Benefits of heat-killed Lactobacillus acidophilus on growth performance, nutrient digestibility, antioxidant status, immunity, and cecal microbiota of rabbits

Introduction Heat-killed probiotics, as a type of inactivated beneficial microorganisms, possess an extended shelf life and broader adaptability compared to their live counterparts. This study aimed to investigate the impact of heat-killed Lactobacillus acidophilus (L. acidophilus, LA) - a deactivated probiotic on the growth performance, digestibility, antioxidant status, immunity and cecal microbiota of rabbits. Methods Two hundred weaned Hyla rabbits were randomly allocated into five equal groups (CON, L-200, L-400, L-600, and L-800). Over a 28-day period, the rabbits were fed basal diets supplemented with 0, 200, 400, 600, and 800 mg/kg of heat-killed LA, respectively. Results Results revealed a significant reduction in the feed-to-gain ratio (F/G) in the L-600 and L-800 groups (p < 0.05). Additionally, the L-800 group exhibited significantly higher apparent digestibility of crude fiber (CF) and crude protein (CP) (p < 0.05). Regarding digestive enzyme activities, enhanced trypsin and fibrinase activities were observed in the L-600 and L-800 groups (p < 0.05). Concerning the regulation of the body's antioxidant status, the L-800 group demonstrated elevated levels of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in both serum and ileal tissue (p < 0.05). In terms of immune capacity modulation, serum tumor necrosis factor-alpha (TNF-alpha) levels were significantly lower in the L-600 and L-800 groups (p < 0.05), while immunoglobulin A (IgA) and immunoglobulin M (IgM) levels were higher (p < 0.05). Additionally, the L-800 group exhibited a substantial increase in secretory immunoglobulin A (SIgA) levels in the intestinal mucosa (p < 0.05). In comparison to the CON group, the L-800 group exhibited a significant increase in the relative abundance of Phascolarctobacterium and Alistipes in the cecum (p < 0.05). Phascolarctobacterium demonstrated a positive correlation with SIgA (p < 0.05), IgM (p < 0.01), and Glutathione peroxidase (GSH-Px) (p < 0.05), while displaying a negative correlation with TNF-alpha levels (p < 0.05). Concurrently, Alistipes exhibited positive correlations with IgA (p < 0.05), IgM (p < 0.05), SIgA (p < 0.01), GSH-Px (p < 0.05), SOD (p < 0.05), and T-AOC (p < 0.01), and a negative correlation with TNF-alpha (p < 0.05). Discussion In conclusion, the dietary incorporation of 600 mg/kg and 800 mg/kg of heat-killed LA positively influenced the growth performance, nutrient digestibility, antioxidant status, immune capacity and cecal microbiota of rabbits. This highlights the potential benefits of utilizing heat-killed probiotics in animal nutrition.