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Objective: <i>Lactobacilli</i> in rabbit intestine is rare and its function in rabbit gut health is not fully understood. The present study aimed to evaluate <i>in vivo</i> the probiotic potential of <i>Lactobacillus casei</i> for suckling rabbits.Methods: Two healthy 5-day-old suckling rabbits with similar weights from each of 12 New Zealand White litters were selected and disturbed to control group and treatment group. All rabbits were artificially fed. The treatment group had been supplemented with live <i>Lactobacillus casei</i> in the milk from the beginning of the trial to 13 days of age. At 15 days of age, healthy paired rabbits were slaughtered to collect intestinal samples.Results: i) Oral administration of Lactobacillus casei significantly increased the proportion of <i>Lactobacilli</i> in the total intestinal bacteria (p<0.01) and obviously reduced that of <i>Escherichia-Shigella</i> (p<0.01); ii) treatment increased the length of vermiform appendix (p<0.05); iii) a higher percentage of degranulated paneth cells was observed in the duodenum and jejunum when rabbits administered with Lactobacillus casei (p<0.01); and iv) the expression of tolllike receptor 9, lysozyme (<i>LYZ</i>), and defensin-7-like (<i>DEFEN</i>) in the duodenum and jejunum was stimulated by supplemented Lactobacillus casei (p<0.05).Conclusion: Orally administered Lactobacillus casei could increase the abundance of intestinal <i>Lactobacilli</i>, decrease the relative abundance of intestinal <i>Escherichia-Shigella</i>, promote the growth of appendix vermiform, stimulate the degranulation of paneth cells and induce the expression of <i>DEFEN</i> and <i>LYS</i>. The results of the present study implied that <i>Lactobacillus casei</i> exhibited probiotic potential for suckling rabbits.

Rabbit is susceptible to intestinal infection, which often results in severe inflammatory response. To investigate whether the special community structure of rabbit intestinal bacteria contributes to this susceptibility, we compared the inflammatory responses of isolated rabbit crypt and villus to heat-treated total bacteria in pig, chicken, and rabbit ileal contents. The dominant phylum in pig and chicken ileum was Firmicutes, while Bacteroidetes was dominant in rabbit ileum. The intestinal bacteria from rabbit induced higher expression of toll-like receptor 4 (TLR4) in rabbit crypt and villus (P < 0.05). TLR2 and TLR3 expression was obviously stimulated by chicken and pig intestinal bacteria (P < 0.05) but not by those of rabbit. The ileal bacteria from those three animals all increased the expression of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) in crypts and villus (P < 0.05). Chicken and pig ileal bacteria also stimulated the expression of anti-inflammatory factors interferon beta (IFN-β) and IL-10 (P < 0.05), while those of rabbit did not (P > 0.05). In conclusion, a higher abundance of Gram-negative bacteria in rabbit ileum did not lead to more expressive pro-inflammatory cytokines in isolated rabbit crypt and villus, but a higher percentage of Lactobacillus in chicken ileum might result in more expressive anti-inflammatory factors.

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