Dose-Dependent Effects of Fermented Apple Pomace on Lactation Performance in Dairy Goats and Associated Antioxidant, Inflammatory, and Gut Microbiota Responses in Rats

Apple pomace, a byproduct of juice processing, requires valorization. This study evaluated the dose-dependent effects of fermented apple pomace (FAP) on growth and lactation performance in dairy goats and associated antioxidant, inflammatory, and gut microbiota responses in rats. Five FAP inclusion levels (0%, 5%, 10%, 15%, and 20%) were tested. In lactating dairy goats, 15% FAP was associated with the most favorable production and metabolic responses among the tested levels, including increased milk yield and average daily gain, reduced feed-to-milk ratio and somatic cell count, and lower blood urea nitrogen and ruminal NH3-N concentrations. However, nitrogen retention was not directly measured, and because FAP replaced corn and wheat bran, the diets were not isonitrogenous or isoenergetic; part of the responses may reflect changes in overall nutrient composition. In rats, 15% FAP was associated with activation of nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant signaling, suppression of Toll-like receptor 4 (TLR4)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inflammation, enrichment of butyrate-producing genera, and elevated cecal butyrate. These mechanistic findings are correlative and hypothesis-generating, requiring validation in ruminants. Collectively, 15% FAP was associated with the most favorable responses among the tested levels, but the mechanistic links between gut microbiota, butyrate, Nrf2/NF-κB signaling, and goat performance remain to be established.