Enzymatic valorization of alkali-treated chickpea straw and sunflower stalks as high fibrous agricultural wastes for sustainable ruminant nutrition

Chickpea straw (CS) and sunflower stalks (SS) are agricultural wastes with high fibre content and low digestibility. To improve their nutritional value and ruminal digestibility, the effects of NaOH and urea treatments combined with exogenous fibrolytic enzymes (EFE) were investigated. The untreated CS (CCS) and SS (CSS), 4% NaOH treated CS (NCS) and SS (NSS), and 4% urea-treated CS (UCS) and SS (USS) were supplemented by two enzymatic complexes (DCX and MaxFiber) composed mainly of cellulase and xylanase activities at increasing doses: 0, 1, 2, 5, and 10 μL DCX/g DM and 0, 0.5, 1, 2, and 4 mg MaxFiber/g DM. The results of in vitro ruminal fermentation proved that the DCX was more efficient than the MaxFiber complex for both CCS and CSS. Indeed, it improved the rate and the extent of ruminal fermentation, metabolizable energy, organic matter digestibility, and volatile fatty acids ( p -value <0.05) by 5 %, 47%, 12%, 12.8%, and 23.8%, respectively, for CCS using 10 μl/g DM and 20.8%, 27.6%, 12.9%, 11.8%, and 22.8%, respectively, for CSS by using 5 μl/g DM. The association between alkali treatments and EFE was depending to the supplemented enzymatic complex, the treated substrate and the alkali treatment. For the CS, the association between alkali and EFE stimulated the ruminal fermentation and improved the digestive use. However, it decreased the efficiency of EFE for SS. Overall, the use of EFE to CS and SS could provide a valuable source of energy from digestible fibre for ruminants.