Effect of citric waste fermented with yeast waste pellet and roughage-to-concentrate ratio on gas production, digestibility, and fermentation characteristics using an in vitro gas production technique

Abstract

Background: Agro-industrial byproducts offer promising solutions for reducing feed costs and mitigating environmental pollution. Efficient waste management through recycling and reuse not only minimizes environmental impact but also opens avenues for innovative animal feed products. The objectives of this research were to determine whether increasing the roughage-to-concentrate diet (R: C) ratio and adding citric waste fermented with yeast waste pellets (CWYWP) would improve gas production, digestibility, and fermentation outcomes. A 2 × 4 factorial experiment was conducted using a completely randomized design. The first factor comprised two levels of R: C ratios: 60:40 and 40:60. Rice straw was used as a roughage source. The second factor involves four levels of CWYWP supplementation (as a top-dressed substrate supplement) at 0%, 2%, 4%, and 6% dry matter (DM), respectively. Results: A significant interaction between CWYWP level and R: C ratio was observed for cumulative gas production, with 2% and 4% CWYWP increasing gas volumes under the 40:60 ratio, peaking at 113.10 mL/0.5 g at 4% inclusion. Similarly, a significant interaction was found for in vitro digestibility at 24 h, where 4% CWYWP under 40:60 R: C significantly enhanced in vitro organic matter digestibility and in vitro dry matter digestibility compared to other levels. CWYWP supplementation elevated ammonia-nitrogen concentrations at both 2 and 4 h and slightly increased ruminal pH at 4% and 6% inclusion, with all pH values remaining within the physiological range. Volatile fatty acid profiles shifted toward higher propionate and lower acetate-to-propionate ratio, particularly at 6% CWYWP under 40:60 R: C, indicating improved glucogenic fermentation. Conclusion: These findings suggest that CWYWP can be safely included at up to 4% in high-concentrate diets without impairing in vitro ruminal fermentation or digestibility.