Abstract
Spent mushroom substrate (SMS) is abundant in nutrients, including polysaccharides, essential amino acids, dietary fiber (DF), and other bioactive compounds. The compound microorganism preparation (CMP), comprising multiple beneficial bacterial groups, is widely used as a feed additive to modulate intestinal microbiota and enhance nutrient absorption in animals. This study investigated the effects of supplementing young sika deer's concentrated feed with SMS and CMP on total intestinal digestibility, growth performance, serum immune indicators, biochemical parameters, and intestinal microbial composition. Ninety animals were randomly assigned to three dietary treatments: control (basal diet), LE1 (basal diet + 5% SMS), and LE2 (basal diet + 5% SMS + 100 mg CMP/deer/day). Results showed that the LE2 group had significantly higher total weight gain (TWG) and average daily gain (ADG) than both the control group and the LE1 group. Levels of crude protein (CP), total protein (TP), albumin (ALB), blood glucose (GLU), and immunoglobulins (IgG, IgM, IgA) were significantly higher in the LE2 group than in the other groups, with LE1 also showing improvement over the control group. Additionally, ether extract (EE) and high-density lipoprotein (HDL) levels were found to be elevated in both the LE1 and LE2 groups when compared to the control group. In contrast, low-density lipoprotein (LDL) levels as well as urea nitrogen concentrations showed a significant increase in the LE1 group compared to both the control and LE2 groups. Notably, when compared to the control group, there was a significant reduction in the abundance of certain pathogenic bacteria within both the LE1 and LE2 groups; conversely, there was a substantial increase in the relative abundance of beneficial bacterial communities. These results demonstrate that combined SMS and CMP supplementation effectively improves growth performance, nutrient utilization, and intestinal health in young sika deer, suggesting its potential as a functional feed additive.