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, L200 , L400 , L600 , and L800 ). 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 L600 and L800 groups ( p  < 0.05). Additionally, the L800 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 L600 and L800 groups ( p  < 0.05). Concerning the regulation of the body's antioxidant status, the L800 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-α (TNF-α) levels were significantly lower in the L600 and L800 groups ( p  < 0.05), while immunoglobulin A (IgA) and immunoglobulin M (IgM) levels were higher ( p  < 0.05). Additionally, the L800 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 L800 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-α 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-α ( 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.