Potential of citric and yeast waste fermentation products supplemented with fiber-degrading enzymes as alternatives to soybean meal in ruminant nutrition

BACKGROUND: This study aimed to investigate the effects of fiber-degrading enzyme supplementation in combination with citric waste fermented yeast waste (CWYW) as a replacement for soybean meal on ruminal fermentation characteristics, gas production kinetics, and digestibility. The in vitro gas production technique was used to evaluate these effects. A 2 × 4 + 1 factorial arrangement in a completely randomized design (CRD) was employed, resulting in nine treatments comprising either CWYW in powder or pellet form with varying enzyme levels (0%, 0.2%, 0.4%, and 0.6%), alongside a control diet containing full soybean meal. RESULTS: The control diet yielded the highest cumulative gas production (P < 0.01), whereas the CWYW-powder without enzyme addition showed the highest gas production rate constant (P < 0.01). The in vitro dry matter digestibility (IVDMD) was also highest in the control group (P < 0.01), while organic matter digestibility (OMD) did not differ significantly among treatments. Increasing levels of fiber-degrading enzymes were associated with a linear decrease in pH at 48 h (P < 0.05) and a corresponding increase in NH₃-N concentrations (P < 0.05). However, there were no statistically significant differences among CWYW treatments in most parameters. CONCLUSION: Although the control diet performed best in terms of gas production and digestibility, the combination of CWYW and 0.4% fiber-degrading enzyme supplementation produced fermentation characteristics and digestibility values comparable to those of the control. These findings suggest that CWYW, particularly when supplemented with 0.4% enzyme, holds potential as a sustainable alternative to soybean meal in ruminant feed formulations.