Fermentative profile and nutritional value of untreated and alkali-treated faba bean (Vicia faba L.) straw supplemented with exogenous fibrolytic enzymes derived from Trichoderma longibrachiatum, Aspergillus strains, and Neurospora intermedia

The faba bean straw (FBS) is a faba bean plant by-product characterized by high fiber and crude protein content, and low digestibility. This study aimed to improve the nutritional value and ruminal fermentation of FBS by combining chemical and biotechnological treatments. The FBS was subject of two alkali treatments: 4% NaOH (NFBS) and 4% urea (UFBS), and exogenous fibrolytic enzyme (EFE) supplementation using two enzymatic complexes: Trichoderma longibrachiatum EFE (DCX) at 0, 1, 2, 5, and 10 μL/gDM and Aspergillus strains and Neurospora intermedia EFE (MaxFiber) at 0, 0.5, 1, 2, and 4 mg/gDM of untreated FBS (CFBS), NFBS, and UFBS. All supplemented FBS preparations were incubated with buffer solution, and fresh cows’ ruminal fluid. At the end of incubation period (96h), the in vitro ruminal fermentation parameters as the extent (A), the rate of GP (Rmax), and the digestive use parameters: organic matter digestibility (OMD), metabolizable energy (ME), and volatile fatty acids (VFA) were determined. Our results proved that EFE’s effect depended on the enzymatic dose and the alkali treatment. The DCX supplementation effect was more pronounced than the MaxFiber. The highest improvements were recorded for CFBS supplemented by DCX (5μL/gDM), by 43.6%, 60.2%, 27%, 25.9%, and 43.5% for A, Rmax, ME, OMD, and VFA, respectively, as compared to the control. However, the association between EFE and alkali decreased the efficiency of EFE. Therefore, using EFE supplementation to the CFBS could generally provide an energy-protein-rich bio-converted by-product as compared to commonly used cereal straw in ruminant nutrition.