ISSUE FOCUS 62 FEED & ADDITIVE MAGAZINE February 2026 increased microbial efficiency rather than through drastic changes in fermentation pathways. EFFECTS OF FF USE ON GRAIN-BASED SUBSTRATES DEGRADATION Four different experimental runs were performed in in vitro simulators of the gastrointestinal system of several species (broilers, pigs, and ruminants) to assess the effect of adding FF on the fermentation of grain-based substrates. A total of 50 data points (32 of simulators with FF and 18 without) were compared. In contrast to forage substrates, FF supplementation did not result in statistically significant differences in grain dry matter degradation after system stabilization (days > 6). When data from stabilized systems were considered, the mean degradation difference was 1.34 % for FF-supplemented treatments (n = 32) compared with the non-supplemented control (n = 18). However, this difference was not statistically significant (p = 0.42), indicating that the effect of FF on grain substrates was limited and more variable than that observed for forage-based substrates. When species-specific responses were examined, clear differences emerged that help explain the variability observed in the pooled analysis (Figure 2). The simulations for ruminants showed a relatively narrow distribution of degradation differences, with values clustered close to zero, indicating a limited and consistent response of grain degradation to FF supplementation. Simulations for broilers displayed the highest median and mean degradation differences, together with a broad upper range, suggesting a stronger but more heterogeneous response to FF in grain-based substrates, but with a clear trend to improve DM degradation. In contrast, the simulations for pigs exhibited a wide dispersion of values, including both positive and negative responses, highlighting a highly variable and inconsistent effect. Overall, these species-specific patterns confirm that the response to FF supplementation in grain substrates is strongly dependent on animal species' diets, and gastrointestinal conditions. In grain-based substrates, FF supplementation did not significantly affect pH, or the individual SCFA concentrations. Nevertheless, there was a trend towards lower values of the acetate-to-propionate ratio. Figure 3 illustrates the box-and-whisker plot of the acetate-to-propionate (A:P) ratio found in different species when FF is supplemented (FF group) and not supplemented (No group). FF supplementation was associated with a lower average A:P ratio across species compared with the non-supplemented control. When data from stabilized systems (days > 6) were considered, mean A:P values consistently shifted downward in the FF group, both within individual species and in the pooled dataset, indicating a relative increase in propionate production at the expense of acetate. This shift in fermentation balance is generally associated with improved energetic efficiency, as propionate represents a more glucogenic short chain fatty acid, particularly relevant for monogastric species and high-energy diets. The observed reduction in the A:P ratio suggests that FF modulates microbial metabolic pathways toward a more efficient use of fermentable substrates, without inducing major disruptions in the overall fermentation profile. Ruminant (n=6) Broilers (n=8) Pigs (n=18) All (n=32) Degradation difference relative to control (%) 20 10 0 -10 Figure 2. Degradation difference (relative to control with no FF) across species in in vitro gastrointestinal simulations using grain-based substrates and FF as an additive.
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