ABSTRACT
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.
ABSTRACT
Carvacrol (CAR) is a plant extract that has been reported to enhance antioxidant activity in animals. However, the effect of CAR on the intestinal health of rabbits is poorly understood. Here, we investigated whether CAR exerts protective effects on the intestinal health of rabbits following lipopolysaccharide (LPS) challenge and whether these effects were mediated via the reduction of intestinal inflammation and the regulation of the intestinal flora. Intestinal damage was assessed in LPS-challenged rabbits treated or not with CAR. The serum levels of inflammatory factors were assessed by enzyme-linked immunosorbent assay. Histopathological changes in the ileum and cecum were examined using hematoxylin and eosin staining. The relative gene expression levels of inflammatory factors and tight junction proteins in the rabbit cecum were determined by qRT-PCR. High-throughput sequencing analysis of the microbial 16S rRNA gene was performed using the Illumina NovaSeq Platform. The results showed that CAR can prevent intestinal inflammation and damage as well as mitigate gut dysbiosis in rabbits following LPS challenge. Our study provides a theoretical reference for the application of dietary CAR in rabbit production.
