Ruminal fermentation kinetics and in vitro gas production of yeast-enriched agro-industrial by-products as alternatives to soybean meal in ruminant diets

This study aimed to evaluate the impact of replacing soybean meal with yeast-enriched acerola, pineapple, and orange agro-industrial residues on ruminal fermentation kinetics and in vitro gas production. Using a 3 × 5 factorial design in a completely randomized design with three replicates, the study tested three agro-industrial residues (acerola, orange, and pineapple) at five replacement levels (0, 25, 50, 75, and 100% on a dry matter basis). Cumulative gas production was measured over time and analyzed using the Gompertz model. Linear and quadratic polynomial contrasts were used to examine the responses of feeds to increasing addition levels of the residues. The inclusion of pineapple residue linearly increased total gas production (P = 0.038), while acerola residue resulted in a linear decrease (P = 0.004) and orange residue had no significant effect on gas production (P > 0.05). Orange residue linearly reduced the lag phase (P = 0.048), acerola showed a quadratic effect with an increase of up to 75% inclusion, followed by a decrease (P = 0.009), while pineapple had no significant effect on the lag phase (P > 0.05). Digestibility of organic matter increased with the inclusion of orange and pineapple residues (P < 0.05) but decreased linearly with higher acerola inclusion (P = 0.008). Overall, replacing soybean meal with yeast-enriched residues affects ruminal fermentation, gas production, and digestibility of organic matter. Pineapple and orange residues are effective substitutes, capable of replacing up to 100% of the soybean meal in the concentrate. However, the inclusion of acerola residue was not efficient, resulting in lower responses in the evaluated parameters compared to the control treatment.