Capsaicin Incorporated into Fermented Concentrate: In Vitro Screening and Effects on Digestibility and Rumen Fermentation in Finishing Yanbian Cattle

This study evaluated the effects of capsaicin addition before feed fermentation on electronic-nose profiles, in vitro fermentation, and animal responses in finishing Yanbian cattle. Electronic-nose analysis compared unfermented and fermented feeds prepared with nominal capsaicin additions of 0, 250, 500, or 750 mg per 500 g substrate. Fermented feeds prepared with 250 and 500 mg (FC250 and FC500) visually resembled the fermented control (FC0) in their sensor response patterns, whereas FC750 showed a more distinct profile. These observations were descriptive; no pairwise comparison was significant after multiplicity adjustment. In vitro, FC500 increased cumulative gas production relative to FC0 at several incubation times, whereas FC250 exceeded FC0 only at 36 h, without significant differences in nutrient digestibility. Thirty female cattle housed in ten pens received FC0 or FC500 at 500 g per animal daily, with five pens per treatment. Using pen as the experimental unit and adjusting for initial body weight, FC500 increased final body weight and average daily gain (both p = 0.018), whereas dry matter intake did not differ significantly. FC500 also increased chewing frequency, and apparent dry matter digestibility (65.73% vs. 63.09%; p = 0.029). At a single sampling point after prolonged fasting, FC500 had higher ruminal pH and propionate concentration, and a lower acetate-to-propionate ratio (p < 0.05). No significant differences were detected in bacterial alpha diversity or overall community structure, and no genus differences survived false discovery rate correction. These findings provide preliminary evidence of improved digestibility and growth with FC500 under the experimental conditions. Because residual capsaicin was not quantified, the responses apply to the fermented preparation as a whole.