Abstract
This study evaluated the effects of replacing SBM with CWYWEP on in vitro rumen fermentation, nutrient degradability, and gas production kinetics. Citric waste was co-fermented with yeast waste and a multi-enzyme complex for 14 days, then sun-dried and pelleted. The final CWYWEP product contained 50.4% crude protein (DM basis). A completely randomized design tested seven diets in which SBM was replaced by CWYWEP or non-enzymatic citric waste-yeast waste pellets (CWYWP) at 0%, 33%, 66%, or 100% inclusion. Replacing SBM with CWYWEP significantly increased cumulative gas production at 96 h, with the 100% CWYWEP group achieving 93.7 mL/0.5 g DM-a 14% increase over the control (p < 0.01). Microbial lag time was reduced to 0.17 h vs. 0.28 h in the control (p < 0.05), suggesting faster microbial colonization. The highest in vitro DM degradability (IVDMD) at 48 h was observed in the 100% CWYWEP group (64.5%), outperforming both the SBM control and all CWYWP treatments (p < 0.01). Notably, CWYWEP increased total volatile fatty acids by 5% at 4 h and propionate by 9% at 2 h, while reducing methane production by 5% (p < 0.05). Other parameters, including pH, ammonia nitrogen, organic matter digestibility, and protozoal counts, were unaffected (p > 0.05). In contrast, CWYWP without enzymes showed minimal improvement. These findings indicate that CWYWEP is a promising high-protein alternative to SBM, enhancing fermentation efficiency and reducing methane under in vitro conditions. Further in vivo studies are warranted to validate these effects.