The present study aimed to evaluate the sustainable utilization of date palm leaves (DPL) and rice straw (RS) as feed materials for ruminants using an in vitro wireless gas production (GP) technique. Date palm leaves and RS were individually ensiled with lactic or malic acids at 5 g/kg DM for 45 days. In a total mixed ration containing concentrate feed mixture, vegetable/fruits byproducts, untreated RS, and berseem hay (control ration), untreated RS was completely replaced with treated RS (ensiled without additives or with lactic or malic acids) whereas berseem hay was replaced with DPL (ensiled without additives or with lactic or malic acid) at 25, 50, 75, and 100% levels. Significant treatment x replacement level interactions were observed (P < 0.01) for most measured parameters of gas, methane (CH4) and carbon dioxide (CO2) productions, and degradability and volatile fatty acid (VFA) concentration. Replacing berseem hay with increasing levels of lactic or malic acid-treated DPL gradually decreased (P < 0.01) the asymptotic total gas and CH4 and CO2 productions, and malic acid-treated DPL decreased the rates of total gas, CH4 and CO2 productions, and the lag time of total GP. Moreover, lactic acid-treated DPL linearly increased (P < 0.05) the concentration of total VFA and acetate. Malic acid-treated DPL did not affect the measured ruminal fermentation parameters. Compared with the malate-treated DPL, lactate-treated DPL increased dry matter and neutral detergent fiber degradability, total VFA and acetate concentrations, and decreased CH4 production. In conclusion, replacing berseem hay with malic or lactic acids improved ruminal fermentation and decreased CH4 and CO2 productions, which can be considered as a sustainable strategy for cleaner ruminant production. Lactic acid treatment of DPL may result in better ruminal fermentation characteristics than the malic acid treatment of DPL.
