Effects of licorice crude extract on serum biochemistry, antioxidant capacity, immune function, rumen fermentation parameters, microbiota, and gastrointestinal enzyme activities in karakul sheep

This study aimed to determine the optimal dietary supplementation level of Licorice Crude Extract (LCE, derived from Glycyrrhiza glabra ) by evaluating its effects on serum biochemistry, antioxidant capacity, immune function, rumen fermentation parameters, microbial community, and gastrointestinal enzyme activities in Karakul sheep. As a by-product of licorice processing, LCE is rich in bioactive components (e.g., flavonoids and polysaccharides) with potential antioxidant, ant-inflammatory, and rumen-modulating properties, making it a promising feed additive for ruminants. Thirty-two sheep with similar body weights were randomly divided into four groups and fed a basal diet supplemented with 0% (control), 1, 2, or 3% LCE for 75 days. The LCE supplementation significantly enhanced serum antioxidant capacity, humoral immunity, and rumen fermentation efficiency, improving systemic antioxidant capacity with a dose-dependent decrease in MDA ( P < 0.05), and humoral immunity with increased immunoglobulins ( P < 0.05) in sheep. These improvements occurred in alongside, a profound reshaping of the rumen microbiota. High-throughput sequencing revealed that LCE supplementation, particularly at 2%, significantly reshaped the microbial community structure (PCoA plot, P < 0.05) and enhanced α-diversity (e.g., increased Shannon index, P < 0.05). This restructuring was characterized by a marked increase in the abundance of the phylum Firmicutes and a significant reduction in the genus g_Prevotella at the 2% LCE level ( P < 0.05). These microbial shifts were functionally consequential, driving significant improvements in the rumen environment such as elevated pH and increased total volatile fatty acids (tVFA) concentration ( P < 0.05). Concomitantly, a significant increase in ruminal cellulase activity was observed ( P < 0.05). In contrast, several fundamental serum metabolic parameters, including TP, BUN, and GLU, remained stable across all groups ( P > 0.05). The most consistent and beneficial effects across the microbial and physiological parameters were observed at the 2% LCE supplementation. These findings reveal that dietary supplementation with LCE can improve the main physiological functions of sheep, with the most beneficial effects observed at the 2% inclusion level for promoting health and enhancing nutrient metabolic efficiency. This study provides a scientific basis for the utilization of LCE as a feasible feed additive in sheep production, contributing to the reduced farming costs and sustainable livestock development.