Dietary Combined Thyme Meal and Bacillus subtilis to Promote Growth Performance, Immune Function, Gene Expression, Antioxidant Defense, and Cecal Microbiota in Growing Rabbits Under Heat Stress Conditions

Abstract

This study investigates the nutritional effects of a thyme meal and B. subtilis mixture on growth performance, immune function, antioxidant capacity, gene expression, and gut microbiota in heat-stressed rabbits. One hundred and twenty male New Zealand White rabbits were divided into four dietary treatments (five replicates/group). The rabbits in the first group were fed a basal diet, while the other three groups were fed a basal diet containing B. subtilis, thyme meal, and their mixture, respectively. The B. subtilis and thyme meal mixture increases the heat-stressed rabbits' body weight gain and carcass weight, and enhances nutrient digestibility and the feed conversion ratio. Supplementing the CBT mixture improved the lipid profile and liver and kidney function via decreasing plasma triglycerides, cholesterol, LDL, creatinine, urea, and AST levels, while increasing total protein and albumin levels. Furthermore, the CBT mixture enhanced the immune response and oxidative stability by increasing IgA and IgG levels, GPx enzyme activity, and SOD, while decreasing plasma MDA content. Adding the CBT mixture enhanced gut health by reducing pathogens and inflammation, as well as increasing volatile fatty acid levels and the expression of CAT-1, MUC-2, and SGLT-1 genes. The combination of a thyme meal and B. subtilis enhanced growth, immune function, antioxidant capacity, gut microbiota modification, and the expression of gut health nutrient absorption-related genes in heat-stressed rabbits.

Keywords: B. subtilis; antioxidant; gene; growing rabbits; growth; heat stress; immunity; thyme.

Figure 1

Temperature–humidity index (THI, (A)) values, pulse rate (PR, (B)), and respiratory rate (RR, B) during the experimental period.

Figure 2

Impact of adding thyme meal, B. subtilis, and their blend on heat-stressed rabbits’ thyroid gland (thyroxine (T4, (A)) and triiodothyronine (T3, (B))); CON, group was fed a basal diet; BS, group was fed a basal diet with B. subtilis; THM, group was fed a basal diet with thyme meal; CBT, group was fed a basal diet with B. subtilis–thyme meal mixture. Statistical significance is denoted as follows: p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***). Asterisks indicate levels of statistical significance: * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001. The greater the number of asterisks, the higher the level of statistical significance.

Figure 3

Impact of adding thyme meal, B. subtilis, and their blend on heat-stressed rabbits’ oxidative stability (malondialdehyde (MDA, (A), glutathione peroxidase (GPx, (B), and superoxide dismutase (SOD, (C)); CON, group was fed a basal diet; BS, group was fed a basal diet with B. subtilis; THM, group was fed a basal diet with thyme meal; CBT, group was fed a basal diet with B. subtilis–thyme meal mixture. Statistical significance is denoted as follows: p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***). Asterisks indicate levels of statistical significance: * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001. The greater the number of asterisks, the higher the level of statistical significance.

Figure 4

Impact of adding thyme meal, B. subtilis, and their blend on heat-stressed rabbits’ immune response (IgA (A), IgG (B), and IgM (C)); CON, group was fed a basal diet; BS, group was fed a basal diet with B. subtilis; THM, group was fed a basal diet with thyme meal; CBT, group was fed a basal diet with B. subtilis–thyme meal mixture. Statistical significance is denoted as follows: p < 0.01 (**). Asterisks indicate levels of statistical significance: ** p < 0.01, and **** p < 0.0001. The greater the number of asterisks, the higher the level of statistical significance.

Figure 5

Impact of adding thyme meal, B. subtilis, and their blend on mRNA relative expressions of inflammation-related genes, including CAT-1 (A), MUC-2 (B), and SGLT-1 (C), on heat-stressed rabbits; CON, group was fed a basal diet; BS, group was fed a basal diet with B. subtilis; THM, group was fed a basal diet with thyme meal; CBT, group was fed a basal diet with B. subtilis–thyme meal mixture. Statistical significance is denoted as follows: p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***) and p < 0.0001 (****).

Figure 6

Impact of adding thyme meal, B. subtilis, and their blend on mRNA relative expressions of nutrient absorption and transport-related genes, including IL-6 (A) and IL-10 (B), on heat-stressed rabbits; CON, group was fed a basal diet; BS, group was fed a basal diet with B. subtilis; THM, group was fed a basal diet with thyme meal; CBT, group was fed a basal diet with B. subtilis–thyme meal mixture. Statistical significance is denoted as follows; p < 0.01 (**), and p < 0.001 (***). Asterisks indicate levels of statistical significance: ** p < 0.01, *** p < 0.001, and **** p < 0.0001. The greater the number of asterisks, the higher the level of statistical significance.