Combined effects of postdistillation residue blends from medicinal plants on in vitro ruminal microorganisms, enzymes, nitrogen and energy efficiency, and antioxidant status

In this study, the combined effects of postdistillation residue blends, including pomace, wastewater, and their mixture, derived from rosemary (RO), fennel (FE), spearmint (SP), and rose (ROS), on in vitro microbial populations, enzymatic activities, fermentation, and antioxidant status were evaluated using the gas production technique. The three phytobiotic blends were MP (mixed pomace of RO, FE, SP, and ROS; 1:1:1:1 ratio), MW (mixed wastewater of RO, FE, SP, and ROS; 1:1:1:1 ratio), and MPW (mixed pomace–wastewater of MP and MW; 1:1 ratio). Each blend was used at 2% and 3% of diet dry matter (DM). The experimental diets were as follows: 1- control (without additive residues), 2- MP2 (MP at 2% of DM), 3- MP3 (MP at 3% of DM), 4- MW2 (MW at 2% of DM), 5- MW3 (MW at 3% of DM), 6- MPW2 (MPW at 2% of DM), and 7- MPW3 (MPW at 3% of DM). Dietary addition of the residues, particularly MW3, increased cellulolytic and proteolytic bacteria and microbial biomass, but reduced protozoa and ammonia-N (p < 0.05). Fibrolytic and amylolytic enzymes, substrate degradation, substrate disappearance, and antioxidant capacity improved with addition of the residues (p < 0.05). With the use of phytobiotics, total volatile fatty acid increased, with a shift towards higher propionate and lower acetate-topropionate ratio (p < 0.05). Estimated CH4 and proportion of CH4+H2 decreased, while CO2 increased due to addition of residues (p < 0.05). Overall, mixed postdistillation residues from RO, FE, SP, and ROS are recommendable as sustainable natural phytobiotic additives to improve ruminal microbial and enzymatic activities, N and energy efficiency, and antioxidant power, with the best improvement in MW3. Mixing postdistillation wastewater with pomace increased the DM content; however, further studies are needed on storage stability, spoilage prevention, and the potential role of absorbents. Finally, in vivo studies should be conducted to validate these findings.