The effect of adding compound microbial preparation to low protein diets on the growth performance, fur quality and gut microbiota of blue foxes

This study investigated the effects of supplementing composite microecological preparation (CMP) to low-protein diets on growth performance, fur quality, and gut microbiota of blue foxes. Fifty blue foxes were randomly allocated to five dietary treatments: a basal low-protein control diet (LP), a high-protein control diet (HP), and the low-protein diet supplemented with 50, 100, and 200 mg/(head·d) of CMP (CMP Ⅰ, CMP Ⅱ, and CMP Ⅲ). The results showed that dietary protein restriction severely compromised fur quality and apparent nutrient digestibility, as evidenced by reduced dry matter digestibility, crude protein digestibility, ether extract digestibility, pelt length, and guard hair length in the LP group compared to the HP group ( P < 0.05). However, CMP supplementation, particularly at the 200 mg/(head·d), significantly improved growth performance fur quality and apparent nutrient digestibility compared to the LP group ( P < 0.05). CMP Ⅲ markedly elevated the systemic antioxidant capacity such as glutathione (GSH), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) compared to the LP and HP group ( P < 0.05). Intestinal morphologically, CMP Ⅲ significantly increased villus height (VH) and the villus height to crypt depth ratio (VH/CD) in the duodenum and ileum compared to the LP and HP group ( P < 0.05), indicating enhanced intestinal absorptive integrity. LP group significantly enriched Prevotella , while HP group enriched Bifidobacterium , Megasphaera , and Streptococcus . β diversity and cluster analysis confirmed that CMP intervention caused a shift in microbial community structure from LP to HP phenotype, indicating that CMP can effectively repair the dysbiosis induced by low protein diets. Functional prediction analysis reveals that carbohydrate metabolism and amino acid metabolism dominated the functional landscape. In conclusion, incorporating CMP into LP diets counteracts the adverse impacts of protein restriction by optimizing nutrient utilization, intestinal health, and microbial ecology, thereby sustaining superior fur quality while lowering feed costs.